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TRPV4 is endogenously expressed in vertebrate spermatozoa and regulates intracellular calcium in human sperm
Accepted Manuscript TRPV4 is endogenously expressed in vertebrate spermatozoa and regulates intracellular calcium in human sperm Ashutosh Kumar, Rakesh Kumar Majhi, Nirlipta Swain, S.C. Giri, Sujata Kar, Luna Samanta, Chandan Goswami PII:
S0006-291X(16)30382-5
DOI:
10.1016/j.bbrc.2016.03.071
Reference:
YBBRC 35503
To appear in:
Biochemical and Biophysical Research Communications
Received Date: 5 March 2016 Accepted Date: 17 March 2016
Please cite this article as: A. Kumar, R.K. Majhi, N. Swain, S.C. Giri, S. Kar, L. Samanta, C. Goswami, TRPV4 is endogenously expressed in vertebrate spermatozoa and regulates intracellular calcium in human sperm, Biochemical and Biophysical Research Communications (2016), doi: 10.1016/ j.bbrc.2016.03.071. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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TRPV4 is endogenously expressed in vertebrate spermatozoa and regulates intracellular calcium in human sperm
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Ashutosh Kumar1, Rakesh Kumar Majhi1,¥, Nirlipta Swain1,2,,¥, S.C. Giri3 , Sujata Kar4, Luna Samanta2, Chandan Goswami1*
1: National Institute of Science Education and Research, Sachivalaya Marg, Bhubaneswar, Orissa, India.
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2: Department of Zoology, Ravenshaw University, Cuttack, Orissa, India. 3: Central Avian Research Institute, Bhubaneswar-751003, India
¥ Equal contribution
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* Correspondence: [email protected]
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4. Kar Clinic and Hospital Pvt. Ltd, Bhubaneswar, Orissa, India.
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Abstract Transient Receptor Potential Vanilloid sub-type 4 (TRPV4) is a non-selective cationic channel involved in regulation of temperature, osmolality and different ligand-dependent Ca2+-influx. Recently, we have demonstrated that TRPV4 is conserved in all vertebrates. Now we demonstrate that TRPV4 is
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endogenously expressed in all vertebrate sperm cells ranging from fish to mammals. In human sperm, TRPV4 is present as N-glycosylated protein and its activation induces Ca2+-influx. Its expression and localization differs in swim-up and swim-down cells suggesting that TRPV4 is an important determining factor for sperm motility. We demonstrate that pharmacological activation or inhibition of TRPV4
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regulates Ca2+-wave propagation from head to tail. Such findings may have wide application in male fertility - infertility, contraception and conservation of endangered species as well.
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Key words: Calcium-wave, Sperm, Evolution, TRP channels, TRPV4, vertebrates
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Running title: TRPV4 regulates sperm functions
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Introduction In case of exogenous fertilization, sperm cells travel a long distance in aqueous media while in case of endogenous fertilization this travel is within the female reproductive tract. In higher mammals, sperm move through mucus, locate the oocyte, penetrate the cumulus and zona-pellucida, and fuse with
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the plasmalemma to deliver the DNA [1]. Each of these events require sperm to constantly detect appropriate chemical and physical cues (such as temperature, pH gradients) and upon reaching vicinity of the oocyte, undergo capacitation and finally fuse with the oocyte. Timing of each of these responses is crucial and these events must not be activated prematurely and/or inappropriately. Since spermatozoa are
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transcriptionally and translationally inactive, all cellular activities within it are carried out by the proteins inherited during differentiation and these proteins regulate sperm functions via secondary messengers such as intracellular Ca2+ [2-3]. In case of ejaculated spermatozoa, intracellular Ca2+ regulates
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chemotaxis, motility and hyperactivation, acrosomal reaction and is also a major regulator of capacitation [4-5]. Sperm cells also need to sense several physical and chemical cues and re-orient themselves towards the oocyte. The local pH, osmolarity and viscosity of the medium have profound effect on fertilizing ability of sperm [6]. In most vertebrates, “thermotaxis” also serves as conserved sensory and guidance mechanism. In mammalian system, temperature gradient guides sperm from the cooler reservoir site (oviductal isthmus) towards the warmer fertilization site [7]. In fact, rabbit and human spermatozoa have
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the capacity to sense minute temperature differences (0.5°C or even lower) during thermotaxis [7]. In mammalian sperm, the signaling events leading to thermotaxis are still unknown. The role of thermosensitive TRP channels in different vertebrates has been investigated recently [8-12]. So far only few reports have shown the presence of different TRPs in sperm from different species. However, the TRPVs are important as these channels are involved in the detection of thermal, chemical, osmotic,
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voltage and pH conditions in a variety of cells. Based on these criteria, TRPVs are expected to be involved in several of these steps. Indeed, TRPV1 is localized in the post acrosomal region in human
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spermatozoa while in boar spermatozoa, it is found at the post acrosomal and in midpiece region [9, 13]. In fish sperm, TRPV1 is located mainly at the neck region [12]. So far presence of other TRPVs in sperm has not been explored.
Among all, TRPV4 is uniquely activated at physiological temperature, changes in osmotic
pressure, mechanical membrane stress, by the derivatives of phorbol esters and also by some endogenous lipids. Such responsiveness makes TRPV4 as an ideal polymodal receptor which can influence the response of sperm in different environments, irrespective of whether fertilization occurs in water or in aqueous medium. In this work we have explored the presence of TRPV4 in the spermatozoa of different vertebrates and investigated its role in human sperm.
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Materials and Methods: Reagents: Antibodies against TRPV4 and β-tubulin, 4αPDD, RN1734 and Progesterone were purchased from Sigma-Aldrich. Another TRPV4 antibody and its blocking peptide were purchased from Alomone
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Lab. Anti-Hsp60 antibody was purchased from AbCam. Fluo-4-AM, DAPI, Alexa-488-labelled secondary antibodies were purchased from Invitrogen. HRP-labelled secondary antibody and PVDFmembrane were obtained from Merck Millipore. Sperm wash Media was obtained from SAR Health line Pvt. Ltd.
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Collection and isolation of cells from different species: Mature sperm from Rohu (Labeo rohita) were collected as described before [12]. Sperm from amphibians and reptiles were obtained from sexually mature common toad (Duttaphrynus melanostictus) (n = 3) and house lizard (Hemidactylus leschenaultii)
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(n = 3) as described before [14]. Avian sperm were collected from white pekin duck (Anas platrhyncos) (n = 4) and fixed with 4% PFA [15]. Freshly ejaculated sperms were collected from healthy bulls (Bos indicus). All experiments were done according to the approval (NISER-IAEC/SBS-AH/07/13/10). Human spermatozoa were collected (with informed consent and approvals, KHPL-04/2013 and NISER/IEC/2015-11) from healthy proven fertile donors after 3 days of sexual abstinence. After liquefaction, basic semen analysis was done to evaluate sperm parameters and then swim-up (highly
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motile, termed “Su”) and swim-down (nearly immotile, termed “Sd”) cells were separated as described before [16]. Either these fractions were treated with drugs or left untreated and then fixed with 4% PFA or were made into gel samples.
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Immunofluorescence analysis and microscopy: Immunocytochemical analysis was performed as described previously [12]. Rabbit polyclonal anti-TRPV4 antibody (1:500 dilution, Alomone Lab, or Sigma-Aldrich) were used. Wherever necessary, the antibody was blocked with a specific peptide
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(CDGHQQGYAPKWRAEDAPL, corresponding to AA853-871 of rTRPV4, Accession number Q9ERZ8). All images were acquired by a confocal laser-scanning microscope (LSM-780, Zeiss) with a 63X-objective and analyzed (Zeiss LSM image examiner software). Ca2+-imaging and intensity calculation: Freshly collected sperm were incubated with TRPV4-specific activator/inhibitor for 1 hour at 37°C, followed by incubation with Fluo4-AM (5µM) for 30 minutes. Subsequently, ~20µl sample was dropped onto the live cell chamber and time-series images were acquired. For intensity calculation ImageJ was used, in which multiple image frames wear merged into a single frame and intensity per unit area was calculated. 4
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SDS-PAGE and Western blot analysis: After quantification, equal number of Human spermatozoa were taken from swim-up and swim-down fractions. Gel samples were prepared by boiling the samples for 5 minutes with Laemmli buffer supplemented with protease inhibitor cocktail (Sigma Aldrich). These
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samples were separated by 10% SDS-PAGE followed by Western blot analysis as described before [12].
Flow-cytometry: Flow cytometry analysis of 10,000 sperm per sample was performed (FACS Calibur, BD Biosciences) and fluorescence (Alexa Fluor-488) intensities of were analyzed by using Cell Quest Pro software. Mean Fluorescence Intensity (MFI) was analyzed as a numerical value of the TRPV4
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expression.
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Deglycosylation of TRPV4 protein with Endoglycosidase-H and N-glycanase:
Equal amount of protein lysate of Sd and Su sample was taken for glycosidase treatment as-per manufacturer’s instructions (NEB). Briefly, sperm protein lysate were mixed with glycoprotein denaturing buffer (1X) and denaturation was carried out at 100°C for 5 minutes. Denatured glycoproteins were chilled in ice for 5 minutes. Subsequently Glyco buffer (1X) and NP-40 was added. Sample mixture was incubated in presence or absence of Endo-H and PNGase-F at 37°C for 6 hours and separated by one-
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dimensional SDS-PAGE and probed for TRPV4.
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Results: Evolutionary conserved and endogenous expression of TRPV4 in vertebrate spermatozoa Comparative analysis of the localization pattern of TRPV4 in different regions of spermatozoa (head, neck, tail) was performed for different vertebrate classes. At least one species from five classes of
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subphylum vertebrata was selected for this study. Spermatozoa were immunostained for TRPV4 and specificity of the TRPV4 antibody was confirmed by pre-incubating the same with blocking peptide. In the three classes of cold-blooded vertebrates, a distinct difference in localization pattern is observed. While in fish/piscean group (osteichthyes class), TRPV4 is primarily restricted at the tail and
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neck regions of Rohu (Labeo rohita) sperm (Fig 1a); for reptilian class, TRPV4 is detectable only in the head of (house lizard, Hemidactylus leschenaultii) sperm (Fig 1c). In contrast, in amphibian sperm, TRPV4 expression is present in head, neck and tail regions of Asian common toad (Duttaphrynus
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melanostictus) sperm (Fig 1b). Similar to amphibian spermatozoa, warm-blooded animals also show TRPV4 distribution throughout the sperm. In avian class, TRPV4 expression is although present at all regions, it is primarily restricted in the tail of Duck (Anas platrhyncos) sperm (Fig 1d). Spermatozoa of bull (Bos gaourus) show faint yet distinct expression of TRPV4 in all these regions (Fig 1e). Furthermore, TRPV4 localization pattern was also studied for spermatozoa of common Indian tree frog (Polypedates maculatus), garden lizard (Calotes versicolor), chicken (Gallus gallus domesticus)
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and a similar distribution pattern is observed (data not shown). Western blot analysis also confirms the presence of TRPV4 with expected size 98 kDa in Rohu and Duck sperm (Suppl Fig 1). These results suggest that TRPV4 is endogenously present in spermatozoa and such expression is evolutionarily conserved in all vertebrates.
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TRPV4 is expressed in human spermatozoa We probed for TRPV4 expression in human (Homo sapiens) sperm and noted very high level of
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expression in the head and neck region but faint expression in the tail region (Fig 2a). This staining was completely blocked by pre-incubating this antibody with specific antigenic peptide (Fig 2a). To confirm the expression in human sperm by Western blot analysis, we used two different antibodies raised against the C-terminus of TRPV4. One antibody (Ab1, Sigma-Aldrich) detects a band of 130 kDa (predicted size: 98 kDa) suggesting that in human sperm TRPV4 is subject to post-translational modification (discussed later) (Fig 2b). The second antibody (Ab2, Alomone Labs) detects bands at 130 and 72 kDa and these signals (Ab1 and Ab2) are blocked by using specific peptide suggesting that these immunoreactivities are specific in nature (Fig 2b). Since the predicted size of TRPV4 is 98 kDa, the higher and lower bands represent post-translational modifications and proteolytically degraded products, respectively (addressed later). 6
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We analyzed the percentage of human spermatozoa expressing TRPV4 by FACS (n = 6). Dot plot analysis revealed that all most all spermatozoa (98.98 ± 0.34%) are TRPV4+ (Fig 2c). Upon preincubation with a specific blocking peptide, the same antibody detects less than 1% cells as TRPV4+ve, and the mean fluorescence intensity values reduce significantly, confirming the specificity of the TRPV4
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antibody in FACS application also (Fig 2c-2d). These experiments confirm the expression of TRPV4 in mature human spermatozoa.
TRPV4 is differentially expressed and localized in swim-up and swim-down human sperm
To explore if there is any difference in TRPV4 expression in case of immotile and highly motile
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sperm, we separated the total sperm population into these two fractions, namely swim-up (Su, cells with progressive motility) and swim-down (Sd, cells with mostly impaired motility) samples. In Su cells,
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TRPV4 is primarily located in the head and faintly in the tail (Fig 3a-b). However, in Sd cells, TRPV4 is mostly absent in the head region and highly accumulated at the neck regions (Fig 3a-b). Western blot analysis was performed using Su and Sd samples obtained from three individuals with proven fertility. The Ab1 detects a distinct band at 130 kDa in Sd fraction of all three donors (Fig 3c). However, the corresponding 130 kDa band is mostly absent or faintly present in Su fraction. Densitometry analysis of the 130 kDa region of all donors revealed nearly 6 fold higher level of TRPV4 in Sd as compared to the Su fraction (Fig 3d). In contrast, several smaller fragments of TRPV4 are
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observed in Su samples. Some of these smaller bands were also observed in Sd samples, but with lesser intensities. This in general suggest for low level of full-length TRPV4 (corresponding to 130 kDa) and more proteolytically-cleaved products in motile sample. Furthermore to analyse the extent of proteolytic activity in Su and Sd samples, we probed the same samples for β-tubulin (abundant in cytoplasm) and
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Hsp60 (abundant in mitochondria). These Western blot analysis suggests for higher proteolytic activity in cytoplasm and in mitochondria of Su samples as both β-tubulin and Hsp60 levels are low in Su fraction as
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compared to Sd fraction (Fig 3c).
We analysed the expression of TRPV4 in Su and Sd samples in a more quantitative manner and
performed FACS. Nearly 98.98±0.34% and 96.15±2.8% cells are TRPV4+ in Su and Sd samples respectively (data not shown). However, the MFI-values for Su fraction is more (121.56±37.79) compared to the Sd fraction (89.03±23.76) (n = 6) (Fig 3e). Though this difference may suggests for the more TRPV4 in swim-up samples than swim-down sample, the difference turned out to be statistically non-significant (p = 0.105).
TRPV4 is a glycosylated protein
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In human sperm TRPV4 shows higher molecular weight band (~130 kDa) suggesting that it may be glycosylated. To confirm this, enzymatic treatments of the glycan moieties were performed using two different
glycosidase:
Endoglycosidase-H
(Endo-H,
cleaves
N-linked
high
mannose-rich
oligosaccharides), and Peptide-N-Glycosidase-F (PNGase-F, cleaves both N-linked high mannose-rich
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oligosaccharides and complex oligosaccharides). Migration of TRPV4 is faster when cell extract was treated with PNGase-F but not with Endo-H. After PNGase-F treatment, the resulting TRPV4 band migrates at expected molecular weight (~ 98 kDa) (Fig 3f). It suggests that sperm TRPV4 contains complex glycosidic bond with different types of oligosaccharides. As Su sample does not have detectable
TRPV4 modulates Ca2+-influx into human sperm
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level of full-length TRPV4, from these experiments definitive conclusion cannot be drawn.
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Ca2+-homeostasis in sperm is precisely regulated by different Voltage Operated Channel (VOC) present in the membrane and by female steroids like progesterone [17]. To evaluate the effect of TRPV4 activator and inhibitor upon the Ca+2-influx, we treated Su and Sd human samples with 4αPDD (5µM) or RN1734 (10µM) for 1 hour and labeled with Fluo-4-AM and analyzed the intracellular Ca2+-levels. 4αPDD treatment in Su fraction results in increased intracellular Ca2+-levels but inhibition by RN1734 (10µM) did not decrease the intracellular Ca2+-levels below that of the control conditions (Fig 4a). Notably, in Su fraction, the effect of TRPV4 activation by 4αPDD is comparable to the effect of
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Progesterone (10µM), a standard inducer of Ca+2-influx into sperm cells. The above observation is supported by quantification of Fluo4-AM signal intensity per unit area (n = 4 individuals), revealing that in Su fraction the effect of 4αPDD and Progesterone is similar (Fig 4b). In Sd fraction, there is no
4b).
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significant difference in basal Ca2+-levels after modulation of TRPV4 by pharmacological agents (Fig
TRPV4 regulates Ca2+-buffering at the mid-piece and Ca2+-wave propagation in tail
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To understand if and how TRPV4 regulates the intracellular Ca2+-waves, we labelled cells with
Fluo4-AM and performed live cell imaging followed by manual tracking of Ca2+-wave propagation within single cells (Fig 4c). In progesterone-treated cells, the level of Ca2+ is high in the head and neck regions. Progesterone-induced Ca2+-wave originates in the mid-region of sperm head and spreads throughout the neck and then propagates to the tail and mostly covers a large portion of the tail. The Ca2+-wave then subsides and a fresh wave originates in the head. This observation matches with previous reports [18]. In 4αPDD-treated cells, the Ca2+-level is also high in the head and neck regions. The patterns of 4αPDDmediated waves are visible at the tail and are mostly similar to progesterone-induced waves. Notably, application of RN1734 results in reduction of the intracellular Ca2+-level in the head region. Nevertheless, 8
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the Ca2+-wave propagation is observed in the tail region at times, though with less intensity and frequency. Indeed, we observed wavy pattern of intracellular Ca2+-level at the neck regions in case of progesterone- and 4αPDD-induced hyper motile cells (Fig 4c). These results may suggest for a possible
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Ca2+-buffering activity mediated by TRPV4 at the neck region.
Discussion:
Sperm cells have highly condensed DNA, no transcriptional activity and negligible translational activity. These cells are motile and show extreme response against number of variable factors such as
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changes in temperature, pH, osmolality, salts, and compounds at very low concentrations indicating their ability to detect and integrate multiple physical and chemical stimuli precisely [7, 19-20]. Notably, sperm cells perform all these tasks by multiple ion channels and receptors regulating complex yet efficient Ca2+-
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signaling events [21]. We show that TRPV4 is endogenously present in the sperm cells of all vertebrates, ranging from fishes to human. Conserved expression indicates that TRPV4 is probably involved in several of the above mentioned events occurring in sperm cells. We correlate the TRPV4 expression with the ability of sperm to sense optimum temperature, osmolality, and different chemicals and subsequent Ca2+-signaling events.
Different parts of the sperm cell, especially head, neck and tail region are the functionally
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important areas which regulate different yet specific functions. Sperms head is responsible for acrosomal reaction; neck region contains several mitochondria which continuously supply ATP and also act as the only available organelle for Ca2+-buffering, and tail region is important for motility. In all conditions, Ca2+ plays an important role in all physiological conditions. Presence of TRPV4 in the tail of sperm from all vertebrates suggests that it could be a critical regulator of sperm motility. Immunostaining results
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suggests for the differential localization of TRPV4 in different species. In human sperm, TRPV4 localizes in all the regions and it is significantly enriched in the head region.
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In this context, our observation that differential localization of TRPV4 in swim-up and swimdown cells from human sperm is highly indicative. Such differential localizations in these two population correlate well with the better motility regulation by TRPV4. In agreement with that, TRPV4 localization also differs after activation or inhibition by pharmacological agents (data not shown). However our western blot results from these two different fractions indicate that the TRPV4 band at 130 kDa is more abundant in Su sample as compare to Sd sample. On the other hand, the MFI values from FACS data suggest that the total TRPV4 immunoreactivity is more in Su fraction than that of the Sd samples. These in general may suggest that higher level of TRPV4 is present in the Su samples and the same is subjected to more proteolytic degradation, probably due to higher level of Ca2+-influx and Ca2+-dependent proteolytic activation. Western blot analysis of β-tubulin (cytoplasmic) and Hsp60 (mitochondrial) also 9
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suggest the same. Western blot results also suggest that in human sperm, TRPV4 migrates at 130 kDa, (higher than the expected size) and therefore suggests for post-translational modification. It is worth mentioning that in other systems too TRPV4 has been reported at higher sizes (~110-120 kDa size) [2223]. Our results indicate that in human sperm, TRPV4 has branched type of glycosylation, which is
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sensitive to PNGase-F but resistant to Endo-H glycosidase. It suggests that TRPV4 does not contain any N-glycosidic-linkage or due to the presence of branched oligosaccharides, this glycosidic bond is not freely accessible to the Endo-H.
We confirm that >95% of both Su- and Sd-cells contain TRPV4. The localization of TRPV4 in human sperm also correlates well with the Ca2+-waves observed in these cells. Untreated sperm shows a
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rhythmic pattern of Ca2+-waves that originates in the head and migrates to the mid-piece. Progesteroneinduced Ca2+-waves are initiated in the equatorial segment and then spread throughout the rest of the head and then moves rapidly to the tail [18]. TRPV4 activation-induced Ca2+-wave pattern is similar with the
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progesterone-evoked Ca2+-waves, while TRPV4 inhibition blocks the Ca2+-wave generation in the sperm head, thereby negligible Ca2+-influx passes to the mid-piece and tail. This indicates that TRPV4 may be involved in the regulation of both Ca2+-wave generation and propagation in human sperm. TRPV4 may also be involved in Ca2+-buffering function at the neck region of sperm cells. We conclude that TRPV4 is endogenously present in sperm cells of all vertebrates and this is an evolutionary conserved phenomenon since vertebrate evolution. TRPV4 regulates several key functions in
Acknowledgements and notes:
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human sperm cells, such as Ca2+-levels, Ca2+-wave propagation and motility.
Support from frozen cattle semen bank (Khapuria, Cuttack), Dr. PK. Mahapatra (RPRC, Bhubaneswar), Dr.
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P. Routray (CIFA, Bhubaneswar) and lab members is acknowledged. Funding from NISER, DST and DBT are
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acknowledged. The authors declare that they have no conflict of interests.
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References
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[1] M. Yoshida, N. Kawano, K. Yoshida, Control of sperm motility and fertility: diverse factors and common mechanisms, Cell Mol Life Sci 65 (2008) 3446-3457. [2] S. Grunewald, U. Paasch, H.J. Glander, et al. Mature human spermatozoa do not transcribe novel RNA, Andrologia 37 (2005) 69-71.
[4] M. Eisenbach, Sperm chemotaxis, Rev Reprod 4 (1999) 56-66.
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[3] A. Asano, J.L. Nelson, S. Zhang, et al. Characterization of the proteomes associating with three distinct membrane raft sub-types in murine sperm, Proteomics 10 (2010) 3494-3505.
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[5] M. Spehr, G. Gisselmann, A. Poplawski, et al. Identification of a testicular odorant receptor mediating human sperm chemotaxis, Science 299 (2003) 2054-2058. [6] A.M. Petrunkina, R.A. Harrison, M. Ekhlasi-Hundrieser, et al. Role of volume-stimulated osmolyte and anion channels in volume regulation by mammalian sperm, Mol Hum Reprod 10 (2004) 815-823. [7] A. Bahat, I. Tur-Kaspa, A. Gakamsky, et al. Thermotaxis of mammalian sperm cells: a potential navigation mechanism in the female genital tract, Nat Med 9 (2003) 149-150. [8] C. Auzanneau, C. Norez, F. Antigny, et al. Transient receptor potential vanilloid 1 (TRPV1) channels in cultured rat Sertoli cells regulate an acid sensing chloride channel, Biochem Pharmacol 75 (2008) 476-483.
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[9] N. Bernabo, M.G. Pistilli, M. Mattioli, et al. Role of TRPV1 channels in boar spermatozoa acquisition of fertilizing ability, Mol Cell Endocrinol 323 (2010) 224-231. [10] G.A. De Blas, A. Darszon, A.Y. Ocampo, et al. TRPM8, a versatile channel in human sperm, PLoS One 4 (2009) e6095.
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[11] M.G. Gervasi, C. Osycka-Salut, J. Caballero, et al. Anandamide capacitates bull spermatozoa through CB1 and TRPV1 activation, PLoS One 6 (2011) e16993.
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[12] R.K. Majhi, A. Kumar, M. Yadav, et al. Thermosensitive ion channel TRPV1 is endogenously expressed in the sperm of a fresh water teleost fish (Labeo rohita) and regulates sperm motility, Channels (Austin) 7 (2013) 483-492. [13] M. Maccarrone, B. Barboni, A. Paradisi, et al. Characterization of the endocannabinoid system in boar spermatozoa and implications for sperm capacitation and acrosome reaction, J Cell Sci 118 (2005) 43934404. [14] R.K. Majhi, S. Saha, A. Kumar, et al. Expression of temperature-sensitive ion channel TRPM8 in sperm cells correlates with vertebrate evolution, PeerJ 3 (2015) e1310. [15] R.K. Majhi, A. Kumar, M. Yadav, et al. Light and electron microscopic study of mature spermatozoa from White Pekin duck (Anas platyrhynchos): an ultrastructural and molecular analysis, Andrology (2016). [16] T. Jameel, Sperm swim-up: a simple and effective technique of semen processing for intrauterine insemination, J Pak Med Assoc 58 (2008) 71-74.
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[17] H.M. Florman, C. Arnoult, I.G. Kazam, et al. A perspective on the control of mammalian fertilization by eggactivated ion channels in sperm: a tale of two channels, Biol Reprod 59 (1998) 12-16. [18] S. Meizel, K.O. Turner, R. Nuccitelli, Progesterone triggers a wave of increased free calcium during the human sperm acrosome reaction, Dev Biol 182 (1997) 67-75.
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[19] S. Hamamah, J.L. Gatti, Role of the ionic environment and internal pH on sperm activity, Hum Reprod 13 Suppl 4 (1998) 20-30. [20] C.H. Yeung, M. Anapolski, M. Depenbusch, et al. Human sperm volume regulation. Response to physiological changes in osmolality, channel blockers and potential sperm osmolytes, Hum Reprod 18 (2003) 1029-1036. [21] W. Alasmari, C.L. Barratt, S.J. Publicover, et al. The clinical significance of calcium-signalling pathways mediating human sperm hyperactivation, Hum Reprod 28 (2013) 866-876.
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[22] V. Benfenati, M. Caprini, M. Dovizio, et al. An aquaporin-4/transient receptor potential vanilloid 4 (AQP4/TRPV4) complex is essential for cell-volume control in astrocytes, PNAS 108 (2011) 2563-2568.
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[23] C.E. Hills, R. Bland, P.E. Squires, Functional expression of TRPV4 channels in human collecting duct cells: implications for secondary hypertension in diabetic nephropathy, Exp Diabetes Res (2012) 936518.
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Figures and figure-legends
Figure 1. TRPV4 is endogenously expressed in vertebrate sperm. Confocal images demonstrating the presence of TRPV4 in Piscean (a, rohu), amphibian (b, common toad), reptilian (c, house lizard), avian (d, duck) and mammalian (e, bovine) sperm are shown. Cells were immunostained for TRPV4-specific antibody in presence (left most column) or absence of a specific blocking peptide. Images of TRPV4 (green) expression and localization in single cell are shown (right panel).
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Figure 2. TRPV4 is endogenously expressed in human sperm. a. Confocal images showing the endogenous expression of TRPV4 (green) in human sperm. TRPV4 is localized in the post acrosomal and neck regions, while faint expression is also present in the acrosomal and tail region (upper panel). TRPV4 signal is abolished upon blocking the primary antibody with its antigenic peptide (lower panel). b. Western blot analysis using different antibodies (Ab1 and Ab2) shows TRPV4-specific band at ~130 kDa (indicated by arrow). These TRPV4-specific signals are blocked by specific antigenic peptide. Corresponding Coomassie-stained gel is shown in right side. c. Representative dot-plot images from FACS (n = 6) showing the percentage of TRPV4+ cells. Application of blocking peptide reduced this number. d. TRPV4 expression is depicted as the MFI values. e. About 98.98±0.34% cells are TRPV4+ (FACS, n = 6 individuals).
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Figure 3. Swim-up and swim-down fractions of human sperm have different levels of TRPV4. a-b. Cluster (a) and enlarged single cells (b) stained for TRPV4 (green) are shown. Strong signal for TRPV4 is observed throughout the head (primarily in acrosomal region) in the swim-up (Su) fraction. TRPV4 is present in the post-acrosomal and neck regions in the swim-down (Sd) fraction. Faint expression is present in the tail region. c. Western blot analysis of Su and Sd fractions (from 3 individuals, Ind 1-3) were probed for TRPV4, β-tubulin and Hsp60. The 130 kDa band (longer arrow) and smaller bands (smaller arrows) represent the full-length (glycosylated) and proteolyticallydegraded TRPV4 respectively. The corresponding Coomassie gels are provided at right. The prominent band/s around 70-50 kDa (in Su and Sd fraction) as observed by Coomassie staining represents protein/s present in sperm media. d. Densitometry analysis of Western blot signal intensities for 130 kDa band of TRPV4 in Su and Sd fractions (n = 3, ANOVA test, ** p value< 0.005). e. Total TRPV4-specific fluorescence from Su and Sd samples detected as MFI values are shown (ns: non-significant; n = 6, ANOVA test, p = 0.105). f. TRPV4 has complex Nglycosidic linkage and branched complex glycosidic bond, which shows ~30 kDa shift only in presence of PNGaseF (red star). Endo-H treatment does not cause any shift of TRPV4 suggesting that the glycosylated TRPV4 is resistant against Endo-H. The corresponding Coomassie gels are shown in side.
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Figure 4. TRPV4 regulates intracellular Ca2+-levels in human sperm. a. Live cell imaging was performed for Su and Sd fractions pre-treated with TRPV4 activator (4αPDD) or inhibitor (RN1734) or with Progesterone for 1 hour and labeled with Fluo-4-AM. The intracellular Ca2+-levels are represented in pseudo color, (red and blue indicating highest and lowest intensity respectively). b. Quantification of average fluorescence intensity/area (in arbitrary unit) is shown. In Su sample, 4αPDD and progesterone increases the intracellular Ca2+-levels as comparison to control (p<0.05). In Sd sample, 4αPDD or RN1734 do not alter intracellular Ca2+-levels. (n = 4). c. Moving sperm (indicated by asterisk, *) was tracked within a fixed time period (Tn to Tn+7) and arrows indicate the high-level of Ca2+ in neck and tail respectively. Magnified (lower panel) image demonstrating the propagation of Ca2+-waves from head to the tail through the neck. In 4αPDD-treated and progesterone-treated cells, Ca2+-wave propagates
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through the mitochondrial coiling (green rings, indicated by arrows). High-level of Ca2+ (red) in the central stalk region is also visible in this case. In RN1734-treated cells, the Ca2+-waves do not propagate through these regions. The central stalk region reveals mostly moderate- to low-level of Ca2+-flux.
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ACCEPTED MANUSCRIPT Highlights: * TRPV4 is endogenously present in all vertebrate spermatozoa * TRPV4 protein is glycosylated in human sperm * TRPV4 localization and expression is different in Swim-up and Swim-down population of human
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* TRPV4 activation increases the intracellular calcium level
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sperm
S0006-291X(16)30382-5
DOI:
10.1016/j.bbrc.2016.03.071
Reference:
YBBRC 35503
To appear in:
Biochemical and Biophysical Research Communications
Received Date: 5 March 2016 Accepted Date: 17 March 2016
Please cite this article as: A. Kumar, R.K. Majhi, N. Swain, S.C. Giri, S. Kar, L. Samanta, C. Goswami, TRPV4 is endogenously expressed in vertebrate spermatozoa and regulates intracellular calcium in human sperm, Biochemical and Biophysical Research Communications (2016), doi: 10.1016/ j.bbrc.2016.03.071. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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TRPV4 is endogenously expressed in vertebrate spermatozoa and regulates intracellular calcium in human sperm
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Ashutosh Kumar1, Rakesh Kumar Majhi1,¥, Nirlipta Swain1,2,,¥, S.C. Giri3 , Sujata Kar4, Luna Samanta2, Chandan Goswami1*
1: National Institute of Science Education and Research, Sachivalaya Marg, Bhubaneswar, Orissa, India.
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2: Department of Zoology, Ravenshaw University, Cuttack, Orissa, India. 3: Central Avian Research Institute, Bhubaneswar-751003, India
¥ Equal contribution
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* Correspondence: [email protected]
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4. Kar Clinic and Hospital Pvt. Ltd, Bhubaneswar, Orissa, India.
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Abstract Transient Receptor Potential Vanilloid sub-type 4 (TRPV4) is a non-selective cationic channel involved in regulation of temperature, osmolality and different ligand-dependent Ca2+-influx. Recently, we have demonstrated that TRPV4 is conserved in all vertebrates. Now we demonstrate that TRPV4 is
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endogenously expressed in all vertebrate sperm cells ranging from fish to mammals. In human sperm, TRPV4 is present as N-glycosylated protein and its activation induces Ca2+-influx. Its expression and localization differs in swim-up and swim-down cells suggesting that TRPV4 is an important determining factor for sperm motility. We demonstrate that pharmacological activation or inhibition of TRPV4
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regulates Ca2+-wave propagation from head to tail. Such findings may have wide application in male fertility - infertility, contraception and conservation of endangered species as well.
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Key words: Calcium-wave, Sperm, Evolution, TRP channels, TRPV4, vertebrates
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Running title: TRPV4 regulates sperm functions
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Introduction In case of exogenous fertilization, sperm cells travel a long distance in aqueous media while in case of endogenous fertilization this travel is within the female reproductive tract. In higher mammals, sperm move through mucus, locate the oocyte, penetrate the cumulus and zona-pellucida, and fuse with
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the plasmalemma to deliver the DNA [1]. Each of these events require sperm to constantly detect appropriate chemical and physical cues (such as temperature, pH gradients) and upon reaching vicinity of the oocyte, undergo capacitation and finally fuse with the oocyte. Timing of each of these responses is crucial and these events must not be activated prematurely and/or inappropriately. Since spermatozoa are
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transcriptionally and translationally inactive, all cellular activities within it are carried out by the proteins inherited during differentiation and these proteins regulate sperm functions via secondary messengers such as intracellular Ca2+ [2-3]. In case of ejaculated spermatozoa, intracellular Ca2+ regulates
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chemotaxis, motility and hyperactivation, acrosomal reaction and is also a major regulator of capacitation [4-5]. Sperm cells also need to sense several physical and chemical cues and re-orient themselves towards the oocyte. The local pH, osmolarity and viscosity of the medium have profound effect on fertilizing ability of sperm [6]. In most vertebrates, “thermotaxis” also serves as conserved sensory and guidance mechanism. In mammalian system, temperature gradient guides sperm from the cooler reservoir site (oviductal isthmus) towards the warmer fertilization site [7]. In fact, rabbit and human spermatozoa have
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the capacity to sense minute temperature differences (0.5°C or even lower) during thermotaxis [7]. In mammalian sperm, the signaling events leading to thermotaxis are still unknown. The role of thermosensitive TRP channels in different vertebrates has been investigated recently [8-12]. So far only few reports have shown the presence of different TRPs in sperm from different species. However, the TRPVs are important as these channels are involved in the detection of thermal, chemical, osmotic,
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voltage and pH conditions in a variety of cells. Based on these criteria, TRPVs are expected to be involved in several of these steps. Indeed, TRPV1 is localized in the post acrosomal region in human
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spermatozoa while in boar spermatozoa, it is found at the post acrosomal and in midpiece region [9, 13]. In fish sperm, TRPV1 is located mainly at the neck region [12]. So far presence of other TRPVs in sperm has not been explored.
Among all, TRPV4 is uniquely activated at physiological temperature, changes in osmotic
pressure, mechanical membrane stress, by the derivatives of phorbol esters and also by some endogenous lipids. Such responsiveness makes TRPV4 as an ideal polymodal receptor which can influence the response of sperm in different environments, irrespective of whether fertilization occurs in water or in aqueous medium. In this work we have explored the presence of TRPV4 in the spermatozoa of different vertebrates and investigated its role in human sperm.
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Materials and Methods: Reagents: Antibodies against TRPV4 and β-tubulin, 4αPDD, RN1734 and Progesterone were purchased from Sigma-Aldrich. Another TRPV4 antibody and its blocking peptide were purchased from Alomone
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Lab. Anti-Hsp60 antibody was purchased from AbCam. Fluo-4-AM, DAPI, Alexa-488-labelled secondary antibodies were purchased from Invitrogen. HRP-labelled secondary antibody and PVDFmembrane were obtained from Merck Millipore. Sperm wash Media was obtained from SAR Health line Pvt. Ltd.
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Collection and isolation of cells from different species: Mature sperm from Rohu (Labeo rohita) were collected as described before [12]. Sperm from amphibians and reptiles were obtained from sexually mature common toad (Duttaphrynus melanostictus) (n = 3) and house lizard (Hemidactylus leschenaultii)
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(n = 3) as described before [14]. Avian sperm were collected from white pekin duck (Anas platrhyncos) (n = 4) and fixed with 4% PFA [15]. Freshly ejaculated sperms were collected from healthy bulls (Bos indicus). All experiments were done according to the approval (NISER-IAEC/SBS-AH/07/13/10). Human spermatozoa were collected (with informed consent and approvals, KHPL-04/2013 and NISER/IEC/2015-11) from healthy proven fertile donors after 3 days of sexual abstinence. After liquefaction, basic semen analysis was done to evaluate sperm parameters and then swim-up (highly
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motile, termed “Su”) and swim-down (nearly immotile, termed “Sd”) cells were separated as described before [16]. Either these fractions were treated with drugs or left untreated and then fixed with 4% PFA or were made into gel samples.
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Immunofluorescence analysis and microscopy: Immunocytochemical analysis was performed as described previously [12]. Rabbit polyclonal anti-TRPV4 antibody (1:500 dilution, Alomone Lab, or Sigma-Aldrich) were used. Wherever necessary, the antibody was blocked with a specific peptide
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(CDGHQQGYAPKWRAEDAPL, corresponding to AA853-871 of rTRPV4, Accession number Q9ERZ8). All images were acquired by a confocal laser-scanning microscope (LSM-780, Zeiss) with a 63X-objective and analyzed (Zeiss LSM image examiner software). Ca2+-imaging and intensity calculation: Freshly collected sperm were incubated with TRPV4-specific activator/inhibitor for 1 hour at 37°C, followed by incubation with Fluo4-AM (5µM) for 30 minutes. Subsequently, ~20µl sample was dropped onto the live cell chamber and time-series images were acquired. For intensity calculation ImageJ was used, in which multiple image frames wear merged into a single frame and intensity per unit area was calculated. 4
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SDS-PAGE and Western blot analysis: After quantification, equal number of Human spermatozoa were taken from swim-up and swim-down fractions. Gel samples were prepared by boiling the samples for 5 minutes with Laemmli buffer supplemented with protease inhibitor cocktail (Sigma Aldrich). These
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samples were separated by 10% SDS-PAGE followed by Western blot analysis as described before [12].
Flow-cytometry: Flow cytometry analysis of 10,000 sperm per sample was performed (FACS Calibur, BD Biosciences) and fluorescence (Alexa Fluor-488) intensities of were analyzed by using Cell Quest Pro software. Mean Fluorescence Intensity (MFI) was analyzed as a numerical value of the TRPV4
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expression.
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Deglycosylation of TRPV4 protein with Endoglycosidase-H and N-glycanase:
Equal amount of protein lysate of Sd and Su sample was taken for glycosidase treatment as-per manufacturer’s instructions (NEB). Briefly, sperm protein lysate were mixed with glycoprotein denaturing buffer (1X) and denaturation was carried out at 100°C for 5 minutes. Denatured glycoproteins were chilled in ice for 5 minutes. Subsequently Glyco buffer (1X) and NP-40 was added. Sample mixture was incubated in presence or absence of Endo-H and PNGase-F at 37°C for 6 hours and separated by one-
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dimensional SDS-PAGE and probed for TRPV4.
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Results: Evolutionary conserved and endogenous expression of TRPV4 in vertebrate spermatozoa Comparative analysis of the localization pattern of TRPV4 in different regions of spermatozoa (head, neck, tail) was performed for different vertebrate classes. At least one species from five classes of
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subphylum vertebrata was selected for this study. Spermatozoa were immunostained for TRPV4 and specificity of the TRPV4 antibody was confirmed by pre-incubating the same with blocking peptide. In the three classes of cold-blooded vertebrates, a distinct difference in localization pattern is observed. While in fish/piscean group (osteichthyes class), TRPV4 is primarily restricted at the tail and
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neck regions of Rohu (Labeo rohita) sperm (Fig 1a); for reptilian class, TRPV4 is detectable only in the head of (house lizard, Hemidactylus leschenaultii) sperm (Fig 1c). In contrast, in amphibian sperm, TRPV4 expression is present in head, neck and tail regions of Asian common toad (Duttaphrynus
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melanostictus) sperm (Fig 1b). Similar to amphibian spermatozoa, warm-blooded animals also show TRPV4 distribution throughout the sperm. In avian class, TRPV4 expression is although present at all regions, it is primarily restricted in the tail of Duck (Anas platrhyncos) sperm (Fig 1d). Spermatozoa of bull (Bos gaourus) show faint yet distinct expression of TRPV4 in all these regions (Fig 1e). Furthermore, TRPV4 localization pattern was also studied for spermatozoa of common Indian tree frog (Polypedates maculatus), garden lizard (Calotes versicolor), chicken (Gallus gallus domesticus)
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and a similar distribution pattern is observed (data not shown). Western blot analysis also confirms the presence of TRPV4 with expected size 98 kDa in Rohu and Duck sperm (Suppl Fig 1). These results suggest that TRPV4 is endogenously present in spermatozoa and such expression is evolutionarily conserved in all vertebrates.
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TRPV4 is expressed in human spermatozoa We probed for TRPV4 expression in human (Homo sapiens) sperm and noted very high level of
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expression in the head and neck region but faint expression in the tail region (Fig 2a). This staining was completely blocked by pre-incubating this antibody with specific antigenic peptide (Fig 2a). To confirm the expression in human sperm by Western blot analysis, we used two different antibodies raised against the C-terminus of TRPV4. One antibody (Ab1, Sigma-Aldrich) detects a band of 130 kDa (predicted size: 98 kDa) suggesting that in human sperm TRPV4 is subject to post-translational modification (discussed later) (Fig 2b). The second antibody (Ab2, Alomone Labs) detects bands at 130 and 72 kDa and these signals (Ab1 and Ab2) are blocked by using specific peptide suggesting that these immunoreactivities are specific in nature (Fig 2b). Since the predicted size of TRPV4 is 98 kDa, the higher and lower bands represent post-translational modifications and proteolytically degraded products, respectively (addressed later). 6
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We analyzed the percentage of human spermatozoa expressing TRPV4 by FACS (n = 6). Dot plot analysis revealed that all most all spermatozoa (98.98 ± 0.34%) are TRPV4+ (Fig 2c). Upon preincubation with a specific blocking peptide, the same antibody detects less than 1% cells as TRPV4+ve, and the mean fluorescence intensity values reduce significantly, confirming the specificity of the TRPV4
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antibody in FACS application also (Fig 2c-2d). These experiments confirm the expression of TRPV4 in mature human spermatozoa.
TRPV4 is differentially expressed and localized in swim-up and swim-down human sperm
To explore if there is any difference in TRPV4 expression in case of immotile and highly motile
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sperm, we separated the total sperm population into these two fractions, namely swim-up (Su, cells with progressive motility) and swim-down (Sd, cells with mostly impaired motility) samples. In Su cells,
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TRPV4 is primarily located in the head and faintly in the tail (Fig 3a-b). However, in Sd cells, TRPV4 is mostly absent in the head region and highly accumulated at the neck regions (Fig 3a-b). Western blot analysis was performed using Su and Sd samples obtained from three individuals with proven fertility. The Ab1 detects a distinct band at 130 kDa in Sd fraction of all three donors (Fig 3c). However, the corresponding 130 kDa band is mostly absent or faintly present in Su fraction. Densitometry analysis of the 130 kDa region of all donors revealed nearly 6 fold higher level of TRPV4 in Sd as compared to the Su fraction (Fig 3d). In contrast, several smaller fragments of TRPV4 are
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observed in Su samples. Some of these smaller bands were also observed in Sd samples, but with lesser intensities. This in general suggest for low level of full-length TRPV4 (corresponding to 130 kDa) and more proteolytically-cleaved products in motile sample. Furthermore to analyse the extent of proteolytic activity in Su and Sd samples, we probed the same samples for β-tubulin (abundant in cytoplasm) and
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Hsp60 (abundant in mitochondria). These Western blot analysis suggests for higher proteolytic activity in cytoplasm and in mitochondria of Su samples as both β-tubulin and Hsp60 levels are low in Su fraction as
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compared to Sd fraction (Fig 3c).
We analysed the expression of TRPV4 in Su and Sd samples in a more quantitative manner and
performed FACS. Nearly 98.98±0.34% and 96.15±2.8% cells are TRPV4+ in Su and Sd samples respectively (data not shown). However, the MFI-values for Su fraction is more (121.56±37.79) compared to the Sd fraction (89.03±23.76) (n = 6) (Fig 3e). Though this difference may suggests for the more TRPV4 in swim-up samples than swim-down sample, the difference turned out to be statistically non-significant (p = 0.105).
TRPV4 is a glycosylated protein
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In human sperm TRPV4 shows higher molecular weight band (~130 kDa) suggesting that it may be glycosylated. To confirm this, enzymatic treatments of the glycan moieties were performed using two different
glycosidase:
Endoglycosidase-H
(Endo-H,
cleaves
N-linked
high
mannose-rich
oligosaccharides), and Peptide-N-Glycosidase-F (PNGase-F, cleaves both N-linked high mannose-rich
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oligosaccharides and complex oligosaccharides). Migration of TRPV4 is faster when cell extract was treated with PNGase-F but not with Endo-H. After PNGase-F treatment, the resulting TRPV4 band migrates at expected molecular weight (~ 98 kDa) (Fig 3f). It suggests that sperm TRPV4 contains complex glycosidic bond with different types of oligosaccharides. As Su sample does not have detectable
TRPV4 modulates Ca2+-influx into human sperm
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level of full-length TRPV4, from these experiments definitive conclusion cannot be drawn.
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Ca2+-homeostasis in sperm is precisely regulated by different Voltage Operated Channel (VOC) present in the membrane and by female steroids like progesterone [17]. To evaluate the effect of TRPV4 activator and inhibitor upon the Ca+2-influx, we treated Su and Sd human samples with 4αPDD (5µM) or RN1734 (10µM) for 1 hour and labeled with Fluo-4-AM and analyzed the intracellular Ca2+-levels. 4αPDD treatment in Su fraction results in increased intracellular Ca2+-levels but inhibition by RN1734 (10µM) did not decrease the intracellular Ca2+-levels below that of the control conditions (Fig 4a). Notably, in Su fraction, the effect of TRPV4 activation by 4αPDD is comparable to the effect of
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Progesterone (10µM), a standard inducer of Ca+2-influx into sperm cells. The above observation is supported by quantification of Fluo4-AM signal intensity per unit area (n = 4 individuals), revealing that in Su fraction the effect of 4αPDD and Progesterone is similar (Fig 4b). In Sd fraction, there is no
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significant difference in basal Ca2+-levels after modulation of TRPV4 by pharmacological agents (Fig
TRPV4 regulates Ca2+-buffering at the mid-piece and Ca2+-wave propagation in tail
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To understand if and how TRPV4 regulates the intracellular Ca2+-waves, we labelled cells with
Fluo4-AM and performed live cell imaging followed by manual tracking of Ca2+-wave propagation within single cells (Fig 4c). In progesterone-treated cells, the level of Ca2+ is high in the head and neck regions. Progesterone-induced Ca2+-wave originates in the mid-region of sperm head and spreads throughout the neck and then propagates to the tail and mostly covers a large portion of the tail. The Ca2+-wave then subsides and a fresh wave originates in the head. This observation matches with previous reports [18]. In 4αPDD-treated cells, the Ca2+-level is also high in the head and neck regions. The patterns of 4αPDDmediated waves are visible at the tail and are mostly similar to progesterone-induced waves. Notably, application of RN1734 results in reduction of the intracellular Ca2+-level in the head region. Nevertheless, 8
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the Ca2+-wave propagation is observed in the tail region at times, though with less intensity and frequency. Indeed, we observed wavy pattern of intracellular Ca2+-level at the neck regions in case of progesterone- and 4αPDD-induced hyper motile cells (Fig 4c). These results may suggest for a possible
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Ca2+-buffering activity mediated by TRPV4 at the neck region.
Discussion:
Sperm cells have highly condensed DNA, no transcriptional activity and negligible translational activity. These cells are motile and show extreme response against number of variable factors such as
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changes in temperature, pH, osmolality, salts, and compounds at very low concentrations indicating their ability to detect and integrate multiple physical and chemical stimuli precisely [7, 19-20]. Notably, sperm cells perform all these tasks by multiple ion channels and receptors regulating complex yet efficient Ca2+-
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signaling events [21]. We show that TRPV4 is endogenously present in the sperm cells of all vertebrates, ranging from fishes to human. Conserved expression indicates that TRPV4 is probably involved in several of the above mentioned events occurring in sperm cells. We correlate the TRPV4 expression with the ability of sperm to sense optimum temperature, osmolality, and different chemicals and subsequent Ca2+-signaling events.
Different parts of the sperm cell, especially head, neck and tail region are the functionally
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important areas which regulate different yet specific functions. Sperms head is responsible for acrosomal reaction; neck region contains several mitochondria which continuously supply ATP and also act as the only available organelle for Ca2+-buffering, and tail region is important for motility. In all conditions, Ca2+ plays an important role in all physiological conditions. Presence of TRPV4 in the tail of sperm from all vertebrates suggests that it could be a critical regulator of sperm motility. Immunostaining results
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suggests for the differential localization of TRPV4 in different species. In human sperm, TRPV4 localizes in all the regions and it is significantly enriched in the head region.
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In this context, our observation that differential localization of TRPV4 in swim-up and swimdown cells from human sperm is highly indicative. Such differential localizations in these two population correlate well with the better motility regulation by TRPV4. In agreement with that, TRPV4 localization also differs after activation or inhibition by pharmacological agents (data not shown). However our western blot results from these two different fractions indicate that the TRPV4 band at 130 kDa is more abundant in Su sample as compare to Sd sample. On the other hand, the MFI values from FACS data suggest that the total TRPV4 immunoreactivity is more in Su fraction than that of the Sd samples. These in general may suggest that higher level of TRPV4 is present in the Su samples and the same is subjected to more proteolytic degradation, probably due to higher level of Ca2+-influx and Ca2+-dependent proteolytic activation. Western blot analysis of β-tubulin (cytoplasmic) and Hsp60 (mitochondrial) also 9
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suggest the same. Western blot results also suggest that in human sperm, TRPV4 migrates at 130 kDa, (higher than the expected size) and therefore suggests for post-translational modification. It is worth mentioning that in other systems too TRPV4 has been reported at higher sizes (~110-120 kDa size) [2223]. Our results indicate that in human sperm, TRPV4 has branched type of glycosylation, which is
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sensitive to PNGase-F but resistant to Endo-H glycosidase. It suggests that TRPV4 does not contain any N-glycosidic-linkage or due to the presence of branched oligosaccharides, this glycosidic bond is not freely accessible to the Endo-H.
We confirm that >95% of both Su- and Sd-cells contain TRPV4. The localization of TRPV4 in human sperm also correlates well with the Ca2+-waves observed in these cells. Untreated sperm shows a
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rhythmic pattern of Ca2+-waves that originates in the head and migrates to the mid-piece. Progesteroneinduced Ca2+-waves are initiated in the equatorial segment and then spread throughout the rest of the head and then moves rapidly to the tail [18]. TRPV4 activation-induced Ca2+-wave pattern is similar with the
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progesterone-evoked Ca2+-waves, while TRPV4 inhibition blocks the Ca2+-wave generation in the sperm head, thereby negligible Ca2+-influx passes to the mid-piece and tail. This indicates that TRPV4 may be involved in the regulation of both Ca2+-wave generation and propagation in human sperm. TRPV4 may also be involved in Ca2+-buffering function at the neck region of sperm cells. We conclude that TRPV4 is endogenously present in sperm cells of all vertebrates and this is an evolutionary conserved phenomenon since vertebrate evolution. TRPV4 regulates several key functions in
Acknowledgements and notes:
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human sperm cells, such as Ca2+-levels, Ca2+-wave propagation and motility.
Support from frozen cattle semen bank (Khapuria, Cuttack), Dr. PK. Mahapatra (RPRC, Bhubaneswar), Dr.
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P. Routray (CIFA, Bhubaneswar) and lab members is acknowledged. Funding from NISER, DST and DBT are
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acknowledged. The authors declare that they have no conflict of interests.
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References
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[1] M. Yoshida, N. Kawano, K. Yoshida, Control of sperm motility and fertility: diverse factors and common mechanisms, Cell Mol Life Sci 65 (2008) 3446-3457. [2] S. Grunewald, U. Paasch, H.J. Glander, et al. Mature human spermatozoa do not transcribe novel RNA, Andrologia 37 (2005) 69-71.
[4] M. Eisenbach, Sperm chemotaxis, Rev Reprod 4 (1999) 56-66.
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[3] A. Asano, J.L. Nelson, S. Zhang, et al. Characterization of the proteomes associating with three distinct membrane raft sub-types in murine sperm, Proteomics 10 (2010) 3494-3505.
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[5] M. Spehr, G. Gisselmann, A. Poplawski, et al. Identification of a testicular odorant receptor mediating human sperm chemotaxis, Science 299 (2003) 2054-2058. [6] A.M. Petrunkina, R.A. Harrison, M. Ekhlasi-Hundrieser, et al. Role of volume-stimulated osmolyte and anion channels in volume regulation by mammalian sperm, Mol Hum Reprod 10 (2004) 815-823. [7] A. Bahat, I. Tur-Kaspa, A. Gakamsky, et al. Thermotaxis of mammalian sperm cells: a potential navigation mechanism in the female genital tract, Nat Med 9 (2003) 149-150. [8] C. Auzanneau, C. Norez, F. Antigny, et al. Transient receptor potential vanilloid 1 (TRPV1) channels in cultured rat Sertoli cells regulate an acid sensing chloride channel, Biochem Pharmacol 75 (2008) 476-483.
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[9] N. Bernabo, M.G. Pistilli, M. Mattioli, et al. Role of TRPV1 channels in boar spermatozoa acquisition of fertilizing ability, Mol Cell Endocrinol 323 (2010) 224-231. [10] G.A. De Blas, A. Darszon, A.Y. Ocampo, et al. TRPM8, a versatile channel in human sperm, PLoS One 4 (2009) e6095.
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[11] M.G. Gervasi, C. Osycka-Salut, J. Caballero, et al. Anandamide capacitates bull spermatozoa through CB1 and TRPV1 activation, PLoS One 6 (2011) e16993.
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[12] R.K. Majhi, A. Kumar, M. Yadav, et al. Thermosensitive ion channel TRPV1 is endogenously expressed in the sperm of a fresh water teleost fish (Labeo rohita) and regulates sperm motility, Channels (Austin) 7 (2013) 483-492. [13] M. Maccarrone, B. Barboni, A. Paradisi, et al. Characterization of the endocannabinoid system in boar spermatozoa and implications for sperm capacitation and acrosome reaction, J Cell Sci 118 (2005) 43934404. [14] R.K. Majhi, S. Saha, A. Kumar, et al. Expression of temperature-sensitive ion channel TRPM8 in sperm cells correlates with vertebrate evolution, PeerJ 3 (2015) e1310. [15] R.K. Majhi, A. Kumar, M. Yadav, et al. Light and electron microscopic study of mature spermatozoa from White Pekin duck (Anas platyrhynchos): an ultrastructural and molecular analysis, Andrology (2016). [16] T. Jameel, Sperm swim-up: a simple and effective technique of semen processing for intrauterine insemination, J Pak Med Assoc 58 (2008) 71-74.
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[17] H.M. Florman, C. Arnoult, I.G. Kazam, et al. A perspective on the control of mammalian fertilization by eggactivated ion channels in sperm: a tale of two channels, Biol Reprod 59 (1998) 12-16. [18] S. Meizel, K.O. Turner, R. Nuccitelli, Progesterone triggers a wave of increased free calcium during the human sperm acrosome reaction, Dev Biol 182 (1997) 67-75.
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[19] S. Hamamah, J.L. Gatti, Role of the ionic environment and internal pH on sperm activity, Hum Reprod 13 Suppl 4 (1998) 20-30. [20] C.H. Yeung, M. Anapolski, M. Depenbusch, et al. Human sperm volume regulation. Response to physiological changes in osmolality, channel blockers and potential sperm osmolytes, Hum Reprod 18 (2003) 1029-1036. [21] W. Alasmari, C.L. Barratt, S.J. Publicover, et al. The clinical significance of calcium-signalling pathways mediating human sperm hyperactivation, Hum Reprod 28 (2013) 866-876.
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[22] V. Benfenati, M. Caprini, M. Dovizio, et al. An aquaporin-4/transient receptor potential vanilloid 4 (AQP4/TRPV4) complex is essential for cell-volume control in astrocytes, PNAS 108 (2011) 2563-2568.
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[23] C.E. Hills, R. Bland, P.E. Squires, Functional expression of TRPV4 channels in human collecting duct cells: implications for secondary hypertension in diabetic nephropathy, Exp Diabetes Res (2012) 936518.
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Figures and figure-legends
Figure 1. TRPV4 is endogenously expressed in vertebrate sperm. Confocal images demonstrating the presence of TRPV4 in Piscean (a, rohu), amphibian (b, common toad), reptilian (c, house lizard), avian (d, duck) and mammalian (e, bovine) sperm are shown. Cells were immunostained for TRPV4-specific antibody in presence (left most column) or absence of a specific blocking peptide. Images of TRPV4 (green) expression and localization in single cell are shown (right panel).
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Figure 2. TRPV4 is endogenously expressed in human sperm. a. Confocal images showing the endogenous expression of TRPV4 (green) in human sperm. TRPV4 is localized in the post acrosomal and neck regions, while faint expression is also present in the acrosomal and tail region (upper panel). TRPV4 signal is abolished upon blocking the primary antibody with its antigenic peptide (lower panel). b. Western blot analysis using different antibodies (Ab1 and Ab2) shows TRPV4-specific band at ~130 kDa (indicated by arrow). These TRPV4-specific signals are blocked by specific antigenic peptide. Corresponding Coomassie-stained gel is shown in right side. c. Representative dot-plot images from FACS (n = 6) showing the percentage of TRPV4+ cells. Application of blocking peptide reduced this number. d. TRPV4 expression is depicted as the MFI values. e. About 98.98±0.34% cells are TRPV4+ (FACS, n = 6 individuals).
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Figure 3. Swim-up and swim-down fractions of human sperm have different levels of TRPV4. a-b. Cluster (a) and enlarged single cells (b) stained for TRPV4 (green) are shown. Strong signal for TRPV4 is observed throughout the head (primarily in acrosomal region) in the swim-up (Su) fraction. TRPV4 is present in the post-acrosomal and neck regions in the swim-down (Sd) fraction. Faint expression is present in the tail region. c. Western blot analysis of Su and Sd fractions (from 3 individuals, Ind 1-3) were probed for TRPV4, β-tubulin and Hsp60. The 130 kDa band (longer arrow) and smaller bands (smaller arrows) represent the full-length (glycosylated) and proteolyticallydegraded TRPV4 respectively. The corresponding Coomassie gels are provided at right. The prominent band/s around 70-50 kDa (in Su and Sd fraction) as observed by Coomassie staining represents protein/s present in sperm media. d. Densitometry analysis of Western blot signal intensities for 130 kDa band of TRPV4 in Su and Sd fractions (n = 3, ANOVA test, ** p value< 0.005). e. Total TRPV4-specific fluorescence from Su and Sd samples detected as MFI values are shown (ns: non-significant; n = 6, ANOVA test, p = 0.105). f. TRPV4 has complex Nglycosidic linkage and branched complex glycosidic bond, which shows ~30 kDa shift only in presence of PNGaseF (red star). Endo-H treatment does not cause any shift of TRPV4 suggesting that the glycosylated TRPV4 is resistant against Endo-H. The corresponding Coomassie gels are shown in side.
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Figure 4. TRPV4 regulates intracellular Ca2+-levels in human sperm. a. Live cell imaging was performed for Su and Sd fractions pre-treated with TRPV4 activator (4αPDD) or inhibitor (RN1734) or with Progesterone for 1 hour and labeled with Fluo-4-AM. The intracellular Ca2+-levels are represented in pseudo color, (red and blue indicating highest and lowest intensity respectively). b. Quantification of average fluorescence intensity/area (in arbitrary unit) is shown. In Su sample, 4αPDD and progesterone increases the intracellular Ca2+-levels as comparison to control (p<0.05). In Sd sample, 4αPDD or RN1734 do not alter intracellular Ca2+-levels. (n = 4). c. Moving sperm (indicated by asterisk, *) was tracked within a fixed time period (Tn to Tn+7) and arrows indicate the high-level of Ca2+ in neck and tail respectively. Magnified (lower panel) image demonstrating the propagation of Ca2+-waves from head to the tail through the neck. In 4αPDD-treated and progesterone-treated cells, Ca2+-wave propagates
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through the mitochondrial coiling (green rings, indicated by arrows). High-level of Ca2+ (red) in the central stalk region is also visible in this case. In RN1734-treated cells, the Ca2+-waves do not propagate through these regions. The central stalk region reveals mostly moderate- to low-level of Ca2+-flux.
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ACCEPTED MANUSCRIPT Highlights: * TRPV4 is endogenously present in all vertebrate spermatozoa * TRPV4 protein is glycosylated in human sperm * TRPV4 localization and expression is different in Swim-up and Swim-down population of human
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* TRPV4 activation increases the intracellular calcium level
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