Streptococcus gordonii induces bone resorption by increasing osteoclast differentiation and reducing osteoblast differentiation

Accepted Manuscript Streptococcus gordonii induces bone resorption by increasing osteoclast differentiation and reducing osteoblast differentiation Ok-Jin Park, Jiseon Kim, Hyun Young Kim, Yeongkag Kwon, Cheol-Heui Yun, Seung Hyun Han PII:

S0882-4010(18)30799-X

DOI:

https://doi.org/10.1016/j.micpath.2018.11.005

Reference:

YMPAT 3242

To appear in:

Microbial Pathogenesis

Received Date: 4 May 2018 Revised Date:

26 July 2018

Accepted Date: 2 November 2018

Please cite this article as: Park O-J, Kim J, Kim HY, Kwon Y, Yun C-H, Han SH, Streptococcus gordonii induces bone resorption by increasing osteoclast differentiation and reducing osteoblast differentiation, Microbial Pathogenesis (2018), doi: https://doi.org/10.1016/j.micpath.2018.11.005. 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.

ACCEPTED MANUSCRIPT 1

Streptococcus gordonii induces bone resorption by increasing osteoclast differentiation

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and reducing osteoblast differentiation

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Ok-Jin Parka, Jiseon Kima, Hyun Young Kima, Yeongkag Kwona,

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Cheol-Heui Yunb,c, Seung Hyun Hana,*

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a

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Dentistry, Seoul National University, Seoul 08826, Republic of Korea; bDepartment of

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Agricultural Biotechnology and Research Institute for Agriculture and Life Sciences, Seoul

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National University, Seoul 08826, Republic of Korea; cInstitute of Green Bio Science

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Technology, Seoul National University, Pyeongchang 25354, Republic of Korea.

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Department of Oral Microbiology and Immunology, DRI and BK21 Plus Program, School of

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*

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BK21 Plus Program, School of Dentistry, Seoul National University, Building 86, 1 Gwanak-

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ro, Gwanak-gu, Seoul 08826, Republic of Korea; Phone: +82-2-880-2310; Fax: +82-2-743-

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0311; E-mail: [email protected]

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Corresponding author: Department of Oral Microbiology and Immunology, DRI and

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Abstract

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Streptococcus gordonii is commonly found in the periapical endodontic lesions of patients

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with apical periodontitis, a condition characterized by inflammation and periapical bone loss.

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Since bone metabolism is controlled by osteoclastic bone resorption and osteoblastic bone

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formation, we investigated the effects of S. gordonii on the differentiation and function of

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osteoclasts and osteoblasts. For the determination of bone resorption activity in vivo, collagen

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sheets soaked with heat-killed S. gordonii were implanted on mouse calvaria, and the

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calvarial bones were scanned by micro-computed tomography. Mouse bone marrow-derived

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macrophages were stimulated with M-CSF and RANKL for 2 days and then differentiated

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into osteoclasts in the presence or absence of heat-killed S. gordonii. Tartrate-resistant acid

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phosphatase staining was performed to determine osteoclast differentiation. Primary

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osteoblast precursors were differentiated into osteoblasts with ascorbic acid and β-

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glycerophosphate in the presence or absence of heat-killed S. gordonii. Alkaline phosphatase

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staining and alizarin red S staining were conducted to determine osteoblast differentiation.

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Western blotting was performed to examine the expression of transcription factors including

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c-Fos, NFATc1, and Runx2. Heat-killed S. gordonii induced bone destruction in a mouse

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calvarial implantation model. The differentiation of RANKL-primed BMMs into osteoclasts

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was enhanced in the presence of heat-killed S. gordonii. Heat-killed S. gordonii increased the

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expression of c-Fos and NFATc1, which are essential transcription factors for osteoclast

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differentiation. On the other hand, heat-killed S. gordonii inhibited osteoblast differentiation

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and reduced the expression of Runx2, an essential transcription factor for osteoblast

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differentiation. S. gordonii exerts bone resorptive activity by increasing osteoclast

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differentiation and reducing osteoblast differentiation, which may be involved in periapical

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bone resorption.

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Key Words: Apical periodontitis, Streptococcus gordonii, Osteoclast differentiation,

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Osteoblast differentiation, Bone resorption

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ACCEPTED MANUSCRIPT 1. Introduction

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Streptococci, including Streptococcus gordonii, are Gram-positive bacteria known as early

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bacterial colonizers of the oral cavity [1, 2]. The entry of S. gordonii into the bloodstream can

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cause systemic diseases such as infective endocarditis and septic arthritis [3, 4]. S. gordonii

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can easily penetrate the dentinal tubules, and therefore is often isolated from the root canals

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of teeth in patients with apical periodontitis [1]. Importantly, periodontal pathogenic bacteria

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such as Porphyromonas gingivalis can coinvade the dentinal tubules by adhering to S.

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gordonii [5]. Therefore, the penetration of bacteria into the dentinal tubules is considered to

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be an etiologic factor in the pathogenesis of primary apical periodontitis [6].

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Apical periodontitis is a periapical inflammatory disease caused by bacterial invasion of the

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dental pulp [6]. The exposure of the dental pulp to bacteria induces inflammatory responses

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and the infiltration of various immune cells (including leukocytes, lymphocytes, and

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macrophages) into periapical lesions [7]. The prolonged presence of bacteria such as S.

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gordonii in the root canals and dentinal tubules leads to chronic apical periodontitis with

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inflammation [7, 8]. Bacteria-induced proinflammatory cytokines such as interleukin (IL)-1β

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and tumor necrosis factor (TNF)-α in periapical lesions contribute to alveolar bone resorption

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by upregulating osteoclastogenesis [9]. Also, the pathologic environment of inflammation can

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directly affect the formation of new bone [10]. Thus, apical periodontitis is characterized by

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inflammation and alveolar bone resorption with non-healing apical lesions.

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The maintenance of bone structure is the result of the balance between bone resorption by

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osteoclasts and bone formation by osteoblasts [11]. It has been suggested that bone-resorbing

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osteoclasts are derived from the monocyte/macrophage lineage of hematopoietic stem cells 4

ACCEPTED MANUSCRIPT [12]. Macrophages treated with macrophage colony-stimulating factor (M-CSF) and receptor

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activator of nuclear factor-kappa B ligand (RANKL) differentiate into osteoclasts through the

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activation of transcription factors such as c-Fos and NFATc1 [13]. On the other hand, bone-

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forming osteoblasts originate from multipotent mesenchymal stem cells. Osteoblast

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precursors differentiate into mature osteoblasts through the induction of Runx2, a master

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transcription factor for osteoblast differentiation [14]. The dysregulation of bone resorption

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and bone formation can lead to skeletal diseases. Some bacterial infections cause bone

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diseases such as osteomyelitis and periodontitis by promoting osteoclastic bone resorption

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[15]. In addition, pathological conditions accompanied by bacterial infections can inhibit

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bone formation [16, 17].

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Although the isolation of S. gordonii from the root canals of teeth in patients with apical

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periodontitis has been reported, how S. gordonii influences bone metabolism has been poorly

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studied. Therefore, in this study, we investigated the resorption activity of S. gordonii using a

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mouse calvarial bone resorption model in vivo, and evaluated the effects of S. gordonii on the

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differentiation and function of osteoclasts and osteoblasts in vitro.

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2. Materials and Methods

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2.1. Reagents and chemicals

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Todd Hewitt broth (THB) and yeast extract were purchased from BD Biosciences (San Diego,

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CA, USA). Recombinant mouse RANKL and M-CSF were obtained from PeproTech (Rocky

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Hill, NJ, USA). Alizarin red S, β-glycerophosphate, and ascorbic acid were purchased from

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Sigma-Aldrich Inc. (St Louis, MO, USA). SB203580 was obtained from Calbiochem

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(Darmstadt, Germany). Antibodies specific to c-Fos, NFATc1, NFATc2, and NF-κB p65 were

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ACCEPTED MANUSCRIPT purchased from Santa Cruz Biotechnology (Santa Cruz, CA, USA). Antibodies specific to

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phospho-c-Jun and c-Jun were purchased from Cell signaling Technology (Beverly, MA,

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USA). Antibodies specific to Runx2 and β-actin were obtained from MBL International

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(Woburn, MA, USA) and Sigma-Aldrich Inc., respectively. Horseradish peroxidase-

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conjugated anti-rabbit IgG and anti-mouse IgG were purchased from Cell Signaling

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Technology. Fetal bovine serum (FBS) was obtained from Gibco-BRL (Carlsbad, CA, USA).

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Alpha-minimal essential medium (α-MEM), trypsin-EDTA, and penicillin/streptomycin were

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purchased from Hyclone (Waltham, MA, USA).

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2.2. Preparation of heat-killed S. gordonii

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S. gordonii CH1 strain bacteria (kindly provided by Dr. Paul M. Sullam, University of

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California at San Francisco, CA, USA) were cultured in THB supplemented with 5% yeast

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extract (THY) at 37°C to mid-log phase. The bacteria were washed with phosphate-buffered

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saline (PBS) three times and then incubated at 80°C for 2 h. To confirm the complete killing

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of S. gordonii, the bacteria were plated on a THY agar plate and cultured at 37°C for 48 h. No

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bacterial colony was observed (data not shown).

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2.3. Calvarial bone implantation assay

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Animal experiments were approved by the Institutional Animal Care and Use Committee of

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Seoul National University. Six-week-old C57BL/6 male mice were obtained from Orient Bio

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(Seongnam, Korea). Collagen sheets soaked with heat-killed S. gordonii (1 × 108 or 1 × 109

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CFU) or PBS were implanted on mouse calvaria as previously described [18]. After 7 days,

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the calvarial bone was scanned by micro-computed tomography (micro-CT) (Skyscan 1172

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scanner; Skyscan, Kontich, Belgium). The micro-CT images were reconstructed with

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SkyScan CT analyzer software. The resorbed area of bone was measured in the ImageJ

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program (National Institutes of Health, Bethesda, MD, USA).

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2.4. Osteoclast differentiation

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Bone marrow cells (BMs) were isolated from mouse femurs and tibiae and incubated in α-

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MEM supplemented with 10% FBS, 100 U/mL of penicillin, and 100 µg/mL of streptomycin

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with 2 ng/mL of M-CSF for 1 day. Non-adherent cells (i.e., stroma-free BMs) were incubated

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with 20 ng/mL of M-CSF for 5 additional days to force their differentiation into BMMs.

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BMMs, as osteoclast precursors, were plated onto a 96-well culture plate at 2.5 × 104

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cells/200 µL/well and incubated with 20 ng/mL of M-CSF and 20 ng/mL of RANKL for 2

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days. Then, the cells were treated with heat-killed S. gordonii in the presence of 20 ng/mL of

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M-CSF for 24 h. The cells were fixed and stained with a tartrate-resistant acid phosphatase

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(TRAP) kit (Sigma-Aldrich Inc.). TRAP-positive multinucleated cells with more than three

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nuclei were enumerated as mature osteoclasts with an inverted phase-contrast microscope.

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2.5. Osteoblast differentiation

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Primary osteoblast precursors from mouse calvaria were prepared as described previously

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[18]. The cells were plated onto a 48-well plate at 2 × 104 cells/400 µL/well and were treated

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with 50 µg/mL of ascorbic acid and 10 mM β-glycerophosphate in the presence or absence of

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heat-killed S. gordonii. The medium was replaced with fresh medium supplemented with 50

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µg/mL of ascorbic acid and 10 mM β-glycerophosphate every 2 days. On day 6, the cells

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were stained with an alkaline phosphatase (ALP) staining kit (Sigma-Aldrich Inc.). On day

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12, the cells were stained with alizarin red S and quantified as described previously [19]. For

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the Western blot assay, the cells were treated with 50 µg/mL of ascorbic acid and 10 mM β-

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glycerophosphate in the presence or absence of heat-killed S. gordonii for 2 days.

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2.6. Reverse transcriptase polymerase chain reaction (RT-PCR)

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The mRNA expression of TRAP, DC-STAMP, ATP6v0d2 and β-actin was determined by

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using RT-PCR as described previously [20]. The specific primers used were as follows:

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TRAP;

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GCCAGGACAGCTGAGTGCGG-3′,

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ACATGTGGGTGCTGTTTGCCG-3′ and reverse 5′-CGGTTTCCCGTCAGCCTCTCTC-3′,

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ATP6v0d2;

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CCGACAGCGTCAAACAAAGG-3′,

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GTGGGGCGCCCCAGGCACCA-3′ and reverse 5′-CTCCTTAATGTCACGCACGATTTC-

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3′.

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reverse

DC-STAMP;

5′-GGCCGTTTCACAGAGATGGA-3′ and

β-actin;

forward

and

reverse

forward

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5′-AACCGTGCAGACGATGGGCG-3′

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2.7. Western blot assay

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The cells were lysed with RIPA buffer (50 mM Tris, 150 mM NaCl, 1% SDS, 1% sodium

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deoxycholate, and 1% Triton X-100) and then were centrifuged at 13,000 × g for 10 min. The

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total cell lysates were separated by 8% SDS-PAGE and transferred to a PVDF membrane as

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described previously [21, 22]. The membrane was blocked with 5% skim milk at room

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temperature for 1 h and incubated with primary antibodies specific to c-Fos, NFATc1,

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NFATc2, NF-κB p65, phospho-c-Jun, c-Jun, Runx2, or β-actin at 4°C overnight. The

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membrane was washed and incubated with a horseradish peroxidase-conjugated antibody at

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room temperature for 1 h. The immunoreactive bands were detected with ECL reagents

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(Neuronex, Daegu, Korea) on a GeneGnome XRQ system (SYNGENE, Fredrick, MD, USA).

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2.8. Statistical analysis

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All experiments were independently performed at least three times. Statistical significance

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was examined with two-tailed t-tests. Differences were considered significant when P < 0.05.

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3. Results

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3.1. Heat-killed S. gordonii induces bone resorption in vivo

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To examine the effects of heat-killed S. gordonii on bone resorption, we performed an in vivo

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resorption assay using a mouse calvarial implantation model. Collagen sheets soaked with

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heat-killed S. gordonii or PBS were implanted on mouse calvaria. Seven days after the

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treatment, the degree of calvarial bone resorption was determined by micro-CT analysis.

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Heat-killed S. gordonii-implanted calvarial bone exhibited higher bone destruction than PBS-

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implanted calvarial bone (Fig. 1A). The resorbed area was also significantly greater in heat-

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killed S. gordonii-implanted calvarial bone than in control bone (Fig. 1B), suggesting that

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heat-killed S. gordonii exerts bone resorptive activity in vivo.

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3.2. Heat-killed S. gordonii increases osteoclast differentiation

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Since heat-killed S. gordonii induced bone resorption in vivo, we investigated whether this

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effect was due to the enhancement of osteoclast differentiation. To generate committed

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osteoclast precursors, we stimulated BMMs with 20 ng/mL of M-CSF and 20 ng/mL of

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RANKL for 2 days. Committed osteoclast precursors were treated with M-CSF in the

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presence or absence of heat-killed S. gordonii. The cells were subjected to TRAP staining to

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determine the degree of osteoclast differentiation. Concordant with the in vivo results, heat-

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killed S. gordonii increased the number of TRAP-positive multinucleated cells in a dose-

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from committed osteoclasts. It is well known that c-Jun and NF-κB signaling in cooperation

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with NFAT is crucial for osteoclast differentiation [23, 24]. Therefore, we next determined

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whether heat-killed S. gordonii induces the phosphorylation of c-Jun and NF-κB signaling in

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committed osteoclasts. As shown in Fig. 2C, heat-killed S. gordonii potently induced the

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phosphorylation of c-Jun in a time-dependent manner. In addition, heat-killed S. gordonii

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induced the expression of NF-κB p65, but not affected the expression of NFATc2, indicating

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that heat-killed S. gordonii induces the osteoclast differentiation through the upregulation of

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NF-κB signaling (Fig. 2D). Moreover, heat-killed S. gordonii increased the expression of c-

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Fos and NFATc1, both of which are essential transcription factors for osteoclast

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differentiation (Fig. 2E). Next, as shown in Fig. 2F, heat-killed S. gordonii increased the

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mRNA expression levels of NFATc1-dependent genes, including DC-STAMP, ATP6v0d2, and

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TRAP. Furthermore, to validate whether MAPK p38 is involved in heat-killed S. gordonii-

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induced c-Fos expression, committed osteoclasts were pre-treated with SB203580 for 1 h

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followed by stimulation with heat-killed S. gordonii for an additional 24 h. As a result, heat-

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killed S. gordonii-induced c-Fos expression was inhibited in the presence of SB203580,

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indicating that p38 is a critical for the induction of c-Fos by heat-killed S. gordonii (Fig. 2G).

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These results suggest that heat-killed S. gordonii induces the osteoclast differentiation

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through the upregulation of c-Jun/NF-κB/NFATc1 signaling.

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3.3. Heat-killed S. gordonii inhibits osteoblast differentiation

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Next, we examined the effect of heat-killed S. gordonii on osteoblast differentiation.

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Calvarial osteoblast precursors were treated with 50 µg/mL of ascorbic acid and 10 mM β-

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glycerophosphate in the presence or absence of heat-killed S. gordonii. The cells were stained 10

ACCEPTED MANUSCRIPT with ALP or alizarin red S. The results demonstrated that heat-killed S. gordonii inhibited

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ALP staining (Fig. 3A). In addition, heat-killed S. gordonii inhibited the number of alizarin

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red S-positive cells, implying its inhibitory action against osteoblast differentiation via down-

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regulating the deposition of the calcified matrix (Fig. 3B). Because Runx2 is an essential

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transcription factor for osteoblast differentiation, we next examined the effect of heat-killed S.

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gordonii on Runx2 expression. Western blot analysis revealed that heat-killed S. gordonii

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reduced Runx2 expression (Fig. 3C). These results suggest that heat-killed S. gordonii

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inhibits osteoblast differentiation by downregulating Runx2.

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4. Discussion

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In the present study, we demonstrated that heat-killed S. gordonii increased osteoclast

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differentiation and inhibited osteoblast differentiation. Moreover, heat-killed S. gordonii

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induced bone resorption in a mouse calvarial implantation model. These results suggest that S.

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gordonii directly causes bone resorption and retards bone regeneration by inducing osteoclast

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differentiation and inhibiting osteoblast differentiation, potentially contributing to alveolar

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bone loss in the lesions with apical periodontitis.

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To the best of our knowledge, this is the first report that S. gordonii facilitates bone

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destruction. Similar to our results, previous reports have shown that Enterococcus faecalis (a

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refractory

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Porphyromonas gingivalis (periodontal pathogens) induce bone resorption [25-27]. These

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studies indicated that pathogenic bacteria are bone-resorbing factors leading to bone loss at

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infection sites. It is well known that bacteria can contribute to the development of

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inflammatory bone diseases such as periodontitis, osteomyelitis, and septic arthritis [28, 29].

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endodontic

pathogen)

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Aggregatibacter

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actinomycetemcomitans

and

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response and alveolar bone destruction [6]. Collectively, it is conceivable that S. gordonii in

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the periapical lesions of patients with apical periodontitis could contribute to the induction of

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alveolar bone destruction.

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We found that heat-killed S. gordonii efficiently increased osteoclast differentiation, which

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may have led to heat-killed S. gordonii-induced bone resorption. These results are in line with

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previous studies showing that P. gingivalis, Campylobacter rectus, and Fusobacterium

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nucleatum induced bone resorption by increasing the osteoclast number [15]. S. aureus has

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been shown to contribute to staphylococcal bone diseases such as septic arthritis and

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osteomyelitis by increasing osteoclast activity, leading to bone destruction [18, 29]. In

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addition, heat-killed S. gordonii increased the expression of c-Fos and NFATc1, critical

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transcription factors for osteoclast differentiation, through the upregulation of c-Jun/NF-κB

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signaling. Moreover, MAPK p38 is critical for heat-killed S. gordonii-induced c-Fos

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expression. Thus, heat-killed S. gordonii increased osteoclast differentiation by inducing c-

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Fos and NFATc1. Therefore, pathogenic bacteria-induced bone resorption via the induction of

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osteoclast differentiation is likely to be a general phenomenon found in pathological

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conditions of altered bone metabolism.

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Our results also indicated that heat-killed S. gordonii inhibited osteoblast differentiation,

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which may have contributed to the bone resorption induced by heat-killed S. gordonii. We

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previously reported that E. faecalis inhibited osteoblast differentiation [19]. Furthermore, oral

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inoculation with P. gingivalis and F. nucleatum has been reported to reduce the number of 12

ACCEPTED MANUSCRIPT osteoblasts [30]. Because Runx2 is an essential transcription factor for osteoblast

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differentiation [14], the downregulation of Runx2 by S. gordonii inevitably inhibited

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osteoblast differentiation. However, further studies are needed to determine the effect of heat-

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killed S. gordonii on the osteoblast maturation or osteocyte formation in vivo. In general,

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bone is resorbed by osteoclasts, and is subsequently formed by osteoblasts [11]. However,

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osteoblasts exposed to pathogenic bacteria can dysregulate bone metabolism. These results

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imply that pathogenic bacteria directly regulate osteoblast differentiation, contributing to

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apical periodontitis.

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5. Conclusion

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This study demonstrated that heat-killed S. gordonii induces bone resorption in vivo. In

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addition, heat-killed S. gordonii stimulates osteoclast differentiation and reduces osteoblast

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differentiation. These results provide insights into the role of S. gordonii in the progression of

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apical periodontitis with accompanying alveolar bone loss.

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Author contributions

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SHH conceived the idea. SHH and O-JP designed the experiments. O-JP, JK, HYK, YK and

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SHH performed the experiments and/or interpreted the data. C-HY provided critical

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comments. All authors contributed to the discussion of the results, followed by writing and

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reviewing the manuscript.

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Conflict of interests

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All authors state that they have no conflicts of interest.

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ACCEPTED MANUSCRIPT Acknowledgements

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This work was supported by grants from the National Research Foundation of Korea, which

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is funded by the Korean government (NRF-2015R1D1A1A09056592 and NRF-

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2018R1A5A2024418), and the Korea Health Technology R&D Project through the Korea

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Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare

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(HI17C1377), Republic of Korea.

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Figure legends

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Fig. 1. Heat-killed S. gordonii induces bone resorption in a calvarial implantation model.

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Collagen sheets soaked with heat-killed S. gordonii (1 × 108 or 1 × 109 CFU) or PBS were

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implanted on mouse calvaria. After 7 days, the calvarial bone was scanned by micro-CT. (A)

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A representative calvarial scanned image is shown. (B) The resorbed areas of bone were

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measured in the ImageJ program. *P < 0.05 when compared with the PBS group. ROI =

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Regions of interest. One of three similar results is shown.

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Fig. 2. Heat-killed S. gordonii induces osteoclast differentiation. BMMs were stimulated

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with 20 ng/mL of M-CSF and 20 ng/mL of RANKL for 2 days. The cells were stimulated

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with 20 ng/mL of M-CSF and heat-killed S. gordonii (0, 1 × 107, or 1 × 108 CFU/mL). (A, B)

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The cells were fixed and then subjected to TRAP staining to determine osteoclast

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differentiation. TRAP-positive multinucleated cells with three or more nuclei were

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enumerated through microscopic analysis. *P < 0.05 when compared with untreated cells. (C,

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D, E) The cell lysates were prepared and equal amounts of proteins were subjected to Western

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blotting as described in Materials and Methods. (F) The mRNA expression levels of DC-

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STAMP, ATP6v0d2, TRAP, and β-actin were determined by RT-PCR. (G) Committed

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osteoclasts were pre-treated with SB203580 or DMSO (vehicle) for 1 h followed by

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stimulation with heat-killed S. gordonii for an additional 24 h. The protein levels of c-Fos and

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β-actin were determined by Western blotting. One of three similar results is shown.

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Fig. 3. Heat-killed S. gordonii inhibits osteoblast differentiation. Calvarial osteoblast

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precursors were treated with 50 µg/mL of ascorbic acid and 10 mM β-glycerophosphate in the 18

ACCEPTED MANUSCRIPT presence or absence of heat-killed S. gordonii (0, 1 × 107, or 1 × 108 CFU/mL). (A) After 6

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days, the cells were subjected to ALP staining. (B) After 12 days, the cells were subjected to

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alizarin red S staining to determine osteoblast differentiation. Alizarin red S precipitates were

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dissolved and measured by spectrophotometric analysis at 450 nm. *P < 0.05 when compared

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with untreated cells. (C) After 2 days, the protein levels of Runx2 and β-actin were

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determined by Western blotting. One of three similar results is shown.

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Figure 1 A Heat-killed S. gordonii (CFU) 108 109

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PBS

40 30 20 10

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Resorbed area per ROI (%)

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Figure 2 A

B Heat-killed S. gordonii (CFU/mL) 108

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*

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TRAP+ MNCs/well

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*

100 50 0

107

0

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C

D Heat-killed S. gordonii (CFU/mL) 108

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p-c-Jun c-Jun

Heat-killed S. gordonii (CFU/mL)

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NFATc1

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Heat-killed S. gordonii (108 CFU/mL)

SB203580 (µM)

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DMSO

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Figure 3 A

Heat-killed S. gordonii (CFU/mL) 107

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Alizarin Red S stain (absorbance at 450 nm)

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Heat-killed S.gordonii (CFU/mL) Runx2

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Highlights


An endodontic pathogen S. gordonii induces bone resorption in a mouse calvarial




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implantation model. S. gordonii increases osteoclast differentiation through up-regulation of c-Fos and NFATc1.

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S. gordonii inhibits osteoblast differentiation by downregulating Runx2.

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