Glial fibrillary acidic protein (GFAP) and the astrocyte intermediate filament system in diseases of the central nervous system

Available online at www.sciencedirect.com

ScienceDirect Glial fibrillary acidic protein (GFAP) and the astrocyte intermediate filament system in diseases of the central nervous system Elly M Hol1,2,3 and Milos Pekny4,5,6 Glial fibrillary acidic protein (GFAP) is the hallmark intermediate filament (IF; also known as nanofilament) protein in astrocytes, a main type of glial cells in the central nervous system (CNS). Astrocytes have a range of control and homeostatic functions in health and disease. Astrocytes assume a reactive phenotype in acute CNS trauma, ischemia, and in neurodegenerative diseases. This coincides with an upregulation and rearrangement of the IFs, which form a highly complex system composed of GFAP (10 isoforms), vimentin, synemin, and nestin. We begin to unravel the function of the IF system of astrocytes and in this review we discuss its role as an important crisis-command center coordinating cell responses in situations connected to cellular stress, which is a central component of many neurological diseases. Addresses 1 Department of Translational Neuroscience, Brain Center Rudolf Magnus, University Medical Center Utrecht, 3584 CG Utrecht, The Netherlands 2 Netherlands Institute for Neuroscience, An Institute of the Royal Netherlands Academy of Arts and Sciences, 1105 BA Amsterdam, The Netherlands 3 Swammerdam Institute for Life Sciences, Center for Neuroscience, University of Amsterdam, 1098 XH Amsterdam, The Netherlands 4 Center for Brain Repair and Rehabilitation, Department of Clinical Neuroscience and Rehabilitation, Institute of Neuroscience and Physiology, Sahlgrenska Academy at the University of Gothenburg, SE405 30 Gothenburg, Sweden 5 Florey Institute of Neuroscience and Mental Health, Parkville, Victoria, Australia 6 Hunter Medical Research Institute, University of Newcastle, New South Wales, Australia Corresponding authors: Hol, Elly M ([email protected]) and Pekny, Milos ([email protected])

Current Opinion in Cell Biology 2015, 32:121–130 This review comes from a themed issue on Cell architecture Edited by Elly M Hol and Sandrine Etienne-Manneville For a complete overview see the Issue and the Editorial

http://dx.doi.org/10.1016/j.ceb.2015.02.004 0955-0674/# 2015 Elsevier Ltd. All rights reserved.

providing an optimal structural and metabolic environment for neurons. Now it is widely acknowledged that astrocytes are actively involved in many aspects of CNS physiology and pathology. This paradigm shift also instigated the interest in unravelling the function of GFAP and its recently discovered isoforms, as this signature astrocyte cytoskeletal protein is highly regulated in disease. GFAP has been implicated to play a role, for example, in cell migration and motility, in anchoring the glutamate transporter GLAST/EAAT1 in the membrane, and in mitosis [1]. Mouse models showed that eliminating GFAP might decrease the resistance of the brain tissue to severe mechanical stress [2]. Overexpression of GFAP resulted in a fatal encephalopathy with accumulations of GFAP in Rosenthal fibers. This finding led to the discovery that Alexander’s disease is caused by mutations in the GFAP gene [3]. Astrocytes employ their GFAP-containing IF network as a signaling platform and a structural scaffold that coordinates the appropriate responses of astrocytes in health and disease.

Astrocytes — a key cell type in the central nervous system Astrocytes are the versatile caretakers of the CNS [4]. They are indispensable for proper brain development [5,6,7,8], play fundamental roles in maintaining ion, neurotransmitter, water [9] and energy homeostasis [10], and modulate neuronal signaling [11,12]. Astrocytes subdivide the grey matter of the CNS into domains encompassing blood vessels, neurons, and synapses [13]. A single astrocyte in the human brain can, within its domain, accommodate as many as 2,000,000 synapses [14]. For this reason, a more appropriate view of an astrocyte is that of a cell integrating the functions of all cellular elements of the nervous tissue. In specific niches in the adult brain astrocytes function as neural progenitors [15]. These cells will continuously produce new astrocytes and neurons, even in brain of the elderly and patients suffering from neurodegenerative disease [16,17]. Deranged neural progenitors or mature astrocytes are thought to be the cause of high grade astrocytoma [18,19], which are highly malignant brain tumors.

Reactive astrogliosis in disease pathogenesis Introduction In the last two decades the view on astrocytes has dramatically changed. For a long time they were considered to be merely bystanders and caretakers in the brain, www.sciencedirect.com

Reactive astrogliosis is a characteristic change in the morphology and function of astrocytes seen in many neurological disorders, such as neurotrauma, ischemic stroke, and neurodegenerative disease, which profoundly Current Opinion in Cell Biology 2015, 32:121–130

122 Cell architecture

affects both the disease progression and the recovery process [20,21,22]. Reactive astrocytes show altered expression of many genes [23,24,25,26] and the upregulation of GFAP, the main constituent of astrocyte IFs, is commonly used as a hallmark of reactive astrocytes (Figures 1 and 2). Cytokines, for example, TGF-a, CNTF, IL-6, LIF, and others, are known to trigger astrocyte activation [27], either directly via STAT3 signaling in astrocytes [28] or, indirectly, via other cell types, for example, microglia, neurons, or endothelial cells. On a morphological level, reactive astrogliosis ranges from mild to prominent, the latter being often accompanied by glial scarring [29]. Depending on the type of the underlying neuropathological process, reactive astrocytes form, together with pericytes [30], a demarcating border around a lesion [31] or can be found throughout the lesion. Reactive gliosis has both general and diseasespecific cellular and molecular features [32]. A mild, but chronic form of reactive gliosis occurs in Alzheimer’s disease. In an Alzheimer’s disease mouse model it was shown that reactive astrocytes were not dividing [33], and assume an immune activated phenotype [23,34]. This is in contrast with acute injury models, in which astrocytes proliferate and sequester the lesion. Elimination of the dividing subpopulation of reactive astrocytes in a mouse transgenic model suggested a positive role for reactive gliosis in the acute repair process through reducing the extent of neurodegeneration and facilitating the blood–brain barrier reconstruction [35,36]. Astrocytespecific genetic ablation of STAT3 inhibits lesion demarcation and results in larger lesions and more prominent functional impairment [37,38,39]. By contrast, ablation of Socs3, a negative feedback molecule of STAT3 [40], leads to increased phosphorylation of STAT3, more prominent contraction of the lesion area, and better functional recovery after spinal cord lesions in mice [38].

Reactive astrocytes and neuronal communication Astrocytes are actively involved in the modulation of neuronal signaling [41]. These cells, together with neurons, form the tripartite synapse [42]. Recently, it has been shown that this concept is also applicable to the human brain [43]. Astrocytes have been shown to be involved in long term potentiation [12], which is important for synaptic plasticity, learning and memory. The decrease in glutamine synthetase in reactive astrocytes results in the depletion of glutamine and consequently reduction of synaptic GABA causing hyperexcitability of hippocampal neuronal circuits [44]. It has been shown in an Alzheimer’s disease mouse model that reactive astrocytes have increased intracellular calcium levels in the vicinity of amyloid plaques thus potentially affecting neuronal signaling [45]. Further, astrocyte function as measured by cell coupling and glutamate reactivity is Current Opinion in Cell Biology 2015, 32:121–130

altered [46], and reactive astrocytes display an abnormally high release of GABA [47]. Upregulation of the mRNA of IF proteins in reactive astrocytes coincides with changes in the immune response, and changed expression of neuronal communication genes [23] as shown in acutely isolated reactive astrocytes from Alzheimer’s disease mice. Thus the upregulation/re-arrangement of the IF network is an early response in a chronic disease process such as Alzheimer’s disease [33,48] and might facilitate changes in cell signaling and lead to functional changes.

The intermediate filament system in astrocytes Intermediate filaments are a highly dynamic part of the cell’s cytoskeleton and their expression is highly cell type specific. Astrocytes express 10 different isoforms of GFAP, together with vimentin, nestin, and synemin [1,49–51] (Figure 3). Astrocytoma and astrocytoma cell lines also express these intermediate filament proteins [52,53], and subclasses of astrocytoma grade IV were identified based on their specific IF network which might be potentially linked to their migratory potential [53,54]. A decrease in GFAP was reported in astrocytoma grade IV, which most likely reflects the dedifferentiated state of these cells. A loss of GFAP does not seem to be a causal step in tumor development, as P53/ mice, that have a high incidence of astrocytoma after ethylnitrosourea induction, showed a comparable incidence and progression of astrocytoma on the GFAP+/+ and GFAP/ background [55]. There is an interesting subcellular localization of the mRNA of the IF proteins in astrocytes. Nestin mRNA is enriched in cell protrusions [56] and the GFAPa mRNA isoform is more localized in protrusions in comparison to GFAPd mRNA, which is dependent on the different 30 -exon sequences included in GFAPa and GFAPd mRNA [57]. The relevance of this subcellular localization is still unknown. To study the function of the IF network in astrocytes, mice deficient for GFAP (GFAP/) were generated independently in four laboratories [58–61], three of these did not detect any pathologies in unchallenged GFAP/ mice [58,60,61] and one reported spontaneous demyelination in the CNS [59]. Observations from some injury paradigms in these mice suggested an increased fragility of the CNS in the absence of GFAP. Specifically, when GFAP/ mice were subjected to head injury from a dropped weight and were placed on a support that allowed head movement at impact, most of them, but none of the wild-type controls, died after the insult, showing prominent subpial and white matter bleeding in the region of the cervical spinal cord, possibly resulting from a vein rupture [62]. On the other hand, GFAP/ mice exhibit normal response to severe mechanical stress imposed on the retina [63], wound healing after fine needle injury of the brain cortex www.sciencedirect.com

Astrocyte intermediate filament system in CNS diseases Hol and Pekny 123

Figure 1

Non-reactive astrocytes

Reactive astrocytes

(a)

GFAP

GFAP

(b)

Injury Reactive astrocytes

Non-reactive astrocytes

Alzheimer

(c)

(d)

A

Control (e)

TBI Current Opinion in Cell Biology

Reactive astrocytes show an upregulation of the IF protein GFAP and hypertrophy of cellular processes, but stay within their tiled domains. (a) Neurotrauma triggers reactive gliosis, as shown here 4 days after enthorhinal cortex lesion, which leads to partial deafferentation of the dentate gyrus of the hippocampus. The bundles of intermediate filaments were visualized with antibodies against GFAP (green) and they reveal hypertrophy of cellular processes of reactive astrocytes (right) compared to those in the uninjured hippocampus (left). (b) Schematic rendering of astrocyte reaction to neurotrauma. Despite the fact that the main processes of reactive astrocytes become thicker (and therefore appear longer; compare the circles), reactive astrocytes stay within their respective tiled domains, that is, they access a comparable volume of brain tissue. (c) Reactive astrocytes surrounding an amyloid plaque in the cortex of an Alzheimer’s disease mouse (6 month-old APP-PS1 mouse). All astrocytes have a red nucleus (expression of sox-2) and some of them show a major increase in the GFAP immunoreactivity (green). (d) and (e) An overview of the cortex of adult mice immunostained for GFAP (red) and cell nuclei (blue) in an injured mouse and 72 hours after traumatic brain injury (TBI, weight drop model), the latter showing massive reactive gliosis. Scale bar: 20 mm (a, c) and 1 mm (d, e). (a) and (b) were reproduced from [26], (c)–(e) are obtained from Willem Kamphuis and Oscar Stassen (Hol lab).

www.sciencedirect.com

Current Opinion in Cell Biology 2015, 32:121–130

124 Cell architecture

Figure 2

CNS pathologies Physiological situation – unchallenged CNS

Astrocytes respond to trauma, stroke, or neurodegenerative diseases by becoming reactive, with GFAP upregulation and process hypertrophy as hallmarks

Reactive astrogliosis

This response helps to: Triggered by e.g. TGFα, CNTF, IL-6, or LIF

Handle acute stress Limit tissue/organ damage Restore homeostasis

Reactive astrogliosis is Physiological functions, e.g. Control of neuronal synapses Neurotransmitter uptake/recycling Maintenance of homeostasis Control of blood-brain barrier Regulation of blood flow Control/modulation of neurogenesis

Disease-specific Can range to mild to very severe (glial scar) Shows regional specificity Can be diffuse or sequestering the lesion area

Persisting reactive gliosis can become maladaptive attenuation of reactive gliosis as a therapeutic goal Current Opinion in Cell Biology

Astrocytes are highly active both in a physiological and pathophysiological context, with reactive astrogliosis being a prominent component of several neurological disorders. Reactive astrogliosis — with the characteristic upregulation of GFAP and other IF proteins - is a positive defensive response that seems to help to handle acute cellular stress, limit the tissue damage and restore homeostasis in the brain or spinal cord. However, it seems that persisting reactive astrogliosis can become maladaptive and reduce regeneration and the extent of functional recovery. Partially adapted from [99].

[64], and scrapie infection has the same progression as in wild-type mice [58,65].

The absence of the intermediate filament system and the consequences for astrocyte function IFs in reactive astrocytes are composed of GFAP, vimentin, nestin, and in a proportion of reactive astrocytes, synemin is also present [66–68]. Combined deficiency of GFAP and vimentin in GFAP/Vim/ mice results in the absence of cytoplasmic IFs in reactive astrocytes [64], because when both GFAP and vimentin are absent, neither nestin [69] nor synemin [68] self-polymerize or co-polymerize into IFs. GFAP/Vim/ mice show attenuated reactive gliosis, impaired formation of glial scar, more prominent synaptic loss after neurotrauma [64,70], and have the CNS tissue less resistant to mechanical stresses [63,71,72]. Reactive astrocytes of GFAP/Vim/ mice do not develop the characteristic thickening (hypertrophy) of cellular processes [26,70]. These results suggested that IF upregulation is an important component of reactive astrogliosis [2,24]. When Current Opinion in Cell Biology 2015, 32:121–130

the GFAP/Vim/ mice were subjected to focal brain ischemia, they developed larger infarction compared to wild-type mice [73]. We are still seeking the mechanistic understanding of some of these phenomena, but a number of studies linked the astrocyte IF system to cell migration [54], viscoelastic properties [74], vesicle trafficking [75–77], activation of Erk and c-fos [78], control of glutamate transport and astrocyte gap junctional communication [73], reaction to hypoosmotic and oxidative stresses [49,79], reconstruction of blood–brain barrier [80], and interaction with microglia [81,82]. Highly interestingly, attenuation of reactive astrogliosis in GFAP/Vim/ mice is also associated with positive outcomes, despite more extensive tissue damage in the initial acute phase of CNS injury [73]. GFAP/Vim/ mice have better post-traumatic synaptic regeneration in the hippocampus [70], show improved axonal regeneration after the optic nerve crush induced in the early postnatal period [83], and display better regeneration and functional recovery after spinal cord trauma [84]. Both the basal and post-traumatic hippocampal neurogenesis www.sciencedirect.com

Astrocyte intermediate filament system in CNS diseases Hol and Pekny 125

Figure 3

Head

Tail

Rod 1A

1B

2A

2B GFAPα GFAPΔ135 GFAPδ GFAPκ GFAPΔexon 7 GFAPΔ164 GFAPΔexon 6 vimentin nestin

synemin

Current Opinion in Cell Biology

Intermediate filament proteins in astrocytes. A scheme of the different GFAP isoforms, vimentin, nestin, and synemin in mouse astrocytes. The head, rod, tail domains are indicated. The different GFAP isoforms mainly differ in the length of the rod domain and the sequence of the tail. However, it needs to be remarked that the N-termini of GFAPDexon 7, D164, and Dexon6 have not been determined by full length cloning. The domains that are similar in each protein have the same shape and colour. GFAPa and GFAPD135 have the same C-terminus (green); GFAPDexon 7, D164, and Dexon6 also have a same C-terminus (dark purple). GFAPd and GFAPk have unique C-termini. Specific antibodies against C-termini are available; see [1,48,51].

in GFAP/Vim/ mice are increased, conceivably due to negative regulation of neurogenesis by astrocytes via Notch signaling from astrocytes to neural stem cells which is dependent on the astrocyte IF system [85]. Also, GFAP/Vim/ mice, when subjected to neonatal hypoxic-ischemic injury, generate more cortical neurons [86]. Adult GFAP/Vim/ mice show improved integration of neural grafts in the retina [87] and increased neuronal and astrocyte differentiation of neural stem cells transplanted in the hippocampus [88]. Thus, the positive side of reactive astrogliosis at the acute stress-handling phase of neurotrauma or stroke is balanced against restricted regenerative potential at a later stage (see Figure 2).

GFAP isoform expression in reactive gliosis and in high grade astrocytomas In a chronic degenerative disease, such as an Alzheimer’s disease mouse model, associated with a slow build-up of pathology, mouse astrocytes display an increase in GFAP isoforms (Table 1). Between 9 and 18 month of age, when full pathology is apparent, GFAPa, b, g, d, z, k, and Dexon 7 were all upregulated (between 2-fold and 6-fold). www.sciencedirect.com

GFAPD135, GFAPDexon6, and GFAPD164 were not expressed. In mice, this coincides with a 2-fold increase in vimentin, but without an increase in synemin H, synemin M, and nestin [51]. These data are in contrast with the reported increase in GFAP, vimentin, and nestin in reactive astrocytes in an acute mouse brain injury model (stabwound) [69] and increase of GFAP, synemin and vimentin in a mouse entorhinal cortex lesion model [68]. In the human Alzheimer’s disease brain, GFAPa, b, d, z, k, D135 are upregulated (2–3 fold). GFAPg was not expressed, D164, Dexon6 and Dexon7 were expressed but at a very low level. However, a clear increase in GFAP+1 protein was present, which is coded by D164, Dexon6, and Dexon7. In the human brain, nestin, vimentin, synemina, and synemin-b were upregulated [48]. In astrocytoma GFAPd is expressed, most likely together with other isoforms [89]. High-invasive astrocytomas have been shown to express higher levels of nestin and GFAPd [90] than low-invasive ones. In addition, a positive correlation has been found between the astrocytoma grade and the intensity of GFAPd immunoreactivity [91,92]. Current Opinion in Cell Biology 2015, 32:121–130

126 Cell architecture

Table 1 Intermediate filament proteins (also known as nanofilaments) in astrocytes and reactive gliosis Astrocyte IF protein

GFAPa GFAPb GFAPg GFAPd * GFAPk GFAPj GFAPD135 ** GFAPD164 ** GFAPDexon6 ** GFAPDexon7 ** Vimentin Nestin Synemin H/A Synemin M/B

Expression in reactive astrocytes

Protein length (aa)

Mouse/human

Mouse

Human

Increased/increased Increased/increased Increased/***not expressed Increased/increased Increased/increased Increased/increased Below detection/increased Not expressed/not clear Below detection/not clear Increased/increased Increased/increased Increased or unchanged/increased Increased or unchanged/increased Increased or unchanged/increased

430 Unknown# Unknown# 428 433 Unknown# 385 368 341 400 466 1846 1561 1259

432 Unknown# Unknown# 431 438 Unknown# 387 366 347 406 466 1621 1565 1253

Transcript

Exon 1–9 (canonical) Alternative upstream start site Lacks exon 1, includes the last 126 bp of intron 1 Exon 1–7a Exon 1–7b Includes last 284 bp of intron 8–9 Part exon 6 deleted Part exon 6 and exon 7 deleted Exon 6 deleted Exon 7 deleted Full length Full length Splice isoform Splice isoform

*

GFAPd is also known as GFAPe. Splice forms were expressed, full length sequences were not experimentally determined but were based on in silico cloning. *** Personal communication Willem Kamphuis. # Only partial but specific mRNA sequences were quantified, full length is unknown. Data are based on [48,51,68,69]. **

The stoichiometry of the different isoforms is important for the formation of the IF network, but the functional consequences of the different constitutions of the IF network are still elusive. In the human brain, it is known that GFAPd is highly expressed in subtypes of astrocytes, such as the neurogenic astrocytes in the subventricular zone [16]. A first indication that a switch in the ratio d/a can have important functional consequences is shown by shifting the isoform expression in favor of GFAPd (by isoform specific silencing), which led to a change in integrin expression, a decrease in plectin, and an increase in laminin [52]. Splicing of GFAP is coupled to the transcription rate of GFAP [93] and a change in splicing has a direct effect on the IF network. In vanishing white matter disease, there is a predominant expression of GFAPd, and these astrocytes show an abnormal IF network [94]. Also in epilepsy an increase in GFAPd [95] and GFAP+1 [96] was observed. A clear example, showing that problems with the IF network can cause a disease, is Alexander disease, a lethal neurodegenerative disease with extensive reactive gliosis. In this disorder de novo mutations in GFAP lead to a pronounced white matter pathology [97] and the expression of mutant GFAP in a mouse model negatively affects neurogenesis and cognition [97,98].

Conclusions GFAP, the principal IF protein of astrocytes, is involved in physiological, but in particular, in pathophysiological functions of astrocytes, the latter ones being connected with astrocyte activation and reactive gliosis. The negative, regeneration inhibiting side of reactive gliosis and glial scar has been known for years. Astrocyte IF proteins and a number of other molecules were implicated as Current Opinion in Cell Biology 2015, 32:121–130

important players in this response and emerged as potential pharmacological targets [99]. What we now seem to appreciate better, is the other side of reactive gliosis, that is, the one that leads to beneficial effects and results in increased resilience to acute cellular stress, potentially leading to increased neuroprotection (Figure 2). It is plausible to think that these acute responses of astrocytes allow better protection of the nervous tissue, but the price for it is a restricted regenerative capacity. This opens interesting opportunities for designing novel experimental modalities, with the right timing, both for treatment and prevention.

Acknowledgements The authors acknowledge Dr. Marcela Pekna for useful comments on the manuscript, Dr. Willem Kamphuis and Oscar Stassen for providing the image of Figure 1, and support from NanoNet COST Action BM1002 (EMH and MP), the Netherlands Organization for Scientific Research (EMH 865.09.003), Internationale Stichting Alzheimer Onderzoek (EMH 04511, 08504 and 12509), FOM (EMH 09MMC06), Hersenstichting Nederland (EMH 13F05.08, 15F07.40), Stichting Parkinson Fonds (EMH), DorpmansWigmans Stichting (EMH), the Swedish Medical Research Council (MP project 11548), AFA Research Foundation (MP), ALF Go¨teborg (MP project 11392), Hja¨rnfonden (MP), Hagstro¨mer’s Foundation Millennium (MP), the Swedish Stroke Foundation (MP), Amlo¨v’s Foundation (MP), E. Jacobson’s Donation Fund (MP), the EU FP 7 Program EduGlia (MP 237956), and the EU FP 7 Program TargetBraIn (MP 279017).

References and recommended reading Papers of particular interest, published within the period of review, have been highlighted as:  of special interest  of outstanding interest 1.

Middeldorp J, Hol EM: GFAP in health and disease. Prog Neurobiol 2011, 93:421-443.

2.

Pekny M, Pekna M: Astrocyte intermediate filaments in CNS pathologies and regeneration. J Pathol 2004, 204:428-437. www.sciencedirect.com

Astrocyte intermediate filament system in CNS diseases Hol and Pekny 127

3.

Liem RK, Messing A: Dysfunctions of neuronal and glial intermediate filaments in disease. J Clin Invest 2009, 119:1814-1824.

4. 

Parpura V, Heneka MT, Montana V, Oliet SH, Schousboe A, Haydon PG, Stout RF Jr, Spray DC, Reichenbach A, Pannicke T et al.: Glial cells in (patho)physiology. J Neurochem 2012, 121:427. A multifaceted review coming from a dozen of European and American laboratories on the role of astroglial cells in physiological and pathophysiological processes.

5. 

Allen NJ, Bennett ML, Foo LC, Wang GX, Chakraborty C, Smith SJ, Barres BA: Astrocyte glypicans 4 and 6 promote formation of excitatory synapses via GluA1 AMPA receptors. Nature 2012, 486:410-414. Important molecular study on the role of astrocytes in synaptogenesis.

6. 

Bialas AR, Stevens B: TGF-beta signaling regulates neuronal C1q expression and developmental synaptic refinement. Nat Neurosci 2013, 16:1773-1782. Key study linking the complement system and TGF-beta in synaptic pruning. Chung WS, Clarke LE, Wang GX, Stafford BK, Sher A, Chakraborty C, Joung J, Foo LC, Thompson A, Chen C et al.: Astrocytes mediate synapse elimination through MEGF10 and MERTK pathways. Nature 2013, 504:394-400. Shows molecular mechanisms contributing to the current understanding of astrocyte-mediated synapse elimination.

7. 

8.

9.

Kucukdereli H, Allen NJ, Lee AT, Feng A, Ozlu MI, Conatser LM, Chakraborty C, Workman G, Weaver M, Sage EH et al.: Control of excitatory CNS synaptogenesis by astrocyte-secreted proteins Hevin and SPARC. Proc Natl Acad Sci USA 2011, 108:E440-E449. Haj-Yasein NN, Vindedal GF, Eilert-Olsen M, Gundersen GA, Skare O, Laake P, Klungland A, Thoren AE, Burkhardt JM, Ottersen OP, Nagelhus EA: Glial-conditional deletion of aquaporin-4 (Aqp4) reduces blood-brain water uptake and confers barrier function on perivascular astrocyte endfeet. Proc Natl Acad Sci USA 2011, 108:17815-17820.

10. Allaman I, Belanger M, Magistretti PJ: Astrocyte-neuron metabolic relationships: for better and for worse. Trends Neurosci 2011, 34:76-87. 11. Giaume C, Koulakoff A, Roux L, Holcman D, Rouach N: Astroglial networks: a step further in neuroglial and gliovascular interactions. Nat Rev Neurosci 2010, 11:87-99. 12. Henneberger C, Papouin T, Oliet SH, Rusakov DA: Long-term potentiation depends on release of D-serine from astrocytes. Nature 2010, 463:232-236. 13. Bushong EA, Martone ME, Ellisman MH: Maturation of astrocyte  morphology and the establishment of astrocyte domains during postnatal hippocampal development. Int J Dev Neurosci 2004, 22:73-86. An important study visualizing the volume of the brain tissue accessed by individual astrocytes and the overlap between neighboring astrocyte domains in a normal developing mouse brain. 14. Oberheim NA, Takano T, Han X, He W, Lin JH, Wang F, Xu Q,  Wyatt JD, Pilcher W, Ojemann JG et al.: Uniquely hominid features of adult human astrocytes. J Neurosci 2009, 29:3276-3287. Experimental evidence is provided demonstrating higher structural complexity of human versus murine astrocytes. It gives yet another reason for using human tissue and astroglial cells, whenever possible for physiological and pathophysiological studies. 15. Mamber C, Kozareva DA, Kamphuis W, Hol EM: Shades of gray: the delineation of marker expression within the adult rodent subventricular zone. Prog Neurobiol 2013, 111:1-16. 16. van den Berge SA, Middeldorp J, Zhang CE, Curtis MA, Leonard BW, Mastroeni D, Voorn P, van de Berg WD, Huitinga I, Hol EM: Longterm quiescent cells in the aged human subventricular neurogenic system specifically express GFAP-delta. Aging Cell 2010, 9:313-326. 17. van den Berge SA, van Strien ME, Korecka JA, Dijkstra AA, Sluijs JA, Kooijman L, Eggers R, De FL, Vescovi AL, Verhaagen J et al.: The proliferative capacity of the subventricular zone is www.sciencedirect.com

maintained in the parkinsonian brain. Brain 2011, 134:3249-3263. 18. Chen J, McKay RM, Parada LF: Malignant glioma: lessons from genomics, mouse models, and stem cells. Cell 2012, 149:36-47. 19. Watkins S, Sontheimer H: Unique biology of gliomas: challenges and opportunities. Trends Neurosci 2012, 35:546-556. 20. Seifert G, Schilling K, Steinhauser C: Astrocyte dysfunction in neurological disorders: a molecular perspective. Nat Rev Neurosci 2006, 7:194-206. 21. Burda JE, Sofroniew MV: Reactive gliosis and the  multicellular response to CNS damage and disease. Neuron 2014, 81:229-248. Reviews the current concept of reactive gliosis in CNS pathologies from both the cellular and molecular perspective. 22. Barres BA: The mystery and magic of glia: a perspective on their roles in health and disease. Neuron 2008, 60:430-440. 23. Orre M, Kamphuis W, Osborn LM, Jansen AH, Kooijman L,  Bossers K, Hol EM: Isolation of glia from Alzheimer’s mice reveals inflammation and dysfunction. Neurobiol Aging 2014. In this study astrocytes are acutely isolated from brains of 15–18 monthold Alzheimer mice and littermate controls. It gives a first insight in the molecular changes in cortical reactive astrocytes and provides evidence that the neuron supportive function of astrocytes is reduced and that the astrocytes are immune activated. 24. Pekny M, Nilsson M: Astrocyte activation and reactive gliosis. Glia 2005, 50:427-434. 25. Sofroniew MV: Molecular dissection of reactive astrogliosis  and glial scar formation. Trends Neurosci 2009, 32:638-647. An important conceptual review on reactive gliosis with an outline of its molecular definition. 26. Wilhelmsson U, Bushong EA, Price DL, Smarr BL, Phung V,  Terada M, Ellisman MH, Pekny M: Redefining the concept of reactive astrocytes as cells that remain within their unique domains upon reaction to injury. Proc Natl Acad Sci USA 2006, 103:17513-17518. Redefines the morphological concept of reactive gliosis in neurotrauma: reactive astrocytes respect their tiled domains and do not significantly enter each other’s territories. Note that this might not be the case in epilepsy as reviewed in [99]. 27. Hostenbach S, Cambron M, D’haeseleer M, Kooijman R, De KJ: Astrocyte loss and astrogliosis in neuroinflammatory disorders. Neurosci Lett 2014, 565:39-41. 28. Sriram K, Benkovic SA, Hebert MA, Miller DB, O’Callaghan JP: Induction of gp130-related cytokines and activation of JAK2/ STAT3 pathway in astrocytes precedes up-regulation of glial fibrillary acidic protein in the 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine model of neurodegeneration: key signaling pathway for astrogliosis in vivo? J Biol Chem 2004, 279:19936-19947. 29. Sofroniew MV: Reactive astrocytes in neural repair and protection. Neuroscientist 2005, 11:400-407. 30. Goritz C, Dias DO, Tomilin N, Barbacid M, Shupliakov O, Frisen J:  A pericyte origin of spinal cord scar tissue. Science 2011, 333:238-242. Conceptually important study introducing pericytes as key players in glial scar formation. Pericytes and their role in CNS pathologies are often overlooked. As astrocytes, pericytes are most probably a highly heterogeneous cell population and need to be defined on a molecular level. It is probable that their molecular signature will depend on the disease context. 31. Voskuhl RR, Peterson RS, Song B, Ao Y, Morales LB, TiwariWoodruff S, Sofroniew MV: Reactive astrocytes form scar-like perivascular barriers to leukocytes during adaptive immune inflammation of the CNS. J Neurosci 2009, 29:11511-11522. 32. Zamanian JL, Xu L, Foo LC, Nouri N, Zhou L, Giffard RG,  Barres BA: Genomic analysis of reactive astrogliosis. J Neurosci 2012, 32:6391-6410. An important study towards molecular classification of reactive astrocytes — such studies will allow to define astrocytes and their subpopulations in molecular terms. In this case, Affymetrics arrays were used to compare gene expression in reactive astrocytes isolated from ischemic Current Opinion in Cell Biology 2015, 32:121–130

128 Cell architecture

stroke and LPS-induced global neuroinflammation. The results suggest that some molecular aspects of reactive gliosis are generic, while others are disease-specific. 33. Kamphuis W, Orre M, Kooijman L, Dahmen M, Hol EM: Differential cell proliferation in the cortex of the APPswePS1dE9 Alzheimer’s disease mouse model. Glia 2012, 60:615-629. 34. Orre M, Kamphuis W, Dooves S, Kooijman L, Chan ET, Kirk CJ, Dimayuga S, Koot V, Mamber S, Jansen C et al.: Reactive glia show increased immunoproteasome activity in Alzheimer’s disease. Brain 2013, 136:1415-1431. 35. Bush TG, Puvanachandra N, Horner CH, Polito A, Ostenfeld T, Svendsen CN, Mucke L, Johnson MH, Sofroniew MV: Leukocyte infiltration, neuronal degeneration, and neurite outgrowth after ablation of scar-forming, reactive astrocytes in adult transgenic mice. Neuron 1999, 23:297-308. 36. Faulkner JR, Herrmann JE, Woo MJ, Tansey KE, Doan NB,  Sofroniew MV: Reactive astrocytes protect tissue and preserve function after spinal cord injury. J Neurosci 2004, 24:2143-2155. Demonstration of the positive role of reactive astrocytes in spinal cord trauma. 37. Herrmann JE, Imura T, Song B, Qi J, Ao Y, Nguyen TK, Korsak RA,  Takeda K, Akira S, Sofroniew MV: STAT3 is a critical regulator of astrogliosis and scar formation after spinal cord injury. J Neurosci 2008, 28:7231-7243. Identifies an important molecular mechanism of astrocyte activation and reactive astrogliosis in spinal cord trauma. 38. Okada S, Nakamura M, Katoh H, Miyao T, Shimazaki T, Ishii K,  Yamane J, Yoshimura A, Iwamoto Y, Toyama Y, Okano H: Conditional ablation of Stat3 or Socs3 discloses a dual role for reactive astrocytes after spinal cord injury. Nat Med 2006, 12:829-834. See annotation to Ref. [37]. 39. Wanner IB, Anderson MA, Song B, Levine J, Fernandez A, GrayThompson Z, Ao Y, Sofroniew MV: Glial scar borders are formed by newly proliferated, elongated astrocytes that interact to corral inflammatory and fibrotic cells via STAT3-dependent mechanisms after spinal cord injury. J Neurosci 2013, 33:12870-12886. 40. Gao Q, Wolfgang MJ, Neschen S, Morino K, Horvath TL, Shulman GI, Fu XY: Disruption of neural signal transducer and activator of transcription 3 causes obesity, diabetes, infertility, and thermal dysregulation. Proc Natl Acad Sci USA 2004, 101:4661-4666. 41. Araque A, Carmignoto G, Haydon PG, Oliet SH, Robitaille R, Volterra A: Gliotransmitters travel in time and space. Neuron 2014, 81:728-739. 42. Perea G, Navarrete M, Araque A: Tripartite synapses: astrocytes process and control synaptic information. Trends Neurosci 2009, 32:421-431. 43. Navarrete M, Perea G, Maglio L, Pastor J, Garcia de SR, Araque A: Astrocyte calcium signal and gliotransmission in human brain tissue. Cereb Cortex 2013, 23:1240-1246. 44. Ortinski PI, Dong J, Mungenast A, Yue C, Takano H, Watson DJ,  Haydon PG, Coulter DA: Selective induction of astrocytic gliosis generates deficits in neuronal inhibition. Nat Neurosci 2010, 13:584-591. An exciting study showing that reactive astrocytes, induced by a viral vector, can disturb neuronal circuits. In this case the disturbance was due to a decrease in the enzyme glutamine synthetase, leading to a lack of GABA. This resulted in a reduction in inhibitory synaptic input and an overactivation of the neuronal network. This study provides important evidence that reactive astrocytes in CNS can affect neuronal functioning, which might have broad implications for many neurological disorders. 45. Kuchibhotla KV, Lattarulo CR, Hyman BT, Bacskai BJ:  Synchronous hyperactivity and intercellular calcium waves in astrocytes in Alzheimer mice. Science 2009, 323:1211-1215. This study is one of the first to show functional changes in astrocytes near amyloid plaques in Alzheimer mice. These astrocytes are most likely reactive. With 2-photon-microscopy they show that the calcium resting state in astrocytes was elevated and that the calcium transients were more frequent. Current Opinion in Cell Biology 2015, 32:121–130

46. Peters O, Schipke CG, Philipps A, Haas B, Pannasch U, Wang LP, Benedetti B, Kingston AE, Kettenmann H: Astrocyte function is modified by Alzheimer’s disease-like pathology in aged mice. J Alzheimers Dis 2009, 18:177-189. 47. Jo S, Yarishkin O, Hwang YJ, Chun YE, Park M, Woo DH, Bae JY,  Kim T, Lee J, Chun H et al.: GABA from reactive astrocytes impairs memory in mouse models of Alzheimer’s disease. Nat Med 2014, 20:886-896. Here an unexpected finding is reported. Reactive astrocytes in Alzheimer mice start to produce and release the inhibitory neurotransmitter GABA, and by doing so they affect neuronal communication. The authors show that the GABA released by astrocytes affects learning and memory. The induction of GABA corresponds with an increase in GFAP, also in a stab wound injury, indicating that this is a general mechanism in reactive gliosis. 48. Kamphuis W, Middeldorp J, Kooijman L, Sluijs JA, Kooi EJ, Moeton M, Freriks M, Mizee MR, Hol EM: Glial fibrillary acidic protein isoform expression in plaque related astrogliosis in Alzheimer’s disease. Neurobiol Aging 2014, 35:492-510. 49. de Pablo Y, Nilsson M, Pekna M, Pekny M: Intermediate filaments are important for astrocyte response to oxidative stress induced by oxygen-glucose deprivation and reperfusion. Histochem Cell Biol 2013, 140:81-91. 50. Correa-Cerro LS, Mandell JW: Molecular mechanisms of astrogliosis: new approaches with mouse genetics. J Neuropathol Exp Neurol 2007, 66:169-176. 51. Kamphuis W, Mamber C, Moeton M, Kooijman L, Sluijs JA, Jansen AH, Verveer M, de Groot LR, Smith VD, Rangarajan S et al.: GFAP isoforms in adult mouse brain with a focus on neurogenic astrocytes and reactive astrogliosis in mouse models of Alzheimer disease. PLoS One 2012, 7:e42823. 52. Moeton M, Kanski R, Stassen OM, Sluijs JA, Geerts D, van TP,  Wiche G, van Strien ME, Hol EM: Silencing GFAP isoforms in astrocytoma cells disturbs laminin-dependent motility and cell adhesion. FASEB J 2014, 28:2942-2954. Shows that changing the GFAPd/GFAPa ratio directly affects the interaction with the extracellular matrix (laminin) and results in a change in cell adhesion. Providing evidence that a change in the stoichometry of the different GFAP isoforms in a cell can have direct functional consequences. 53. Skalli O, Wilhelmsson U, Orndahl C, Fekete B, Malmgren K,  Rydenhag B, Pekny M: Astrocytoma grade IV (glioblastoma multiforme) displays 3 subtypes with unique expression profiles of intermediate filament proteins. Hum Pathol 2013, 44:2081-2088. Study on tumor material of 47 grade IV astrocytoma patients. Three subtypes based on intermediate filament protein expression could be identified. Subtype A: with high expression of GFAP, nestin and synemin; subtype B: with low expression of GFAP, nestin, vimentin, and synemin; and subtype C: with high expression of nestin, and low expression of GFAP, vimentin, and synemin. This paper shows the the heterogeneity of the IF network in grade IV astrocytoma. 54. Lepekhin EA, Eliasson C, Berthold CH, Berezin V, Bock E, Pekny M: Intermediate filaments regulate astrocyte motility. J Neurochem 2001, 79:617-625. 55. Wilhelmsson U, Eliasson C, Bjerkvig R, Pekny M: Loss of GFAP expression in high-grade astrocytomas does not contribute to tumor development or progression. Oncogene 2003, 22:3407-3411. 56. Thomsen R, Pallesen J, Daugaard TF, Borglum AD, Nielsen AL: Genome wide assessment of mRNA in astrocyte protrusions by direct RNA sequencing reveals mRNA localization for the intermediate filament protein nestin. Glia 2013, 61:1922-1937. 57. Thomsen R, Daugaard TF, Holm IE, Nielsen AL: Alternative mRNA splicing from the glial fibrillary acidic protein (GFAP) gene generates isoforms with distinct subcellular mRNA localization patterns in astrocytes. PLoS One 2013, 8:e72110. 58. Gomi H, Yokoyama T, Fujimoto K, Ikeda T, Katoh A, Itoh T, Itohara S: Mice devoid of the glial fibrillary acidic protein develop normally and are susceptible to scrapie prions. Neuron 1995, 14:29-41. www.sciencedirect.com

Astrocyte intermediate filament system in CNS diseases Hol and Pekny 129

59. Liedtke W, Edelmann W, Bieri PL, Chiu FC, Cowan NJ, Kucherlapati R, Raine CS: GFAP is necessary for the integrity of CNS white matter architecture and long-term maintenance of myelination. Neuron 1996, 17:607-615.

74. Lu YB, Iandiev I, Hollborn M, Korber N, Ulbricht E, Hirrlinger PG, Pannicke T, Wei EQ, Bringmann A, Wolburg H et al.: Reactive glial cells: increased stiffness correlates with increased intermediate filament expression. FASEB J 2011, 25:624-631.

60. McCall MA, Gregg RG, Behringer RR, Brenner M, Delaney CL, Galbreath EJ, Zhang CL, Pearce RA, Chiu SY, Messing A: Targeted deletion in astrocyte intermediate filament (Gfap) alters neuronal physiology. Proc Natl Acad Sci USA 1996, 93:6361-6366.

75. Vardjan N, Gabrijel M, Potokar M, Svajger U, Kreft M, Jeras M, de PY, Faiz M, Pekny M, Zorec R: IFN-gamma-induced increase in the mobility of MHC class II compartments in astrocytes depends on intermediate filaments. J Neuroinflamm 2012, 9:144.

61. Pekny M, Leveen P, Pekna M, Eliasson C, Berthold CH, Westermark B, Betsholtz C: Mice lacking glial fibrillary acidic protein display astrocytes devoid of intermediate filaments but develop and reproduce normally. EMBO J 1995, 14:1590-1598.

76. Potokar M, Kreft M, Li L, Daniel AJ, Pangrsic T, Chowdhury HH, Pekny M, Zorec R: Cytoskeleton and vesicle mobility in astrocytes. Traffic 2007, 8:12-20.

62. Nawashiro H, Messing A, Azzam N, Brenner M: Mice lacking GFAP are hypersensitive to traumatic cerebrospinal injury. Neuroreport 1998, 9:1691-1696.

77. Potokar M, Stenovec M, Gabrijel M, Li L, Kreft M, Grilc S, Pekny M, Zorec R: Intermediate filaments attenuate stimulationdependent mobility of endosomes/lysosomes in astrocytes. Glia 2010, 58:1208-1219.

63. Lundkvist A, Reichenbach A, Betsholtz C, Carmeliet P, Wolburg H, Pekny M: Under stress, the absence of intermediate filaments from Muller cells in the retina has structural and functional consequences. J Cell Sci 2004, 117:3481-3488. 64. Pekny M, Johansson CB, Eliasson C, Stakeberg J, Wallen A,  Perlmann T, Lendahl U, Betsholtz C, Berthold CH, Frisen J: Abnormal reaction to central nervous system injury in mice lacking glial fibrillary acidic protein and vimentin. J Cell Biol 1999, 145:503-514. Demonstrates the importance of astrocyte IFs in astrocyte activation and glial scar formation in brain and spinal cord trauma. 65. Tatzelt J, Maeda N, Pekny M, Yang SL, Betsholtz C, Eliasson C, Cayetano J, Camerino AP, DeArmond SJ, Prusiner SB: Scrapie in mice deficient in apolipoprotein E or glial fibrillary acidic protein. Neurology 1996, 47:449-453. 66. Stahlberg A, Andersson D, Aurelius J, Faiz M, Pekna M, Kubista M, Pekny M: Defining cell populations with single-cell gene expression profiling: correlations and identification of astrocyte subpopulations. Nucleic Acids Res 2011, 39:e24. 67. Pekny T, Faiz M, Wilhelmsson U, Curtis MA, Matej R, Skalli O, Pekny M: Synemin is expressed in reactive astrocytes and Rosenthal fibers in Alexander disease. APMIS 2014, 122:76-80. 68. Jing R, Wilhelmsson U, Goodwill W, Li L, Pan Y, Pekny M, Skalli O: Synemin is expressed in reactive astrocytes in neurotrauma and interacts differentially with vimentin and GFAP intermediate filament networks. J Cell Sci 2007, 120:1267-1277. 69. Eliasson C, Sahlgren C, Berthold CH, Stakeberg J, Celis JE,  Betsholtz C, Eriksson JE, Pekny M: Intermediate filament protein partnership in astrocytes. J Biol Chem 1999, 274:23996-24006. Defines which IF proteins in astrocytes can form IFs on their own (GFAP) and which need another IF protein as a polymerization partner (nestin needs vimentin; it can neither self-polymerize, nor co-polymerize with GFAP). 70. Wilhelmsson U, Li L, Pekna M, Berthold CH, Blom S, Eliasson C,  Renner O, Bushong E, Ellisman M, Morgan TE, Pekny M: Absence of glial fibrillary acidic protein and vimentin prevents hypertrophy of astrocytic processes and improves posttraumatic regeneration. J Neurosci 2004, 24:5016-5021. Shows that the absence of astrocyte IFs in mice is connected with the initial increase in the synaptic loss in the hippocampus after de-afferentation (entorhinal cortex lesion model), but largely improved synaptic regeneration later on. 71. Pekny M, Lane EB: Intermediate filaments and stress. Exp Cell Res 2007, 313:2244-2254. 72. Verardo MR, Lewis GP, Takeda M, Linberg KA, Byun J, Luna G, Wilhelmsson U, Pekny M, Chen DF, Fisher SK: Abnormal reactivity of muller cells after retinal detachment in mice deficient in GFAP and vimentin. Invest Ophthalmol Vis Sci 2008, 49:3659-3665. 73. Li L, Lundkvist A, Andersson D, Wilhelmsson U, Nagai N,  Pardo AC, Nodin C, Stahlberg A, Aprico K, Larsson K et al.: Protective role of reactive astrocytes in brain ischemia. J Cereb Blood Flow Metab 2008, 28:468-481. Demonstration of the importance of astrocyte IFs and reactive astrocytes for the protection of the ischemic penumbra in a mouse model of ischemic stroke. www.sciencedirect.com

78. Nakazawa T, Takeda M, Lewis GP, Cho KS, Jiao J, Wilhelmsson U, Fisher SK, Pekny M, Chen DF, Miller JW: Attenuated glial reactions and photoreceptor degeneration after retinal detachment in mice deficient in glial fibrillary acidic protein and vimentin. Invest Ophthalmol Vis Sci 2007, 48:2760-2768. 79. Ding M, Eliasson C, Betsholtz C, Hamberger A, Pekny M: Altered taurine release following hypotonic stress in astrocytes from mice deficient for GFAP and vimentin. Brain Res Mol Brain Res 1998, 62:77-81. 80. Pekny M, Stanness KA, Eliasson C, Betsholtz C, Janigro D: Impaired induction of blood-brain barrier properties in aortic endothelial cells by astrocytes from GFAP-deficient mice. Glia 1998, 22:390-400. 81. Kraft AW, Hu X, Yoon H, Yan P, Xiao Q, Wang Y, Gil SC, Brown J, Wilhelmsson U, Restivo JL et al.: Attenuating astrocyte activation accelerates plaque pathogenesis in APP/PS1 mice. FASEB J 2013, 27:187-198. 82. Macauley SL, Pekny M, Sands MS: The role of attenuated astrocyte activation in infantile neuronal ceroid lipofuscinosis. J Neurosci 2011, 31:15575-15585. 83. Cho KS, Yang L, Lu B, Feng MH, Huang X, Pekny M, Chen DF: Re-establishing the regenerative potential of central nervous system axons in postnatal mice. J Cell Sci 2005, 118:863-872. 84. Menet V, Prieto M, Privat A, Ribotta M: Axonal plasticity and functional recovery after spinal cord injury in mice deficient in both glial fibrillary acidic protein and vimentin genes. Proc Natl Acad Sci USA 2003, 100:8999-9004. 85. Wilhelmsson U, Faiz M, de PY, Sjoqvist M, Andersson D, Widestrand A, Potokar M, Stenovec M, Smith PL, Shinjyo N et al.: Astrocytes negatively regulate neurogenesis through the Jagged1-mediated Notch pathway. Stem Cells 2012, 30:2320-2329. 86. Jarlestedt K, Rousset CI, Faiz M, Wilhelmsson U, Stahlberg A, Sourkova H, Pekna M, Mallard C, Hagberg H, Pekny M: Attenuation of reactive gliosis does not affect infarct volume in neonatal hypoxic-ischemic brain injury in mice. PLoS One 2010, 5:e10397. 87. Kinouchi R, Takeda M, Yang L, Wilhelmsson U, Lundkvist A,  Pekny M, Chen DF: Robust neural integration from retinal transplants in mice deficient in GFAP and vimentin. Nat Neurosci 2003, 6:863-868. Suggests that attenuation of reactive gliosis (by genetic ablation of astrocyte IF proteins) can improve the integration, differentiation, and survival of cells grafted in the mouse CNS. 88. Widestrand A, Faijerson J, Wilhelmsson U, Smith PL, Li L, Sihlbom C, Eriksson PS, Pekny M: Increased neurogenesis and astrogenesis from neural progenitor cells grafted in the hippocampus of GFAPS/S VimS/S mice. Stem Cells 2007, 25:2619-2627. 89. Andreiuolo F, Junier MP, Hol EM, Miquel C, Chimelli L, Leonard N, Chneiweiss H, Daumas-Duport C, Varlet P: GFAPdelta immunostaining improves visualization of normal and pathologic astrocytic heterogeneity. Neuropathology 2009, 29:31-39. Current Opinion in Cell Biology 2015, 32:121–130

130 Cell architecture

90. Brehar FM, Arsene D, Brinduse LA, Gorgan MR:  Immunohistochemical analysis of GFAP-delta and nestin in cerebral astrocytomas. Brain Tumor Pathol 2014 http:// dx.doi.org/10.1007/s10014-014-0199-8. Epub Sep. 2. Shows potential involvement of GFAPd and nestin in invasiveness of the astrocytoma. Immunostaining of the biopsies from the tumor were linked to MRI images. 91. Choi KC, Kwak SE, Kim JE, Sheen SH, Kang TC: Enhanced glial fibrillary acidic protein-delta expression in human astrocytic tumor. Neurosci Lett 2009, 463:182-187. 92. Heo DH, Kim SH, Yang KM, Cho YJ, Kim KN, Yoon DH, Kang TC: A histopathological diagnostic marker for human spinal astrocytoma: expression of glial fibrillary acidic protein-delta. J Neurooncol 2012, 108:45-52. 93. Kanski R, Sneeboer MA, van Bodegraven EJ, Sluijs JA, Kropff W,  Vermunt MW, Creyghton MP, De FL, Vescovi A, Aronica E et al.: Histone acetylation in astrocytes suppresses GFAP and stimulates a re-organization of the intermediate filament network. J Cell Sci 2014, 127:4368-4380. In this study it is shown that an increase in histone acetylation and a decrease in GFAP transcription both lead to an increase in the GFAPd/ GFAPa isoform ratio, and a reorganization of the intermediate filament (including vimentin) network in astrocytes. 94. Bugiani M, Boor I, van KB, Postma N, Polder E, van BC, van Kesteren RE, Windrem MS, Hol EM, Scheper GC et al.: Defective

Current Opinion in Cell Biology 2015, 32:121–130

glial maturation in vanishing white matter disease. J Neuropathol Exp Neurol 2011, 70:69-82. 95. Martinian L, Boer K, Middeldorp J, Hol EM, Sisodiya SM, Squier W, Aronica E, Thom M: Expression patterns of glial fibrillary acidic protein (GFAP)-delta in epilepsy-associated lesional pathologies. Neuropathol Appl Neurobiol 2009, 35:394-405. 96. Boer K, Middeldorp J, Spliet WG, Razavi F, van Rijen PC, Baayen JC, Hol EM, Aronica E: Immunohistochemical characterization of the out-of frame splice variants GFAP Delta164/Deltaexon 6 in focal lesions associated with chronic epilepsy. Epilepsy Res 2010, 90:99-109. 97. Messing A, Brenner M, Feany MB, Nedergaard M, Goldman JE: Alexander disease. J Neurosci 2012, 32:5017-5023. 98. Hagemann TL, Paylor R, Messing A: Deficits in adult neurogenesis, contextual fear conditioning, and spatial learning in a Gfap mutant mouse model of Alexander disease. J Neurosci 2013, 33:18698-18706. 99. Pekny M, Pekna M: Astrocyte reactivity and reactive  astrogliosis: costs and benefits. Physiol Rev 2014, 94:1077-1098. A recent review outlining the positive role of reactive gliosis in reducing acute cellular stress and tissue damage in CNS diseases, and its possible negative effect on adaptive neural plasticity mechanisms. An emphasis is given to the IF system of astrocytes.

www.sciencedirect.com