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Aim: Astrocytes play a homeostatic role in the central nervous system and influence numerous aspects of neurophysiology via intracellular trafficking of vesicles. Intermediate filaments (IFs), also known as nanofilaments, regulate a number of cellular processes including organelle trafficking and adult hippocampal neurogenesis. We have recently demonstrated that the IF protein nestin, a marker of neural stem cells and immature and reactive astrocytes, is also expressed in some astrocytes in the unchallenged hippocampus and regulates neurogenesis through Notch signalling from astrocytes to neural stem cells, possibly via altered trafficking of vesicles containing the Notch ligand Jagged‐1. Methods: We thus investigated whether nestin affects vesicle dynamics in astrocytes by examining single vesicle interactions with the plasmalemma and vesicle trafficking with high‐resolution cell‐attached membrane capacitance measurements and confocal microscopy. We used cell cultures of astrocytes from nestin‐deficient (Nes−/−) and wild‐type (wt) mice, and fluorescent dextran and Fluo‐2 to examine vesicle mobility and intracellular Ca2+ concentration respectively. Results: Nes−/− astrocytes exhibited altered sizes of vesicles undergoing full fission and transient fusion, altered vesicle fusion pore geometry and kinetics, decreased spontaneous vesicle mobility and altered ATP‐evoked mobility. Purinergic stimulation evoked Ca2+ signalling that was slightly attenuated in Nes−/− astrocytes, which exhibited more oscillatory Ca2+ responses than wt astrocytes. Conclusion: These results demonstrate at the single vesicle level that nestin regulates vesicle interactions with the plasmalemma and vesicle trafficking, indicating its potential role in astrocyte vesicle‐based communication. [ABSTRACT FROM AUTHOR]

Astrocytes have multiple roles in the CNS including control of adult neurogenesis. We recently showed that astrocyte inhibition of neurogenesis through Notch signaling depends on the intermediate filament proteins glial fibrillary acidic protein ( GFAP) and vimentin. Here, we used real-time quantitative PCR to analyze gene expression in individual mouse astrocytes in primary cultures and in GFAP POS or Aldh1L1 POS astrocytes freshly isolated from uninjured, contralesional and lesioned hippocampus 4 days after entorhinal cortex lesion. To determine the Notch signaling competence of individual astrocytes, we measured the mRNA levels of Notch ligands and Notch1 receptor. We found that whereas most cultured and freshly isolated astrocytes were competent to receive Notch signals, only a minority of astrocytes were competent to send Notch signals. Injury increased the fraction of astrocyte subpopulation unable to send and receive Notch signals, thus resembling primary astrocytes in vitro. Astrocytes deficient of GFAP and vimentin showed decreased Notch signal sending competence and altered expression of Notch signaling pathway-related genes Dlk2, Notch1, and Sox2. Furthermore, we identified astrocyte subpopulations based on their mRNA and protein expression of nestin and HB- EGF. This study improves our understanding of astrocyte heterogeneity, and points to astrocyte cytoplasmic intermediate filaments as targets for neural cell replacement strategies. [ABSTRACT FROM AUTHOR]

Alexander disease (AxD) is a neurodegenerative disorder with prominent white matter degeneration and the presence of Rosenthal fibers containing aggregates of glial fibrillary acidic protein ( GFAP), and small stress proteins HSP27 and αB-crystallin, and widespread reactive gliosis. AxD is caused by mutations in GFAP, the main astrocyte intermediate filament protein. We previously showed that intermediate filament protein synemin is upregulated in reactive astrocytes after neurotrauma. Here, we examined immunohistochemically the presence of synemin in reactive astrocytes and Rosenthal fibers in two patients with AxD. There was an abundance of GFAP-positive Rosenthal fibers and widespread reactive gliosis in the white matter and subpial regions. Many of the GFAP-positive reactive astrocytes were positive for synemin, and synemin was also present in Rosenthal fibers. We show that synemin is expressed in reactive astrocytes in AxD, and is also present in Rosenthal fibers. The potential role of synemin in AxD pathogenesis remains to be investigated. [ABSTRACT FROM AUTHOR]

The accumulation of aggregated amyloid-β (Aβ) in amyloid plaques is a neuropathological hallmark of Alzheimer's disease (AD). Reactive astrocytes are intimately associated with amyloid plaques; however, their role in AD pathogenesis is unclear. We deleted the genes encoding two intermediate filament proteins required for astrocyte activation--gUM fibrillary acid protein (Gfap) and vimentin (Vim)--m transgenic mice expressing mutant human amyloid precursor protein and presenilin-1 (APP/PS1). The gene deletions increased amyloid plaque load: APP/PS1 Gfap-/-Vim-/- mice had twice the plaque load of APP/PS1 Gfap+/+ Vim+/+ mice at 8 and 12 mo of age. APP expression and soluble and interstitial fluid Aβ levels were unchanged, suggesting that the deletions had no effect on APP processing or Aβ generation. Astrocyte morphology was markedly altered by the deletions: wild-type astrocytes had hypertrophied processes that surrounded and infiltrated plaques, whereas Gfap-/- Vim-/- astrocytes had little process hypertrophy and lacked contact with adjacent plaques. Moreover, Gfap and Vim gene deletion resulted in a marked increase in dystrophic neurites (2- to 3-fold higher than APP/PS1 Gfap+/+Vim+/+ mice), even after normalization for amyloid load. These results suggest that astrocyte activation limits plaque growth and attenuates plaque-related dystrophic neurites. These activities may require intimate contact between astrocyte and plaque. [ABSTRACT FROM AUTHOR]

Increased stiffness of reactive glial cells may impede neurite growth and contribute to the poor regenerative capabilities of the mammalian central nervous system. We induced reactive gliosis in rodent retina by ischemia-reperfusion and assessed intermediate filament (IF) expression and the viscoelastic properties of dissociated single glial cells in wild-type mice, mice lacking glial fibrillary acidic protein and vimentin (GFAP-/-Vim-/-) in which glial cells are consequently devoid of IFs, and normal Long-Evans rats. In response to ischemia-reperfusion, glial cells stiffened significantly in wild-type mice and rats but were unchanged in GFAP-/-Vim-/- mice. Cell stiffness (elastic modulus) correlated with the density of IFs. These results support the hypothesis that rigid glial scars impair nerve regeneration and that IFs are important determinants of cellular viscoelasticity in reactive glia. Thus, therapeutic suppression of IF up-regulation in reactive glial cells may facilitate neuroregeneration. [ABSTRACT FROM AUTHOR]