Characterization and identification of primarily cultured astrocytes and microglia / 生物工程学报

The aim of this study was to investigate the growth characteristics of primarily cultured astrocytes and microglia of different generations and then optimize the method for obtaining primary astrocytes and microglia effectively. Primarily cultured microglia were isolated and purified from the cortices of neonatal mice. The proliferation curve of mixed glia cells was measured by Cell Counting Kit-8 (CCK-8) assay, the proportion of astrocytes and microglia was detected by flow cytometry, and the polarization of the two types of glia cells was identified by immunofluorescence staining. Cell growth results showed that the mixed glia cells of P0 and P1 generation had the best proliferative activity; 97.3% of the high purity microglia could be obtained by mechanical shaking at 170 r/min for 30 min, and there was no significant difference in the morphology of ionized calcium-binding adapter molecule 1 (Iba-1) positive microglia and the proportion of M1 and M2 phenotype among the P0, P1 and P2 generations of microglia isolated by the above methods. Moreover, 95.7 % of the high purity astrocytes could be obtained by astrocyte cell surface antigen-2 (ACSA-2) magnetic beads separation, and there was no significant difference in the morphology of glial fibrillary acidic protein (GFAP) positive astrocyte and the proportion of A1 and A2 phenotype among the P0, P1 and P2 generations of astrocyte isolated by the above methods. Taken together, this study observed the growth characteristics of primarily cultured microglia and astrocyte in vitro, and then proved the best generations for purifying microglia and astrocytes. Finally, we optimized the methods of obtaining microglia and astrocyte, and verified that continuous culture within 2 generations will not affect the functional phenotypes of glia cells. These results provide technical support for studying the molecular mechanism of inflammation-associated diseases in nervous system.

Unbiased transcriptomic analyses reveal distinct effects of immune deficiency in CNS function with and without injury

The mammalian central nervous system (CNS) is considered an immune privileged system as it is separated from the periphery by the blood brain barrier (BBB). Yet, immune functions have been postulated to heavily influence the functional state of the CNS, especially after injury or during neurodegeneration. There is controversy regarding whether adaptive immune responses are beneficial or detrimental to CNS injury repair. In this study, we utilized immunocompromised SCID mice and subjected them to spinal cord injury (SCI). We analyzed motor function, electrophysiology, histochemistry, and performed unbiased RNA-sequencing. SCID mice displayed improved CNS functional recovery compared to WT mice after SCI. Weighted gene-coexpression network analysis (WGCNA) of spinal cord transcriptomes revealed that SCID mice had reduced expression of immune function-related genes and heightened expression of neural transmission-related genes after SCI, which was confirmed by immunohistochemical analysis and was consistent with better functional recovery. Transcriptomic analyses also indicated heightened expression of neurotransmission-related genes before injury in SCID mice, suggesting that a steady state of immune-deficiency potentially led to CNS hyper-connectivity. Consequently, SCID mice without injury demonstrated worse performance in Morris water maze test. Taken together, not only reduced inflammation after injury but also dampened steady-state immune function without injury heightened the neurotransmission program, resulting in better or worse behavioral outcomes respectively. This study revealed the intricate relationship between immune and nervous systems, raising the possibility for therapeutic manipulation of neural function via immune modulation.

Single-cell transcriptomics reveals gene signatures and alterations associated with aging in distinct neural stem/progenitor cell subpopulations

Aging associated cognitive decline has been linked to dampened neural stem/progenitor cells (NSC/NPCs) activities manifested by decreased proliferation, reduced propensity to produce neurons, and increased differentiation into astrocytes. While gene transcription changes objectively reveal molecular alterations of cells undergoing various biological processes, the search for molecular mechanisms underlying aging of NSC/NPCs has been confronted by the enormous heterogeneity in cellular compositions of the brain and the complex cellular microenvironment where NSC/NPCs reside. Moreover, brain NSC/NPCs themselves are not a homogenous population, making it even more difficult to uncover NSC/NPC sub-type specific aging mechanisms. Here, using both population-based and single cell transcriptome analyses of young and aged mouse forebrain ependymal and subependymal regions and comprehensive "big-data" processing, we report that NSC/NPCs reside in a rather inflammatory environment in aged brain, which likely contributes to the differentiation bias towards astrocytes versus neurons. Moreover, single cell transcriptome analyses revealed that different aged NSC/NPC subpopulations, while all have reduced cell proliferation, use different gene transcription programs to regulate age-dependent decline in cell cycle. Interestingly, changes in cell proliferation capacity are not influenced by inflammatory cytokines, but likely result from cell intrinsic mechanisms. The Erk/Mapk pathway appears to be critically involved in regulating age-dependent changes in the capacity for NSC/NPCs to undergo clonal expansion. Together this study is the first example of using population and single cell based transcriptome analyses to unveil the molecular interplay between different NSC/NPCs and their microenvironment in the context of the aging brain.