Astrocytes, the most abundant glial cells in the central nervous system (CNS), comprise a heterogeneous population of cells. However, how this heterogeneity impacts their function within brain homeostasis and response to injury and disease is still largely unknown. Recently, astrocytes have been recognized as important regulators of synapse formation and maturation. Here, we analyzed the synaptogenic property of astrocytes from different regions of the CNS. The effect of conditioned medium derived from astrocytes (astrocyte-conditioned medium (ACM)) from cerebral cortex, hippocampus, midbrain and cerebellum, in synapse formation, was evaluated. Synapse formation was analyzed by quantification of pre- and postsynaptic proteins, synaptophysin, and postsynaptic density protein 95 (PSD-95). ACM from the four regions increased significantly the number of synaptophysin/PSD-95 puncta on neurons from the same and different brain regions. Differences on astrocytic synaptogenic potential between the regions were observed according to ACM protein concentration. Thus, cerebellar astrocytes have higher synaptogenic effect when ACM is less concentrated. Also, heterotypical co-culture assays revealed that neurons from cerebral cortex and midbrain equally respond to ACM, indicating that differences in synapse effect are unlike to be neuron-autonomous. The expression profile of the synaptogenic molecules secreted by astrocytes from distinct brain regions was analyzed by qPCR. Gene expression of glypicans 4 and 6, hevin, and secreted protein-acidic and rich in cysteine (SPARC) greatly varies between astrocytes from different brain regions. Furthermore, in vivo analysis of hevin protein confirmed that variance. These findings highlight the heterogeneity of astrocytes and suggest that their synaptogenic potential may be different in each brain region, mainly due to distinct gene expression profiles.
Astrocyte Synapse Growth factors And heterogeneity
This is a preview of subscription content, log in to check access.
We thank Marcelo Meloni and Grasiela Ventura for technical assistance. This work was supported by grants from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Ministério da Saúde, Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), and Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ).
ACM synaptogenic property has a protein nature. Neuronal cultures with 12 DIV from cerebral cortex were treated for 3 h with DMEM/F12 (control), with cortex ACM and with boiled cortex ACM (boiled for 5 min). Excitatory synapse formation was analyzed by quantification of synaptic proteins puncta numbers. (n = 3). ***P < 0.001. (GIF 17 kb)
Cahoy JD, Emery B, Kaushal A, Foo LC, Zamanian JL, Christopherson KS, Xing Y, Lubischer JL et al (2008) A transcriptome database for astrocytes, neurons, and oligodendrocytes: a new resource for understanding brain development and function. J Neurosci Off J Soc Neurosci 28(1):264–278. doi:10.1523/JNEUROSCI.4178-07.2008CrossRefGoogle Scholar
Regan MR, Huang YH, Kim YS, Dykes-Hoberg MI, Jin L, Watkins AM, Bergles DE, Rothstein JD (2007) Variations in promoter activity reveal a differential expression and physiology of glutamate transporters by glia in the developing and mature CNS. J Neurosci Off J Soc Neurosci 27(25):6607–6619. doi:10.1523/JNEUROSCI.0790-07.2007CrossRefGoogle Scholar
Di Castro MA, Chuquet J, Liaudet N, Bhaukaurally K, Santello M, Bouvier D, Tiret P, Volterra A (2011) Local Ca2+ detection and modulation of synaptic release by astrocytes. Nat Neurosci 14(10):1276–1284. doi:10.1038/nn.2929CrossRefPubMedGoogle Scholar
Bushong EA, Martone ME, Ellisman MH (2004) Maturation of astrocyte morphology and the establishment of astrocyte domains during postnatal hippocampal development. International journal of developmental neuroscience : the official journal of the International Society for Developmental Neuroscience 22(2):73–86. doi:10.1016/j.ijdevneu.2003.12.008CrossRefGoogle Scholar
Schipke CG, Ohlemeyer C, Matyash M, Nolte C, Kettenmann H, Kirchhoff F (2001) Astrocytes of the mouse neocortex express functional N-methyl-D-aspartate receptors. FASEB journal: official publication of the Federation of American Societies for Experimental Biology 15(7):1270–1272CrossRefGoogle Scholar
Ziak D, Chvatal A, Sykova E (1998) Glutamate-, kainate- and NMDA-evoked membrane currents in identified glial cells in rat spinal cord slice. Physiological research/Academia Scientiarum Bohemoslovaca 47(5):365–375Google Scholar
Seifert G, Steinhauser C (1995) Glial cells in the mouse hippocampus express AMPA receptors with an intermediate Ca2+ permeability. Eur J Neurosci 7(9):1872–1881CrossRefPubMedGoogle Scholar