Astrocyte

Function

Perform at least five essential jobs. They clear extracellular glutamate through GLT-1 and GLAST and recycle it via the glutamate-glutamine cycle. They buffer extracellular K+ through Kir4.1. They form the tripartite synapse, releasing gliotransmitters (glutamate, ATP/adenosine, D-serine). They induce synapse formation by secreting thrombospondins, hevin, SPARC, and glypicans. And they couple neuronal activity to blood flow via endfeet wrapping cerebral capillaries.

Morphology

Two morphotypes: protoplasmic astrocytes in gray matter, with bushy processes that tile nonoverlapping domains and ensheath synapses; fibrous astrocytes in white matter, with longer, straighter processes that track along axons. Human astrocytes are markedly larger and more branched than their rodent counterparts.

Specification

• Receptors: Glutamate; GABA; Purinergic
• Location: Ubiquitous in CNS. Specialised types include Bergmann glia in cerebellum, Müller cells in retina, tanycytes in the third ventricle, and the radial glia of development, which serve as both scaffolds and the primary neural stem cells of the embryonic cortex.
• Projections: Blood vessels; Synapses
• Firing: Non-spiking (Calcium waves)
• Markers: ALDH1L1; GFAP; S100B; AQP4; SLC1A2/EAAT2/GLT-1; SLC1A3/GLAST; SOX9
• Developmental origin: Neural tube (Radial glia)
• Disease: Astrogliosis in injury; Alzheimer's; Alexander disease
• Cell Ontology: CL:0000127

References

1. Oberheim NA et al. (2009). Uniquely hominid features of adult human astrocytes.. J Neurosci 29: 3276–3287 PMID 19279265
2. Christopherson KS et al. (2005). Thrombospondins are astrocyte-secreted proteins that promote CNS synaptogenesis.. Cell 120: 421–433 PMID 15707899