Astrocyte: Definition, Function & the Role in Aging

Introducing Astrocytes

Astrocytes are star-shaped cells that play a pivotal role in the functioning of the central nervous system (CNS). As a major cellular compartment in the CNS, they are involved in various functions essential for maintaining normal brain function. This article delves into the definition, functions, and particularly the role of astrocytes in ageing.

Definition and Types

Astrocytes are a type of neuroglia found in both invertebrates and vertebrates. They can be subdivided into fibrous and protoplasmic types. Fibrous astrocytes are prevalent among myelinated nerve fibres in the white matter of the CNS​​.

Function in the CNS

Astrocytes perform several crucial functions in the CNS. They regulate local cerebral blood flow, maintain ion and neurotransmitter homeostasis, provide metabolic support, regulate synaptic activity, and respond to brain injury, insults, and infection​​. Additionally, they play key roles in synapse formation and function, control neurotransmitter release and uptake, and produce trophic factors essential for neuronal survival​​.

Role in Aging

Aging impacts astrocytes both morphologically and functionally. There’s evidence of morphological atrophy and loss of function with aging, including a decrease in synaptic coverage, deficiency in glutamate and potassium clearance, and reduced synthesis of synaptogenic factors​​. Aging also leads to a loss of normal function in astrocytes, impairing their ability to maintain a healthy CNS environment and contributing to the heightened inflammatory state characteristic of aging​​.

Research by Lee et al. using single-cell RNA sequencing in aged mouse hippocampi revealed distinct clusters of astrocytic cell populations affected by aging. One novel population, found exclusively in the aged hippocampus, showed upregulated gene expression related to astrocyte homeostasis, synaptogenesis, and synapse elimination​​. This finding raises questions about their contribution to cognitive decline in the aging brain.

Additionally, aging is associated with disrupted proteostatic signaling in astrocytes, leading to defects in morphology, protein trafficking, and synapse maintenance, particularly in the aging hippocampus​​.

Conclusion

Astrocytes are integral to the proper functioning of the CNS, playing roles in maintaining homeostasis, defending against injury, and aiding regeneration. The aging process introduces significant changes in these cells, leading to alterations in their functions and potentially contributing to brain aging and the development of neurodegenerative diseases. Understanding these changes is crucial for developing strategies to mitigate age-related cognitive decline and neurodegenerative conditions.

References

1. Ferrer, I. (2017). “A role of astrocytes in health, aging and disease.” NCBI
2. Britannica: “Astrocyte | Definition, Function, & Facts.”
3. Frontiers in Aging Neuroscience: “Astrocyte Heterogeneity: Impact to Brain Aging and Disease.”
4. Nature Aging: “Astrocytic traffic jams in the aging brain.”
5. ScienceDirect: “An emerging role of astrocytes in aging/neuroinflammation and gut-brain axis.”