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Figure 1. Regulation of neurogenesis and NSC changes in healthy aging. Regulation of neurogenesis includes intrinsic factors (transcription factors, cell cycle regulators, epigenetic modifications), extrinsic factors (neurotransmitters, neurotrophic and growth factors, hormones, neuroinflammation, and other external factors), neural circuit activity, and pathological conditions. In aging, NSCs show a decline in proliferation, imbalanced differentiation favoring gliogenesis and preventing neurogenesis, age-related epigenetic modifications, changed niche signaling with less supportive factors and chronic inflammation, alterations in protein homeostasis and autophagy, and declined response to injury and diseases. NSC: Neural stem cell; Aβ: amyloid β; α-Syn: α-synuclein; TFs: transcription factors.