Human Microglial Molecular Alterations in Aging and Alzheimer's Disease

Microglia, the resident innate immune cells of the central nervous system, are central players in brain development, healthy aging, and degenerative pathology, including Alzheimer's disease (AD). Aging is a major risk factor for AD, and various studies have identified alterations in microglial molecular signatures and morphological patterns that overlap with microglial states during aging. However, the mechanisms underlying the divergence of aging trajectories toward disease remain unclear. Thus, understanding the molecular changes in microglia during aging and AD pathology is crucial to elucidating the mechanisms that drive disease progression. In this review, we examine current advances in understanding the phenotypic alterations in human microglia, highlighting gene signatures and morphological changes that may aid in defining microglia's molecular and functional programs in healthy aging and over the course of AD. We further explore the roles of oxidative stress and cellular senescence in driving the development of a chronic reactive state in microglia during aging, which may also contribute to the complex process underlying the onset and progression of AD pathology. This review highlights the advancements in therapeutic strategies focused on targeting pertinent pathological microglial changes during aging and in disease to mitigate the AD neurodegenerative process.