Microglial Dysfunction and Amyloid-Beta Pathology in Alzheimer's Disease and HIV-Associated Neurocognitive Disorders.

Chronic neuroinflammation and impaired protein clearance are hallmarks of neurodegenerative diseases such as Alzheimer's disease (AD) and HIV-associated neurocognitive disorders (HAND). Central to these processes are microglia, the brain's resident immune cells, which normally maintain brain homeostasis by clearing amyloid-beta (Aβ) and other misfolded proteins through phagocytosis and receptor-mediated degradation. However, in both AD and HAND, microglial dysfunction promotes ongoing inflammation, impaired Aβ clearance, and progressive neuronal damage. This review synthesizes evidence from human and animal studies showing how key microglial pattern recognition receptors, including the Triggering receptor expressed on myeloid cells 2 (TREM2), Toll-like receptors (TLRs), and scavenger receptors (SR-AI/II, CD36, SR-BI, CD163), coordinate Aβ sensing, uptake, and inflammatory responses. We describe how HIV infection and viral proteins such as the trans-activator of transcription (Tat) and glycoprotein 120 (gp120) disrupt these pathways by altering receptor expression, lysosomal function, and microglial metabolism, creating a cycle of neurotoxicity and amyloid buildup. We further highlight current scientific gaps in elucidating how HIV affects microglial function and implications for HAND.