Microglial immunometabolism in Alzheimer's disease: A stage-resolved trajectory from adaptive remodeling to the metabolic paradox.

Microglia are central regulators of the cellular phase of Alzheimer's disease (AD). Under chronic exposure to amyloid-β, pathological tau, and aging-associated bioenergetic decline, these cells undergo immunometabolic remodeling that may initially be adaptive. As stress persists, this remodeling can become maladaptive, marked by disordered glycolysis, disturbed lipid handling, mitochondrial dysfunction, and compensatory failure. In this review, we organize these changes as a stage-dependent trajectory from adaptive remodeling to functional decompensation. We introduce the "metabolic paradox" as an operational descriptor: a concurrent, same-cell mismatch between increased substrate uptake or inflammatory activation and declining bioenergetic efficiency and homeostatic function. Along this trajectory we examine neurovascular energy bottlenecks, substrate redistribution, triggering receptor expressed on myeloid cells 2 (TREM2)/apolipoprotein E (APOE)-dependent lipid homeostasis, mitochondrial and proteostatic collapse, and their links to persistent neuroinflammation, defective phagocytosis, aberrant synaptic pruning, and senescence-like dysfunction. We synthesize prior primary findings and stratify each major claim by evidentiary strength, avoiding the overinterpretation of model-specific results as patient-level mechanisms. Finally, we frame immunoprevention as mechanism-based, early-stage metabolic intervention to preserve homeostatic microglial function, a strategy whose clinical benefit remains a hypothesis requiring prospective testing.