Alzheimer’s Disease: Amyloid, Tau, and the Biology of Progressive Network Injury

Abstract

Alzheimer’s disease is a clinicobiological syndrome in which cognitive decline is commonly accompanied by characteristic molecular and cellular changes in the brain. Two central pathological features are extracellular deposits containing beta-amyloid (Aβ) and intracellular aggregates of abnormally modified tau that form neurofibrillary tangles. Neither feature is adequately explained by a simple statement that a protein is “overproduced.” Aβ burden reflects the balance among amyloid precursor protein processing, peptide aggregation, transport, proteolytic degradation, and clearance through cellular, vascular, and fluid pathways. Tau pathology involves altered phosphorylation and other post-translational modifications, loss of normal microtubule-associated behavior, mislocalization, formation of soluble assemblies and fibrils, and probable spread through connected neural systems.

Human biomarker, neuropathological, genetic, and clinical-trial findings strongly support the relevance of amyloid and tau to Alzheimer’s disease. They do not reduce the disorder to a single linear cascade in every person. Synaptic injury, glial and immune responses, vascular disease, metabolic stress, and coexisting proteinopathies can modify both symptoms and trajectory. Current evidence suggests that amyloid abnormalities often emerge before widespread neocortical tau pathology and clinical symptoms, whereas the anatomical distribution and burden of tau pathology tend to track more closely with neuronal injury and cognitive impairment. Anti-amyloid antibodies have demonstrated substantial biomarker effects and modest average slowing of decline in selected early symptomatic populations, while also introducing clinically important safety risks. The next phase of therapeutic research will likely require increasingly precise staging, better biological subtyping, and combinations that address more than one component of disease biology.

Educational notice: This abstract is for scientific education only. It is not medical advice, diagnosis, or treatment guidance.