Estrogen mediated differential regulation of APOE4 and its Role in Neurofibrillary tangle formation and Alzheimer’s Disease progression

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder affecting around 50 million people worldwide, with cases expected to triple by 2050. Women exhibit almost twice the risk of developing AD compared to men, which could be explained by estrogen-mediated differential regulation of APOE4. Estrogen acts through two receptor subtypes with opposing effects on ApoE expression. In APOE4 carriers, receptor polymorphisms and disrupted estrogenic signaling reduce ApoE protein production, impair amyloid-beta clearance, and promote neuroinflammation. These disruptions interact with amyloid-beta plaques and intraneural tau neurofibrillary tangles, together accelerating synaptic failure and neuronal death. During menopause the reduction of estrogen further reduces receptor responsiveness and neuroprotective signaling, potentially contributing to a shift in the brian from a neuroprotective to a neurodegenerative state. Clinical evidence from hormone therapy studies reinforces this framework, as estrogen therapy reduces cognitive impairment risk in APOE4-negative women but may worsen outcomes in APOE4- positive individuals. Although the precise initiating trigger of AD pathology remains unknown, understanding the intersection of hormonal regulation and synaptic resilience, may guide the development of more effective treatment strategies.