Beyond the Amyloid Hypothesis: Systemic Drivers, CNS-PNS Crosstalk, and the Future of Alzheimer’s Disease Therapeutics

Alzheimer’s disease (AD) is undergoing a profound paradigm shift, transitioning from a localized, monolithic proteinopathy into a complex, multisystem disorder. This critical review synthesizes recent mechanistic, translational, and clinical insights to dismantle the traditional linear amyloid cascade hypothesis. We explore the synergistic interplay between amyloid-β (Aβ) and tau propagation, positioning chronic neuroinflammation, endolysosomal failure, and metabolic starvation—often framed as “Type 3 Diabetes”—as fundamental disease drivers. Crucially, we highlight the emerging biological bridge of CNS-PNS crosstalk, where central neurodegeneration and peripheral neuropathies are linked by systemic immune activation and microbiota–gut–brain axis dysbiosis. The recent validation of disease-modifying therapies (DMTs) confirms Aβ clearance as a viable pharmacological target; however, the marginal clinical gains and severe radiological risks, such as Amyloid-Related Imaging Abnormalities (ARIA), expose the profound limitations of monotherapy. Ultimately, we argue that isolated amyloid clearance is merely an induction phase. The future of AD therapeutics mandates a sequential combination approach—pairing early plaque debulking with lifelong metabolic and neuroimmune maintenance. Supported by scalable fluid biomarkers (e.g., plasma p-tau217) and the expanded ATN(I) framework, the field must embrace proactive precision medicine and inclusive clinical trial designs to successfully transform AD into a manageable chronic condition.