Microbiome Integrity Protects Against Glial-Mediated Tau and Amyloid Pathology Through Circadian and Autophagy Homeostasis.

Alzheimer's disease (AD) is characterized not only by tau and amyloid-β aggregation but also by systemic disruptions in circadian rhythms, metabolism, and gut-brain communication that exacerbate neuroinflammation and neurodegeneration. While glial cells play central roles in inflammatory signaling and proteostasis, the contribution of the gut microbiome to glia-driven AD pathology remains poorly understood. Here, we used Drosophila models with glial-specific expressions of human tau and amyloid-associated transgenes to investigate how microbiome integrity influences disease progression. AD models exhibited significant shifts in gut microbial composition, particularly in Lactobacillus and Acetobacter species, suggesting an adaptive microbial response to pathological stress. Strikingly, microbiome depletion (axenic condition) markedly worsened behavioral and physiological outcomes, including disrupted sleep-circadian rhythms, impaired memory, and reduced locomotor function. These deficits were accompanied by amplified neuroinflammatory signaling (Upd-Dome-Hop-Stat92e axis), increased apoptotic gene expression, lipid dysregulation, and altered synaptic markers. Moreover, microbiome loss induced energy stress marked by elevated phospho-AMPK (p-AMPK), yet failed to restore proteostasis, as evidenced by accumulation of ubiquitinated proteins and the autophagy adaptor Ref2p, indicating impaired autophagic flux. This dysfunction correlated with increased tau, phospho-tau, and Aβ42 accumulation. Together, our findings demonstrate that microbiome depletion exacerbates glial-mediated inflammation, disrupts circadian and metabolic homeostasis, impairs, and accelerates cognitive and motor decline. This work highlights a previously underappreciated role of the gut microbiome in restraining glial dysfunction and mitigating AD-like pathology, positioning microbial homeostasis as a critical modulator of neurodegenerative disease progression.