Complex III-derived reactive oxygen species in mitochondrial-nuclear crosstalk in Alzheimer's disease and related dementias - SUMMARY Alzheimer's disease (AD) and related dementias involve multifactorial and interconnected mechanisms, including APP/amyloid-β (Aβ) pathology, tauopathy, neuroimmune responses, neuronal impairments, and glial alterations. Mitochondrial dysfunction is an early event influenced by various disease-related factors, including Aβ and apolipoprotein E4 (APOE4), the strongest genetic risk factor for late-onset AD. Mitochondria produce energy, but are also a major source of reactive oxygen species (ROS). Mitochondrial ROS (mtROS) increase in aging and disease, are associated with pathogenic processes, including protein misfolding, synaptic deficits, and neuroinflammation, and can diffuse to other subcellular compartments to signal and influence metabolic, redox and health status. Complex III (CIII) of the mitochondrial respiratory chain has the largest capacity for ROS production and can release ROS toward the intermembrane space and extra-mitochondrial compartments, thus poising CIII-derived ROS (CIII-ROS) to affect signaling pathways and nuclear functions. However, the mechanisms by which CIII-ROS may influence nuclear processes and affect AD pathogenesis are not defined. Astrocytes are reported to produce high levels of mtROS. Thus, we examined the regulation and roles of astrocytic mtROS using live-cell redox imaging, site-selective mtROS suppressors, targeted genetic manipulations, molecular profiling, and preclinical testing, among other approaches. Our findings reveal that disease-linked factors, including Aβ, induce astrocytic CIII-ROS in a temporally defined and NF-κB-dependent manner. Induction of CIII-ROS caused selective oxidation of target proteins and amplified STAT3 activation and gene expression changes linked to astrocytic reactivity and disease responses. Suppression of CIII-ROS decreased brain pathology and neuroimmune responses, and extended lifespan in mice with tauopathy. Notably, APOE is highly enriched in astrocytes and influences mtROS levels. Our data suggest that the APOE4 variant exacerbates astrocytic mtROS responses whereas the AD-resilience variant of APOE (R136S Christchurch) inhibits these responses. However, the exact effects of APOE variants on astrocytic mtROS dynamics and the roles of mtROS in gene regulation and dementia risk are not clear. In the current project, we will examine the underlying mechanisms and effects of astrocytic mtROS-nuclear crosstalk in neural cultures and knock-in mouse models. We will define mtROS responses and their regulation and roles using cutting-edge live-cell imaging, multiomic profiling, functional measures, and other complementary methods. Together, our study will leverage advanced model systems and technologies to identify new molecular networks mediating mitochondrial-nuclear crosstalk and reveal novel redox-linked therapeutic strategies for AD and related neurodegenerative disorders.
