RESTORING CELLULAR HOMEOSTASIS IN ALZHEIMER’S DISEASE ASTROCYTES BY STABILIZING ER–MITOCHONDRIA INTERACTION

Alzheimer’s disease (AD), a major form of age-related dementia, currently has no effective therapy. Astrocytes play key role in early AD pathogenesis due to loss of their homeostatic and supportive functions, although molecular mechanisms of their dyshomeostasis are poorly understood. ER-mitochondria contact sites (MERCS) are altered in AD, yet they are involved in many cellular functions, such as Ca²⁺ signaling, bioenergetics and proteostasis. We hypothesized that i) alterations of MERCS in astrocytes may lead to their dysfunction in AD, and ii) stabilization of MERCS may rescue astrocytic dysfunction, hence be beneficial in AD. We used calcium and fluorescent protein imaging, Western blots, enzymatic assays and qPCR. We report that stabilizing MERCS using synthetic linkers in hippocampal astrocytes from 3xTg-AD mice we were able to either reproduce AD-related pathology in WT astrocytes, or rescue astrocytic homeostasis in 3xTg-AD astrocytes in an ER-mitochondria distance-dependent manner. Specifically, expression of 10nm linker in WT astrocytes led to impairment of ER-mitochondrial Ca²⁺ flow, low grade ER stress, and impairment of protein synthesis and degradation, leading to reduced homeostatic support to neurons and endothelial cells. Contrarily, expression of 20nm linker in 3xTg-AD astrocytes rescued cell dysfunctions at molecular and functional levels. Intriguingly, pharmacological activation of mitochondrial Ca²⁺ uptake reverted part of the alterations. Taken together, our data suggest that stabilizing ER-mitochondria interaction at the specific distance of 20nm may represent valuable strategy for preventing loss of homeostasis in AD astrocytes, thereby preventing neurodegeneration.