Disrupted synaptic vacuolar H+-ATPase renders synaptic vulnerability to Alzheimer's disease.

Defective synaptic transmission is a prominent pathology that underlies cognitive deficits in Alzheimer's disease (AD), highlighting the need to elucidate molecular mechanisms of synaptic failure. Vacuolar H+-ATPase (V-ATPase), a proton-pumping enzyme, is essential for synaptic vesicle acidification and neurotransmitter loading. However, whether SV-associated V-ATPase is vulnerable to AD remains unclear. Here, using SV-rich fractions from postmortem brain tissues, we identified SV-associated V-ATPase deficits, including decreased enzymatic activity, impaired complex assembly, and altered expression of its key subunits in AD. SV-associated V-ATPase dysfunction was further associated with pathological and clinical characteristics of AD. Genetic downregulation of the V-ATPase V1D subunit, a component reduced in AD brains, disrupted V-ATPase proton transport and impaired SV acidification. Further experiments using 5×FAD mice, which exhibited AD-like SV-associated V-ATPase deficits, demonstrated the deleterious impact of V-ATPase dysfunction on SV acidification and synaptic transmission including presynaptic neurotransmitter release. In addition, ex vivo studies identified amyloid β-induced oxidative stress as a driver of V1D loss and V-ATPase disassembly, linking AD pathology to SV-associated V-ATPase dysfunction. These findings indicate that SV-associated V-ATPase dysfunction contributes to synaptic failure and cognitive deficits in AD. Therapeutic avenues to mitigate V-ATPase dysfunction have the potential to attenuate synaptic failure for the management of AD.