Alzheimer's disease (AD) is characterized by amyloid-β (Aβ)-associated synaptic failure, intracellular Ca2+ dysregulation, and progressive impairment of lysosome-dependent clearance pathways. Aβ induces sustained Ca2+ overload, resulting in pathological hyperactivation of CaMKII, which normally participates in the regulation of autophagy. However, whether CaMKII hyperactivation contributes to Aβ-induced late-stage autophagy-lysosomal dysfunction and mitophagy failure remains unclear. This study aimed to examine the effects of the CaMKII inhibitor KN93 in Aβ25-35-exposed rat organotypic hippocampal slice cultures (OHSCs, ex vivo model) and the mouse brain in vivo. The results showed that Aβ25-35 induced intracellular Ca2+ elevation, CaMKII hyperactivation, and marked accumulation of LC3-II and p62. Ultrastructural and biochemical analyses revealed impaired lysosomal maturation, defective autophagosome-lysosome coupling, and accumulation of autophagic vacuoles, consistent with a blockade of late-stage autophagic flux. Increased levels of immature cathepsin D and reduced colocalization of LC3 with lysosomal markers further supported compromised lysosomal competence. Damaged mitochondria were recruited to lysosomal compartments but failed to undergo effective degradation, indicating abortive mitophagy under Aβ25-35 exposure. KN93 attenuated Aβ25-35-induced defects in lysosomal protease maturation, autophagosome-lysosome fusion, and mitochondrial clearance in both the ex vivo OHSCs model and the in vivo mouse brain. KN93 also ameliorated cognitive impairment in Aβ25-35-exposed mice. Taken together, these findings indicate that CaMKII hyperactivation contributes to Aβ25-35-induced autophagy-lysosomal dysfunction and neuronal damage, and that pharmacological inhibition of CaMKII with KN93 restores intracellular degradative capacity and ameliorates cognitive impairment under Aβ stress.
