CAPNS1 restoration partially alleviates mitochondrial dysfunction and synaptic deficits in Alzheimer's disease...

Alzheimer's disease (AD), a progressive neurodegenerative disorder characterized by brain atrophy and cognitive decline. While the amyloid cascade hypothesis remains the dominant framework, accumulating evidence indicates that mitochondrial dysfunction critically contributes to AD progression. Although improving mitochondrial function has been shown to rescue cognitive deficits in AD models, the underlying molecular mechanisms remain elusive. In this study, we identified a significant reduction in calpain small subunit 1 (CAPNS1) expression in both AD patient samples and male transgenic mouse models. Decreased CAPNS1 levels were strongly correlated with mitochondrial ultrastructural damage, reduced mitochondrial DNA (mtDNA) copy number, and progressive synaptic loss. Mechanistically, we found that CAPNS1 positively regulated mtDNA transcription and mitochondrial gene expression, and pharmacological data suggested the involvement of the Ca²⁺-CaMKIIβ-MAPK-PGC-1α signaling axis, a master pathway governing mitochondrial biogenesis and respiratory capacity. This activation subsequently restored cellular ATP production and reduced mitochondrial reactive oxygen species accumulation. Importantly, neuronal-specific CAPNS1 upregulation in APP/PS1 transgenic mice markedly improved mitochondrial cristae integrity, reversed hippocampal long-term potentiation deficits, increased dendritic spine density, and partially alleviated spatial memory deficits in behavioral tests. We noted that loss-of-function experiments (e.g., CAPNS1 knockdown or knockout) were not performed in this study, and the proposed Ca²⁺-CaMKIIβ-MAPK-PGC-1α axis should therefore be interpreted as a suggestive working model requiring further validation. Collectively, our findings indicate that CAPNS1 serves as a key regulator of mitochondrial function. By linking Ca²⁺ signaling to mitochondrial gene expression and synaptic integrity, CAPNS1 represents a promising therapeutic target for ameliorating synaptic loss and cognitive decline in AD.