Genetic Rescue of Mitochondrial Calcium Efflux in Alzheimer's Disease Preserves Mitochondrial Function and Protects against Neuronal Cell Death

Abstract

Background. Alzheimer's disease (AD) is characterized by neurodegeneration, specifically the progressive loss of neuronal populations in the frontal cortex and hippocampus. Numerous studies have shown that neuronal cell death and metabolic dysregulation are fundamental cellular mechanisms driving the progression of AD and other dementia-related diseases. Previous studies have suggested numerous mechanisms whereby intracellular Ca2+ load is increased in AD and thereby likely significantly impacts mCa2+ signaling. Methods. To discern if mCa2+ signaling is causative in the progression of AD, human AD brain samples, an AD mutant mouse model (3xTg) and an AD-mutant cell line (N2a/APPswe) were examined for mitochondrial alterations in: Ca2+ handling, ROS generation, membrane potential (ΔΨ), permeability transition pore activation, OxPhos, APP metabolism and cell death. Results. 3xTg-AD mice and human AD brain samples displayed significant alterations in the expression of key mCa2+ exchange genes, most notably a reduction in the expression of the mitochondrial Na+/Ca2+ exchanger (mNCX, SLC8B1), the major efflux pathway in excitable cells. We discovered that mCa2+ efflux and mCa2+ retention capacity was severely impaired in N2a/APPswe cells. Rescue of mCa2+ extrusion, via adenoviral expression of mNCX, enhanced the clearance of pathogenic mCa2+, recovered (ΔΨ), enhanced OxPhos, reduced extracellular Aβ1-40 levels and protected from ionomycin-, glutamate- and ROS-induced cell death. Conclusions. Our data suggest that impaired mCa2+ exchange is a central contributor to neuronal cell death in AD and that mNCX represents a new therapeutic target to inhibit or reverse AD progression.