Capacitative calcium entry deficits and elevated luminal calcium content in mutant presenilin-1 knockin mice

Dysregulation of calcium signaling has been causally implicated in brain ag ing and Alzheimer's disease. Mutations in the presenilin genes (PS1, PS2), the leading cause of autosomal dominant familial Alzheimer's disease (FAD), cause highly specific alterations in intracellular calcium signaling pathw ays that may contribute to the neurodegenerative and pathological lesions o f the disease. To elucidate the cellular mechanisms underlying these distur bances, we studied calcium signaling in fibroblasts isolated from mutant PS 1 knockin mice. Mutant PS1 knockin cells exhibited a marked potentiation in the amplitude of calcium transients evoked by agonist stimulation. These c ells also showed significant impairments in capacitative calcium entry (CCE , also known as store-operated calcium entry), an important cellular signal ing pathway wherein depletion of intracellular calcium stores triggers infl ux of extracellular calcium into the cytosol. Notably, deficits in CCE were evident after agonist stimulation, but nor if intracellular calcium stores were completely depleted with thapsigargin. Treatment with ionomycin and t hapsigargin revealed that calcium levels within the ER were significantly i ncreased in mutant PS1 knockin cells. Collectively, our findings suggest th at the overfilling of calcium stores represents the fundamental cellular de fect underlying the alterations in calcium signaling conferred by presenili n mutations.