Unravelling the pathogenic role of lysosomal TPC2 Ca2+ channel in Alzheimer’s disease

Alzheimer’s disease (AD) is the most common form of dementia that is currently untreatable. Although many drugs are under developing that target to different pathogenic hypotheses, none of the developing drugs based on the g-secretase inhibitor has passed the phase III clinical trials suggested that g-secretase may not be the disease origin. This unsatisfactory outcome urged for the identification of novel pathogenic target that may help for the future anti-AD drug development. Mounting evidence suggests disrupted intracellular Ca2+ signaling and/or autophagy impairment have been implicated in AD pathogenesis. However, how disrupted Ca 2+ impinges on autophagy impairment in AD is largely unexplored.

Tetrandrine, a Chinese medicinal compound that has been shown to regulate the autophagy pathway and improve memory function in rat AD model with unknown molecular target. Our preliminary data on transgenic 5xFAD mice revealed autophagy impairment in brain with lysosomal alkalization. 5xFAD mice treated with tetrandrine showed reduction in amyloid plaques in hippocampal and cortical regions and improved memory functions in 5xFAD mice. Mechanistically, our in vitro data demonstrated excessive Ca2+ release through the lysosomal two-pore channel (TPC2) can cause alkalization of lysosomes in AD neuronal cell model and fibroblast samples isolated from AD patients. The dyshomeostasis in lysosomal Ca 2+ and pH reduced cathepsin D activity which is responsible for amyloid clearance, thus may lead to amyloid plaques accumulation in AD brain. Intriguingly, inhibition of lysosomal TPC2 channel by its antagonists or genetically knockdown TPC2 using siRNA rescued Ca2+ dyshomeostasis, restored the acidic pH and cathepsin D activity of the lysosomes. Altogether, we hypothesize the overactivity of lysosomal TPC2 channel may be the underlying cause of autophagy impairment and contributes to AD pathologies.

In this study, we will employ biochemical, cellular and transgenic and conditional TPC2 knockout animal approaches:
(1) to consolidate the gain-of-function of the lysosomal TPC2 channel activity in chemical-induced human AD neurons;
(2) to investigate the consequences of functional impairment of TPC2 in chemical-induced human AD neurons; and
(3) to determine the therapeutic effect of inhibiting lysosomal TPC2 in AD using tetrandrine and/or cKO TPC2 in 5xFAD mice.

Results from this research project will broaden our current knowledge on the roles of TPC2 channel in the lysosomal functions. The identification of TPC2 as a pathogenic site will provide novel target for anti-AD drug development. Ultimately, we wish therapeutic agents targeting to the lysosomal TPC2 channel would be an effective cure for the Alzheimer’s disease.