Presenilin‐2 dampens intracellular Ca2+ stores by increasing Ca2+ leakage and reducing Ca2+ uptake

AbstractWe have previously shown that familial Alzheimer’s disease mutants of presenilin‐2 (PS2) and, to a lesser extent, of presenilin‐1 (PS1) lower the Ca2+ concentration of intracellular stores. We here examined the mechanism by which wild‐type and mutant PS2 affect store Ca2+ handling. By using HeLa, SH‐SY5Y and MEFs as model cells, and recombinant aequorins as Ca2+ probes, we show evidence that transient expression of either wild‐type or mutant PS2 increases the passive Ca2+ leakage: both ryanodine‐ and IP3‐receptors contribute to Ca2+ exit out of the ER, whereas the ribosome translocon complex is not involved. In SH‐SY5Y cells and MEFs, wild‐type and mutant PS2 potently reduce the uptake of Ca2+ inside the stores, an effect that can be counteracted by over‐expression of SERCA‐2B. On this line, in wild‐type MEFs, lowering the endogenous level of PS2 by RNA interference, increases the Ca2+‐loading capability of intracellular stores. Furthermore, we show that in PS double knockout MEFs, reduction of Ca2+ stores is mimicked by the expression of PS2‐D366A, a loss‐of‐function mutant, uncleaved because also devoid of presenilinase activity but not by co‐expression of the two catalytic active fragments of PS2. In summary, both physiological and increased levels of wild‐type and mutant PS2 reduce the Ca2+ uptake by intracellular stores. To exert this newly described function, PS2 needs to be in its full‐length form, even if it can subsequently be cleaved.