Loosening ER-Mitochondria Coupling by the Expression of the Presenilin 2 Loop Domain.

Presenilin 2 (PS2), one of the three proteins in which mutations are linked to familial Alzheimer's disease (FAD), exerts different functions within the cell independently of being part of the γ-secretase complex, thus unrelated to toxic amyloid peptide formation. In particular, its enrichment in endoplasmic reticulum (ER) membrane domains close to mitochondria (i.e., mitochondria-associated membranes, MAM) enables PS2 to modulate multiple processes taking place on these signaling hubs, such as Ca2+ handling and lipid synthesis. Importantly, upregulated MAM function appears to be critical in AD pathogenesis. We previously showed that FAD-PS2 mutants reinforce ER-mitochondria tethering, by interfering with the activity of mitofusin 2, favoring their Ca2+ crosstalk. Here, we deepened the molecular mechanism underlying PS2 activity on ER-mitochondria tethering, identifying its protein loop as an essential domain to mediate the reinforced ER-mitochondria connection in FAD-PS2 models. Moreover, we introduced a novel tool, the PS2 loop domain targeted to the outer mitochondrial membrane, Mit-PS2-LOOP, that is able to counteract the activity of FAD-PS2 on organelle tethering, which possibly helps in recovering the FAD-PS2-associated cellular alterations linked to an increased organelle coupling.