Aβ42 oligomers modulate β-secretase through an XBP-1s-dependent pathway involving HRD1

The aspartyl protease beta-site APP cleaving enzyme, BACE1, is the rate-limiting enzyme involved in the production of amyloid-beta peptide, which accumulates in both sporadic and familial cases of Alzheimer's disease and is at the center of gravity of the amyloid cascade hypothesis. In this context, unravelling the molecular mechanisms controlling BACE1 expression and activity in both physiological and pathological conditions remains of major importance. We previously demonstrated that A beta controlled BACE1 transcription in an NF kappa B-dependent manner. Here, we delineate an additional cellular pathway by which natural and synthetic A beta 42 oligomers enhance active X-box binding protein XBP-1s. XBP-1s lowers BACE1 expression and activity indirectly, via the up-regulation of the ubiquitin-ligase HRD1 that acts as an endogenous down-regulator of BACE1. Thus, we delineate a novel pathway by which cells could compensate for A beta 42 oligomers production and thus, associated toxicity, by triggering a compensatory mechanism aimed at lowering BACE-1-mediated A beta production by a molecular cascade involving XBP-1s and HRD1. It thus identifies HRD1 as a potential target for a novel A beta-centered therapeutic strategy.