Regulation of the alternative ß-secretase meprin ß by ADAM-mediated shedding.

ABSTRACT

Alzheimer's Disease (AD) is the sixth-leading cause of death in industrialized countries. Neurotoxic amyloid-ß (Aß) plaques are one of the pathological hallmarks in AD patient brains. Aß accumulates in the brain upon sequential, proteolytic processing of the amyloid precursor protein (APP) by ß- and γ-secretases. However, so far disease-modifying drugs targeting ß- and γ-secretase pathways seeking a decrease in the production of toxic Aß peptides have failed in clinics. It has been demonstrated that the metalloproteinase meprin ß acts as an alternative ß-secretase, capable of generating truncated Aß2-x peptides that have been described to be increased in AD patients. This indicates an important ß-site cleaving enzyme 1 (BACE-1)-independent contribution of the metalloprotease meprin ß within the amyloidogenic pathway and may lead to novel drug targeting avenues. However, meprin ß itself is embedded in a complex regulatory network. Remarkably, the anti-amyloidogenic α-secretase a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) is a direct competitor for APP at the cell surface, but also a sheddase of inactive pro-meprin ß. Overall, we highlight the current cellular, molecular and structural understanding of meprin ß as alternative ß-secretase within the complex protease web, regulating APP processing in health and disease.