Meprin β is specifically inhibited by its cognate synthetic propeptide

Meprin β is a zinc-dependent metalloprotease of the astacin family highly expressed in kidney and intestine. Dysregulation of meprin β expression and activity was observed in several pathological conditions such as Alzheimer's disease, cancer, fibrosis, and inflammatory bowel disease. Therefore, inhibition of meprin β could be a promising therapeutic option to treat pathological conditions influenced by this protease. However, available small-molecule compounds such as the broad-spectrum metalloproteinases inhibitors marimastat or actinonin lack specificity. Hence, more selective meprin β inhibitors needs to be developed. Here, we provide evidence that the synthetically generated cognate meprin β propeptide serves as highly specific inhibitor for the protease (IC₅₀ = 1.35 µM), while other related metalloproteases such as meprin α and a disintegrin and metalloproteinases (ADAMs) are not affected. Employing a targeted approach revealed that removal of the last four C-terminal amino acids of the propeptide significantly improved its inhibitory capacity (IC₅₀ = 0.68 µM). In cell-based experiments, treatment with the propeptide resulted in diminished meprin β activity and decreased cleavage of its substrates, including the interleukin-6 receptor (IL-6R) and the G protein-coupled receptor latrophilin-3 (LPHN3). Suitability was further confirmed in ex vivo cultivated organotypic brain slices, where the administration of the propeptide also resulted in decreased meprin β activity and diminished latrophilin-3 cleavage. Thus, not only the synthetic wildtype propeptide but especially a C-terminally truncated propeptide of meprin β represent highly specific inhibitors with potential for therapeutic application.