Loss Of Pkd1/Polycystin-1 Impairs Lysosomal Activity In A Capn (Calpain)-Dependent Manner

Mutations in thePKD1gene result in autosomal dominant polycystic kidney disease (ADPKD), the most common monogenetic cause of end-stage renal disease (ESRD) in humans. Previous reports suggested that PKD1, together with PKD2/polycystin-2, may function as a receptor-cation channel complex at cilia and on intracellular membranes and participate in various signaling pathways to regulate cell survival, proliferation and macroautophagy/autophagy. However, the exact molecular function of PKD1 and PKD2 has remained enigmatic. Here we usedPkd1-deficient mouse inner medullary collecting duct cells (mIMCD3) genetically deleted forPkd1, and tubular epithelial cells isolated from nephrons of doxycycline-inducible conditionalpkd1(fl/fl);Pax8(rtTA);TetOCre(+)knockout mice to show that the lack ofPkd1caused diminished lysosomal acidification, LAMP degradation and reduced CTSB/cathepsin B processing and activity. This led to an impairment of autophagosomal-lysosomal fusion, a lower delivery of ubiquitinated cargo from multivesicular bodies (MVB)/exosomes to lysosomes and an enhanced secretion of unprocessed CTSB into the extracellular space. The TFEB-dependent lysosomal biogenesis pathway was however unaffected.Pkd1-deficient cells exhibited increased activity of the calcium-dependent CAPN (calpain) proteases, probably due to a higher calcium influx. Consistent with this notion CAPN inhibitors restored lysosomal function, CTSB processing/activity and autophagosomal-lysosomal fusion, and blocked CTSB secretion and LAMP degradation inpkd1knockout cells. Our data reveal for the first time a lysosomal function of PKD1 which keeps CAPN activity in check and ensures lysosomal integrity and a correct autophagic flux.