Fibrocystin/Polyductin releases a C-terminal fragment that translocates into mitochondria and suppresses cystogenesis

Fibrocystin/Polyductin (FPC), encoded by PKHD1 , is associated with autosomal recessive polycystic kidney disease (ARPKD), yet its precise role in cystogenesis remains unclear. Here we show that FPC undergoes complex proteolytic processing in developing kidneys, generating three soluble C-terminal fragments (ICDs). Notably, ICD 15 , contains a novel mitochondrial targeting sequence at its N-terminus, facilitating its translocation into mitochondria. This enhances mitochondrial respiration in renal epithelial cells, partially restoring impaired mitochondrial function caused by FPC loss. FPC inactivation leads to abnormal ultrastructural morphology of mitochondria in kidney tubules without cyst formation. Moreover, FPC inactivation significantly exacerbates renal cystogenesis and triggers severe pancreatic cystogenesis in a Pkd1 mouse mutant Pkd1 V/V in which cleavage of Pkd1 -encoded Polycystin-1 at the GPCR Proteolysis Site is blocked. Deleting ICD 15 enhances renal cystogenesis without inducing pancreatic cysts in Pkd1 V/V mice. These findings reveal a direct link between FPC and a mitochondrial pathway through ICD 15 cleavage, crucial for cystogenesis mechanisms.