Autophagy loss impedes cancer-associated fibroblast activation via downregulating proline biosynthesis

Cancer-associated fibroblasts (CAFs) are considered one of the most critical stromal cells that interact with pancreatic ductal adenocarcinoma (PDAC) and promote tumor growth, metastasis, and treatment resistance. Previous studies illustrated macroautophagy/autophagy contributes to CAF activation during tumor progression. Here in our study, we found that autophagy deficiency in CAFs impedes CAF activation by inhibiting proline biosynthesis and collagen production. Furthermore, we uncovered that autophagy promotes proline biosynthesis through mitophagy-mediated regulation of NADK2 (NAD kinase 2, mitochondrial), an enzyme responsible for production of mitochondrial NADP(H). Using an orthotopic mouse model of PDAC, we found that inhibiting mitophagy by targeting PRKN (parkin RBR E3 ubiquitin protein ligase) in the stroma reduced tumor weight. Thus, inhibition of CAFs mitophagy might be an attractive strategy for stroma-focused anti-cancer intervention. Abbreviations: ACTA2/α-SMA: actin alpha 2, smooth muscle, aorta; ACTB/β-actin: actin, beta; ALDH18A1/P5CS: aldehyde dehydrogenase 18 family, member A1; ATG3: autophagy related 3; ATG5: autophagy related 5; BNIP3L: BCL2/adenovirus E1B interacting protein 3-like; CAFs:cancer-associated fibroblasts; COL1A1: collagen, type I, alpha 1; DES: desmin; ECM: extracellular matrix; FABP4: fatty acid binding protein 4, adipocyte; FAP/FAPα: fibroblast activation protein; IHC: immunohistochemical staining; LAMP1: lysosomal-associated membrane protein 1; NADK2: NAD kinase 2, mitochondrial; PC1: pro-collagen 1; PDAC: pancreatic ductal adenocarcinoma; PDGFR: platelet derived growth factor receptor; PDPN: podoplanin; PRKN: parkin RBR E3 ubiquitin protein ligase; PSCs: pancreatic stellate cells; VIM: vimentin; WT: wild-type.