Hepatic stellate cells increase proline production from glutamine upon activation during liver fibrosis, and PYCR1 is upregulated and proline oxidase (PRODH), which recycles proline back to P5C, is downregulated, showing that fibroblast activation pushes cells towards proline synthesis, although whether this affected collagen production was not investigated (58). Here, PRODH is linked to Hepatic fibrosis.