Autophagy dependent HIF1α proteostasis is compromised in models of PEX1 deficiencies

Peroxisomes, along with mitochondria, coordinate and compartmentalize oxidative metabolism in eukaryotic cells. Rare genetic disorders caused by mutations in PEX genes impair peroxisome function and cause Peroxisome Biogenesis Disorders, which are characterized by liver and neurological dysfunction, hearing and vision loss, and metabolic abnormalities. The majority of Peroxisome Biogenesis Disorders (PBDs) are caused by mutations in the gene encoding PEX1, which together with PEX6 forms a hetero-hexameric AAA-ATPase complex that drives the import of enzymes into the peroxisome lumen. One particular destabilizing mutation - PEX1 ^G843D - results in almost 30% of all cases. Here we show that deficiencies in PEX1 lead to increased levels of the oxygen-responsive transcription factor HIF1α in normoxia, as well as a HIF1α transcriptional signature. The increase in HIF1α protein was rescued by overexpression of PEX1 ^WT , suggesting PEX1 deficiencies modulate HIF1α signaling. The increased levels of HIF1α were not explained by defects in the oxygen responsive degradation pathway of HIF1α that relies on proline hydroxylase domain enzyme-dependent hydroxylation and von Hippel Lindau tumor suppressor protein-dependent ubiquitination. Instead, we found that PEX1 deficiency alters HIF1α proteostasis by reducing degradation through a hydroxylation- and autophagy-dependent mechanism. Notably, enhancing autophagic capacity by ULK1 agonism was sufficient to reduce HIF1α levels in PEX1 deficient cells. Lastly, we demonstrate that upon hypoxia-reoxygenation, PEX1 deficient cells are slower to reset HIF1α levels. Our results suggest that PBD patients with PEX1 deficiency may be susceptible to dysregulation of the HIF1α pathway, particularly in tissues where oxygen gradients are physiological or developmentally required.