Biophysical and biochemical studies support PHD inhibitor development as a TPI deficiency therapy

Triosephosphate isomerase deficiency (TPI Df) is an ultra-rare genetic enzymopathy. Previously, the TPIR5G allele was found to cause TPI Df when combined with a null allele. Here we report a 1.15 angstrom TPIR5G crystal structure providing insight into disease pathogenesis. Previously, we conducted a high-throughput screen that identified TPI-inducing compounds, including predicted Hypoxia Inducible Factor (HIF) inducers. Here we have investigated repurposing HIF activators/prolyl hydroxylase domain inhibitors (PHDIs) as TPI Df treatments. We tested the efficacy of these compounds in TPI Df patient cells. Our results demonstrate PHDIs increase TPI protein levels and TPI activity, suggesting they should be further developed for TPI Df. RNA sequencing and reverse transcription quantitative polymerase chain reaction (RT-qPCR) experiments were performed to analyze PHDI-induced gene expression changes. We discovered chronic PHDI treatment results in HIF1-anti-sense 2 (HIF1-AS2) activation, which operates as a negative feedback loop in the HIF pathway. These results demonstrate repurposing PHDIs for TPI Df is a promising avenue deserving of further investigation. Our results also suggest PHDIs may also benefit dozens of other heritable disease conditions if treatment avoids HIF1-AS2 activation.