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 Å 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. We have investigated repurposing HIF activators/prolyl hydroxylase domain inhibitors (PHDIs) as TPI Df treatments. We tested the efficacy of these compounds in cells from individuals with TPI Df. Our results demonstrate that 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 that chronic PHDI treatment results in HIF1-antisense 2 (HIF1-AS2) activation, which operates as a negative feedback loop in the HIF pathway. These results demonstrate that repurposing PHDIs for TPI Df is a promising avenue of research deserving further investigation. Our results also suggest that PHDIs may also benefit dozens of other heritable disease conditions if treatment avoids HIF1-AS2 activation.