Carla Koehler, PhD
The Koehler laboratory has continued to characterize protein trafficking of mutant alanineglyoxyate transaminase (AGT P11LG170R) that results in primary hyperoxaluria 1 (PH1). In PH1, mutant AGT is functional but mislocalizes to mitochondria (the powerhouse of the cell) instead of peroxisomes, the organelle that is its normal home. Our team conducts small molecule screens to identify candidate molecules (called Mito-BloCK compounds) that block the import of mitochondrial proteins from the mitochondrion. We have used this as a strategy to redirect mutant AGT from mitochondria to peroxisomes. From our preliminary studies, we identified an FDA-approved compound dequalinium chloride (Deca/MB-12).
With generous funds from OHF, we have been investigating the trafficking pathway of mutant AGT and testing additional MitoBloCK compounds to see if they rescue AGT trafficking. In addition to Deca, we show that molecule MitoBloCK-20 (MB-20), also inhibits mutant AGT import into mitochondria. We will test additional MitoBloCK compounds that target different mitochondrial translocation components, because this will form a framework for understanding the import pathway of AGT. We have also been doing biochemical experiments to understand how the MitoBloCK compounds target the mitochondrial translocation components. Deca seems to target the membrane components and potentially destabilize the TIM23 translocon, whereas MB-20 prevents the translocation motor from interacting with the TIM23 translocation channel. We will move these studies into cultured cell models to determine what molecules are suitable for trafficking mutant AGT back to peroxisomes and to determine the critical events in the cytosol that direct mutant AGT back to peroxisomes. Previous studies had suggested that mitochondrial uncouplers might be favorable for restoring mutant AGT trafficking. However, we find that treatment with uncouplers results in aggregation of mutant AGT in the cytosol and does not rescue trafficking in a cell model. Therefore, small molecules that slow mitochondrial protein import may be a platform for developing therapeutic strategies for a subset of patients with PH1.