Dissecting the molecular mechanisms of cellular injury in the kidney

Abstract

More than 850 million people are affected by chronic kidney disease (CKD) globally. Despite the prevalence of CKD, there are few options for treatment apart from dialysis or kidney transplantation. The complexities underlying kidney biology and limited in vitro models have impeded advancements in treatments for CKD. Thus, the goal of this research is to further our understanding of kidney disease mechanisms and effectively model kidney disease biology to find new therapeutic strategies. First, given the current limited experimental models for studying podocytes, essential post-mitotic cells of the kidney filter, we introduced the application of human iPSC-derived 2D and 3D in vitro models and an experimentally tractable PAN nephrosis rat model as tools to study podocyte biology. We established the functional presence of disease-relevant TRPC5 channel activity in human iPSC-derived podocytes and demonstrated the podocyte-protective effects of inhibiting TRPC5 channel activity. To further explore podocyte-specific injury mechanisms, we studied a rare genetic mutation in PDSS2, an enzyme involved in the first committed step of Coenzyme Q (CoQ) biosynthesis in the inner mitochondrial membrane. Transcriptomics and metabolomic analyses revealed that loss of PDSS2 induces changes in polyunsaturated fatty acid metabolism and lipid peroxidation accompanied by perturbations in Braf/Mapk signaling. Treatment with Braf-targeting GDC-0879 restored the integrity of the kidney filter in CoQ deficient mice. This study revealed new insights about podocyte biology and a podocyte-protective therapeutic strategy. Beyond rare monogenic disorders, perturbations in lipid metabolism are strongly associated with highly prevalent chronic kidney diseases. To investigate lipid-related injury in the kidney, we identified free fatty acids that induce toxicity in kidney tubular epithelial cells (TECs). A genome-wide CRISPR/Cas9 screen revealed new genetic mediators of lipotoxicity in TECs. We specifically found that FAF2 depletion protects cells from exposure to palmitic acid, a saturated fatty acid, by regulating membrane fluidity in an SCD1-dependent manner. Further, regulation of SCD1 levels by FAF2 was dependent on VCP and proteasomal activity. Thus, we revealed a novel FAF2-dependent mechanism for the regulation of lipid metabolism in the context of lipotoxicity. Altogether, these findings revealed new injury mechanisms in the kidney and identified targetable pathways for therapeutic development.