NEW ISIGHTS INTO UNDERLYING CAUSES OF DIABETIC KIDNEY DISEASE

Chronic kidney disease (CKD) remains among the top causes of morbidity and mortality in the world, affecting around 10% of the population globally. The number of people receiving renal replacement therapy worldwide exceeds 2.5 million and is expected to double to 5.4 million by 2030. Currently, there is no cure for this disease and the treatment primarily focuses on disease management. Over a period of time, patients with CKD starts to lose their kidney function and may progress to end-stage kidney disease (ESKD) when the kidneys are no longer able to work at a level needed for day-to-day life. The economic burden of CKD and ESKD is staggering worldwide. Diabetes remain a significant (~ 40%) contributor to CKD in adults. However, our knowledge of the underlying molecular mechanisms involved in new-onset diabetic kidney disease (DKD) and its progression to ESKD remains limited. Prohibitin-1 (PHB1) is an evolutionarily conserved pleiotropic protein that primarily resides in the mitochondria. Transgenic mouse models of PHB1 and mutant-PHB1Y114F have revealed its role in biological sex-related differences in adipose and immune functions. However, the mechanisms involved remain largely unclear. Moreover, it is not known whether PHB1 plays a role in sex-related differences in other cell and tissue types.

To explore this at the systemic level, we focused on two key conserved post-translational modification sites in PHB1 (i.e., the Cys69 and Tyr114 residues, which we have identified before) and developed Phb1C69A and Phb1Y114F knock-in mouse models (together referred to as the Phb1-Ki mice) using state-of-the-art CRISPR-Cas9 technology. Their phenotypic characterization were performed using a combination of cellular and molecular biology tools and techniques.

Consistent with previous findings from the PHB1 and mutant-PHB1Y114F transgenic mice, both Phb1-Ki mouse models displayed altered sex-related differences in immunometabolism, signifying the importance of the Cys69- and Tyr114-linked functions in the sexually dimorphic features of PHB1. Interestingly, a sex-related difference in their kidney sizes were apparent. Further analysis revealed structural abnormalities in PTECs mitochondria and in glomerular podocytes in the Phb1-Ki mice compared with the wild-type mice. When challenged with experimentally-induced T1D and T2D, the Phb1-Ki mice displayed increased susceptibility to DKD, indicating the role of PHB1 in kidney biology and an effect of its dysregulation in the development of DKD. This prompted us to examine PHB1 levels in kidney tissues from the diabetes-linked mouse models of DKD. A significant decrease in their PHB1 levels was apparent indicating a potential link between them. Similarly, a decrease in PHB1 levels was found in human renal cells exposed to high glucose levels (mimicking diabetes-related hyperglycemia) indicating a direct effect of high glucose on PHB1 levels in them.

The Phb1-Ki mouse models have created an opportunity to advance our understanding of PHB1’s role in renal mitochondrial biology, including in sex-related differences, and of its dysregulation in new-onset and progressive DKD. Specially, the models provide insight into the role of PHB1’s Cys69- and Tyr114-linked function in these processes, which are virtually unknown in current literature.