Loss of biliverdin reductase-A promotes lipid accumulation and lipotoxicity in mouse proximal tubule cells.

Obesity and increased lipid availability have been implicated in the development and progression of chronic kidney disease. One of the major sites of renal lipid accumulation is in the proximal tubule cells of the kidney, suggesting that these cells may be susceptible to lipotoxicity. We previously demonstrated that loss of hepatic biliverdin reductase A (BVRA) causes fat accumulation in livers of mice on a high-fat diet. To determine the role of BVRA in mouse proximal tubule cells, we generated a CRISPR targeting BVRA for a knockout in mouse proximal tubule cells (BVRA KO). The BVRA KO cells had significantly less metabolic potential and mitochondrial respiration, which was exacerbated by treatment with palmitic acid, a saturated fatty acid. The BVRA KO cells also showed increased intracellular triglycerides which were associated with higher fatty acid uptake gene cluster of differentiation 36 as well as increased de novo lipogenesis as measured by higher neutral lipids. Additionally, neutrophil gelatinase-associated lipocalin 1 expression, annexin-V FITC staining, and lactate dehydrogenase assays all demonstrated that BVRA KO cells are more sensitive to palmitic acid-induced lipotoxicity than wild-type cells. Phosphorylation of BAD which plays a role in cell survival pathways, was significantly reduced in palmitic acid-treated BVRA KO cells. These data demonstrate the protective role of BVRA in proximal tubule cells against saturated fatty acid-induced lipotoxicity and suggest that activating BVRA could provide a benefit in protecting from obesity-induced kidney injury.

Sex-Dependent Effects of HO-1 Deletion from Adipocytes in Mice.

Induction of heme oxygenase-1 (HO-1) has been demonstrated to decrease body weight and improve insulin sensitivity in several models of obesity in rodents. To further study the role of HO-1 in adipose tissue, we created an adipose-specific HO-1 knockout mouse model. Male and female mice were fed either a control or a high-fat diet for 30 weeks. Body weights were measured weekly and body composition, fasting blood glucose and insulin levels were determined every six weeks. Adipocyte-specific knockout of HO-1 had no significant effect on body weight in mice fed a high-fat diet but increased body weight in female mice fed a normal-fat diet. Although body weights were not different in females fed a high fat diet, loss of HO-1 in adipocytes resulted in significant alterations in body composition. Adipose-specific HO-1 knockout resulted in increased fasting hyperglycemia and insulinemia in female but not male mice on both diets. Adipose-specific knockout of HO-1 resulted in a significant loss of HO activity and a decrease in the protein levels of adiponectin in adipose tissue. These results demonstrate that loss of HO-1 in adipocytes has greater effects on body fat and fasting hyperglycemia in a sex-dependent fashion and that expression of HO-1 in adipose tissue may have a greater protective role in females as compared to males.