Targeted deletion of von-Hippel-Lindau in the proximal tubule conditions the kidney against early diabetic kidney disease.

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease. Glomerular hyperfiltration and albuminuria subject the proximal tubule (PT) to a subsequent elevation of workload, growth, and hypoxia. Hypoxia plays an ambiguous role in the development and progression of DKD and shall be clarified in our study. PT-von-Hippel-Lindau (Vhl)-deleted mouse model in combination with streptozotocin (STZ)-induced type I diabetes mellitus (DM) was phenotyped. In contrary to PT-Vhl-deleted STZ-induced type 1 DM mice, proteinuria and glomerular hyperfiltration occurred in diabetic control mice the latter due to higher nitric oxide synthase 1 and sodium and glucose transporter expression. PT Vhl deletion and DKD share common alterations in gene expression profiles, including glomerular and tubular morphology, and tubular transport and metabolism. Compared to diabetic control mice, the most significantly altered in PT Vhl-deleted STZ-induced type 1 DM mice were Ldc-1, regulating cellular oxygen consumption rate, and Zbtb16, inhibiting autophagy. Alignment of altered genes in heat maps uncovered that Vhl deletion prior to STZ-induced DM preconditioned the kidney against DKD. HIF-1α stabilization leading to histone modification and chromatin remodeling resets most genes altered upon DKD towards the control level. These data demonstrate that PT HIF-1α stabilization is a hallmark of early DKD and that targeting hypoxia prior to the onset of type 1 DM normalizes renal cell homeostasis and prevents DKD development.

Inhibition of human carbonyl reducing enzymes by plant anthrone and anthraquinone derivatives.

Members of the aldo-keto reductase and short-chain dehydrogenase/reductase enzyme superfamilies catalyze the conversion of a wide range of substrates, including carbohydrates, lipids, and steroids. These enzymes also participate in the transformation of xenobiotics, inactivation of the cytostatics doxo- and daunorubicin, and play a role in the development of cancer. Therefore, inhibitors of such enzymes may improve therapeutic outcomes. Plant-derived compounds such as anthraquinones have been used for medicinal purposes for several centuries. In the current study, the inhibitory potential of selected anthrone and anthraquinone derivatives (from plants) was tested on six recombinant human carbonyl reducing enzymes (AKR1B1, AKR1B10, AKR1C3, AKR7A2, AKR7A3, CBR1) isolated from an Escherichia coli expression system. Overall, the least inhibition was observed with the anthrone derivative aloin, while IC50 values obtained with the anthraquinone derivatives (frangula emodin, aloe emodin, frangulin A, and frangulin B) and the aldo-keto reductase AKR1B10 were in the low micromolar range (3.5-16.6 µM). AKR1B1 inhibition was significantly weaker in comparison with AKR1B10 inhibition (IC50 values > 50 µM). The strongest inhibition was observed with the short-chain dehydrogenase/reductase CBR1. AKR7A2, AKR7A3, and AKR1C3 were not, or less inhibited by inhibitor concentrations of up to 50 µM. Analysis of the kinetic data suggests noncompetitive or uncompetitive inhibition mechanisms. The new inhibitors described here may serve as lead structures for the development of future drugs.

Microbial regulation of hexokinase 2 links mitochondrial metabolism and cell death in colitis.

Hexokinases (HK) catalyze the first step of glycolysis limiting its pace. HK2 is highly expressed in gut epithelium, contributes to immune responses, and is upregulated during inflammation. We examined the microbial regulation of HK2 and its impact on inflammation using mice lacking HK2 in intestinal epithelial cells (Hk2ΔIEC). Hk2ΔIEC mice were less susceptible to acute colitis. Analyzing the epithelial transcriptome from Hk2ΔIEC mice during colitis and using HK2-deficient intestinal organoids and Caco-2 cells revealed reduced mitochondrial respiration and epithelial cell death in the absence of HK2. The microbiota strongly regulated HK2 expression and activity. The microbially derived short-chain fatty acid (SCFA) butyrate repressed HK2 expression via histone deacetylase 8 (HDAC8) and reduced mitochondrial respiration in wild-type but not in HK2-deficient Caco-2 cells. Butyrate supplementation protected wild-type but not Hk2ΔIEC mice from colitis. Our findings define a mechanism how butyrate promotes intestinal homeostasis and suggest targeted HK2-inhibition as therapeutic avenue for inflammation.