Gut microbial metabolite butyrate protects against proteinuric kidney disease through epigenetic- and GPR109a-mediated mechanisms.

Butyrate is a short-chain fatty acid derived from the metabolism of indigestible carbohydrates by the gut microbiota. Butyrate contributes to gut homeostasis, but it may also control inflammatory responses and host physiology in other tissues. Butyrate inhibits histone deacetylases, thereby affecting gene transcription, and also signals through the metabolite-sensing G protein receptor (GPR)109a. We produced an mAb to mouse GPR109a and found high expression on podocytes in the kidney. Wild-type and Gpr109a-/- mice were induced to develop nephropathy by a single injection of Adriamycin and treated with sodium butyrate or high butyrate-releasing high-amylose maize starch diet. Butyrate improved proteinuria by preserving podocyte at glomerular basement membrane and attenuated glomerulosclerosis and tissue inflammation. This protective phenotype was associated with increased podocyte-related proteins and a normalized pattern of acetylation and methylation at promoter sites of genes essential for podocyte function. We found that GPR109a is expressed by podocytes, and the use of Gpr109a-/- mice showed that the protective effects of butyrate depended on GPR109a expression. A prebiotic diet that releases high amounts of butyrate also proved highly effective for protection against kidney disease. Butyrate and GPR109a play a role in the pathogenesis of kidney disease and provide one of the important molecular connections between diet, the gut microbiota, and kidney disease.-Felizardo, R. J. F., de Almeida, D. C., Pereira, R. L., Watanabe, I. K. M., Doimo, N. T. S., Ribeiro, W. R., Cenedeze, M. A., Hiyane, M. I., Amano, M. T., Braga, T. T., Ferreira, C. M., Parmigiani, R. B., Andrade-Oliveira, V., Volpini, R. A., Vinolo, M. A. R., Mariño, E., Robert, R., Mackay, C. R., Camara, N. O. S. Gut microbial metabolite butyrate protects against proteinuric kidney disease through epigenetic- and GPR109a-mediated mechanisms.

Bradykinin receptor 1 activation exacerbates experimental focal and segmental glomerulosclerosis.

Focal and segmental glomerulosclerosis (FSGS) is one of the most important causes of end-stage renal failure. The bradykinin B1 receptor has been associated with tissue inflammation and renal fibrosis. To test for a role of the bradykinin B1 receptor in podocyte injury, we pharmacologically modulated its activity at different time points in an adriamycin-induced mouse model of FSGS. Estimated albuminuria and urinary protein to creatinine ratios correlated with podocytopathy. Adriamycin injection led to loss of body weight, proteinuria, and upregulation of B1 receptor mRNA. Early treatment with a B1 antagonist reduced albuminuria and glomerulosclerosis, and inhibited the adriamycin-induced downregulation of podocin, nephrin, and α-actinin-4 expression. Moreover, delayed treatment with antagonist also induced podocyte protection. Conversely, a B1 agonist aggravated renal dysfunction and even further suppressed the levels of podocyte-related molecules. Thus, we propose that kinin has a crucial role in the pathogenesis of FSGS operating through bradykinin B1 receptor signaling.

Invariant natural killer T cell agonist modulates experimental focal and segmental glomerulosclerosis.

A growing body of evidence demonstrates a correlation between Th2 cytokines and the development of focal and segmental glomerulosclerosis (FSGS). Therefore, we hypothesized that GSL-1, a monoglycosylceramide from Sphingomonas ssp. with pro-Th1 activity on invariant Natural Killer T (iNKT) lymphocytes, could counterbalance the Th2 profile and modulate glomerulosclerosis. Using an adriamycin(ADM)-based model of FSGS, we found that BALB/c mice presented albuminuria and glomerular degeneration in association with a Th2-like pro-fibrogenic profile; these mice also expressed a combination of inflammatory cytokines, such as IL-4, IL-1α, IL-1ß, IL-17, TNF-α, and chemokines, such as RANTES and eotaxin. In addition, we observed a decrease in the mRNA levels of GD3 synthase, the enzyme responsible for GD3 metabolism, a glycolipid associated with podocyte physiology. GSL-1 treatment inhibited ADM-induced renal dysfunction and preserved kidney architecture, a phenomenon associated with the induction of a Th1-like response, increased levels of GD3 synthase transcripts and inhibition of pro-fibrotic transcripts and inflammatory cytokines. TGF-ß analysis revealed increased levels of circulating protein and tissue transcripts in both ADM- and GSL-1-treated mice, suggesting that TGF-ß could be associated with both FSGS pathology and iNKT-mediated immunosuppression; therefore, we analyzed the kidney expression of phosphorylated SMAD2/3 and SMAD7 proteins, molecules associated with the deleterious and protective effects of TGF-ß, respectively. We found high levels of phosphoSMAD2/3 in ADM mice in contrast to the GSL-1 treated group in which SMAD7 expression increased. These data suggest that GSL-1 treatment modulates the downstream signaling of TGF-ß through a renoprotective pathway. Finally, GSL-1 treatment at day 4, a period when proteinuria was already established, was still able to improve renal function, preserve renal structure and inhibit fibrogenic transcripts. In conclusion, our work demonstrates that the iNKT agonist GSL-1 modulates the pathogenesis of ADM-induced glomerulosclerosis and may provide an alternative approach to disease management.

Induction of heme oxygenase-1 can halt and even reverse renal tubule-interstitial fibrosis.

BACKGROUND: The tubule-interstitial fibrosis is the hallmark of progressive renal disease and is strongly associated with inflammation of this compartment. Heme-oxygenase-1 (HO-1) is a cytoprotective molecule that has been shown to be beneficial in various models of renal injury. However, the role of HO-1 in reversing an established renal scar has not yet been addressed. AIM: We explored the ability of HO-1 to halt and reverse the establishment of fibrosis in an experimental model of chronic renal disease. METHODS: Sprague-Dawley male rats were subjected to unilateral ureteral obstruction (UUO) and divided into two groups: non-treated and Hemin-treated. To study the prevention of fibrosis, animals were pre-treated with Hemin at days -2 and -1 prior to UUO. To investigate whether HO-1 could reverse established fibrosis, Hemin therapy was given at days 6 and 7 post-surgery. After 7 and/or 14 days, animals were sacrificed and blood, urine and kidney tissue samples were collected for analyses. Renal function was determined by assessing the serum creatinine, inulin clearance, proteinuria/creatininuria ratio and extent of albuminuria. Arterial blood pressure was measured and fibrosis was quantified by Picrosirius staining. Gene and protein expression of pro-inflammatory and pro-fibrotic molecules, as well as HO-1 were performed. RESULTS: Pre-treatment with Hemin upregulated HO-1 expression and significantly reduced proteinuria, albuminuria, inflammation and pro-fibrotic protein and gene expressions in animals subjected to UUO. Interestingly, the delayed treatment with Hemin was also able to reduce renal dysfunction and to decrease the expression of pro-inflammatory molecules, all in association with significantly reduced levels of fibrosis-related molecules and collagen deposition. Finally, TGF-ß protein production was significantly lower in Hemin-treated animals. CONCLUSION: Treatment with Hemin was able both to prevent the progression of fibrosis and to reverse an established renal scar. Modulation of inflammation appears to be the major mechanism behind HO-1 cytoprotection.