Dietary Fiber Protects against Diabetic Nephropathy through Short-Chain Fatty Acid–Mediated Activation of G Protein–Coupled Receptors GPR43 and GPR109A
Authors: Li Yan Jun , Chen Xiaochen , Kwan Tony K. , Loh Yik Wen , Singer Julian , Liu Yunzi , Ma Jin , Tan Jian , Macia Laurence , Mackay Charles R. , Chadban Steven J. , Wu Huiling 
Published: May 2020

Significance Statement
The gut microbiota and its metabolites, in particular short-chain fatty acids derived from gut microbes’ fermentation of fiber, are emerging therapeutic targets for systemic inflammatory and metabolic diseases, including diabetic nephropathy. The authors report that high-fiber diets or supplementation with short-chain fatty acids (acetate, butyrate, or propionate) afforded protection against development of kidney disease in diabetic mice. Dietary fiber restored gut microbial ecology, corrected “dysbiotic” changes, and increased production of short-chain fatty acids. Mice deficient in the metabolite-sensing G protein–coupled receptors GPR43 or GPR109A were not protected by short-chain fatty acids, suggesting that protection was mediated by downstream binding to these receptors. Tapping into the metabolic potential of the gut microbiota through diet may offer a novel approach to address diabetic nephropathy.

Background
Studies have reported “dysbiotic” changes to gut microbiota, such as depletion of gut bacteria that produce short-chain fatty acids (SCFAs) through gut fermentation of fiber, in CKD and diabetes. Dietary fiber is associated with decreased inflammation and mortality in CKD, and SCFAs have been proposed to mediate this effect.

Methods
To explore dietary fiber’s effect on development of experimental diabetic nephropathy, we used streptozotocin to induce diabetes in wild-type C57BL/6 and knockout mice lacking the genes encoding G protein–coupled receptors GPR43 or GPR109A. Diabetic mice were randomized to high-fiber, normal chow, or zero-fiber diets, or SCFAs in drinking water. We used proton nuclear magnetic resonance spectroscopy for metabolic profiling and 16S ribosomal RNA sequencing to assess the gut microbiome.

Results
Diabetic mice fed a high-fiber diet were significantly less likely to develop diabetic nephropathy, exhibiting less albuminuria, glomerular hypertrophy, podocyte injury, and interstitial fibrosis compared with diabetic controls fed normal chow or a zero-fiber diet. Fiber beneficially reshaped gut microbial ecology and improved dysbiosis, promoting expansion of SCFA-producing bacteria of the genera Prevotella and Bifidobacterium, which increased fecal and systemic SCFA concentrations. Fiber reduced expression of genes encoding inflammatory cytokines, chemokines, and fibrosis-promoting proteins in diabetic kidneys. SCFA-treated diabetic mice were protected from nephropathy, but not in the absence of GPR43 or GPR109A. In vitro, SCFAs modulated inflammation in renal tubular cells and podocytes under hyperglycemic conditions.

Conclusions
Dietary fiber protects against diabetic nephropathy through modulation of the gut microbiota, enrichment of SCFA-producing bacteria, and increased SCFA production. GPR43 and GPR109A are critical to SCFA-mediated protection against this condition. Interventions targeting the gut microbiota warrant further investigation as a novel renoprotective therapy in diabetic nephropathy.