Short-chain fatty acid mitigates adenine-induced chronic kidney disease via FFA2 and FFA3 pathways

Highlights

• FFA2 and FFA3 were predominantly expressed in the distal renal tubules and collecting tubules in mouse kidneys.

• The administration of propionate significantly mitigated adenine-induced renal in a dose-dependent manner.

• The administration of propionate significantly ameliorated renal damage through FFA2 and FFA3.

Abstract

Short-chain fatty acids (SCFAs), including acetate, butyrate, and propionate, are produced when colonic bacteria in the human gastrointestinal tract ferment undigested fibers. Free fatty acid receptor 2 (FFA2) and FFA3 are G-protein-coupled receptors recently identified as SCFA receptors that may modulate inflammation. We previously showed through in vitro experiments that SCFAs activate FFA2 and FFA3, thereby mitigating inflammation in human renal cortical epithelial cells. This study used a murine model of adenine-induced renal failure to investigate whether or not SCFAs can prevent the progression of renal damage. We also examined whether or not these FFA2 and FFA3 proteins have some roles in this protective mechanism in vivo. Immunohistochemical analyses of mouse kidneys showed that FFA2 and FFA3 proteins were expressed mainly in the distal renal tubules and collecting tubules. First, we observed that the administration of propionate mitigated the renal dysfunction and pathological deterioration caused by adenine. Consistent with this, the expression of inflammatory cytokines and fibrosis-related genes was reduced. Furthermore, the mitigation of adenine-induced renal damage by the administration of propionate was significantly attenuated in FFA2^−/− and FFA3^−/− mice. Therefore, the administration of propionate significantly protects against adenine-induced renal failure, at least in part, via the FFA2 and FFA3 pathways. Our data suggest that FFA2 and FFA3 are potential new therapeutic targets for preventing or delaying the progression of chronic kidney disease.

Introduction

Chronic kidney disease (CKD) is a progressive and irreversible condition and has the risk of progressing to end-stage kidney disease. In addition, CKD has been shown to be an independent risk factor for cardiovascular and cerebrovascular diseases and is deeply involved in their onset and progression [1]. Thus, in order to prevent or delay CKD progression, new target molecules must be identified.

Accumulated evidence suggests that alterations in the intestinal environment, including the intestinal flora, are linked to the pathology of kidney disease [2,3]. It has also been reported that the composition of intestinal microbiota changes with the deterioration of CKD [3]. Thus, it is becoming clear that there is a close connection between the intestine and kidney. It was recently proposed that the regulation of intestinal bacterial flora is a potential new target for the treatment of kidney disease [4,5]. Andrade-Oliveira et al. reported that administration of short-chain fatty acids (SCFAs) lowered expression of inflammatory cytokines and ameliorated acute renal injury in a murine model of ischemia-reperfusion-induced kidney failure [5]. Mishima et al. reported that treatment with the CLCN2 chloride channel activator lubiprostone modified the intestinal environment, resulting in a significant reduction in renal inflammation and fibrosis in mice with adenine-induced CKD [4]. Thus, molecules produced by intestinal microbiota may have a strong direct influence on both the etiology and progression of kidney disease.

SCFAs are saturated fatty acids composed of six or fewer carbon atoms and consist mainly of acetate (C2), propionate (C3), and butyrate (C4). SCFAs are produced when colonic bacteria in the human gastrointestinal tract ferment undigested fibers, such as inulin [6], and are absorbed into the blood stream from the gastrointestinal tract [7]. In the circulatory system, SCFAs act as ligands for G-protein-coupled receptors, including free fatty acid receptor 2 (FFA2), FFA3, GPR109a, and olfactory receptor 78, which couple with either Gi/o proteins, Gq proteins, or both [8,9].

Kimura et al. reported that SCFAs regulate sympathetic nervous activity via FFA3, which regulates body energy expenditure in mice [10]. Kimura et al. also showed that SCFA suppressed insulin-mediated Akt phosphorylation via FFA2 activation in adipocytes in mice [11]. Therefore, FFA2 and FFA3 may play a role in metabolic homeostasis [12]. Studies using mice deficient in FFA2 or FFA3 have provided conflicting results on the biological effects of these genes on chronic inflammatory diseases, such as arthritis, asthma, and colitis [13]. For example, Maslowski et al. reported that knockout of FFA2 increased the severity of dextran sodium sulfate (DSS)-induced colitis [14], while Sina et al. reported that knockout of FFA2 decreased the severity of this condition [15]. Therefore, whether or not these receptors are involved in the etiology of chronic inflammatory disorders remains unclear.

In this study, we used a murine model of adenine-induced renal failure to investigate whether or not SCFAs could prevent or delay the progression of CKD. We also examined whether or not FFA2 or FFA3 participate in this renoprotective mechanism in vivo using FFA2^−/− and FFA3^−/− mice.