Gut Microbial Metabolites Induce Donor-Specific Tolerance of Kidney Allografts through Induction of T Regulatory Cells by Short-Chain Fatty Acids.

BACKGROUND: Short-chain fatty acids derived from gut microbial fermentation of dietary fiber have been shown to suppress autoimmunity through mechanisms that include enhanced regulation by T regulatory cells (Tregs). METHODS: Using a murine kidney transplantation model, we examined the effects on alloimmunity of a high-fiber diet or supplementation with the short-chain fatty acid acetate. Kidney transplants were performed from BALB/c(H2d) to B6(H2b) mice as allografts in wild-type and recipient mice lacking the G protein-coupled receptor GPR43 (the metabolite-sensing receptor of acetate). Allograft mice received normal chow, a high-fiber diet, or normal chow supplemented with sodium acetate. We assessed rejection at days 14 (acute) and 100 (chronic), and used 16S rRNA sequencing to determine gut microbiota composition pretransplantation and post-transplantation. RESULTS: Wild-type mice fed normal chow exhibited dysbiosis after receiving a kidney allograft but not an isograft, despite the avoidance of antibiotics and immunosuppression for the latter. A high-fiber diet prevented dysbiosis in allograft recipients, who demonstrated prolonged survival and reduced evidence of rejection compared with mice fed normal chow. Allograft mice receiving supplemental sodium acetate exhibited similar protection from rejection, and subsequently demonstrated donor-specific tolerance. Depletion of CD25+ Tregs or absence of the short-chain fatty acid receptor GPR43 abolished this survival advantage. CONCLUSIONS: Manipulation of the microbiome by a high-fiber diet or supplementation with sodium acetate modified alloimmunity in a kidney transplant model, generating tolerance dependent on Tregs and GPR43. Diet-based therapy to induce changes in the gut microbiome can alter systemic alloimmunity in mice, in part through the production of short-chain fatty acids leading to Treg cell development, and merits study as a potential clinical strategy to facilitate transplant acceptance.

Preconditioning with recombinant high-mobility group box 1 protein protects the kidney against ischemia-reperfusion injury in mice.

A preconditioning effect occurs when exposure to a nonharmful quantity of a mediator of injury provides protection against injury upon subsequent reexposure. High-mobility group box 1 (HMGB1) protein, an endogenous ligand for Toll-like receptor (TLR) 4, is a TLR4-dependent mediator of kidney ischemia-reperfusion injury. Here we determined whether preconditioning with recombinant HMGB1 can block kidney ischemia-reperfusion injury, whether this effect is TLR4 dependent and, if so, how preconditioning downregulates TLR signaling. Wild-type mice pretreated with rHMGB1 before ischemia were protected against kidney ischemia-reperfusion injury, indicated by lower serum creatinine, less tubular damage, less tubulointerstitial neutrophil and macrophage infiltration, and less tubular epithelial cell apoptosis versus control mice. Gene expression of TLR-downstream cytokines and chemokines in ischemia-reperfusion injury kidney were also significantly reduced. While TLR4 and TLR2 knockout mice were protected against kidney ischemia-reperfusion injury, HMGB1 preconditioning provided additional protection to TLR2 but not TLR4 knockout mice. The protective effect of rHMGB1 preconditioning involved Siglec-G upregulation, a negative regulator of HMGB1-mediated TLR4 pathway activation. Thus, preconditioning with rHMGB1 affords significant protection from TLR4-dependent kidney ischemia-reperfusion injury, indicating therapeutic potential.