Gut Microbiome Manipulation Promotes Bone Anabolism via Regulatory T‐Cell Differentiation in Obese Mice
Authors: Behera Jyotirmaya , Kelly Kimberly E. , Mondal Nandan K. , Tyagi Neetu 
Published: June 2021

Probiotics are viable bacterial components that exert beneficial effects on the host, have been shown to prevent multiple comorbidities. Probiotics mostly act by changing the composition of the gut microbiota and increase gastrointestinal barrier integrity, which leads to the modulation of the immune system. However, the effects of probiotics in the pathological setting like obesity‐induced osteoporotic bone phenotype and their immunomodulatory effect are largely obscure. Therefore, we aimed to investigate the beneficial effects of probiotics accompanied by the high‐fat diet (HFD) on the bone loss and immune‐regulation at the molecular and epigenetic levels. To test this hypothesis, 10‐week‐old female mice were fed on the high‐fat diet (HFD; 42%) for 12 weeks. Probiotics (GSL#5) were given at the dose of 1 X 109 total bacteria 5 times/week through intragastric administration.ResultsIn vivo, μCT measurements revealed that HFD induced a significant increase of bone loss in trabecular bone phenotype (BV/TV; 42 %, BMD; 30% in the femur) and probiotics administration can able to prevent the bone loss. In vitro study revealed that probiotics induce mouse BMMSC derived osteoblast mineralization in HFD condition. In contrary, osteoclast differentiation and function were reduced as analyzed for the presence of RANK+, CD11b+ cells by flow cytometry. Mechanistic studies revealed that probiotics epigenetically regulates immune‐bone homeostasis by up‐regulating bone marrow (BM) regulatory T cells (Tregs CD4+Foxp3hi) differentiation, a suppressive population of naïve CD4+ T cells. Western blots and ChIP assays revealed that Tregs maintained expression of methylcytosine dioxygenases Tet1 and Tet2 via sulfhydration of nuclear transcription factor Y subunit beta (NFYB) to facilitate its binding to Tet1 and Tet2 promoters. Thereby Tet1 and Tet2 mediated catabolism of 5‐methylcytosine (5mC) to 5‐hydroxymethylcytosine (5hmC) in CpG islands of the Foxp3 promoter to establish a Tregs‐specific Foxp3 hypomethylation and Tregs differentiation. Further, Tregs induced the release of the IL10 and TGF‐β, leading to inhibit osteoclastogenesis and bone resorption, while increased bone formation under probiotics treatment. In vivo blockade of Tregs expansion by treatment with anti CD25 Ab or silencing of Foxp3 by siRNA based RNA interference in mice prevented the bone anabolic activity of probiotics. Collectively, these data provide the evidence that gut microbiota dysbiosis deregulates immune system; that is critical for osteoporotic bone loss in HFD induced obese female mice. Our data further suggest that the probiotic treatment in obesity‐induced osteoporotic bone loss seems to have a novel therapeutic potential via Treg/IL‐10 dependent pathway.Support or Funding InformationThis work is financially supported by National Institute of health grant AR‐067667 and HL‐107640‐NT are greatly acknowledged.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.