Document Type

Poster

Publication Date

4-30-2020

Institution/Department

Maine Medical Center, Medical Education, Maine Medical Center Research Institute

MeSH Headings

Bone Marrow Cells, Humans, Bone Marrow, Fasting, Adipose Tissue

Abstract

The administration of a high fat content diet (HFD) is an accelerating factor for metabolic syndrome, impaired glucose tolerance, and early type 2 diabetes. The present study aims to assess the impact of a high fat diet or acute weight gain on human marrow adipose tissue. Adipose tissues secrete numerous active substances termed adipokines, including adiponectin, leptin, resistin, interleukin-6 (IL-6), etc. Adipokines physiologically regulate development, metabolism, eating behavior, fat storage, insulin sensitivity, hemostasis, blood pressure, immunity, and inflammation. Our objective is to determine the effect of HFD on adipokines from marrow adipose tissue, as well as, the effect of HFD on resistin, TNF?, RCAN2 and SEMA3E/PLXND1 gene expression. Marrow serum, peripheral blood serum as well as marrow adipocytes from healthy adult human who underwent either 10 days of fasting or 10 days of HFD, were collected according to published protocols. To analyze the expression of resistin, IL-6, TNF? and adiponectin in human serum from marrow and peripheral blood, we used DuoSet ELISA kit (R&D systems) respectively. To analyze the gene expression of resistin, TNF?, RCAN2 and SEMA3E/PLXND1 on marrow adipocytes, qRT-PCR were performed. All primers were synthesized by Integrated DNA Technologies (Coralville, IA). Results were normalized to GAPDH and all samples were run in duplicate. Our results show that in paired aspirates, resistin increased markedly with a HFD, but not with fasting, and not in the circulation, without significant changes on adiponectin neither IL-6 levels. Resistin is a cytokine produced in WAT (adipocytes in rodents, macrophages in human) and is thought to mediate type 2 diabetes mellitus (T2DM) and cardiovascular disease and to mark macrophage activation and TLR4 signaling. In our previous studies with mouse models, PLXND1 is highly expressed on marrow stromal cells and has been linked to adiposity and type 2 diabetes. Also, inhibition of the SEMA3E(ligand)/PLXND1(receptor) axis markedly reduced adipose tissue inflammation and improved systemic insulin resistance in mouse model. PLXND1 also was one of the most highly expressed genes in a MSCs from a mouse with high marrow adiposity and consistent with our findings noted in human volunteers. RCAN2, one of the three main regulators of calcineurin, is located 43.7 Mb on mouse chromosome 17 and in a QTL study of marrow fat from DO strains, that region gave the highest LOD score. Our data show that expression of SEMA3E/PLXND1, RCAN2 and TNF? were increased on marrow adipocytes from the HFD volunteers. Also we identified up-regulation of the macrophage gene marker, EMR-1 (homologous to F4/80 in mice), suggestive of an inflammatory response in the marrow of normal volunteers on a HFD but not fasting. The bone microenviroment can be modulated by various factors including aging, obesity, and inflammation. Stress signal could be modulated by SEMA3E/PLXND1 axis as a chemoattractant for macrophages, provoking adipose tissue inflammation, and also by RCAN2, through calcineurin activity, which is indispensable for osteoclast differentiation, creating less bone resorption and impaired normal bone homeostasis. Further analysis are needed to understanding the immune response in the context of marrow adiposity in humans and mouse models.

Comments

2020 Costas T. Lambrew Research Retreat

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