Inflammatory mediators have the potential to impact a surprising range of diseases, including obesity and its associated metabolic syndrome. In this paper, we show that the proinflammatory cytokine IL-17 inhibits adipogenesis, moderates adipose tissue (AT) accumulation, and regulates glucose metabolism in mice. IL-17 deficiency enhances diet-induced obesity in mice and accelerates AT accumulation even in mice fed a low-fat diet. In addition to potential systemic effects, IL-17 is expressed locally in AT by leukocytes, predominantly by γδ T cells. IL-17 suppresses adipocyte differentiation from mouse-derived 3T3-L1 preadipocytes in vitro, and inhibits expression of genes encoding proadipogenic transcription factors, adipokines, and molecules involved in lipid and glucose metabolism. IL-17 also acts on differentiated adipocytes, impairing glucose uptake, and young IL-17–deficient mice show enhanced glucose tolerance and insulin sensitivity. Our findings implicate IL-17 as a negative regulator of adipogenesis and glucose metabolism in mice, and show that it delays the development of obesity.

Fluorescent cellular barcoding and mass-tag cellular barcoding are cytometric methods that enable high sample throughput, minimize inter-sample variation, and reduce reagent consumption. Previously employed barcoding protocols require that barcoding be performed after surface marker staining, complicating combining the technique with measurement of alcohol-sensitive surface epitopes. This report describes a method of barcoding fixed cells after a transient partial permeabilization with 0.02% saponin that results in efficient and consistent barcode staining with fluorescent or mass-tagged reagents while preserving surface marker staining. This approach simplifies barcoding protocols and allows direct comparison of surface marker staining of multiple samples without concern for variations in the antibody cocktail volume, antigen-antibody ratio, or machine sensitivity. Using this protocol, cellular barcoding can be used to reliably detect subtle differences in surface marker expression.

Inflammatory mediators have the potential to impact a surprising range of diseases, including obesity, obesity associated metabolic syndrome, and autoimmunity. Adipocyte development and their function in lipid storage and metabolism are regulated in a complex fashion by inflammatory cytokines. Although IL-17 appears to mediate inflammation-associated bone loss, studies indicate IL-17 also has important homeostatic roles in facilitating wound repair and promoting cell proliferation. Recent evidence indicates IL-17 has an anti-adipogenic role while at the same time having an unexpected osteoprotective role; however the mechanisms of IL-17 mediated osteoprotection are ill defined. We show IL-17 is expressed in adipose tissue by leukocytes and is upregulated in obese fat. IL-17 deficiency enhances diet-induced obesity in mice. IL-17 suppresses adipocyte differentiation from mouse derived 3T3-L1 preadipocytes in vitro, and inhibits expression of adipocyte genes. Surprisingly, IL-17R and IL-17 deficiency led to increased bone mineral density in vivo in the absence of inflammation, and IL-17 treatment led to increased osteoblastogenesis in vitro. Over expression of IL-17 inhibited diet-induced obesity while leading to a pro-osteogenic serum profile in mice. Our findings indicate IL-17 as a homeostatic, anti-adipogenic, pro-osteogenic cytokine, capable of inducing osteoblasts from multipotent progenitors, and establishes a potential role for IL-17 in the bone/fat axis.

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