Adipose tissue induced chronic low-grade inflammation is a critical link between obesity and insulin resistance. Despite studies demonstrating the importance of adipose tissue T cells (ATT) in insulin resistance, fundamental gaps in knowledge regarding CD4+ ATT function impedes progress towards understanding their role in diabetes. Little is known about the mechanisms of ATT activation and chemokine profiles. We hypothesized that high fat diet induced obesity would potentiate ATT inflammatory properties. To maximize the viability and number of ATTs in-vitro, T cell activation assays were performed by adding α-CD3/CD28 beads to the entire stromal vascular fraction (SVF). Three days after T cell receptor (TCR) stimulation, supernatants were collected and cells were analyzed using flow cytometry. Surprisingly, ATTs from obese epididymal white adipose tissue had senescent characteristics. Stimulation failed to induce CD25 upregulation, ATT proliferation, or heightened IFNγ and IL-2 secretion, which is seen in lean samples. Human samples collected from diabetic bariatric surgery patients also have an exhausted phenotype unlike nondiabetic controls. Both cell intrinsic and extrinsic factors are implicated in ATT dysfunction. Diabetic humans and mice both have significantly increased expression of the co-inhibitory receptor, PD1, on the cell surface. Despite experiments showing that T cell intrinsic factors, such as major-histocompatibility complex II signals are necessary for ATT dysfunction in obese mice, blocking PD1 fails to rescue this phenotype. Most likely this is due to additional extrinsic factors, since co-culturing lean ATTs in obese SVF results in reduced pro-inflammatory cytokine secretion post-TCR stimulation. Further studies are required to elucidate whether ATT dysfunction is a protective mechanism that reduces inflammation, and whether relieving intrinsic and extrinsic blocks on ATTs results in a more robust inflammatory response and worsened glucose tolerance.
C.E. Porsche: None. J. DelProposto: None. L.M. Geletka: None. R.W. O’Rourke: None. C. Lumeng: None.
National Institutes of Health (F31DK118811, T32HL125242 to C.E.P.), R01DK090262-06A1 (to C.L.)