Adipose tissue specific CCL18 associates with cardiometabolic diseases in non-obese individuals implicating CD4⁺ T cells

Aim: Obesity is linked to cardiometabolic diseases, however non-obese individuals are also at risk for type 2 diabetes (T2D) and cardiovascular disease (CVD). White adipose tissue (WAT) is known to play a role in both T2D and CVD, but the contribution of WAT inflammatory status especially in non-obese patients with cardiometabolic diseases is less understood. Therefore, we aimed to find associations between WAT inflammatory status and cardiometabolic diseases in non-obese individuals.

Methods: In a population-based cohort containing non-obese healthy (n = 17), T2D (n = 16), CVD (n = 18), T2D + CVD (n = 19) individuals, seventeen different cytokines were measured in WAT and in circulation. In addition, 13-color flow cytometry profiling was employed to phenotype the immune cells. Human T cell line (Jurkat T cells) was stimulated by rCCL18, and conditioned media (CM) was added to the in vitro cultures of human adipocytes. Lipolysis was measured by glycerol release. Blocking antibodies against IFN-γ and TGF-β were used in vitro to prove a role for these cytokines in CCL18-T-cell-adipocyte lipolysis regulation axis.

Results: In CVD, T2D and CVD + T2D groups, CCL18 and CD4⁺ T cells were upregulated significantly compared to healthy controls. WAT CCL18 secretion correlated with the amounts of WAT CD4⁺ T cells, which also highly expressed CCL18 receptors suggesting that WAT CD4⁺ T cells are responders to this chemokine. While direct addition of rCCL18 to mature adipocytes did not alter the adipocyte lipolysis, CM from CCL18-treated T cells increased glycerol release in in vitro cultures of adipocytes. IFN-γ and TGF-β secretion was significantly induced in CM obtained from T cells treated with CCL18. Blocking these cytokines in CM, prevented CM-induced upregulation of adipocyte lipolysis.

Conclusion: We suggest that in T2D and CVD, increased production of CCL18 recruits and activates CD4⁺ T cells to secrete IFN-γ and TGF-β. This, in turn, promotes adipocyte lipolysis - a possible risk factor for cardiometabolic diseases.