White adipose tissue-infiltrated CD11b+ myeloid cells are a source of S100A4, a new potential marker of hepatic damage.

CONTEXT

The endocrine and immunological properties of subcutaneous vs visceral adipose tissue (sWAT and vWAT, respectively) have turned a milestone in the study of metabolic diseases. The cytokine S100A4 is increased in obesity and has a role in adipose tissue dysfunction. However, the cellular source and its potential role in hepatic damage in obesity has not been elucidated.

OBJECTIVE

We aim to study the regulation of S100A4 in immune cells present in sWAT and vWAT, as well as its potential role as a circulating marker of hepatic inflammation and steatosis.

DESIGN

A cohort of 60 patients with obesity and distinct metabolic status was analyzed. CD11b+ myeloid cells and T cells were isolated from sWAT and vWAT by magnetic-activating cell sorting, and RNA was obtained. S100A4 gene expression was measured, and correlation analysis with clinical data was performed. Liver biopsies were obtained from 20 patients, and S100A4 circulating levels were measured to check the link with hepatic inflammation and steatosis.

RESULTS

S100A4 gene expression was strongly upregulated in sWAT- vs vWAT-infiltrated CD11b+ cells, but this modulation was not observed in T cells. S100A4 mRNA levels from sWAT (and not from vWAT) CD11b+ cells positively correlated with glycemia, triglycerides, TNF-α gene expression and proliferation markers. Finally, circulating S100A4 directly correlated with liver steatosis and hepatic inflammatory markers.

CONCLUSION

Our data suggest that sWAT-infiltrated CD11b+ cells could be a major source of S100A4 in obesity. Moreover, our correlations identify circulating S100A4 as a potential novel biomarker of hepatic damage and steatosis.