Introduction: Obesity development and subsequent white adipose tissue (WAT) expansion is often accompanied by WAT fibrosis which leads to adipocyte dysfunction. Fibrosis is a condition in which extracellular matrix (ECM) proteins are increased aberrantly and results in immune cell infiltration, cytokine production and insulin resistance. Visfatin is an adipokine that is implicated in obesity and its metabolic consequences; however, its role in WAT fibrosis has not been previously explored.
The aim of this study was to evaluate the levels of visfatin and its correlation with endotrophin as the secretory part of collagen IV in obese children and adolescents and to investigate the effect of visfatin on the gene and protein expression of the main proteins involved in fibrosis in adipocytes and pre-adipocytes.
Methods: 60 subjects (30 obese, 30 control) were enrolled after clinical and anthropometric evaluation and their plasma levels of visfatin and endotrophin, as well as lipid profile and insulin resistance parameters were measured. For the cellular studies, 3T3-L1 pre-adipocytes were cultured and treated with 200 ng/ml recombinant visfatin in serum-free medium. Cells were also differentiated to adipocytes using medium enriched with isobutylmethylxanthine, dexamethasone, and insulin. Cell viability was assessed by MTT. Gene expression levels of collagen IV, osteopontin, and matrix metalloproteinases (MMP) 2, 9 were analyzed by real-time PCR after RNA extraction and cDNA synthesis. Expression of ECM proteins was measured by western blotting.
Results: plasma levels of endotrophin and visfatin were higher in obese subjects compared with control subjects. A significant positive correlation was found between visfatin and endotrophin. Visfatin was also positively correlated with indices of insulin resistance including glucose, insulin, and HOMA-IR. Visfatin increased the gene and protein expression of collagen VI and osteopontin in pre-adipocytes. In order to evaluate the signaling mechanism of visfatin, cells were treated with the inhibitors of major signaling pathways, one hour prior to visfatin treatment. The results showed that visfatin exerts its effect on collagen VI gene expression through PI3K, JNK, and NF-κB pathways, while induces osteopontin gene expression via PI3K, JNK, MAPK/ERK, and NOTCH1 signaling pathways. Visfatin also induced gene expression of MMP-2 and MMP-9 in pre-adipocytes.
Conclusion: Visfatin increases the expression of ECM proteins and therefore is involved in WAT fibrosis and remodeling. The relationship between visfatin, endotrophin and insulin resistance parameters in obesity as well as the cellular findings suggest that the WAT fibrosis might serve as a link between visfatin and insulin resistance.
19 - 21 Sep 2019
European Society for Paediatric Endocrinology