The development of insulin resistance and type 2 diabetes mellitus (T2DM) in obesity involves (a) adipose inflammation, and (b) restricted adipose expansion with ectopic lipid deposition. Metalloproteinases (MPs) and tissue inhibitors of metalloproteinases (TIMPs) constitute a key regulatory system in inflammation and tissue remodelling. Evidence of MP and TIMP involvement in adipose tissue inflammation and modulation of adipose expansion is currently restricted to work in adipocyte cell lines and murine systems. Our study aims to identify which MPs and TIMPs are expressed by primary human adipocytes, and how this expression is influenced by inflammation. Preadipocytes were isolated from subcutaneous adipose tissue (Norfolk REC 10/H0310/21), cultured to confluence and differentiated in vitro. Adipocyte cultures were then stimulated with TNF-alpha or LPS for 24 hours. Taqman® Low Density Arrays (TLDAs) were used to quantify basal and stimulated expression of all human MPs/TIMPs in cultures from 3 donors. MMP-2, MMP-14, ADAM-9, ADAM-12 and TIMPs-1 to -4 were expressed at high levels in unstimulated adipocytes (Ct range 2126). On stimulation with TNF-alpha or LPS, MMP-1 expression increased 46-fold and 34-fold respectively (P<0.001). With TNF-alpha, expression of TIMPs-3 & -4 was reduced by 66% (P<0.001), whereas with LPS they were downregulated by ~50% (P=0.0559). Downregulation of TIMP-3 expression to ~33% of basal by TNF-alpha was confirmed on dedicated qRT-PCR. Increased MMP-1 expression on stimulation with TNF-alpha (19-fold increase) and LPS (12-fold increase) was confirmed by ELISA of cell culture supernatants (both P<0.001). MPs and TIMPs are therefore expressed by primary human adipocytes and their expression varies with inflammatory stimulation. These proteins may integrate inflammatory signals with pathways controlling preadipocyte differentiation, adipose matrix remodelling and adipose expansion. We hypothesise that these processes contribute to ectopic lipid deposition, development of insulin resistance and T2DM in obesity.
Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.