|Title||TLR-3 is present in human adipocytes, but its signalling is not required for obesity- Induced inflammation in adipose tissue in vivo|
|Author(s)||Ballak, Dov B.; Asseldonk, Edwin J.P. Van; Diepen, Janna A. Van; Jansen, Henry; Hijmans, Anneke; Joosten, Leo A.B.; Tack, Cees J.; Netea, Mihai G.; Stienstra, Rinke|
|Source||PLoS One 10 (2015)4. - ISSN 1932-6203|
Chair Nutrition Metabolism and Genomics
|Publication type||Refereed Article in a scientific journal|
Innate immunity plays a pivotal role in obesity-induced low-grade inflammation originating from adipose tissue. Key receptors of the innate immune system including Toll-like receptors- 2 and -4 (TLRs) are triggered by nutrient excess to promote inflammation. The role of other TLRs in this process is largely unknown. In addition to double-stranded viral mRNA, TLR-3 can also recognize mRNA from dying endogenous cells, a process that is frequently observed within obese adipose tissue. Here, we identified profound expression of TLR-3 in adipocytes and investigated its role during diet-induced obesity. Human adipose tissue biopsies (n=80) and an adipocyte cell-line were used to study TLR-3 expression and function. TLR-3-/- and WT animals were exposed to a high-fat diet (HFD) for 16 weeks to induce obesity. Expression of TLR-3 was significantly higher in human adipocytes compared to the non-adipocyte cells part of the adipose tissue. In vitro, TLR-3 expression was induced during differentiation of adipocytes and stimulation of the receptor led to elevated expression of pro-inflammatory cytokines. In vivo, TLR-3 deficiency did not significantly influence HFDinduced obesity, insulin sensitivity or inflammation. In humans, TLR-3 expression in adipose tissue did not correlate with BMI or insulin sensitivity (HOMA-IR). Together, our results demonstrate that TLR-3 is highly expressed in adipocytes and functionally active. However, TLR-3 appears to play a redundant role in obesity-induced inflammation and insulin resistance.