Significant association of TREM-1 with HMGB1, TLRs and RAGE in the pathogenesis of insulin resistance in obese diabetic populations.

Activated cell surface and intracellular receptors lead to insulin resistance in obesity. Among these receptors, triggering receptors expressed on myeloid cells (TREM)-1, toll like receptors (TLRs), and receptors for advanced glycation end products (RAGE) play a significant role in the induction of inflammatory response in innate immunity. TREM-1 potentially amplifies TLRs and RAGE synergistically with DNA-binding high-mobility group box 1 (HMGB-1). The objective of the study was to analyze the association between TREM-1/DAP12 and HMGB-1, RAGE and TLRs in obesity-induced insulin resistance. We examined the mRNA expression by RT-PCR and protein expression by Western blotting and immunofluorescence for TREM-1, TREM-2, DAP-12, HMGB-1, RAGE, TLR-4 and TLR-2 in omentum, subcutaneous and liver biopsy tissues of obese diabetic (n=22) and non-diabetic subjects (n=24) and compared with the non-obese non-diabetic controls (n=5). There was a significantly increased expression of TREM-1, DAP-12, HMGB-1, RAGE, TLR-4 and TLR-2 and decreased expression of TREM-2 in the omentum, subcutaneous and liver biopsy of obese diabetic subjects compared to obese non-diabetics and the non-obese population. Overall, obese diabetic subjects had high expression of TREM-1 in association with HMGB1 (100% vs 58.3%, P=0.003), RAGE (77.3% vs 41.7%, P=0.045), TLR4 (100% vs 58.3%, P=0.003), and TLR2 (100% vs 50%, P=0.003) in liver biopsy samples in comparison to obese non-diabetic subjects. Obese diabetics have significantly increased TREM-1, HMGB1, RAGE, and TLRs compared to obese non-diabetics. Our findings suggest a potential pathophysiological role of TREM-1 in conjunction with HMGB1 and inflammatory cell receptors (RAGE, TLR-4 and TLR-2) in obesity-induced insulin resistance.