Dietary n-3 vs n-6 PUFA Differentially Modulate Macrophage-Myocyte Inflammatory Cross-Talk

Abstract

Abstract Objectives Skeletal muscle is the primary site for insulin-stimulated glucose uptake. In obesity, increased circulating inflammatory cytokines interfere with skeletal muscle insulin signaling, leading to local and whole-body insulin resistance (IR). Moreover, obese skeletal muscle is characterized by accumulation of infiltrated M1 macrophages and ensuing macrophage-myocyte paracrine interactions (cross-talk) contribute to local inflammation and IR. Such macrophage-myocyte inflammatory cross-talk provides a potential intervention target for anti-inflammatory nutrients, including dietary long-chain n-3 polyunsaturated fatty acids (PUFA). Methods Using a co-culture model designed to mimic the degree of CD11b+ cell accumulation in obese skeletal muscle (40% of immune cells), differentiated L6 myocytes were co-cultured with purified splenic CD11b+ cells from male Sprague Dawley rats (7-wk old) consuming one of three isocaloric diets: i) high-fat (HF; 54% kcal lard, 6% kcal soybean oil), ii) high-fat with n-3 PUFA (HFn-3; 39% kcal lard + 15% kcal menhaden oil + 6% kcal soybean oil) or iii) high-fat with n-6 PUFA (HFn-6; 45% kcal lard + 15% kcal soybean oil) for 2, 8 or 12-wk (n = 8–12/diet). Co-cultures were stimulated for 24 h with lipopolysaccharide (LPS, 10 ng/mL) to mimic in vivo obese endotoxin levels. CD11b+ cells were also cultured alone for 24 h in conditioned media collected from L6 myocytes stimulated with LPS for 24 h (LCM). Results In co-cultures, HFn-6 increased mRNA expression of inflammatory markers compared to HF and HFn-3 at 8- (iNos; P ≤ 0.05) and 12-wk (Tnf-α, Il-6, Il-1β; P ≤ 0.05). Similarly, at 8-wk CD11b+ cells from HFn-6 rats that were treated with LCM, had increased mRNA expression of inflammatory cytokines (Tnf-α, Il-1β) and M1 polarization markers (iNos, Cd86) compared to both HF and HFn-3, and the same effects were seen with Il-6 and Il-1β at 12-wk (P ≤ 0.05). Lastly, HFn-3 reduced mRNA expression of Tnf-α compared to HF at 12-wk (P ≤ 0.05). Conclusions Together, these data suggest that n-6 PUFA support macrophage-myocyte inflammatory cross-talk, in part by promoting M1 macrophage polarization. Further, these data provide mechanistic insight into the benefits of n-3 vs n-6 PUFA inclusion in a high-fat diet in mitigating skeletal muscle inflammation in obesity. Funding Sources Natural Sciences and Engineering Research Council (NSERC) of Canada.