Obesity-induced inflammation in white adipose tissue is attenuated by loss of melanocortin-3 receptor signaling.
Metabolic syndrome, a complex of highly debilitating disorders that includes insulin resistance, hypertension, and dyslipidemia, is associated with the development of obesity in humans as well as rodent models. White adipose tissue (WAT) inflammation, caused in part by macrophage infiltration, and fat accumulation in the liver are both linked to development of the metabolic syndrome. Despite large increases in body fat, melanocortin 3-receptor (MC3-R)-deficient mice do not get fatty liver disease or severe insulin resistance. This is in contrast to obese melanocortin 4-receptor (MC4-R)-deficient mice and diet-induced obese (DIO) mice, which show increased adiposity, fatty liver disease, and insulin resistance. We hypothesized that defects in the inflammatory response to obesity may underlie the protection from metabolic syndrome seen in MC3-R null mice. MC4-R mice fed a chow diet show increased proinflammatory gene expression and macrophage infiltration in WAT, as do wild-type (WT) DIO mice. In contrast, MC3-R-deficient mice fed a normal chow diet show neither of these inflammatory changes, despite their elevated adiposity and a comparable degree of adipocyte hypertrophy to the MC4-R null and DIO mice. Furthermore, even when challenged with high-fat chow for 4 wk, a period of time shown to induce an inflammatory response in WAT of WT animals, MC3-R nulls showed an attenuated up-regulation in both monocyte chemoattractant protein-1 (MCP-1) and TNFalpha mRNA in WAT compared with WT high-fat-fed animals.
Ellacott
Kate L J
KL
Center for the Study of Weight Regulation and Associated Disorders (L481), Oregon Health and Science University, 3181 Southwest Sam Jackson Park Road, Portland, OR 97239-3098, USA.
Murphy
Jonathan G
JG
Marks
Daniel L
DL
Cone
Roger D
RD
D052436:Adipose Tissue, White / Q000378:metabolism* / Q000473:pathology; D050154:Adiposity / Q000187:drug effects / Q000235:genetics; D000818:Animals; D018932:Chemokine CCL2 / Q000235:genetics; D004041:Dietary Fats; D004797:Enzyme-Linked Immunosorbent Assay; D007150:Immunohistochemistry; D007249:Inflammation / Q000209:etiology / Q000235:genetics / Q000378:metabolism*; D007333:Insulin Resistance; D020738:Leptin / Q000097:blood; D008099:Liver / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009765:Obesity / Q000097:blood / Q000139:chemically induced / Q000150:complications*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D044104:Receptor, Melanocortin, Type 3 / Q000235:genetics / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*; D014280:Triglycerides / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics
C491768:Ccl2 protein, mouse; D018932:Chemokine CCL2; D004041:Dietary Fats; D020738:Leptin; D012333:RNA, Messenger; D044104:Receptor, Melanocortin, Type 3; D014280:Triglycerides; D014409:Tumor Necrosis Factor-alpha