Alpha‐Melanocyte Stimulating Hormone (α‐MSH) Affects Adipose Tissue Physiology in Broiler Chicks

Abstract

The melanocortin system plays an important role in whole‐body energy homeostasis. In mammals, α‐melanocyte stimulating hormone (α‐MSH) induces satiety via the hypothalamus and stimulates lipolysis in adipose tissue. In chickens, it is also highly anorexigenic, but effects on adipose physiology have not been reported in an avian species. The objective of this study was to determine the effects of exogenous α‐MSH on adipose tissue physiology in broiler chicks. We hypothesized that peripheral α‐MSH injection would be associated with changes in transcriptional regulation of the melanocortin system, and lipid metabolism‐associated factors in adipose tissue. At four days post‐hatch, using a randomized complete block design with body weight as the blocking factor, individually caged Cobb‐500 broilers were assigned to receive intraperitoneal injection of 0 (vehicle), 5, 10, or 50 micrograms of α‐MSH (n=10/treatment) and euthanized at 60 minutes post‐injection and feed intake recorded. Subcutaneous and abdominal adipose tissue and Pectoralis major were collected for quantifying mRNA abundance of adipose lipid metabolism‐associated factors, and melanocortin receptors 1–5. Additionally, an in vitro study was conducted where the stromal‐vascular fraction of cells was isolated from the abdominal fat of 14 day‐old Cobb‐500 broilers. At 80% confluence, cells were treated with 0 (control), 1, 10, or 100 nM α‐MSH (n=3 independent experiments) and total RNA isolated at 4 hours to measure mRNA abundance of the same genes. Data were analyzed by ANOVA using the Fit Model platform of JMP (SAS Institute) and the statistical model included the main effect of treatment (sex was non‐significant for all variables and removed from the model), with Dunnett's test used for pairwise comparisons. Food intake was decreased (P < 0.0001) at 60 minutes in chicks that received 50 μg of α‐MSH as compared to vehicle. MC5R mRNA was increased (P < 0.05) in subcutaneous adipose tissue of chicks that received 10 and 50 μg of α‐MSH, but was not affected in the abdominal adipose or Pectoralis major, compared to vehicle‐injected chicks, and increased in vitro in cells receiving 10 and 100 nM α‐MSH, compared to control‐treated cells. The mRNA abundance of fatty acid binding protein 4 (FABP4) was also greater (P = 0.02) in 100 nM α‐MSH‐ than control‐treated cells. In conclusion, α‐MSH injection reduced feed intake, and was associated with increased gene expression of MC5R. Thus, in birds, peripheral α‐MSH may reduce feed intake, and effects in adipose tissue may be depot‐dependent and mediated through melanocortin receptor subtype 5.Support or Funding InformationThis research was supported by a National Science Foundation EAGER grant (IOS 1420285). Funding for this work was also provided in part, by the Virginia Agricultural Experiment Station and the Hatch Program of the National Institute of Food and Agriculture, U.S. Department of Agriculture.