title: Alpha-MSH signalling via melanocortin 5 receptor promotes lipolysis and impairs re-esterification in adipocytes.
abstract: The melanocortin system has a clear effect on the mobilisation of stored lipids in adipocytes. The aim of the current study was to investigate the role of melanocortin 5 receptor (MC5R) on alpha-melanocyte-stimulating hormone (alpha-MSH)-induced lipolysis in 3T3-L1 adipocytes. To this end, MC5R expression was decreased by small interfering RNA (siRNA), which significantly impaired the alpha-MSH stimulation of lipolysis, as determined by glycerol and nonesterified fatty-acid (NEFA) quantification. The functional role of alpha-MSH/MC5R on triglyceride (TG) hydrolysis was mediated by hormone-sensitive lipase (HSL), adipose triglyceride lipase (ATGL), perilipin 1 (PLIN1) and acetyl-CoA carboxylase (ACC). Immunofluorescence microscopy revealed that phosphorylated HSL clearly surrounded lipid droplets in alpha-MSH-stimulated adipocytes, whereas PLIN1 left the immediate periphery of lipids. These observations were lost when the expression of MC5R was suppressed. In 3T3-L1 adipocytes, alpha-MSH-activated MC5R signals through the cAMP/PKA and MAPK/ERK1/2 pathways. PKA was fundamental for HSL and PLIN1 activation and lipolysis regulation. ERK1/2 inhibition strongly interfered with the release of NEFAs but not glycerol. In addition, the intracellular TG levels, which were decreased after MC5R activation, were restored after ERK1/2 inhibition, indicating that these kinases are involved in NEFA re-esterification rather than lipolysis regulation. This notion is also supported by the observation that the alpha-MSH-mediated activation of phosphoenolpyruvate carboxykinase (PEPCK) was abolished in the presence of ERK1/2 inhibitors. Altogether, these results indicate that alpha-MSH-activated MC5R regulates two tightly coupled pathways in adipocytes: lipolysis and re-esterification. The global effect is a decrease in adipocyte fat mass, which is important for strategies to ameliorate obesity.
authors.affiliation: Department of Experimental Biology, Faculty of Medicine of Porto, Alameda Prof Hernâni Monteiro, 4200-319 Porto, Portugal.
authors.forename: Adriana R
authors.initials: AR
authors.lastname: Rodrigues
authors.forename: Henrique
authors.initials: H
authors.lastname: Almeida
authors.forename: Alexandra M
authors.initials: AM
authors.lastname: Gouveia
mesh_terms: D041721:3T3-L1 Cells; D000103:Acetyl-CoA Carboxylase / Q000378:metabolism; D017667:Adipocytes / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004951:Esterification; D008049:Lipase / Q000378:metabolism; D008066:Lipolysis; D020935:MAP Kinase Signaling System; D051379:Mice; D000070778:Perilipin-1; D010750:Phosphoproteins / Q000378:metabolism; D034622:RNA Interference; D044101:Receptors, Melanocortin / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D002787:Sterol Esterase / Q000378:metabolism; D000521:alpha-MSH / Q000378:metabolism*; D000217:Acyltransferases
chemical_list: D000103:Acetyl-CoA Carboxylase; D002352:Carrier Proteins; D017868:Cyclic AMP-Dependent Protein Kinases; D008049:Lipase; D000070778:Perilipin-1; D010750:Phosphoproteins; D044101:Receptors, Melanocortin; D002787:Sterol Esterase; D000521:alpha-MSH; C000602979:Plin1 protein, mouse; C086971:melanocortin 5 receptor; C494445:PNPLA2 protein, mouse; D000217:Acyltransferases