α-MSH signalling via melanocortin 5 receptor promotes lipolysis and impairs re-esterification in adipocytes

• Published in: Biochimica et biophysica acta 2013-07, Vol.1831 (7), p.1267-1275
• Main Authors: Rodrigues, Adriana R., Almeida, Henrique, Gouveia, Alexandra M.
• Format: Article
• Language: English
• Subjects: 3T3-L1 Cells; acetyl-CoA carboxylase; Acetyl-CoA Carboxylase - metabolism; Adipocyte; adipocytes; Adipocytes - cytology; Adipocytes - metabolism; alpha-melanocyte-stimulating hormone; alpha-MSH - metabolism; Animals; cAMP-dependent protein kinase; Carrier Proteins - metabolism; cyclic AMP; Cyclic AMP-Dependent Protein Kinases - metabolism; droplets; Esterification; fluorescence microscopy; free fatty acids; glycerol; hydrolysis; Lipase - metabolism; Lipolysis; MAP Kinase Signaling System; Melanocortin 5 receptor; Melanocortins; Mice; obesity; Perilipin-1; Phosphoproteins - metabolism; Re-esterification; Receptors, Melanocortin - genetics; Receptors, Melanocortin - metabolism; RNA Interference; Signal Transduction; small interfering RNA; Sterol Esterase - metabolism; triacylglycerol lipase; triacylglycerols
• ISSN: 1388-1981; 0006-3002; 1879-2618
• DOI: 10.1016/j.bbalip.2013.04.008

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 α-melanocyte-stimulating hormone (α-MSH)-induced lipolysis in 3T3-L1 adipocytes. To this end, MC5R expression was decreased by small interfering RNA (siRNA), which significantly impaired the α-MSH stimulation of lipolysis, as determined by glycerol and nonesterified fatty-acid (NEFA) quantification. The functional role of α-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 α-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, α-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 α-MSH-mediated activation of phosphoenolpyruvate carboxykinase (PEPCK) was abolished in the presence of ERK1/2 inhibitors. Altogether, these results indicate that α-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. •In adipocytes MC5R promotes lipolysis and represses re-esterification.•MC5R stimulates lipolysis through PKA activation of HSL, ATGL and PLIN1.•Fatty acid re-esterification involves glyceroneogenesis and is regulated by ERK1/2.