Melanocortin Receptor 4 (MC4R) Signaling System in Nile Tilapia

Abstract

The melanocortin receptor 4 (MC4R) signaling system consists of MC4R, MC4R ligands [melanocyte-stimulating hormone (MSH), adrenocorticotropin (ACTH), agouti-related protein (AgRP)], and melanocortin-2 receptor accessory protein 2 (MRAP2), and it has been proposed to play important roles in feeding and growth in vertebrates. However, the expression and functionality of this system have not been fully characterized in teleosts. Here, we cloned tilapia MC4R, MRAP2b, AgRPs (AgRP, AgRP2), and POMCs (POMCa1, POMCb) genes and characterized the interaction of tilapia MC4R with MRAP2b, AgRP, α-MSH, and ACTH in vitro. The results indicate the following. (1) Tilapia MC4R, MRAP2b, AgRPs, and POMCs share high amino acid identity with their mammalian counterparts. (2) Tilapia MRAP2b could interact with MC4R expressed in CHO cells, as demonstrated by Co-IP assay, and thus decrease MC4R constitutive activity and enhance its sensitivity to ACTH1-40. (3) As in mammals, AgRP can function as an inverse agonist and antagonist of MC4R, either in the presence or absence of MRAP2b. These data, together with the co-expression of MC4R, MRAP2b, AgRPs, and POMCs in tilapia hypothalamus, suggest that as in mammals, ACTH/α-MSH, AgRP, and MRAP2 can interact with MC4R to control energy balance and thus play conserved roles in the feeding and growth of teleosts.

Depletion of Alpha-Melanocyte-Stimulating Hormone Induces Insatiable Appetite and Gains in Energy Reserves and Body Weight in Zebrafish

“…Most of these associated features might be regulated by α-MSH [19,45], suggesting their critical functions in controlling metabolism observed in our α-MSH mutant zebrafish (Figure 7B). In line with previous reports, most metabolic defects observed in fish [62], mammalian models [4,63,64], and humans [65][66][67] have been attributed to the impairment of functional MC4R signaling in various pomc mutants.…”

Characterization of Chicken α2A-Adrenoceptor: Molecular Cloning, Functional Analysis, and Its Involvement in Ovarian Follicular Development

“…As described in our previous studies [ 48 , 50 ], CHO cells transfected with cADRA2A expression plasmid were cultured on a 24-well plate at 37 °C and then treated by NE (10 μM) for 10 min. Then, the cells were lysed and used for Western blot detection of β-actin, phosphorylated CREB (pCREB) (43 kDa) and (or) ERK1/2 (pERK1/2) (44/42 kDa).…”

Reversion of MRAP2 Protein Sequence Generates a Functional Novel Pharmacological Modulator for MC4R Signaling

“…As a paralogue of MRAP, MRAP2 shares a conserved functional domain and similar structural features with MRAP. However, unlike MRAP, which mainly regulates MC2R in the adrenal gland, MRAP2 shows more preference for the other four MCRs [ 16 , 17 , 18 , 19 , 20 ], as well as several non-melanocortin receptors, such as orexin receptor and ghrelin receptor [ 21 , 22 , 23 , 24 , 25 ]. MRAP2 is involved in energy balance and metabolism by regulating MC4R activity in many organisms [ 18 , 20 , 26 , 27 ].…”

“…However, unlike MRAP, which mainly regulates MC2R in the adrenal gland, MRAP2 shows more preference for the other four MCRs [ 16 , 17 , 18 , 19 , 20 ], as well as several non-melanocortin receptors, such as orexin receptor and ghrelin receptor [ 21 , 22 , 23 , 24 , 25 ]. MRAP2 is involved in energy balance and metabolism by regulating MC4R activity in many organisms [ 18 , 20 , 26 , 27 ]. MRAP2 -deficient mice develop severe obesity, which is presumably resulting from a significant decrease in MC4R sensitivity to α-MSH in the absence of MRAP2 protein [ 28 ].…”