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Functional Characterization of Melanocortin-3 Receptor in a Hibernating Cavefish Onychostoma macrolepis.

ABSTRACT: Melanocortin-3 receptor (MC3R) plays an important role in the energy homeostasis of animals under different nutritional conditions. Onychostoma macrolepis is a hibernating cavefish found in the northern part of the Yangtze River, and its adaptation to a nutrient-poor environment has attracted growing interest. In this study, we characterized the protein structure of Onychostoma macrolepis Mc3r (omMc3r), examined its tissue distribution, and investigated its function in mediating cellular signaling. We showed that the CDS of omMc3r is 978 bp, encoding a putative protein of 325 amino acids. Homology and phylogenetic analyses indicated that omMc3r is evolutionary close to cyprinids. Real-time quantitative PCR (RT-qPCR) revealed that omMc3r was highly expressed in the liver and brain. The functions of omMc3r to mediate ligands activating downstream signaling have also been confirmed by using signal pathway-specific reporters. The four agonists α-MSH, β-MSH, NDP-MSH, and ACTH (1-24) can all activate the cAMP and MAPK/ERK signaling pathway, albeit with different potency orders. The "primitive" ligand ACTH (1-24) had the highest potency on the cAMP signaling pathway, while the synthetic ligand NDP-MSH had the highest activation effect on the MAPK/ERK signaling pathway. This research will lay the foundation for studying the energy regulation mechanism of cavefish in an oligotrophic environment.

SUBMITTER: Wu L

PROVIDER: S-EPMC8749556 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The present research was conducted to assess the influences of starvation and refeeding on growth, nonspecific immunity and lipid metabolic adaptation in Onychostoma macrolepis. To date, there have been no similar reports in O. macrolepis. The fish were randomly assigned into two groups: control group (continuous feeding for six weeks) and starved-refed group (starvation for three weeks and then refeeding for three weeks). After three weeks of starvation, the results showed that the body weight (BW, 1.44 g), condition factor (CF, 1.17%), visceral index (VSI, 3.96%), hepatopancreas index (HSI, 0.93%) and intraperitoneal fat index (IPFI, 0.70%) of fish were significantly lower compared to the control group (BW, 5.72 g; CF, 1.85%; VSI, 6.35%; HSI, 2.04%; IPFI, 1.92%) (p < 0.05). After starvation, the serum triglyceride (TG, 0.83 mmol/L), total cholesterol (T-GHOL, 1.15 mmol/L), high-density lipoprotein (HDL, 1.13 mmol/L) and low-density lipoprotein (LDL, 0.46 mmol/L) concentrations were significantly lower than those in the control group (TG, 1.69 mmol/L; T-GHOL, 1.86 mmol/L; HDL, 1.62 mmol/L; LDL, 0.63 mmol/L) (p < 0.05). The activities of intestinal digestive enzymes (amylase, lipase and protease) in the starved-refed group were significantly lower than those in the control group after three weeks of starvation (p < 0.05). The highest activities of immune enzymes such as lysozyme (LZM), acid phosphate (ACP), alkaline phosphate (ALP), superoxide dismutase (SOD), glutathione peroxidase (GSH-PX) and catalase (CAT) in the hepatopancreas were presented in the starved-refed group at second week, and significantly higher than those in the control group (p < 0.05). Meanwhile, starvation significantly improved intestinal immune enzymes activities (p < 0.05). the lowest TG contents and the highest expression levels of lipolysis genes including hormone-sensitive lipase (HSL) and carnitine palmitoyl transferase 1 isoform A (CPT-1A) appeared in the hepatopancreas, muscle and intraperitoneal fat after starvation, indicating the mobilization of fat reserves in these tissues (p < 0.05). After refeeding, the recovery of TG content might be mediated by the upregulation of the expression levels of lipogenesis genes such as sterol regulatory element binding protein 1 (SREBP1) and fatty acid synthase (FAS). Understanding the duration of physiological and metabolic changes in O. macrolepis and their reversibility or irreversibility to supplementary feeding response could provide valuable reference for the adaptability of O. macrolepis in large-scale culturing, proliferation and release.

Project description:The use of insect products in aquatic feed is the focus of the aquaculture industry. Black soldier fly larvae oil (BSFLO) has been examined as a potential lipid source for diets for some fish species, but its utilization on Onychostoma macrolepis has not been explored. The influences of substituting fish oil (FO) with BSFLO in the diet on growth, biological indicators, approximate composition, serum biochemistry, antioxidant capacity and expression of lipid metabolism genes in juvenile O. macrolepis were investigated in an eight-week feeding experiment. Four experimental diets were prepared by replacing 0 (control), 25% (BSFLO-25), 50% (BSFLO-50) and 100% (BSFLO-100) FO with BSFLO, and then randomly assigned to twelve aquariums with ten fish (1.75 ± 0.05 g) in each aquarium. The findings showed that the growth indicators, body composition and serum biochemistry in the BSFLO-25 and BSFLO-50 groups had no statistical differences from those of the control group. The activities of superoxide dismutase (SOD) (91.22-94.96 U/mgprot) and the contents of malondialdehyde (MDA) (1.12-1.16 nmol/mgprot) in the liver appeared to be significantly the highest and the lowest in the BSFLO-25, BSFLO-50 and BSFLO-100 groups (p < 0.05). The adipocyte size and intraperitoneal fat index value of fish fed on the BSFLO-100 diet were significantly decreased compared to the control group (p < 0.05). The expression levels of lipid catabolism genes pparα, (peroxisome proliferators-activated receptor alpha) and cpt1a (carnitine palmitoyltransferase 1 isoform a) in the BSFLO-100 group were significantly higher than those of the control group (p < 0.05). The above results indicated that it was feasible to replace 25-50% dietary FO with BSFLO in juvenile O. macrolepis. Dietary BSFLO supplementation could enhance the antioxidant capacity of the liver and suppress intraperitoneal fat accumulation in O. macrolepis. The use of other insect oils in the diets of this species will be evaluated in future research.

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Functional Characterization of Melanocortin-3 Receptor in a Hibernating Cavefish Onychostoma macrolepis.

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