Endocrine Abstracts

Introduction: Obesity is a global epidemic that involves environmental and genetic factors. In humans, loss-of-function mutations in the melanocortin-4-receptor (MC4R) is the most common cause of monogenic obesity. MC4R is one of the five melanocortin receptors known to regulate appetite and nutrients metabolism. Different animal models exist to study the role of MC4R in appetite and metabolism. Here we study a zebrafish model of MC4R loss of function (sa122 mutant line) to define food intake and body fat accumulation.

Methods: We utilized IVF to rederive the MC4R sa122 mutant zebrafish line generated with TALEN technology by the Sanger Institute. The zebrafish was genotyped with a PACE assay. We quantified food intake using DiA;4-Di-16-ASP-stained paramecium and fluorescence was measured with FLUOstar Omega Microplate Reader at 7 dpf (days post fertilization). To study fat accumulation, at 5 dpf, before oral nutrition starts, we performed Oil Red O staining to identify adipose tissue and quantified with ImageJ. Statistical analysis was undertaken using Prism 9.

Results: At 7 dpf, MC4R sa122 zebrafish mutants showed no significant difference in food intake when non-fasted compared to wild-type (WT) controls (P = 0.99). However, food intake assessment following fasting was increased compared to WT-controls (P = 0.02). At 5 dpf, fat accumulation was not statistically different (P = 0.82) between MC4R sa122 mutants and WT zebrafish.

Discussion: The MC4R sa122 mutant line shows a difference in food intake under fasting conditions but no difference without fasting. We showed no difference in fat accumulation between MC4R sa122 and WT.