👤 Kosuke Hitaka

Melanocortin 4 receptor (MC4R) is a G-protein-coupled receptor expressed in the hypothalamus, playing a key role in regulating feeding behavior and energy homeostasis. MC4R is integral to the POMC-MC4R and leptin-MC4R pathways, which control food intake and body weight. Mutations in the POMC gene lead to severe early-onset obesity and increased food consumption. Recently, glucagon-like peptide-1 (GLP-1) analogs, including semaglutide, tirzepatide, and retatrutide, have been explored as potential anti-obesity therapies. This study aimed to assess and compare the efficacy of these GLP-1 analogs in MC4R knockout (KO) mice, which are deficient in the POMC-MC4R pathway. GLP-1 analogs were administered for 21 days to MC4R KO mice and compared their efficacy. The percentage of body weight reduction was 19.7 ± 4.1% for semaglutide, 31.6 ± 7.6% for tirzepatide, and 24.1 ± 5.8% for retatrutide. Body composition analysis, including fat and lean mass, was performed using the Echo-MRI system, revealing significant suppression of both fat and lean mass by all three GLP-1 analogs. Furthermore, GLP-1 analogs improved plasma insulin levels, HOMA-IR, cholesterol levels, and markers of liver damage (AST and ALT), as well as reduced liver hypertrophy. While GLP-1 analogs suppressed genes related to fatty acid synthesis, they had no significant effect on inflammation-related gene expressions. Additionally, GLP-1 analogs reduced energy expenditure, with only tirzepatide showing a significant decrease in the respiratory quotient (RQ) in MC4R KO mice. Our findings demonstrate that all three GLP-1 analogs, semaglutide, tirzepatide, and retatrutide, exhibit significant anti-obesity effects in MC4R KO mice. These results suggest that GLP-1 analogs may provide an effective treatment option for patients with MC4R-POMC pathway deficiencies. Moreover, the efficacy of these drugs in MC4R KO mice aligns with clinical studies, indicating that MC4R KO mice serve as a reliable animal model for obesity research. Show less

Metabolic dysfunction-associated steatotic liver disease (MASLD) can progress to steatohepatitis (MASH), which is closely associated with obesity and insulin resistance. Resmetirom, and semaglutide, have been shown to have therapeutic effects in clinical studies. We compared these mechanisms in western diet (WD)-fed melanocortin 4 receptor knockout (MC4R-KO) mice, a human MASH pathology model. Male MC4R-KO mice were fed WD for 6 weeks starting from 22 weeks of age for disease induction and were administered drugs for 7 weeks with WD feeding, for a total duration of 13 weeks. Both resmetirom and semaglutide treatments for 7 weeks substantially improved these parameters. Although resmetirome and semaglutide improved liver hydroxyproline deposition and total fat mass, semaglutide markedly suppressed total lean mass. Moreover, resmetirom enhanced oxygen consumption, whereas semaglutide reduced energy expenditure. Histopathological evaluation showed that resmetirom significantly and semaglutide tended to improve liver steatosis score. On the fibrosis score, semaglutide significantly reduced it. Resmetirom and semaglutide have different mechanisms of action against MASH. Similar to clinical evidence, semaglutide treatment, might cause muscle mass reduction due to food intake suppression. This is the first study to simultaneously compare the effects of resmetirom and semaglutide on MASH phenotypes and reveal the differences on their mechanisms of action in WD-fed MC4R-KO mice. Show less