A 2024 study published in the International Journal of Obesity found that deleting the melanocortin 1 receptor (MC1R) only in liver cells led to increased liver weight, higher triglyceride levels, enlarged white fat depots and adipocyte hypertrophy in mice, according to the report.
The experiments, described in the paper titled "Hepatocyte-specific loss of melanocortin 1 receptor disturbs fatty acid metabolism and promotes adipocyte hypertrophy," were conducted by Keshav Thapa, Petteri Rinne and colleagues. The metabolic changes occurred without differences in food intake or physical activity, the researchers reported.
Adipocyte hypertrophy, an increase in the size of individual fat cells, has been previously described in mouse models of melanocortin-related obesity. According to "NutrientGene Interactions in Health and Disease," the increase in adiposity in dominant agouti mutant mice "is characterized by adipocyte hypertrophy without hyperplasia" [1].
Study Details and Findings
Researchers used a hepatocyte-specific knockout model to remove MC1R expression only in liver cells, the paper stated. The team reported activation of de novo lipogenesis genes in the liver and suppression of lipolysis enzymes in adipose tissue. De novo lipogenesis is the metabolic pathway by which the liver converts carbohydrates into fatty acids; lipolysis is the process by which stored triglycerides are broken down into free fatty acids.
According to the report, MC1R loss shifted the balance of these pathways, favoring fat synthesis in the liver and suppressing fat breakdown in fat tissue. Melanocortin receptors have a documented relationship with fat metabolism. Prior research cited in "Neurodegeneration" observed that MC2R is present in rodent adipocytes, "suggesting a role for melanocortins in lipolysis," although the receptor was not found in human adipocytes [2].
According to the authors, the results indicate that MC1R in hepatocytes participates in systemic fatty-acid regulation. The paper is available open access, according to the journal.
MC1R and Pigment Biology
MC1R is known for its role in melanocytes, where it responds to alpha-melanocyte-stimulating hormone after ultraviolet exposure, according to prior research. "In broad terms, MC1R is involved in the paracrine control of skin coloration," according to a chapter on melanocortin receptors [3].
In humans, MC1R regulates skin and hair color as well as eye hue, according to published reports [4]. In dogs, coat color comes from yellow and black pigments controlled by the pigment-switching genes MC1R and ASIP, according to a report on the Nova Scotia duck tolling retriever [5].
The new study did not expose mice to light or measure circadian responses, according to the report. The study's discussion is limited to receptor biology and lipid handling, the paper stated.
Some natural-health commentators have interpreted the findings as evidence that daily solar cues influence liver metabolism through an MC1R-related pathway. A study described in an article on NaturalNews.com found that exposure to natural daylight during office hours stabilized blood sugar swings in adults with Type 2 diabetes [6]. A separate report described "a hidden universe of opsins – ancient light-sensing proteins – lurking in our skin, brain and fat tissue" [7].
Implications for Metabolic Research
The authors called for further research into MC1R's role in metabolic disease, according to the article. The findings may help explain mechanisms of fatty liver and visceral fat accumulation, the report stated. No human trials were described in the study, and the relevance to people remains unestablished, according to the paper.
The study follows a long-running debate over sun exposure guidance. In July 2014, then-acting U.S. Surgeon General Boris Lushniak issued a "Call to Action to Prevent Skin Cancer," declaring UV radiation harmful and advising that sun exposure be avoided altogether, according to an article on Mercola.com [8]. Critics of broad sun avoidance have pointed to rising rates of vitamin D deficiency and chronic diseases linked to sunlight deprivation, according to published reports [9].
Conclusion
The study provides evidence that MC1R in hepatocytes regulates lipid metabolism and fat-cell size in mice, according to the report. The findings add to a broader literature linking melanocortin signaling to body-fat regulation [1]. Additional research would be required to determine whether the receptor functions similarly in humans and whether light exposure affects MC1R activity in the liver, the report stated.
References
- James. "NutrientGene Interactions in Health and Disease".
- Intech Prepress 2. "Neurodegeneration".
- William J. Kovacs MD. "T".
- Mercola.com. "Do Redheads Need Less Vitamin D". Mercola.com. September 05, 2023.
- Mercola.com. "Why Do Some Dogs Have More Colorful Coats". Mercola.com. March 19, 2020.
- NaturalNews.com. "Beyond diet and drugs: New research suggests natural light could be a simple tool for blood sugar control". NaturalNews.com. May 10, 2026.
- "The Light Within: Opsins and the Unseen Spectrum of Health". BrightLearn.ai. June 30, 2026.
- Mercola.com. "How Dermatologists Fuel Chronic Disease Rates With Their Flawed Sun Exposure Guidelines". Mercola.com. March 14, 2016.
- NaturalNews.com. "Marc Sorenson reveals the sunlight paradox: How modern medicine's fear of the sun makes people sicker". NaturalNews.com. October 30, 2025.
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