Introduction to Murine Models of Obesity (Part 1): LEP/LEPR Classic Pathway Model

To effectively conduct research on obesity and its prevention and treatment, it is crucial to comprehend the mechanisms underlying obesity. Leveraging mouse models of obesity-related diseases is essential for gaining meaningful insights into the prevention and treatment of obesity and its complications.?

Mechanisms of Obesity

Many obese individuals have a family history of the condition because family members often share similar genes,?dietary habits, and activity patterns. Abnormal?regulation?in processes such as appetite, stress,?anxiety, fat synthesis and breakdown, and energy metabolism within the body can all contribute to the development of obesity. Among these, abnormalities in the leptin signaling pathway and molecular signals that mediate leptin function in neurons and cells are the most common genetic factors associated with obesity [1].

Classic Obesity Models: ob/ob and db/db Mice

Leptin (LEP) is produced by white adipose tissue cells and plays a crucial role in the regulation of body weight through binding to the Leptin receptor (LEPR) and activating downstream signaling. It is involved in a negative feedback mechanism between adipose tissue and the hypothalamus. Mutations in LEP and LEPR can both lead to obesity in?humans and mice.

ob/ob mice (Obesity mouse) carry a spontaneous homozygous mutation in the Lep?gene, resulting in excessive eating and causing a very severe obesity phenotype [2]. On the other hand, db/db mice (Diabetes mouse) carry a homozygous mutation in the Lepr?gene, and these mice begin to overeat and gain weight starting at one month of age. Simultaneously, insulin levels rise, leading to the development of type 2 diabetes [3].

Cyagen has developed ob/ob mice (product number: C001368) and db/db mice (product number: C001291) by knocking out or introducing mutations in the Lep?and Lepr?genes, respectively. The results show that these mice exhibit the same phenotypes as the classic models, including severe obesity and high blood sugar levels, making them suitable for research on obesity and type 2 diabetes.

LEP/LEPR Downstream Pathway Deficiency Model

1. Pomc-KO Mice

In the arcuate nucleus of the hypothalamus, pro-opiomelanocortin (POMC) positive neurons are direct targets of leptin. POMC serves as a precursor for various biologically active peptides, including alpha-melanocyte-stimulating hormone (αMSH). In the brain, αMSH is a potent anorexigenic (appetite-suppressing) neuropeptide. It reduces food intake and increases energy expenditure by activating melanocortin receptors (MCR3/MCR4) in the paraventricular nucleus of the hypothalamus and other regions. POMC?gene knockout and subsequent POMC peptide deficiency in mice leads to overeating and significant obesity. In the presence of a high-fat diet, obesity becomes more severe.?Heterozygous POMC-KO mice exhibit a milder obesity phenotype [4].

2. Mc4r-KO Mice

Agouti-related peptide (AgRP)-expressing?neurons and αMSH affect energy balance through melanocortin receptors (MCR), with melanocortin receptor subtype 4 (MCR4) being the main receptor involved in regulating food intake control. MCR4?plays a crucial role in satiety and energy homeostasis, and its mutations are also one of the common genetic causes of human obesity. By selectively knocking out Mc4r?to inactivate it, mice develop hyperphagia and pathological obesity, accompanied by glucose-related phenotypes such as?hyperinsulinemia, hyperglycemia, and hyperleptinemia. Unlike many other obesity models, Mc4r-KO mice do not show an elevation in circulating corticosterone levels and do not respond to leptin, AgRP, or αMSH [5].

3. Mc3r-KO Mice

Melanocortin receptor subtype 3 (MC3R) is also a protein involved in regulating energy balance. MC3R, along with MC4R, serves as a key receptor for melanocortin peptides in the leptin-melanocortin signaling cascade. Variations in MC3R have been associated with obesity in some populations, and certain rare mutations may have a greater impact on individual susceptibility to weight gain. Mc3r-KO mice exhibit a mild obesity phenotype and metabolic syndrome characterized by reduced lean mass, increased fat mass, accelerated diet-induced obesity (DIO), reduced daytime-restricted feeding behavior, diminished metabolic adaptability, as well as symptoms of hyperleptinemia, relatively mild hyperinsulinemia, and reduced physical activity?[6-8].

4. Mc3r/Mc4r-DKO Mice

MC3R and MC4R are neural melanocortin receptors that exhibit certain synergistic effects and can regulate energy balance. Consequently, mice with double gene knockout for Mc3r?and Mc4r?(Mc3r/Mc4r-DKO) show a significantly higher degree of obesity compared to mice with single gene knockout for either Mc3r?or Mc4r?[9]. Similar phenomena have been observed in rats as well, where Mc3r/Mc4r double knockout?results in more severe glucose intolerance and hyperglycemia than single gene knockout for either Mc3r?or Mc4r single gene knockout rats[10].

Recommendations for Obesity Research Models

Genetically edited murine?models play a crucial role in obesity and metabolic disease mechanisms research, as well as in subsequent?drug development and evaluation. Cyagen offers thousands of independently developed gene-edited mouse strains and numerous metabolic disease?and diet-induced obesity (DIO)?modeling options. Our platform encompasses a diverse array of metabolic models and CRO testing capabilities that aim to advance our comprehension and treatment of metabolic disorders, ultimately addressing the interconnected complexities of cardiovascular diseases and other related pathologies. We can provide a variety of gene knockout or conditional knockout mouse models, including LEP, LEPR, POMC, MC3R/MC4R, among others. Additionally, we offer gene?customization services to accelerate your research projects.

Cyagen can also develop other metabolic and cardiovascular disease research models, including spontaneous, induced, composite, & surgical models:

The diet-induced obesity (DIO) model recapitulates metabolic factors implicated in human obesity, which has led to its use in studying the relationship between diet, genes, and other factors in the developmental processes of obesity, diabetes, and related metabolic disorders. Check out our?diet-induced obesity (DIO)?modeling options.

Cyagen can provide you with various obesity mouse models and phenotype analysis services - please contact us?today for more information and custom project quotes.

References:

[1] Liu J, Yang X, Yu S, Zheng R. The Leptin Signaling. Adv Exp Med Biol. 2018;1090:123-144.

[2] Zhang Y, Proenca R, Maffei M, Barone M, Leopold L, Friedman JM. Positional cloning of the mouse obese gene and its human homologue. Nature. 1994 Dec 1;372(6505):425-32.

[3] Coleman DL. Obese and diabetes: two mutant genes causing diabetes-obesity syndromes in mice. Diabetologia. 1978 Mar;14(3):141-8.

[4] Yaswen L, Diehl N, Brennan MB, Hochgeschwender U. Obesity in the mouse model of pro-opiomelanocortin deficiency responds to peripheral melanocortin. Nat Med. 1999 Sep;5(9):1066-70.

[5] Huszar D, Lynch CA, Fairchild-Huntress V, Dunmore JH, Fang Q, Berkemeier LR, Gu W, Kesterson RA, Boston BA, Cone RD, Smith FJ, Campfield LA, Burn P, Lee F. Targeted disruption of the melanocortin-4 receptor results in obesity in mice. Cell. 1997 Jan 10;88(1):131-41.

[6] Butler AA, Kesterson RA, Khong K, Cullen MJ, Pelleymounter MA, Dekoning J, Baetscher M, Cone RD. A unique metabolic syndrome causes obesity in the melanocortin-3 receptor-deficient mouse. Endocrinology. 2000 Sep;141(9):3518-21.

[7] Sutton GM, Begriche K, Kumar KG, Gimble JM, Perez-Tilve D, Nogueiras R, McMillan RP, Hulver MW, Tsch?p MH, Butler AA. Central nervous system melanocortin-3 receptors are required for synchronizing metabolism during entrainment to restricted feeding during the light cycle. FASEB J. 2010 Mar;24(3):862-72.

[8] Feng Y, Cao L, Metzger JM, Strack AM, Camacho RE, Mellin TN, Nunes CN, Min W, Fisher J, Gopal-Truter S, MacIntyre DE, Chen HY, Van der Ploeg LH. Inactivation of the mouse melanocortin-3 receptor results in increased fat mass and reduced lean body mass. Nat Genet. 2000 Sep;26(1):97-102.

[9] Chen AS, Marsh DJ, Trumbauer ME, Frazier EG, Guan XM, Yu H, Rosenblum CI, Vongs A, Feng Y, Cao L, Metzger JM, Strack AM, Camacho RE, Mellin TN, Nunes CN, Min W, Fisher J, Gopal-Truter S, MacIntyre DE, Chen HY, Van der Ploeg LH. Inactivation of the mouse melanocortin-3 receptor results in increased fat mass and reduced lean body mass. Nat Genet. 2000 Sep;26(1):97-102.

[10] You P, Hu H, Chen Y, Zhao Y, Yang Y, Wang T, Xing R, Shao Y, Zhang W, Li D, Chen H, Liu M. Effects of Melanocortin 3 and 4 Receptor Deficiency on Energy Homeostasis in Rats. Sci Rep. 2016 Oct 7;6:34938.

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