Novel Insights into the Animal Models of Diabetes

Diabetes is a chronic disease characterized by relative or absolute insulin deficiency, resulting in hyperglycemia. Chronic hyperglycemia can lead to multiple complications, such as neuropathy, nephropathy, and retinopathy, and increase the risk of cardiovascular disease (CVD). According to the World Health Organization (WHO), diabetes will become the seventh leading cause of death globally by 2030.

There are three main types of diabetes mellitus, the most common of which are type 1 diabetes (T1D) and type 2 diabetes (T2D). They are both multifactorial diseases that develop due to the interaction of very complex genetic and environmental factors. As of 2019, an estimated 463 million people had diabetes worldwide, with type 2 diabetes making up about 90% of the cases. Lifestyles and health factors such as obesity, poor diet, and lack of exercise play important roles in the risk of developing type 2 diabetes.

Due to the high incidence of diabetes worldwide, its treatments have attracted much attention. For now, to combat the disease pathogenesis, extensive research is needed to develop new anti-diabetes drugs and identify their mechanisms. Therefore, many animal models of diabetes have been developed and improved in recent years, among which, the rat and mouse models are the most comprehensively established.

Animal Models of Type 1 Diabetes (T1D)

Type 1 diabetes (T1D) is an autoimmune disease characterized by loss of the insulin-producing beta-cells of the pancreatic islets, leading to insulin deficiency. Animal models of type I diabetes include rodents that spontaneously develop autoimmune diabetes, as well as non-rodent large animal models constructed by pancreatectomy or chemical ablation of beta-cells. There are many ways to establish animal models of T1D, such as the use of anti-insulin serum, pancreatectomy, glucose infusion, beta cytotoxic drugs, and viruses. They are of great importance in both basic and preclinical research, not only for understanding the pathogenesis of T1D, but also for evaluating new therapies (monotherapy or combination therapy) with therapeutic potential. There are five commonly used spontaneous models for type 1 diabetes, with the most widely used including non-obese diabetic (NOD) mice and biobreeding (BB) rats.

Figure 1. Animal models of type 1 diabetes (T1D).

NOD mice

NOD mice, developed by Shionogi Laboratory in Osaka, Japan in 1974 ^[4], are the preferred animal model for studying the pathophysiological mechanisms of autoimmune diseases (such as T1D). NOD mice develop insulitis at 3-4 weeks of age, and the islets are infiltrated by innate immune cells, which are mainly CD4+ lymphocytes and CD8+ lymphocytes as well as natural killer (NK) cells and B cells, dendritic cells, macrophages, and neutrophils ^[5][6]. This process in NOD mice is the same as in humans, and similar immune cells are also found in human islet infiltration ^[7]. From approximately 4-6 weeks of age, the infiltration of innate immune cells into islets further attracts CD4+ and CD8+ T-cell subsets of the adaptive immune system ^[8]. The above-mentioned activities of infiltrating pancreatic islets by innate and adaptive immune cells begin to destroy islet cells through immune response or apoptosis, which is a necessary condition for the occurrence of diabetes. Furthermore, insulitis results in the destruction of beta-cells and approximately 90% of pancreatic insulin is lost within 10-14 weeks of the onset of overt diabetes. Apparently, diabetic NOD mice lost weight rapidly and required insulin treatment to keep them alive longer, up to 30 weeks of age.

Since the NOD mouse model develops spontaneous diseases similar to humans, it closely resembles humans in disease characterization. NOD mice have played a very important role in understanding the pathophysiology of the autoimmune disease, including identifying new human-like autoantigens and biomarkers, and helping researchers design and screen therapeutic targets for T1D^[9].

More than 50 loci of genes related to immune function and regulation as well as pancreatic beta-cell function were found in NOD mice and humans, which play an important role in mediating susceptibility to T1D ^[10]. However, most of the susceptibility in NOD mice and humans is caused by a single locus of major histocompatibility complex (MHC) class II ^[11]. Many studies have shown that MHC class II proteins in NOD mice are structurally similar to humans, which may be the reason why both NOD mice and humans are similarly resistant or susceptible to autoimmune diseases ^[12]. Therefore, NOD mice are considered to be an ideal clinical animal model for testing treatments related to the regulation of autoimmune responses.

Biobreeding (BB, BBDP) rats

Biobreeding rat also known as the BB or BBDP rat is an inbred laboratory rat strain that spontaneously develops autoimmune Type 1 Diabetes. They were originally derived from a Canadian colony of outbred Wistar rats. Subsequent BB rat colonies have since been established. One in Worcester, Massachusetts, has been inbred and known as BBDP/Wor and another one in Ottawa, Canada, an outbred strain known as BBdp. BB rats generally develop diabetes after the developmental period without any gender differences. The diabetic phenotype of BB rats is very extreme, characterized by hyperglycemia, hypoinsulinemia, weight loss, and ketonuria ^[3]. After the onset of the disease, the BB rats required immediate insulin therapy to maintain survival. BB rats with insulitis had major immune cells such as T-cells, B-cells, macrophages, and NK-cells, but severely reduced CD4+ T-cells and CD8+ T-cells which are almost entirely lost. In addition, a lack of ART2+ T-cells are also demonstrated in rats: where ART2 represents a mature T cell alloantigen, which is required for the identification of cells with immunomodulatory effects. BB rats are the preferred small animal model for inducing islet allograft tolerance ^[2], and have been used in the intervention and genetic studies of diabetic neuropathy. Pancreatitis develops in both sexes of BB rats, followed by selective destruction of beta-cells, leading to diabetes at 50-90 days of age. The natural course of insulitis in spontaneously diabetic BB rats differs from that seen in NOD mice.

Animal Models of Type 2 Diabetes (T2D)

Type 2 diabetes (T2D) has varying degrees of insulin resistance and beta-cell dysfunction in both obese and non-obese animal models. Thus, animal models of type 2 diabetes mainly include insulin resistance models and/or beta-cell dysfunction models. Many animal models of type 2 diabetes are obesity models, indicating that obesity is closely related to the pathogenesis of type 2 diabetes in humans. The establishment of T2D animal models is of great significance to both basic and preclinical research ^[13]. The common models of spontaneous type 2 diabetes include Lep^ob/ob mice, Zucker fat rats and Zucker diabetic fatty (ZDF) rats. There are various methods for establishing T2D animal models, such as monogenic obesity, polygenic obesity, high-fat diet, non-obesity model and genetically induced model.

Figure 2. Animal models of type 2 diabetes (T2D).

Lep^ob/ob mice

First identified by Jackson Laboratory in 1949, the Lep^ob/ob mouse model of severe obesity is generated by a spontaneous mutation of chromosome 6 in C57BL/6 mice. However, it was not discovered until 1994 that the mutant protein resulting from this was leptin ^[14]. Lep^ob/ob mice begin to gain weight at 2 weeks of age with hyperinsulinemia and can reach up to 3 times the body weight of wild-type normal mice. Hyperglycemia occurs after 4 weeks of age, and the blood glucose concentration gradually increases, reaching a peak within 3-5 months, and then begins to decrease with the age of the mice ^[15]. Other abnormal symptoms include hyperlipidemia, ineffective thermoregulation, decreased physical activity, and infertility ^[16]. Furthermore, in Lep^ob/ob mice, islet cells are drastically reduced and insulin release is abnormal ^[17]. Leptin injection in obese mice can reduce body weight gain, decrease food intake, increase energy expenditure, and improve insulin sensitivity ^[18]. Lep^ob/ob mice are severely obese with hyperinsulinemia and lifelong insulin resistance, which makes them useful for the development of drugs that improve peripheral insulin sensitivity and reduce body weight (e.g., insulin sensitizers, anti-obesity, and other anti-hyperglycemic drugs) ^[19].

Zucker fatty rats and Zucker diabetic fatty (ZDF) rats

Zucker fatty rats (fa/fa, ZR) were first generated in 1961 by crossing Merck M-Strain and Sherman rats ^[20]. They are characterized by mutations in leptin receptor, which can induce phagocytosis, obesity, and insulin resistance. Zucker fatty rats have become widely used as models for prediabetes and obesity. Obese rats have metabolic disorders such as hyperinsulinemia, hyperlipidemia, hypertension, and impaired glucose tolerance. Type 2 diabetes develops in male rats following a homozygous mutation (fa/fa) in the leptin hormone receptor under the influence of a high-energy rodent diet.

The Zucker diabetic fatty (ZDF) rat is a substrain of the Zucker fatty rat (fa/fa, ZR), which was derived from hyperglycemic ZRs to gain a model with diabetic features. To this end, severe insulin resistance and glucose intolerance develop within 3-8 weeks of age, high levels of diabetes develop at 8-10 weeks of age, and by 10-11 weeks of age glucose levels in the fed state further increase to 500mg/dL. It can be confirmed that the increase of islet DNA content is related to serum insulin, suggesting that islet hyperplasia plays an important role in the occurrence and development of hyperinsulinemia in ZDF rats.

Obese rats have higher triglyceride and cholesterol levels than normal rats, which is due to the excessive metabolism of skeletal muscle and pancreatic islet fatty acids ^[23]. Obese ZDF rats can also be induced to produce very high levels of fat by feeding them a diet high in saturated fat and sucrose. Inducing mutations in ZDF rats can generate a subline of inbred ZDF rats that are less obese than Zucker Fatty rats, but are more insulin resistant due to increased levels of beta-cell apoptosis; this subline is characterized by hyperinsulinemia at eight weeks, followed by a decrease in insulin levels with age ^[24]. Notably, female ZDF rats do not develop overt diabetes. Leptin receptor-deficient male ZDF rats (ZDF/CrlCrlj) have emerged as a popular T2D model in preclinical studies, manifested by disrupted islet architecture, B-cell degranulation, and increased B-cell death.

Why Choose Cyagen?

Cyagen is the world's largest provider of custom-engineered mouse and rat models. As an expert on animal genetic modification, Cyagen is well known for its services with top quality, full guarantees, and budget-friendly prices. We can provide you with a variety of diabetes mouse models, such as: NOD mice, high-fat diet-induced obesity mouse model (DIO), and T2DM mouse model constructed by high-sugar and high-fat diet combined with low-dose intraperitoneal injection of streptozotocin (STZ).

In addition, Cyagen Knockout Catalog Models also provides you with a variety of diabetes-related gene editing mouse models, such as Cd28, Abcc8, Gck, Hkdc1, etc., to meet the various needs of scientific research institutions and pharmaceutical R&D enterprises for animal models. If required, you can contact us to request a customized quote for your research.

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