Role of major histocompatibility complex class II in the development of autoimmune type 1 diabetes and thyroiditis in rats

Hyperinsulinemic male LEW.1WR1 rats show early signs of impaired liver metabolism

Weanling LEW.1WR1 (1WR1) rats are susceptible to type 1 diabetes (T1D) and hyperinsulinemic. Similar to human patients with T1D, these animals are susceptible to developing fatty liver infiltrates. Insulin resistance-related steatosis can lead to the development of severe forms of nonalcoholic fatty liver disease (NAFLD). Previous work in 1WR1 rats suggests that in the absence of T1D, they have increased body mass that is not reconciled by measuring their abdominal fat pads; this suggests 1WR1 rats have an underlying predisposition to store fat in the liver unrelated to diabetes status. We hypothesized that 1WR1 rats show early signs of NAFLD development. We assessed proteomics changes in the livers of glucose intolerant and hyperinsulinemic young adult 1WR1 rats to identify early detectable characteristics of NAFLD development. Our results show young adult 1WR1 rats have UBD/FAT10 gene over expression in the liver. Additionally, they have decreased mitochondrial protein levels, which may lead to lipid accumulation in the liver. A quantitative proteomic analysis showed protein expression related to branch chain fatty acid metabolism, fatty acid beta-oxidation, and oxidative phosphorylation in the liver is significantly different in 1WR1 rats compared to control LEW/SsNHsd (SsNHsd) rats. In summary, our study shows that 1WR1 rats developed early characteristics of mitochondrial dysfunction and insulin resistance in the liver independent of T1D, which are commonly observed with NAFLD development.

Preclinical models for Type 1 Diabetes Mellitus - A practical approach for research

Numerous preclinical models have been developed to advance biomedical research in type 1 diabetes mellitus (T1DM). They are essential for improving our knowledge of T1DM development and progression, allowing researchers to identify potential therapeutic targets and evaluate the effectiveness of new medications. A deeper comprehension of these models themselves is critical not only to determine the optimal strategies for their utilization but also to fully unlock their potential applications in both basic and translational research. Here, we will comprehensively summarize and discuss the applications, advantages, and limitations of the commonly used animal models for human T1DM and also overview the up-to-date human tissue bioengineering models for the investigation of T1DM. By combining these models with a better understanding of the pathophysiology of T1DM, we can enhance our insights into disease initiation and development, ultimately leading to improved therapeutic responses and outcomes.

Animal models for diabetes: Understanding the pathogenesis and finding new treatments

Diabetes mellitus is a lifelong, metabolic disease that is characterised by an inability to maintain normal glucose homeostasis. There are several different forms of diabetes, however the two most common are Type 1 and Type 2 diabetes. Type 1 diabetes is caused by the autoimmune destruction of pancreatic beta cells and a subsequent lack of insulin production, whilst Type 2 diabetes is due to a combination of both insulin resistance and an inability of the beta cells to compensate adequately with increased insulin release. Animal models are increasingly being used to elucidate the mechanisms underlying both Type 1 and Type 2 diabetes as well as to identify and refine novel treatments. However, a wide range of different animal models are currently in use. The majority of these models are suited to addressing certain specific aspects of diabetes research, but may be of little use in other studies. All have pros and cons, and selecting an appropriate model for addressing a specific question is not always a trivial task and will influence the study results and their interpretation. Thus, as the number of available animal models increases it is important to consider the potential roles of these models in the many different aspects of diabetes research. This review gathers information on the currently used experimental animal models of both Type 1 and Type 2 diabetes and evaluates their advantages and disadvantages for research purposes and details the factors that should be taken into account in their use.

Characterization of the Prediabetic State in a Novel Rat Model of Type 2 Diabetes, the ZFDM Rat

We recently established a novel animal model of obese type 2 diabetes (T2D), the Zucker fatty diabetes mellitus (ZFDM) rat strain harboring the fatty mutation (fa) in the leptin receptor gene. Here we performed a phenotypic characterization of the strain, focusing mainly on the prediabetic state. At 6-8 weeks of age, fa/fa male rats exhibited mild glucose intolerance and severe insulin resistance. Although basal insulin secretion was remarkably high in the isolated pancreatic islets, the responses to both glucose stimulation and the incretin GLP-1 were retained. At 10-12 weeks of age, fa/fa male rats exhibited marked glucose intolerance as well as severe insulin resistance similar to that at the earlier age. In the pancreatic islets, the insulin secretory response to glucose stimulation was maintained but the response to the incretin was diminished. In nondiabetic Zucker fatty (ZF) rats, the insulin secretory responses to both glucose stimulation and the incretin in the pancreatic islets were similar to those of ZFDM rats. As islet architecture was destroyed with age in ZFDM rats, a combination of severe insulin resistance, diminished insulin secretory response to incretin, and intrinsic fragility of the islets may cause the development of T2D in this strain.

A review of the genetics of hypoadrenocorticism

Hypoadrenocorticism is an uncommon disease in dogs and rare in humans, where it is known as Addison disease (ADD). The disease is characterized by a deficiency in corticosteroid production from the adrenal cortex, requiring lifelong hormone replacement therapy. When compared with humans, the pathogenesis of hypoadrenocorticism in dogs is not well established, although the evidence supports a similar autoimmune etiology of adrenocortical pathology. Several immune response genes have been implicated in determining susceptibility to Addison disease in humans, some of which are shared with other autoimmune syndromes. Indeed, other types of autoimmune disease are common (approximately 50%) in patients affected with ADD. Several lines of evidence suggest a genetic component to the etiology of canine hypoadrenocorticism. Certain dog breeds are overrepresented in epidemiologic studies, reflecting a likely genetic influence, supported by data from pedigree analysis. Molecular genetic studies have identified similar genes and signaling pathways, involved in ADD in humans, to be also associated with susceptibility to canine hypoadrenocorticism. Immune response genes such as the dog leukocyte antigen (DLA) and cytotoxic T-lymphocyte-associated protein 4 (CTLA4) genes seem to be particularly important. It is clear that there are genetic factors involved in determining susceptibility to canine hypoadrenocorticism, although similar to the situation in humans, this is likely to represent a complex genetic disorder.

Variable immune cell frequencies in peripheral blood of LEW.1AR1-iddm rats over time compared to other congenic LEW strains

The LEW.1AR1-iddm rat is an animal model of human type 1 diabetes (T1D), which arose through a spontaneous mutation within the major histocompatibility complex (MHC)-congenic background strain LEW.1AR1. The LEW.1AR1-iddm rat is characterized by two phenotypes: diabetes development with a diabetes incidence of 60% and a variable T cell frequency in peripheral blood. In this study the immune cell repertoire of LEW.1AR1-iddm rats was analysed over time from days 30 to 90 of life and compared to the background strain LEW.1AR1 and the LEW rat strain as well as the LEW.1WR1 rat strain. The LEW.1AR1-iddm rats are characterized by a high variability of CD3(+), CD4(+) and CD8(+) T cell frequencies in peripheral blood over time, and the frequency is unique for each animal. The variability within the frequencies resulted in changes of the CD4(+) : CD8(+) T cell ratio. The other three rat strains studied were characterized by a stable but nevertheless strain-specific T cell frequency resulting in a specific CD4(+) : CD8(+) T cell ratio. The frequency of natural killer (NK) cells and B cells in LEW.1AR1-iddm rats was increased, with a higher variability compared to the other strains. Only monocytes showed no differences in frequency and variability between all strains studied. These variabilities of immune cell frequencies in the LEW.1AR1-iddm rats might lead to imbalances between autoreactive and regulatory T cells in peripheral blood as a prerequisite for diabetes development.

Autoantigen-induced focusing of Vβ13+ T cells precedes onset of autoimmune diabetes in the LEW.1WR1 rat

The earliest events leading to autoimmune type 1 diabetes (T1D) are not known in any species. A T-cell receptor (TCR)-variable region, TCR-Vβ13, is required for susceptibility to autoimmune diabetes in rats, and selective depletion of Vβ13(+) T cells with an allele-specific monoclonal antibody prevents disease in multiple rat strains. To investigate the role of Vβ13 early in diabetes, we examined islet T-cell transcripts in susceptible (LEW.1WR1) and resistant (LEW.1W and Wistar Furth) strains induced with polyinosinic:polycytidylic acid. Vβ13(+) T cells displayed antigenic focusing in LEW.1WR1 islets 5 days postinduction and were characterized by a substantial decrease in complementarity determining region 3 diversity. This occurred prior to significant islet T-cell accumulation (day 7) or frank diabetes (days 10-14). Vβ13(+) transcripts increased in LEW.1WR1 islets during diabetes progression, but not in resistant rats. We also analyzed transcript clonality of rat TCR-Vα5, an ortholog of the dominant TCR-Vα chain found on insulin B:9-23-reactive T cells in nonobese diabetic rat islets. We observed clonal expansion of Vα5(+) transcripts in prediabetic LEW.1WR1 islets, suggesting that rat Vα5 is also an important component of islet autoantigen recognition. These data provide additional evidence that genome-encoded TCR sequences are important determinants of genetic susceptibility to T1D.

A Novel Rat Model of Type 2 Diabetes: The Zucker Fatty Diabetes Mellitus ZFDM Rat

The Zucker fatty (ZF) rat harboring a missense mutation (fatty, fa) in the leptin receptor gene (Lepr) develops obesity without diabetes; Zucker diabetic fatty (ZDF) rats derived from the ZF strain exhibit obesity with diabetes and are widely used for research on type 2 diabetes (T2D). Here we establish a novel diabetic strain derived from normoglycemic ZF rats. In our ZF rat colony, we incidentally found fa/fa homozygous male rats having reproductive ability, which is generally absent in these animals. During maintenance of this strain by mating fa/fa males and fa/+ heterozygous females, we further identified fa/fa male rats exhibiting diabetes. We then performed selective breeding using the fa/fa male rats that exhibited relatively high blood glucose levels at 10 weeks of age, resulting in establishment of a diabetic strain that we designated Hos:ZFDM-Lepr(fa) (ZFDM). These fa/fa male rats developed diabetes as early as 10 weeks of age, reaching 100% incidence by 21 weeks of age, while none of the fa/+ male rats developed diabetes. The phenotypic characteristics of this diabetic strain are distinct from those of normoglycemic ZF rats. ZFDM rat strain having high reproductive efficiency should serve as a more useful animal model of T2D.