Diets influence the diabetic phenotype of transgenic mice expressing a dominant negative glucose-dependent insulinotropic polypeptide receptor (GIPRdn)

[Pathogenesis of diabetes mellitus and diabetic complications. Studies on diabetic mouse models]

Diabetic mouse models created via random mutagenesis or genetic modification are essential tools to unravel the mechanisms involved in the development of diabetes mellitus and associated diseases. Three diabetic mutant mouse lines derived from the Munich N-ethyl-N-nitrosourea (ENU) mouse mutagenesis project and one transgenic mouse line were analyzed with respect to diabetes-relevant clinical, pathomorphological and therapeutic aspects. An Ins2 mutation and two Gck mutations were identified as the cause of diabetes mellitus in the mutant lines. Heterozygous Ins2 and homozygous Gck mutants serve as model for permanent neonatal diabetes mellitus (PNDM) and heterozygous Gck mutants develop maturity onset diabetes of the young type 2. Dominant-negative glucose-dependent insulinotropic polypeptide receptor (GIPR(dn)) transgenic mice exhibit defective postnatal islet growth, develop PNDM and progressive diabetes-associated kidney lesions. The mutant and transgenic diabetic mouse models analyzed in the study were shown to represent valuable models to study the pathogenesis of monogenic diabetes and to establish novel treatment strategies.

The physiology of incretins

The discovery of incretins − glucagon-like peptide (GLP)-1 and glucose-dependent insulinotrop peptide (GIP) −, clarification of their physiological properties as well as therapeutic application of incretin-based blood glucose lowering drugs opened new perspectives in the medical management of type 2 diabetes. New results of basic research investigations led to revaluation of the role of GIP in metabolic processes and a more established use of GLP-1 action. The article overviews the most relevant data of production and effects of incretins, as well as future possibilities of their therapeutic use. Orv. Hetil., 2011, 152, 1922–1930.

Postnatal development of numbers and mean sizes of pancreatic islets and beta-cells in healthy mice and GIPR(dn) transgenic diabetic mice

The aim of this study was to examine postnatal islet and beta-cell expansion in healthy female control mice and its disturbances in diabetic GIPR^dn transgenic mice, which exhibit an early reduction of beta-cell mass. Pancreata of female control and GIPR^dn transgenic mice, aged 10, 45, 90 and 180 days were examined, using state-of-the-art quantitative-stereological methods. Total islet and beta-cell volumes, as well as their absolute numbers increased significantly until 90 days in control mice, and remained stable thereafter. The mean islet volumes of controls also increased slightly but significantly between 10 and 45 days of age, and then remained stable until 180 days. The total volume of isolated beta-cells, an indicator of islet neogenesis, and the number of proliferating (BrdU-positive) islet cells were highest in 10-day-old controls and declined significantly between 10 and 45 days. In GIPR^dn transgenic mice, the numbers of islets and beta-cells were significantly reduced from 10 days of age onwards vs. controls, and no postnatal expansion of total islet and beta-cell volumes occurred due to a reduction in islet neogenesis whereas early islet-cell proliferation and apoptosis were unchanged as compared to control mice. Insulin secretion in response to pharmacological doses of GIP was preserved in GIPR^dn transgenic mice, and serum insulin to pancreatic insulin content in response to GLP-1 and arginine was significantly higher in GIPR^dn transgenic mice vs. controls. We could show that the increase in islet number is mainly responsible for expansion of islet and beta-cell mass in healthy control mice. GIPR^dn transgenic mice show a disturbed expansion of the endocrine pancreas, due to perturbed islet neogenesis.

Diabetic kidney lesions of GIPRdn transgenic mice: podocyte hypertrophy and thickening of the GBM precede glomerular hypertrophy and glomerulosclerosis

Diabetic nephropathy is the leading cause of end-stage renal disease and the largest contributor to the total cost of diabetes care. Rodent models are excellent tools to gain more insight into the pathogenesis of diabetic nephropathy. In the present study, we characterize the age-related sequence of diabetes-associated kidney lesions in GIPRdn transgenic mice, a novel mouse model of early-onset diabetes mellitus. Clinical-chemical analyses as well as qualitative and quantitative morphological analyses of the kidneys of GIPRdn transgenic animals and nontransgenic littermate controls were performed at 3, 8, 20, and 28 wk of age. Early renal changes of transgenic mice consisted of podocyte hypertrophy, reduced numerical volume density of podocytes in glomeruli, and homogenous thickening of the glomerular basement membrane, followed by renal and glomerular hypertrophy as well as mesangial expansion and matrix accumulation. At 28 wk of age, glomerular damage was most prominent, including advanced glomerulosclerosis, tubulointerstitial lesions, and proteinuria. Real-time PCR demonstrated increased glomerular expression of Col4a1, Fn1, and Tgfb1. Immunohistochemistry revealed increased mesangial deposition of collagen type IV, fibronectin, and laminin. The present study shows that GIPRdn transgenic mice exhibit renal changes that closely resemble diabetes-associated kidney alterations in humans. Data particularly from male transgenic mice indicate that podocyte hypertrophy is directly linked to hyperglycemia, without the influence of mechanical stress. GIPRdn transgenic mice are considered an excellent new tool to study the mechanisms involved in onset and progression of diabetic nephropathy.