Transgenic mice for the study of diabetes mellitus

Correction of autophagy impairment inhibits pathology in the NOD.H-2h4 mouse model of primary Sjögren's syndrome

Dysregulation of autophagy has been implicated in the development of various disease indications including autoimmune diseases. Here we identified hitherto unsuspected molecular alterations of autophagy occurring at an early stage of the macroautophagy pathway in the salivary glands and spleen of NOD.H-2h4 mice that develop a primary Sjögren's-like syndrome. In this study we investigated the capacity of phosphopeptide P140 to correct immune alteration in NOD.H-2h4 mice and the effect on neogenesis of tertiary lymphoid structures in salivary glands, which is hallmark characteristic of SS. Phosphopeptide P140 known to lower excessive autophagy processes, rescued sick NOD.H-2h4 mice from some autophagy defects and significantly reduced formation of tertiary lymphoid structures in salivary glands. Mechanistically, the frequency of activated CD44^high/CD62L^low CD4⁺ T cell populations was significantly decreased and this reduction was correlated with an increased number of CD44^low/CD62L^high resting T cells. The CD8 T cell compartment was not affected. P140 down-regulated the maturation and differentiation of B cells into plasma cells, and decreased IgG and autoantibody secretion. It had no effect on germinal centers B cells (B220⁺ FAS⁺GL-7⁺) that are an important compound of the B cell humoral immune response. Together with previous data generated in MRL/lpr mice that develop some features of Sjögren's syndrome associated to other inflammatory and autoimmune defects, our present findings strongly reinforce the potential of autophagy modulators, such as P140, for treating patients with Sjögren's syndrome.

Lessons from transgenic and knockout animals about noninsulin-dependent diabetes mellitus

The application of transgenic techniques to alter gene expression in vivo has provided new models to evaluate the role of specific genes in the complex pathogenesis of noninsulin-dependent diabetes mellitus (NIDDM). In this review, we summarize methods used to create transgenic animals and highlight results from those models which have contributed to our understanding of the overall pathophysiology of NIDDM. Transgenic animal models have clearly demonstrated the requirement for normal insulin action in skeletal muscle, adipose tissue, and liver, as well as normal insulin secretion by the pancreatic beta-cell, in the maintenance of glucose homeostasis. In addition, these data confirm that isolated defects in single critical genes, including the insulin receptor, IRS-1, and glucokinase, may play a role in the development of some types of insulin resistance and NIDDM. However, it is likely that multiple additive defects, both genetic and acquired, are required to produce the full clinical syndrome typical of more common forms of NIDDM.

Defective glycolysis and calcium signaling underlie impaired insulin secretion in a transgenic mouse

Pancreatic beta cells from mice that overexpress the Ca(2+)-binding protein calmodulin have a unique secretory defect that leads to chronic hyperglycemia. To further understand the molecular basis underlying this defect, we have studied signaling pathways in these beta cells. Measurements of cytosolic free Ca2+ concentration ([Ca2+]i) using fura-2 or indo-1 revealed a markedly reduced response when glucose was the stimulant. However, eliciting membrane depolarization with 50 mM K+ or the addition of the ATP-sensitive K+ (K+ ATP) channel antagonist tolbutamide restored [Ca2+]i transients to near normal levels. Electrophysiological analysis of the beta cell ion channels revealed that Ca2+ currents, delayed rectifier K+ currents, and K+ATP channel currents were similar in transgenic and nontransgenic cells, suggesting that these ion channels were able to function normally. However, whereas K+ATP channel currents in control cells were reduced by 50% by the presence of high glucose, those in transgenic cells were unaltered. Addition of tolbutamide inhibited this channel and enhanced the secretion of insulin in response to glucose for both control and transgenic cells. As these observations implicated a metabolic defect, glucose utilization, which is an indicator of glucose metabolism and ATP production in beta cells, was measured and found to be reduced by 40% in the transgenic cells. These data support the contention that excessive levels of calmodulin may compromise the ability of the beta cell to metabolize glucose and to modulate the state of the K+ATP channel, resulting in an inadequate control of the membrane potential, which collectively impair [Ca2+]i and thus insulin secretion in response to glucose.

Models of human endocrine disorders in transgenic rodents

Although the primary etiology of some endocrine diseases is obvious, for many of them the initiating abnormality is not known. Usually this uncertainty is due to a slow development of significant clinical symptoms, combined with the fact that an abnormality in any one endocrine gland will lead to secondary endocrine abnormalities. The ability to introduce relatively specific and (sometimes) subtle genetic changes into rodents provides an opportunity to test hypotheses concerning primary events in human endocrine disorders. This review deals with the development of transgenic rodent models of the more common, classically defined human endocrine abnormalities.

Genetic control of diabetes mellitus

Genetic inheritance predisposing individuals to diabetes mellitus was discussed in this work group. The two forms of the disease, Type 1 (insulin-dependent) and Type 2 (non-insulin-dependent) were discussed separately since the pattern of inheritance and genes involved appear to be distinctly different. Within these subtypes there is considerable genetic heterogeneity, and superimposed environmental factors confound the analysis. New technologies that will allow finer molecular analysis, as well as new candidates genes, were presented.