Studies on a diabetic (KK) strain of the mouse

Approaches to lipid metabolism gene identification and characterization in the postgenomic era

The availability of genomic resources has already had a tremendous impact on biomedical research. In this review, we describe how whole genome sequence and high-throughput functional genomics projects have facilitated the identification and characterization of important genes in lipid metabolism and disease. We review key approaches and lipid genes identified in the first years of this century and discuss how genomic resources are likely to streamline gene identification and functional characterization in the future.

Reduction in ABCG1 in Type 2 diabetic mice increases macrophage foam cell formation

Atherosclerosis development is accelerated severalfold in patients with Type 2 diabetes. In the initial stages of disease, monocytes transmigrate into the subendothelial space and differentiate into foam cells. Scavenger receptors and ATP binding cassette (ABC) Transporters play an important role in foam cell formation as they regulate the influx and efflux of oxidized lipids. Here, we show that peritoneal macrophages isolated from Type 2 diabetic db/db mice have decreased expression of the ABC transporter ABCG1 and increased expression of the scavenger receptor CD36. We found a 2-fold increase in accumulation of esterified cholesterol in diabetic db/db macrophages compared with wild-type control macrophages. Diabetic db/db macrophages also had impaired cholesterol efflux to high density lipoprotein but not to lipid-free apo A-I, suggesting that the increased esterified cholesterol in diabetic db/db macrophages was due to a selective loss of ABCG1-mediated efflux to high density lipoprotein. Additionally, we were able to confirm down-regulation of ABCG1 using C57BL/6J peritoneal macrophages cultured in elevated glucose in vitro (25 mM glucose for 7 days), suggesting that ABCG1 expression in diabetic macrophages is regulated by chronic exposure to elevated glucose. Diabetic KK(ay) mice were also studied and were found to have decreased ABCG1 expression without an increase in CD36. These observations demonstrate that ABCG1 plays a major role in macrophage cholesterol efflux and that decreased ABCG1 function can facilitate foam cell formation in Type 2 diabetic mice.

Animal models of diabetes mellitus

Animal models have been used extensively in diabetes research. Early studies used pancreatectomised dogs to confirm the central role of the pancreas in glucose homeostasis, culminating in the discovery and purification of insulin. Today, animal experimentation is contentious and subject to legal and ethical restrictions that vary throughout the world. Most experiments are carried out on rodents, although some studies are still performed on larger animals. Several toxins, including streptozotocin and alloxan, induce hyperglycaemia in rats and mice. Selective inbreeding has produced several strains of animal that are considered reasonable models of Type 1 diabetes, Type 2 diabetes and related phenotypes such as obesity and insulin resistance. Apart from their use in studying the pathogenesis of the disease and its complications, all new treatments for diabetes, including islet cell transplantation and preventative strategies, are initially investigated in animals. In recent years, molecular biological techniques have produced a large number of new animal models for the study of diabetes, including knock-in, generalized knock-out and tissue-specific knockout mice.

Confirmation and characterization of murine body weight QTLs, Bwq1 and Bwq2, identified in C57BL/6J x KK-Ay/a F2-Ay/a mice

Body weight quantitative trait loci (QTLs), Bwq1 and Bwq2, identified previously in C57BL/6J x KK-Ay/a F2-Ay/a mice, were further confirmed and characterized. Body weight measurement was done from 21 days after birth (Day 21) through Day 100, at 10-day intervals. Bwq1 was statistically significant only on Days 40, 50, and 60, whereas Bwq2 was statistically significant on and after Day 40. When body weight gain (WG) between two successive weight measurements was evaluated, both Bwq1 and Bwq2 were statistically significant only for WG between Days 30 and 40. The results suggest that variations in body weight among F2-Ay/a individuals in later life have been determined by variations in WG during the period shortly after weaning. The results also suggest that Bwq1 is related to increased body weight in the KK strain, because the effect of Bwq1 on the body weight is observed not only in F2-Ay/a, but also in F2-a/a. On the other hand, it is suggested that Bwq2 is related to enhanced obesity caused by Ay mutation and therefore is a genetic modifier that specifically interacts with the Ay allele, because the effect of Bwq2 is only observed in F2-A y/a. There are two candidate genes, Pparg and Hrh1, which are located near the 95% confidence interval of Bwq2, and which are expressed in the adipose tissue; however, we could not find any nucleotide differences in both cDNAs between KK and C57BL/6J strains.

Lipoprotein lipase activator NO-1886 improves fatty liver caused by high-fat feeding in streptozotocin-induced diabetic rats

NO-1886 is a lipoprotein lipase (LPL) activator. Administration of NO-1886 results in an increase in plasma high-density lipoprotein cholesterol (HDL-C) and a decrease in plasma triglyceride (TG) levels. The aim of this study was to ascertain whether NO-1886 improves fatty liver caused by high-fat feeding in streptozotocin (STZ)-induced diabetic rats. Administration of NO-1886 resulted in increased plasma HDL-C levels and decreased TG levels without affecting total cholesterol and glucose levels in the diabetic rats. NO-1886 dose-dependently decreased liver TG contents and cholesterol contents, resulting in improvement of fatty liver. NO-1886 also reduced plasma aspartate aminotransferase (AST) and alanine aminotransferase (ALT) that accompany fatty liver. The liver cholesterol contents were inversely correlated with plasma HDL-C levels (r = -0.5862, P <.001) and were positively correlated with plasma TG levels (r = 0.4083, P <.003). The liver TG contents were inversely correlated with plasma HDL-C levels (r = -0.6195, P <.001) and were positively correlated with plasma TG levels (r = 0.5837, P <.001). There was no correlation between plasma cholesterol levels, and cholesterol and TG contents in liver. These results indicate that reducing plasma TG levels and elevating in HDL-C levels may result in improving fatty liver.

Lamr1 functional retroposon causes right ventricular dysplasia in mice

Arrhythmogenic right ventricular dysplasia (ARVD) is a hereditary cardiomyopathy that causes sudden death in the young. We found a line of mice with inherited right ventricular dysplasia (RVD) caused by a mutation of the gene laminin receptor 1 (Lamr1). This locus contained an intron-processed retroposon that was transcribed in the mice with RVD. Introduction of a mutated Lamr1 gene into normal mice by breeding or by direct injection caused susceptibility to RVD, which was similar to that seen in the RVD mice. An in vitro study of cardiomyocytes expressing the product of mutated Lamr1 showed early cell death accompanied by alteration of the chromatin architecture. We found that heterochromatin protein 1 (HP1) bound specifically to mutant LAMR1. HP1 is a dynamic regulator of heterochromatin sites, suggesting that mutant LAMR1 impairs a crucial process of transcriptional regulation. Indeed, mutant LAMR1 caused specific changes to gene expression in cardiomyocytes, as detected by gene chip analysis. Thus, we concluded that products of the Lamr1 retroposon interact with HP1 to cause degeneration of cardiomyocytes. This mechanism may also contribute to the etiology of human ARVD.

Regulation of the angiopoietin-like protein 3 gene by LXR

Angiopoietins are members of the vascular endothelial growth factor family. One family member, angiopoietin-like protein 3 (Angptl3), was recently shown to be predominantly expressed in the liver and to play an important role in regulating lipid metabolism. In this study, we show that the Angptl3 gene is a direct target of the liver X receptor (LXR). Mice fed a high cholesterol diet exhibited a significant increase in Angptl3 expression in the liver. Oral administration to mice of T0901317, a synthetic LXR-selective agonist, increases levels of plasma lipids and Angptl3 mRNA in the liver. Treatment of HepG2 cells with LXR selective agonists led to a dose-dependent increase of Angptl3 mRNA. Analysis of the DNA sequence just 5' of the Angptl3 transcriptional start site revealed the presence of several potential transcription factor binding sites, including that for LXR. When transfected into HepG2 cells, the promoter activity of Angptl3 was significantly induced by LXR- or retinoid X receptor-selective agonists. Mutation of the predicted LXR binding site (DR4 element) completely abolished the LXR agonist-mediated activation of the promoter. Together, these studies show that Angptl3 is transcriptionally regulated by LXR, and reveals a novel mechanism by which LXR may regulate lipid metabolism.

A quantitative trait locus that accounts for glucose intolerance maps to chromosome 8 in hereditary obese KK-A(y) mice

KK and KK-A(y) mice serve as animal models of non-insulin-dependent diabetes mellitus with moderate obesity. Quantitative trait locus (QTL) analysis was performed to identify gene loci that account for fasting hyperglycemia, glucose intolerance and plasma insulin in 91 F(2) females of a C57BL/6JxKK-A(y) intercross. For glucose intolerance, a significant QTL was identified on chromosome 8, with a maximum lod score of 5.6. This locus had strong influence on the late phase of the intraperitoneal glucose tolerance test (IPGTT), suggesting that the locus may have role in glucose clearance rather than in mere hyperglycemia. In addition, three suggestive QTLs were identified on chromosomes 1 (fasting glucose), 3 (fasting insulin) and 4, (blood glucose at 120 min during IPGTT, and glucose intolerance).

ANGPTL3 decreases very low density lipoprotein triglyceride clearance by inhibition of lipoprotein lipase

KK/San is a mutant mouse strain established in our laboratory from KK obese mice. KK/San mice show low plasma lipid levels compared with wild-type KK mice despite showing signs of hyperglycemia and hyperinsulinemia. Recently, we identified a mutation in the gene encoding angiopoietin-like protein 3 (Angptl3) in KK/San mice, and injection of adenoviruses encoding Angptl3 or recombinant ANGPTL3 protein to mutant KK/San mice raised plasma lipid levels. To elucidate the regulatory mechanism of ANGPTL3 on lipid metabolism, we focused on the metabolic pathways of triglyceride in the present study. Overexpression of Angptl3 in KK/San mice resulted in a marked increase of triglyceride-enriched very low density lipoprotein (VLDL). In vivo studies using Triton WR1339 revealed that there is no significant difference between mutant and wild-type KK mice in the hepatic VLDL triglyceride secretion rate. However, turnover studies using radiolabeled VLDL revealed that the clearance of (3)H-triglyceride-labeled VLDL was significantly enhanced in KK/San mice, whereas the clearance of (125)I-labeled VLDL was only slightly enhanced. In vitro analysis of recombinant protein revealed that ANGPTL3 directly inhibits LPL activity. These data strongly support the hypothesis that ANGPTL3 is a new class of lipid metabolism modulator, which regulates VLDL triglyceride levels through the inhibition of LPL activity.

Angptl3 regulates lipid metabolism in mice

The KK obese mouse is moderately obese and has abnormally high levels of plasma insulin (hyperinsulinemia), glucose (hyperglycemia) and lipids (hyperlipidemia). In one strain (KK/San), we observed abnormally low plasma lipid levels (hypolipidemia). This mutant phenotype is inherited recessively as a mendelian trait. Here we report the mapping of the hypolipidemia (hypl) locus to the middle of chromosome 4 and positional cloning of the autosomal recessive mutation responsible for the hypolipidemia. The hypl locus encodes a unique angiopoietin-like lipoprotein modulator, which we named Allm1. It is identical to angiopoietin-like protein 3, encoded by Angptl3, and has a highly conserved counterpart in humans. Overexpression of Angptl3 or intravenous injection of the purified protein in KK/San mice elicited an increase in circulating plasma lipid levels. This increase was also observed in C57BL/6J normal mice. Taken together, these data suggest that Angptl3 regulates lipid metabolism in animals.

Podocyte injury promotes progressive nephropathy in zucker diabetic fatty rats

The zucker diabetic fatty (ZDF-fa/fa) rat is one of the attractive models for type II diabetes based on impaired glucose tolerance caused by the inherited insulin-resistance gene fa. Characterization of nephropathy in this model may provide useful insights into the mechanism of the progression of diabetic nephropathy. The present study analyzed the pathophysiology of diabetes and nephropathy, including the process of glomerulosclerosis in this model by biochemical and morphometric analyses. In addition, we conducted studies in podocytes in culture to examine the direct effects of high glucose on podocytes. ZDF-fa/fa rats showed overt diabetes despite hyperinsulinemia as early as 3 months of age. Blood glucose levels increased further with a considerable decrease of insulin levels at 5 months. Glomerular filtration rate (GFR) was significantly elevated until 3 months, but fell to the level seen in lean rats by 7 months. Proteinuria started to rise during the period of increased GFR, and increased further after GFR had fallen to within the normal range. Renal fibronectin, collagen iv, and vascular endothelial growth factor mRNA levels were increased at 7 months. Glomerulosclerosis commenced as early as 5 months of age, and was associated with glomerular hypertrophy and mild mesangial expansion with evidence of accentuated podocyte injury, as revealed by increased expression of desmin. Electron microscopy suggested that degeneration of podocytes and the development of tuft adhesions were responsible for the glomerular sclerosis in this model. In addition, glomeruli from the diabetic rats showed up-regulation of the cyclin kinase inhibitors, p21 and p27. Further studies suggested that the increase in p27 expression was predominantly caused by podocytes, because predominant immunolocalization of p27 in podocytes in diabetic rats and high glucose medium induced cell hypertrophy accompanied by p27 up-regulation in differentiated podocyte cell lines. In conclusion, progressive diabetic nephropathy in ZDF-fa/fa rats is associated with evidence of podocyte injury. High concentrations of ambient glucose induced podocyte hypertrophy and stress in vitro, suggesting that the podocyte is a likely target of the diabetic milieu.

Disease model: hyperinsulinemia and insulin resistance. Part B--polygenic and other animal models

Deficiency of leptin or its receptor produces hyperinsulinemia with marked obesity. Paradoxically, severe insulin resistance also accompanies lipodystrophy. Animal models of these contrasting conditions have enabled us to observe the profound and complicated aspects of the underlying pathologies. In addition, conventional polygenic rodents with known genetic backgrounds, such as the spontaneously hypertensive rat and the Goto-Kakisaki rat, have also been used to investigate these abnormalities.

Complex trait analysis in the mouse: The strengths, the limitations and the promise yet to come

In 1990, David Baltimore predicted that the 1990s would be the decade of the mouse (). This certainly proved to be true: The mouse has contributed immensely to biological research through transgenic, embryonic stem cell (ES) knockout, and classical genetic technologies. But its usefulness as a model organism is by no means over; indeed it is still rising to its peak: The mouse as a model mammalian organism still has much to offer. This article reviews use of the mouse to dissect complex genetic traits using quantitative trait analysis, with a particular emphasis on medically important diseases.

Electrophysiological properties of ventricular muscle obtained from spontaneously diabetic mice

The electrophysiological properties of cardiac muscle in KK/Ta mouse (hereafter referred to as KK mouse), an animal model of human non-insulin-dependent diabetes mellitus, were investigated, and the findings compared with those obtained from a non-diabetic control mouse (C57BL/6J mouse; referred to as B6 mouse). The ages of the B6 mice were 23.9 +/- 5.4 weeks (n = 24) and those of the KK mice used were 25.7 +/- 10.8 weeks (n = 34). The KK mice had mild obesity, hyperglycemia and hyperinsulinemia. Ventricular muscles from both mice were examined by light microscopy. Partial myocardial fibrosis and filament disorder in the ventricular muscles were found only in the KK mice. The resting membrane potential of the ventricular muscle was less negative in the KK mice than in the control mice. The maximum rate of rise in the upstroke of the action potential was significantly decreased in the KK mice compared with that of the control mice. These suggest a decrease in a time-independent K+ current (IK1) in the KK mice. The duration of the action potential (APD) at all levels of repolarization was significantly longer in the KK mice than in the B6 mice. A blocker of transient outward current (I(to)), 4-aminopyridine, significantly prolonged the APD of the B6 mice, but failed to prolong it in the KK mice, suggesting that Ito in the diabetic mice is very small. A Ca2+ channel blocker, CoCl2, dramatically lengthened all levels of APD in both groups, suggesting that there is no difference between B6 mice and KK mice in L-type Ca2+ current via Ca2+ channels. These suggest the malfunction or deficiency of ionic channels which carry, at least Ito and IK1 in diabetic mice.

Leptin and leptin receptor expression in normal and neoplastic human pituitary: evidence of a regulatory role for leptin on pituitary cell proliferation

Leptin is a circulating hormone secreted by adipose and a few other tissues. The leptin receptor consists of a single transmembrane-spanning polypeptide that is present as a long physiologically important form as well as in several short isoforms. Recent studies have suggested that the anterior pituitary may have a role in the regulatory effects of leptin in animal models. To test this possibility in human pituitaries, we examined the expression of leptin and OB-R in normal and neoplastic pituitaries, and the possible functions of leptin in the pituitary were also analyzed. Leptin was present in 20-25% of anterior pituitary cells and was expressed in most normal anterior pituitary cells, including ACTH (70% of ACTH cells), GH (21%), FSH (33%), LH (29%), TSH (32%), and folliculo-stellate cells (64%), but was colocalized with very few PRL cells (3%), as detected by double labeling immunohistochemistry with two different antileptin antibodies. In addition, leptin expression was detected by RT-PCR in some pituitary tumors, including ACTH (three of four), GH (one of four), null cells (two of four), and gonadotroph (one of four) tumors as well as in normal pituitary. Immunohistochemical staining showed greater immunoreactivity for leptin in normal pituitaries compared to adenomas. Treatment of an immortalized cultured anterior pituitary cell line, HP75, with leptin stimulated pancreastatin secretion in vitro. Leptin also inhibited cell growth in the human HP75 and in the rat pituitary GH3 cell lines. Both long (OB-Rb) and common (OB-Ra) forms of the leptin receptor messenger ribonucleic acid and leptin receptor protein were expressed in normal and neoplastic anterior pituitary cells. These findings show for the first time that leptin is expressed by most human anterior pituitary cell types and that there is decreased leptin protein immunoreactivity in pituitary adenomas compared to that in normal pituitary tissues. We also show that OB-Rb is widely expressed by normal and neoplastic anterior pituitary cells, implicating an autocrine/paracrine loop in the production and regulation of leptin in the pituitary.

Quantitative trait loci that regulate plasma lipid concentration in hereditary obese KK and KK-Ay mice

To identify quantitative trait loci (QTLs) responsible for regulating plasma lipid concentration associated with obesity, linkage analysis was carried out on the 190 F2 progeny of a cross between C57BL/6J female and KK-Ay (Ay allele at the agouti locus congenic) male. In F2 a/a (agouti locus genotype) mice, two QTLs were identified on chromosome 1 and a QTL on chromosome 3 for total-cholesterol. A QTL for HDL-cholesterol was identified on chromosome 1 and a QTL for NEFA on chromosome 9. In F2 Ay/a mice, two QTLs for HDL-cholesterol were found on chromosome 1. Loci for other lipids with suggestive linkage were also identified. In both F2 mice, one QTL on chromosome 1 for total- and HDL-cholesterol was mapped near D1Mit150, in the vicinity of the apolipoprotein A-II (Apoa2) locus. Seven nucleotide substitutions out of 309 nucleotide apolipoprotein A-II cDNA sequences were identified between KK and C57BL/6J. The Ay allele may be an indication of the plasma lipid levels, but its influence was less apparent than in the case of weight control. The loci for lipids were not on identical chromosomes with those previously identified for obesity, suggesting that hyperlipidemia in KK does not coincidentally occur with obesity.

Role of nerve growth factor in cutaneous wound healing: accelerating effects in normal and healing-impaired diabetic mice

Four full-thickness skin wounds made in normal mice led to the significant increase in levels of nerve growth factor (NGF) in sera and in wounded skin tissues. Since sialoadenectomy before the wounds inhibited the rise in serum levels of NGF, the NGF may be released from the salivary gland into the blood stream after the wounds. In contrast, the fact that messenger RNA and protein of NGF were detected in newly formed epithelial cells at the edge of the wound and fibroblasts consistent with the granulation tissue produced in the wound space, suggests that NGF was also produced at the wounded skin site. Topical application of NGF into the wounds accelerated the rate of wound healing in normal mice and in healing-impaired diabetic KK/Ta mice. This clinical effect of NGF was evaluated by histological examination; the increases in the degree of reepithelialization, the thickness of the granulation tissue, and the density of extracellular matrix were observed. NGF also increased the breaking strength of healing linear wounds in normal and diabetic mice. These findings suggested that NGF immediately and constitutively released in response to cutaneous injury may contribute to wound healing through broader biological activities, and NGF improved the diabetic impaired response of wound healing.

Improvement of glucose tolerance with immunomodulators on type 2 diabetic animals

Cytokine-inducers prevent insulin-dependent diabetes mellitus (IDDM) in animal models. We extend this therapy to non-insulin-dependent diabetes mellitus (NIDDM), because it was reported that diabetes of KK-Ay mice, a model for NIDDM, was recovered by allogenic bone-marrow transplantation that also prevented IDDM in animal models. An i.p. or i.v. injection of streptococcal preparation (OK-432) lowered fasting blood glucose (FBG) levels and markedly improved glucose tolerance test (GTT) in KK-Ay mice for more than 32 h regardless of the glucose loading routes (oral, i.v. or i.p.), while an i.v. injection of BCG improved FBG and GTT for more than 4 wks without body weight loss. The improvement of FBG and GTT with OK-432 was brought about in other NIDDM animals, GK rats and Wistar fatty rats. Among various cytokines possibly induced by OK-432 and BCG, IL-1 alpha, TNF alpha and lymphotoxin significantly improved FBG and GTT in KK-Ay mice, whereas IL-2 and IFN gamma did not. There were no differences between the OK-432-treated KK-Ay mice and control in histology of the pancreas, degree of insulin-induced decrease in blood glucose levels, and muscle glycogen synthase activities. As to insulin secretion, there is a tendency that the OK-432-treatment less that 1 week did not affect insulin levels during GTT, whereas the treatment more than 2 weeks increased the insulin levels. Thus, cytokine-inducers improved FBG and glucose tolerance of NIDDM animals probably via cytokines. The results imply a role of the cytokines in glucose tolerance of NIDDM, although precise immune and metabolic mechanisms remain to be elucidated.

Bone marrow transplantation as a strategy for treatment of non-insulin-dependent diabetes mellitus in KK-Ay mice

The effects of allogeneic bone marrow transplantation (BMT) on non-insulin-dependent diabetes mellitus (NIDDM) were examined using KK-Ay mice. KK-Ay mice reconstituted with KK-Ay bone marrow cells showed glycosuria, hyperinsulinemia, and hyperlipidemia. However, KK-Ay mice (H-2b) that had been lethally irradiated (9.0 Gy) and then reconstituted with T cell-depleted bone marrow cells from normal BALB/c mice (H-2d) showed negative urine sugar with decreases in serum insulin and lipid levels 4 mo after BMT. Morphological recovery of islets and glomeruli was also noted after allogeneic BMT. These findings suggest that BMT can be used to treat not only a certain type of NIDDM but also its complications such as hyperlipidemia and diabetic nephropathy.

Hyperlipoproteinemia in spontaneously diabetic guinea pigs

A colony of Hartley guinea pigs that exhibit hyperglycemia, glucosuria, and hypertriglyceridemia characteristic of human diabetes mellitus was developed. Initially, a group of guinea pigs that had normal serum glucose concentrations (less than or equal to 200 mg/dL of serum) at 3 to 4 weeks of age was obtained; however, in some of the animals progressively severe hyperglycemia (300 to 500 mg/dL of serum) and glucosuria (greater than 2 g of glucose/24 h) occurred as the animals matured. In addition, the animals exhibiting hyperglycemia and glucosuria had plasma insulin concentrations that were similar to those animals that were not hyperglycemic. The diabetic animals were found to be hypertriglyceridemic, with plasma triglyceride levels of 140 to 290 mg/dL at four months of age. Nondiabetic animals (plasma glucose concentration of less than or equal to 200 mg/dL and no glucosuria) had plasma triglyceride concentrations between 37 and 76 mg/dL. Lipoprotein analysis of plasma from nondiabetic and diabetic animals indicated that the diabetics had a fourfold increase in VLDL triglyceride and protein concentrations. The VLDL had an abnormal apolipoprotein composition and had reduced levels of apoprotein-E. The progeny from the mating of diabetic males and females also exhibited the diabetic trait, suggesting that the origin of the disease is genetic. This colony of guinea pigs is being further investigated as a suitable model for the study of the hyperlipoproteinemia of human noninsulin-dependent diabetes mellitus.

Renal vessel changes in diabetic KK-mice

Glomerular hyperfiltration is thought to be of pathogenic importance in the structural abnormalities seen in diabetic nephropathy but its cause is not known. It has been suggested that the changes in the preglomerular vascular system may lead to a disturbance of glomerular blood flow in diabetes. We therefore examined the potential role of changes in the vascular system supplying the glomerulus in diabetic mice. The kidneys of 15 diabetic KK-mice (aged 2, 5 and 12 months) were studied and compared with those of 15 non-diabetic NMRI-mice. We determined vessel cross-sectional, wall and lumen areas of 408 small intrarenal arteries, 5,140 arterioles and 518 preglomerular afferent arterioles using a morphometric method. At 2 months, diabetic arteries and arterioles were considerably smaller than the controls, while preglomerular afferent arterioles were the same size. At 12 months, however, all diabetic vessels measured were much larger than the controls. This was chiefly due to an excessive increase in lumen area: in the diabetic arteries the mean (+/- SEM) lumen area at 12 months was 1,057 +/- 142 vs 616 +/- 72 sq mu in controls (P less than 0.001), in arterioles 176 +/- 7 vs 115 +/- 4 sq mu (P less than 0.001) and in preglomerular afferent arterioles (at 5 months) 131 +/- 8 vs 95 +/- 7 sq mu (P less than 0.001). The dilatation of small intrarenal arteries and arterioles in diabetic mice may result from progressive impairment of vasoconstriction and may be a cause of the glomerular hyperfiltration in diabetes.

Morphological aspects on pancreatic islets of non-obese diabetic (NOD) mice

The pancreatic islets of female non-obese diabetic (NOD) mice (a model of insulin-dependent diabetes mellitus), have been examined by both light and electron microscopy. At about the age of 2 weeks, mononuclear cells began to infiltrate in or near the islets and some of these cells were in contact with the islet cells. Following this degeneration of islet B-cells took place, the process occurring in two ways. In many cells numerous secretory granules with extremely dense cores occupied the cytoplasm. Other cells, however, were filled with low-density secretory granules and the nuclei of these cells became pycnotic. After degeneration of B-cells, the islets were effaced by numerous mononuclear cells. With the onset of the diabetic state these mononuclear cells gradually disappeared, and thereafter small islets remained. By electron microscopy, retrovirus-like particles were observed in cisternae of the rough endoplasmic reticulum in islet B-cells at all stages. With an anti-retrovirus serum (goat anti-KiMSV-NIHxeno serum), positive immunofluorescence was observed in some pancreatic islet cells of NOD mice aged 1 day and 4, 6, 8, 9, 10 and 14 weeks. It is suggested that these virus particles may be intimately related to the inflammatory reaction occurring in the islets and to the development of diabetes mellitus.

Cultured heart cells from the spontaneously diabetic KK mouse

In order to clarify the mechanism of myocardial changes in KK mice, cultured heart cells from both normal and spontaneously diabetic KK mice were studied by electron microscopy, photoelectric recording, and 45Ca activity. Compared with cultured heart cells from normal mice, those from KK mice showed a decrease in beating frequency and ceased beating more rapidly. The rhythm of the beating cells from KK mice became irregular, while that of the heart cells from normal mice was not changed significantly over a period of 10 days. Electron micrographs of cultured heart cells from KK mice showed an increased number of mitochondria, an intricate arrangement of myofibrils, poorly formed Z bands, and a lipidlike substance. The 45Ca activity of heart cells from KK mice, after incubation for 24 h in a medium containing 45Ca, was increased compared with heart cells from normal mice. Based on these findings, we conclude that ultrastructural alterations exist in cultured heart cells from KK mice and we suggest that an increase of intracellular Ca might play an important role in the pathogenesis.

Histologic and ultrastructural studies on the myocardium in spontaneously diabetic KK mice: a new animal model of cardiomyopathy

The hearts from spontaneously diabetic KK mice and control mice were examined by light and electron microscopy. Myocardial degeneration, myocardial fibrosis and calcium deposits in the myocardium were extensive in KK mice aged 8 weeks. In myocytes of newborn KK mice, an irregular arrangement of myofibrils and poorly formed Z bands were found. Ultrastructural changes in myocytes of KK mice aged 4 weeks consisted of destruction of mitochondria, degenerated myofibrils and abnormalities of Z bands. However, increased mucopolysaccharides in interstitium and thickened basement membranes of capillaries were not found in KK mice, in contrast to the previous reports of myocardial changes in diabetic C57BL/KsJ mice, alloxan-diabetic dogs and hypertensive-diabetic rats. These observations suggest that the cardiomyopathy found in KK mice is not secondary to diabetes mellitus but is caused by other factors. In conclusion, myocardial ultrastructural abnormalities are present in newborn KK mice. Thus, this animal can be used as a model of cardiomyopathy.

Hypoglycemic activity of 1-alpha-(3,4-dimethoxyphenethylaminomethyl) -2-hydroxybenzylalcohol 1/2 fumarate (TA-078) in the mouse, rat and dog

1-alpha-(3,4-Dimethoxyphenethylaminomethyl)-2-hydroxybenzylalcohol 1/2 fumarate (TA-078) is a new hypoglycemic agent structurally different from any existing hypoglycemic drug. It depresses the rise of blood glucose when it is orally administered to glucose-loaded mice, rats and beagle dogs at minimal doses of 1, 10 and 2.5 mg/kg, respectively. In contrast with tolbutamide, TA-078 hardly affected fasting blood glucose levels in rats and dogs and only weakly reduced fasting blood glucose levels in mice. Oral administration of TA-078 to KK mice also improved glucose tolerance, while no improvement was observed in streptozotocin-diabetic rats. TA-078 elevated plasma immunoreactive insulin (IRI) levels in mice and rats soon after its oral administration. In fasted rats, TA-078 caused only a transient increase in plasma IRI but did not affect plasma immunoreactive glucagon (IRG) levels in the early phase after its administration. On the other hand, tolbutamide induced a sustained increase in plasma IRI and a transient but marked decrease in plasma IRG. In perfused rat pancreas, TA-078 stimulated insulin secretion. The stimulation by 10 micrograms/ml TA-078 in the perfusion liquid required the presence of a normal concn (5.6 mM) of glucose, whereas the same concn of tolbutamide stimulated insulin release even at a low glucose concn (2.8 mM).

Islet organ, blood glucose and glucose tolerance of lean and obese Mongolian gerbils. A quantitative study

Gerbils were divided, on the basis of body weight, into obese (greater than 80 gms) and lean (less than 80 gms) groups. Fasting blood glucose estimations on all 31 gerbils, and glucose tolerance tests on 9 lean and 6 obese animals, were carried out. All lean and some obese gerbils were normoglycaemic and other obese were hyperglycaemic. All obese gerbils exhibited glucose intolerance. General morphological studies were undertaken as follows: (i) assessment of mesenteric fat deposits, (ii) measurement of anterior abdominal wall thickness, (iii) ratio of animal length to width at specified loci (index of shape). The degree of obesity was less than previously reported in this species though blood glucose abnormality was comparable. The index of animal shape showed a strong correlation with body weight. The following kinds of histological observation were made on pancreases from 4 lean and 4 obese gerbils: (i) % islet representation, (ii) islet size distribution, (iii) beta-cell granularity, (iv) islet vascularity, (v) islet/duct association, (vi) proportions of alpha- and D-cells, (vii) glycogen deposition in islet and duct cells. The pancreases of obese gerbils contained a higher proportion of islet tissue than those of lean due to generally larger islets: this hyperplasia was mainly attributable to beta-cell proliferation. Many obese gerbil islets exhibited hyperaemia and beta-cell degranulation. There was no evidence of glycogen deposition.

Laboratory animals exhibiting obesity and diabetes syndromes

Spontaneous hyperglycemia, hyperinsulinemia and obesity are common features for at least one period of the lifetime in some strains of mice. Both genetic and environmental factors are involved in the pathogenesis of the diabetes-like syndrome, making these strains excellent models for studies in both obesity and diabetes-like states. The metabolic peculiarities can be due to a dominant gene, as for the yellow obese, or a single recessive gene, as in the obese and the diabetes mouse; or they can be of polygenic origin, as for the KK and the NZO mouse. However, the severity of the metabolic disorder is due to the interaction of the mutant genes iwth modifiers in the bat genes themselves. Studies on the pathophysiology and biochemistry of these animals have revealed interstrain differences, different patterns of development of the metabolic disorder, and different degrees of severity of the diabetes-like syndrome. Although the primary causes of the syndrome remain unclear in some strains, an involvement of hypothalamic feeding centers has been implicated.

Pre- and postnatal distribution of lipids in the liver of genetic diabetic mice

Triglycerides, phospholipids, cholesterol and cholesterol esters were determined by thin layer chromatography in the fetal and neonate livers of normal (Swiss albino) and genetic diabetic (KK) mice. In general, the lipids were elevated in the fetal liver of the KK mice. Despite this elevation in liver lipids, no increase in the weight of the newborn was observed.

Decreased binding of insulin to liver plasma membrane receptors in hereditary diabetic mice

The interaction of insulin with its receptors was studied in liver plasma membranes of the young non-obese hereditary diabetic mouse (KK strain). Under identical conditions of preparation and incubation, the membranes of the KK mouse bind only 55-70% as much insulin per mg of protein as those of the control mouse (Swiss albino). Scatchard analysis suggests that this decrease in binding is due to a decrease in the number of receptor sites in the membrane of the diabetic mouse. However, the membranes of diabetic and control mice do not exhibit significant differences in hexosamine and sialic acid contents, enzyme activities, and protein and glycoprotein analysis. The decrease in insulin receptors in the KK mouse seems to correlate with the insulin resistance which they exhibit.