Continuity of diabetes care among elderly Japanese patients: a medical record review study in a specialized diabetes clinic.

Aims: Continuity of diabetes care is relevant among elderly patients. The aim of this study is to investigate the impact of clinical characteristics on continuing outpatient visits to a specialized diabetes clinic in elderly Japanese patients with diabetes. Methods: We included outpatients with type 2 diabetes aged ≥ 65 years who first visited our clinic from 2006 to 2009. The information of patients' characteristics was obtained through medical record review from the CoDiC database. We have tracked whether the patients continued to visit the clinic until May 31, 2019. A Cox proportional hazards regression model identified variables related to withdrawal. Results: Among 128 patients, 63 patients (49.2%) were withdrawn during the follow-up periods. The average visit duration of withdrawals was 4.6 (range 1, 10) years. The patients who discontinued to visit were older (72.6 vs. 69.5 years old, p = 0.005) compared with those who continued to visit. No significant differences in clinical conditions such as complication of diabetes, Charlson Comorbidity Index and polypharmacy between the first and last visit were observed in each group. Age (≥ 75 years) was significantly associated with withdrawal (hazard ratio 2.72 [95% confidence interval 1.59, 4.63], p < 0.001). Except for age, no significant differences were observed in all variables when adjusted for confounders. Conclusions: Our findings indicated that continuous outpatient visits were difficult in elderly Japanese patients with diabetes. Older age (≥ 75 years) independently affected withdrawal. Future multicenter studies with adequate populations and social and geriatric factors are necessary to confirm our findings.

Skeletal muscle-specific HMG-CoA reductase knockout mice exhibit rhabdomyolysis: A model for statin-induced myopathy.

HMG-CoA reductase (HMGCR) catalyzes the conversion of HMG-CoA to mevalonic acid (MVA); this is the rate-limiting enzyme of the mevalonate pathway that synthesizes cholesterol. Statins, HMGCR inhibitors, are widely used as cholesterol-reducing drugs. However, statin-induced myopathy is the most adverse side effect of statins. To eludicate the mechanisms underlying statin the myotoxicity and HMGCR function in the skeletal muscle, we developed the skeletal muscle-specific HMGCR knockout mice. Knockout mice exhibited postnatal myopathy with elevated serum creatine kinase levels and necrosis. Myopathy in knockout mice was completely rescued by the oral administration of MVA. These results suggest that skeletal muscle toxicity caused by statins is dependent on the deficiencies of HMGCR enzyme activity and downstream metabolites of the mevalonate pathway in skeletal muscles rather than the liver or other organs.

Circulating malondialdehyde-modified LDL-related variables and coronary artery stenosis in asymptomatic patients with type 2 diabetes.

AIMS: To elucidate the levels of malondialdehyde-modified LDL (MDA-LDL)-related variables for predicting coronary artery stenosis (CAS) by coronary CT angiography (CCTA) in asymptomatic patients with type 2 diabetes (T2DM). METHODS: Enrolled were 36 Japanese patients with T2DM who underwent CCTA and in whom MDA-LDL levels were measured. Definition of CAS was luminal narrowing of ≥50%. Trends through tertiles of each MDA-LDL-related variable were analyzed with a general linear model. The ability of each MDA-LDL-related variable to predict CAS was compared to areas under the curve (AUCs) in receiver operating characteristic curve (ROC) analysis. RESULTS: Seventeen patients had CAS. Each MDA-LDL-related variable was an independent predictor of CAS (P = 0.039 for MDALDL, P = 0.013 for MDA-LDL/LDL-C, P = 0.047 for MDA-LDL/HDL-C, and P = 0.013 for (MDA-LDL/LDL-C)/HDL-C). AUCs of MDA-LDL, MDA-LDL/LDL-C, MDA-LDL/HDL-C, and (MDA-LDL/LDL-C)/HDL-C were 0.675 (95% CI 0.496-0.854), 0.765 (0.602-0.927), 0.752 (0.592-0.913), and 0.799 (0.643-0.955), respectively, for predicting CAS. Trends throughout the tertiles showed significant associations between MDA-LDL/LDL-C, MDA-LDL/HDL-C, or (MDALDL/LDL-C)/HDL-C and CAS (P = 0.003 for MDA-LDL/LDL-C, P = 0.042 for MDA-LDL/HDL-C, and P = 0.001 for (MDA-LDL/LDL-C)/HDL-C). CONCLUSIONS: Data suggest that measurements of MDA-LDL/LDL-C, MDA-LDL/HDLC, and (MDA-LDL/LDL-C)/HDL-C are useful for predicting CAS.

Hepatic CREB3L3 controls whole-body energy homeostasis and improves obesity and diabetes.

Transcriptional regulation of metabolic genes in the liver is the key to maintaining systemic energy homeostasis during starvation. The membrane-bound transcription factor cAMP-responsive element-binding protein 3-like 3 (CREB3L3) has been reported to be activated during fasting and to regulate triglyceride metabolism. Here, we show that CREB3L3 confers a wide spectrum of metabolic responses to starvation in vivo. Adenoviral and transgenic overexpression of nuclear CREB3L3 induced systemic lipolysis, hepatic ketogenesis, and insulin sensitivity with increased energy expenditure, leading to marked reduction in body weight, plasma lipid levels, and glucose levels. CREB3L3 overexpression activated gene expression levels and plasma levels of antidiabetic hormones, including fibroblast growth factor 21 and IGF-binding protein 2. Amelioration of diabetes by hepatic activation of CREB3L3 was also observed in several types of diabetic obese mice. Nuclear CREB3L3 mutually activates the peroxisome proliferator-activated receptor (PPAR) α promoter in an autoloop fashion and is crucial for the ligand transactivation of PPARα by interacting with its transcriptional regulator, peroxisome proliferator-activated receptor gamma coactivator-1α. CREB3L3 directly and indirectly controls fibroblast growth factor 21 expression and its plasma level, which contributes at least partially to the catabolic effects of CREB3L3 on systemic energy homeostasis in the entire body. Therefore, CREB3L3 is a therapeutic target for obesity and diabetes.

Ablation of Elovl6 protects pancreatic islets from high-fat diet-induced impairment of insulin secretion.

ELOVL family member 6, elongation of very long-chain fatty acids (Elovl6) is a microsomal enzyme that regulates the elongation of C12-16 saturated and monounsaturated fatty acids and is related to the development of obesity-induced insulin resistance via the modification of the fatty acid composition. In this study, we investigated the role of systemic Elovl6 in the pancreatic islet and ß-cell function. Elovl6 is expressed in both islets and ß-cell lines. In mice fed with chow, islets of the Elovl6(-/-) mice displayed normal architecture and ß-cell mass compared with those of the wild-type mice. However, when fed a high-fat, high-sucrose (HFHS) diet, the islet hypertrophy in response to insulin resistance observed in normal mice was attenuated and glucose-stimulated insulin secretion (GSIS) increased in the islets of Elovl6(-/-) mice compared with those of the wild-type mice. Enhanced GSIS in the HFHS Elovl6(-/-) islets was associated with an increased ATP/ADP ratio and the suppression of ATF-3 expression. Our findings suggest that Elovl6 could be involved in insulin secretory capacity per ß-cell and diabetes.

Comparison of the Framingham risk score, UK Prospective Diabetes Study (UKPDS) Risk Engine, Japanese Atherosclerosis Longitudinal Study-Existing Cohorts Combine (JALS-ECC) and maximum carotid intima-media thickness for predicting coronary artery stenosis in patients with asymptomatic type 2 diabetes.

AIMS: To compare the efficacy of Framingham Risk Score (FRS), UK Prospective Diabetes Study (UKPDS) risk engine, a risk score based on the Japanese Atherosclerosis Longitudinal Study-Existing Cohorts Combine (JALS-ECC), the maximum intima-media thickness (max-IMT) determined on coronary computed tomography angiography (CCTA) and their combination in asymptomatic patients with type 2 diabetes. METHODS: A total of 116 Japanese patients with type 2 diabetes underwent CCTA. The risk of coronary heart disease was calculated according to the FRS, UKPDS and JALS-ECC. We evaluated the reclassification of coronary artery stenosis (CAS) based on the risk score categories after adding each IMT related variable. RESULTS: Sixty-eight patients had CAS. The areas under the curves (AUCs) in the receiver operating characteristic curve analyses of FRS, UKPDS and JALS-ECC were 0.763 (95% confidence interval [CI]: 0.674-0.853), 0.785 (95% CI: 0.703-0.868) and 0.767 (95% CI: 0.681-0.853), respectively. The AUCs for FRS, UKPDS and JALS-ECC combined with the max-IMT were 0.788 (95% CI: 0.705-0.872), 0.800 (95% CI: 0.720-0.879) and 0.786 (95% CI: 0.703-0.869), respectively. Combining the max-IMT with the risk scores improved the identification of subjects with stenotic lesions, in particular, those in the first, second and third tertiles of the FRS, first and second tertiles of the UKPDS and first and second tertiles of the JALS-ECC (P=0.054, P=0.056, P=0.015, P=0.082, P=0.060, P=0.007, and P=0.080, respectively). The net reclassification improvement increased following the addition of a max-IMT of ≥ 1.9 mm (32.4% in FRS, 19.9% in UKPDS and 51.7% in JALS-ECC). CONCLUSIONS: These data suggest that combining a risk score with the max-IMT improves the prediction of CAS in comparison with the risk score alone.

Carotid artery plaque and LDL-to-HDL cholesterol ratio predict atherosclerotic status in coronary arteries in asymptomatic patients with type 2 diabetes mellitus.

AIMS: To investigate the clinical predictors of coronary atherosclerosis and to assess the utility of maximum-IMT for predicting coronary atherosclerosis in asymptomatic type 2 diabetic patients. METHODS: One hundred one Japanese patients with type 2 diabetes underwent computed tomography coronary angiography. Definitions of coronary artery stenosis and vulnerable coronary plaque were luminal narrowing of ≥50% and any coronary plaque with positive vessel remodeling and low attenuation, respectively. Carotid intima-media thickness (IMT) was assessed using B-mode ultrasound. RESULTS: Of the 101 patients, 40 had coronary artery stenosis without vulnerable coronary plaque, 7 had vulnerable coronary plaque without coronary artery stenosis, and 23 had coronary artery stenosis with vulnerable coronary plaque. Male sex (p=0.031), duration of diabetes (p=0.024), systolic blood pressure (SBP) (p=0.039), and the LDL/HDL ratio (LDL/HDL) (p=0.013) were independent predictors of coronary artery stenosis and the LDL/HDL (p=0.042) independently predicted vulnerable coronary plaque by logistic regression analyses. Areas under the curves in receiver operating characteristic curve analysis of the maximum-IMT, LDL/HDL, and these two parameters combined were 0.711 (95% CI 0.601-0.820), 0.618 (0.508-0.728), and 0.732 (0.632-0.831), respectively, for predicting coronary artery stenosis and 0.655 (0.537-0.773), 0.629 (0.504-0.754), and 0.710 (0.601-0.818), respectively, for predicting vulnerable coronary plaque. CONCLUSIONS: Male sex, duration of diabetes, elevated SBP, and LDL/HDL were independent predictors of coronary artery stenosis. LDL/HDL was an independent predictor of vulnerable coronary plaque. Maximum-IMT predicted both coronary stenosis and vulnerable coronary plaque. Adding LDL/HDL improved the prediction of coronary artery stenosis and vulnerable coronary plaque.

[Granular cell tumor of the neurohypophysis observed with hypoglycemic attack].

Granular cell tumor of the neurohypophysis (GCT) occurs as a solitary, small, nodular tumor and rarely grows to a sufficient size to present symptoms. The authors report a case of a 30-year-old man with GCT presenting with hypoglycemic attack. Hypoglycemic attack could be due to dysfunction of the hypothalamus and one of the important symptoms of GCT.

Elovl6 promotes nonalcoholic steatohepatitis.

UNLABELLED: Nonalcoholic steatohepatitis (NASH) is associated with obesity and type 2 diabetes, and an increased risk for liver cirrhosis and cancer. ELOVL family member 6, elongation of very long chain fatty acids (Elovl6), is a microsomal enzyme that regulates the elongation of C12-16 saturated and monounsaturated fatty acids (FAs). We have shown previously that Elovl6 is a major target for sterol regulatory element binding proteins in the liver and that it plays a critical role in the development of obesity-induced insulin resistance by modifying FA composition. To further investigate the role of Elovl6 in the development of NASH and its underlying mechanism, we used three independent mouse models with loss or gain of function of Elovl6, and human liver samples isolated from patients with NASH. Our results demonstrate that (1) Elovl6 is a critical modulator for atherogenic high-fat diet-induced inflammation, oxidative stress, and fibrosis in the liver; (2) Elovl6 expression is positively correlated with severity of hepatosteatosis and liver injury in NASH patients; and (3) deletion of Elovl6 reduces palmitate-induced activation of the NLR family pyrin domain-containing 3 inflammasome; this could be at least one of the underlying mechanisms by which Elovl6 modulates the progress of NASH. CONCLUSION: Hepatic long-chain fatty acid composition is a novel determinant in NASH development, and Elovl6 could be a potential therapeutic target for the prevention and treatment of NASH.

TFE3 regulates muscle metabolic gene expression, increases glycogen stores, and enhances insulin sensitivity in mice.

The role of transcription factor E3 (TFE3), a bHLH transcription factor, in immunology and cancer has been well characterized. Recently, we reported that TFE3 activates hepatic IRS-2 and hexokinase, participates in insulin signaling, and ameliorates diabetes. However, the effects of TFE3 in other organs are poorly understood. Herein, we examined the effects of TFE3 on skeletal muscle, an important organ involved in glucose metabolism. We generated transgenic mice that selectively express TFE3 in skeletal muscles. These mice exhibit a slight acceleration in growth prior to adulthood as well as a progressive increase in muscle mass. In TFE3 transgenic muscle, glycogen stores were more than twofold than in wild-type mice, and this was associated with an upregulation of genes involved in glucose metabolism, specifically glucose transporter 4, hexokinase II, and glycogen synthase. Consequently, exercise endurance capacity was enhanced in this transgenic model. Furthermore, insulin sensitivity was enhanced in transgenic mice and exhibited better improvement after 4 wk of exercise training, which was associated with increased IRS-2 expression. The effects of TFE3 on glucose metabolism in skeletal muscle were different from that in the liver, although they did, in part, overlap. The potential role of TFE3 in regulating metabolic genes and glucose metabolism within skeletal muscle suggests that it may be used for treating metabolic diseases as well as increasing endurance in sport.

Inhibition of ubiquitin ligase F-box and WD repeat domain-containing 7α (Fbw7α) causes hepatosteatosis through Krüppel-like factor 5 (KLF5)/peroxisome proliferator-activated receptor γ2 (PPARγ2) pathway but not SREBP-1c protein in mice.

F-box and WD repeat domain-containing 7α (Fbw7α) is the substrate recognition component of a ubiquitin ligase that controls the degradation of factors involved in cellular growth, including c-Myc, cyclin E, and c-Jun. In addition, Fbw7α degrades the nuclear form of sterol regulatory element-binding protein (SREBP)-1a, a global regulator of lipid synthesis, particularly during mitosis in cultured cells. This study investigated the in vivo role of Fbw7α in hepatic lipid metabolism. siRNA knockdown of Fbw7α in mice caused marked hepatosteatosis with the accumulation of triglycerides. However, inhibition of Fbw7α did not change the level of nuclear SREBP-1 protein or the expression of genes involved in fatty acid synthesis and oxidation. In vivo experiments on the gain and loss of Fbw7α function indicated that Fbw7α regulated the expression of peroxisome proliferator-activated receptor (PPAR) γ2 and its target genes involved in fatty acid uptake and triglyceride synthesis. These genes included fatty acid transporter Cd36, diacylglycerol acyltransferase 1 (Dgat1), and fat-specific protein 27 (Cidec). The regulation of PPARγ2 by Fbw7α was mediated, at least in part, by the direct degradation of the Krüppel-like factor 5 (KLF5) protein, upstream of PPARγ2 expression. Hepatic Fbw7α contributes to normal fatty acid and triglyceride metabolism, functions that represent novel aspects of this cell growth regulator.

Macrophage Elovl6 deficiency ameliorates foam cell formation and reduces atherosclerosis in low-density lipoprotein receptor-deficient mice.

OBJECTIVE: Elovl6, a long-chain fatty acid elongase, is a rate-limiting enzyme that elongates saturated and monounsaturated fatty acids and has been shown to be related to obesity-induced insulin resistance via modification of fatty acid composition. In this study, we investigated the roles of Elovl6 in foam cell formation in macrophages and atherosclerosis in mice. METHODS AND RESULTS: To investigate the roles of Elovl6 in macrophages in the progression of atherosclerosis, we transplanted bone marrow cells of wild-type or Elovl6(-/-) mice into irradiated LDL-R(-/-) mice that were fed a western diet. Aortic atherosclerotic lesion areas and infiltration of macrophages were significantly smaller in Elovl6(-/-) bone marrow cells-transplanted LDL-R(-/-) mice than in wild-type. Accumulation of esterified cholesterol on exposure to acetylated-LDL was less severe in peritoneal macrophages from Elovl6(-/-) mice than those from wild-type. Cholesterol efflux and expression of cholesterol efflux transporters were increased in Elovl6(-/-) macrophages, although no difference in uptake of acetylated-LDL was found between the two groups. On analysis of fatty acid composition of the esterified cholesterol fraction in macrophages, n-6 polyunsaturated fatty acids were decreased by absence of Elovl6. CONCLUSIONS: These findings suggest that Elovl6 in macrophages may contribute to foam cell formation and progression of atherosclerosis.

Sterol regulatory element-binding protein-1 determines plasma remnant lipoproteins and accelerates atherosclerosis in low-density lipoprotein receptor-deficient mice.

OBJECTIVE: Sterol regulatory element-binding protein-1 (SREBP-1) is nutritionally regulated and is known to be a key transcription factor regulating lipogenic enzymes. The goal of this study was to evaluate the roles of SREBP-1 in dyslipidemia and atherosclerosis. METHODS AND RESULTS: Transgenic mice that overexpress SREBP-1c in the liver and SREBP-1-deficient mice were crossed with low-density lipoprotein receptor (LDLR)-deficient mice, and the plasma lipids and atherosclerosis were analyzed. Hepatic SREBP-1c overexpression in LDLR-deficient mice caused postprandial hypertriglyceridemia, increased very-low-density lipoprotein (VLDL) cholesterol, and decreased high-density lipoprotein cholesterol in plasma, which resulted in accelerated aortic atheroma formation. Conversely, absence of SREBP-1 suppressed Western diet-induced hyperlipidemia in LDLR-deficient mice and ameliorated atherosclerosis. In contrast, bone marrow-specific SREBP-1 deficiency did not alter the development of atherosclerosis. The size of nascent VLDL particles secreted from the liver was increased in SREBP-1c transgenic mice and reduced in SREBP-1-deficient mice, accompanied by upregulation and downregulation of phospholipid transfer protein expression, respectively. CONCLUSIONS: Hepatic SREBP-1c determines plasma triglycerides and remnant cholesterol and contributes to atherosclerosis in hyperlipidemic states. Hepatic SREBP-1c also regulates the size of nascent VLDL particles.

Thunderclap headache without hypertension in a patient with pheochromocytoma.

Pheochromocytoma is a well known, catecholamine-producing tumor characterized by hypertension, headache, hyperglycemia, hypermetabolism, and hyperhydrosis. Approximately 65% of cases of pheochromocytoma were shown to be associated with hypertension. A case of pheochromocytoma that presented with thunderclap headache (TCH) and palpitations is reported. The patient never showed hypertension during the course of the disease. Paroxysmal headache and palpitations led to the identification of the underlying condition, and the final diagnosis was confirmed by histopathological examination of a surgical specimen. Pheochromocytoma should be identified as a less common although important cause of TCH. In addition, due to its lack of utility in identifying this disorder, negative cranial imaging may impede further investigation of extracranial lesions that may be the cause of a patient's headache. According to the International Classification of Headache Disorders (ICHD)-II, headache attributed to pheochromocytoma usually develops concomitantly with an abrupt increase in blood pressure. In our case, however, hypertension was never observed, even when the patient was symptomatic. This is the first report of a case of pheochromocytoma with TCH without hypertension.

Protein kinase Cbeta mediates hepatic induction of sterol-regulatory element binding protein-1c by insulin.

Sterol-regulatory element binding protein-1c (SREBP-1c) is a transcription factor that controls lipogenesis in the liver. Hepatic SREBP-1c is nutritionally regulated, and its sustained activation causes hepatic steatosis and insulin resistance. Although regulation of SREBP-1c is known to occur at the transcriptional level, the precise mechanism by which insulin signaling activates SREBP-1c promoter remains to be elucidated. Here we show that protein kinase C beta (PKCbeta) is a key mediator of insulin-mediated activation of hepatic SREBP-1c and its target lipogenic genes. Activation of SREBP-1c in the liver of refed mice was suppressed by either adenoviral RNAi-mediated knockdown or dietary administration of a specific inhibitor of protein kinase C beta. The effect of PKCbeta inhibition was cancelled in insulin depletion by streptozotocin (STZ) treatment of mice. Promoter analysis indicated that PKCbeta activates SREBP-1c promoter through replacement of Sp3 by Sp1 for binding to the GC box in the sterol regulatory element (SRE) complex, a key cis-element of SREBP-1c promoter. Knockdown of Sp proteins demonstrated that Sp3 and Sp1 play reciprocally negative and positive roles in nutritional regulation of SREBP-1c, respectively. This new understanding of PKCbeta involvement in nutritional regulation of SREBP-1c activation provides a new aspect of PKCbeta inhibition as a potential therapeutic target for diabetic complications.

The liver-enriched transcription factor CREBH is nutritionally regulated and activated by fatty acids and PPARalpha.

To elucidate the physiological role of CREBH, the hepatic mRNA and protein levels of CREBH were estimated in various feeding states of wild and obesity mice. In the fast state, the expression of CREBH mRNA and nuclear protein were high and profoundly suppressed by refeeding in the wild-type mice. In ob/ob mice, the refeeding suppression was impaired. The diet studies suggested that CREBH expression was activated by fatty acids. CREBH mRNA levels in the mouse primary hepatocytes were elevated by addition of the palmitate, oleate and eicosapenonate. It was also induced by PPARalpha agonist and repressed by PPARalpha antagonist. Luciferase reporter gene assays indicated that the CREBH promoter activity was induced by fatty acids and co-expression of PPARalpha. Deletion studies identified the PPRE for PPARalpha activation. Electrophoretic mobility shift assay and chromatin immunoprecipitation (ChIP) assay confirmed that PPARalpha directly binds to the PPRE. Activation of CREBH at fasting through fatty acids and PPARalpha suggest that CREBH is involved in nutritional regulation.

The up-regulation of microRNA-335 is associated with lipid metabolism in liver and white adipose tissue of genetically obese mice.

MicroRNAs (miRNAs) are short non-coding RNA that post-transcriptionally regulates gene expression. Some miRNAs have been proposed to be associated with obesity. However, miRNAs, which are related to the development of obesity in vivo remains unknown. Here in, we found the up-regulation of miR-335 in obesity using microarray analysis for miRNA. The expressions of miR-335 in liver and white adipose tissue (WAT) were up-regulated in obese mice including ob/ob, db/db, and KKAy mice. Increased miR-335 expressions were associated with an elevated body, liver and WAT weight, and hepatic triglyceride and cholesterol. Furthermore, miR-335 levels were closely correlated with expression levels of adipocyte differentiation markers such as PPARgamma, aP2, and FAS in 3T3-L1 adipocyte. These findings provide the first evidence that the up-regulated expressions of miR-335 in liver and WAT of obese mice might contribute to the pathophysiology of obesity.

Nuclear SREBP-1a causes loss of pancreatic beta-cells and impaired insulin secretion.

Transgenic mice expressing nuclear sterol regulatory element-binding protein-1a under the control of the insulin promoter were generated to determine the role of SREBP-1a in pancreatic beta-cells. Only low expressors could be established, which exhibited mild hyperglycemia, impaired glucose tolerance, and reduced plasma insulin levels compared to C57BL/6 controls. The islets isolated from the transgenic mice were fewer and smaller, and had decreased insulin content and unaltered glucagon staining. Both glucose- and potassium-stimulated insulin secretions were decreased. The transgenic islets consistently expressed genes for fatty acids and cholesterol synthesis, resulting in accumulation of triglycerides but not cholesterol. PDX-1, BetaEpsilonTauAlpha2, MafA, and IRS-2 were suppressed, partially explaining the loss and dysfunction of beta-cell mass. The transgenic mice on a high fat/high sucrose diet still exhibited impaired insulin secretion and continuous beta-cell growth defect. Therefore, nuclear SREBP-1a, even at a low level, strongly disrupts beta-cell mass and function.

Cholesterol accumulation and diabetes in pancreatic beta-cell-specific SREBP-2 transgenic mice: a new model for lipotoxicity.

To determine the role of cholesterol synthesis in pancreatic beta-cells, a transgenic model of in vivo activation of sterol-regulatory element binding protein 2 (SREBP-2) specifically in beta-cells (TgRIP-SREBP-2) was developed and analyzed. Expression of nuclear human SREBP-2 in beta-cells resulted in severe diabetes as evidenced by greater than 5-fold elevations in glycohemoglobin compared with C57BL/6 controls. Diabetes in TgRIP-SREBP-2 mice was primarily due to defects in glucose- and potassium-stimulated insulin secretion as determined by glucose tolerance test. Isolated islets of TgSREBP-2 mice were fewer in number, smaller, deformed, and had decreased insulin content. SREBP-2-expressing islets also contained increased esterified cholesterol and unchanged triglycerides with reduced ATP levels. Consistently, these islets exhibited elevated expression of HMG-CoA synthase and reductase and LDL receptor, with suppression of endogenous SREBPs. Genes involved in beta-cell differentiation, such as PDX1 and BETA2, were suppressed, explaining loss of beta-cell mass, whereas IRS2 expression was not affected. These phenotypes were dependent on the transgene expression. Taken together, these results indicate that activation of SREBP-2 in beta-cells caused severe diabetes by loss of beta-cell mass with accumulation of cholesterol, providing a new lipotoxic model and a potential link of disturbed cholesterol metabolism to impairment of beta-cell function.

Cyclin-dependent kinase inhibitor, p21WAF1/CIP1, is involved in adipocyte differentiation and hypertrophy, linking to obesity, and insulin resistance.

Both adipocyte hyperplasia and hypertrophy are determinant factors for adipocyte differentiation during the development of obesity. p21(WAF1/CIP1), a cyclin-dependent kinase inhibitor, is induced during adipocyte differentiation; however, its precise contribution to this process is unknown. Using both in vitro and in vivo systems, we show that p21 is crucial for maintaining adipocyte hypertrophy and obesity-induced insulin resistance. The absence of p21 in 3T3-L1 fibroblasts by RNA-mediated interference knockdown or in embryonic fibroblasts from p21(-/-) mice impaired adipocyte differentiation, resulting in smaller adipocytes. Despite normal adipose tissue mass on a normal diet, p21(-/-) mice fed high energy diets had reduced adipose tissue mass and adipocyte size accompanied by a marked improvement in insulin sensitivity. Knockdown of p21 in enlarged epididymal fat of diet-induced obese mice and also in fully differentiated 3T3-L1 adipocytes caused vigorous apoptosis by activating p53. Thus, p21 is involved in both adipocyte differentiation and in protecting hypertrophied adipocytes against apoptosis. Via both of these mechanisms, p21 promotes adipose tissue expansion during high fat diet feeding, leading to increased downstream pathophysiological consequences such as insulin resistance.