Vitamin D Receptor Regulates Liver Regeneration After Partial Hepatectomy in Male Mice.

Vitamin D signals through the vitamin D receptor (VDR) to induce its end-organ effects. Hepatic stellate cells control development of liver fibrosis in response to stressors and vitamin D signaling decreases fibrogenesis. VDR expression in hepatocytes is low in healthy liver, and the role of VDR in hepatocyte proliferation is unclear. Hepatocyte-VDR null mice (hVDR) were used to assess the role of VDR and vitamin D signaling in hepatic regeneration. hVDR mice have impaired liver regeneration and impaired hepatocyte proliferation associated with significant differential changes in bile salts. Notably, mice lacking hepatocyte VDR had significant increases in expression of conjugated bile acids after partial hepatectomy, consistent with failure to normalize hepatic function by the 14-day time point tested. Real-time PCR of hVDR and control livers showed significant changes in expression of cell-cycle genes including cyclins D1 and E1 and cyclin-dependent kinase 2. Gene expression profiling of hepatocytes treated with vitamin D or control showed regulation of groups of genes involved in liver proliferation, hepatitis, liver hyperplasia/hyperproliferation, and liver necrosis/cell death. Together, these studies demonstrate an important functional role for VDR in hepatocytes during liver regeneration. Combined with the known profibrotic effects of impaired VDR signaling in stellate cells, the studies provide a mechanism whereby vitamin D deficiency would both reduce hepatocyte proliferation and permit fibrosis, leading to significant liver compromise.

The association between tobacco smoking and systolic toe pressures in active foot ulceration.

Smoking may increase the risk of diabetic foot disease and ulceration. It does so by impairing glycaemic control and promoting the formation of advanced glycated end-products. Additionally, smoking is known to delay surgical wound healing and accelerate peripheral arterial disease. We aimed to determine whether toe pressures differed in smokers with a foot ulcer, when compared to non-smokers and ex-smokers, as well as ulcer outcomes at 12 months, among patients attending Blacktown Hospital High Risk Foot Service (HRFS). This study is a retrospective analysis of our prospectively collected clinic database. Eligible participants were adults attending the HRFS between June 2020 and April 2022. Participants were included if they had an ulcer, at least one systolic toe pressure reading completed at their initial visit and attended at least one follow-up visit. Participants were followed until healing, loss to follow-up or a minimum of 12 months. A total of 195 participants were included; 36 smokers, 82 ex-smokers, and 77 controls who had never smoked. Smoking status was by self-report. Current smokers were significantly younger at initial presentation (p = .002) and tended towards lower socioeconomic status (p = .067). Current smokers were significantly more likely to have ischaemic grade 3 toe pressures (< 30 mmHg) of their left foot (p = .027), suggestive of reduced perfusion. At the end of follow up period, smokers had the numerically highest rates of minor amputations. In conclusion, smokers ulcerate younger and are more likely to have grade 3 ischaemia. Collecting information about the brachial artery pressures and the time since the last cigarette may clarify any relationship between smoking and toe pressures.Trial registration: WSLHD HREC ethics approval 2111-02 and ANZCTR registration 382470. Registered on 15/09/2021.

The Role of Vitamin D in Skeletal Muscle Repair and Regeneration in Animal Models and Humans: A Systematic Review.

Vitamin D deficiency, prevalent worldwide, is linked to muscle weakness, sarcopenia, and falls. Muscle regeneration is a vital process that allows for skeletal muscle tissue maintenance and repair after injury. PubMed and Web of Science were used to search for studies published prior to May 2023. We assessed eligible studies that discussed the relationship between vitamin D, muscle regeneration in this review. Overall, the literature reports strong associations between vitamin D and skeletal myocyte size, and muscle regeneration. In vitro studies in skeletal muscle cells derived from mice and humans showed vitamin D played a role in regulating myoblast growth, size, and gene expression. Animal studies, primarily in mice, demonstrate vitamin D's positive effects on skeletal muscle function, such as improved grip strength and endurance. These studies encompass vitamin D diet research, genetically modified models, and disease-related mouse models. Relatively few studies looked at muscle function after injury, but these also support a role for vitamin D in muscle recovery. The human studies have also reported that vitamin D deficiency decreases muscle grip strength and gait speed, especially in the elderly population. Finally, human studies reported the benefits of vitamin D supplementation and achieving optimal serum vitamin D levels in muscle recovery after eccentric exercise and surgery. However, there were no benefits in rotator cuff injury studies, suggesting that repair mechanisms for muscle/ligament tears may be less reliant on vitamin D. In summary, vitamin D plays a crucial role in skeletal muscle function, structural integrity, and regeneration, potentially offering therapeutic benefits to patients with musculoskeletal diseases and in post-operative recovery.

Metabolic effects of lipectomy and of adipose tissue transplantation.

OBJECTIVE: The goal of this study was to review the metabolic effects of fat transplantation. METHODS: Fat (adipose tissue [AT]) transplantation has been performed extensively for many years in the cosmetic reconstruction industry. However, not all fats are equal. White, brown, and beige AT differ in energy storage and use. Brown and beige AT consume glucose and lipids for thermogenesis and, theoretically, may provide greater metabolic benefit in transplantation. Here, the authors review the metabolic effects of AT transplantation. RESULTS: Removal of subcutaneous human AT does not have beneficial metabolic effects. Most studies find no benefit from visceral AT transplantation and some studies report harmful effects. In contrast, transplantation of inguinal or subcutaneous AT in mice has positive effects. Brown AT transplant studies have variable results depending on the model but most show benefit. CONCLUSIONS: Many technical improvements have optimized fat grafting and transplantation in cosmetic surgery. Transplantation of subcutaneous AT has the potential for significant metabolic benefits, although there are few studies in humans or using human AT. Brown AT transplantation is beneficial but not readily feasible in humans thus ex vivo "beiging" may be a useful strategy. AT transplantation may provide clinical benefits in metabolic disorders, especially in the setting of lipodystrophy.

Iron chelation increases beige fat differentiation and metabolic activity, preventing and treating obesity.

Beige and brown fat consume glucose and lipids to produce heat, using uncoupling protein 1 (UCP1). It is thought that full activation of brown adipose tissue (BAT) may increase total daily energy expenditure by 20%. Humans normally have more beige and potentially beige-able fat than brown fat. Strategies to increase beige fat differentiation and activation may be useful for the treatment of obesity and diabetes. Mice were fed chow or high-fat diet (HFD) with or without the iron chelator deferasirox. Animals fed HFD + deferasirox were markedly lighter than their HFD controls with increased energy expenditure (12% increase over 24 h, p < 0.001). Inguinal fat from HFD + deferasirox mice showed increased beige fat quantity with greater Ucp1 and Prdm16 expression. Inguinal adipose tissue explants were studied in a Seahorse bioanalyser and energy expenditure was significantly increased. Deferasirox was also effective in established obesity and in ob/ob mice, indicating that intact leptin signalling is not needed for efficacy. These studies identify iron chelation as a strategy to preferentially activate beige fat. Whether activating brown/beige fat is effective in humans is unproven. However, depleting iron to low-normal levels is a potential therapeutic strategy to improve obesity and related metabolic disorders, and human studies may be warranted.

Unravelling Checkpoint Inhibitor Associated Autoimmune Diabetes: From Bench to Bedside.

Immune checkpoint inhibitors have transformed the landscape of oncological therapy, but at the price of a new array of immune related adverse events. Among these is ß-cell failure, leading to checkpoint inhibitor-related autoimmune diabetes (CIADM) which entails substantial long-term morbidity. As our understanding of this novel disease grows, parallels and differences between CIADM and classic type 1 diabetes (T1D) may provide insights into the development of diabetes and identify novel potential therapeutic strategies. In this review, we outline the knowledge across the disciplines of endocrinology, oncology and immunology regarding the pathogenesis of CIADM and identify possible management strategies.

Beta-Cell-Specific Expression of Nicotinamide Adenine Dinucleotide Phosphate Oxidase 5 Aggravates High-Fat Diet-Induced Impairment of Islet Insulin Secretion in Mice.

Aims: Nicotinamide adenine dinucleotide phosphate oxidases (NOX-es) produce reactive oxygen species and modulate ß-cell insulin secretion. Islets of type 2 diabetic subjects present elevated expression of NOX5. Here, we sought to characterize regulation of NOX5 expression in human islets in vitro and to uncover the relevance of NOX5 in islet function in vivo using a novel mouse model expressing NOX5 in doxycycline-inducible, ß-cell-specific manner (RIP/rtTA/NOX5 mice). Results:In situ hybridization and immunohistochemistry employed on pancreatic sections demonstrated NOX5 messenger ribonucleic acid (mRNA) and protein expressions in human islets. In cultures of dispersed islets, NOX5 protein was observed in somatostatin-positive (δ) cells in basal (2.8 mM glucose) conditions. Small interfering ribonucleic acid (siRNA)-mediated knockdown of NOX5 in human islets cultured in basal glucose concentrations resulted in diminished glucose-induced insulin secretion (GIIS) in vitro. However, when islets were preincubated in high (16.7 mM) glucose media for 12 h, NOX5 appeared also in insulin-positive (ß) cells. In vivo, mice with ß-cell NOX5 expression developed aggravated impairment of GIIS compared with control mice when challenged with 14 weeks of high-fat diet. Similarly, in vitro palmitate preincubation resulted in more severe reduction of insulin release in islets of RIP/rtTA/NOX5 mice compared with their control littermates. Decreased insulin secretion was most distinct in response to theophylline stimulation, suggesting impaired cyclic adenosine monophosphate (cAMP)-mediated signaling due to increased phosphodiesterase activation. Innovation and Conclusions: Our data provide the first insight into the complex regulation and function of NOX5 in islets implying an important role for NOX5 in δ-cell-mediated intraislet crosstalk in physiological circumstances but also identifying it as an aggravating factor in ß-cell failure in diabetic conditions.

Myeloid cell deletion of Aryl hydrocarbon Receptor Nuclear Translocator (ARNT) induces non-alcoholic steatohepatitis.

BACKGROUND AND AIM: Non-alcoholic steatohepatitis (NASH) is predicted to become the most common cause of cirrhosis and liver failure. Risk factors include obesity, insulin resistance and diabetes. Macrophages and other myeloid cells play crucial roles in initiating and driving inflammation. Aryl hydrocarbon Receptor Nuclear Translocator (ARNT) is a transcription factor which binds to a range of partners to mediate responses to environmental signals, including the diet. In people with diabetes it is decreased in liver. We hypothesised that myeloid cell ARNT activity may contribute to the development of liver pathology. METHODS: Floxed-ARNT mice were bred with LysM-Cre mice to generate mice with reduced ARNT in myeloid cells. Animals were fed a high fat diet (HFD) and liver pathology was assessed. Histology, mRNA, fat accumulation and metabolism were studied. RESULTS: Animals with reduced myeloid ARNT developed steatohepatitis on a HFD, with additional alterations of metabolism and fat deposition. Steatohepatitis was accompanied by hepatic macrophage infiltration and expression of both M1 and M2 markers. Expression of mRNAs for Cxcl1, Mcp-1, Tnf-α and Tgf-ß1 were increased. Human livers from controls and people with NASH were tested; ARNT mRNA was decreased by 80% (p = 0.0004). CONCLUSIONS: Decreased myeloid ARNT may play a role in the conversion from non-alcoholic fatty liver to steatohepatitis. Increasing ARNT may be a therapeutic strategy to reduce NASH.

Mice with myocyte deletion of vitamin D receptor have sarcopenia and impaired muscle function.

BACKGROUND: It has long been recognized that vitamin D deficiency is associated with muscle weakness and falls. Vitamin D receptor (VDR) is present at very low levels in normal muscle. Whether vitamin D plays a direct role in muscle function is unknown and is a subject of hot debate. Myocyte-specific deletion of VDR would provide a strategy to answer this question. METHODS: Myocyte-specific vitamin D receptor (mVDR) null mice were generated by crossing human skeletal actin-Cre mice with floxed VDR mice. The effects of gene deletion on the muscle phenotype were studied in terms of body tissue composition, muscle tissue histology, and gene expression by real-time PCR. RESULTS: Unlike whole-body VDR knockout mice, mVDR mice showed a normal body size. The mVDR showed a distinct muscle phenotype featuring reduced proportional lean mass (70% vs. 78% of lean mass), reduced voluntary wheel-running distance (22% decrease, P = 0.009), reduced average running speed, and reduced grip strength (7-16% reduction depending on age at testing). With their decreased voluntary exercise, and decreased lean mass, mVDR have increased proportional fat mass at 20% compared with 13%. Surprisingly, their muscle fibres showed slightly increased diameter, as well as the presence of angular fibres and central nuclei suggesting ongoing remodelling. There were, however, no clear changes in fibre type and there was no increase in muscle fibrosis. VDR is a transcriptional regulator, and changes in the expression of candidate genes was examined in RNA extracted from skeletal muscle. Alterations were seen in myogenic gene expression, and there was decreased expression of cell cycle genes cyclin D1, D2, and D3 and cyclin-dependent kinases Cdk-2 and Cdk-4. Expression of calcium handling genes sarcoplasmic/endoplasmic reticulum calcium ATPases (SERCA) Serca2b and Serca3 was decreased and Calbindin mRNA was lower in mVDR muscle. CONCLUSIONS: This study demonstrates that vitamin D signalling is needed for myocyte function. Despite the low level of VDR protein normally found muscle, deleting myocyte VDR had important effects on muscle size and strength. Maintenance of normal vitamin D signalling is a useful strategy to prevent loss of muscle function and size.

Hepatic Aryl hydrocarbon Receptor Nuclear Translocator (ARNT) regulates metabolism in mice.

BACKGROUND & AIMS: Aryl hydrocarbon Receptor Nuclear Translocator (ARNT) and its partners hypoxia-inducible factors (HIF)-1α and HIF-2α are candidate factors for the well-known link between the liver, metabolic dysfunction and elevation in circulating lipids and glucose. Methods: Hepatocyte-specific ARNT-null (LARNT), HIF-1α-null (LHIF1α) and HIF-2α-null (LHIF2α) mice were created. RESULTS: LARNT mice had increased fasting glucose, impaired glucose tolerance, increased glucose production, raised post-prandial serum triglycerides (TG) and markedly lower hepatic ATP versus littermate controls. There was increased expression of G6Pase, Chrebp, Fas and Scd-1 mRNAs in LARNT animals. Surprisingly, LHIF1α and LHIF2α mice exhibited no alterations in any metabolic parameter assessed. CONCLUSIONS: These results provide convincing evidence that reduced hepatic ARNT can contribute to inappropriate hepatic glucose production and post-prandial dyslipidaemia. Hepatic ARNT may be a novel therapeutic target for improving post-prandial hypertriglyceridemia and glucose homeostasis.

Fluconazole in the treatment of Cushing's disease.

UNLABELLED: Ketoconazole was a first-line agent for suppressing steroidogenesis in Cushing's disease. It now has limited availability. Fluconazole, another azole antifungal, is an alternative, although its in vivo efficacy is unclear. A 61-year-old female presented with weight gain, abdominal striae and worsening depression. HbA1c increased to 76 mmol/mol despite increasing insulin. Investigations confirmed cortisol excess; afternoon serum cortisol was 552 nmol/l with an inappropriate ACTH of 9.3 pmol/l. In total, 24-h urinary free cortisol (UFC):creatinine ratio was 150 nmol/mmol with failure to suppress after 48 h of low-dose dexamethasone. Pituitary MRI revealed a 4-mm microadenoma. Inferior petrosal sinus sampling confirmed Cushing's disease. Transsphenoidal resection was performed and symptoms improved. However, disease recurred 6 months later with elevated 24-h UFC >2200 nmol/day. Metyrapone was commenced at 750 mg tds. Ketoconazole was later added at 400 mg daily, with dose reduction in metyrapone. When ketoconazole became unavailable, fluconazole 200 mg daily was substituted. Urine cortisol:creatinine ratio rose, and the dose was increased to 400 mg daily with normalisation of urine hormone levels. Serum cortisol and urine cortisol:creatinine ratios remain normal on this regimen at 6 months. In conclusion, to our knowledge, this is the first case demonstrating prolonged in vivo efficacy of fluconazole in combination with low-dose metyrapone for the treatment of Cushing's disease. Fluconazole has a more favourable toxicity profile, and we suggest that it is a potential alternative for medical management of Cushing's disease. LEARNING POINTS: Surgery remains first line for the management of Cushing's disease with pharmacotherapy used where surgery is unsuccessful or there is persistence of cortisol excess.Ketoconazole has previously been used to treat cortisol excess through inhibition of CYP450 enzymes 11-ß-hydroxylase and 17-α-hydroxylase, though its availability is limited in many countries.Fluconazole shares similar properties to ketoconazole, although it has less associated toxicity.Fluconazole represents a suitable alternative for the medical management of Cushing's disease and proved an effective addition to metyrapone in the management of this case.

Hepatocyte-specific deletion of ARNT (aryl hydrocarbon Receptor Nuclear Translocator) results in altered fibrotic gene expression in the thioacetamide model of liver injury.

BACKGROUND & AIMS: Recent studies have shown that increased expression of liver hypoxia inducible factor 2-α (HIF-2α) leads to liver inflammation and a pro-fibrotic gene expression signature. Aryl hydrocarbon Receptor Nuclear Translocator (ARNT) is required for HIF-2α transcriptional activity and has previously been shown to regulate hepatic metabolism in mice. In these studies we examined the role of hepatocyte ARNT in the thioacetamide (TAA)-induced model of liver fibrosis. METHODS: Hepatocyte-specific ARNT-null (LARNT) mice were created using an albumin promoter-driven Cre recombinase. LARNT and floxed control (FC) littermates were placed on chow diet and received twice weekly intraperitoneal injections of 0.15mg/g body weight of TAA for 13 weeks. RESULTS: TAA treated LARNT and FC mice had a similar pattern of fibrosis. Quantification of Sirius red histology staining and hydroxyproline content revealed mixed results in terms of collagen deposition in LARNT livers. There was no significant difference in hepatocyte apoptosis or proliferation, as assessed by cleaved Caspase-3 and Ki67 respectively. LARNT mice had decreased macrophage accumulation, and decreased liver mRNA expression of Col1A1, Col1A2, Col5A1, Tgfß1, Tgfß2, Timp1 and Timp2. CONCLUSIONS: Deletion of hepatocyte ARNT leads to altered expression of collagen associated mRNA and reduced macrophage infiltration in the TAA-induced model of liver fibrosis. It appears that hepatocyte ARNT is not a requirement for initiation of liver fibrogenesis, but does regulate pro-fibrotic gene expression and macrophage accumulation.

Higher ferritin levels, but not serum iron or transferrin saturation, are associated with Type 2 diabetes mellitus in adult men and women free of genetic haemochromatosis.

CONTEXT: Iron overload predisposes to diabetes and higher ferritin levels have been associated with diabetes. However, it is unclear whether ferritin reflects differences in iron-related parameters between diabetic and nondiabetic persons. We examined associations of serum ferritin, iron and transferrin saturation with Type 2 diabetes in adults without genetic predisposition to iron overload. DESIGN, PARTICIPANTS AND MEASUREMENTS: Cross-sectional analysis of community-dwelling men and women aged 17-97 years from the Busselton Health Survey, Western Australia. Men and women carrying genotypes associated with haemochromatosis (C282Y/C282Y or C282Y/H63D) were excluded. Serum ferritin, iron and transferrin saturation were assayed. RESULTS: There were 1834 men (122 with diabetes, 6·6%) and 2351 women (141 with diabetes, 6%). In men, higher serum ferritin was associated with diabetes after adjusting for age, smoking, alcohol, cardiovascular history, body mass index (BMI), waist, blood pressure, lipids, C-reactive protein (CRP), adiponectin, alanine transaminase (ALT) and gamma-glutamyl transpeptidase (GGT) [odds ratio (OR): 1·29 per 1 unit increase log ferritin, 95% confidence interval (CI) = 1·01-1·65, P = 0·043]. In women, higher serum ferritin was associated with diabetes [fully adjusted OR: 1·31 per 1 unit increase log ferritin, 95% CI = 1·04-1·63, P = 0·020; 1·84 for tertile (T) 3 vs T1, 95% CI = 1·09-3·11]. Neither iron levels nor transferrin saturation were associated with diabetes risk in men or women. Higher ferritin was not associated with insulin resistance in nondiabetic adults. CONCLUSIONS: In adults, higher ferritin levels are independently associated with prevalent diabetes while iron and transferrin saturation are not. Ferritin is a robust biomarker for diabetes risk, but further investigation is needed to clarify whether this relationship is mediated via iron metabolism.

Vitamin D receptor-mediated stromal reprogramming suppresses pancreatitis and enhances pancreatic cancer therapy.

The poor clinical outcome in pancreatic ductal adenocarcinoma (PDA) is attributed to intrinsic chemoresistance and a growth-permissive tumor microenvironment. Conversion of quiescent to activated pancreatic stellate cells (PSCs) drives the severe stromal reaction that characterizes PDA. Here, we reveal that the vitamin D receptor (VDR) is expressed in stroma from human pancreatic tumors and that treatment with the VDR ligand calcipotriol markedly reduced markers of inflammation and fibrosis in pancreatitis and human tumor stroma. We show that VDR acts as a master transcriptional regulator of PSCs to reprise the quiescent state, resulting in induced stromal remodeling, increased intratumoral gemcitabine, reduced tumor volume, and a 57% increase in survival compared to chemotherapy alone. This work describes a molecular strategy through which transcriptional reprogramming of tumor stroma enables chemotherapeutic response and suggests vitamin D priming as an adjunct in PDA therapy. PAPERFLICK:

Reduction of ARNT in myeloid cells causes immune suppression and delayed wound healing.

Aryl hydrocarbon receptor nuclear translocator (ARNT) is a transcription factor that binds to partners to mediate responses to environmental signals. To investigate its role in the innate immune system, floxed ARNT mice were bred with lysozyme M-Cre recombinase animals to generate lysozyme M-ARNT (LAR) mice with reduced ARNT expression. Myeloid cells of LAR mice had altered mRNA expression and delayed wound healing. Interestingly, when the animals were rendered diabetic, the difference in wound healing between the LAR mice and their littermate controls was no longer present, suggesting that decreased myeloid cell ARNT function may be an important factor in impaired wound healing in diabetes. Deferoxamine (DFO) improves wound healing by increasing hypoxia-inducible factors, which require ARNT for function. DFO was not effective in wounds of LAR mice, again suggesting that myeloid cells are important for normal wound healing and for the full benefit of DFO. These findings suggest that myeloid ARNT is important for immune function and wound healing. Increasing ARNT and, more specifically, myeloid ARNT may be a therapeutic strategy to improve wound healing.

Vitamin D signaling regulates proliferation, differentiation, and myotube size in C2C12 skeletal muscle cells.

Vitamin D deficiency is linked to a range of muscle disorders including myalgia, muscle weakness, and falls. Humans with severe vitamin D deficiency and mice with transgenic vitamin D receptor (VDR) ablation have muscle fiber atrophy. However, molecular mechanisms by which vitamin D influences muscle function and fiber size remain unclear. A central question is whether VDR is expressed in skeletal muscle and is able to regulate transcription at this site. To address this, we examined key molecular and morphologic changes in C2C12 cells treated with 25-hydroxyvitamin D (25OHD) and 1,25-dihydroxyvitamin D (1,25(OH)(2)D). As well as stimulating VDR expression, 25(OH)D and 1,25(OH)(2)D dose-dependently increased expression of the classic vitamin D target cytochrome P450, family 24, subfamily A, polypeptide 1 (CYP24A1), demonstrating the presence of an autoregulatory vitamin D-endocrine system in these cells. Luciferase reporter studies demonstrated that cytochrome P450, family 27, subfamily B, polypeptide 1 (CYP27B1) was functional in these cells. Both 25OHD and 1,25(OH)(2)D altered C2C12 proliferation and differentiation. These effects were related to the increased expression of genes involved in G(0)/G(1) arrest (retinoblastoma protein [Rb], 1.3-fold; ATM, 1.5-fold, both P < .05), downregulation of mRNAs involved in G(1)/S transition, including myc and cyclin-D1 (0.7- and 0.8-fold, both P < .05) and reduced phosphorylation of Rb protein (0.3-fold, P < .005). After serum depletion, 1,25(OH)(2)D (100nM) suppressed myotube formation with decreased mRNAs for key myogenic regulatory factors (myogenin, 0.5-fold; myf5, 0.4-fold, P < .005) but led to a 1.8-fold increase in cross-sectional size of individual myotubes associated with markedly decreased myostatin expression (0.2-fold, P < .005). These data show that vitamin D signaling alters gene expression in C2C12 cells, with effects on proliferation, differentiation, and myotube size.

Beta-cell ARNT is required for normal glucose tolerance in murine pregnancy.

AIMS: Insulin secretion increases in normal pregnancy to meet increasing demands. Inability to increase beta-cell function results in gestational diabetes mellitus (GDM). We have previously shown that the expression of the transcription factor ARNT (Aryl-hydrocarbon Receptor Nuclear Translocator) is reduced in the islets of humans with type 2 diabetes. Mice with a beta-cell specific deletion of ARNT (ß-ARNT mice) have impaired glucose tolerance secondary to defective insulin secretion. We hypothesised that ARNT is required to increase beta-cell function during pregnancy, and that ß-ARNT mice would be unable to compensate for the beta-cell stress of pregnancy. The aims of this study were to investigate the mechanisms of ARNT regulation of beta-cell function and glucose tolerance in pregnancy. METHODS: ß-ARNT females were mated with floxed control (FC) males and FC females with ß-ARNT males. RESULTS: During pregnancy, ß-ARNT mice had a marked deterioration in glucose tolerance secondary to defective insulin secretion. There was impaired beta-cell proliferation in late pregnancy, associated with decreased protein and mRNA levels of the islet cell-cycle regulator cyclinD2. There was also reduced expression of Irs2 and G6PI. In contrast, in control mice, pregnancy was associated with a 2.1-fold increase in ARNT protein and a 1.6-fold increase in cyclinD2 protein, and with increased beta-cell proliferation. CONCLUSIONS: Islet ARNT increases in normal murine pregnancy and beta-cell ARNT is required for cyclinD2 induction and increased beta-cell proliferation in pregnancy.

High passage MIN6 cells have impaired insulin secretion with impaired glucose and lipid oxidation.

Type 2 diabetes is a metabolic disorder characterized by the inability of beta-cells to secrete enough insulin to maintain glucose homeostasis. MIN6 cells secrete insulin in response to glucose and other secretagogues, but high passage (HP) MIN6 cells lose their ability to secrete insulin in response to glucose. We hypothesized that metabolism of glucose and lipids were defective in HP MIN6 cells causing impaired glucose stimulated insulin secretion (GSIS). HP MIN6 cells had no first phase and impaired second phase GSIS indicative of global functional impairment. This was coupled with a markedly reduced ATP content at basal and glucose stimulated states. Glucose uptake and oxidation were higher at basal glucose but ATP content failed to increase with glucose. HP MIN6 cells had decreased basal lipid oxidation. This was accompanied by reduced expressions of Glut1, Gck, Pfk, Srebp1c, Ucp2, Sirt3, Nampt. MIN6 cells represent an important model of beta cells which, as passage numbers increased lost first phase but retained partial second phase GSIS, similar to patients early in type 2 diabetes onset. We believe a number of gene expression changes occurred to produce this defect, with emphasis on Sirt3 and Nampt, two genes that have been implicated in maintenance of glucose homeostasis.

Position statement of the Australian Diabetes Society: individualisation of glycated haemoglobin targets for adults with diabetes mellitus.

Tight glycaemic control reduces the risk of development and progression of organ complications in people with type 1 or type 2 diabetes. In this position statement, the Australian Diabetes Society recommends a general target glycated haemoglobin (HbA(1c)) level of

Ablation of ARNT/HIF1beta in liver alters gluconeogenesis, lipogenic gene expression, and serum ketones.

We have previously shown that expression of the transcription factor ARNT/HIF1beta is reduced in islets of humans with type 2 diabetes. We have now found that ARNT is also reduced in livers of diabetics. To study the functional effect of its reduction, we created mice with liver-specific ablation (L-ARNT KO) using ARNT loxP mice and adenoviral-mediated delivery of Cre. L-ARNT KO mice had normal blood glucose but increased fed insulin levels. These mice also exhibited features of type 2 diabetes with increased hepatic gluconeogenesis, increased lipogenic gene expression, and low serum beta-hydroxybutyrate. These effects appear to be secondary to increased expression of CCAAT/enhancer-binding protein alpha (C/EBPalpha), farnesoid X receptor (FXR), and sterol response element-binding protein 1c (SREBP-1c) and a reduction in phosphorylation of AMPK without changes in the expression of enzymes in ketogenesis, fatty acid oxidation, or FGF21. These results demonstrate that a deficiency of ARNT action in the liver, coupled with that in beta cells, could contribute to the metabolic phenotype of human type 2 diabetes.