Insulin resistance and dyslipidemia are both considered to be risk factors for metabolic syndrome. Low levels of IGF1 are associated with insulin resistance. Elevation of low-density lipoprotein cholesterol (LDL-C) concomitant with depression of high-density lipoprotein cholesterol (HDL-C) increase the risk of obesity and type 2 diabetes mellitus (T2DM). Liver secretes IGF1 and catabolizes cholesterol regulated by the rate-limiting enzyme of bile acid synthesis from cholesterol 7α-hydroxylase (CYP7A1). NO-1886, a chemically synthesized lipoprotein lipase activator, suppresses diet-induced insulin resistance with the improvement of HDL-C. The goal of the present study is to evaluate whether NO-1886 upregulates IGF1 and CYP7A1 to benefit glucose and cholesterol metabolism. By using human hepatoma cell lines (HepG2 cells) as an in vitro model, we found that NO-1886 promoted IGF1 secretion and CYP7A1 expression through the activation of signal transducer and activator of transcription 5 (STAT5). Pretreatment of cells with AG 490, the inhibitor of STAT pathway, completely abolished NO-1886-induced IGF1 secretion and CYP7A1 expression. Studies performed in Chinese Bama minipigs pointed out an augmentation of plasma IGF1 elicited by a single dose administration of NO-1886. Long-term supplementation with NO-1886 recovered hyperinsulinemia and low plasma levels of IGF1 suppressed LDL-C and facilitated reverse cholesterol transport by decreasing hepatic cholesterol accumulation through increasing CYP7A1 expression in high-fat/high-sucrose/high-cholesterol diet minipigs. These findings indicate that NO-1886 upregulates IGF1 secretion and CYP7A1 expression to improve insulin resistance and hepatic cholesterol accumulation, which may represent an alternative therapeutic avenue of NO-1886 for T2DM and metabolic syndrome.
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- Abstract: Diabetes x
- Abstract: Islets x
- Abstract: Insulin x
- Abstract: BetaCells x
- Abstract: Pancreas x
- Abstract: Obesity x
- Abstract: Hyperglycemia x
- Abstract: Hypoglycemia x
- Abstract: Insulinoma x
- Abstract: Glucagon x
- Abstract: IGF* x
- Abstract: Type 1 x
- Abstract: Type 2 x
Qinkai Li, Weidong Yin, Manbo Cai, Yi Liu, Hongjie Hou, Qingyun Shen, Chi Zhang, Junxia Xiao, Xiaobo Hu, Qishisan Wu, Makoto Funaki and Yutaka Nakaya
Hong Liu, Jian Guo, Lin Wang, Ning Chen, Andrew Karaplis, David Goltzman and Dengshun Miao
To assess the roles of 1,25-dihydroxyvitamin D (1,25(OH)2D) and parathyroid hormone (PTH) in hard tissue formation in oro-facial tissues, we examined the effect of either 1,25(OH)2D or PTH deficiency on dentin and dental alveolar bone formation and mineralization in the mandibles, and osteoblastic bone formation in long bones of 1α-hydroxylase knockout (1α(OH)ase−/−) mice. Compared with wild-type mice, the mineral density was decreased in the teeth and mandibles, and unmineralized dentin (predentin and biglycan immunopositive dentin) and unmineralized bone matrix in the dental alveolar bone were increased in 1α(OH)ase−/− mice. The dental volume, reparative dentin volume, and dentin sialoprotein immunopositive areas were reduced in 1α(OH)ase−/− mice. The cortical thickness, dental alveolar bone volume, and osteoblast number were all decreased significantly in the mandibles; in contrast, the osteoblast number and surface were increased in the trabecular bone of the tibiae in 1α(OH)ase−/− mice consistent with their secondary hyperparathyroidism. The expression of PTH receptor and IGF1 was reduced slightly in mandibles, but enhanced significantly in the long bones in the 1α(OH)ase−/− mice. To control for the role of secondary hyperparathyroidism, we also examined teeth and mandibles in 6-week-old PTH−/− mice. In these animals, dental and bone volumes in mandibles were not altered when compared with their wild-type littermates. These results suggest that 1,25(OH)2D3 plays an anabolic role in both dentin and dental alveolar bone as it does in long bones, whereas PTH acts predominantly in long bones rather than mandibular bone.
A Alidibbiat, C E Marriott, K T Scougall, S C Campbell, G C Huang, W M Macfarlane and J A M Shaw
Generation of new β-cells from the adult pancreas or the embryonic stem cells is being pursued by research groups worldwide. Success will be dependent on confirmation of true β-cell phenotype evidenced by capacity to process and store proinsulin. The aim of these studies was to robustly determine endocrine characteristics of the AR42J rat pancreatic acinar cell line before and after in vitro transdifferentiation. β-cell phenotypic marker expression was characterised by RT-PCR, immunostaining, western blotting, ELISA and in human preproinsulin transgene over-expression studies in wild-type AR42J cells and after culture on Matrigel basement membrane matrix with and without growth/differentiation factor supplementation. Pancreatic duodenal homeobox 1 (PDX1), forkhead box transcription factor a2 (Foxa2), glucokinase, pancreatic polypeptide and low-level insulin gene transcription in wild-type AR42J cells were confirmed by RT-PCR. Culture on Matrigel-coated plates and supplementation of medium with glucagon-like peptide 1 induced expression of the β-cell Glut 2 with maintained expression of insulin and PDX1. Increased biosynthesis and secretion of proinsulin were confirmed by immunocytochemical staining and sensitive ELISA. Absence of the regulated secretory pathway was demonstrated by undetectable prohormone convertase expression. In addition, inability to process and store endogenous proinsulin or human proinsulin translated from a constitutively over-expressed preproinsulin transgene was confirmed. The importance of robust phenotypic characterisation at the protein level in attempted β-cell transdifferentiation studies has been confirmed. Rodent and human sensitive/specific differential proinsulin/insulin ELISA in combination with human preproinsulin over-expression enables detailed elucidatation of core endocrine functions of proinsulin processing and storage in putative new β-cells.
P. J. Miettinen, T. Otonkoski and R. Voutilainen
To understand the development of the human pancreas better, we studied the expression and regulation of insulin, insulin-like growth factor-II (IGF-II) and transforming growth factor-α (TGF-α) genes in the human fetal pancreas and islet-like cell clusters (ICC) from the second trimester human fetuses. Northern blot analysis revealed an abundant expression of IGF-II, insulin and TGF-α mRNAs in the intact pancreas and the cultured ICCs. Furthermore, transcripts for insulin receptor, type-1 and -2 IGF receptors, and GH receptor could be amplified by polymerase chain reaction analysis from the pancreas and the ICCs. With in-situ hybridization, IGF-II mRNA was found in abundance in both the exocrine and endocrine pancreas, exceeding the amount of insulin mRNA. In ICCs, insulin mRNA-containing cells were present as small clusters in the periphery and in the centre of the clusters corresponding to the immunolocation of insulin. The ICCs also contained many epidermal growth factor-, insulin- and type-1 IGF receptor- and TGF-α-positive cells.
When the ICCs were cultured in the presence of various secretagogues, only dibutyryl cyclic AMP was found to up-regulate insulin mRNA (39%; P < 0·05). IGF-II mRNA was also under cyclic AMP-dependent regulation (threefold increase; P = 0·025). Furthermore, blocking the type-1 IGF receptor with a monoclonal receptor antibody drastically reduced insulin expression (87%; P = 0·005) and additionally down-regulated IGF-II mRNA (49%; P = 0·005). IGF-1, IGF-II, TGF-α or epidermal growth factor-receptor antibody had no significant effect on either insulin or IGF-II mRNA. Exogenous TGF-α inhibited the release of insulin by the ICCs. It was concluded that IGF-II and TGF-α may be involved in the regulation of islet growth and differentiation.
Journal of Endocrinology (1993) 138, 127–136
Wenpeng Dong, Ye Jia, Xiuxia Liu, Huan Zhang, Tie Li, Wenlin Huang, Xudong Chen, Fuchun Wang, Weixia Sun and Hao Wu
Oxidative stress contributes to the pathogenesis of diabetic nephropathy (DN). Nuclear factor erythroid 2-related factor 2 (NRF2) plays a key role in cellular defense against oxidative stress. NRF2 activators have shown promising preventive effects on DN. Sodium butyrate (NaB) is a known activator of NRF2. However, it is unknown whether NRF2 is required for NaB protection against DN. Therefore, streptozotocin-induced diabetic C57BL/6 Nrf2 knockout and their wild-type mice were treated in the presence or absence of NaB for 20 weeks. Diabetic mice, but not NaB-treated diabetic mice, developed significant renal oxidative damage, inflammation, apoptosis, fibrosis, pathological changes and albuminuria. NaB inhibited histone deacetylase (HDAC) activity and elevated the expression of Nrf2 and its downstream targets heme oxygenase 1 and NAD(P)H dehydrogenase quinone 1. Notably, deletion of the Nrf2 gene completely abolished NaB activation of NRF2 signaling and protection against diabetes-induced renal injury. Interestingly, the expression of Kelch-like ECH-associated protein 1, the negative regulator of NRF2, was not altered by NaB under both diabetic and non-diabetic conditions. Moreover, NRF2 nuclear translocation was not promoted by NaB. Therefore, the present study indicates, for the first time, that NRF2 plays a key role in NaB protection against DN. Other findings suggest that NaB may activate Nrf2 at the transcriptional level, possibly by the inhibition of HDAC activity.
K E Lines, P J Newey, C J Yates, M Stevenson, R Dyar, G V Walls, M R Bowl and R V Thakker
Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder characterised by the combined occurrence of parathyroid, pituitary and pancreatic islet tumours, and is due to mutations of the MEN1 gene, which encodes the tumour suppressor protein menin. Menin has multiple roles in genome stability, transcription, cell division and proliferation, but its mechanistic roles in tumourigenesis remain to be fully elucidated. miRNAs are non-coding single-stranded RNAs that post-transcriptionally regulate gene expression and have been associated with tumour development, although the contribution of miRNAs to MEN1-associated tumourigenesis and their relationship with menin expression are not fully understood. Alterations in miRNA expression, including downregulation of three putative ‘tumour suppressor’ miRNAs, miR-15a, miR-16-1 and let-7a, have been reported in several tumour types including non-MEN1 pituitary adenomas. We have therefore investigated the expression of miR-15a, miR-16-1 and let-7a in pituitary tumours that developed after 12 months of age in female mice with heterozygous knockout of the Men1 gene (Men1 +/ − mice). The miRNAs miR-15a, miR-16-1 and let-7a were significantly downregulated in pituitary tumours (by 2.3-fold, P < 0.05; 2.1-fold P < 0.01 and 1.6-fold P < 0.05, respectively) of Men1 +/ − mice, compared to normal WT pituitaries. miR-15a and miR-16-1 expression inversely correlated with expression of cyclin D1, a known pro-tumourigenic target of these miRNAs, and knockdown of menin in a human cancer cell line (HeLa), and AtT20 mouse pituitary cell line resulted in significantly decreased expression of miR-15a (P < 0.05), indicating that the decrease in miR-15a may be a direct result of lost menin expression.
Ghania Ramdani, Nadine Schall, Hema Kalyanaraman, Nisreen Wahwah, Sahar Moheize, Jenna J Lee, Robert L Sah, Alexander Pfeifer, Darren E Casteel and Renate B Pilz
NO/cGMP signaling is important for bone remodeling in response to mechanical and hormonal stimuli, but the downstream mediator(s) regulating skeletal homeostasis are incompletely defined. We generated transgenic mice expressing a partly-activated, mutant cGMP-dependent protein kinase type 2 (PKG2R242Q) under control of the osteoblast-specific Col1a1 promoter to characterize the role of PKG2 in post-natal bone formation. Primary osteoblasts from these mice showed a two- to three-fold increase in basal and total PKG2 activity; they proliferated faster and were resistant to apoptosis compared to cells from WT mice. Male Col1a1-Prkg2 R242Q transgenic mice had increased osteoblast numbers, bone formation rates and Wnt/β-catenin-related gene expression in bone and a higher trabecular bone mass compared to their WT littermates. Streptozotocin-induced type 1 diabetes suppressed bone formation and caused rapid bone loss in WT mice, but male transgenic mice were protected from these effects. Surprisingly, we found no significant difference in bone micro-architecture or Wnt/β-catenin-related gene expression between female WT and transgenic mice; female mice of both genotypes showed higher systemic and osteoblastic NO/cGMP generation compared to their male counterparts, and a higher level of endogenous PKG2 activity may be responsible for masking effects of the PKG2R242Q transgene in females. Our data support sexual dimorphism in Wnt/β-catenin signaling and PKG2 regulation of this crucial pathway in bone homeostasis. This work establishes PKG2 as a key regulator of osteoblast proliferation and post-natal bone formation.
B D Green, N Irwin, V A Gault, C J Bailey, F P M O’Harte and P R Flatt
Glucagon-like peptide-1 (GLP-1) is a potent insulinotropic hormone proposed to play a role in both the pathophysiology and treatment of type 2 diabetes. This study has employed the GLP-1 receptor antagonist, exendin-4(9–39)amide (Ex(9–39)) to evaluate the role of endogenous GLP-1 in genetic obesity-related diabetes and related metabolic abnormalities using ob/ob and normal mice. Acute in vivo antagonistic potency of Ex(9–39) was confirmed in ob/ob mice by blockade of the insulin-releasing and anti-hyperglycaemic actions of intraperitoneal GLP-1. In longer term studies, ob/ob mice were given once daily injections of Ex(9–39) or vehicle for 11 days. Feeding activity, body weight, and both basal and glucose-stimulated insulin secretion were not significantly affected by chronic Ex(9–39) treatment. However, significantly elevated basal glucose concentrations and impaired glucose tolerance were evident at 11 days. These disturbances in glucose homeostasis were independent of changes of insulin sensitivity and reversed by discontinuation of the Ex(9–39) for 9 days. Similar treatment of normal mice did not affect any of the parameters measured. These findings illustrate the physiological extrapancreatic glucose-lowering actions of GLP-1 in ob/ob mice and suggest that the endogenous hormone plays a minor role in the metabolic abnormalities associated with obesity-related diabetes.
Sanhua Leng, Wenshuo Zhang, Yanbin Zheng, Ziva Liberman, Christopher J Rhodes, Hagit Eldar-Finkelman and Xiao Jian Sun
High glucose (HG) has been shown to induce insulin resistance in both type 1 and type 2 diabetes. However, the molecular mechanism behind this phenomenon is unknown. Insulin receptor substrate (IRS) proteins are the key signaling molecules that mediate insulin's intracellular actions. Genetic and biological studies have shown that reductions in IRS1 and/or IRS2 protein levels are associated with insulin resistance. In this study we have shown that proteasome degradation of IRS1, but not of IRS2, is involved in HG-induced insulin resistance in Chinese hamster ovary (CHO) cells as well as in primary hepatocytes. To further investigate the molecular mechanism by which HG induces insulin resistance, we examined various molecular candidates with respect to their involvement in the reduction in IRS1 protein levels. In contrast to the insulin-induced degradation of IRS1, HG-induced degradation of IRS1 did not require IR signaling or phosphatidylinositol 3-kinase/Akt activity. We have identified glycogen synthase kinase 3β (GSK3β or GSK3B as listed in the MGI Database) as a kinase required for HG-induced serine332 phosphorylation, ubiquitination, and degradation of IRS1. Overexpression of IRS1 with mutation of serine332 to alanine partially prevents HG-induced IRS1 degradation. Furthermore, overexpression of constitutively active GSK3β was sufficient to induce IRS1 degradation. Our data reveal the molecular mechanism of HG-induced insulin resistance, and support the notion that activation of GSK3β contributes to the induction of insulin resistance via phosphorylation of IRS1, triggering the ubiquitination and degradation of IRS1.
Suwattanee Kooptiwut, Wanthanee Hanchang, Namoiy Semprasert, Mutita Junking, Thawornchai Limjindaporn and Pa-thai Yenchitsomanus
Hypogonadism in men is associated with an increased incidence of type 2 diabetes. Supplementation with testosterone has been shown to protect pancreatic β-cell against apoptosis due to toxic substances including streptozotocin and high glucose. One of the pathological mechanisms of glucose-induced pancreatic β-cell apoptosis is the induction of the local rennin–angiotensin–aldosterone system (RAAS). The role of testosterone in regulation of the pancreatic RAAS is still unknown. This study aims to investigate the protective action of testosterone against glucotoxicity-induced pancreatic β-cell apoptosis via alteration of the pancreatic RAAS pathway. Rat insulinoma cell line (INS-1) cells or isolated male mouse islets were cultured in basal and high-glucose media in the presence or absence of testosterone, losartan, and angiotensin II (Ang II), then cell apoptosis, cleaved caspase 3 expression, oxidative stress, and expression of angiotensin II type 1 receptor (AGTR1) and p47phox mRNA and protein were measured. Testosterone and losartan showed similar effects in reducing pancreatic β-cell apoptosis. Testosterone significantly reduced expression of AGTR1 protein in INS-1 cells cultured in high-glucose medium or high-glucose medium with Ang II. Testosterone decreased the expression of AGTR1 and p47phox mRNA and protein in comparison with levels in cells cultured in high-glucose medium alone. Furthermore, testosterone attenuated superoxide production when co-cultured with high-glucose medium. In contrast, when cultured in basal glucose, supplementation of testosterone did not have any effect on cell apoptosis, oxidative stress, and expression of AGT1R and p47phox. In addition, high-glucose medium did not increase cleaved caspase 3 in AGTR1 knockdown experiments. Thus, our results indicated that testosterone prevents pancreatic β-cell apoptosis due to glucotoxicity through reduction of the expression of ATGR1 and its signaling pathway.