You are looking at 111 - 120 of 13,908 items for

  • All content x
Clear All
Restricted access

Baiyang You, Yaoshan Dun, Wenliang Zhang, Lingjun Jiang, Hui Li, Murong Xie, Yuan Liu, and Suixin Liu

Mitochondrial quality control (MQC) and function are determinants for cellular energy metabolism, and their disorders are reported to play an important role in the development of insulin resistance (IR). Salidroside was reported to have beneficial effects on MQC through AMPK pathway; however, it is unknown whether salidroside exerts anti-IR effect with this action. This study sought to investigate the effects of salidroside on IR with an exploration of the mechanisms of its action. Experimental IR models were adopted in high-fat-diet (HFD)-fed mice and palmitate-treated C2C12 myotubes, respectively. Blood levels of glucose and insulin as well as cellular glucose uptake were determined, and mitochondrial function and MQC-associated parameters and reactive oxygen species (ROS) production were analyzed based on treatments with the activator (AICAR), inhibitors (compound C and EX-527) or specific siRNA of Ampk/Sirt1 and mitochondrial ROS scavenger (mito-TEMPO). Protein expression level was determined by Western blot, cellular observation by transmission electron microscope and ROS production by functional analysis kits. Salidroside reduced IR and activated insulin signaling along with the stimulation of AMPK/SIRT1 signaling and downstream regulation of MQC and ROS production. These salidroside effects were comparable to those of AICAR and could be prevented by AMPK/SIRT1 inhibitors or siRNAs, respectively. Salidroside reduces IR and regulates MQC and ROS production by activating AMPK/SIRT1 signaling pathway. Since IR is a critical issue for public health, to explore a potent agent against IR is of high interest. The anti-IR effects of salidroside warrant further experimental and clinical studies.

Restricted access

Jiali Liu, Yue Li, Xiaoyan Zhou, Xi Zhang, Hao Meng, Sanyuan Liu, Lei Zhang, Juntao He, Qian He, and Yan Geng

High-fat diet (HFD) not only induces insulin resistance in liver, but also causes autophagic imbalance and metabolic disorders, increases chronic inflammatory response and induces mitochondrial dysfunction. Calcium/calmodulin-dependent protein kinase IV (CaMKIV) has recently emerged as an important regulator of glucose metabolism and skeletal muscle insulin action. Its activation has been involved in the improvement of hepatic and adipose insulin action. But the underlying mechanism is not fully understood. In the present study, we aimed to address the direct effects of CaMKIV in vivo and to evaluate the potential interaction of impaired insulin sensitivity and autophagic disorders in hepatic insulin resistance. Our results indicated obese mice receiving CaMKIV showed decreased blood glucose and serum insulin and improved insulin sensitivity as well as increased glucose tolerance compared with vehicle injection. Meanwhile, defective hepatic autophagy activity, impaired insulin signaling, increased inflammatory response and mitochondrial dysfunction in liver tissues which are induced by high-fat diet were also effectively alleviated by injection of CaMKIV. Consistent with these results, the addition of CaMKIV to the culture medium of BNL cl.2 hepatocytes markedly restored palmitate-induced hepatic insulin resistance and autophagic imbalance. These effects were nullified by blockade of cyclic AMP response element-binding protein (CREB), indicating the causative role of CREB in action of CaMKIV. Our findings suggested that CaMKIV restores hepatic autophagic imbalance and improves impaired insulin sensitivity via phosphorylated CREB signaling pathway, which may offer novel opportunities for treatment of obesity and diabetes.

Restricted access

Olena A Fedorenko, Pawitra Pulbutr, Elin Banke, Nneoma E Akaniro-Ejim, Donna C Bentley, Charlotta S Olofsson, Sue Chan, and Paul A Smith

L-type channel antagonists are of therapeutic benefit in the treatment of hyperlipidaemia and insulin resistance. Our aim was to identify L-type voltage-gated Ca2+ channels in white fat adipocytes, and determine if they affect intracellular Ca2+, lipolysis and lipogenesis. We used a multidisciplinary approach of molecular biology, confocal microscopy, Ca2+ imaging and metabolic assays to explore this problem using adipocytes isolated from adult rat epididymal fat pads. CaV1.2, CaV1.3 and CaV1.1 alpha1, beta and alpha2delta subunits were detected at the gene expression level. The CaV1.2 and CaV1.3 alpha1 subunits were identified in the plasma membrane at the protein level. Confocal microscopy with fluorescent antibodies labelled CaV1.2 in the plasma membrane. Ca2+ imaging revealed that the intracellular Ca2+ concentration, [Ca2 +]i was reversibly decreased by removal of extracellular Ca2+, an effect mimicked by verapamil, nifedipine and Co2+, all blockers of L-type channels, whereas the Ca2+ channel agonist BAY-K8644 increased [Ca2+]i. The finding that the magnitude of these effects correlated with basal [Ca2+]i suggests that adipocyte [Ca2+]i is controlled by L-type Ca2+ channels that are constitutively active at the adipocyte depolarized membrane potential. Pharmacological manipulation of L-type channel activity modulated both basal and catecholamine-stimulated lipolysis but not insulin-induced glucose uptake or lipogenesis. We conclude that white adipocytes have constitutively active L-type Ca2+ channels which explains their sensitivity of lipolysis to Ca2+ channel modulators. Our data suggest CaV1.2 as a potential novel therapeutic target in the treatment of obesity.

Open access

Bernadette M Trojanowski, Heba H Salem, Heike Neubauer, Eric Simon, Martin Wagner, Rajkumar Dorajoo, Bernhard O Boehm, Leticia Labriola, Thomas Wirth, and Bernd Baumann

Maturity-onset diabetes of the young (MODY) is a group of monogenetic forms of diabetes mellitus caused by mutations in genes regulating β-cell development and function. MODY represents a heterogeneous group of non-insulin-dependent diabetes arising in childhood or adult life. Interestingly, clinical heterogeneity in MODY patients like variable disease onset and severity is observed even among individual family members sharing the same mutation, an issue that is not well understood. As high blood glucose levels are a well-known factor promoting β-cell stress and ultimately leading to cell death, we asked whether additional β-cell stress might account for the occurrence of disease heterogeneity in mice carrying a MODY4 mutation. In order to challenge β-cells, we established a MODY4 animal model based on Pdx1 (pancreatic and duodenal homeobox 1) haploinsufficiency, which allows conditional modulation of cell stress by genetic inhibition of the stress-responsive IKK/NF-κB signalling pathway. While Pdx1+/− mice were found glucose intolerant without progressing to diabetes, additional challenge of β-cell function by IKK/NF-κB inhibition promoted rapid diabetes development showing hyperglycaemia, hypoinsulinemia and loss of β-cell mass. Disease pathogenesis was characterized by deregulation of genes controlling β-cell homeostasis and function. Importantly, restoration of normal IKK/NF-κB signalling reverted the diabetic phenotype including normalization of glycaemia and β-cell mass. Our findings implicate that the avoidance of additional β-cell stress can delay a detrimental disease progression in MODY4 diabetes. Remarkably, an already present diabetic phenotype can be reversed when β-cell stress is normalized.

Restricted access

Michal Silber, Irit Miller, Hadas Bar-Joseph, Ido Ben-Ami, and Ruth Shalgi

PCOS is the most common endocrinopathy in women; associated with obesity and insulin resistance (IR). IR leads to accumulation of advanced-glycation-end-products (AGEs) and their receptor, RAGE. PCOS patients have increased levels of vascular endothelial growth factor (VEGF), interleukin 6/8 (IL-6/8) and anti-Mϋllerian-hormone (AMH). PEDF is a secreted-glycoprotein known for its anti-angiogenic and anti-inflammatory properties. We aimed to elucidate the role of PEDF in the pathogenesis and treatment of PCOS. We used a prenatal PCOS mouse model and fed the female offspring a high-fat diet, inducing metabolic PCOS (met.PCOS) characteristics. Female offspring were divided into three groups: control; met.PCOS; met.PCOS + recombinant PEDF (rPEDF). Met.PCOS mice gained more weight, had elevated serum IL-6 and higher mRNA levels of AMH, PEDF and RAGE in their granulosa cells (GCs) than met.PCOS + rPEDF mice. An in vitro Met.PCOS model in human GCs (KGN) line was induced by prolonged incubation with insulin/AGEs, causing development of IR. Under the same conditions, we observed an elevation of VEGF, IL-6/8 mRNAs, concomitantly with an increase in PEDF mRNA, intracellular protein levels, and an elevation of PEDF receptors (PEDF-Rs) mRNA and protein. Simultaneously, a reduction in the secretion of PEDF from GCs, was measured in the medium. The addition of rPEDF (5 nM) activated P38 signaling, implying that PEDF-Rs maintained functionality, and negated AGE-induced elevation of IL-6/8 and VEGF mRNAs. Decreased PEDF secretion may be a major contributor to hyperangiogenesis and chronic inflammation, which lie at the core of PCOS pathogenesis. rPEDF treatment may restore physiological angiogenesis inflammatory balance, thus suggesting a potential therapeutic role in PCOS.

Restricted access

Akiko Mizokami, Satoru Mukai, Jing Gao, Tomoyo Kawakubo-Yasukochi, Takahito Otani, Hiroshi Takeuchi, Eijiro Jimi, and Masato Hirata

Osteocalcin is a bone-derived hormone that in its uncarboxylated form (GluOC) plays an important role in glucose and energy metabolism by stimulating insulin secretion and pancreatic β-cell proliferation through its putative receptor GPRC6A. We previously showed that the effect of GluOC on insulin secretion is mediated predominantly by glucagon-like peptide-1 (GLP-1) released from intestinal endocrine cells in response to GluOC stimulation. Moreover, oral administration of GluOC was found to reduce the fasting blood glucose level, to improve glucose tolerance, and to increase the fasting serum insulin concentration and β-cell area in the pancreas in wild-type mice. We have now examined the effects of oral GluOC administration for at least 4 weeks in GLP-1 receptor-knockout mice. Such administration of GluOC in the mutant mice triggered glucose intolerance, enhanced gluconeogenesis and promoted both lipid accumulation in the liver as well as adipocyte hypertrophy and inflammation in adipose tissue. Furthermore, inactivation of GLP-1 receptor signaling in association with GluOC administration induced activation of the transcription factor FoxO1 and expression of its transcriptional coactivator PGC1α in the liver, likely accounting for the observed upregulation of gluconeogenic gene expression. Our results thus indicate that the beneficial metabolic effects of GluOC are dependent on GLP-1 receptor signaling.

Restricted access

Erin Faught and Mathilakath M Vijayan

During early development, stress or exogenous glucocorticoid (GC) administration reduces body mass in vertebrates, and this is associated with the glucocorticoid receptor (GR) activation. Although GCs also activate the mineralocorticoid receptor (MR), the physiological significance of MR activation on early developmental growth is unknown. We tested the hypothesis that activation of both GR and MR are required for postnatal growth suppression by GCs. Differential regulation of GR and MR activation was achieved by using ubiquitous GR- (GRKO) and MR- (MRKO) knockout zebrafish (Danio rerio) in combination with exogenous cortisol treatment. MR activation increased protein deposition in zebrafish larvae and also upregulated lepa and downregulated lepr transcript abundance. Cortisol treatment reduced body mass and protein content in the WT, and this corresponded with the upregulation of muscle proteolytic markers, including murf1 and redd1 by GR activation. The combined activation of MR and GR by cortisol also upregulated the gh and igf1 transcript abundance, and insulin expression compared to the WT. However, cortisol-mediated reduction in body mass and protein content required the activation of both MR and GR, as activation by GR alone (MRKO + cortisol) did not reduce the larval protein content. Collectively, our results indicate that MR activation favors protein deposition and GR activation stimulates proteolysis, while their combined activation is involved in cortisol-mediated growth suppression. Overall, this work provides insight into the physiological significance of MR activation in regulating protein deposition during early development at a systems level.

Restricted access

Umberto Simeoni, Clive Osmond, Ricardo Garay, Christophe Buffat, Farid Boubred, Christophe Chagnaud, Elisabeth Jouve, Christine Audebert, Jean-Michel Antoine, and Kent Thornburg

Low weight in early infancy is a known risk factor for cardio-metabolic syndrome in adult life. However, little is known either about developmental programming in subjects of normal birthweight or about events between the ages which separate early programming and the occurrence of disease at late adulthood. We tested the hypothesis that circulating concentrations of leptin, adiponectin and insulin in young, healthy adults, born with a birth size within the normal range, are influenced by early life growth patterns. In an observational study of 188 healthy volunteers aged 18–25 years (97 males, 91 females) we investigated the association of metabolic function with their birth size, their growth during childhood and their body composition. High plasma leptin in early adulthood, a risk factor for cardio-metabolic syndrome, was associated with low weight at age 2 years (correlation coefficient controlled for adult weight = −0.21, P < 0.01). It was also positively associated with pre-prandial insulin and with HOMA (Homeostasis Model Assessment) insulin resistance. Leptin, leptin-adiponectin ratio and insulin correlated with lean mass, fat mass and percent fat (P < 0.0001). In conclusion, high leptin in early adulthood was associated with both low weight at age 2 years and insulin resistance. We speculate that high leptin is developmentally programmed and can contribute to the association between low weight in early infancy and increased cardio-metabolic risk in adulthood in healthy subjects.

Restricted access

Nan Li, James A Oakes, Karl-Heinz Storbeck, Vincent T Cunliffe, and Nils P Krone

Cytochrome P450 side-chain cleavage enzyme, encoded by the CYP11A1 gene, catalyzes the first and rate-limiting step of steroid hormone biosynthesis. Previous morpholino-knockdown studies in zebrafish suggested cyp11a2 is a functional equivalent of human CYP11A1 and is essential for interrenal steroidogenesis in zebrafish larvae. The role of Cyp11a2 in adult zebrafish, particularly in gonadal steroidogenesis, remains elusive. To explore the role of Cyp11a2 in adults, we developed zebrafish mutant lines by creating deletions in cyp11a2 using the CRISPR/Cas9 genomic engineering approach. Homozygous cyp11a2 mutant zebrafish larvae showed an upregulation of the hypothalamic–pituitary–interrenal axis. Furthermore, these Cyp11a2-deficient zebrafish demonstrated profound glucocorticoid and androgen deficiencies. Cyp11a2 homozygotes only developed into males with feminized secondary sex characteristics. Adult cyp11a2 −/− mutant fish showed a lack of natural breeding behaviors. Histological characterization revealed disorganized testicular structure and significantly decreased numbers of mature spermatozoa. These findings are further supported by the downregulation of the expression of several pro-male genes in the testes of cyp11a2 homozygous zebrafish, including sox9a, dmrt1 and amh. Moreover, the spermatogonia markers nanos2 and piwil1 were upregulated, while the spermatocytes marker sycp3 and spermatids marker odf3b were downregulated in the testes of cyp11a2 homozygous mutants. Our expression analysis is consistent with our histological studies, suggesting that spermatogonia are the predominant cell types in the testes of cyp11a2 homozygous mutants. Our work thus demonstrates the crucial role of Cyp11a2 in interrenal and gonadal steroidogenesis in zebrafish larvae and adults.

Restricted access

Eileen I Chang, Paul J Rozance, Stephanie R Wesolowski, Leanna M Nguyen, Steven C Shaw, Robert A Sclafani, Kristen K Bjorkman, Angela K Peter, William W Hay Jr, and Laura D Brown

Intrauterine growth-restricted (IUGR) fetuses are born with reduced skeletal muscle mass. We hypothesized that reduced rates of myogenesis would contribute to fewer and smaller myofibers in IUGR fetal hindlimb muscle compared to the normally growing fetus. We tested this hypothesis in IUGR fetal sheep with progressive placental insufficiency produced by exposing pregnant ewes to elevated ambient temperatures from 38 to 116 days gestation (dGA; term = 147 dGA). Surgically catheterized control (CON, n = 8) and IUGR (n = 13) fetal sheep were injected with intravenous 5-bromo-2′-deoxyuridine (BrdU) prior to muscle collection (134 dGA). Rates of myogenesis, defined as the combined processes of myoblast proliferation, differentiation, and fusion into myofibers, were determined in biceps femoris (BF), tibialis anterior (TA), and flexor digitorum superficialis (FDS) muscles. Total myofiber number was determined for the entire cross-section of the FDS muscle. In IUGR fetuses, the number of BrdU+ myonuclei per myofiber cross-section was lower in BF, TA, and FDS (P < 0.05), total myonuclear number per myofiber cross-section was lower in BF and FDS (P < 0.05), and total myofiber number was lower in FDS (P < 0.005) compared to CON. mRNA expression levels of cyclins, cyclin-dependent protein kinases, and myogenic regulatory factors were lower (P < 0.05), and inhibitors of the cell cycle were higher (P < 0.05) in IUGR BF compared to CON. Markers of apoptosis were not different in IUGR BF muscle. These results show that in IUGR fetuses, reduced rates of myogenesis produce fewer numbers of myonuclei, which may limit hypertrophic myofiber growth. Fewer myofibers of smaller size contribute to smaller muscle mass in the IUGR fetus.