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Ulas Ozkurede, Rishabh Kala, Cameron Johnson, Ziqian Shen, Richard A Miller and Gonzalo G Garcia

It has been hypothesized that transcriptional changes associated with lower mTORC1 activity in mice with reduced levels of growth hormone and insulin-like growth factor 1 are responsible for the longer healthy lifespan of these mutant mice. Cell lines and tissues from these mice show alterations in the levels of many proteins that cannot be explained by corresponding changes in mRNAs. Such post-transcriptional modulation may be the result of preferential mRNA translation by the cap-independent translation of mRNA bearing the N6-methyl-adenosine (m6A) modification. The long-lived endocrine mutants – Snell dwarf, growth hormone receptor deletion and pregnancy-associated plasma protein-A knockout – all show increases in the N6-adenosine-methyltransferases (METTL3/14) that catalyze 6-methylation of adenosine (m6A) in the 5′ UTR region of select mRNAs. In addition, these mice have elevated levels of YTH domain-containing protein 1 (YTHDF1), which recognizes m6A and promotes translation by a cap-independent mechanism. Consistently, multiple proteins that can be translated by the cap-independent mechanism are found to increase in these mice, including DNA repair and mitochondrial stress response proteins, without changes in corresponding mRNA levels. Lastly, a drug that augments cap-independent translation by inhibition of cap-dependent pathways (4EGI-1) was found to elevate levels of the same set of proteins and able to render cells resistant to several forms of in vitro stress. Augmented translation by cap-independent pathways facilitated by m6A modifications may contribute to the stress resistance and increased healthy longevity of mice with diminished GH and IGF-1 signals.

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Isabel Moscoso, María Cebro-Márquez, Moisés Rodríguez-Mañero, José Ramón González-Juanatey and Ricardo Lage

Irisin is a newly identified adipokine critical to modulate body metabolism, fatty acid metabolism and oxidative stress; recent evidence suggests a cardioprotective role in ischemic injury. Loss of cardiomyocytes during acute myocardial infarction is strongly associated with energetic changes and lipotoxic-induced apoptosis. Our aim was to study FNDC5/irisin’s potential protective role against hypoxia and lipotoxicity, both related with myocardial infarction environment. H9c2 cells were treated with palmitate and/or irisin in normoxic/hypoxic conditions. Cell viability and apoptosis were assessed by MTT assay and annexin V/PI staining. Immunoblotting was used to confirm apoptotic cascade regulation. Irisin counteracts lipotoxic-induced apoptosis in hypoxic cardiomyoblasts by activating Akt signaling pathway suggesting the potential therapeutic role of irisin in ischemic heart disease.

Open access

Yan Zheng and Kevin D Houston

G protein-coupled estrogen receptor 1 (GPER1) is a seven-transmembrane receptor that mediates rapid cell signaling events stimulated by estrogens. While the role that GPER1 has in the modulation of E2-responsive tissues and cancers is well documented, the molecular mechanisms that regulate GPER1 expression are currently not well defined. The recently identified GPER1-dependent mechanism of tamoxifen action in breast cancer cells underscores the importance of identifying mechanisms that regulate GPER1 expression in this cell type. We hypothesized that GPER1 expression in breast cancer cells is sensitive to [D-glucose] and provide data showing increased GPER1 expression when cells were cultured in low [D-glucose]. To determine if the observed accumulation of GPER1 was AMP-activated protein kinase (AMPK)-dependent, small molecule stimulation or inhibition of AMPK was performed. AMPK inhibition decreased GPER1 accumulation in cells grown in low [D-glucose] while the AMPK-activating compound AICAR increased GPER1 accumulation in cells grown in high [D-glucose] media. Additionally, transfection of cells with a plasmid expressing constitutively active AMPK resulted in increased GPER1 accumulation. To determine if [D-glucose]-dependent GPER1 accumulation altered breast cancer cell response to tamoxifen, cells grown in the presence of decreasing [D-glucose] were co-treated with tamoxifen and IGFBP-1 transcription was measured. The results from these experiments reveal that D-glucose deprivation increased GPER1-mediated and tamoxifen-induced IGFBP-1 transcription suggesting that [D-glucose] may increase breast cancer cell sensitivity to tamoxifen. Taken together, these results identify a previously unknown mechanism that regulates GPER1 expression that modifies one aspect tamoxifen action in breast cancer cells.

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Fabio Arturo Grieco, Andrea Alex Schiavo, Flora Brozzi, Jonas Juan-Mateu, Marco Bugliani, Piero Marchetti and Décio L Eizirik

miRNAs are a class of small non-coding RNAs that regulate gene expression. Type 1 diabetes is an autoimmune disease characterized by insulitis (islets inflammation) and pancreatic beta cell destruction. The pro-inflammatory cytokines interleukin 1 beta (IL1B) and interferon gamma (IFNG) are released during insulitis and trigger endoplasmic reticulum (ER) stress and expression of pro-apoptotic members of the BCL2 protein family in beta cells, thus contributing to their death. The nature of miRNAs that regulate ER stress and beta cell apoptosis remains to be elucidated. We have performed a global miRNA expression profile on cytokine-treated human islets and observed a marked downregulation of miR-211-5p. By real-time PCR and Western blot analysis, we confirmed cytokine-induced changes in the expression of miR-211-5p and the closely related miR-204-5p and downstream ER stress related genes in human beta cells. Blocking of endogenous miRNA-211-5p and miR-204-5p by the same inhibitor (it is not possible to block separately these two miRs) increased human beta cell apoptosis, as measured by Hoechst/propidium Iodide staining and by determination of cleaved caspase-3 activation. Interestingly, miRs-211-5p and 204-5p regulate the expression of several ER stress markers downstream of PERK, particularly the pro-apoptotic protein DDIT3 (also known as CHOP). Blocking CHOP expression by a specific siRNA partially prevented the increased apoptosis observed following miR-211-5p/miR-204-5p inhibition. These observations identify a novel crosstalk between miRNAs, ER stress and beta cell apoptosis in early type 1 diabetes.

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Caroline M Gorvin

Twenty-five years have elapsed since the calcium-sensing receptor (CaSR) was first identified in bovine parathyroid and the receptor is now recognized as a fundamental contributor to extracellular Ca2+ (Ca2+ e) homeostasis, regulating parathyroid hormone release and urinary calcium excretion. The CaSR is a class C G-protein-coupled receptor (GPCR) that is functionally active as a homodimer and couples to multiple G-protein subtypes to activate intracellular signalling pathways. The importance of the CaSR in the regulation of Ca2+ e has been highlighted by the identification of >400 different germline loss- and gain-of-function CaSR mutations that give rise to disorders of Ca2+ e homeostasis. CaSR-inactivating mutations cause neonatal severe hyperparathyroidism, characterised by marked hypercalcaemia, skeletal demineralisation and failure to thrive in early infancy; and familial hypocalciuric hypercalcaemia, an often asymptomatic disorder associated with mild-moderately elevated serum calcium concentrations. Activating mutations are associated with autosomal dominant hypocalcaemia, which is occasionally associated with a Bartter’s-like phenotype. Recent elucidation of the CaSR extracellular domain structure enabled the locations of CaSR mutations to be mapped and has revealed clustering in locations important for structural integrity, receptor dimerisation and ligand binding. Moreover, the study of disease-causing mutations has demonstrated that CaSR signals in a biased manner and have revealed specific residues important for receptor activation. This review presents the current understanding of the genetic landscape of CaSR mutations by summarising findings from clinical and functional studies of disease-associated mutations. It concludes with reflections on how recently uncovered signalling pathways may expand the understanding of calcium homeostasis disorders.

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Shilpa Thakur, Brianna Daley and Joanna Klubo-Gwiezdzinska

Incidence of endocrine cancers is rising every year. Over the last decade, evidence has accumulated that demonstrates the anti-cancer effects of an anti-diabetic drug, metformin, in endocrine malignancies. We performed a literature review utilizing the PubMed, Medline and databases using the keyword ‘metformin’ plus the following terms: ‘thyroid cancer’, ‘thyroid nodules’, ‘parathyroid’, ‘hyperparathyroidism’, ‘adrenal adenoma’, ‘Cushing syndrome’, ‘hyperaldosteronism’, ‘adrenocortical cancer’, ‘neuroendocrine tumor (NET)’, ‘pancreatic NET (pNET)’, ‘carcinoid’, ‘pituitary adenoma’, ‘pituitary neuroendocrine tumor (PitNET)’, ‘prolactinoma’, ‘pheochromocytoma/paraganglioma’. We found 37 studies describing the preclinical and clinical role of metformin in endocrine tumors. The available epidemiological data show an association between exposure of metformin and lower incidence of thyroid cancer and pNETs in diabetic patients. Metformin treatment has been associated with better response to cancer therapy in thyroid cancer and pNETs. Preclinical evidence suggests that the primary direct mechanisms of metformin action include inhibition of mitochondrial oxidative phosphorylation via inhibition of both mitochondrial complex I and mitochondrial glycerophosphate dehydrogenase, leading to metabolic stress. Decreased ATP production leads to an activation of a cellular energy sensor, AMPK, and subsequent downregulation of mTOR signaling pathway, which is associated with decreased cellular proliferation. We also describe several AMPK-independent mechanisms of metformin action, as well as the indirect mechanisms targeting insulin resistance. Overall, repositioning of metformin has emerged as a promising strategy for adjuvant therapy of endocrine tumors. The mechanisms of synergy between metformin and other anti-cancer agents need to be elucidated further to guide well-designed prospective trials on combination therapies in endocrine malignancies.

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Pabitra B Pal, Himangshu Sonowal, Kirtikar Shukla, Satish K Srivastava and Kota V Ramana

Although hyperglycemia-mediated death and dysfunction of endothelial cells have been reported to be a major cause of diabetes associated vascular complications, the mechanisms through which hyperglycemia cause endothelial dysfunction is not well understood. We have recently demonstrated that aldose reductase (AR, AKR1B1) is an obligatory mediator of oxidative and inflammatory signals induced by growth factors, cytokines and hyperglycemia. However, the molecular mechanisms by which AR regulates hyperglycemia-induced endothelial dysfunction is not well known. In this study, we have investigated the mechanism(s) by which AR regulates hyperglycemia-induced endothelial dysfunction. Incubation of human umbilical vein endothelial cells (HUVECs) with high glucose (HG) decreased the cell viability and inhibition of AR prevented it. Further, AR inhibition prevented the HG-induced ROS generation and expression of BCL-2, BAX and activation of Caspase-3 in HUVECs. AR inhibition also prevented the adhesion of THP-1 monocytes on HUVECs, expression of iNOS and eNOS and adhesion molecules ICAM-1 and VCAM-1 in HG-treated HUVECs. Further, AR inhibition restored the HG-induced depletion of SIRT1 in HUVECs and increased the phosphorylation of AMPKα1 along-with a decrease in phosphorylation of mTOR in HG-treated HUVECs. Fidarestat decreased SIRT1 expression in HUVECs pre-treated with specific SIRT1 inhibitor but not with the AMPKα1 inhibitor. Similarly, knockdown of AR in HUVECs by siRNA prevented the HG-induced HUVECs cell death, THP-1 monocyte adhesion and SIRT1 depletion. Furthermore, fidarestat regulated the phosphorylation of AMPKα1 and mTOR, and expression of SIRT1 in STZ-induced diabetic mice heart and aorta tissues. Collectively, our data suggest that AR regulates hyperglycemia-induced endothelial death and dysfunction by altering the ROS/SIRT1/AMPKα1/mTOR pathway.

Free access

Jie Sun, Yan Liu, Jinhui Yu, Jin Wu, Wenting Gao, Liyuan Ran, Rujiao Jiang, Meihua Guo, Dongyu Han, Bo Liu, Ning Wang, Youwei Li, He Huang, Li Zeng, Ying Gao, Xin Li and Yingjie Wu

Astragalus polysaccharide (APS) is the main component of Astragalus membranaceus, an anti-diabetic herb being used for thousands of years in Traditional Chinese medicine (TCM). In this study, we aimed to evaluate the impact of APS on hepatic insulin signaling, autophagy and ER stress response in high-fat-diet (HFD)-induced insulin resistance (IR) mice. APS was intra-gastrically administrated and metformin was used as a control medicine. Apart from monitoring the changes in the important parameters of IR progression, the gene and protein expression of the key factors marking the state of hepatic ER stress and autophagic flux were examined. We found that, largely comparable to the metformin regime, APS treatment resulted in an overall improvement of IR, as indicated by better control of body weight and blood glucose/lipid levels, recovery of liver functions and regained insulin sensitivity. In particular, the excessive and pro-apoptotic ER stress response and inhibition of autophagy, as a result of prolonged HFD exposure, were significantly corrected by APS administration, indicating a switch of the cellular fate in favor of cell survival. Using the HepG2/IR cell model, we demonstrated that APS modulated the insulin-initiated phosphorylation cascades in a similar manner to metformin. This study provides a rationale for exploiting the insulin-sensitizing potential of APS, which has a therapeutic performance almost equivalent to metformin, to enrich our options in the treatment of IR.

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Tae Woo Jung, Hyoung-Chun Kim, Yong Kyoo Shin, Hyeyoung Min, Seong-Wan Cho, Zi Soo Kim, Su Mi Han, A M Abd El-Aty, Ahmet Hacımüftüoğlu and Ji Hoon Jeong

An aqueous extract of Humulus japonicus (AH) has been documented to ameliorate hypertension and non-alcoholic fatty liver disease (NAFLD). Here, we investigated the effects of an aqueous extract of AH on thermogenesis and palmitate-induced oxidative stress in adipocytes. To verify the effect of AH on browning, we measured the expression levels of specific markers in 3T3-L1 adipocytes using qPCR and Western blotting, respectively. To assess the role of oxidative stress, cells were stained with DCFDA and observed by fluorescence microscopy. AH increased the expression of brown adipose tissue-specific markers. Additionally, it induced fatty acid oxidation and lipolysis and suppressed both lipogenic markers and lipid accumulation. Furthermore, AH ameliorated hydrogen peroxide-induced oxidative stress. Enhanced expression of these markers contributed to fat browning, fatty acid oxidation and lipolysis of 3T3-L1 adipocytes via the AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor delta (PPARδ) signaling pathways. Moreover, AMPK and PPARδ resulting in protective effects of AH against oxidative stress. In sum, AH could promote the browning, lipolysis and thermogenesis in 3T3-L1 adipocytes and would suppress the hydrogen peroxide-induced oxidative stress and lipogenesis during differentiation. We therefore suggest that AH could be used as a potential candidate for treating obesity and related metabolic disorders.

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Choa Park, Joonwoo Park, Myeong Kuk Shim, Mee-Ra Rhyu, Byung-Koo Yoon, Kyung Sook Kim and YoungJoo Lee

Atherosclerosis is the most common root cause of arterial disease, such as coronary artery disease and carotid artery disease. Hypoxia is associated with the formation of macrophages and increased inflammation and is known to be present in lesions of atherosclerotic. Vascular smooth muscle cells (VSMCs) are one of the major components of blood vessels, and hypoxic conditions affect VSMC inflammation, proliferation and migration, which contribute to vascular stenosis and play a major role in the atherosclerotic process. Estrogen receptor (ER)-β is thought to play an important role in preventing the inflammatory response in VSMCs. In this report, we studied the anti-inflammatory effect of indazole (In)-Cl, an ERβ-specific agonist, under conditions of hypoxia. Expression of cyclooxygenase-2 reduced by hypoxia was inhibited by In-Cl treatment in VSMCs, and this effect was antagonized by an anti-estrogen compound. Additionally, the production of reactive oxygen species induced under conditions of hypoxia was reduced by treatment with In-Cl. Increased cell migration and invasion by hypoxia were also dramatically decreased following treatment with In-Cl. The increase in cell proliferation following treatment with platelet-derived growth factor was attenuated by In-Cl in VSMCs. RNA sequencing analysis was performed to identify changes in inflammation-related genes following In-Cl treatment in the hypoxic state. Our results suggest that ERβ is a potential therapeutic target for the suppression of hypoxia-induced inflammation in VSMCs.