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Marina C Muñoz, Verónica G Piazza, Valeria Burghi, Jorge F Giani, Carolina S Martinez, Nadia S Cicconi, Nadia V Muia, Yimin Fang, Sergio Lavandero, Ana I Sotelo, Andrzej Bartke, Patricia A Pennisi, Fernando P Dominici, and Johanna G Miquet

Growth hormone (GH) exerts major actions in cardiac growth and metabolism. Considering the important role of insulin in the heart and the well-established anti-insulin effects of GH, cardiac insulin resistance may play a role in the cardiopathology observed in acromegalic patients. As conditions of prolonged exposure to GH are associated with a concomitant increase of circulating GH, IGF1 and insulin levels, to dissect the direct effects of GH, in this study, we evaluated the activation of insulin signaling in the heart using four different models: (i) transgenic mice overexpressing GH, with chronically elevated GH, IGF1 and insulin circulating levels; (ii) liver IGF1-deficient mice, with chronically elevated GH and insulin but decreased IGF1 circulating levels; (iii) mice treated with GH for a short period of time; (iv) primary culture of rat cardiomyocytes incubated with GH. Despite the differences in the development of cardiomegaly and in the metabolic alterations among the three experimental mouse models analyzed, exposure to GH was consistently associated with a decreased response to acute insulin stimulation in the heart at the receptor level and through the PI3K/AKT pathway. Moreover, a blunted response to insulin stimulation of this signaling pathway was also observed in cultured cardiomyocytes of neonatal rats incubated with GH. Therefore, the key novel finding of this work is that impairment of insulin signaling in the heart is a direct and early event observed as a consequence of exposure to GH, which may play a major role in the development of cardiac pathology.

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Jianqiu Gu, Weijuan Shao, Dinghui Liu, Jia Nuo Feng, Juan Pang, and Tianru Jin

Although canonical Wnt signaling pathway activation was shown to negatively regulate adipogenesis, recent investigations suggest that Wnt pathway effectors TCF7L2 and β-catenin (β-cat) in adipose tissues are also involved in energy homeostasis during adulthood. In assessing the metabolic beneficial effect of GLP-1-based diabetes drugs in high-fat diet (HFD)-challenged mice, we observed that liraglutide treatment affected the expression of a battery of adipose tissue-specific genes, including those that encode adiponectin and leptin, mainly in epididymal white adipose tissue (eWAT). Fourteen-week HFD challenge repressed TCF7L2 and β-cat S675 phosphorylation in eWAT, while such repression was reversed by liraglutide treatment (150 µg/kg body weight daily) during weeks 10–14. In Glp1r−/− mice, liraglutide failed in stimulating TCF7L2 or β-cat in eWAT. We detected Glp1r expression in mouse eWAT and its level is enriched in its stromal vascular fraction (SVF). Mouse eWAT-SVF showed reduced expression of Tcf7l2 and its Tcf7l2 level could not be stimulated by liraglutide treatment; while following adipogenic differentiation, rat eWAT-SVF showed elevated Tcf7l2 expression. Direct in vitro liraglutide treatment in eWAT-SVF stimulated CREB S133, β-cat S675 phosphorylation, and cellular cAMP level. Thus, cAMP/β-cat signaling cascade can be stimulated by liraglutide in eWAT via GLP-1R expressed in eWAT-SVF.

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Xuefeng Peng, Fang He, Yanling Mao, Yihui Lin, Jingwen Fang, Yangchun Chen, Zhichun Sun, Yafen Zhuo, and Jianjia Jiang

We tried to unveil the clinical significance of miR-146a as a biomarker in M2 macrophage polarization in diabetic wound healing. Initially, we found reduced miR-146a in macrophages of diabetic patients. Next, dual-luciferase assay verified that toll-like receptor 4 (TLR4) was a target gene of miR-146 and was negatively regulated by miR-146. Moreover, after ectopic expression and depletion experiments of miR-146 and/or TLR4, lipopolysaccharide-induced inflammatory response of macrophages was detected. The results revealed that overexpression of miR-146a promoted the M2 macrophage polarization by suppressing the TLR4/nuclear factor-kappaB (NF-κB) axis, so as to enhance wound healing in diabetic ulcers. Further, mouse models with diabetic ulcers were established to investigate the effects of miR-146a on diabetic wound healing in vivo, which revealed that miR-146a promoted wound healing in diabetic ulcers by inhibiting the TLR4/NF-κB axis. In conclusion, we demonstrate that miR-146a can induce M2 macrophage polarization to enhance wound healing in diabetic ulcers by inhibiting the TLR4/NF-κB axis.

Open access

Shalinee Dhayal, Kaiyven Afi Leslie, Mohammad Baity, Pouria Akhbari, Sarah J Richardson, Mark A Russell, and Noel G Morgan

During the development of type 1 diabetes, interferons (IFN) are elaborated from islet-infiltrating immune cells and/or from virally infected β-cells. They act via specific receptors to increase, acutely, the phosphorylation of the transcription factors STAT1 and 2. However, the longer-term impacts of chronic IFN stimulation are poorly understood and were investigated in the current study. Human EndoC-βH1 cells were treated with IFNα, IFNγ or IFNλ either acutely (<2 h) or chronically (≥24 h) and STAT phosphorylation, expression and activity were assessed by Western blotting and transcriptional reporter assays. Exposure of β-cells to IFNα or IFNλ induced a swift increase in the phosphorylation of both STAT1 and STAT2, whereas IFNγ increased only pSTAT1. Over more extended periods (≥24 h), STAT phosphorylation declined but STAT1 and STAT2 expression were enhanced in a sustained manner. All IFNs stimulated ISRE transcriptional activity (but with different time courses), whereas GAS activity was responsive only to IFNγ. The re-addition of a second bolus of IFNα, 24 h after an initial dose, failed to cause renewed STAT1/2 phosphorylation. By contrast, when IFNγ was added 24 h after exposure to IFNα, rapid STAT1 phosphorylation was re-initiated. Exposure of β-cells to IFNs leads to rapid, transient, STAT phosphorylation and to slower and more sustained increases in total STAT1/2 levels. The initial phosphorylation response is accompanied by marked desensitisation to the cognate agonist. Together, the results reveal that the response of β-cells to IFNs is regulated both temporally and quantitatively to achieve effective signal integration.

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Varun S Venkatesh, Patricia K Russell, Barbara Fam White, Michele V Clarke, Suzanne Golub, Salvatore Mangiofico, Christian Haralambous, Julie Lokan, Sof Andrikopoulos, Jeffrey D Zajac, and Rachel A Davey

We previously identified a novel pathway of testosterone action via the androgen receptor (AR) in bone marrow mesenchymal precursor cells (BM-PCs) to negatively regulate fat mass and improve metabolic function in male mice. This was achieved using our PC-AR Gene Replacement mouse model in which the AR is only expressed in BM-PCs and deleted in all other tissues. We hypothesise that the markedly reduced fat mass and increased insulin sensitivity of PC-AR Gene Replacements will confer protection from diet-induced overweight and obesity. To test this, 6-week-old male PC-AR Gene Replacements and controls (WT, global-AR knockouts (KOs)) were fed a chow or high-caloric diet (HCD) for 8 or 18 weeks. Following 8 weeks (short-term) of HCD, WT and Global-ARKOs had markedly increased subcutaneous white adipose tissue (WAT) and retroperitoneal visceral adipose tissue (VAT) mass compared to chow-fed controls. In contrast, PC-AR Gene Replacements were resistant to WAT and VAT accumulation following short-term HCD feeding accompanied by fewer large adipocytes and upregulation of expression of the metabolic genes Acaca and Pnlpa2. Following long-term HCD feeding for 18 weeks, the PC-AR Gene Replacements were no longer resistant to increased WAT and VAT adiposity, however, maintained their improved whole-body insulin sensitivity with an increased rate of glucose disappearance and increased glucose uptake into subcutaneous WAT. In conclusion, the action of testosterone via the AR in BM-PCs to negatively regulate fat mass and improve metabolism confers resistance from short-term diet-induced weight gain and partial protection from long-term diet-induced obesity in male mice.

Open access

Carolin Lisa Michaela Ludwig, Simon Bohleber, Alexander Rebl, Eva Katrin Wirth, Marzia Tindara Venuto, Martina Langhammer, Ulrich Schweizer, Joachim M Weitzel, and Marten Michaelis

The Dummerstorf high-fertility mouse line FL1 is a worldwide unique selection experiment for increased female reproductive performance. After more than 190 generations of selection, these mice doubled the amount of offspring per litter compared to the unselected control line. FL1 females have a superior lifetime fecundity and the highest Silver fecundity index that has been described in mice, while their offspring show no signs of growth retardation. The reasons for the increased reproductive performance remained unclear. Thus, this study aims to characterize the Dummerstorf high-fertility mouse line FL1 on endocrine and molecular levels on the female side. We analyzed parameters of the hypothalamic pituitary gonadal axis on both hormonal and transcriptional levels. Gonadotropin-releasing hormone and follicle-stimulating hormone (FSH) concentrations were decreased in FL1 throughout the whole estrous cycle. Luteinizing hormone (LH) was increased in FL1 mice in estrus. Progesterone concentrations were decreased in estrus in FL1 mice and not affected in diestrus. We used a holistic gene expression approach in the ovary to obtain a global picture of how the high-fertility phenotype is achieved. We found several differentially expressed genes in the ovaries of FL1 mice that are associated with different female fertility traits. Our results indicate that ovulation rates in mice can be increased despite decreased FSH levels. Cycle-related alterations of progesterone and LH levels have the potential to improve follicular maturation, and interactions of endocrine and molecular factors lead to enhanced follicular survival, more successful folliculogenesis and therefore higher ovulation rates in female FL1 mice.

Free access

Debolina Chakraborty, Ashish Sarkar, Sonia Mann, Monu, Prachi Agnihotri, Mohd Saquib, Swati Malik, Rajkamal Kumavat, Anushka Mathur, and Sagarika Biswas

Exploration of the dual and opposing facets of estrogen necessitates a clear understanding to diminish the controversy of estrogen regulation in averting the systemic, autoimmune, joint degrading disorder, and rheumatoid arthritis (RA). Experimental evidences consider estrogen as a pivotal enzyme to modulate the disease progression via managing several cellular mechanisms targeting inflammatory markers such as TNF, ILs, nuclear factor kappa B, and other regulatory proteins like matrix metalloproteinases impeding joint erosion and cartilage degradation. Estrogen modulates cellular signaling associated with inflammation, oxidative stress, related cardiovascular risk, and miRNA regulation during RA progression. Studies determining estrogen regulation in RA complicate the resemblance of the outcome as they represent both hyper and hypo level of estrogen is linked to the disease. Although some reports deliver estrogen as malign, there is now increasing evidence of rendering protection dose dependently. Variation in estrogen level causes differential expression of certain proteins and their related signaling which is directly or indirectly linked to RA pathogenesis. This review summarizes the variations in protein expression levels by focusing on the in vitro, in vivo,and clinical studies of estrogen deficiency and treatment. Construction of protein–protein interaction network, GO, and KEGG pathway enrichment analysis of the differentially expressed proteins assist in hypothesizing a potential molecular mechanism of estrogen in RA via in silico studies. Targeting these differential proteins can emerge a new path for developing advanced therapeutic strategies.

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Tracy Maree Josephs, Frankie Zhang, Le Vi Dinh, Andrew N Keller, Arthur D Conigrave, Ben Capuano, Karen Joan Gregory, and Katie Leach

Loss-of-function calcium-sensing receptor (CASR) mutations cause mineral metabolism disorders, familial hypocalciuric hypercalcemia, or neonatal severe hyperparathyroidism and increase the risk of femoral fracture, chronic kidney disease, coronary heart disease, and other diseases. In severe cases, CaSR mutations are lethal. Off-label use of the CaSR-positive allosteric modulator (PAM), cinacalcet, corrects hypercalcemia in some patients with CaSR mutations. However, other patients remain unresponsive to cinacalcet, attesting to the need for novel treatments. Here, we compared the effects of cinacalcet to two other clinically approved synthetic CaSR activators, evocalcet and etelcalcetide, as well as a novel PAM, 1-(2,4-dimethylphenyl)-1-(4,5-dimethylthiazol-2-yl)ethan-1-ol (MIPS-VD-836-108) on clinically relevant CaSR mutations. We assessed the compounds in CaSR-expressing HEK293 cells for correction of mutation-induced impairments in intracellular calcium (Ca2+ i) mobilization and cell surface expression. While cinacalcet, MIPS-VD-836-108 and evocalcet rescued the signaling of cell surface-expressed mutants, albeit to varying degrees, etelcalcetide was ineffective. Cinacalcet and evocalcet, but not MIPS-VD-836-108 or etelcalcetide, restored the expression of a R680H mutant. However, no compound rescued expression of I81K and C582R mutants or a receptor missing 77 amino acids in the extracellular domain mimicking deletion of CASRexon 5, which impairs CaSR function. These data suggest specific compounds may be clinically effective in some patients with CaSR mutations, but other patients will remain refractory to treatment with currently available CaSR-targeting activators, highlighting the need for new generation drugs to rescue both the signaling and expression of mutant CaSRs.

Free access

Drake Hechter, Brett Vahkal, Tiana Tiede, and Sara V Good

There is no common consensus on the physiological role of insulin-like peptide 5 (INSL5) and its cognate receptor, relaxin family peptide receptor 4 (RXFP4). The experimental data for INSL5–RXFP4 expression and function point to a potential role of the peptide hormone and receptor pair in linking energy availability, homeostasis, and inflammation. In this review, we summarize studies on the INSL5–RXFP4 system and propose that the current findings from diverse experimental settings point broadly to a role as a protective energy sensor (PES). Specifically, we review the evidence that (1) INSL5–RXFP4 could regulate immune response by decreasing the production of proinflammatory cytokines and may be involved in the stress response via the HPA axis; (2) INSL5–RXFP4 may signal through sensory neurons on the vagus nerve, transmitting signals to the CNS; and (3) INSL5–RXFP4 could have local autocrine/paracrine roles within the intestinal tract and immune cells. Further investigation and clarification of these proposed roles of INSL5–RXFP4 may prove a greater physiological relevance for the pair and add to existing evidence of INSL5–RXFP4 role as a PES.

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Naoki Hattori, Ayato Yamada, Shunya Nakatsuji, Takeshi Matsuda, Norito Nishiyama, and Akira Shimatsu

Telmisartan and irbesartan are angiotensin II receptor blockers (ARBs) and reportedly stimulate adiponectin secretion from adipocytes via partial peroxisome proliferator-activated receptor γ (PPARγ) activation. However, quantitative evaluation among different ARBs has not been performed. Adiponectin exerts strong protection against a number of pathological events by suppressing cell death, inhibiting inflammation, and enhancing cell survival, while leptin promotes inflammation, oxidative stress, atherogenesis, and thrombosis. The aim of this study was to identify the most effective ARB enhancing adiponectin secretion without raising leptin secretion from human white adipocytes (HWAs). Among seven ARBs (azilsartan, candesartan, irbesartan, losartan, olmesartan, telmisartan, and valsartan), telmisartan was the most effective ARB for the increase of adiponectin secretion and irbesartan was the second, whereas the other ARBs at 1 µM had no effect on adiponectin secretion. GW9662, a PPARγ antagonist, completely blocked pioglitazone (PPARγ agonist)-induced adiponectin secretion and mRNA expression, whereas it unexpectedly blocked neither telmisartan- nor irbesartan-induced adiponectin secretion and mRNA expression but rather increased them. GW6471, PPARα antagonist, and siRNA for PPARα suppressed telmisartan- and irbesartan-induced adiponectin secretion, suggesting that PPARα is the main target of these ARBs to increase adiponectin secretion in HWAs. Leptin secretion was not affected by any ARBs at 1 µM and GW9662 significantly decreased the basal secretion of leptin, suggesting that basal leptin secretion is regulated in a PPARγ-dependent manner. We conclude that telmisartan is the most effective ARB to increase adiponectin secretion via PPARα without raising leptin secretion from HWAs.