Correction to: Chronomedicine and type 2 diabetes: shining some light on melatonin.

The authors have been made aware that the following sentence is incorrect: 'Like IIK7, both ramelteon and tasimelteon have a greater affinity for the MT2 receptor [162].'

Chronomedicine and type 2 diabetes: shining some light on melatonin.

In mammals, the circadian timing system drives rhythms of physiology and behaviour, including the daily rhythms of feeding and activity. The timing system coordinates temporal variation in the biochemical landscape with changes in nutrient intake in order to optimise energy balance and maintain metabolic homeostasis. Circadian disruption (e.g. as a result of shift work or jet lag) can disturb this continuity and increase the risk of cardiometabolic disease. Obesity and metabolic disease can also disturb the timing and amplitude of the clock in multiple organ systems, further exacerbating disease progression. As our understanding of the synergy between the timing system and metabolism has grown, an interest has emerged in the development of novel clock-targeting pharmaceuticals or nutraceuticals for the treatment of metabolic dysfunction. Recently, the pineal hormone melatonin has received some attention as a potential chronotherapeutic drug for metabolic disease. Melatonin is well known for its sleep-promoting effects and putative activity as a chronobiotic drug, stimulating coordination of biochemical oscillations through targeting the internal timing system. Melatonin affects the insulin secretory activity of the pancreatic beta cell, hepatic glucose metabolism and insulin sensitivity. Individuals with type 2 diabetes mellitus have lower night-time serum melatonin levels and increased risk of comorbid sleep disturbances compared with healthy individuals. Further, reduced melatonin levels, and mutations and/or genetic polymorphisms of the melatonin receptors are associated with an increased risk of developing type 2 diabetes. Herein we review our understanding of molecular clock control of glucose homeostasis, detail the influence of circadian disruption on glucose metabolism in critical peripheral tissues, explore the contribution of melatonin signalling to the aetiology of type 2 diabetes, and discuss the pros and cons of melatonin chronopharmacotherapy in disease management.

Phosphate-induced apoptosis of hypertrophic chondrocytes is associated with a decrease in mitochondrial membrane potential and is dependent upon Erk1/2 phosphorylation.

Growth plate abnormalities, associated with impaired hypertrophic chondrocyte apoptosis, are observed in humans and animals with abnormalities of vitamin D action and renal phosphate reabsorption. Low circulating phosphate levels impair hypertrophic chondrocyte apoptosis, whereas treatment of these cells with phosphate activates the mitochondrial apoptotic pathway. Because phosphate-mediated apoptosis of chondrocytes is differentiation-dependent, studies were performed to identify factors that contribute to hypertrophic chondrocyte apoptosis. An increase in the percentage of cells with low mitochondrial membrane potential, evaluated by JC-1 fluorescence, was observed during hypertrophic differentiation of primary murine chondrocytes in culture. This percentage was further increased by treatment of hypertrophic, but not proliferative, chondrocytes with phosphate. Phosphate-mediated apoptosis was observed as early as 30 min post-treatment and was dependent upon Erk1/2 phosphorylation. Inhibition of Erk1/2 phosphorylation in vivo confirmed an important role for this signaling pathway in regulating hypertrophic chondrocyte apoptosis in growing mice. Murine embryonic metatarsals cultured under phosphate-restricted conditions demonstrated a 2.5-fold increase in parathyroid hormone-related protein mRNA expression accompanied by a marked attenuation in phospho-Erk immunoreactivity in hypertrophic chondrocytes. Thus, these investigations point to an important role for phosphate in regulating mitochondrial membrane potential in hypertrophic chondrocytes and growth plate maturation by the parathyroid hormone-related protein signaling pathway.

GLP-1 Analogs Are Superior in Mediating Weight Loss But Not Glycemic Control in Diabetic Patients on Antidepressant Medications: A Retrospective Cohort Study.

Objective: Both antipsychotic and antidepressant medications have been associated with weight gain and hyperglycemia. Our previously published retrospective cohort study suggests that GLP-1 (glucagon-like peptide-1) analogs may be superior to alternative regimens for both glycemic and weight control in patients on antipsychotic plus/minus antidepressant medications. In the current study, we asked whether GLP-1 analogs or SGLT-2 (sodium-glucose-transporter-2) inhibitors would be similarly beneficial in patients on antidepressant medications alone.Methods: In this retrospective cohort study, we included all patients with type 2 diabetes on antidepressant medications referred to our endocrine clinics between January 1, 2016, and January 1, 2017. Overall, 61 patients were started on a GLP-1 analog, 9 patients were started on an SGLT-2 inhibitor, and 134 were on alternative regimens (controls).Results: The groups did not differ in age, sex, ethnicity, and glycosylated hemoglobin (HbA1c) levels, although body mass index levels were higher in patients started on a GLP-1 analog (P < .0001). After 12 months, patients on GLP-1 analogs lost 4 kg, patients on SGLT-2 inhibitors lost 2.4 kg, and controls gained 0.8 kg (P < .001 for controls versus GLP-1 analog group). Subanalyses revealed that GLP-1 analog-related weight loss was most notable in women and patients on selective serotonin reuptake inhibitors. On the other hand, all serotonin-norepinephrine reuptake inhibitor users lost weight over time, independent of the antidiabetic regimen applied. In contrast to the above noted differences in weight control, HbA1c reductions were comparable and somewhat diminished in all patients on antidepressant medications (-0.3% to 0.6%).Conclusions: In this retrospective cohort study, we confirm superiority of GLP-1 analogs in mediating weight loss in patients on psychotropic and, more specifically, antidepressant medications. We also note overall blunted glycemic improvements in patients on antidepressant medications, a finding that was independent of the treatment strategy used. It could be a result of mental distress or suboptimal self-care and clearly requires further attention by future, prospective studies.

Glucagon-Like Peptide Analogs Are Superior for Diabetes and Weight Control in Patients on Antipsychotic Medications: A Retrospective Cohort Study.

OBJECTIVE: Glucagon-like peptide (GLP-1) analogs promote diabetes control and weight loss. Most GLP-1 analogs also lower adverse cardiovascular outcomes, making them ideal agents for patients with severe mental illness. The objective of this study was to analyze diabetic patients taking antipsychotic medications, comparing those on GLP-1 analogs with those on other diabetes treatments. METHODS: A total of 46 patients referred to outpatient diabetes clinics between July 2010 and April 2017 who were prescribed antipsychotic medications during the entire study period were included in this retrospective analysis. Eleven (24%) patients were started on a GLP-1 analog (cases), and 35 (76%) were treated with alternative antidiabetic agents (controls). RESULTS: Cases and controls did not differ in age, sex, height, weight, or medical therapies at the time of referral. Within 1 year, a reduction in mean ± SE glycosylated hemoglobin (HbA1c) levels was noted for both groups (cases: -1.26% ± 0.17%, controls: -1.47% ± 0.45%). However, while patients on GLP-1 analogs lost 7.07 ± 2.62 kg, control patients gained 1.93 ± 1.14 kg (P < .05). Blunted HbA1c reductions were also noted in patients who took antipsychotic medication in addition to antidepressant medication (on antidepressant medication [n = 22]: -0.77% ± 0.29%, off antidepressant medication [n = 9]: -2.97% ± 0.6%, P < .001). This observation did not apply to patients treated with GLP-1 analogs, as they had larger HbA1c reductions than patients on alternative regimens (controls [n = 15]: -0.46% ± 0.4%, cases [n = 7]: -1.43% ± 0.15%, P < .05). CONCLUSIONS: GLP-1 analogs promote both diabetes and weight control in diabetic patients on antipsychotic medications with or without antidepressant medications.

Functional desensitization of the extracellular calcium-sensing receptor is regulated via distinct mechanisms: role of G protein-coupled receptor kinases, protein kinase C and beta-arrestins.

The extracellular calcium-sensing receptor (CaR) senses small fluctuations of the extracellular calcium (Ca(2+)(e)) concentration and translates them into potent changes in parathyroid hormone secretion. Dissecting the regulatory mechanisms of CaR-mediated signal transduction may provide insights into the physiology of the receptor and identify new molecules as potential drug targets for the treatment of osteoporosis and/or hyperparathyroidism. CaR can be phosphorylated by protein kinase C (PKC) and G protein-coupled receptor kinases (GRKs), and has been shown to bind to beta-arrestins, potentially contributing to desensitization of CaR, although the mechanisms by which CaR-mediated signal transduction is terminated are not known. We used a PKC phosphorylation site-deficient CaR, GRK and beta-arrestin overexpression or down-regulation to delineate CaR-mediated desensitization. Fluorescence-activated cell sorting was used to determine whether receptor internalization contributed to desensitization. Overexpression of GRK 2 or 3 reduced Ca(2+)(e)-dependent inositol phosphate accumulation by more than 70%, whereas a GRK 2 mutant deficient in G alpha(q) binding (D110A) was without major effect. Overexpression of GRK 4-6 did not reduce Ca(2+)(e)-dependent inositol phosphate accumulation. Overexpression of beta-arrestin 1 or 2 revealed a modest inhibitory effect on Ca(2+)(e)-dependent inositol phosphate production (20-30%), which was not observed for the PKC phosphorylation site-deficient CaR. Agonist-dependent receptor internalization (10-15%) did not account for the described effects. Thus, we conclude that PKC phosphorylation of CaR contributes to beta-arrestin-dependent desensitization of CaR coupling to G proteins. In contrast, GRK 2 predominantly interferes with G protein-mediated inositol-1,4,5-trisphosphate formation by binding to G alpha(q).

Paxillin and embryonic PolyAdenylation Binding Protein (ePABP) engage to regulate androgen-dependent Xenopus laevis oocyte maturation - A model of kinase-dependent regulation of protein expression.

Steroid-triggered Xenopus laevis oocyte maturation is an elegant physiologic model of nongenomic steroid signaling, as it proceeds completely independent of transcription. We previously demonstrated that androgens are the main physiologic stimulator of oocyte maturation in Xenopus oocytes, and that the adaptor protein paxillin plays a crucial role in mediating this process through a positive feedback loop in which paxillin first enhances Mos protein translation, ensued by Erk2 activation and Erk-dependent phosphorylation of paxillin on serine residues. Phosphoserine-paxillin then further augments Mos protein translation and downstream Erk2 activation, resulting in meiotic progression. We hypothesized that paxillin enhances Mos translation by interacting with embryonic PolyAdenylation Binding Protein (ePABP) on polyadenylated Mos mRNA. Knockdown of ePABP phenocopied paxillin knockdown, with reduced Mos protein expression, Erk2 and Cdk1 activation, as well as oocyte maturation. In both Xenopus oocytes and mammalian cells (HEK-293), paxillin and ePABP constitutively interacted. Testosterone (Xenopus) or EGF (HEK-293) augmented ePABP-paxillin binding, as well as ePABP binding to Mos mRNA (Xenopus), in an Erk-dependent fashion. Thus, ePABP and paxillin work together in an Erk-dependent fashion to enhance Mos protein translation and promote oocyte maturation.

Aromatase deficiency in a male patient - Case report and review of the literature.

OBJECTIVE: Aromatase, or CYP19A1, is a type II cytochrome CYP450 enzyme that catalyzes the conversion of C19 androgens to C18 estrogens. Its crucial role in both female and male physiology has been deduced from human and animal studies using aromatase inhibitors, genetically altered mice, and patients with aromatase deficiency. The latter is an extremely rare disorder. Its diagnosis is particularly difficult in males, who go through puberty normally and therefore usually present as adults with elevated testosterone, bone abnormalities (e.g., delayed bone age and low bone mass), and metabolic syndrome. In this report, we describe a new case of a male patient with aromatase deficiency harboring a known mutation who presented with less severe clinical and biochemical features. CASE REPORT: The patient presented with low bone mass and delayed bone age after a finger fracture at age 25years. FSH, LH and testosterone levels were normal, but estradiol and estrone levels were absent or barely detectable, raising suspicion for aromatase deficiency. A homozygous c.628G>A mutation in exon 5 was confirmed by direct sequencing. Unlike previously reported cases of aromatase deficiency, he did not display biochemical features of insulin resistance, dyslipidemia, or overweight/obese status. Therapy with estradiol led to the closure of growth plates and a dramatic increase in bone mass. CONCLUSIONS: Here we explore genotype/phenotype associations of this new case compared to cases reported previously. We conclude that the specific nature of mutation c.628G>A, which can potentially result in several different forms of the aromatase enzyme, may lend an explanation to the variable phenotypes associated with this particular genotype.

Calcium sensing receptors as integrators of multiple metabolic signals.

Calcium sensing receptors are critical to maintenance of organismal Ca2+ homeostasis, translating small changes in serum Ca2+ into changes in PTH secretion by the parathyroid glands and Ca2+ excretion by the kidneys. Calcium sensing receptors are also expressed in many cells and tissues not directly involved in Ca2+ homeostasis where their role(s) are less defined. Recent studies have demonstrated that calcium sensing receptors integrate a variety of metabolic signals, including polyvalent cations, pH, ionic strength, amino acids, and polypeptides, making CaR uniquely capable of generating cell- and tissue-specific responses, sensing not only Ca2+, but the local metabolic environment. The challenge for future studies is to define CaR responsiveness in each varied physiological context.

Paxillin and steroid signaling: from frog to human.

Paxillin is a well-characterized cytoplasmic adaptor protein that is known to play important roles in cytoskeletal rearrangement, cell adhesion, and cell motility. In addition to its structural functions, paxillin has more recently been shown to function as a regulator of cell division-mediating steroid-triggered meiosis in oocytes as well as steroid- and growth factor-induced proliferation in prostate and breast cancer. Paxillin mediates these processes through a conserved pathway that involves both extranuclear (nongenomic) and nuclear (genomic) steroid signaling, as well as both cytoplasmic and nuclear kinase signaling. In fact, paxillin appears to serve as a critical liaison between extranuclear and nuclear signaling in response to multiple stimuli, making it a fascinating molecule to study when trying to determine how growth signals from the membrane lead to important proliferative changes in the nucleus. This chapter outlines recent advances in understanding how paxillin regulates both steroid and growth factor signaling, focusing on the conserved nature of its actions from a frog germ cell to a human cancer cell.

The receptor-dependent actions of 1,25-dihydroxyvitamin D are required for normal growth plate maturation in NPt2a knockout mice.

Rickets is a growth plate abnormality observed in growing animals and humans. Rachitic expansion of the hypertrophic chondrocyte layer of the growth plate, in the setting of hypophosphatemia, is due to impaired apoptosis of these cells. Rickets is observed in humans and mice with X-linked hypophosphatemia that is associated with renal phosphate wasting secondary to elevated levels of fibroblast growth factor-23. Rickets is also seen in settings of impaired vitamin D action, due to elevated PTH levels that increase renal phosphate excretion. However, mice with hypophosphatemia secondary to ablation of the renal sodium-dependent phosphate transport protein 2a (Npt2a), have not been reported to develop rickets. Because activation of the mitochondrial apoptotic pathway by phosphate is required for hypertrophic chondrocyte apoptosis in vivo, investigations were undertaken to address this paradox. Analyses of the Npt2a null growth plate demonstrate expansion of the hypertrophic chondrocyte layer at 2 wk of age, with resolution of this abnormality by 5 wk of age. This is temporally associated with an increase in circulating levels of 1,25-dihydroxyvitamin D. To address whether the receptor-dependent actions of this steroid hormone are required for normalization of the growth plate phenotype, the Npt2a null mice were mated with mice lacking the vitamin D receptor or were rendered vitamin D deficient. These studies demonstrate that the receptor-dependent actions of 1,25-dihydroxyvitamin D are required for maintenance of a normal growth plate phenotype in the Npt2a null mice.

Eliminating phosphorylation sites of the parathyroid hormone receptor type 1 differentially affects stimulation of phospholipase C and receptor internalization.

The parathyroid hormone (PTH)/PTH-related peptide (PTHrP) receptor (PTH1R) belongs to family B of seven-transmembrane-spanning receptors and is activated by PTH and PTHrP. Upon PTH stimulation, the rat PTH1R becomes phosphorylated at seven serine residues. Elimination of all PTH1R phosphorylation sites results in prolonged cAMP accumulation and impaired internalization in stably transfected LLC-PK1 cells. The present study explores the role of individual PTH1R phosphorylation sites in PTH1R signaling through phospholipase C, agonist-dependent receptor internalization, and regulation by G protein-coupled receptor kinases. By means of transiently transfected COS-7 cells, we demonstrate that the phosphorylation-deficient (pd) PTH1R confers dramatically enhanced coupling to G(q/11) proteins upon PTH stimulation predominantly caused by elimination of Ser(491/492/493), Ser(501), or Ser(504). Reportedly, impaired internalization of the pd PTH1R, however, is not dependent on a specific phosphorylation site. In addition, we show that G protein-coupled receptor kinase 2 interferes with pd PTH1R signaling to G(q/11) proteins at least partially by direct binding to G(q/11) proteins.

Homology modeling of the transmembrane domain of the human calcium sensing receptor and localization of an allosteric binding site.

A homology model for the human calcium sensing receptor (hCaR) transmembrane domain utilizing bovine rhodopsin (bRho) structural information was derived and tested by docking the allosteric antagonist, NPS 2143, followed by mutagenesis of predicted contact sites. Mutation of residues Phe-668 (helix II), Arg-680, or Phe-684 (helix III) to Ala (or Val or Leu) and Glu-837 (helix VII) to Ile (or Gln) reduced the inhibitory effects of NPS 2143 on [Ca2+]i responses. The calcimimetic NPS R-568 increases the potency of Ca2+ in functional assays of CaR. Mutations at Phe-668, Phe-684, or Glu-837 attenuated the effects of this compound, but mutations at Arg-680 had no effect. In all cases, mutant CaRs responded normally to Ca2+ or phenylalanine, which act at distinct site(s). Discrimination by the Arg-680 mutant is consistent with the structural differences between NPS 2143, which contains an alkyl bridge hydroxyl group, and NPS R-568, which does not. The homology model of the CaR transmembrane domain robustly accounts for binding of both an allosteric antagonist and agonist, which share a common site, and provides a basis for the development of more specific and/or potent allosteric modulators of CaR. These studies suggest that the bRho backbone can be used as a starting point for homology modeling of even distantly related G protein-coupled receptors and provide a rational framework for investigation of the contributions of the transmembrane domain to CaR function.