Chemical genetic identification of the histamine H1 receptor as a stimulator of insulin-induced adipogenesis

A high-throughput chemical-genetics screen in murine adipocytes identifies insulin-regulatory pathways

Pathways linking activation of the insulin receptor to downstream targets of insulin have traditionally been studied using a candidate gene approach. To elucidate additional pathways regulating insulin activity, we performed a forward chemical-genetics screen based on translocation of a glucose transporter 4 (Glut4) reporter expressed in murine 3T3-L1 adipocytes. To identify compounds with known targets, we screened drug-repurposing and natural product libraries. We identified, confirmed, and validated 64 activators and 65 inhibitors that acutely increase or rapidly decrease cell-surface Glut4 in adipocytes stimulated with submaximal insulin concentrations. These agents were grouped by target, chemical class, and mechanism of action. All groups contained multiple hits from a single drug class, and several comprised multiple structurally unrelated hits for a single target. Targets include the β-adrenergic and adenosine receptors. Agonists of these receptors increased and inverse agonists/antagonists decreased cell-surface Glut4 independently of insulin. Additional activators include insulin sensitizers (thiazolidinediones), insulin mimetics, dis-inhibitors (the mTORC1 inhibitor rapamycin), cardiotonic steroids (the Na⁺/K⁺-ATPase inhibitor ouabain), and corticosteroids (dexamethasone). Inhibitors include heterocyclic amines (tricyclic antidepressants) and 21 natural product supplements and herbal extracts. Mechanisms of action include effects on Glut4 trafficking, signal transduction, inhibition of protein synthesis, and dissipation of proton gradients. Two pathways that acutely regulate Glut4 translocation were discovered: de novo protein synthesis and endocytic acidification. The mechanism of action of additional classes of activators (tanshinones, dalbergiones, and coumarins) and inhibitors (flavonoids and resveratrol) remains to be determined. These tools are among the most sensitive, responsive, and reproducible insulin-activity assays described to date.

Promethazine Hydrochloride Inhibits Ectopic Fat Cell Formation in Skeletal Muscle

Fatty degeneration of skeletal muscle leads to muscle weakness and loss of function. Preventing fatty degeneration in skeletal muscle is important, but no drug has been used clinically. In this study, we performed drug repositioning using human platelet-derived growth factor receptor α (PDGFRα)-positive mesenchymal progenitors that have been proved to be an origin of ectopic adipocytes in skeletal muscle. We found that promethazine hydrochloride (PH) inhibits adipogenesis in a dose-dependent manner without cell toxicity. PH inhibited expression of adipogenic markers and also suppressed phosphorylation of cAMP response-element binding protein, which was reported to be a primary regulator of adipogenesis. We established a mouse model of tendon rupture with intramuscular fat deposition and confirmed that emerged ectopic adipocytes are derived from PDGFRα⁺ cells using lineage tracing mice. When these injured mice were treated with PH, formation of ectopic adipocytes was suppressed significantly. Our results show that PH inhibits PDGFRα⁺ mesenchymal progenitor-dependent ectopic adipogenesis in skeletal muscle and suggest that treatment with PH can be a promising approach to prevent fatty degeneration of skeletal muscle.

Histamine-induced Ca²⁺ signalling is mediated by TRPM4 channels in human adipose-derived stem cells

Intracellular Ca2+ oscillations are frequently observed during stem cell differentiation, and there is evidence that it may control adipogenesis. The transient receptor potential melastatin 4 channel (TRPM4) is a key regulator of Ca2+ signals in excitable and non-excitable cells. However, its role in human adipose-derived stem cells (hASCs), in particular during adipogenesis, is unknown. We have investigated TRPM4 in hASCs and examined its impact on histamine-induced Ca2+ signalling and adipogenesis. Using reverse transcription (RT)-PCR, we have identified TRPM4 gene expression in hASCs and human adipose tissue. Electrophysiological recordings revealed currents with the characteristics of those reported for the channel. Furthermore, molecular suppression of TRPM4 with shRNA diminished the Ca2+ signals generated by histamine stimulation, mainly via histamine receptor 1 (H1) receptors. The increases in intracellular Ca2+ were due to influx via voltage-dependent Ca2+ channels (VDCCs) of the L-type (Ca(v)1.2) and release from the endoplasmic reticulum. Inhibition of TRPM4 by shRNA inhibited adipogenesis as indicated by the reduction in lipid droplet accumulation and adipocyte gene expression. These results suggest that TRPM4 is an important regulator of Ca2+ signals generated by histamine in hASCs and is required for adipogenesis.

Association of prescription H1 antihistamine use with obesity: results from the National Health and Nutrition Examination Survey

The incidence of obesity in the United States has reached epidemic proportions. Previous research has shown several medications exert noticeable effects on body-weight regulation. Histamine-1 (H1) receptor blockers commonly used to alleviate allergy symptoms are known to report weight gain as a possible side effect. Therefore, we investigated the association between prescription H1 antihistamine use and obesity in adults using data from the 2005-2006 National Health and Nutrition Examination Survey (NHANES). Adults taking prescription H1 antihistamines were matched by age and gender with controls and compared on the basis of body measurements, plasma glucose, insulin concentrations, and lipid levels. Prescription H1 antihistamine users had a significantly higher weight, waist circumference, and insulin concentration than matched controls. The odds ratio (OR) for being overweight was increased in prescription H1 antihistamine users. H1 antihistamine use may contribute to the increased prevalence of obesity and the metabolic syndrome in adults given these medications are also commonly used as over-the-counter remedies.

Biochemical target isolation for novices: affinity-based strategies

Although a number of genomic and biochemical technologies are now used to elucidate the mechanisms of action of bioactive small molecules, affinity-based isolation of molecular targets is a classic, but still powerful, approach. This review highlights recent cases where biochemical isolation of target proteins of bioactive small molecules highlighted general strategies for a successful isolation and identification of molecular targets. This review is intended to be both an update on the most recent findings for those already active in the field of forward chemical genetics and a guide for scientists entering this burgeoning field.

A phenotypic small-molecule screen identifies an orphan ligand-receptor pair that regulates neural stem cell differentiation

High-throughput identification of small molecules that selectively modulate molecular, cellular, or systems-level properties of the mammalian brain is a significant challenge. Here we report the chemical genetic identification of the orphan ligand phosphoserine (P-Ser) as an enhancer of neurogenesis. P-Ser inhibits neural stem cell/progenitor proliferation and self-renewal, enhances neurogenic fate commitment, and improves neuronal survival. We further demonstrate that the effects of P-Ser are mediated by the group III metabotropic glutamate receptor 4 (mGluR4). siRNA-mediated knockdown of mGluR4 abolished the effects of P-Ser and increased neurosphere proliferation, at least in part through upregulation of mTOR pathway activity. We also found that P-Ser increases neurogenesis in human embryonic stem cell-derived neural progenitors. This work highlights the tremendous potential of developing effective small-molecule drugs for use in regenerative medicine or transplantation therapy.

Histamine induces the expression of uncoupling protein 2 (UCP2) and acid-binding protein (aP2) in white adipocytes

BACKGROUND

The aim of the present study was to investigate whether histamine induces up-regulated expression of uncoupling protein 2 (UCP2) and fat acid-binding protein (aP2) in white adipocytes (differentiated 3T3-L1 cells).

METHODS

Differentiation of 3T3-L1 preadipocytes to adipocytes was induced by the addition of 5 microg/mL insulin, 1 micromol/L dexamethasone, 10 mmol/L 1-isobutyl-3-methylxanthine, 1% dimethylsulfoxide, and 10% fetal bovine serum in Dulbecco's modification of Eagle's medium. Total RNA from differentiated 3T3-L1 cells was extracted and semi-quantitative RT-PCR was performed to determine the levels of UCP2 and aP2 mRNA. The expression level of UCP2 protein was determined by Western blot analysis.

RESULTS

Histamine at a concentration of 30 micromol/L significantly increased the expression of UCP2 mRNA and UCP2 protein, and expression levels reached a peak value. There were significant differences in the expression levels of UCP2 mRNA and UCP2 protein in adipocytes treated with 30 micromol/L histamine at various time points within 48 h, and their levels reached a peak value after 6 h of incubation. In addition, histamine increased the expression level of aP2 mRNA in adipocytes. Expression of aP2 mRNA in adipocytes reached the highest value at a concentration of 20 micromol/L histamine after 6-h incubation. Finally, we found that diphenhydramine (a H1 receptor antagonist) significantly decreased expression levels of UCP2 mRNA and protein, as well as aP2 mRNA. There were significant differences in expression levels of UCP2 and aP2 mRNA in adipocytes treated at concentrations of 20 micromol/L histamine and diphenhydramine, respectively.

CONCLUSIONS

These data reveal that histamine up-regulated the expression of UCP2 and aP2 in vitro in white adipocytes.

Linking tumor cell cytotoxicity to mechanism of drug action: an integrated analysis of gene expression, small-molecule screening and structural databases

An integrated, bioinformatic analysis of three databases comprising tumor-cell-based small molecule screening data, gene expression measurements, and PDB (Protein Data Bank) ligand-target structures has been developed for probing mechanism of drug action (MOA). Clustering analysis of GI50 profiles for the NCI's database of compounds screened across a panel of tumor cells (NCI60) was used to select a subset of unique cytotoxic responses for about 4000 small molecules. Drug-gene-PDB relationships for this test set were examined by correlative analysis of cytotoxic response and differential gene expression profiles within the NCI60 and structural comparisons with known ligand-target crystallographic complexes. A survey of molecular features within these compounds finds thirteen conserved Compound Classes, each class exhibiting chemical features important for interactions with a variety of biological targets. Protein targets for an additional twelve Compound Classes could be directly assigned using drug-protein interactions observed in the crystallographic database. Results from the analysis of constitutive gene expressions established a clear connection between chemo-resistance and overexpression of gene families associated with the extracellular matrix, cytoskeletal organization, and xenobiotic metabolism. Conversely, chemo-sensitivity implicated overexpression of gene families involved in homeostatic functions of nucleic acid repair, aryl hydrocarbon metabolism, heat shock response, proteasome degradation and apoptosis. Correlations between chemo-responsiveness and differential gene expressions identified chemotypes with nonselective (i.e., many) molecular targets from those likely to have selective (i.e., few) molecular targets. Applications of data mining strategies that jointly utilize tumor cell screening, genomic, and structural data are presented for hypotheses generation and identifying novel anticancer candidates.