Downregulation of miR-181a upregulates sirtuin-1 (SIRT1) and improves hepatic insulin sensitivity

AIMS/HYPOTHESIS

Sirtuin-1 (SIRT1) is a potential therapeutic target to combat insulin resistance and type 2 diabetes. This study aims to identify a microRNA (miRNA) targeting SIRT1 to regulate hepatic insulin sensitivity.

METHODS

Luciferase assay combined with mutation and immunoblotting was used to screen and verify the bioinformatically predicted miRNAs. miRNA and mRNA levels were measured by real-time PCR. Insulin signalling was detected by immunoblotting and glycogen synthesis. Involvement of SIRT1 was studied with adenovirus, inhibitor and SIRT1-deficient hepatocytes. The role of miR-181a in vivo was explored with adenovirus and locked nucleic acid antisense oligonucleotides.

RESULTS

miR-181a targets the 3' untranslated region (3'UTR) of Sirt1 mRNA through a miR-181a binding site, and downregulates SIRT1 protein abundance at the translational level. miR-181a is increased in insulin-resistant cultured hepatocytes and liver, and in the serum of diabetic patients. Overexpression of miR-181a decreases SIRT1 protein levels and activity, and causes insulin resistance in hepatic cells. Inhibition of miR-181a by antisense oligonucleotides increases SIRT1 protein levels and activity, and improves insulin sensitivity in hepatocytes. Ectopic expression of SIRT1 abrogates the effect of miR-181a on insulin sensitivity, and inhibition of SIRT1 activity or SIRT1 deficiency markedly attenuated the improvement in insulin sensitivity induced by antisense miR-181a. In addition, overexpression of miR-181a by adenovirus impairs hepatic insulin signalling, and intraperitoneal injection of locked nucleic acid antisense oligonucleotides for miR-181a improves glucose homeostasis in diet-induced obesity mice.

CONCLUSIONS/INTERPRETATION

miR-181a regulates SIRT1 and improves hepatic insulin sensitivity. Inhibition of miR-181a might be a potential new strategy for treating insulin resistance and type 2 diabetes.

Effect of MWCNTs on Gastric Emptying in Mice

After making model of gastric functional disorder (FD), part of model mice were injected intravenously (i.v.) with oxide multi-walled carbon nanotubes (oMWCNTs) to investigate effect of carbon nanotubes on gastric emptying. The results showed that NO content in stomach, compared with model group, was decreased significantly and close to normal level post-injection with oMWCNTs (500 and 800 μg/mouse). In contrast to FD or normal groups, the content of acetylcholine (Ach) in stomach was increased obviously in injection group with 500 or 800 μg/mouse of oMWCNTs. The kinetic curve of emptying was fitted to calculate gastric motility factor k; the results showed that the k of injection group was much higher than FD and normal. In other words, the gastric motility of FD mice was enhanced via injection with oMWCNTs. In certain dosage, oMWCNTs could improve gastric emptying and motility.

Performance of culture and drug susceptibility testing in pulmonary tuberculosis patients in northern China

Multidrug-resistant tuberculosis (MDR-TB) is a growing problem in China. In 2008, all smear-positive pulmonary TB patients in a city in northern China were expected to undergo routine culture and drug susceptibility testing (DST). We assessed the performance of this system. There were 915 patients, of whom 356 (39%) had culture performed; 275 (30%) had positive cultures and 236 (26%) had DST. Of the 236 patients with DST, 6% of new and 32% of previously treated patients had MDR-TB. Culture and DST is an important service for the correct management of patients, and solutions to improve the current system need to be considered.

Multiple roles of the p75 neurotrophin receptor in the nervous system

The p75 neurotrophin receptor (p75NTR) is a transmembrane protein that binds nerve growth factor (NGF) and has multiple functions in the nervous system where it is expressed widely during the developmental stages of life, although expression decreases dramatically by adulthood. Expression of p75NTR can increase in pathological states related to neural cell death. p75NTR is a member of the tumour necrosis factor (TNF) receptor family and it consists of intracellular, transmembrane and extracellular domains which are different from other TNF receptors. Either by interacting with tropomyosin receptor kinase (Trk) receptors or via the independent binding of neurotrophin, p75NTR can induce neurite outgrowth and cellular survival or cell apoptosis through several complicated signal transduction pathways. Most of these signalling pathways remain to be elucidated. By interacting with different cellular factors, p75NTR can induce neuron growth cone collapse or regrowth. p75NTR is also expressed in a variety of glial populations. The many functions of p75NTR require further study.

Increased renal gene transcription of protein kinase C-beta in human diabetic nephropathy: relationship to long-term glycaemic control

AIMS/HYPOTHESIS

Activation of protein kinase C (PKC) isoforms has been implicated as a central mediator in the pathogenesis of diabetic nephropathy. Although high glucose levels stimulate catalytic activity of PKC, the effects of high glucose levels on the expression of genes encoding PKC isoforms are unknown. We sought to determine whether in addition to activation, diabetes may lead to increased transcription of two PKC isoforms that have been implicated in the pathogenesis of diabetic nephropathy, PKC-alpha and PKC-beta.

METHODS

Recent advances in molecular biological techniques now permit quantitative analysis of mRNA from archival, formalin-fixed, paraffin-embedded tissue sections. RNA was extracted from scraped 6 microm sections of biopsy tissue, and PRKC-alpha and PRKC-beta (also known as PRKCA and PRKCB) mRNA measured using real-time PCR. Expression of genes encoding PKC isoforms was examined in renal biopsies (n=25) with classical histological features of diabetic nephropathy and compared with that in normal control tissue (n=6). Peptide localisation of PKC-alpha, PKC-beta and the activated forms phosphorylated PKC-alpha and -beta was also performed on matched paraffin-embedded sections of renal biopsies using immunohistochemistry. The effects of high glucose on PRKC-beta expression and peptide production in cultured human proximal tubular epithelial cells were assessed.

RESULTS

Quantitative real-time PCR demonstrated a 9.9-fold increase in PRKC-beta mRNA in kidney biopsies of diabetic patients relative to control (p<0.001). No increase in PRKC-alpha expression was seen. In addition, a correlation between renal PRKC-beta mRNA and HbA(1c) was observed in diabetic patients (r=0.63, p<0.05). There was co-localisation of PKC-beta and phospho-PKC-beta predominantly to proximal tubules. A 60% increase in PRKC-beta mRNA and peptide in cultured human proximal tubular epithelial cells exposed to high glucose (p<0.05) was seen in vitro.

CONCLUSIONS/INTERPRETATION

PKC-beta is upregulated at the gene expression level in human diabetic nephropathy. PRKC-beta mRNA correlates closely with serum HbA(1c), possibly partially explaining the relationship between glycaemic control and progression of diabetic nephropathy. Archival human tissue provides a valuable resource for molecular analyses.

Prospective observational study of acute coronary syndromes in China: practice patterns and outcomes

OBJECTIVE

To describe the investigation and management of patients admitted to hospitals in China with suspected acute coronary syndromes (ACS) and to identify potential areas for improvement in practice.

DESIGN

A multicentre prospective survey of sociodemographic characteristics, medical history, clinical features, in-hospital investigations, treatment practices and major events among patients with suspected ACS.

SETTING

Large urban public hospitals.

PATIENTS

Consecutive patients admitted to in-patient facilities with a diagnosis of suspected acute myocardial infarction (MI) or unstable angina pectoris.

MAIN OUTCOME MEASURES

Myocardial infarction/re-infarction, heart failure, death.

RESULTS

Between September 2004 and May 2005, data were collected prospectively from 2973 patients admitted to 51 hospitals in 18 provinces of China. An initial diagnosis of ST elevation MI, non-ST elevation MI and unstable angina was made in 43%, 11% and 46% of patients, respectively. Diagnosis was inconsistent with objective measures in up to 20% of cases. At both tertiary and non-tertiary centres, there was little evidence that clinical risk stratification was used to determine the intensity of investigation and management. The mortality rate during hospitalisation was 5% overall and similar in tertiary and non-tertiary centres, but reported in-hospital re-infarction rates (8%) and heart failure rates (16%) were substantially higher at non-tertiary centres.

CONCLUSION

This study has identified a number of areas in the management of ACS patients, including diagnosis and risk stratification, which deviate from current guidelines. These findings will help inform the introduction of widely used quality improvement initiatives such as clinical pathways.

Evidence that a prostanoid produced by cyclo-oxygenase-2 enhances contractile responses of the porcine isolated coronary artery following exposure to lipopolysaccharide

BACKGROUND

Prolonged incubation of porcine isolated coronary artery (PCA) to lipopolysaccharide (LPS) causes a moderate reduction in vessel constrictive responsiveness. This has been attributed mainly to the induction of nitric oxide synthase (NOS). We aimed to investigate the role of induction of cyclo-oxygenase (COX) and expression of endothelin receptor 1-A (ET1(A)) in modulating the vascular responses of PCA in vitro.

METHODS

Segments of PCA were exposed to 100 microg ml(-1) LPS overnight. L-Arginine 0.4 mM was included in the medium in some preparations to examine the influence of intracellular nitric oxide, and the influence of extracellular donor sodium nitroprusside (SNP) was also examined in separate experiments. After overnight incubation, the contractile function of the artery was evaluated by the isometric tension recording test. The non-selective NOS inhibitor (L-NAME), non-selective COX inhibitor (indomethacin), COX-1 inhibitor (FR 122047), COX-2 inhibitor (NS 398), and ET1(A) receptor antagonist (FR 139317) were added into the organ bath 30 min before eliciting contractile responses to KCl or U46619 separately or in combinations. Vascular relaxations to 10 nM Substance P (SP) were also assessed.

RESULTS

L-Arginine did not potentiate the effects of LPS. SNP caused a quantitatively larger reduction in the responsiveness to KCl and U46619 compared with 100 microg ml(-1) LPS. Post exposure to a combination of indomethacin and FR 139317, indomethacin or NS 398 alone enhanced the inhibitory effects of LPS, but FR 122047 or FR 139317 alone failed to modify the responses to LPS. L-NAME fully reversed the changes induced by LPS combined with indomethacin and NS398. In terms of the relaxation by SP, LPS failed to change the magnitude; none of the agents used affected the response except L-NAME which abolished it.

CONCLUSION

NOS and COX-2 are both activated by overnight exposure to LPS in vascular smooth muscle from PCA in vitro. The prostanoid produced by COX-2 functionally antagonizes the effects of induction of NOS.

Tranilast attenuates connective tissue growth factor-induced extracellular matrix accumulation in renal cells

Tranilast (N-[3,4-dimethoxycinnamoyl]anthranilic acid) is a synthetic compound that we have recently reported to inhibit transforming growth factor-beta1 (TGF-beta1)-induced tubulointerstitial fibrosis in the kidney. Connective tissue growth factor (CTGF) is recognized as a potent downstream mediator of TGF-beta1. Both proximal tubule cells (PTCs) and cortical fibroblasts (CFs) are considered to be responsible for the production of tubulointerstitial extracellular matrix (ECM). These studies were undertaken to assess the profibrotic effects of CTGF in an in vitro model of the human PTCs and CFs, and to determine whether tranilast is effective in limiting the in vitro matrix responses induced by CTGF. Primary cultures of PTCs and CFs were exposed to CTGF (20 ng/ml)+/-tranilast (100 microM). Cell hypertrophy and the secretion of the ECM proteins fibronectin and collagen IV were determined. The effects of tranilast on TGF-beta1-induced CTGF mRNA expression and on phosphorylation of Smad2 were determined. CTGF significantly induced cell hypertrophy, increased fibronectin, and collagen IV secretion in PTCs and CFs. In all cases, the CTGF-induced increase in ECM protein was inhibited in the presence of tranilast. Tranilast reduced CTGF mRNA and phosphorylation of Smad2, which were induced by TGF-beta1 in PTCs and CFs. These results suggest that tranilast is a potential effective antifibrotic compound in the kidney, exerting its effects via inhibition of TGF-beta1-induced CTGF expression and downstream activation of the Smad2 pathway in both PTCs and CFs.

The spindle checkpoint and chromosomal stability

Normal human somatic cells contain 46 chromosomes (22 pairs of autosomes and two sex chromosomes). Chromosome missegregation leads to abnormal numbers of chromosomes or aneuploidy. This form of genetic instability alters the dosages of large subsets of genes, which can result in severe disease phenotypes. Most human cancer cells are aneuploid. It is generally believed that aneuploidy contributes to cancer formation. The spindle checkpoint is a cell-cycle surveillance mechanism that ensures the fidelity of chromosome segregation during mitosis and meiosis. In this article, we review our current understanding of the molecular basis of the spindle checkpoint and the recent evidence that links the malfunction of this checkpoint to aneuploidy and tumorigenesis.

Absence of Fer protein tyrosine kinase exacerbates endotoxin induced intestinal epithelial barrier dysfunction in vivo

BACKGROUND AND AIMS

Fer kinase is activated by a number of growth factors and cytokines, and phosphorylates cortactin during cell shape change induced cortical actin reorganisation. In addition, Fer participates in cytoskeletal interactions mediated by cadherins, platelet endothelial cell adhesion molecule 1 (PECAM-1), and integrins, and has recently been implicated in limiting the innate immune response. Here we examined the role of Fer in modulating leucocyte recruitment and epithelial barrier function in the gut in response to lipopolysaccharide (LPS).

METHODS

Mice targeted with a kinase inactivating mutation (FerDR) or strain matched wild-type (129Sv/J) mice were studied after intraperitoneal injection of LPS. Intravital microscopy was used to examine intestinal leucocyte kinetics, and leucocyte infiltration was assessed by fluorescence activated cell sorting. Systemic inflammation was assessed by measuring lung myeloperoxidase activity. Epithelial barrier function was assessed in vivo using blood to lumen 51Cr-EDTA clearance, with or without antibody based depletion of circulating neutrophils.

RESULTS

LPS induced a significant increase in leucocyte adhesion and neutrophil infiltration into the intestinal tissue, and increased blood to lumen 51Cr-EDTA clearance. Pretreatment with neutrophil depleting antibody completely abrogated this response in wild-type mice. In FerDR mice, LPS induced leucocyte adhesion within the intestinal venules was exacerbated and associated with a trend towards increased neutrophil transmigration relative to wild-type mice. Surprisingly, LPS induced epithelial barrier permeability was increased 2.5-fold in FerDR mice relative to wild-type mice, and this barrier defect was only partly attenuated by depleting circulating neutrophils by >93 %.

CONCLUSIONS

Fer plays a role in regulating LPS induced epithelial barrier dysfunction in vivo through both neutrophil dependent and neutrophil independent mechanisms.

Integrated actions of transforming growth factor-beta1 and connective tissue growth factor in renal fibrosis

Matrix accumulation in the renal tubulointerstitium is predictive of a progressive decline in renal function. Transforming growth factor-beta(1) (TGF-beta(1)) and, more recently, connective tissue growth factor (CTGF) are recognized to play key roles in mediating the fibrogenic response, independently of the primary renal insult. Further definition of the independent and interrelated effects of CTGF and TGF-beta(1) is critical for the development of effective antifibrotic strategies. CTGF (20 ng/ml) induced fibronectin and collagen IV secretion in primary cultures of human proximal tubule cells (PTC) and cortical fibroblasts (CF) compared with control values (P < 0.005 in all cases). This effect was inhibited by neutralizing antibodies to either TGF-beta or to the TGF-beta type II receptor (TbetaRII). TGF-beta(1) induced a greater increase in fibronectin and collagen IV secretion in both PTC (P < 0.01) and CF (P < 0.01) compared with that observed with CTGF alone. The combination of TGF-beta(1) and CTGF was additive in their effects on both PTC and CF fibronectin and collagen IV secretion. TGF-beta(1) (2 ng/ml) stimulated CTGF mRNA expression within 30 min, which was sustained for up to 24 h, with a consequent increase in CTGF protein (P < 0.05), whereas CTGF had no effect on TGF-beta(1) mRNA or protein expression. TGF-beta(1) (2 ng/ml) induced phosphorylated (p)Smad-2 within 15 min, which was sustained for up to 24 h. CTGF had a delayed effect on increasing pSmad-2 expression, which was evident at 24 h. In conclusion, this study has demonstrated the key dependence of the fibrogenic actions of CTGF on TGF-beta. It has further uniquely demonstrated that CTGF requires TGF-beta, signaling through the TbetaRII in both PTCs and CFs, to exert its fibrogenic response in this in vitro model.

Biochemical reactivity of melatonin with reactive oxygen and nitrogen species: a review of the evidence

Melatonin (N-acetyl-5-methoxytryptamine), an endogenously produced indole found throughout the animal kingdom, was recently reported, using a variety of techniques, to be a scavenger of a number of reactive oxygen and reactive nitrogen species both in vitro and in vivo. Initially, melatonin was discovered to directly scavenge the high toxic hydroxyl radical (*OH). The methods used to prove the interaction of melatonin with the *OH included the generation of the radical using Fenton reagents or the ultraviolet photolysis of hydrogen peroxide (H202) with the use of spin-trapping agents, followed by electron spin resonance (ESR) spectroscopy, pulse radiolysis followed by ESR, and several spectrofluorometric and chemical (salicylate trapping in vivo) methodologies. One product of the reaction of melatonin with the *OH was identified as cyclic 3-hydroxymelatonin (3-OHM) using high-performance liquid chromatography with electrochemical (HPLC-EC) detection, electron ionization mass spectrometry (EIMS), proton nuclear magnetic resonance (1H NMR) and COSY 1H NMR. Cyclic 3-OHM appears in the urine of humans and other mammals and in rat urine its concentration increases when melatonin is given exogenously or after an imposed oxidative stress (exposure to ionizing radiation). Urinary cyclic 3-OHM levels are believed to be a biomarker (footprint molecule) of in vivo *OH production and its scavenging by melatonin. Although the data are less complete, besides the *OH, melatonin in cell-free systems has been shown to directly scavenge H2O2, singlet oxygen (1O2) and nitric oxide (NO*), with little or no ability to scavenge the superoxide anion radical (O2*-) In vitro, melatonin also directly detoxifies the peroxynitrite anion (ONOO-) and/or peroxynitrous acid (ONOOH), or the activated form of this molecule, ONOOH*; the product of the latter interaction is proposed to be 6-OHM. How these in vitro findings relate to the in vivo antioxidant actions of melatonin remains to be established. The ability of melatonin to scavenge the lipid peroxyl radical (LOO*) is debated. The weight of the evidence is that melatonin is probably not a classic chain-breaking antioxidant, since its ability to scavenge the LOO* seems weak. Its ability to reduce lipid peroxidation may stem from its function as a preventive antioxidant (scavenging initiating radicals), or yet unidentified actions. In sum, in vitro melatonin acts as a direct free radical scavenger with the ability to detoxify both reactive oxygen and reactive nitrogen species; in vivo, it is an effective pharmacological agent in reducing oxidative damage under conditions in which excessive free radical generation is believed to be involved.