Hypoxia aggravates non-alcoholic steatohepatitis in mice lacking hepatocellular PTEN

The metabolic disorders that predispose patients to NASH (non-alcoholic steatohepatitis) include insulin resistance and obesity. Repeated hypoxic events, such as occur in obstructive sleep apnoea syndrome, have been designated as a risk factor in the progression of liver disease in such patients, but the mechanism is unclear, in particular the role of hypoxia. Therefore we studied the influence of hypoxia on the development and progression of steatohepatitis in an experimental mouse model. Mice with a hepatocellular-specific deficiency in the Pten (phosphatase and tensin homologue deleted on chromosome 10) gene, a tumour suppressor, were exposed to a 10% O2 (hypoxic) or 21% O2 (control) atmosphere for 7 days. Haematocrit, AST (aspartate aminotransferase), glucose, triacylglycerols (triglycerides) and insulin tolerance were measured in blood. Histological lesions were quantified. Expression of genes involved in lipogenesis and mitochondrial beta-oxidation, as well as FOXO1 (forkhead box O1), hepcidin and CYP2E1 (cytochrome P450 2E1), were analysed by quantitative PCR. In the animals exposed to hypoxia, the haematocrit increased (60+/-3% compared with 50+/-2% in controls; P<0.01) and the ratio of liver weight/body weight increased (5.4+/-0.2% compared with 4.7+/-0.3% in the controls; P<0.01). Furthermore, in animals exposed to hypoxia, steatosis was more pronounced (P<0.01), and the NAS [NAFLD (non-alcoholic fatty liver disease) activity score] (8.3+/-2.4 compared with 2.3+/-10.7 in controls; P<0.01), serum AST, triacylglycerols and glucose were higher. Insulin sensitivity decreased in mice exposed to hypoxia relative to controls. The expression of the lipogenic genes SREBP-1c (sterol-regulatory-element-binding protein-1c), PPAR-gamma (peroxisome-proliferator-activated receptor-gamma), ACC1 (acetyl-CoA carboxylase 1) and ACC2 (acetyl-CoA carboxylase 2) increased significantly in mice exposed to hypoxia, whereas mitochondria beta-oxidation genes [PPAR-alpha (peroxisome-proliferator-activated receptor-alpha) and CPT-1 (carnitine palmitoyltransferase-1)] decreased significantly. In conclusion, the findings of the present study demonstrate that hypoxia alone aggravates and accelerates the progression of NASH by up-regulating the expression of lipogenic genes, by down-regulating genes involved in lipid metabolism and by decreasing insulin sensitivity.

Antagonistic effects of oxidized low density lipoprotein and alpha-tocopherol on CD36 scavenger receptor expression in monocytes: involvement of protein kinase B and peroxisome proliferator-activated receptor-gamma

Vitamin E deficiency increases expression of the CD36 scavenger receptor, suggesting specific molecular mechanisms and signaling pathways modulated by alpha-tocopherol. We show here that alpha-tocopherol down-regulated CD36 expression (mRNA and protein) in oxidized low density lipoprotein (oxLDL)-stimulated THP-1 monocytes, but not in unstimulated cells. Furthermore, alpha-tocopherol treatment of monocytes led to reduction of fluorescent oxLDL-3,3'-dioctadecyloxacarbocyanine perchlorate binding and uptake. Protein kinase C (PKC) appears not to be involved because neither activation of PKC by phorbol 12-myristate 13-acetate nor inhibition by PKC412 was affected by alpha-tocopherol. However, alpha-tocopherol could partially prevent CD36 induction after stimulation with a specific agonist of peroxisome proliferator-activated receptor-gamma (PPARgamma; troglitazone), indicating that this pathway is susceptible to alpha-tocopherol action. Phosphorylation of protein kinase B (PKB) at Ser473 was increased by oxLDL, and alpha-tocopherol could prevent this event. Expression of PKB stimulated the CD36 promoter as well as a PPARgamma element-driven reporter gene, whereas an inactive PKB mutant had no effect. Moreover, coexpression of PPARgamma and PKB led to additive induction of CD36 expression. Altogether, our results support the existence of PKB/PPARgamma signaling pathways that mediate CD36 expression in response to oxLDL. The activation of CD36 expression by PKB suggests that both lipid biosynthesis and fatty acid uptake are stimulated by PKB.

Stejnulxin, a novel snake C-type lectin-like protein from Trimeresurus stejnegeri venom is a potent platelet agonist acting specifically via GPVI

Stejnulxin, a novel snake C-type lectin-like protein with potent platelet activating activity, was purified and characterized from Trimeresurus stejnegeri venom. Under non-reducing conditions, it migrated on a SDS-polyacrylamide gel with an apparent molecular mass of 120 kDa. On reduction, it separated into three polypeptide subunits with apparent molecular masses of 16 kDa (alpha), 20 kDa (beta1) and 22 kDa (beta2), respectively. The complete amino acid sequences of its subunits were deduced from cloned cDNAs. The N-terminal sequencing and cDNA cloning indicated that beta1 and beta2 subunits of stejnulxin have identical amino acid sequences and each contains two N-glycosylation sites. Accordingly, the molecular mass difference between beta1 and beta2 is caused by glycosylation heterogenity. The subunit amino acid sequences of stejnulxin are similar to those of convulxin, with sequence identities of 52.6% and 66.4% for the alpha and beta, respectively. Stejnulxin induced human platelet aggregation in a dose-dependent manner. Antibodies against alphaIIbbeta3 inhibited the aggregation response to stejnulxin, indicating that activation of alphaIIbbeta3 and binding of fibrinogen are involved in stejnulxin-induced platelet aggregation. Antibodies against GPIbalpha or alpha2beta1 as well as echicetin or rhodocetin had no significant effect on stejnulxin-induced platelet aggregation. However, platelet activation induced by stejnulxin was blocked by anti-GPVI antibodies. In addition, stejnulxin induced a tyrosine phosphorylation profile in platelets that resembled that produced by convulxin. Biotinylated stejnulxin bound specifically to platelet membrane GPVI.

Surface expression and functional characterization of alpha-granule factor V in human platelets: effects of ionophore A23187, thrombin, collagen, and convulxin

Factor V (FV) present in platelet alpha-granules has a significant but incompletely understood role in hemostasis. This report demonstrates that a fraction of platelets express very high levels of surface-bound, alpha-granule FV on simultaneous activation with 2 agonists, thrombin and convulxin, an activator of the collagen receptor glycoprotein VI. This subpopulation of activated platelets represents 30.7% +/- 4.7% of the total population and is referred to as convulxin and thrombin-induced-FV (COAT-FV) platelets. COAT-FV platelets are also observed on activation with thrombin plus collagen types I, V, or VI, but not with type III. No single agonist examined was able to produce COAT-FV platelets, although ionophore A23187 in conjunction with either thrombin or convulxin did generate this population. COAT-FV platelets bound annexin-V, indicating exposure of aminophospholipids and were enriched in young platelets as identified by the binding of thiazole orange. The functional significance of COAT-FV platelets was investigated by demonstrating that factor Xa preferentially bound to COAT-FV platelets, that COAT-FV platelets had more FV activity than either thrombin or A23187-activated platelets, and that COAT-FV platelets were capable of generating more prothrombinase activity than any other physiologic agonist examined. Microparticle production by dual stimulation with thrombin and convulxin was less than that observed with A23187, indicating that microparticles were not responsible for all the activities observed. These data demonstrate a new procoagulant component produced from dual stimulation of platelets with thrombin and collagen. COAT-FV platelets may explain the unique role of alpha-granule FV and the hemostatic effectiveness of young platelets. (Blood. 2000;95:1694-1702)

Effects of Toll-like receptor 2 agonist Pam(3)CysSK(4) on inflammation and brain damage in experimental pneumococcal meningitis

TLR2 signaling participates in the pathogenesis of pneumococcal meningitis. In infant rats, the TLR2 agonist Pam(3)CysSK(4) was applied intracisternally (0.5 microg in 10 microl saline) alone or after induction of pneumococcal meningitis to investigate the effect of TLR2 activation on cerebrospinal fluid (CSF) inflammation and hippocampal apoptosis. A dose effect of Pam(3)CysSK(4) on apoptosis was investigated by intracisternal application of 0.5 microg in 10 microl saline and 40 microg in 20 microl saline. Pam(3)CysSK(4) neither induced apoptosis in sham-operated mice nor aggravated apoptosis in acute infection. However, Pam(3)CysSK(4) induced pleocytosis, TNF-alpha and MMP-9 in CSF in sham-infection but not during acute meningitis. We conclude that TLR2 signaling triggered by Pam(3)CysSK(4) at a dosage capable to induce a neuroinflammatory response does not induce hippocampal apoptosis in the infant rat model of experimental pneumococcal meningitis.

Distinct roles of estrogen receptors alpha and beta mediating acute vasodilation of epicardial coronary arteries.

This study investigated the contribution of estrogen receptors (ERs) alpha and beta for epicardial coronary artery function, vascular NO bioactivity, and superoxide (O(2)(-)) formation. Porcine coronary rings were suspended in organ chambers and precontracted with prostaglandin F(2alpha) to determine direct effects of the selective ER agonists 4,4',4''-(4-propyl-[(1)H]pyrazole-1,3,5-triyl)tris-phenol (PPT) or 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN) or the nonselective ER agonist 17beta-estradiol. Indirect effects on contractility to U46619 and relaxation to bradykinin were assessed and effects on NO, nitrite, and O(2)(-) formation were measured in cultured cells. Within 5 minutes, selective ERalpha activation by PPT, but not 17beta-estradiol or the ERbeta agonist DPN, caused rapid, NO-dependent, and endothelium-dependent relaxation (49+/-5%; P<0.001 versus ethanol). PPT also caused sustained endothelium- and NO-independent vasodilation similar to 17beta-estradiol after 60 minutes (72+/-3%; P<0.001 versus ethanol). DPN induced endothelium-dependent NO-independent relaxation via endothelium-dependent hyperpolarization (40+/-4%; P<0.01 versus ethanol). 17beta-Estradiol and PPT, but not DPN, attenuated the responses to U46619 and bradykinin. All of the ER agonists increased NO and nitrite formation in vascular endothelial but not smooth muscle cells and attenuated vascular smooth muscle cell O(2)(-) formation (P<0.001). ERalpha activation had the most potent effects on both nitrite formation and inhibiting O(2)(-) (P<0.05). These data demonstrate novel and differential mechanisms by which ERalpha and ERbeta activation control coronary artery vasoreactivity in males and females and regulate vascular NO and O(2)(-) formation. The findings indicate that coronary vascular effects of sex hormones differ with regard to affinity to ERalpha and ERbeta, which will contribute to beneficial and adverse effects of hormone replacement therapy.