Sequestosome1/p62: a regulator of redox-sensitive voltage-activated potassium channels, arterial remodeling, inflammation, and neurite outgrowth

Sequestosome1/p62 (SQSTM1) is an oxidative stress-inducible protein regulated by the redox-sensitive transcription factor Nrf2. It is not an antioxidant but known as a multifunctional regulator of cell signaling with an ability to modulate targeted or selective degradation of proteins through autophagy. SQSTM1 implements these functions through physical interactions with different types of proteins including atypical PKCs, nonreceptor-type tyrosine kinase p56(Lck) (Lck), polyubiquitin, and autophagosomal factor LC3. One of the notable physiological functions of SQSTM1 is the regulation of redox-sensitive voltage-gated potassium (Kv) channels which are composed of α and β subunits: (Kvα)4 (Kvβ)4. Previous studies have established that SQSTM1 scaffolds PKCζ, enhancing phosphorylation of Kvβ which induces inhibition of pulmonary arterial Kv1.5 channels under acute hypoxia. Recent studies reveal that Lck indirectly interacts with Kv1.3 α subunits and plays a key role in acute hypoxia-induced Kv1.3 channel inhibition in T lymphocytes. Kv1.3 channels provide a signaling platform to modulate the migration and proliferation of arterial smooth muscle cells and activation of T lymphocytes, and hence have been recognized as a therapeutic target for treatment of restenosis and autoimmune diseases. In this review, we focus on the functional interactions of SQSTM1 with Kv channels through two key partners aPKCs and Lck. Furthermore, we provide molecular insights into the functions of SQSTM1 in suppression of proliferation of arterial smooth muscle cells and neointimal hyperplasia following carotid artery ligation, in T lymphocyte differentiation and activation, and in NGF-induced neurite outgrowth in PC12 cells.

Detection of platelet sensitivity to inhibitors of COX-1, P2Y₁, and P2Y₁₂ using a whole blood microfluidic flow assay

BACKGROUND

Microfluidic devices recreate the hemodynamic conditions of thrombosis.

METHODS

Whole blood inhibited with PPACK was treated ex vivo with inhibitors and perfused over collagen for 300 s (wall shear rate=200 s(-1)) using a microfluidic flow assay. Platelet accumulation was measured in the presence of COX-1 inhibitor (aspirin, ASA), P2Y₁ inhibitor (MRS 2179), P2Y₁₂ inhibitor (2MeSAMP) or combined P2Y1 and P2Y₁₂ inhibitors.

RESULTS

High dose ASA (500 μM), 2MeSAMP (100 μM), MRS 2179 (10 μM), or combined 2MeSAMP and MRS 2179 decreased total platelet accumulation by 27.5%, 75.6%, 77.7%, and 87.9% (p<0.01), respectively. ASA reduced secondary aggregation rate between 150 and 300 s without effect on primary deposition rate on collagen from 60 to 150 s. In contrast, 2MeSAMP and MRS 2179 acted earlier and reduced primary deposition to collagen between 60 and 105 s and secondary aggregation between 105 and 300 s. R(COX) and R(P2Y) (defined as a ratio of secondary aggregation rate to primary deposition rate) demonstrated 9 of 10 subjects had R(COX)<1 or R(P2Y)<1 following ASA or 2MeSAMP addition, while 6 of 10 subjects had R(P2Y)<1 following MRS 2179 addition. Combined MRS 2179 and 2MeSAMP inhibited primary platelet deposition rate and platelet secondary aggregation beyond that of each individual inhibitor. Receiver-Operator Characteristic area under the curve (AUC) indicated the robustness of R(COX) and R(P2Y) to detect inhibition of secondary platelet aggregation by ASA, 2MeSAMP, and MRS 2179 (AUC of 0.874 0.966, and 0.889, respectively).

CONCLUSIONS

Microfluidic devices can detect platelet sensitivity to antiplatelet agents. The R-value can serve as a self-normalized metric of platelet function for a single blood sample.

Ginsenoside Rg1 inhibits platelet activation and arterial thrombosis

INTRODUCTION

Derived from the root of Panax ginseng C.A.Mey, Panax notoginsenosides (PNS) is a widely used herbal medicine to treat atherothrombotic diseases in Asian medicine. Ginsenoside Rg1 is one of the main compounds responsible for the pharmaceutical actions of PNS. As platelets play pivotal roles in atherothrombogenesis, we therefore studied the effect of Rg1 on platelet activation and its underlying mechanisms.

MATERIALS AND METHODS

Human platelets are obtained from healthy subjects. Platelet activation and the inhibition of Rg1 were assessed by Born aggregometer, flow cytmetry, flow chamber and western blot. The in vivo thrombosis model was induced by 10% FeCl3 on mesenteric arterioles of wild type B57/b6 mice.

RESULTS

Rg1 significantly inhibited platelet aggregation induced by thrombin, ADP, collagen and U46619, e.g., aggregation rate stimulated by 0.1UmL(-1) thrombin was decreased 46% by Rg1. Rg1 also reduced thrombin (0.1UmL(-1))-enhanced fibrinogen binding and P-selectin expression of single platelet by 81% and 66%, respectively. Rg1 affected αIIbβ3-mediated outside-in signaling as demonstrated by diminished platelet spreading on immobilized fibrinogen. Rg1 also decreased the rate of clot retraction in platelet rich plasma. Furthermore, Rg1 decreased platelet adhesion on collagen surface under a shear rate correlated to the arterial flow (1000s(-1)) by approximately 70%. Western blot showed that Rg1 potently inhibited ERK phosphrylation. The in vitro findings were further evaluated in the mouse model of in vivo arterial thrombosis, and Rg1 was found to prolong the mesenteric arterial occlusion time (34.9±4.1min without and 64.3±4.9min with Rg1; p<0.01).

CONCLUSIONS

Rg1 inhibits platelet activation via the inhibition of ERK pathway, and attenuates arterial thrombus formation in vivo.

Thromboxane A2 synthase inhibitors prevent production of infectious hepatitis C virus in mice with humanized livers

BACKGROUND & AIMS

A 3-dimensional (3D) culture system for immortalized human hepatocytes (HuS-E/2 cells) recently was shown to support the lifecycle of blood-borne hepatitis C virus (HCV). We used this system to identify proteins that are active during the HCV lifecycle under 3D culture conditions.

METHODS

We compared gene expression profiles of HuS-E/2 cells cultured under 2-dimensional and 3D conditions. We identified signaling pathways that were activated differentially in the cells, and analyzed their functions in the HCV lifecycle using a recombinant HCV-producing cell-culture system, with small interfering RNAs and chemical reagents. We investigated the effects of anti-HCV reagents that altered these signaling pathways in mice with humanized livers (carrying human hepatocytes).

RESULTS

Microarray analysis showed that cells cultured under 2-dimensional vs 3D conditions expressed different levels of messenger RNAs encoding prostaglandin synthases. Small interfering RNA-mediated knockdown of thromboxane A2 synthase (TXAS) and incubation of hepatocytes with a TXAS inhibitor showed that this enzyme is required for production of infectious HCV, but does not affect replication of the HCV genome or particle release. The TXAS inhibitor and a prostaglandin I2 receptor agonist, which has effects that are opposite those of thromboxane A2, reduced serum levels of HCV and inhibited the infection of human hepatocytes by blood-borne HCV in mice.

CONCLUSIONS

An inhibitor of the prostaglandin synthase TXAS inhibits production of infectious HCV particles in cultured hepatocytes and HCV infection of hepatocytes in mice with humanized livers. It therefore might be therapeutic for HCV infection.

Mechanisms of aspirin resistance

Aspirin is integral to the secondary prevention of cardiovascular disease and acts to impair the development of platelet-mediated atherothromboembolic events by irreversible inhibition of platelet cyclooxygenase-1 (COX-1). Inhibition of this enzyme prevents the synthesis of the potent pro-aggregatory prostanoid thromboxane A2. A large number of patients continue to experience atherothromboembolic events despite aspirin therapy, so-called 'aspirin treatment failure', and this is multifactorial in aetiology. Approximately 10% however do not respond appropriately to aspirin in a phenomenon known as 'aspirin resistance', which is defined by various laboratory techniques. In this review we discuss the reasons for aspirin resistance in a systematic manner, starting from prescription of the drug and ending at the level of the platelet. Poor medication adherence has been shown to be a cause of apparent aspirin resistance, and may in fact be the largest contributory factor. Also important is high platelet turnover due to underlying inflammatory processes, such as atherosclerosis and its complications, leading to faster regeneration of platelets, and hence of COX-1, at a rate that diminishes the efficacy of once daily dosing. Recent developments include the identification of platelet glycoprotein IIIa as a potential biomarker (as well as possible underlying mechanism) for aspirin resistance and the discovery of an anion efflux pump that expels intracellular aspirin from platelets. The absolute as well as relative contributions of such factors to the phenomenon of aspirin resistance are the subject of continuing research.

Chitosan stabilizes platelet growth factors and modulates stem cell differentiation toward tissue regeneration

The idea of using chitosan as a functional delivery aid to support simultaneously PRP, stem cells and growth factors (GF) is associated with the intention to use morphogenic biomaterials to modulate the natural healing sequence in bone and other tissues. For example, chitosan-chondroitin sulfate loaded with platelet lysate was included in a poly(D,L-lactate) foam that was then seeded with human adipose-derived stem cells and cultured in vitro under osteogenic stimulus: the platelet lysate provided to the bone tissue the most suitable assortment of GF which induces the osteogenic differentiation of the mesenchymal stem cells. PDGF, FGF, IGF and TGF-β were protagonists in the repair of callus fractures. The release of GF from the composites of chitosan-PRP and either nano-hydroxyapatite or tricalcium phosphate was highly beneficial for enhancing MSC proliferation and differentiation, thus qualifying chitosan as an excellent vehicle. A number of biochemical characteristics of chitosan exert synergism with stem cells in the regeneration of soft tissues.

Rosuvastatin inhibits human airway smooth muscle cells mitogenic response to eicosanoid contractile agents

BACKGROUND

The concept of permanent narrowing of the airways resulting from chronic inflammation and fibrosis is called remodeling and is a common feature of asthma and chronic obstructive pulmonary disease (COPD). The eicosanoid contractile agents thromboxane A(2) (TxA(2)) and cysteinyl-leukotriene D(4) (LTD(4)) are among the recognized mitogens for human airway smooth muscle (ASM) cells. Statins are known to possess anti-inflammatory and immunomodulatory properties that are independent on their cholesterol-lowering effects and may result in clinical lung benefits. Rosuvastatin is the last agent of the lipid-lowering drugs to be introduced and experimental evidence indicates that it possess favorable pleiotropic effects in the cardiovascular and nervous systems. Yet, no data is available in the literature regarding its effects on human airway remodeling. The present study was aimed at examining the effect of rosuvastatin and the involvement of prenylated proteins in the response of human ASM cells to serum, epidermal growth factor (EGF) and eicosanoid contractile mitogens that activate TxA(2) prostanoid and LTD(4) receptors.

METHODS

Cell growth was assessed by nuclear incorporation of [(3)H]thymidine in human ASM cells serum-starved and then stimulated for 48 h in MEM plus 0.1% BSA containing mitogens in the absence and presence of modulators of the mevalonate and prenylation pathways.

RESULTS

We found that rosuvastatin dose-dependently inhibited serum-, EGF-, the TxA(2) stable analog U46619-, and LTD(4)-induced human ASM cells growth. All these effects were prevented by pretreatment with mevalonate. Addition of the prenylation substrates farnesol and geranylgeraniol reversed the effect of rosuvastatin on EGF and U46619, respectively. Interestingly, only mevalonate showed restoration of cell growth following rosuvastatin treatment in LTD(4) and LTD(4) plus EGF treated cells, suggesting a possible involvement of both farnesylated and geranylgeranylated proteins in the cysteinyl-LT-induced cell growth.

CONCLUSIONS

The hydrophilic statin rosuvastatin exerts direct effects on human ASM cells mitogenic response in vitro by inhibiting prenylation of signaling proteins, likely small G proteins. These findings are consistent with previous observed involvement of small GTPase signaling in EGF- and U46619-induced human airway proliferation and corroborate the recent interest in the potential clinical benefits of statins in asthma/COPD.

Suppressive effects of antimycotics on thymic stromal lymphopoietin production in human keratinocytes

BACKGROUND

Thymic stromal lymphopoietin (TSLP) is produced by epidermal keratinocytes, and it induces Th2-mediated inflammation. TSLP expression is enhanced in lesions with atopic dermatitis, and is a therapeutic target. Antimycotic agents improve the symptoms of atopic dermatitis.

OBJECTIVE

The objective of this study was to examine whether antimycotics suppress TSLP expression in human keratinocytes.

METHODS

Normal human keratinocytes were incubated with polyinosinic-polycytidylic acid (poly I:C) plus IL-4 in the presence of antimycotics. TSLP expression was analyzed by ELISA and real time PCR. Luciferase assays were performed to analyze NF-κB activity. IκBα degradation was analyzed by Western blot analysis.

RESULTS

Poly I:C plus IL-4 increased the secretion and mRNA levels of TSLP, which was suppressed by an NF-κB inhibitor, and also enhanced NF-κB transcriptional activities and induced the degradation of IκBα in keratinocytes. The antimycotics itraconazole, ketoconazole, luliconazole, terbinafine, butenafine, and amorolfine suppressed the secretion and mRNA expression of TSLP, NF-κB activity, and IκBα degradation induced by poly I:C plus IL-4. These suppressive effects were similarly manifested by 15-deoxy-Δ-(12,14)-PGJ2 (15d-PGJ2), a prostaglandin D2 metabolite. Antimycotics increased the release of 15d-PGJ2 from keratinocytes and decreased the release of thromboxane B2, a thromboxane A2 metabolite. Antimycotic-induced suppression of TSLP production and NF-κB activity was counteracted by an inhibitor of lipocalin type-prostaglandin D synthase.

CONCLUSIONS

Antimycotics itraconazole, ketoconazole, luliconazole, terbinafine, butenafine, and amorolfine may suppress poly I:C plus IL-4-induced production of TSLP by inhibiting NF-κB via increasing 15d-PGJ2 production in keratinocytes. These antimycotics may block the overexpression of TSLP in lesions with atopic dermatitis.

Synthesis and pharmacological evaluation of 2-aryloxy/arylamino-5-cyanobenzenesulfonylureas as novel thromboxane A₂ receptor antagonists

New series of original 2-aryloxy/arylamino-5-cyanobenzenesulfonylureas were synthesized and evaluated as thromboxane A2 receptor (TP receptor) antagonists. A functional pharmacological test was used, which consisted of measuring the inhibition of intracellular calcium mobilization in a model of mammalian cell line that specifically over-expressed the individual TPα or TPβ isoforms. 2-Arylamino-5-cyanobenzenesulfonylureas exhibited virtually identical affinity and/or functional activity than 2-aryloxy-5-cyanobenzenesulfonylureas for both TPα and TPβ, but some 2-aryloxy-substituted compounds showed increased selectivity for TPβ relative to TPα. Several compounds were found to be as potent as the 2-arylamino-5-nitrobenzenesulfonylurea reference compound BM-573, supporting the view that the bioisosteric replacement of the nitro group by a cyano group was tolerated. TP receptor antagonist activity of the most promising molecules was confirmed in a platelet aggregation assay using the TP receptor agonist U-46619 as a proaggregant. Three compounds (7e, 7h and 8h) were identified as leads for further non-clinical pharmacological and toxicological studies.

ASP6537, a novel highly selective cyclooxygenase-1 inhibitor, exerts potent antithrombotic effect without "aspirin dilemma"

INTRODUCTION

Aspirin inhibits both the cyclooxygenase (COX)-1-dependent production of thromboxane A2 (TXA2) in platelets and COX-2-dependent production of anti-aggregatory prostaglandin I2 (PGI2) in vessel walls, resulting in "aspirin dilemma." Our objective is to investigate whether ASP6537 can overcome aspirin dilemma and exert a potent antithrombotic effect without a concurrent ulcerogenic effect.

METHODS

We evaluated the inhibitory effects of ASP6537 on recombinant human COX-1 (rhCOX-1) and rhCOX-2 activities using a COX-1/2 selectivity test. To determine whether ASP6537 induces aspirin dilemma, we examined the effects of ASP6537 on in vitro TXA2 and PGI2 metabolite production from platelets and isolated aorta of guinea pigs, and on plasma concentrations of TXA2 and PGI2 metabolites in aged rats. Finally, we evaluated the antithrombotic effects and ulcerogenic activity of ASP6537 using an electrically induced carotid arterial thrombosis model and a gastric ulcer model in guinea pigs.

RESULTS

The IC50 ratios of rhCOX-2 to rhCOX-1 for ASP6537 and aspirin were >142,000 and 1.63 fold, respectively. ASP6537 inhibited TXA2 production more selectively than aspirin in in vitro and in vivo TXA2/PGI2 production studies. ASP6537 exerted a significant antithrombotic effect at ≥3 mg/kg, while aspirin tended to inhibit thrombosis at 300 mg/kg but it was not statistically significant. Further, ASP6537 did not induce ulcer formation at 100 mg/kg, whereas aspirin exhibited an ulcerogenic effect at doses of ≥100 mg/kg.

CONCLUSIONS

ASP6537 functions as a highly selective COX-1 inhibitor with a superior ability to aspirin for normalizing TXA2/PGI2 balance, and exerts antithrombotic effect without ulcerogenic effect.