Nitric oxide induces heat-shock protein 70 expression in vascular smooth muscle cells via activation of heat shock factor 1

Cyclic strain stress-induced mitogen-activated protein kinase (MAPK) phosphatase 1 expression in vascular smooth muscle cells is regulated by Ras/Rac-MAPK pathways

Recently, we demonstrated that mechanical stress results in rapid phosphorylation or activation of platelet-derived growth factor receptors in vascular smooth muscle cells (VSMCs) followed by activation of mitogen-activated protein kinases (MAPKs) and AP-1 transcription factors (Hu, Y., Bock, G., Wick, G., and Xu, Q. (1998) FASEB J. 12, 1135-1142). Herein, we provide evidence that VSMC responses to mechanical stress also include induction of MAPK phosphatase-1 (MKP-1), which may serve as a negative regulator of MAPK signaling pathways. When rat VSMCs cultivated on a flexible membrane were subjected to cyclic strain stress (60 cycles/min, 5-30% elongation), induction of MKP-1 proteins and mRNA was observed in time- and strength-dependent manners. Concomitantly, mechanical forces evoked rapid and transient activation of all three members of MAPKs, i.e. extracellular signal-regulated kinases (ERKs), c-Jun NH(2)-terminal protein kinases (JNKs), or stress-activated protein kinases (SAPKs), and p38 MAPKs. Suramin, a growth factor receptor antagonist, completely abolished ERK activation, significantly blocked MKP-1 expression, but not JNK/SAPK and p38 MAPK activation, in response to mechanical stress. Interestingly, VSMC lines stably expressing dominant negative Ras (Ras N17) or Rac (Rac N17) exhibited a marked decrease in MKP-1 expression; the inhibition of ERK kinases (MEK1/2) by PD 98059 or of p38 MAPKs by SB 202190 resulted in a down-regulation of MKP-1 induction. Furthermore, overexpressing MKP-1 in VSMCs led to the dephosphorylation and inactivation of ERKs, JNKs/SAPKs, and p38 MAPKs and inhibition of DNA synthesis. Taken together, our findings demonstrate that mechanical stress induces MKP-1 expression regulated by two signal pathways, including growth factor receptor-Ras-ERK and Rac-JNK/SAPK or p38 MAPK, and that MKP-1 inhibits VSMC proliferation via MAPK inactivation. These results suggest that MKP-1 plays a crucial role in mechanical stress-stimulated signaling leading to VSMC growth and differentiation.

Inhibition of neointima hyperplasia of mouse vein grafts by locally applied suramin

BACKGROUND

Saphenous vein grafts are widely used for aortocoronary bypass surgery as treatment for severe atherosclerosis and often are complicated by subsequent occlusion of the graft vessel.

METHODS AND RESULTS

We described a mouse model of venous bypass graft arteriosclerosis that can be effectively retarded by locally applied suramin, a growth factor receptor antagonist. Mouse isogeneic vessels of the vena cava veins pretreated with suramin were grafted end to end into the carotid arteries and enveloped with a mixture of suramin (1 mmol/L) and pluronic-127 gel. In the untreated group, vessel wall thickening was observed as early as 1 week after surgery and progressed to 4-fold and 10-fold the original thickness in grafted veins at 4 and 8 weeks, respectively. Pluronic-127 gel alone did not influence neointima formation. Suramin treatment reduced the neointima hyperplasia 50% to 70% compared with untreated controls. Immunohistochemical studies demonstrated that a significant proliferation of vascular smooth muscle cells (SMCs) constituted neointimal lesions between 4 and 8 weeks. The majority of SMCs expressed platelet-derived growth factor (PDGF) receptors-alpha and -beta, which were significantly reduced by suramin treatment. In vitro studies indicated that suramin completely blocked PDGF receptor activation or phosphorylation stimulated by PDGF-AB, inhibited activation of mitogen-activated protein kinase (ERK) kinases (MEK1/2) and ERK1/2, and abrogated transcription factor AP-1 DNA-binding activity.

CONCLUSIONS

Suramin inhibited SMC migration and proliferation in vivo and in vitro by blocking PDGF-initiated PDGF receptor and MAPK-AP-1 signaling. These findings indicate that locally applied suramin is effective in a mouse model of venous bypass graft arteriosclerosis.

LDL stimulates mitogen-activated protein kinase phosphatase-1 expression, independent of LDL receptors, in vascular smooth muscle cells

Low density lipoprotein (LDL) is a well-established risk factor for atherosclerosis, stimulating vascular smooth muscle cell (SMC) differentiation and proliferation, but the signal transduction pathways between LDL stimulation and cell proliferation are poorly understood. Because mitogen-activated protein kinases (MAPKs) play a crucial role in mediating cell growth, we studied the effect of LDL on the induction of MAPK phosphatase-1 (MKP-1) in human SMCs and found that LDL stimulated induction of MKP-1 mRNA and proteins in a time- and dose-dependent manner. Heparin, inhibiting LDL-receptor binding, did not influence LDL-stimulated MKP-1 mRNA expression, and human LDL also induced MKP-1 expression in rat SMCs and fibroblasts derived from LDL receptor-deficient mice, indicating an LDL receptor-independent process. Pretreatment of SMCs with pertussis toxin markedly inhibited LDL-induced MKP-1 expression. Depletion of protein kinase C (PKC) by phorbol 12-myristate 13 acetate or inhibition of PKC by calphostin C blocked MKP-1 induction, but the phospholipase C inhibitor U73122 had no effect. Pretreatment of SMCs with genistein or herbimycin A abrogated LDL-stimulated MKP-1 induction. The MAPK kinase inhibitor PD98059 abolished LDL-stimulated activation of extracellular signal-regulated protein kinases (ERKs) but not MKP-1 induction. Furthermore, constitutive expression of MKP-1 in vivo reduced LDL-induced expression of Elk-1-dependent reporter genes, and SMC lines overexpressing recombinant MKP-1 exhibited decreased ERK activities and retarded proliferation in response to LDL. Our findings demonstrate that LDL induces MKP-1 expression in SMCs via activation of PKC and tyrosine kinases, independent of LDL receptors and ERK-MAPKs, and that MKP-1 plays an important role in the regulation of LDL-initiated signal transductions leading to SMC proliferation.

Dinitrosyl iron complexes with thiol-containing ligands and S-nitroso-D,L-penicillamine as inductors of heat shock protein synthesis in H35 hepatoma cells

The concentration-dependent effect of various nitric oxide donors on synthesis of different heat shock proteins was evaluated in Reuber H35 hepatoma cells and their heat shock protein-inducing ability was compared with the effect of a heat shock. A 6 h incubation of H35 cells with the dimeric (diamagnetic) form of dinitrosyl iron complex with glutathione or N-acetyl-L-cysteine activated synthesis of various heat shock proteins, heat shock protein 28, 32, 60, 70, 90 and 100. Synthesis of these proteins was evaluated by [35S]methionine and [35S]cysteine labelling with subsequent separation of proteins by polyacrylamide gel electrophoresis. The dinitrosyl iron complex with glutathione appeared to be the most efficient inductor of heat shock protein synthesis and initiated the synthesis of heat shock protein 28 even more efficiently than a 30 min heating of cells. In the same experiments, S-nitroso-D,L-penicillamine exerted a considerably lesser effect on the synthesis of heat shock proteins. It was suggested that the active moiety of dinitrosyl iron complexes as inductors of heat shock protein synthesis is represented by their Fe+(NO+)2 groups which move to thiol groups of the proteins participating in the initiation of heat shock protein synthesis.

Activation of Fas inhibits heat-induced activation of HSF1 and up-regulation of hsp70

Activation of heat shock factor (HSF) 1-DNA binding and inducible heat shock protein (hsp) 70 (also called hsp72) expression enables cells to resist various forms of stress and survive. Fas, a membrane-bound protein, is a central proapoptotic factor; its activation leads to a cascade of events, resulting in programmed cell death. These two mechanisms with contradictory functions, promoting either cell survival or death, were examined for their potential to inhibit each other's activation. Induction of FAS-mediated signaling was followed by a rapid decrease in HSF1-DNA binding and inducible hsp70 expression. Inhibition of HSF1-DNA binding was demonstrated to be based on absent hyperphosphorylation of HSF1 during FAS signaling. These effects of FAS activation on the HSF1/hsp70 stress response were blocked by ICE (caspase 1) inhibitors, suggesting an ICE-mediated process. Furthermore, inhibition of HSF1/hsp70 was accompanied by an increase in apoptosis rates from 20% to 50% in response to heat stress. When analyzing the effects of HSF1/hsp70 activation on Fas-mediated apoptosis, protection from apoptosis was seen in cells with induced hsp70 protein levels, but not in cells that were just induced for HSF1-DNA binding. Thus, we conclude that inhibition of HSF1/hsp70 stress response during Fas-mediated apoptosis and vice versa may facilitate a cell to pass a previously chosen pathway, stress resistance or apoptosis, without the influence of inhibitory signals.

Regulation of Cytosolic COX-2 and Prostaglandin E2 Production by Nitric Oxide in Activated Murine Macrophages

Murine macrophages (RAW 264.7) when stimulated with LPS show 90% distribution of cyclooxygenase-2 (COX-2) in the nuclear fraction and ∼10% in the cytosolic fraction. Further analysis of this cytosolic fraction at 100,000 × g indicates that the COX-2 is distributed both in the 100,000 × g soluble fraction and membrane fraction. Stimulation of RAW 264.7 cells with LPS in the presence of inducible nitric oxide synthase inhibitor l-NMMA at concentrations that inhibit nitrite accumulation by ≤80% is inadequate to augment PGE2 production. However, inhibition of nitrite accumulation by ≥85% with higher concentrations of l-NMMA shows 1) up-regulation of PGE2 production, 2) accumulation of COX-2 protein in the 100,000 × g soluble and membrane fractions of the cytosolic fraction, and 3) with no significant effects on the accumulation of COX-2 mRNA. These experiments suggest that low concentrations of nitric oxide (10–15% of the total) attenuate PGE2 production in response to LPS in RAW 264.7 cells. This inhibition is, in part, due to decreased expression of cytosolic COX-2 protein.

Heat stress response and myocardial protection

Prior whole-body hyperthermia is able to protect the myocardium against ischaemia-reperfusion injury by reducing cellular necrosis, preserving the ventricular function and preventing the occurrence of arrhythmias. These cardioprotective effects are associated with reduction of oxidative stress, preservation of the high-energy phosphate levels and synthesis of heat stress proteins. A better understanding of this powerful protective adaptation of the myocytes would be of interest for potential clinical application, and rational design of specific agents that activate this mechanism will hopefully follow soon.

Induction of mitogen-activated protein kinase phosphatase-1 by arachidonic acid in vascular smooth muscle cells

Arachidonic acid (AA) and its metabolites play important roles in a variety of biological processes, such as signal transduction, contraction, chemotaxis, and cell proliferation and differentiation. It was demonstrated recently that AA can activate mitogen-activated protein kinases (MAPKs), which are crucial for transducing signals initiating cell growth and apoptosis. Here we studied the effect of AA on the induction of MAPK phosphatase-1 (MKP-1) in vascular smooth muscle cells (VSMCs) and found that AA stimulated induction of MKP-1 mRNA and proteins in VSMCs in a time- and dose-dependent manner. Specific inhibitors of cyclooxygenase-, lipoxygenase-, and cytochrome P450-dependent metabolism did not affect AA-induced MKP-1 expression, indicating that eicosanoid biosynthesis was not involved in this process. The glutathione precursor N-acetylcysteine, an antioxidant, abolished AA-stimulated MKP-1 gene expression, whereas inhibition of protein kinase C by calphostin C had no influence on MKP-1 induction. VSMC pretreatment with genistein, a tyrosine kinase inhibitor, completely blocked AA-stimulated MKP-1 induction. MAPK kinase inhibitor PD 98059 did abolish AA-stimulated activation of extracellular signal-regulated kinases but not MKP-1 induction. Furthermore, agonists that increase AA release stimulated MKP-1 induction and activation of MAPKs, including extracellular signal-regulated kinases and c-Jun NH2-terminal protein kinases or stress-activated protein kinases. Taken together, our findings demonstrate that AA induced MKP-1 expression in VSMCs via activation of tyrosine kinases involving AA-induced free radical generation, suggesting an important role for MKP-1 in the regulation of AA-initiated signal transduction in VSMCs.

Cyclic GMP-dependent and cyclic GMP-independent actions of nitric oxide on the renal afferent arteriole

1. The effects of exogenous NO and endothelial-derived NO (EDNO) on the afferent arteriole were investigated in the in vitro perfused hydronephrotic rat kidney. Vessels were pre-constricted with angiotensin II (0.1-0.3 nM) or KCl (30 mM). NO was infused directly into the renal artery at concentrations ranging from 30-9000 nM. ODQ (10, 30 microM) was administered to examine the effects of guanylyl cyclase inhibition. Kidneys were treated with ibuprofen (10 microM) to avoid actions of prostaglandins. 2. During angiotensin II-induced vasoconstriction, NO elicited vasodilation at concentrations of 30 900 nM (EC50=200 nM) and ODQ caused a 10 fold shift in NO-sensitivity (EC50 1600 nM). During KCl-induced vasoconstriction, NO elicited a maximal dilation of 82+9% at 9000 nM (EC50 2000 nM) and ODQ had no effect. Thus in the presence of ODQ, the NO concentration-response curves for KCI- and angiotensin II-induced vasoconstriction were identical (P>0.2). 3. To assess the possible role of cyclic GMP-independent mechanisms in the actions of EDNO, we compared the effects of L-NAME, ODQ and ODQ+L-NAME on acetylcholine-induced vasodilation. Angiotensin II reduced afferent arteriolar diameters from 16.7+/-0.5 to 8.1+/-0.8 microns and acetylcholine fully reversed this effect (16.9+/-0.5 microns). ODQ restored the angiotensin II response in the presence of acetylcholine (7.1+/-0.6 microns) and the subsequent addition of L-NAME had no further effect (6.8+/-0.7 microns). Similarly, L-NAME alone, fully reversed the actions of acetylcholine. 4. Our findings indicate that exogenous NO is capable of eliciting renal afferent arteriolar vasodilation through both cyclic GMP-dependent and cyclic GMP-independent mechanisms. The cyclic GMP-independent action of NO did not require K+ channel activation, as it could be elicited in the presence of 30 mM KCl. Finally, although cyclic GMP-independent effects of exogenous NO could be demonstrated in our model, EDNO appears to act exclusively through cyclic GMP.

Ramipril-induced delayed myocardial protection against free radical injury involves bradykinin B2 receptor-NO pathway and protein synthesis

1. The aim of the present study was to examine whether ramipril induces delayed myocardial protection against free radical injuries ex vivo and to determine the possible role of the bradykinin B2-nitric oxide (NO) pathway, prostaglandins(PGs) and protein synthesis in this delayed adaptive response. 2. Rats were pretreated with ramipril (10 or 50 microg kg(-1), i.v.) and hearts were isolated after 24, 48 and 72 h. Langendorff hearts were subjected to 1,1-diphenyl-2-picryl-hydrazyl (DPPH) free radical-induced injury. 3. Left ventricular developed pressure (LVDP) and its maximal increase velocity (+ dP/dtmax), coronary flow (CF), heart rate (HR), lactate dehydrogenase (LDH) in coronary effluent and thiobarbituric acid reactive substances (TBARS) in the myocardium were measured. 4. The results showed that in the DPPH control group, 20 min after free radical-induced injury, LVDP, +dP/dtmax, CF, HR declined, whereas TBARS and LDH increased significantly. The above cardiac function parameters were significantly improved in RAM-pretreated rats after 24 and 48 h. 5. Pretreatment with HOE 140, the selective bradykinin B2 receptor antagonist, NG-nitro-L-arginine, the NO synthase inhibitor, and actinomycin D, the RNA transcription inhibitor, prior to ramipril injection abolished the beneficial effects of ramipril at 24 h while indomethacin, a cyclooxygenase inhibitor, pretreatment had no effect on ramipril-induced delayed protection. 6. In conclusion, ramipril induces delayed myocardial protection against free radical injury in the rat heart. This delayed protection was sustained for 48 h, is associated with the bradykinin B2 receptor-NO pathway and depends on protein but not prostaglandin synthesis.

Activation of PDGF receptor alpha in vascular smooth muscle cells by mechanical stress

Hypertension increases mechanical force on the arterial wall by as much as 30%, resulting in marked alterations in signal transductions and gene expression in vascular smooth muscle cells (VSMCs) that contribute to matrix protein synthesis, cell proliferation, and differentiation. How the mechanical stimuli are converted into a biological signal in cells has yet to be studied. We investigated the role of both cyclic strain and shear stresses in initiating the cellular signaling on cultured VSMCs and found that mechanical forces evoked activation of mitogen-activated protein kinases, followed by enhanced DNA binding activity of transcription factor AP-1. Physical forces rapidly induced phosphorylation of platelet-derived growth factor receptor (PDGFR) alpha, an activated state. When GRB2, an adapter protein, was immunoprecipitated from treated VSMCs followed by Western blot analysis with anti-phosphotyrosine, -PDGFR alpha, and -GRB2 antibodies, respectively, phosphotyrosine positive staining was observed on PDGFR alpha bands of the same blot in stretch-stressed VSMCs, supporting the mechanical stress-induced activation of PDGFR alpha. Conditioned medium from stretch-stressed VSMCs did not result in PDGFR alpha phosphorylation, and antibodies binding to all forms of PDGFs did not block stress-induced PDGFR alpha activation. Thus, mechanical stresses may directly perturb the cell surface or alter receptor conformation, thereby initiating signaling pathways normally used by growth factors.

Stress (heat shock) proteins: molecular chaperones in cardiovascular biology and disease

How a cell responds to stress is a central problem in cardiovascular biology. Diverse physiological stresses (eg, heat, hemodynamics, mutant proteins, and oxidative injury) produce multiple changes in a cell that ultimately affect protein structures and function. Cells from different phyla initiate a cascade of events that engage essential proteins, the molecular chaperones, in decisions to repair or degrade damaged proteins as a defense strategy to ensure survival. Accumulative evidence indicates that molecular chaperones such as the heat shock family of stress proteins (HSPs) actively participate in an array of cellular processes, including cytoprotection. The versatility of the ubiquitous HSP family is further enhanced by stress-inducible regulatory networks, both at the transcriptional and posttranscriptional levels. In the present review, we discuss the regulation and function of HSP chaperones and their clinical significance in conditions such as cardiac hypertrophy, vascular wall injury, cardiac surgery, ischemic preconditioning, aging, and, conceivably, mutations in genes encoding contractile proteins and ion channels.

Enhanced expression of heat shock protein 70 (hsp70) and heat shock factor 1 (HSF1) activation in rheumatoid arthritis synovial tissue. Differential regulation of hsp70 expression and hsf1 activation in synovial fibroblasts by proinflammatory cytokines, shear stress, and antiinflammatory drugs

Heat shock proteins (hsp) have been repeatedly implicated to participate in the pathogenesis of rheumatoid arthritis (RA). Herein, we investigated the regulation of synovial hsp70 expression by analyzing the DNA-binding activity of heat shock transcription factor 1 (HSF1) as well as inducible hsp70 expression. Experiments were performed both on synovial tissue and on synovial fibroblast-like cells (SFC). Gel mobility shift analysis revealed increased HSF1 activation, and Western blotting and immunohistochemistry revealed increased hsp70 expression in RA synovial tissue, but not in synovial tissue derived from patients with osteoarthritis. Proinflammatory cytokines (TNF-alpha, IL-1alpha, IL-6), but not IFN-gamma or TGF-beta, induced activation of HSF1-DNA binding and hsp70 expression in cultivated SFC. Activation of HSF1 in SFC was accompanied by hyperphosphorylation and nuclear translocation of HSF1. Furthermore, shear stress also induced a complete heat shock response in cultivated synovial cells. In contrast, nonsteroidal antiinflammatory drugs triggered only an incomplete heat shock response, with HSF1 activation but not hsp70 induction, whereas steroids and immunosuppressive drugs did not affect the heat shock response at all. In summary, these data suggest that induction of hsp70 expression in rheumatoid synovial tissue is based on transcriptional activation of HSF1 due to the presence of proinflammatory cytokines (and possibly also shear stress).

Characterization of the Hsp110/SSE gene family response to hyperosmolality and other stresses

Hsp110, Osp94, and Hsp70RY are members of the recently described Hsp110/SSE subfamily of (heat and osmotic) stress proteins whose members are structurally related to the Hsp70/BiP gene superfamily. To date, little is known about the response of this gene family to stresses in vitro or in vivo. In this study, an analysis of mRNA expression showed that Hsp110 and Osp94, like Hsp70, are induced in renal murine inner medullary collecting duct (mIMCD3) epithelial cells by heat shock, hyperosmotic NaCl, and cadmium, whereas low pH had a suppressive effect on Osp94. H2O2 decreased expression of Osp94 while inducing levels of Hsp110 and Hsp70 message. Tunicamycin, hypertonic urea, and tumor necrosis factor- had no effects. Hsp70RY was responsive exclusively to cadmium chloride. Moreover, enhanced expression of Hsp110 and Osp94 was subsequent to induction of Hsp70 and was suppressed by inhibition of protein synthesis by cycloheximide. RT-PCR analysis showed Hsp110, Osp94, and Hsp70RY are ubiquitously expressed in mouse tissues. In murine kidney, there was a corticomedullary gradient of expression of Hsp110, Osp94, Hsp70RY, and Hsp70 but not Hsc70 or BiP. Furthermore, dehydration increased inner medullary expression of Hsp110 and Osp94. An analysis of stress tolerance in mIMCD3 cells showed that heat shock and hyperosmotic NaCl stress are cross-tolerant stresses, suggesting hyperosmolality is a physiological correlate of heat shock in mammalian kidney. Thus Hsp110 and Osp94 behave as heat shock proteins, although they are regulated differently than Hsp70.