HSP70 increases extracellular matrix production by human vascular smooth muscle through TGF-ß1 up-regulation.

The circulating levels of heat shock proteins (HSP) are increased in cardiovascular diseases; however, the implication of this for the fibrotic process typical of such diseases remains unclear. HSP70 can interact with the vascular smooth muscle cells (SMC), the major producer of extracellular matrix (ECM) proteins, through the Toll-like receptors 4 (TLR4). The transforming growth factor type-ß1 (TGF-ß1) is a well known vascular pro-fibrotic cytokine that is regulated in part by AP-1-dependent transcriptional mechanisms. We hypothesized that extracellular HSP70 could interact with SMCs, inducing TGF-ß1 synthesis and subsequent changes in the vascular ECM. We demonstrate that extracellular HSP70 binds to human aorta SMC TLR4, which up-regulates the AP-1-dependent transcriptional activity of the TGF-ß1 promoter. This is achieved through the mitogen activated protein kinases JNK and ERK, as demonstrated by the use of specific blockers and the knockdown of TLR4 with specific small interfering RNAs. The TGF-ß1 upregulation increase the expression of the ECM proteins type I collagen and fibronectin. This novel observation may elucidate the mechanisms by which HSP70 contributes in the inflammation and fibrosis present in atherosclerosis and other fibrosis-related diseases.

Intracellular redox equilibrium is essential for the constitutive expression of AP-1 dependent genes in resting cells: studies on TGF-ß1 regulation.

The mechanisms involved in the continuous expression of constitutive genes are unclear. We hypothesize that steady state intracellular reactive oxygen species (ROS), which their levels are tightly maintained, could be regulating the expression of these constitutive genes in resting cells. We analyzed the regulation of an important constitutive gene, TGF-ß1, after decreasing intracellular ROS concentration in human mesangial cells. Decreased intracellular hydrogen peroxide by catalase addition reduced TGF-ß1 protein, mRNA expression and promoter activity. Furthermore, catalase decreased the basal activity of Activated Protein-1 (AP-1) that regulates TGF-ß1 promoter activity. This effect disappeared when AP-1 binding site was removed. Similar results were observed with another protein containing AP-1 binding sites in its promoter, such as eNOS, but it was not the case in other constitutive genes without any AP-1 binding site, as COX1 or PKG1. The pharmacological inhibition of the different ROS synthesis sources by blocking NADPH oxidase, the mitochondrial respiratory chain or xanthine oxidase, or the use of human fibroblasts with genetically deficient mitochondrial activity, induced a similar, significant reduction of steady state ROS concentration as the one observed with catalase. Moreover, there was decreased TGF-ß1 expression in all the cases excepting the xanthine oxidase blockade. These findings suggest a novel role for the steady state intracellular ROS concentration, where the compartmentalized, different systems involved in the intracellular ROS production, could be essential for the expression of constitutive AP1-dependent genes, as TGF-ß1.

H2O2 regulation of vascular function through sGC mRNA stabilization by HuR.

OBJECTIVE: Hydrogen peroxide (H(2)O(2)) is an important mediator in the vasculature, but its role in the regulation of soluble guanylate cyclase (sGC) activity and expression is not completely understood. The aim of this study was to test the effect of H(2)O(2) on sGC expression and function and to explore the molecular mechanism involved. METHODS AND RESULTS: H(2)O(2) increased sGCß1 protein steady-state levels in rat aorta and aortic smooth muscle cells (RASMCs) in a time- and dose-dependent manner, and this effect was blocked by catalase. sGCα2 expression increased along with ß1 subunit, whereas α1 subunit remained unchanged. Vascular relaxation to an NO donor (sodium nitroprusside) was enhanced by H(2)O(2), and it was prevented by ODQ (sGC inhibitor). cGMP production in both freshly isolated vessels and RASMCs exposed to H(2)O(2) was greatly increased after sodium nitroprusside treatment. The H(2)O(2)-dependent sGCß1 upregulation was attributable to sGCß1 mRNA stabilization, conditioned by the translocation of the mRNA-binding protein HuR from the nucleus to the cytosol, and the increased mRNA binding of HuR to the sGCß1 3' untranslated region. HuR silencing reversed the effects of H(2)O(2) on sGCß1 levels and cGMP synthesis. CONCLUSIONS: Our results identify H(2)O(2) as an endogenous mediator contributing to the regulation of vascular tone and point to a key role of HuR in sGCß1 mRNA stabilization.