Urotensin II and atherosclerosis

Urotensin II, through its interaction with its UT receptor, is a potent vasoactive peptide in humans and in several animal models. Recent studies have demonstrated elevated plasma U-II levels in patients with atherosclerosis and coronary artery disease. U-II is expressed in endothelial cells, smooth muscle cells and infiltrating macrophages of atherosclerotic human coronary arteries. UT receptor expression is up-regulated by inflammatory stimuli. Activation of UT receptor by U-II stimulates endothelial and smooth muscle cell proliferation and monocytes chemotaxis. Therefore, in addition to its primary vasoactive effect, these observations suggest a role of U-II and UT receptor in the initiation and/or progression of atherosclerosis.     

RhoA and resistance artery remodeling

Resistance arteries are able to adapt to physiological and pathophysiological stimuli to maintain adequate perfusion according to the metabolic demand of the tissue. Although vasomotor control allows rapid adaptation of lumen diameter, vascular remodeling constitutes an active process that occurs in response to long-term alterations of hemodynamic parameters. Unfortunately, this initially adaptive process contributes to the pathology of vascular diseases. Recent studies have demonstrated the participation of Rho protein signaling pathways in several cardiovascular pathologies including hypertension, coronary artery spasm, effort angina, atherosclerosis, and restenosis. Functional analyses have further revealed that RhoA-dependent pathways are involved in excessive contraction, migration, and proliferation associated with arterial diseases. The present review focuses on the role of Rho proteins, in particular RhoA, in vascular smooth muscle cells and the involvement of Rho-dependent signaling pathways in resistance artery remodeling, more particularly in relation to hypertension.     

Urotensin II is a new chemotactic factor for UT receptor-expressing monocytes

Urotensin II (U-II), a vasoactive cyclic neuropeptide which activates the G protein-coupled receptor UT receptor, exerts various cardiovascular effects and may play a role in the pathophysiology of atherosclerosis. In this study, we report that the UT receptor is expressed and functional on human PBMC and rat splenocytes. PBMC surface expression of the UT receptor was mainly found in monocytes and NK cells, also in a minority of B cells, but not in T cells. Stimulation of monocytes with LPS increased UT receptor mRNA and protein expression. Cloning and functional characterization of the human UT receptor gene promoter revealed the presence of NF-kappaB-binding sites involved in the stimulation of UT receptor gene expression by LPS. Activation of the UT receptor by U-II induced chemotaxis with maximal activity at 10 and 100 nM. This U-II effect was restricted to monocytes. Analysis of the signaling pathway involved indicated that U-II-mediated chemotaxis was related to RhoA and Rho kinase activation and actin cytoskeleton reorganization. The present results thus identify U-II as a chemoattractant for UT receptor-expressing monocytes and indicate a pivotal role of the RhoA-Rho kinase signaling cascade in the chemotaxis induced by U-II.     

Enteric GFAP expression and phosphorylation in Parkinson's disease

Enteric glial cells (EGCs) are in many respects similar to astrocytes of the central nervous system and express similar proteins including glial fibrillary acidic protein (GFAP). Changes in GFAP expression and/or phosphorylation have been reported during brain damage or central nervous system degeneration. As in Parkinson's disease (PD) the enteric neurons accumulate α‐synuclein, and thus are showing PD‐specific pathological features, we undertook the present survey to study whether the enteric glia in PD become reactive by assessing the expression and phosphorylation levels of GFAP in colonic biopsies. Twenty‐four PD, six progressive supranuclear palsy (PSP), six multiple system atrophy (MSA) patients, and 21 age‐matched healthy controls were included. The expression levels and the phosphorylation state of GFAP were analyzed in colonic biopsies by western blot. Additional experiments were performed using real‐time PCR for a more precise analysis of the GFAP isoforms expressed by EGCs. We showed that GFAPκ was the main isoform expressed in EGCs. As compared to control subjects, patients with PD, but not PSP and MSA, had significant higher GFAP expression levels in their colonic biopsies. The phosphorylation level of GFAP at serine 13 was significantly lower in PD patients compared to control subjects. By contrast, no change in GFAP phosphorylation was observed between PSP, MSA and controls. Our findings provide evidence that enteric glial reaction occurs in PD and further reinforce the role of the enteric nervous system in the initiation and/or the progression of the disease.

     

Thrombopoietin induces histidine decarboxylase gene expression in c-mpl transfected UT7 cells

The leukemic cell line UT7 is endowed with both megakaryocyte and basophil differentiation potential, as judged by its capacity to respond to PMA by displaying megakaryocytic and basophilic markers and to produce histamine by neosynthesis. Herein, we addressed the question whether the biological activities characteristic of basophil differentiation were still induced when c-mpl-transfected UT7 cells received a specific megakaryocytic differentiation signal delivered by thrombopoietin (TPO). Surprisingly, we found that histamine synthesis did effectively occur in response to the growth factor. This activity was not associated with megakaryopoiesis since it was not detected in megakaryocytes generated from CD34(+) cells cultured in the presence of TPO. Comparing different c-mpl-transfected cell lines, we found that the amount of histamine generated in response to TPO correlated with their responsiveness to PMA, but not with their level of c-mpl expression, thus revealing an intrinsic basophil differentiation potential. Both PMA- and TPO-induced histamine synthesis was reduced by PKC and MEKs inhibitors, indicating that the induction occurred through a common signalling pathway.     

Transglutaminase-dependent RhoA activation and depletion by serotonin in vascular smooth muscle cells

The small G protein RhoA plays a major role in several vascular processes and cardiovascular disorders. Here we analyze the mechanisms of RhoA regulation by serotonin (5-HT) in arterial smooth muscle. 5-HT (0.1-10 microM) induced activation of RhoA followed by RhoA depletion at 24-72 h. Inhibition of 5-HT1 receptors reduced the early phase of RhoA activation but had no effect on 5-HT-induced delayed RhoA activation and depletion, which were suppressed by the 5-HT transporter inhibitor fluoxetine and the transglutaminase inhibitor monodansylcadaverin and in type 2 transglutaminase-deficient smooth muscle cells. Coimmunoprecipitations demonstrated that 5-HT associated with RhoA both in vitro and in vivo. This association was calcium-dependent and inhibited by fluoxetine and monodansylcadaverin. 5-HT promotes the association of RhoA with the E3 ubiquitin ligase Smurf1, and 5-HT-induced RhoA depletion was inhibited by the proteasome inhibitor MG132 and the RhoA inhibitor Tat-C3. Simvastatin, the Rho kinase inhibitor Y-27632, small interfering RNA-mediated RhoA gene silencing, and long-term 5-HT stimulation induced Akt activation. In contrast, inhibition of 5-HT-mediated RhoA degradation by MG132 prevented 5-HT-induced Akt activation. Long-term 5-HT stimulation also led to the inhibition of the RhoA/Rho kinase component of arterial contraction. Our data provide evidence that 5-HT, internalized through the 5-HT transporter, is transamidated to RhoA by transglutaminase. Transamidation of RhoA leads to RhoA activation and enhanced proteasomal degradation, which in turn is responsible for Akt activation and contraction inhibition. The observation of transamidation of 5-HT to RhoA in pulmonary artery of hypoxic rats suggests that this process could participate in pulmonary artery remodeling and hypertension.