Deleterious effects of nifedipine on smooth muscle cells implies alterations of intracellular calcium signaling

Clarification of serotonin-induced effects in peripheral artery disease observed through the femoral artery response in models of diabetes and vascular occlusion: The role of calcium ions

Recent findings have demonstrated that serotonin is an important participant in the development and progression of peripheral artery diseases. Taking this into consideration, the goals of this study were to investigate the effects of serotonin on isolated Wistar rat femoral arteries in both healthy and diabetic animals, with and without artery occlusion, with a particular focus on determining the role of calcium in this process. Contraction experiments with serotonin on intact and denuded femoral artery rings, in the presence or absence of nifedipine and ouabain (both separately, or in combination), as well as Ca²⁺ -free Krebs-Ringer bicarbonate solution were performed. The serotonin-induced results were concentration dependent, but only in healthy animals. The endothelium-dependent contraction of the femoral artery was assessed. In healthy animals, the endothelium-reliant part of contraction was dependent on the extracellular calcium, while the smooth muscle-related part was instead dependent on the intracellular calcium. In diabetic animals, both nifedipine and ouabain influenced serotonin-induced vascular effects by blocking intracellular calcium pathways. However, this was diminished after the simultaneous administration of both blockers.

Subendothelial resistin enhances monocyte transmigration in a co-culture of human endothelial and smooth muscle cells by mechanisms involving fractalkine, MCP-1 and activation of TLR4 and Gi/o proteins signaling

The cytokine resistin and the chemokine fractalkine (FKN) were found at increased levels in human atherosclerotic plaque, in the subendothelium, but their role in this location still needs to be characterized. Recently, high local resistin in the arterial vessel wall was shown to contribute to an enhanced accumulation of macrophages by mechanisms that need to be clarified. Our recent data showed that resistin activated smooth muscle cells (SMC) by up-regulating FKN and MCP-1 expression and monocyte chemotaxis by activating toll-like receptor 4 (TLR4) and Gi/o proteins. Since in the vessel wall both endothelial cells (EC) and SMC respond to cytokines and promote atherosclerosis, we questioned whether subendothelial resistin (sR) has a role in vascular cells cross-talk leading to enhanced monocyte transmigration and we investigated the mechanisms involved. To this purpose we used an in vitro system of co-cultured SMC and EC activated by sR and we analyzed monocyte transmigration. Our results indicated that: (1) sR enhanced monocyte transmigration in EC/SMC system compared to EC cultured alone; (2) sR activated TLR4 and Gi/o signaling in EC/SMC system and induced the secretion of more FKN and MCP-1 compared to EC cultured alone and used both chemokines to specifically recruit monocytes by CX3CR1 and CCR2 receptors. Moreover, FKN produced by resistin in EC/SMC system, by acting on CX3CR1 on EC/SMC specifically contributes to MCP-1 secretion in the system and to the enhanced monocyte transmigration. Our study indicates new possible targets for therapy to reduce resistin-dependent enhanced macrophage infiltration in the atherosclerotic arterial wall.

Cross talk between smooth muscle cells and monocytes/activated monocytes via CX3CL1/CX3CR1 axis augments expression of pro-atherogenic molecules

OBJECTIVE

In atherosclerotic lesions, fractalkine (CX3CL1) and its receptor (CX3CR1) expressed by smooth muscle cells (SMC) and monocytes/macrophages, mediate the heterotypic anchorage and chemotaxis of these cells. We questioned whether, during the close interaction of monocytes with SMC, the CX3CL1/CX3CR1 pair modulates the expression of pro-atherogenic molecules in these cells.

METHODS AND RESULTS

SMC were co-cultured with monocytes or LPS-activated monocytes (18h) and then the cells were separated and individually investigated for the gene and protein expression of TNFα, IL-1β, IL-6, CX3CR1 and metalloproteinases (MMP-2, MMP-9). We found that SMC-monocyte interaction induced, in each cell type, an increased mRNA and protein expression of TNFα, IL-1β, IL-6, CX3CR1, MMP-2 and MMP-9. Blocking the binding of fractalkine to CX3CR1 (by pre-incubation of monocytes with anti-CX3CR1 or by CX3CR1 siRNA transfection) before cell co-culture decreased the production of TNFα, CX3CR1 and MMP-9. Monocyte-SMC interaction induced the phosphorylation of p38MAPK and activation of AP-1 transcription factor. Silencing the p65 (NF-kB subunit) inhibited the IL-1β and IL-6 and silencing c-jun inhibited the TNFα, CX3CR1 and MMP-9 induced by SMC-monocyte interaction.

CONCLUSIONS

The cross-talk between SMC and monocytes augments the inflammatory response in both cell types as revealed by the increased expression of TNFα, IL-1β, IL-6, CX3CR1 and MMPs. Up-regulation of TNFα, CX3CR1 and MMP-9 is further increased upon interaction of SMC with activated monocytes and is dependent on fractalkine/CXRCR1 pair. These data imply that the fractalkine/CX3RCR1 axis may represent a therapeutic target to impede the inflammatory process associated with atherosclerosis.

Long-term high glucose concentration influences Akt, ERK1/2, and PTP1B protein expression in human aortic smooth muscle cells

Hyperglycemia stimulates a plethora of intracellular signaling pathways within the cells of the vascular wall resulting in dysfunction-associated pathologies. Most of the studies reported so far explored the effect of rather short-time exposure of smooth muscle cells to high glucose concentrations. To mimic situation in Type 2 diabetes in which vascular wall is constantly exposed to circulating hyperglycemia, we report here the long-term (7days) effect of high glucose concentration on human media artery smooth muscle cells. This consists in up-regulation of PTP1B protein expression, down-regulation of basal Akt phosphorylation, and elevation of basal ERK1/2 activation. Acute stimulation of cells in high glucose with insulin down-regulated PTP1B expression, slightly decreased ERK1/2 activity, and activated Akt, whereas oxidative stress up-regulated Akt and ERK1/2 phosphorylation. In conclusion, long-term high glucose and acute oxidative stress and insulin stimulation imbalance the expression of activated kinases Akt and ERK1/2 and of dephosphorylating PTP1B in the insulin signaling pathway.

Ca2+-independent activation of Bruton's tyrosine kinase is required for store-mediated Ca2+ entry in human platelets

Store-mediated Ca(2+) entry (SMCE), which is rapidly activated by depletion of the intracellular Ca(2+) stores, is a major mechanism for Ca(2+) influx. Several studies have involved tyrosine kinases in the activation of SMCE, such as pp60(src), although at present those involved in the early activation steps are unknown. Here we report the involvement of Bruton's tyrosine kinase (Btk) in the early stages of SMCE in human platelets. Cell treatment with thrombin or thapsigargin (TG) plus ionomycin (Iono) results in rapid activation of Btk, which was independent of rise in intracellular Ca(2+) concentration ([Ca(2+)](i)) but dependent on H(2)O(2) generation. Platelet treatment with Btk inhibitors, LFM-A13 or terreic acid, significantly reduced TG+Iono- and thrombin-evoked SMCE. Btk was rapidly activated by addition of low concentrations of H(2)O(2), whose effect on Ca(2+) entry was prevented by Btk inhibitors. Our results indicate that pp60(src) and Btk co-immunoprecipitate after platelet stimulation with TG+Iono, thrombin or H(2)O(2). In addition, we have found that LFM-A13 impaired actin filament reorganization after store depletion and agonist-induced activation of pp60(src), while the inhibitor of pp60(src), a protein that requires actin reorganization for its activation, did not modify Btk activation, suggesting that Btk is upstream of pp60(src). We propose a role for Btk in the early steps of activation of SMCE in human platelets.

L-type voltage-dependent Ca2+ channels in cerebral microvascular endothelial cells and ET-1 biosynthesis

We investigated the role of intracellular calcium concentration ([Ca2+]i) in endothelin-1 (ET-1) production, the effects of potential vasospastic agents on [Ca2+]i, and the presence of L-type voltage-dependent Ca2+ channels in cerebral microvascular endothelial cells. Primary cultures of endothelial cells isolated from piglet cerebral microvessels were used. Confluent cells were exposed to either the thromboxane receptor agonist U-46619 (1 microM), 5-hydroxytryptamine (5-HT; 0.1 mM), or lysophosphatidic acid (LPA; 1 microM) alone or after pretreatment with the Ca2+-chelating agent EDTA (100 mM), the L-type Ca2+ channel blocker verapamil (10 microM), or the antagonist of receptor-operated Ca2+ channel SKF-96365 HCl (10 microM) for 15 min. ET-1 production increased from 1.2 (control) to 8.2 (U-46619), 4.9 (5-HT), or 3.9 (LPA) fmol/microg protein, respectively. Such elevated ET-1 biosynthesis was attenuated by verapamil, EDTA, or SKF-96365 HCl. To investigate the presence of L-type voltage-dependent Ca2+ channels in endothelial cells, the [Ca2+]i signal was determined fluorometrically by using fura 2-AM. Superfusion of confluent endothelial cells with U-46619, 5-HT, or LPA significantly increased [Ca2+]i. Pretreatment of endothelial cells with high K+ (60 mM) or nifedipine (4 microM) diminished increases in [Ca2+]i induced by the vasoactive agents. These results indicate that 1) elevated [Ca2+]i signals are involved in ET-1 biosynthesis induced by specific spasmogenic agents, 2) the increases in [Ca2+]i induced by the vasoactive agents tested involve receptor as well as L-type voltage-dependent Ca2+ channels, and 3) primary cultures of cerebral microvascular endothelial cells express L-type voltage-dependent Ca2+ channels.