Chronic high pressure potentiates the antiproliferative effect and abolishes contractile phenotypic changes caused by endothelial cells in cocultured smooth muscle cells

Enhancing biocompatibility and corrosion resistance of biodegradable Mg-Zn-Y-Nd alloy by preparing PDA/HA coating for potential application of cardiovascular biomaterials

In this paper the poly-dopamine (PDA)/hyaluronic acid (HA) coatings with different HA molecular weight (MW, 4 × 10³, 1 × 10⁵, 5 × 10⁵ and 1 × 10⁶ Da) were prepared onto the NaOH passivated Mg-Zn-Y-Nd alloy aiming at potential application of cardiovascular implants. The characterization of weight loss, polarization curves and surface morphology indicated that the coatings with HA MW of 1 × 10⁵ (PDA/HA-2) and 1 × 10⁶ Da (PDA/HA-4) significantly enhanced the corrosion resistance of Mg-Zn-Y-Nd. In vitro biological test also suggested better hemocompatibility, pro-endothelialization, anti-hyperplasia and anti-inflammation functions of the PDA/HA-2- and PDA/HA-4-coated Mg-Zn-Y-Nd alloy. Nevertheless, the in vivo implantation of SD rats' celiac artery demonstrated that the PDA/HA-2 had preferable corrosion resistance and biocompatibility.

Aortic valve: mechanical environment and mechanobiology

The aortic valve (AV) experiences a complex mechanical environment, which includes tension, flexure, pressure, and shear stress forces due to blood flow during each cardiac cycle. This mechanical environment regulates AV tissue structure by constantly renewing and remodeling the phenotype. In vitro, ex vivo and in vivo studies have shown that pathological states such as hypertension and congenital defect like bicuspid AV (BAV) can potentially alter the AV's mechanical environment, triggering a cascade of remodeling, inflammation, and calcification activities in AV tissue. Alteration in mechanical environment is first sensed by the endothelium, which in turn induces changes in the extracellular matrix, and triggers cell differentiation and activation. However, the molecular mechanism of this process is not understood very well. Understanding these mechanisms is critical for advancing the development of effective medical based therapies. Recently, there have been some interesting studies on characterizing the hemodynamics associated with AV, especially in pathologies like BAV, using different experimental and numerical methods. Here, we review the current knowledge of the local AV mechanical environment and its effect on valve biology, focusing on in vitro and ex vivo approaches.

Development of an endothelial-smooth muscle cell coculture model using phenotype-controlled smooth muscle cells

A coculture of endothelial cells (ECs) and smooth muscle cells (SMCs), which mimics cellular interactions appearing in vivo, has been performed in studies on the relationship between atherogenesis and fluid shear stress conditions. Although healthy arteries in vivo consist of contractile phenotype SMCs, cultured cells used in many studies normally exhibit a synthetic phenotype. Here, we developed an EC-SMC coculture model to investigate the interactions between ECs and contractile SMCs, and examined the effect of shear stress applied to ECs on SMC phenotypes. Cultured human umbilical artery SMCs were differentiated into contractile states by arresting cell growth using a serum-free medium. Western blotting confirmed that SMC expression of contractile protein markers, α-smooth muscle actin (SMA) and calponin, increased to levels similar to those observed in arterial cells. After coculturing contractile SMCs with ECs separated by a collagen gel layer, the expression of α-SMA decreased under static conditions, indicating that the SMC phenotype tended to be synthetic by coculturing with ECs, but shear stress applied to cocultured ECs maintained the level of α-SMA expression in SMCs. The coculture model constructed in the present study will be a useful tool to investigate interactions between ECs and contractile SMCs under shear conditions.

Smooth muscle cell phenotype alters cocultured endothelial cell response to biomaterial-pretreated leukocytes

Model in vitro culturing systems were developed to analyze roles of biomaterial-induced leukocyte activation on endothelial cell (EC) and smooth muscle cell (SMC) phenotype, and their crosstalk. Isolated monocytes or neutrophils were pretreated with model biomaterial beads and applied directly to "more secretory" (cultured in media containing 5% fetal bovine serum) or forced contractile (serum and growth factor starved) human aortic SMCs (HASMCs), or to the human aortic EC (HAEC) surface of HAEC/HASMC cocultures (HASMC phenotype varied to be "more or less secretory") for 5 or 24 h of static culture. Surface expression of proinflammatory [ICAM-1, VCAM-1, E-selectin], procoagulant (tissue factor), and anticoagulant (thrombomodulin) markers, as well as HAEC proliferation, were assessed by flow cytometry. Incubation of HAEC with biomaterial-pretreated monocytes (and neutrophils to lesser degree) suppressed HAEC proliferation and induced a proinflammatory/procoagulant HAEC phenotype. This HAEC phenotype was amplified in coculture with "more secretory" HASMCs and subdued in coculture with "less secretory" HASMCs. Direct incubation of biomaterial-pretreated monocytes or neutrophils with "more secretory" HASMCs further increased HASMC ICAM-1 and tissue factor expression. Direct incubation of biomaterial-pretreated monocytes or neutrophils with forced contractile HASMCs upregulated ICAM-1, VCAM-1, and tissue factor expression above the presence of serum-containing media alone.

Complimentary endothelial cell/smooth muscle cell co-culture systems with alternate smooth muscle cell phenotypes

Development of in vitro models of native and injured vasculature is crucial for better understanding altered wound healing in disease, device implantation, or tissue engineering. Conditions were optimized using polyethyleneteraphalate transwell filters for human aortic endothelial cell (HAEC)/smooth muscle cell (HASMC) co-cultures with divergent HASMC phenotypes ('more or less secretory') while maintaining quiescent HAECs. Resulting HASMC phenotype was studied at 48 and 72 h following co-culture initiation, and compared to serum and growth factor starved monocultured 'forced contractile' HASMCs. Forced contractile HASMCs demonstrated organized alpha-smooth muscle actin filaments, minimal interleukin-8 (IL-8) and monocyte chemotactic protein-1 (MCP-1) secretion, and low intracellular cell adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and tissue factor expression. Organization of alpha-smooth muscle actin was lost in 'more secretory' HASMCs in co-culture with HAECs, and IL-8 and MCP-1 secretion, as well as ICAM-1, VCAM-1, and tissue factor expression were significantly upregulated at both time points. Alternately, 'less secretory' HASMCs in co-culture with HAECs showed similar characteristics to forced contractile HASMCs at the 48 h time point, while by the 72 h time point they behaved similarly to 'more secretory' HASMCs. These co-culture systems could be useful in better understanding vascular healing, however there remain time constraint considerations for maintaining culture integrity/cell phenotype.

Ambient pressure upregulates nitric oxide synthase in a phosphorylated-extracellular regulated kinase– and protein kinase C–dependent manner

PURPOSE

Using endothelial cell/smooth muscle cell (SMC) cocultures, we have demonstrated that pressurized endothelial cell coculture inhibits SMC proliferation and promotes apoptosis, and that this effect is transferable through pressurized endothelial medium. We now hypothesized that endothelial nitric oxide synthase (eNOS) plays a significant role in mediating these pressure-induced effects.

METHODS

Conditioned media from endothelial cells and SMCs exposed to ambient and increased pressure were transferred to recipient SMCs. We counted cells after 5 days of incubation with these media and evaluated eNOS and inducible NOS (iNOS) levels by Western blot.

RESULTS

Conditioned media from pressurized endothelial cells significantly decreased recipient SMC counts. This effect was sustained when N-nitro-L-arginine-methyl ester (L-NAME) was added to recipient cells but abolished when L-NAME was added to donor cells. SMCs were then exposed to control and pressurized conditions in monoculture or in coculture with endothelial cells. Pressure and coculture caused similar increase in iNOS levels but had no additive effect in combination. Finally, endothelial cells were exposed to control and pressurized environments. Pressure caused a 24% +/- 1.6% increase in eNOS protein (P = .04, n = 12). This effect was sustained when cells were treated with L-NAME (32% +/- 1.6% increase, P = .02) but abolished when endothelial cells were treated with calphostin C or PD98059 to block protein kinase C (PKC) or extracellular regulated kinase (ERK). Pressure also increased endothelial phosphorylated ERK (p-ERK) by 1.8-fold to 2.6-fold compared with control conditions after exposure of 2, 4, and 6 hours (P = .02, n = 4). This increase was sustained after pretreatment with calphostin C.

CONCLUSION

Pressure modulates endothelial cell effects on SMC growth by increasing eNOS in an ERK-dependent and PKC-dependent manner.

CLINICAL RELEVANCE

Intimal hyperplasia is the main cause for restenosis that complicates 10% to 30% of all such vascular procedures and 30% to 40% of endovascular procedures. This article provides some novel information about smooth muscle cell/endothelial cell interaction, one of the main regulators of vascular remodeling and intimal hyperplasia. The role of endothelial cell/smooth muscle cell interaction cannot be studied well in vivo because these interactions cannot be distinguished from other factors that coexist in vivo, such as flow dynamics, matrix proteins, inflammatory factors, and interactions with other cells in the vascular wall and in the bloodstream. In this work, we use pressure as a triggering stimulus to alter in vitro endothelial behavior and identify important changes in endothelial regulation of smooth muscle cell biology. The pathways involved in this process and discussed in this article could ultimately be used to manipulate endothelial cell/smooth muscle cell interaction in clinical disease.

Shear stress protects against endothelial regulation of vascular smooth muscle cell migration in a coculture system

Vascular endothelial cells (ECs) are constantly exposed to blood flow-induced shear stress; these forces strongly influence the behaviors of neighboring vascular smooth muscle cells (VSMCs). VSMC migration is a key event in vascular wall remodeling. In this study, the authors assessed the difference between VSMC migration in VSMC/EC coculture under static and shear stress conditions. Utilizing a parallel-plate coculture flow chamber system and Transwell migration assays, they demonstrated that human ECs cocultured with VSMCs under static conditions induced VSMC migration, whereas laminar shear stress (1.5 Pa, 15 dynes/cm2) applied to the EC side for 12 h significantly inhibited this process. The changes in VSMC migration is mainly dependent on the close interactions between ECs and VSMCs. Western blotting showed that there was a consistent correlation between the level of Akt phosphorylation and the efficacy of shear stress-mediated EC regulation of VSMC migration. Wortmannin and Akti significantly inhibited the EC-induced effect on VSMC Akt phosphorylation and migration. These results indicate that shear stress protects against endothelial regulation of VSMC migration, which may be an atheroprotective function on the vessel wall.

Pressure and endothelial coculture upregulate myocytic Fas-FasL pathway and induce apoptosis by way of direct and paracrine mechanisms

BACKGROUND

Pressurized endothelial cell (EC)-smooth muscle cell (SMCs) coculture significantly increases the apoptosis of SMCs. Our current hypothesis was that in EC-SMC coculture, pressure upregulates SMC apoptosis SMCs through EC-derived paracrine factors and that SMC apoptosis is induced through Fas-Fas ligand (FasL) activation.

METHODS

Conditioned media (CM) from ECs and SMCs exposed to ambient or high pressure was transferred to recipient SMCs. SMCs were stained with terminal deoxynucleotide transferase-mediated deoxy uridine triphosphate nick-end labeling. Fas and FasL expression was assessed in SMC grown in monoculture, coculture with EC, pressurized monoculture, and pressurized coculture with EC.

RESULTS

CM from pressurized ECs caused a 30% increase in SMC apoptosis compared with CM from control ECs (P < .05). Pressure increased Fas and FasL expression in monocultured and cocultured SMCs (1.6-fold and 2.3-fold for Fas [P < .05] and 1.65-fold and 1.7-fold for FasL [P < or = .05]). Coculture had synergistic effect on Fas expression and no effect on FasL expression.

CONCLUSIONS

Pressure plays significant role in EC-SMC interaction, SMC apoptosis, and vascular remodeling.

Mechanical stress promotes the expression of smooth muscle-like properties in marrow stromal cells

OBJECTIVE

It is poorly understood what kind of factors are involved in lineage commitment and maturation of mesenchymal stem cells. The present study investigates whether mechanical stress promotes expression of smooth muscle cell (SMC)-specific cytoskeletal protein in marrow stromal cells.

METHODS

Fibroblast-like stromal cells expressing STRO-1 antigen were isolated from rat bone marrow by density gradient separation. After preincubation for 7, 14, or 21 days in static condition, cells were exposed to one of three types of fluid flow-induced mechanical forces (flow dominant, pressure dominant, or combined) for 36 hours. The expression of SMC-specific cytoskeletal protein [alpha smooth muscle actin (alphaSMA) and smooth muscle myosin heavy chain (SMMHC)] was evaluated by immunofluorescence staining and Western blotting.

RESULTS

The proportion of SMMHC-positive cells was increased with longer preincubation periods (p < 0.01 vs 7-day incubation) and by any types of mechanical stimulation (p < 0.01 vs static control condition). The SMMHC-positive fraction after exposure to pressure-dominant forces (0.9% +/- 0.2%, 2.9% +/- 0.9%, and 12.6% +/- 0.8% for 7, 14, and 21 days of preincubation) or to combined forces (1.2% +/- 0.2%, 3.1% +/- 1.6%, and 15.5% +/- 2.8%) was higher than after flow-dominant stimulation (0, 1.2% +/- 0.1%, and 7.2% +/- 2.0%) (p < 0.01). In Western blotting, pressure-dominant or combined stimulation upregulated alphaSMA and SMMHC expression compared to static control condition.

CONCLUSION

The long-term cell incubation and subsequent mechanical stimulation, especially compressive strain, promote expression of SMC-specific cytoskeletal protein in marrow stromal cells.

Extracellular pressure stimulates colon cancer cell proliferation via a mechanism requiring PKC and tyrosine kinase signals

Pressure in colonic tumours may increase during constipation, obstruction or peri-operatively. Pressure enhances colonocyte adhesion by a c-Src- and actin-cytoskeleton-dependent PKC-independent pathway. We hypothesized that pressure activates mitogenic signals.

METHODS

Malignant colonocytes on a collagen I matrix were subjected to 15 mmHg pressure. ERK, p38, c-Src and Akt phosphorylation and PKCalpha redistribution were assessed by western blot after 30 min and PKC activation by ELISA. Cells were counted after 24 h and after inhibition of each signal, tyrosine phosphorylation or actin depolymerization.

RESULTS

Pressure time-dependently increased SW620 and HCT-116 cell counts on collagen or fibronectin (P < 0.01). Pressure increased the SW620 S-phase fraction from 28 +/- 1 to 47 +/- 1% (P = 0.0002). Pressure activated p38, ERK, and c-Src (P < 0.05 each) but not Akt/PKB. Pressure decreased cytosolic PKC activity, and translocated PKCalpha to a membrane fraction. Blockade of p38, ERK, c-Src or PI-3-K or actin depolymerization did not inhibit pressure-stimulated proliferation. However, global tyrosine kinase blockade (genistein) and PKC blockade (calphostin C) negated pressure-induced proliferation.

CONCLUSIONS

Extracellular pressure stimulates cell proliferation and activates several signals. However, the mitogenic effect of pressure requires only tyrosine kinase and PKCalpha activation. Pressure may modulate colon cancer growth and implantation by two distinct pathways, one stimulating proliferation and the other promoting adhesion.

Activation of p38 MAPKalpha by extracellular pressure mediates the stimulation of macrophage phagocytosis by pressure

We have previously demonstrated that constant 20 mmHg extracellular pressure increases serum-opsonized latex bead phagocytosis by phorbol 12-myristate 13-acetate (PMA)- differentiated THP-1 macrophages in part by inhibiting focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK). Because p38 MAPK is activated by physical forces in other cells, we hypothesized that modulation of p38 MAPK might also contribute to the stimulation of macrophage phagocytosis by pressure. We studied phagocytosis in PMA-differentiated THP-1 macrophages, primary human monocytes, and human monocyte-derived macrophages (MDM). p38 MAPK activation was inhibited using SB-203580 or by p38 MAPKalpha small interfering RNA (siRNA). Pressure increased phagocytosis in primary monocytes and MDM as in THP-1 cells. Increased extracellular pressure for 30 min increased phosphorylated p38 MAPK by 46.4 +/- 20.5% in DMSO-treated THP-1 macrophages and by 20.9 +/- 9% in primary monocytes (P < 0.05 each). SB-203580 (20 microM) reduced basal p38 MAPK phosphorylation by 34.7 +/- 2.1% in THP-1 macrophages and prevented pressure activation of p38. p38 MAPKalpha siRNA reduced total p38 MAPK protein by 50-60%. Neither SB-203580 in THP-1 cells and peripheral monocytes nor p38 MAPK siRNA in THP-1 cells affected basal phagocytosis, but each abolished pressure-stimulated phagocytosis. SB-203580 did not affect basal or pressure-reduced FAK activation in THP-1 macrophages, but significantly attenuated the reduction in ERK phosphorylation associated with pressure. p38 MAPKalpha siRNA reduced total FAK protein by 40-50%, and total ERK by 10-15%, but increased phosphorylated ERK 1.4 +/- 0.1-fold. p38 MAPKalpha siRNA transfection did not affect the inhibition of FAK-Y397 phosphorylation by pressure but prevented inhibition of ERK phosphorylation. Changes in extracellular pressure during infection or inflammation regulate macrophage phagocytosis by a FAK-dependent inverse effect on p38 MAPKalpha that might subsequently downregulate ERK.

Pressure alters endothelial effects upon vascular smooth muscle cells by decreasing smooth muscle cell proliferation and increasing smooth muscle cell apoptosis

BACKGROUND

Although de-endothelialization after vascular intervention is associated with intimal hyperplasia, endothelial cells (ECs) increase smooth muscle cell (SMC) numbers in conventional cocultures. In previously published work, SMCs cocultured with ECs in a chronic high-pressure environment exhibited significantly decreased cell counts compared to monocultured SMCs in the same high pressure. This finding contrasted with SMCs cocultured with ECs in ambient pressure, which exhibited significantly higher cell counts than the monocultured SMCs in ambient pressure. We now hypothesize that extracellular pressure decreases SMC number during coculture with ECs by decreasing SMC proliferation through nuclear protein regulation and by increasing SMC apoptosis. Furthermore, this effect depends on the EC response to pressure.

METHODS

Rat aortic SMCs were cultured independently (SMC/0) or cocultured with EC (SMC/EC) under either atmospheric or increased pressure (130-135 mmHg over ambient, SMC/0-P and SMC/EC-P) for 5 days. We assessed SMC proliferative potential by determining c-myc expression (by protein analysis), apoptosis (by cell counting, staining with acridine orange or TUNEL technique), and topoisomerase IIalpha levels. Parallel studies measured the effects of conditioned media from monocultured EC and SMC exposed for 5 days to control or increased pressure on recipient SMC growing in conventional culture.

RESULTS

In high-pressure conditions, SMC/EC-P exhibited 42% less c-myc expression than SMC/0s (P = .00028). Significantly increased apoptotic activity (22 +/- 1.8%) in SMC/EC-Ps compared to SMC/0s was coupled with significantly lower topoisomerase IIalpha levels. Interestingly, pressure (SMC/0-P) and EC coculture (SMC/EC) each separately raised myocyte apoptotic activity to 15 +/- 1.3% and 17 +/- 2.0%, respectively. Conditioned media from pressurized ECs caused a 20% decrease in cell counts in target SMC compared to conditioned media from ECs in atmospheric pressure. Media from pressurized SMCs did not affect target SMCs.

CONCLUSIONS

In a model designed to study SMC/EC interactions in a dynamic environment, EC exposure to pressure alters the growth characteristics and apoptotic activity of SMCs via a secreted factor. Extracellular pressure may alter EC regulation of SMC behavior and regulate intimal hyperplasia.