Role of p120-catenin in the morphological changes of endothelial cells exposed to fluid shear stress

Analysis of differentially expressed circular RNAs in endothelial cells under impinging flow

BACKGROUND

Circular RNAs (circRNAs) are a special type of non-coding RNA. To elucidate the relationship between hemodynamics and the function of circRNAs in endothelial cells (ECs), a modified T chamber system was designed and produced for the present experiment. This T chamber system can be used to simulate the hemodynamic environment at the bifurcation of the arteries.

METHODS

Normal ECs cultured on glass slides were placed in the T chamber, the cell layer was impacted at a flow rate of 500 mL/min, and high-throughput microarrays were used to analyze the expression profiles of circRNAs in ECs. The differential expressions of circRNAs in the ECs treated with impinging flow were compared to those in ECs in conventional culture conditions. The characteristics of the differentially expressed circRNAs were analyzed with bioinformatics and quantitative reverse transcription polymerase chain reaction analyses were conducted to verify results.

RESULTS

Compared to normal samples, there were changes in the expressions of many circRNAs. A total of 974 circRNAs were differentially expressed, and of these, 378 were upregulated and 596 were downregulated (fold change [FC] ≥ 2 and P < 0.05), which suggests that these circRNAs were altered under hemodynamic conditions.

CONCLUSIONS

We present the differential expression profiles of circRNAs in ECs after the application of impinging flow; our results indicate that these differentially expressed circRNAs may be involved in inflammatory responses and damage in ECs. The present findings provide valuable information on cRNA profiles as well as clues for future studies that will investigate the roles that circRNAs play in ECs after inflammatory injury.

Role of Vascular Endothelial-Cadherin and p120-Catenin in the Formation of Experimental Intracranial Aneurysm in Animals

BACKGROUND

Dysfunction of endothelial cells (ECs) constitutes a critical factor in the formation of intracranial aneurysms (IAs). However, little is known about the response of ECs to hemodynamic insults and its contribution to IA formation.

METHODS

IAs models were constructed in both adult female New Zealand white rabbits and male Sprague-Dawley rats. Morphologic changes of vessel wall were detected by hematoxylin and eosin staining. Molecular and cellular changes, including p120-catenin (p120ctn) and vascular endothelial-cadherin, in the median sagittal section of the artery bifurcation were analyzed by fluorescent staining.

RESULTS

Destructive aneurysmal remodeling and the formation of morphologic IAs were observed at the basilar termini of experimental rabbits and the anterior cerebral artery-olfactory artery bifurcation of rats. The expression of p120ctn colocalized with vascular endothelial-cadherin in ECs decreased. Moreover, the expression of p120ctn colocalized with nucleus of ECs increased. These events suggested that p120ctn was transported from the membrane to the nucleus of ECs.

CONCLUSIONS

The potential mechanism, that IAs are always localizing in the bifurcation apices, may be that the endothelium injury of vessel wall can be induced by different hemodynamic conditions. Hemodynamic changes in artery bifurcation may initiate the formation of IAs.

Knockdown of P120 catenin aggravates endothelial injury under an impinging flow by inducing breakdown of adherens junctions

At present, the mechanisms underlying intracranial aneurysm (IA) development remain unclear; however, hemodynamics is considered a crucial factor in the induction of IA. To elucidate the association between hemodynamics and endothelial cell (EC) functions, a modified T chamber system was designed to simulate the adjustable hemodynamic conditions of an artery bifurcation. Normal human umbilical vein ECs (HUVECs) and HUVECs with P120 catenin (P120ctn) knockdown were cultured on coverslips and placed in the chamber. A flow rate of 250 or 500 ml/min impinged on the cell layer. Subsequently, the expression levels of P120ctn and other proteins, and EC morphological alterations, were examined. In normal HUVECs, after 3 h under a flow rate of 500 ml/min, the expression levels of P120ctn, vascular endothelial (VE)‑Cadherin, Kaiso and α‑catenin were decreased, whereas matrix metalloproteinase‑2 (MMP‑2) was increased. In HUVECs with P120ctn knockdown, the period during which ECs adhered to the coverslip was reduced to 1 h under a flow rate of 500 ml/min. In addition, the expression levels of VE‑Cadherin, Kaiso and α‑catenin in ECs were decreased, whereas those of MMP‑2 were increased after 1 h; more prominent alterations were detected under a 500 ml/min flow rate compared with a 250 ml/min flow rate. Adherens junctions (AJs) are critical to the maintenance of normal morphology and EC functioning in the vascular wall, and P120ctn is an important regulator of AJs. Loss of P120ctn may be induced by hemodynamic alterations. In response to changes in hemodynamic conditions, a loss of P120ctn may aggravate AJs between ECs, thus inducing inflammation in the vascular wall. Clinically, hemodynamic alterations may result in a loss of P120ctn and endothelial injury; therefore, P120ctn may have a critical role in inducing intracranial aneurysms.

Examination of the role of transient receptor potential vanilloid type 4 in endothelial responses to shear forces

Shear stress is the major mechanical force applied on vascular endothelial cells by blood flow, and is a crucial factor in normal vascular physiology and in the development of some vascular pathologies. The exact mechanisms of cellular mechano-transduction in mammalian cells and tissues have not yet been elucidated, but it is known that mechanically sensitive receptors and ion channels play a crucial role. This paper describes the use of a novel and efficient microfluidic device to study mechanically-sensitive receptors and ion channels in vitro, which has three independent channels from which recordings can be made and has a small surface area such that fewer cells are required than for conventional flow chambers. The contoured channels of the device enabled examination of a range of shear stresses in one field of view, which is not possible with parallel plate flow chambers and other previously used devices, where one level of flow-induced shear stress is produced per fixed flow-rate. We exposed bovine aortic endothelial cells to different levels of shear stress, and measured the resulting change in intracellular calcium levels ([Ca(2+)]i) using the fluorescent calcium sensitive dye Fluo-4AM. Shear stress caused an elevation of [Ca(2+)]i that was proportional to the level of shear experienced. The response was temperature dependant such that at lower temperatures more shear stress was required to elicit a given level of calcium signal and the magnitude of influx was reduced. We demonstrated that shear stress-induced elevations in [Ca(2+)]i are largely due to calcium influx through the transient receptor potential vanilloid type 4 ion channel.

Adaptation of endothelial cells to physiologically-modeled, variable shear stress

Endothelial cell (EC) function is mediated by variable hemodynamic shear stress patterns at the vascular wall, where complex shear stress profiles directly correlate with blood flow conditions that vary temporally based on metabolic demand. The interactions of these more complex and variable shear fields with EC have not been represented in hemodynamic flow models. We hypothesized that EC exposed to pulsatile shear stress that changes in magnitude and duration, modeled directly from real-time physiological variations in heart rate, would elicit phenotypic changes as relevant to their critical roles in thrombosis, hemostasis, and inflammation. Here we designed a physiological flow (PF) model based on short-term temporal changes in blood flow observed in vivo and compared it to static culture and steady flow (SF) at a fixed pulse frequency of 1.3 Hz. Results show significant changes in gene regulation as a function of temporally variable flow, indicating a reduced wound phenotype more representative of quiescence. EC cultured under PF exhibited significantly higher endothelial nitric oxide synthase (eNOS) activity (PF: 176.0±11.9 nmol/10⁵ EC; SF: 115.0±12.5 nmol/10⁵ EC, p = 0.002) and lower TNF-a-induced HL-60 leukocyte adhesion (PF: 37±6 HL-60 cells/mm²; SF: 111±18 HL-60/mm², p = 0.003) than cells cultured under SF which is consistent with a more quiescent anti-inflammatory and anti-thrombotic phenotype. In vitro models have become increasingly adept at mimicking natural physiology and in doing so have clarified the importance of both chemical and physical cues that drive cell function. These data illustrate that the variability in metabolic demand and subsequent changes in perfusion resulting in constantly variable shear stress plays a key role in EC function that has not previously been described.

Cathepsin L stimulates autophagy and inhibits apoptosis of ox-LDL-induced endothelial cells: potential role in atherosclerosis

The activation of endothelial cells by oxidized low-density lipoprotein (ox-LDL) with subsequent increases in endothelial permeability occurs in the early stage of atherosclerosis. Cathepsin L (CATL) is one of the cysteine proteases and has been implicated in advanced atherosclerotic lesions and plaque instability. This study aimed to explore the role of CATL in ox-LDL-induced early atherosclerotic events and to delineate the underlying mechanism. Results showed that ox-LDL upregulated CATL protein levels and activation in human umbilical vein endothelial cells (ECs) in a concentration-dependent manner and stimulated EC autophagy and apoptosis and increased EC monolayer permeability. Concomitantly, VE-cadherin expression was decreased. When ECs were pretreated with a CATL inhibitor, ox-LDL-induced autophagy was inhibited while apoptosis was further increased. In addition, the VE-cadherin protein level was increased, and the EC monolayer permeability was reduced. Taken together, the present study showed that the upregulated expression and activation of CATL induced by ox-LDL, increased EC autophagy and antagonized EC apoptosis, which partly neutralized the effect of increased EC monolayer permeability mediated by the downregulation of VE-cadherin. Thus, the proatherogenic effect of CATL was partly neutralized by inducing autophagy and inhibiting apoptosis in early stages of atherosclerosis.