Relationships between phosphatidylcholine-specific phospholipase C and integrins in cell-substratum adhesion and apoptosis in vascular endothelial cells

Regulation of apoptosis and autophagy by sphingosylphosphorylcholine in vascular endothelial cells

Sphingosylphosphorylcholine (SPC), an important cardiovascular mediator derived from sphingomyelin that has atheroprotective effects via actions on vascular endothelial cells (VECs) at normal levels in vivo. However, the underlying mechanism is not well known. To clarify this question, we first investigated the effect of SPC on VEC apoptosis and autophagy induced by deprivation of serum and fibroblast growth factor 2 (FGF-2). SPC at 5-20 µM inhibited apoptosis and induced autophagy in vitro. To understand the underlying mechanism, we investigated the role of integrin β4 in SPC-induced autophagy in VECs. SPC significantly decreased the level of integrin β4, whereas overexpression of integrin β4 inhibited SPC-induced autophagy. Moreover, knockdown of integrin β4 promoted VEC autophagy. To understand the downstream factors of integrin β4 in this process, we observed the effects of SPC on phosphatidylcholine-specific phospholipase C (PC-PLC) activity and level of p53. PC-PLC activity and p53 level in cytoplasm was decreased during autophagy induced by SPC, and knockdown of integrin β4 inhibited the activity of PC-PLC and the cytoplasmic level of p53. SPC may promote autophagy via integrin β4. Moreover, PC-PLC and p53 may be the downstream factors of integrin β4 in autophagy of VECs deprived of serum and FGF-2.

Contrasting Effects of Phosphatidylinosital-and Phosphatidylcholine-Specific Phospholipase C on Apoptosis in Cultured Endothelial Cells

In the authors' previous studies, they found that phosphatidylcholine-specific phospholipase C (PC-PLC) and phosphatidylinositol-specific phospholipase C (PI-PLC) played contrary roles in the apoptosis of vascular endothelial cells (VECs), but the mechanism underlying the phenomenon remains unclear. To address this question, in this study, the authors investigated the changes of cell cycle distribution, the expression of P53, and the phosphorylation of Akt when PI-PLC was inhibited by its specific inhibitor compound 48/80, and they also examined the phosphorylation of Akt when VEC apoptosis was inhibited by D609, a specific inhibitor of PC-PLC. The results showed that suppression of PI-PLC promoted VEC apoptosis by inhibiting Akt phosphorylation, elevating P53 expression, and affecting the cell cycle distribution. Contrarily, suppression of PC-PLC promoted the phosphorylation of Akt. The data suggested that PI-PLC and PC-PLC might control the apoptosis by jointly regulating Akt phosphorylation, P53 expression, and affecting cell cycle in VECs.

Promotion of autophagy and inhibition of apoptosis by low concentrations of cadmium in vascular endothelial cells

Recent reports, highlighting the relationships of cadmium exposure and vascular diseases, indicated that vascular endothelial cell was the target of cadmium (Cd) toxicity. However, the underlying mechanisms have not been fully elucidated. In this study, we evaluated the internalization of Cd2+ into human umbilical vein endothelial cells (HUVECs) by a novel Cd2+-selective sensor suitable for living cells. Then, we detected apoptosis in the treated cells. Our results showed that Cd2+ at low concentrations (< 10 micromol/l) inhibited apoptosis induced by deprivation of serum and basic fibroblast growth factor (bFGF). To investigate the corresponding molecular mechanisms, we employed acridine orange staining and Western blotting of MAP1 LC3 to detect autophagy, and analyzed the levels of integrin beta4, caveolin-1 and activity of PC-PLC. Our results showed that low concentrations of Cd2+ promoted autophagy and depressed the levels of integrin beta4, caveolin-1 and PC-PLC activity. The data suggested that autophagy played a key role in Cd2+ induced endothelial dysfunction; integrin beta4, caveolin-1 and PC-PLC might be the targets of Cd2+ in vascular endothelial cells.

Phosphatidylcholine-specific phospholipase C, p53 and ROS in the association of apoptosis and senescence in vascular endothelial cells

Previously, we found that phosphatidylcholine-specific phospholipase C (PC-PLC) participated in apoptosis signaling of vascular endothelial cells (VECs). Here, to explore whether PC-PLC is involved in the association of apoptosis and senescence in VECs, we analyzed p53 expression and intracellular reactive oxygen species (ROS) levels in young and senescent VECs before and after inhibiting PC-PLC activity. The results showed that suppressing PC-PLC inhibited apoptosis and the elevation of p53 expression induced by apoptosis in young cells, but not in senescent cells, and that inhibiting PC-PLC depressed intracellular ROS levels both in young and senescent cells. The data suggested that PC-PLC was involved in the association of apoptosis and senescence. Its function might be closely related to the level of p53 in VECs.

Suppressing Akt phosphorylation and activating Fas by safrole oxide inhibited angiogenesis and induced vascular endothelial cell apoptosis in the presence of fibroblast growth factor-2 and serum

At present, vascular endothelial cell (VEC) apoptosis induced by deprivation of fibroblast growth factor-2 (FGF-2) and serum has been well studied. But how to trigger VEC apoptosis in the presence of FGF-2 and serum is not well known. To address this question, in this study, the effects of safrole oxide on angiogenesis and VEC growth stimulated by FGF-2 were investigated. The results showed that safrole oxide inhibited angiogenesis and induced VEC apoptosis in the presence of FGF-2 and serum. To understand the possible mechanism of safrole oxide acting, we first examined the phosphorylation of Akt and the activity of nitric oxide synthase (NOS); secondly, we analyzed the expressions and distributions of Fas and P53; then we measured the activity of phosphatidylcholine specific phospholipase C (PC-PLC) in the VECs treated with and without safrole oxide. The results showed that this small molecule obviously suppressed Akt phosphorylation and the activity of NOS, and promoted the expressions of Fas and P53 markedly. Simultaneously, Fas protein clumped on cell membrane, instead of homogenously distributed. The activity of PC-PLC was not changed obviously. The data suggested that safrole oxide effectively inhibited angiogenesis and triggered VEC apoptosis in the presence of FGF-2 and serum, and it might perform its functions by suppressing Akt/NOS signal pathway, upregulating the expressions of Fas and P53 and modifying the distributing pattern of Fas in VEC. This finding provided a powerful chemical probe for promoting VEC apoptosis during angiogenesis stimulated by FGF-2.

Safrole oxide induced human umbilical vein vascular endothelial cell differentiation into neuron-like cells by depressing the reactive oxygen species level at the low concentration

Previously, we found that 5-25 microg/ml safrole oxide could inhibit apoptosis and dramatically make a morphological change in human umbilical vein vascular endothelial cells (HUVECs). But the possible mechanism by which safrole oxide function is unknown. To answer this question, in this study, we first investigated the effects of it on the activity of nitric oxide synthetase (NOS), the expressions of Fas and integrin beta4, which play important roles in HUVEC growth and apoptosis, respectively. The results showed that, at the low concentration (10 microg/ml), safrole oxide had no effects on NOS activity and the expressions of Fas and integrin beta4. Then, we investigated whether HUVECs underwent differentiation. We examined the expressions of neuron-specific enolase (NSE) and neurofilament-L (NF-L). Furthermore, we analyzed the changes of intracellular reactive oxygen species (ROS). After 10 h of treatment with 10 microg/ml safrole oxide, some HUVECs became neuron-like cells in morphology, and intensively displayed positive NSE and NF-L. Simultaneously, ROS levels dramatically decreased during HUVECs differentiation towards neuron-like cells. At the low concentration, safrole oxide induced HUVECs differentiation into neuron-like cells. Furthermore, our data suggested that safrole oxide might perform this function by depressing intracellular ROS levels instead of by affecting cell growth or apoptosis signal pathways.

The beta4 integrin subunit rescues A431 cells from apoptosis through a PI3K/Akt kinase signaling pathway

To study whether alpha6beta4 integrin regulates apoptosis, human A431 cells were plated on bacteria plates in the presence or absence of mAb beta4. In the absence of mAb beta4, A431 cells demonstrated morphological characteristics of apoptosis by 24 h and most cells died by 48 h. In contrast, in the presence of mAb beta4, cells remained viable, and at the end of 48 h, 70-80% of cells survived. Treatment of A431 cells with mAb beta4 resulted in tyrosine phosphorylation of the p85 subunit of PI3 kinase; PI3 kinase activity increased within 15 min and peaked at 60 min. Stimulation of beta4 in A431 cells resulted in a time-dependent phosphorylation of Akt with a concomitant and parallel phosphorylation of Bad. Inactivation of PI3 kinase with inhibitors blocked the anti-apoptotic effect induced by mAb beta4. These are the first results to suggest that ligation of alpha6beta4 integrin protects cells from apoptosis through a PI3K/Akt kinase signaling pathway.

Role of endothelial cell survival and death signals in angiogenesis

Angiogenesis, the process of new microvessel development, is encountered in a select number of physiological processes and is central to the pathogenesis of a wide variety of diseases. There is now convincing evidence that regulated patterns of endothelial cell survival and death, a process known as apoptosis, play a central role in the periodic remodeling of the vasculature, and in the timely evolution and regression of angiogenic responses. In this review we discuss the current evidence suggesting a role for inducers and inhibitors of angiogenesis as well as other mediators that modify endothelial cells functions in the survival and death of endothelial cells. We also discuss how dysregulation of apoptosis can lead to aberrant angiogenesis as demonstrated in the pathogenesis of retinopathy of prematurity and cancer.