Emodin Blocks mPTP Opening and Improves LPS-Induced HMEC-1 Cell Injury by Upregulation of ATP5A1

BACKGROUND

Emodin has been shown to exert anti-inflammatory and cytoprotective effects. Our study aimed to identify a novel anti-inflammatory mechanism of emodin.

METHODS

An LPS-induced model of microvascular endothelial cell (HMEC-1) injury was constructed. Cell proliferation was examined using a CCK-8 assay. The effects of emodin on reactive oxygen species (ROS), cell migration, the mitochondrial membrane potential (MMP), and the opening of the mitochondrial permeability transition pore (mPTP) were evaluated. Actin-Tracker Green was used to examine the relationship between cell microfilament reconstruction and ATP5A1 expression. The effects of emodin on the expression of ATP5A1, NALP3, and TNF-α were determined. After treatment with emodin, ATP5A1 and inflammatory factors (TNF-α, IL-1, IL-6, IL-13 and IL-18) were examined by Western blotting.

RESULTS

Emodin significantly increased HMEC-1 cell proliferation and migration, inhibited the production of ROS, increased the mitochondrial membrane potential, and blocked the opening of the mPTP. Moreover, emodin could increase ATP5A1 expression, ameliorate cell microfilament remodeling, and decrease the expression of inflammatory factors. In addition, when ATP5A1 was overexpressed, the regulatory effect of emodin on inflammatory factors was not significant.

CONCLUSION

Our findings suggest that emodin can protect HMEC-1 cells against inflammatory injury. This process is modulated by the expression of ATP5A1.

Pregnancy-specific enhancement of agonist-stimulated ERK-1/2 signaling in uterine artery endothelial cells increases Ca(2+) sensitivity of endothelial nitric oxide synthase as well as cytosolic phospholipase A(2)

Uterine artery endothelial cells (UAEC) from pregnant ewes (P-UAEC) demonstrate generally enhanced ability to couple growth factor and G protein-coupled receptors to the ERK-1/2 signaling pathway and stimulate NO production independently of elevated [Ca(2+)]. Herein we investigate the signaling and vasodilator responses to ATP, an agonist that also elevates [Ca(2+)](i) in both NP and P-UAEC, to determine the relative importance of Ca(2+) vs. ERK-1/2 in the activation of eNOS. We observed in both NP-UAEC and P-UAEC that ATP acts through G protein-coupled P(2Y) receptors to activate phospholipase C and dose-dependently elevate [Ca(2+)](i) independently of extracellular Ca(2+). The small reduction in the [Ca(2+)](i) response in NP vs. P-UAEC did not, however, account for the difference in NO production by P-UAEC>>NP-UAEC. ATP had no stimulatory effect on Akt phosphorylation but rapidly stimulated ERK-1/2 phosphorylation in P-UAEC>>NP-UAEC in a manner that correlated with NO production. In both NP- and P-UAEC, both ERK-1/2 and Ca(2+) were absolutely required for eNOS as well as cPLA(2) activation and the Ca(2+) sensitivity of eNOS was enhanced through the cytosolic [Ca(2+)](i) range in P-UAEC>>NP-UAEC. Thus ERK-1/2 may regulate the Ca(2+) sensitivity of eNOS to an even greater extent than is known to occur for cPLA(2).

Pregnancy-dependent changes in cell signaling underlie changes in differential control of vasodilator production in uterine artery endothelial cells

During pregnancy, the uterine vasculature shows a marked increase in vasodilator production [prostacyclin (PGI2) and nitric oxide (NO)] in response to a number of agonists including angiotensin II (AII) and ATP. As a consequence vascular resistance is kept low, and uterine blood flow is maximized to meet the needs of the growing fetus. Studies of the molecular basis underlying this change in control of endothelial NO and PGI2 production have been hampered by the lack of availability of a suitable cell model. To that end we have developed and characterized a new ovine uterine artery endothelial cell (UAEC) culture model derived from nonpregnant (NP) or pregnant (P) ewes. Endothelial cells were isolated from pregnant (120-130 days; n = 6) and nonpregnant (n = 4) ewes and maintained in primary culture. Endothelial cells at passage 4 showed uniform expression of endothelial nitric oxide synthase (eNOS; an endothelial marker) as well as AII type 1 receptor and growth factor receptors and uniform uptake of acetylated low density lipoprotein (a property of endothelial cells not shared by fibroblasts or vascular smooth muscle cells), thus demonstrating cell purity. Expressions of eNOS, cyclooxygenase-1, PGI2 synthase, cytosolic phospholipase A2, AII type 1 receptor, and growth factor receptors are also maintained at passage 4. Mitogenesis is maintained in response to basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), and vascular endothelial growth factor (VEGF) in both NP-UAEC and P-UAEC. The differential production of vasodilators by NP-UAEC and P-UAEC is maintained in a manner similar to that previously reported in vivo. Thus, P-UAEC make NO in response to AII, ATP, bFGF, EGF, and VEGF, whereas NP-UAEC make NO in response to bFGF, EGF, and VEGF only. Similarly, P-UAEC make PGI2 in response to AII, ATP, bFGF, and VEGF, whereas NP-UAEC make PGI2 only in response to ATP and VEGF. As both cytosolic phospholipase A2 and eNOS may be regulated by both Ca2+ and protein kinases, we investigated the effects of these agonists on Ca2+ mobilization and ERK-1/2 phosphorylation. ATP consistently elevates Ca2+ levels in both P-UAEC and NP-UAEC. All other agonists were without acute (0-4 min) effect on Ca2+ in P-UAEC or NP-UAEC. In contrast, all agonists stimulated an acute (10 min) phosphorylation of ERK-1/2 in P-UAEC, whereas only EGF stimulated activation in NP-UAEC. P-UAEC production of PGI2 by agonists of both heptahelical receptors and growth factor receptors correlates closely with ERK-2 phosphorylation alone. For NO, this correlation holds for heptahelical receptor agonists, but additional signaling pathways are also implicated for bFGF and VEGF. In contrast, in NP-UAEC the lack of ERK-2 phosphorylation in response to all agonists other than EGF, and the dissociation between NO or PGI2 production and ERK-2 phosphorylation suggest that alternate pathways play a predominant role.

Pregnancy induces expression of cPLA2 in ovine uterine artery but not systemic artery endothelium

OBJECTIVE

To determine whether pregnancy increases cytosolic phospholipase A2 (cPLA2) expression in uterine artery (UA) endothelial cells and vascular smooth-muscle (VSM) cells, and whether ovarian steroids mediate this effect.

METHODS

Uterine arteries and omental arteries (systemic control) were isolated from pregnant (120-130 days' gestation) ewes and from nonpregnant ewes synchronized to the corresponding phases of the ovarian cycle (follicular or luteal) or ovariectomized. In addition, ovariectomized ewes were treated with vehicle, estradiol-17 beta (E2 beta), progesterone (P4), or combined E2 beta/P4 for 10 days, and UAs were collected. Arteries from all studies were separated into mechanically isolated endothelial and VSM fractions. Proteins were then solubilized and separated on 7.5% sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by Western immunoblotting using an affinity-purified mouse monoclonal antibody for cPLA2.

RESULTS

Both UA endothelium and VSM fractions were seen to express cPLA2, detected as a single band with a molecular mass similar to that observed in myometrium (about 100 kD). Distribution of cPLA2, when expressed per microgram of protein, was observed as 40% in UA endothelium compared with 60% in VSM fractions. Uterine artery endothelial cPLA2 expression was specifically increased 1.9-fold in pregnancy (P < .05), whereas there was no significant change from VSM. Furthermore, in ovariectomized sheep versus intact luteal or follicular phase animals, there was no significant change in cPLA2 expression in endothelium or VSM. Administration of E2 beta, P4, or their combination in ovariectomized sheep also failed to reproduce the pregnancy-induced increase in cPLA2 expression in UA endothelium. Omental artery endothelial and VSM cPLA2 expression was observed at similar magnitudes as UA expression, but levels were consistently unchanged by pregnancy, the ovarian cycle, or ovariectomy.

CONCLUSIONS

cPLA2 was expressed throughout the endothelium and VSM of both uterine and omental arteries, but only in UA endothelium was pregnancy associated with elevated cPLA2 expression. The lack of change in cPLA2 expression with the ovarian cycle or in ovariectomized animals, even after prolonged treatment with E2 beta, P4, or E2 beta/P4 combined suggests this pregnancy-induced increase in cPLA2 may not be estrogen and/or progesterone dependent.