Inhibition of Orai1-mediated Ca2+ entry limits endothelial cell inflammation by suppressing calcineurin-NFATc4 signaling pathway.

Orai1-dependent Ca2+ entry plays an essential role in inflammatory response through regulating T cell and macrophage activation and neutrophil infiltration. However, whether Orai1 Ca2+ entry contributes to endothelial activation, one of the early steps of vascular inflammation, remains elusive. In the present study, we observed that knockdown of Orai1 reduced, whereas overexpression of Orai1 potentiated, TNFα-induced expression of adhesion molecules such as ICAM-1 and VCAM-1 in HUVECs, and subsequently blocked adhesion of monocyte to HUVECs. In vivo, Orai1 downregulation attenuated TNFα-induced ICAM-1 and VCAM-1 expression in mouse aorta and the levels of pro-inflammatory cytokines in the serum. In addition, Orai1 knockdown also dramatically decreased the expression of pro-inflammatory cytokines and neutrophil infiltration in the lung after TNFα treatment, and thus protected lung tissue injury. Notably, among all isoforms of nuclear factor of activated T cells (NFATs), TNFα only triggered NFATc4 nuclear accumulation in HUVECs. Knockdown of Orai1 or inhibition of calcineurin prevented TNFα-induced NFATc4 nuclear translocation and reduced ICAM-1 and VCAM-1 expression in HUVECs. Overexpression of NFATc4 further enhanced ICAM-1 and VCAM-1 expression induced by TNFα. Our study demonstrates that Orai1-Ca2+-calcineurin-NFATc4 signaling is an essential inflammatory pathway required for TNFα-induced endothelial cell activation and vascular inflammation. Therefore, Orai1 may be a potential therapeutic target for treatment of inflammatory diseases.

Inhibition of Orai1-mediated Ca2+ entry enhances chemosensitivity of HepG2 hepatocarcinoma cells to 5-fluorouracil.

Increasing evidence supports that activation of store-operated Ca2+ entry (SOCE) is implicated in the chemoresistance of cancer cells subjected to chemotherapy. However, the molecular mechanisms underlying chemoresistance are not well understood. In this study, we aim to investigate whether 5-FU induces hepatocarcinoma cell death through regulating Ca2+ -dependent autophagy. [Ca2+ ]i was measured using fura2/AM dye. Protein expression was determined by Western blotting and immunohistochemistry. We found that 5-fluorouracil (5-FU) induced autophagic cell death in HepG2 hepatocarcinoma cells by inhibiting PI3K/AKT/mTOR pathway. Orai1 expression was obviously elevated in hepatocarcinoma tissues. 5-FU treatment decreased SOCE and Orai1 expressions, but had no effects on Stim1 and TRPC1 expressions. Knockdown of Orai1 or pharmacological inhibition of SOCE enhanced 5-FU-induced inhibition of PI3K/AKT/mTOR pathway and potentiated 5-FU-activated autophagic cell death. On the contrary, ectopic overexpression of Orai1 antagonizes 5-FU-induced autophagy and cell death. Our findings provide convincing evidence to show that Orai1 expression is increased in hepatocarcinoma tissues. 5-FU can induce autophagic cell death in HepG2 hepatocarcinoma cells through inhibition of SOCE via decreasing Orai1 expression. These findings suggest that Orai1 expression is a predictor of 5-FU sensitivity for hepatocarcinoma treatment and blockade of Orai1-mediated Ca2+ entry may be a promising strategy to sensitize hepatocarcinoma cells to 5-FU treatment.

Inhibition of Orai1 Store-Operated Calcium Channel Prevents Foam Cell Formation and Atherosclerosis.

OBJECTIVE: To determine the role of orai1 store-operated Ca(2+) entry in foam cell formation and atherogenesis. APPROACH AND RESULTS: Acute administration of oxidized low-density lipoprotein (oxLDL) activates an orai1-dependent Ca(2+) entry in macrophages. Chelation of intracellular Ca(2+), inhibition of orai1 store-operated Ca(2+) entry, or knockdown of orai1 dramatically inhibited oxLDL-induced upregulation of scavenger receptor A, uptake of modified LDL, and foam cell formation. Orai1-dependent Ca(2+) entry induces scavenger receptor A expression and foam cell formation through activation of calcineurin but not calmodulin kinase II. Activation of nuclear factor of activated T cells is not involved in calcineurin signaling to foam cell formation. However, oxLDL dephosohorylates and activates apoptosis signal-regulating kinase 1 in macrophages. Orai1 knockdown prevents oxLDL-induced apoptosis signal-regulating kinase 1 activation. Knockdown of apoptosis signal-regulating kinase 1, or inhibition of its downstream effectors, JNK and p38 mitogen-activated protein kinase, reduces scavenger receptor A expression and foam cell formation. Notably, orai1 expression is increased in atherosclerotic plaques of apolipoprotein E(-/-) mice fed with high-cholesterol diet. Knockdown of orai1 with adenovirus harboring orai1 siRNA or inhibition of orai1 Ca(2+) entry with SKF96365 for 4 weeks dramatically inhibits atherosclerotic plaque development in high-cholesterol diet feeding apolipoprotein E(-/-) mice. In addition, inhibition of orai1 Ca(2+) entry prevents macrophage apoptosis in atherosclerotic plaque. Moreover, the expression of inflammatory genes in atherosclerotic lesions and the infiltration of myeloid cells into the aortic sinus plaques are decreased after blocking orai1 signaling. CONCLUSIONS: Orai1-dependent Ca(2+) entry promotes atherogenesis possibly by promoting foam cell formation and vascular inflammation, rendering orai1 Ca(2+) channel a potential therapeutic target against atherosclerosis.

Reduction of Intracellular Chloride Concentration Promotes Foam Cell Formation.

BACKGROUND: Previous work has demonstrated that the volume-regulated chloride channel is activated during foam cell formation, and inhibition of chloride movement prevents intracellular lipid accumulation. However, the mechanism explaining how chloride movement promotes foam cell formation is not clear. METHODS AND RESULTS: Foam cell formation was determined by Oil Red O staining. Western blotting and co-immunoprecipitation were used to examine protein expression and protein-protein interaction. [Cl(-)]iwas measured using 6-methoxy-N-ethylquinolinium iodide dye. The results showed that [Cl(-)]iwas decreased in monocytes/macrophages from patients with hypercholesterolemia and from apoE(-/-)mice fed with a high-fat diet. Lowering [Cl(-)]iupregulated scavenger receptor A (SR-A) expression, increased the binding and uptake of oxLDL, enhanced pro-inflammatory cytokine production and subsequently accelerated foam cell formation in macrophages from humans and mice. In addition, low Cl(-)solution stimulated the activation of JNK and p38 mitogen-activated protein kinases. Inhibition of JNK and p38 blocked Cl(-)reduced medium-induced SR-A expression and lipid accumulation. In contrast, reduction of [Cl(-)]ipromoted the interaction of SR-A with caveolin-1, thus facilitating caveolin-1-dependent SR-A endocytosis. Moreover, disruption of caveolae attenuated SR-A internalization, JNK and p38 activation, and ultimately prevented SR-A expression and foam cell formation stimulated by low Cl(-)medium. CONCLUSIONS: This data provide strong evidence that reduction of [Cl(-)]iis a critical contributor to intracellular lipid accumulation, suggesting that modulation of [Cl(-)]iis a novel avenue to prevent foam cell formation and atherosclerosis.

Methylophiopogonanone A, an Ophiopogon homoisoflavonoid, alleviates high-fat diet-induced hyperlipidemia: assessment of its potential mechanism.

Methylophiopogonanone A (MO-A), a homoisoflavonoid extracted from Ophiopogon japonicus, has been shown to attenuate myocardial apoptosis and improve cerebral ischemia/reperfusion injury. However, the hypolipidemic effects remain unknown. This study was performed to investigate a potential hypolipidemic effect of MO-A in hyperlipidemia rats, as well as its underlying mechanism of action. A rat model of hyperlipidemia was induced by a high-fat diet (HFD). Animals were randomly divided into three groups (n=8/group): normal control group (NC), HFD group, and HFD+MO-A (10 mg·kg-1·d-1) treatment group. The effects of MO-A on serum lipids, body weight, activity of lipoprotein metabolism enzyme, and gene expression of lipid metabolism were evaluated in HFD-induced rats. In HFD-induced rats, pretreatment with MO-A decreased the body weight gain and reduced serum and hepatic lipid levels. In addition, pretreatment with MO-A improved the activities of lipoprotein lipase and hepatic lipase in serum and liver, down-regulated mRNA expression of acetyl CoA carboxylase and sterol regulatory element-binding protein 1c, and up-regulated mRNA expression of low-density lipoprotein receptor and peroxisome proliferator-activated receptor α in the liver. Our results indicated that MO-A showed strong ability to ameliorate the hyperlipidemia in HFD-induced rats. MO-A might be a potential candidate for prevention of overweight and dyslipidemia induced by HFD.

Methylophiopogonanone A, an Ophiopogon homoisoflavonoid, alleviates high-fat diet-induced hyperlipidemia: assessment of its potential mechanism

Methylophiopogonanone A (MO-A), a homoisoflavonoid extracted from Ophiopogon japonicus, has been shown to attenuate myocardial apoptosis and improve cerebral ischemia/reperfusion injury. However, the hypolipidemic effects remain unknown. This study was performed to investigate a potential hypolipidemic effect of MO-A in hyperlipidemia rats, as well as its underlying mechanism of action. A rat model of hyperlipidemia was induced by a high-fat diet (HFD). Animals were randomly divided into three groups (n=8/group): normal control group (NC), HFD group, and HFD+MO-A (10 mg·kg-1·d-1) treatment group. The effects of MO-A on serum lipids, body weight, activity of lipoprotein metabolism enzyme, and gene expression of lipid metabolism were evaluated in HFD-induced rats. In HFD-induced rats, pretreatment with MO-A decreased the body weight gain and reduced serum and hepatic lipid levels. In addition, pretreatment with MO-A improved the activities of lipoprotein lipase and hepatic lipase in serum and liver, down-regulated mRNA expression of acetyl CoA carboxylase and sterol regulatory element-binding protein 1c, and up-regulated mRNA expression of low-density lipoprotein receptor and peroxisome proliferator-activated receptor α in the liver. Our results indicated that MO-A showed strong ability to ameliorate the hyperlipidemia in HFD-induced rats. MO-A might be a potential candidate for prevention of overweight and dyslipidemia induced by HFD.