Serotonin induces vasoconstriction of smooth muscle cell-rich neointima through 5-hydroxytryptamine2A receptor in rabbit femoral arteries

Summary.  Background:  Smooth muscle cell (SMC)-rich intima is a morphological feature of atherosclerotic lesions that is observed in eroded plaque and spastic arteries. Arteries with SMC-rich intima are susceptible to vasoconstriction or vasospasm against some vasoactive agents. Objective:  The present study evaluates the contribution of SMC-rich intima to thrombogenic vasoconstriction. Methods:  We established SMC-rich neointima by damaging rabbit femoral arteries using balloons and then measured the isometric tension of the femoral strips against 5-hydroxytryptamine (5-HT), adenosine diphosphate, adenosine triphosphate and thrombin. Results:  Among these agents, only 5-HT induced a hypercontractile response of the injured arteries with SMC-rich neointima, compared with non-injured arteries. Smooth muscle cells of both the neointima and media expressed 5-HT_2A receptor, and sarpogrelate, a selective 5-HT_2A receptor antagonist significantly inhibited the hypercontraction. Furthermore, 5-HT induced contraction of separated neointima and hypercontraction of separated media compared with non-injured media. Sarpogrelate and fasudil, a specific Rho-kinase inhibitor, significantly suppressed such contraction of both the neointima and media of injured arteries. Conclusions:  These results suggest that 5-HT plays a crucial role in thrombogenic vasoconstriction, and that SMC-rich intima as well as media directly contributes to the hypercontractile response of atherosclerotic vessels through the 5-HT_2A receptor and the Rho-kinase pathway.     

Human plasminogen kringle 1–5 reduces atherosclerosis and neointima formation in mice by suppressing the inflammatory signaling pathway

Summary. Background: Activation of vascular endothelial cells plays an important role in atherogenesis and plaque instability. Recent research has demonstrated that late‐stage inhibition of plaque angiogenesis by angiostatin (kringle 1–4) reduces macrophage accumulation and slows the progression of advanced atherosclerosis. Kringle 1–5 (K_1–5) is a variant of angiostatin that contains the first five kringle domains of plasminogen. Objective: To investigate whether K_1–5 has an inhibitory effect on early‐stage atherosclerosis, using the apolipoprotein E (ApoE)‐deficient mouse model and a carotid artery ligation model. Methods: ApoE‐deficient mice received K_1–5 treatment for 4 weeks, and the severity of aortic atherosclerosis was measured. In the ligation model, the left common carotid arteries of C57BL/6 mice were ligated near the carotid bifurcation, and the mice received K_1–5 for 4 weeks. Human umbilical vein endothelial cells were pretreated with K_1–5 before tumor necrosis factor‐α (TNF‐α) treatment to explore the anti‐inflammatory effect of K_1–5. Results: The areas of the lesion in the aortas of ApoE‐deficient mice that received K_1–5 treatment were notably decreased, and the formation of carotid neointima in the C57BL/6 mice was decreased by treatment with K_1–5. Expression of TNF‐α‐induced intercellular adhesion molecule‐1 and vascular cell adhesion molecule‐1 was inhibited by K_1–5 treatment, possibly via downregulation of translocation of nuclear factor‐κB and expression of reactive oxygen species. Conclusions: K_1–5 reduced atherosclerosis and neointima formation in mice, possibly through inhibition of intercellular adhesion molecule‐1 and vascular cell adhesion molecule‐1 expression in endothelial cells.     

溶血磷脂酸在卵巢癌细胞内HER2/neu的激活作用

目的探索溶血磷脂酸(LPA)在卵巢癌细胞内HER2/neu的激活作用。方法通过免疫沉淀反应和蛋白印迹法检测卵巢癌细胞中HER2的变化。结果 LPA能诱导卵巢癌细胞中HER2的快速和瞬态的磷酸化。结论 LPA在卵巢癌细胞中作为HER2的上游分子,对卵巢癌细胞有强有力的刺激,可诱导卵巢癌细胞中HER2磷酸化。     

过氧化物酶体增殖因子激活受体γ介导5-烯丙基-7-二氟亚甲基白杨素诱导人卵巢癌CoC1细胞凋亡的研究

目的 探讨5-烯丙基-7-二氟亚甲基白杨素(ADFMChR)诱导人卵巢癌CoC1细胞凋亡作用的分子机制.方法 采用MTT法测定ADFMChR对卵巢癌CoC1细胞系细胞增殖抑制作用;DNA琼脂糖凝胶电泳证实ADFMChR诱导CoC1细胞凋亡作用;Western印迹检测ADFMChR对CoC1细胞过氧化物酶体增殖物激活受体(PPARγ)、Bcl-2及Bax蛋白表达的影响.结果 MTT法显示ADFMChR呈剂量依赖性抑制CoC1细胞增殖作用,IC50值为7.76 μmol/L;ADFMChR(30.0 μmol/L)处理CoC1细胞48 h的DNA琼脂糖凝胶电泳呈现典型"梯形"条带,加用PPARγ阻断剂(GW9662)后条带消失;Western印迹分析ADFMChR作用CoC1细胞后PPARγ和Bax蛋白表达上调,而Bcl-2蛋白表达下调(P<0.05或P<0.01);GW9662具有阻断ADFMChR对Bcl-2的下调和Bax上调作用.结论 ADFMChR通过活化PPARγ,进而减少Bcl-2/Bax比例,诱导CoC1细胞凋亡.     

Disturbed blood flow induces erosive injury to smooth muscle cell‐rich neointima and promotes thrombus formation in rabbit femoral arteries

Summary. Background: Plaque erosion is a cause of atherothrombosis that preferentially occurs on smooth muscle cell (SMC)‐ and proteoglycan‐rich rather than lipid‐rich plaques. However, its underlying mechanisms remain unknown. Objective: To determine whether disturbed blood flow induces erosive injury and thrombus formation on SMC‐rich neointima. Methods: Three weeks after balloon injury, SMC‐rich neointima with increased tissue factor (TF) activity developed in rabbit femoral arteries that were narrowed with a vascular occluder to disturb blood flow after stenosis. Neointimal injury and thrombus formation were assessed at 15, 30, and 180 min after the vascular narrowing. Results: Endothelial detachment, platelet adhesion and neointimal cell apoptosis became evident at the post‐stenotic regions of all femoral arteries (n = 5) within 15 min of narrowing. Mural thrombi composed of platelet and fibrin developed after 30 min, and then occlusive thrombi were generated in three out of five vessels after 180 min. The identical vascular narrowing of normal femoral arteries also induced endothelial detachment with small platelet thrombi at post‐stenotic regions, but fibrin and occlusive thrombi did not develop. Computational simulation analysis indicated that oscillatory shear stress contributes to the development of erosive damage to the neointima. Conclusions: These results suggest that disturbed post‐stenotic blood flow can induce erosive injury in SMC‐rich plaques and promote thrombus formation that results in vascular events.     

藤黄酸通过MAPK通路诱导Jurkat细胞凋亡的机理

本研究探讨藤黄酸对Jurkat细胞的抑制作用及可能机理。以不同浓度藤黄酸与抑制剂处理Jurkat细胞,AnnexinⅤ/PI双染法检测细胞的凋亡;流式细胞仪检测荧光素激活的caspase 3、caspase 8、caspase 9阳性细胞水平;免疫印迹检测pro-caspase 3、pro-caspase 9、磷酸化JNK及P38蛋白水平。结果表明,藤黄酸呈浓度依赖性诱导Jurkat细胞凋亡;藤黄酸作用Jurkat细胞后caspase 3、caspase 8、caspase 9阳性细胞水平升高,caspase 3、caspase 9活化蛋白及磷酸化JNK及P38蛋白水平升高;ROS、CaMKⅡ、caspase 3、caspase 9、MAPKK、JNK1/2及P38抑制剂减弱藤黄酸诱导Jurkat细胞凋亡的作用;ROS、CaMKⅡ、MAPKK、JNK1/2及P38抑制剂降低藤黄酸作用Jurkat细胞后caspase 3、caspase 9活化蛋白水平;ROS、CaMKⅡ、MAPKK、JNK1/2抑制剂降低藤黄酸作用Jurkat细胞后磷酸化JNK蛋白水平;ROS、CaMKⅡ、MAPKK、P38抑制剂减弱藤黄酸作用Jurkat细胞后磷酸化P38蛋白水平。结论:藤黄酸通过激活caspase途径诱导Jurkat细胞凋亡,该过程可能与ROS-CaMKⅡ-MAPKK-JNK/P38通路有关。     

Globular adiponectin induces platelet activation through the collagen receptor GPVI-Fc receptor γ chain complex

Summary.  Background:  The adipocyte-derived cytokine, adiponectin (Ad), exerts potent vascular effects, although the direct effects of Ad on blood platelets are unclear. Objective:  The influence of globular Ad (gAd) on blood platelet function was investigated. Research design and methods:  We measured platelet aggregation and tyrosine phosphorylation signaling events in human and mouse platelets. The ability of gAd to activate Glycoprotein VI (GPVI) activity was determined with a NFAT luciferase reporter assay. Results:  gAd, but not full length Ad, induced rapid aggregation and granule secretion of human and mouse platelets through a pathway that is ablated under conditions of Src kinase inhibition, indicating a tyrosine kinase-dependent mechanism. Consistent with this, gAd stimulates rapid tyrosine phosphorylation of several proteins in human and mouse platelets. The pattern of increase in tyrosine phosphorylation was similar to that induced by collagen, with the tyrosine kinase Syk and PLCγ2 being identified among the list of tyrosine phosphorylated proteins. As collagen activates platelet through the GPVI-Fc receptor γ-chain (FcRγ) complex, we used FcRγ null platelets (which also lack GPVI) to explore the mechanism by which gAd stimulates platelets. Stimulation of tyrosine phosphorylation and platelet aggregation by gAd was abolished in FcRγ null platelets and markedly reduced in the absence of PLCγ2. Further, GPVI was confirmed as a collagen receptor for gAd by increased luciferase activity in Jurkat T-cells transfected with GPVI. Conclusions:  We identify gAd as a novel ligand for GPVI that stimulates tyrosine kinase-dependent platelet aggregation. Our data raise the possibility that gAd may promote unwanted platelet activation at sites of vascular injury.     

吲哚美辛诱导K562细胞凋亡过程中半胱天冬酶及细胞内游离钙浓度的变化

目的了解在吲哚美辛诱导的K562细胞凋亡过程中半胱天冬酶3,8的表达、活化情况及亚细胞定位;细胞内游离钙离子浓度(［fCa2+］i)变化及其机制;并探讨其凋亡调控是否依赖于环氧化酶(COX)的活性抑制。方法用共聚焦激光扫描显微镜(LSCM)观察在吲哚美辛诱导凋亡过程中K562细胞内半胱天冬酶3,8的变化及亚细胞定位,并用Westernblot分析其蛋白质的表达、活化情况;用钙荧光探针结合LSCM检测K562细胞［fCa2+］i变化,并行钙螯合剂乙二醇双四乙酸(EGTA)阻断试验探讨细胞内［fCa2+］i变化的可能机制;对K562细胞加用COX抑制剂并观察细胞活力变化(MTT试验)。结果①半胱天冬酶3,8分子呈散点状分布于胞浆及胞核,在吲哚美辛诱导凋亡过程中其表达水平随吲哚美辛浓度增加而上调,Westernblot分析证实其表达上调并被裂解激活。②K562细胞内［fCa2+］i随吲哚美辛浓度增高而增高;在Ca2+螯合剂EGTA阻断胞外Ca2+内流的情况下,吲哚美辛仍能诱导细胞内［fCa2+］i增高及细胞凋亡,但增高的幅度较无EGTA干预明显为低。③低浓度吲哚美辛对K562细胞活力无明显影响,高浓度则明显抑制细胞活力。结论①半胱天冬酶3,8的表达上调和裂解激活是吲哚美辛诱导K562细胞凋亡的重要机制;活化的半胱天冬酶3,8呈弥漫性散点状分布于胞浆和胞核。②细胞内［fCa2+］i增高在吲哚美辛诱导K562细胞凋亡过程中可能起重要作用;胞外钙内流是细胞内［fCa2+］i增高的主要原因;胞内钙库释放可致［fCa2+］i浓度增高并能触发细胞凋亡。③吲哚美辛诱导的K562细胞凋亡不依赖于COX活性抑制。     

Chronic compression or acute dissociation of dorsal root ganglion induces cAMP-dependent neuronal hyperexcitability through activation of PAR2

Chronic compression (CCD) or dissociation of dorsal root ganglion (DRG) can induce cyclic adenosine monophosphate (cAMP)-dependent DRG neuronal hyperexcitability and behaviorally expressed hyperalgesia. Here, we report that protease-activated receptor 2 (PAR2) activation after CCD or dissociation mediates the increase of cAMP activity and protein kinase A (PKA) and cAMP-dependent hyperexcitability and hyperalgesia in rats. CCD and dissociation, as well as trypsin (a PAR2 activator) treatment, increased level of cAMP concentration, mRNA, and protein expression for PKA subunits PKA-RII and PKA-c and protein expression of PAR2, in addition to producing neuronal hyperexcitability and, in CCD rats, thermal hyperalgesia. The increased expression of PAR2 was colocalized with PKA-c subunit. A PAR2 antagonistic peptide applied before and/or during the treatment, prevented or largely diminished the increased activity of cAMP and PKA, neuronal hyperexcitability, and thermal hyperalgesia. However, posttreatment with the PAR2 antagonistic peptide failed to alter either hyperexcitability or hyperalgesia. In contrast, an adenylyl cyclase inhibitor, SQ22536, administrated after dissociation or CCD, successfully suppressed hyperexcitability and hyperalgesia, in vitro and/or in vivo. Trypsin-induced increase of the intracellular calcium [Ca(2+)](i) was prevented in CCD or dissociation DRG neurons. These alterations were further confirmed by knockdown of PAR2 with siRNA. In addition, trypsin and PAR2 agonistic peptide-induced increase of cAMP was prevented by inhibition of PKC, but not Gαs. These findings suggest that PAR2 activation is critical to induction of nerve injury-induced neuronal hyperexcitability and cAMP-PKA activation. Inhibiting PAR2 activation may be a potential target for preventing/suppressing development of neuropathic pain.     

Asiatic acid, a triterpene, induces apoptosis and cell cycle arrest through activation of extracellular signal-regulated kinase and p38 mitogen-activated protein kinase pathways in human breast cancer cells

This study first investigates the anticancer effect of asiatic acid in two human breast cancer cell lines, MCF-7 and MDA-MB-231. Asiatic acid exhibited effective cell growth inhibition by inducing cancer cells to undergo S-G2/M phase arrest and apoptosis. Blockade of cell cycle was associated with increased p21/WAF1 levels and reduced amounts of cyclinB1, cyclinA, Cdc2, and Cdc25C in a p53-independent manner. Asiatic acid also reduced Cdc2 function by increasing the association of p21/WAF1/Cdc2 complex and the level of inactivated phospho-Cdc2 and phospho-Cdc25C. Asiatic acid treatment triggered the mitochondrial apoptotic pathway indicated by changing Bax/Bcl-2 ratios, cytochrome c release, and caspase-9 activation, but it did not act on Fas/Fas ligand pathways and the activation of caspase-8. We also found that mitogen-activated protein kinases (MAPKs), extracellular signal-regulated kinase (ERK1/2), and p38, but not c-Jun NH2-terminal kinase (JNK), are critical mediators in asiatic acid-induced cell growth inhibition. U0126 [1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene] or SB203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imidazole], specific inhibitors of mitogen-activated protein kinase kinase and p38 kinase activities, significantly decreased or delayed apoptosis. Asiatic acid was likely to confine the breast cancer cells in the S-G2/M phase mainly through the p38 pathway, because both SB203580 and p38 small interfering RNA (siRNA) inhibition significantly attenuated the accumulation of inactive phospho-Cdc2 and phospho-Cdc25C proteins and the cell numbers of S-G2/M phase. Moreover, U0126 and ERK siRNA inhibition completely suppressed asiatic acid-induced Bcl-2 phosphorylation and Bax up-regulation, and caspase-9 activation. Together, these results imply a critical role for ERK1/2 and p38 but not JNK, p53, and Fas/Fas ligand in asiatic acid-induced S-G2/M arrest and apoptosis of human breast cancer cells.     

Ellagic acid induces a dose- and time-dependent depolarization of mitochondria and activation of caspase-9 and -3 in human neuroblastoma cells

The polyphenol ellagic acid is found in many natural food sources and has been proposed as a candidate compound for clinical applications due to its anti-oxidative capacity and as a potential anti-tumorigenic compound. The objective of the present study was to evaluate the sensitivity to and possible apoptosis mechanism induced by ellagic acid in neuronal tumor cells. As a model the human neuroblastoma SH-SY5Y cell line was used. The methods applied were bright field and phase contrast microscopy, XTT- and LDH-assays, western blot, and flow cytometric analysis of DNA degradation and mitochondrial membrane potential. Ellagic acid treatment was found to induce a reduction in cell number preceded by alterations of the mitochondrial membrane potential and activation of caspase-9 and -3, DNA-fragmentation and cell death by apoptosis. The apoptotic cell death studied was not due to anoikis since it was significant in the adherent fraction of the cells. We conclude that ellagic acid induces dose- and time-dependent apoptosis, at least partly by the mitochondrial pathway, in an embryonal neuronal tumor cell system. This finding is in agreement with previously reported data on adult carcinoma cells thus suggesting a more general effect of ellagic acid on tumor cells.     

[6]-Shogaol,a dietary phenolic compound,induces oxidative stress mediated mitochondrial dependant apoptosis through activation of proapoptotic factors in Hep-2 cells

Ginger (Zingiber officinale) is a well-known herb used in ethnomedicine. [6]-shogaol, a phenolic nature is a major constituent of ginger. In this study, we investigated the anticancer activity of [6]-shogaol in Laryngeal cancer (Hep-2) cells. We demonstrated the effects of [6]-shogaol on the cell growth and apoptosis in Hep-2 cells were analyzed by the generation of reactive oxygen species (ROS), the level of mitochondrial membrane potential (ΔYm), DNA damage and apoptotic morphological changes were analyzed by AO/EtBr, AO and Hoechst staining. Further, apoptotic protein expressions were analyzed by western blot analysis. Our results indicated that [6]-shogaol induces apoptosis as evidenced by loss of cell viability, enhanced ROS, lipid peroxidation results in altered mitochondrial membrane potential, increased DNA damage in Hep-2 cells. Further, the prooxidant role of [6]-shogaol inhibit Bcl-2 expression with the simultaneous up-regulation of Bax, Cytochrome c, Caspase-9 and -3 protein expressions were observed in Hep-2 cells. Thus, [6]-shogaol induces apoptosis in Hep-2 cells through inducing oxidative damage and modulate apoptotic marker expressions. Therefore, [6]-shogaol might be used as a therapeutic agent for the treatment of laryngeal cancer.     

Interleukin‐6 induces microglial CX3CR1 expression in the spinal cord after peripheral nerve injury through the activation of p38 MAPK

Peripheral nerve injury leading to neuropathic pain induces the upregulation of interleukin (IL)‐6 and microglial CX3CR1 expression, and activation of p38 mitogen‐activated protein kinase (MAPK) in the spinal cord. Here, we investigated whether IL‐6 regulates CX3CR1 expression through p38 MAPK activation in the spinal cord in rats with chronic constriction injury (CCI) of the sciatic nerve. Similar temporal changes in the expression of IL‐6, phosphorylated p38 MAPK and CX3CR1 were observed following CCI. The increases in CX3CR1 expression, p38 MAPK activation and pain behavior after CCI were suppressed by blocking IL‐6 action with a neutralizing antibody, while they were enhanced by supplying exogenous recombinant rat IL‐6 (rrIL‐6). rrIL‐6 also induced increases in spinal CX3CR1 expression, p38 MAPK activation and pain behavior in naïve rats without nerve injury. Furthermore, treatment with the p38 MAPK‐specific inhibitor, SB203580, suppressed the increase in CX3CR1 expression induced by CCI or rrIL‐6 treatment. Finally, blocking CX3CR1 or p38 MAPK activation prevented the development of mechanical allodynia and thermal hyperalgesia induced by CCI or rrIL‐6 treatment. These results suggest a new mechanism of neuropathic pain, in which IL‐6 induces microglial CX3CR1 expression in the spinal cord through p38 MAPK activation, enhancing the responsiveness of microglia to fractalkine in the spinal cord, thus playing an important role in neuropathic pain after peripheral nerve injury.     

Platelet collagen receptor Glycoprotein VI‐dimer recognizes fibrinogen and fibrin through their D‐domains,contributing to platelet adhesion and activation during thrombus formation

Essentials

• Glycoprotein VI (GPVI) binds collagen, starting thrombogenesis, and fibrin, stabilizing thrombi.
• GPVI‐dimers, not monomers, recognize immobilized fibrinogen and fibrin through their D‐domains.
• Collagen, D‐fragment and D‐dimer may share a common or proximate binding site(s) on GPVI‐dimer.
• GPVI‐dimer–fibrin interaction supports spreading, activation and adhesion involving αIIbβ3.

Summary

Background

Platelet collagen receptor Glycoprotein VI (GPVI) binds collagen, initiating thrombogenesis, and stabilizes thrombi by binding fibrin.

Objectives

To determine if GPVI‐dimer, GPVI‐monomer, or both bind to fibrinogen substrates, and which region common to these substrates contains the interaction site.

Methods

Recombinant GPVI monomeric extracellular domain (GPVI_ex) or dimeric Fc‐fusion protein (GPVI‐Fc₂) binding to immobilized fibrinogen derivatives was measured by ELISA, including competition assays involving collagenous substrates and fibrinogen derivatives. Flow adhesion was performed with normal or Glanzmann thrombasthenic (GT) platelets over immobilized fibrinogen, with or without anti‐GPVI‐dimer or anti‐αIIbβ3.

Results

Under static conditions, GPVI_ex did not bind to any fibrinogen substrate. GPVI‐Fc₂ exhibited specific, saturable binding to both D‐fragment and D‐dimer, which was inhibited by mFab‐F (anti‐GPVI‐dimer), but showed low binding to fibrinogen and fibrin under our conditions. GPVI‐Fc₂ binding to D‐fragment or D‐dimer was abrogated by collagen type III, Horm collagen or CRP‐XL (crosslinked collagen‐related peptide), suggesting proximity between the D‐domain and collagen binding sites on GPVI‐dimer. Under low shear, adhesion of normal platelets to D‐fragment, D‐dimer, fibrinogen and fibrin was inhibited by mFab‐F (inhibitor of GPVI‐dimer) and abolished by Eptifibatide (inhibitor of αIIbβ3), suggesting that both receptors contribute to thrombus formation on these substrates, but αIIbβ3 makes a greater contribution. Notably, thrombasthenic platelets showed limited adhesion to fibrinogen substrates under flow, which was further reduced by mFab‐F, supporting some independent GPVI‐dimer involvement in this interaction.

Conclusion

Only dimeric GPVI interacts with fibrinogen D‐domain, at a site proximate to its collagen binding site, to support platelet adhesion/activation/aggregate formation on immobilized fibrinogen and polymerized fibrin.     

Caffeic acid inhibits the formation of 1-hydroxyethyl radical in the reaction mixture of rat liver microsomes with ethanol partly through its metal chelating activity

Effect of caffeic acid on the formation of 1-hydroxyethyl radicals via the microsomal ethanol-oxidizing system pathway was examined. The electron spin resonance spin trapping showed that 1-hydroxyethyl radicals form in the control reaction mixture which contained 0.17 M ethanol, 1 mg protein/ml rat river microsomes, 0.1 M α-(4-pyridyl-1-oxide)-N-tert-butylnitrone, 5 mM nicotinamide adenine dinucleotide phosphate and 30 mM phosphate buffer (pH 7.4). When the electron spin resonance spectra of the control reaction mixtures with caffeic acid were measured, caffeic acid inhibited the formation of 1-hydroxyethyl radicals in a concentration dependent manner. Gallic acid, dopamine, l-dopa, chlorogenic acid and catechin also inhibited the formation of 1-hydroxyethyl radicals. Above results indicated that the catechol moiety is essential to the inhibitory effect. Caffeic acid seems to chelate of iron ion at the catechol moiety. Indeed, the inhibitory effect by caffeic acid was greatly diminished in the presence of desferrioxamine, a potent iron chelator which removes iron ion in the Fe (III)-caffeic acid complex. Since Fe (III)-desferrioxamine complex is active for the 1-hydroxyethyl radicals formation, caffeic acid inhibits the formation of 1-hydroxyethyl radicals in the reaction mixture partly through its metal chelating activity.     

N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine induces apoptosis through the activation of caspases-3 and -8 in human platelets. A role for endoplasmic reticulum stress

Summary. Background: Apoptosis or programmed cell death involves a number of biochemical events, including the activation of caspases, which lead to specific cell morphology changes and ultimately cell death. Traditionally, two apoptotic pathways have been described: the cell‐surface death receptor‐dependent extrinsic pathway and the mitochondria‐dependent intrinsic pathway. Alternatively, apoptosis has been reported to be induced by endoplasmic reticulum (ER) stress, which is mainly induced by a reduction in intraluminal free Ca²⁺ concentration ([Ca²⁺]_ER). Objectives: The present study aimed to investigate the development of apoptotic events after ER stress induced by N,N,N′,N′‐tetrakis(2‐pyridylmethyl)ethylenediamine (TPEN), an ER Ca²⁺ chelator, in human platelets. Methods: Changes in cytosolic free Ca²⁺ concentration, caspase activity and phosphatidylserine externalization were determined by fluorimetric techniques. Results: Our results indicate that TPEN reduces the amount of free Ca²⁺ releasable by the Ca²⁺‐mobilizing agonist thrombin. TPEN induced activation of caspase‐3, ‐8 and ‐9 and subsequent phosphatidylserine externalization. The ability of TPEN to induce phosphatidylserine externalization was smaller than that of thrombin. In addition, TPEN was able to induce phosphorylation of the eukaryotic initiation factor 2α (eIF2α). TPEN‐mediated caspase‐3 activation requires functional caspase‐8, but is independent of H₂O₂ generation. Activation of caspase‐3 and ‐8 by TPEN was prevented by salubrinal, an agent that prevents ER stress‐induced apoptosis. Conclusion: These findings provide experimental evidence for the existence of ER stress‐mediated apoptosis in human platelets, a process that might limit platelet life span upon prolonged stimulation with agonists.