Endothelial microparticles (EMPs) are small vesicular structures that serve as a marker of endothelial function. Angiotensin II receptor type 1 autoantibody (AT1-AA) can cause endothelial dysfunction. However, whether AT1-AA promotes EMPs formation and the mechanism remains obscure.
The titres of sera AT1-AA of 126 hypertensive patients and 30 normotensive individuals were evaluated by ELISA. EMPs in the sera and the supernatants of human umbilical vein endothelial cells (HUVECs) were measured by flow cytometry. The phosphorylation levels of mitogen-activated protein kinase (MAPK) pathways in HUVECs treated by AT1-AA were assessed and their correlation with microparticle formation was also analysed. Furthermore, the production of intracellular reactive oxygen species (ROS) and nitric oxide in HUVECs was examined after incubation with "injured" endothelial microparticle (iEMPs) (EMPs derived from AT1-AA treated HUVECs).
The positive rate of AT1-AA in 126 hypertensive patients was 21.4% (27/126), and higher than that in normotensive individuals [3.3% (1/30), P < 0.01]. Circulating EMP (CD31+/CD42b–) levels were corresponding to the AT1-AA titres in hypertensive group (r 2 = 0.3661, P < 0.01). AT1-AA promoted EMPs generation from HUVECs in a time and dose-dependent manner than the vehicle or nonspecific IgG. Meanwhile, AT1-AA significantly elevated phosphorylation level of P38 and ERK in HUVECs. Lorsartan and P38 inhibitor could suppress the AT1-AA's stimulation effect on EMPs generation. Moreover, the iEMP greatly increased ROS production and reduced nitric oxide synthesis in HUVECs.
Our findings showed that circulating EMPs levels positively correlate to the serum AT1-AA titres in essential hypertension patients. The AT1-AA could promote EMPs generation in HUVECs through activation of P38 MAPK signalling pathway, and this effect could be effectively inhibited by losartan or p38 inhibitor. Angiotensin receptor blockers (ARBs) may be more suitable for AT1-AA(+) hypertensive patients on account of suppressing the AT1-AA's stimulation effect on EMPs generation.
aLaboratory of Cardiovascular Immunology, Key Laboratory of Molecular Targeted Therapies of the Ministry of Education, Institute of Cardiology, Union Hospital, Tongji Medical College of Huazhong University of Science and Technology
bDepartment of Cardiology, Guangdong Cardiovascular Institute, Guangdong General Hospital, Guangdong Academy of Medical Sciences, Guangzhou, China
*These authors contributed to the work equally.
Correspondence to Zihua Zhou, MD, PhD, Laboratory of Cardiovascular Immunology, Institute of Cardiology, Union Hospital, Huazhong University of Science and Technology, Wuhan 430022, China. Tel: +86 27 85726376; fax: +86 27 85727340; e-mail: firstname.lastname@example.org
Abbreviations: ACEI, angiotensin-converting enzyme inhibitor; ARB, angiotensin receptor blocker; AT1-AA, angiotensin II receptor type 1 autoantibody; DAF-2 DA, 4,5-diaminofluo-rescein diacetate; DCF-DA, 2[Combining Acute Accent],7[Combining Acute Accent]-dichlorofluorescin diacetate; DMEM, Dulbecco's modified Eagle's medium; EMPs, endothelial microparticles; ERK, extracellular signal-regulated kinase; FCS, fetal calf serum; FSC, forward scatter; HUVECs, human umbilical vein endothelial cells; IgGs, immunoglobulins; JNK, cJun Nterminal kinase; MAPK, mitogen-activated protein kinase; nIgG, nonspecific IgG; OD, optical density; PFP, platelet-free plasma; ROS, reactive oxygen species; SSC, side scatter
Received 11 September, 2012
Accepted 20 November, 2013