Submitted on February 15, 2007
Accepted on November 22, 2007
Leptin increases endothelin type A receptor levels in vascular smooth muscle cells
Chi-Chang Juan1*, Tung-Yueh Chuan2, Chih-Chen Lien3, Yen-Jie Lin4, Seng-Wong Huang5, Ching Kwok6, and Low-Tone Ho7
1 Physiology, National Yang-Ming University, Taipei, Taiwan - Republic of China; Department of Medical Research & Education, Taipei Veterans General Hospital, Taipei, Taiwan - Republic of China
2 Physiology, National Yang-Ming University, Taipei, Taiwan - Republic of China
3 taipei, Taiwan - Republic of China; Physiology, National Yang-Ming University, Taipei, Taiwan - Republic of China
4 Physiology, National Yang-Ming University, 155, Li-Nong St., Sec.2, Peitou, Taipei, Taiwan, R.O.C., Taipei, 112, Taiwan - Republic of China
5 Department of Surgery, National Yang-Ming University, Taipei, Taiwan - Republic of China; Department of Medical Research & Education, Taipei Veterans General Hospital, Taipei, Taiwan - Republic of China
6 Division of Endocrinology and Metabolism, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taipei, Taiwan - Republic of China; Faculty of Medicine, School of Medicine, National Yang-Ming University, Taipei, Taiwan - Republic of China
7 Department of Medical Research & Education, Taipei Veterans General Hospital, Taipei, Taiwan - Republic of China; Division of Endocrinology and Metabolism, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taipei, Taiwan - Republic of China; Physiology, National Yang-Ming University, 155, Li-Nong St., Sec.2, Peitou, Taipei, Taiwan, R.O.C., Taipei, 112, Taiwan - Republic of China; Faculty of Medicine, School of Medicine, National Yang-Ming University, Taipei, Taiwan - Republic of China
* To whom correspondence should be addressed. E-mail: ccjuan{at}ym.edu.tw.
Leptin, one of adipocyte-secreted peptides, is involved in the control of appetite and body weight. Several studies have demonstrated that plasma leptin levels are elevated in obese subjects and are positively correlated with body weight. The arterial endothelin (ET) system plays an important role in the regulation of vascular tone, and ET-1 overexpression may be involved in the pathogenesis of the hypertension associated with insulin resistance. This study was performed to explore the regulatory effects of leptin on ET receptor expression and ET binding in A10 vascular smooth muscle cells (VSMCs) using Northern blotting, immunoblotting, and an [125I]-ET-1 binding assay. The effect of leptin on ET receptor-mediated cell proliferation was also tested. The results showed that leptin caused a significant increase in [125I]-ET-1 binding, which was time- and dose-dependent. Immunoblotting showed that expression of the ET type A receptor (ETAR) in leptin (10-7 M)-treated cells was maximally increased 2.3-fold compared to controls. Levels of ETAR mRNA measured by Northern blotting were also maximally increased 2.2-fold in leptin (10-7 M)-treated cells. Pretreatment with an ERK inhibitor PD98059 (2.5x10-5 M) blocked the leptin-induced increase in [125I]-ET-1 binding. Finally, ET-1(10-7 M)-stimulated cell proliferation was enhanced by leptin (10-7 M) pretreatment, with a maximal increase of 2-fold compared to controls. In conclusion, leptin increases ETAR expression in VSMCs in a dose- and time-dependent manner. This effect is ERK-dependent and is associated with increased ET-1-stimulated cell proliferation. These findings provide support for roles for leptin and the ET system in the pathogenesis of obesity-associated hypertension.
