Kim Sung Hun, Yoo Chong Il, Kim Hui Taek, Park Ji Yeon, Kwon Chae Hwa, Kim Yong Keun
Department of Orthopedic Surgery, College of Medicine, Pusan National University, Pusan, Korea.
Toxicol Appl Pharmacol. 2006 Sep 1;215(2):198-207. doi: 10.1016/j.taap.2006.03.001. Epub 2006 Apr 17.
The present study was undertaken to determine the role of the mitogen-activated protein kinase (MAPK) subfamilies in cell death induced by PPARgamma agonists in osteoblastic cells. Ciglitazone and troglitazone, PPARgamma agonists, resulted in a concentration- and time-dependent cell death, which was largely attributed to apoptosis. But a PPARalpha agonist ciprofibrate did not affect the cell death. Ciglitazone caused reactive oxygen species (ROS) generation and ciglitazone-induced cell death was prevented by antioxidants, suggesting an important role of ROS generation in the ciglitazone-induced cell death. ROS generation and cell death induced by ciglitazone were inhibited by the PPARgamma antagonist GW9662. Ciglitazone treatment caused activation of extracellular signal-regulated kinase (ERK) and p38. Activation of ERK was dependent on epidermal growth factor receptor (EGFR) and that of p38 was independent. Ciglitazone-induced cell death was significantly prevented by PD98059, an inhibitor of ERK upstream kinase MEK1/2, and SB203580, a p38 inhibitor. Ciglitazone treatment increased Bax expression and caused a loss of mitochondrial membrane potential, and its effect was prevented by N-acetylcysteine, PD98059, and SB203580. Ciglitazone induced caspase activation, which was prevented by PD98059 and SB203580. The general caspase inhibitor z-DEVD-FMK and the specific inhibitor of caspases-3 DEVD-CHO exerted the protective effect against the ciglitazone-induced cell death. The EGFR inhibitors AG1478 and suramin protected against the ciglitazone-induced cell death. Taken together, these findings suggest that the MAPK signaling pathways play an active role in mediating the ciglitazone-induced cell death of osteoblasts and function upstream of a mitochondria-dependent mechanism. These data may provide a novel insight into potential therapeutic strategies for treatment of osteoporosis.
本研究旨在确定丝裂原活化蛋白激酶（MAPK）亚家族在成骨细胞中由过氧化物酶体增殖物激活受体γ（PPARγ）激动剂诱导的细胞死亡中的作用。PPARγ激动剂环格列酮和曲格列酮导致浓度和时间依赖性的细胞死亡，这在很大程度上归因于细胞凋亡。但PPARα激动剂环丙贝特不影响细胞死亡。环格列酮导致活性氧（ROS）生成，抗氧化剂可预防环格列酮诱导的细胞死亡，这表明ROS生成在环格列酮诱导的细胞死亡中起重要作用。环格列酮诱导的ROS生成和细胞死亡被PPARγ拮抗剂GW9662抑制。环格列酮处理导致细胞外信号调节激酶（ERK）和p38激活。ERK的激活依赖于表皮生长因子受体（EGFR），而p38的激活则与之无关。ERK上游激酶MEK1/2的抑制剂PD98059和p38抑制剂SB203580可显著预防环格列酮诱导的细胞死亡。环格列酮处理增加了Bax表达并导致线粒体膜电位丧失，其作用被N-乙酰半胱氨酸、PD98059和SB203580阻断。环格列酮诱导半胱天冬酶激活，这被PD98059和SB203580阻断。通用半胱天冬酶抑制剂z-DEVD-FMK和半胱天冬酶-3特异性抑制剂DEVD-CHO对环格列酮诱导的细胞死亡具有保护作用。EGFR抑制剂AG1478和苏拉明对环格列酮诱导的细胞死亡具有保护作用。综上所述，这些发现表明MAPK信号通路在介导环格列酮诱导的成骨细胞死亡中起积极作用，并在线粒体依赖性机制的上游发挥作用。这些数据可能为骨质疏松症的潜在治疗策略提供新的见解。
