| Summary: | 博士 === 國立臺灣大學 === 動物學研究所 === 100 === Part I:
Oxidative stress and nitrosative stress are both suggested to be involved in cardiac ischemia-reperfusion (I/R) injury. This study investigate whether reperfusion-induced intracellular Zn2+ (Zn2+i) release activates GSK-3B, resulting in cardiac I/R-injury, and whether acute chelation of the Zn2+i release salvages the live myocardium. Using time-lapse confocal microscopy of cardiomyocytes and high affinity O2-• and Zn2+ probes, the present study is the first to show that I/R, ROS, and RNS all cause a marked increase in the [O2-•]i, resulting in cytosolic and mitochondrial Zn2+ release. Exposure to a cell-penetrating, high affinity Zn2+i chelator, TPEN, largely abolished the Zn2+i release and markedly protected myocytes from I/R-, ROS-, RNS-, or Zn2+/K+ (Zn2+i supplementation)-induced myocyte apoptosis for at least 24 hr after TPEN removal. In adult rat hearts, TPEN or baicalein (a potent flavonoid) again markedly inhibited cardiac I/R injury. Flavonoids and U0126 (a MEK1/2 inhibitor) largely inhibited the myocyte apoptosis and the TPEN-sensitive I/R- or Zn2+i supplement-induced persistent ERK1/2 phosphorylation, dephosphorylation of p-Ser9 on GSK-3B, and the translocation into and accumulation of p-Tyr216 GSK-3B and p53 in, the nucleus. Silencing of GSK-3B or p53 expression was cardioprotective, indicating that activation of the ERK-GSK-3B-p53 signaling pathway is involved in Zn2+i-sensitive myocyte death. Moreover, the ERK-dependent Noxa-Mcl-1 pathway is also involved, since silencing of Noxa expression was cardioprotective and U0126 abolished both the increase in Noxa expression and Mcl-1 degradation. Our results demonstrated that Zn2+i -sensitive activation of GSK-3B is involved in cardiac I/R injury. TPEN always provided more cardioprotection than the other tested inhibitors. Thus, acute upstream Zn2+i chelation at the start of reperfusion and the use of natural products, i.e. flavonoids, may be beneficial in the treatment of cardiac I/R injury.
Part II:
Caffeic acid (CA), a natural phenolic compound, is abundant in medicinal plants. CA possesses multiple biological effects such as anti-bacterial and anti-cancer growth. CA was also reported to induce fore stomach and kidney tumors in mouse model. Here we used two human lung cancer cell lines, A549 and H1299, to clarify the role of CA in cancer cell proliferation. The growth assay showed that CA promoted the proliferation of the lung cancer cells moderately. Furthermore, pre-treatment of CA rescues the proliferation inhibition induced by sub-IC50 dose of paclitaxel (PTX), an anticancer drug. Western blot showed that CA up-regulated the pro-survival proteins survivin and Bcl-2, the down-stream targets of NF-kB. This is consistent with the observation that CA induced nuclear translocation of NF-kB p65. Our study suggested that the pro-survival effect of CA on PTX-treated lung cancer cells was mediated through NF-kB signaling pathway. This may provide mechanistic insights into chemoresistance of cancer cells.
|
|---|
