L5 Research Center, China Medical University Hospital, Taichung, Taiwan.
Apoptosis. 2012 Sep;17(9):1009-18. doi: 10.1007/s10495-012-0726-1.
Cardiomyocyte apoptosis has a critical role in the pathogenesis of heart failure. L5, the most negatively charged subfraction of human plasma low-density lipoprotein (LDL), induces several atherogenic responses in endothelial cells (ECs), including apoptosis. We hypothesized that L5 also contributes to cardiomyocyte apoptosis and studied whether it does so indirectly by inducing the secretion of factors from ECs. We examined apoptosis of rat cardiomyocytes treated with culture-conditioned medium (CCM) of rat ECs that were exposed to L5 or L1 (the least negatively charged LDL subfraction). Apoptosis at early and late time points was twofold greater in cardiomyocytes treated with L5 CCM than in those treated with L1 CCM. The indirect effect of L5 on cardiomyocyte apoptosis was significantly reduced by pretreating ECs with inhibitors of phosphatidylinositol 3-kinase (PI3K) or CXC receptor 2 (CXCR2). Studies with cytokine protein arrays revealed that L5 CCM, but not L1 CCM, contained high levels of ELR(+) CXC chemokines, including lipopolysaccharide-induced chemokine (LIX) and interleukin (IL)-8. The L5-induced release of these chemokines from ECs was abolished by inhibiting the lectin-like oxidized LDL receptor-1 (LOX-1). Addition of recombinant LIX or IL-8 to CCM-free cardiomyocyte cultures increased apoptosis and enhanced production of tumor necrosis factor (TNF)-α and IL-1β by increasing the translocation of NF-κB into the nucleus; these effects were attenuated by inhibiting PI3K and CXCR2. In conclusion, L5 may indirectly induce cardiomyocyte apoptosis by enhancing secretion of ELR(+) CXC chemokines from ECs, which in turn activate CXCR2/PI3K/NF-κB signaling to increase the release of TNF-α and IL-1β.
心肌细胞凋亡在心力衰竭的发病机制中起着关键作用。L5 是人血浆低密度脂蛋白（LDL）的最带负电荷的亚组分，可诱导内皮细胞（EC）发生几种动脉粥样硬化反应，包括凋亡。我们假设 L5 也有助于心肌细胞凋亡，并研究它是否通过诱导 EC 分泌因子间接起作用。我们检查了用暴露于 L5 或 L1（LDL 带负电荷最少的亚组分）的大鼠 EC 的培养条件培养基（CCM）处理的大鼠心肌细胞的凋亡。与用 L1 CCM 处理的心肌细胞相比，用 L5 CCM 处理的心肌细胞的早期和晚期凋亡增加了两倍。用 PI3K 或 CXC 受体 2（CXCR2）抑制剂预处理 EC，可显著降低 L5 对心肌细胞凋亡的间接作用。细胞因子蛋白阵列研究表明，L5 CCM 含有高水平的 ELR(+)CXC 趋化因子，包括脂多糖诱导的趋化因子（LIX）和白细胞介素（IL）-8，但 L1 CCM 则没有。抑制凝集素样氧化 LDL 受体-1（LOX-1）可消除 L5 诱导的这些趋化因子从 EC 中的释放。将重组 LIX 或 IL-8 添加到无 CCM 的心肌细胞培养物中，可通过增加 NF-κB 向细胞核内易位，增加肿瘤坏死因子（TNF）-α 和 IL-1β 的产生，从而增加细胞凋亡；这些作用通过抑制 PI3K 和 CXCR2 而减弱。总之，L5 可能通过增强 EC 分泌 ELR(+)CXC 趋化因子来间接诱导心肌细胞凋亡，进而激活 CXCR2/PI3K/NF-κB 信号通路，增加 TNF-α 和 IL-1β 的释放。
