Department of Pediatrics, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, China.
Chin Med J (Engl). 2010 Jan 20;123(2):216-20.
Mesangial hypercellularity is a critical early histopathological finding in human and experimental glomerular diseases. Hyperlipidemia and the glomerular deposition of lipoproteins are commonly associated with mesangial hypercellularity and play an important pathobiological role in the development of glomerular diseases. The activated cytoplasmic mitogen-activated protein kinase (MAPK), including mainly extracellular-signal regulated protein kinase (ERK), c-Jun amino-terminal kinase (JNK), and p38, has been thought to translocate into the nucleus and activate various transcription factors and protooncogenes associated with cell growth and proliferation. Lipoprotein (a) (Lp(a)) has been shown to stimulate proliferation of mesangial cells, but the events of Lp(a) signaling have not yet been characterized. The purpose of this study was to investigate the signal transduction pathways involved in Lp(a)-induced cell proliferation and provide an evidence for the participation of Lp(a) in intracellular signaling pathways for mesangial cell proliferation.
Lp(a) was isolated from a patient who was being treated with low density lipoprotein (LDL)-apheresis by density gradient ultracentrifugation and then chromatography. Human mesangial cells (HMCs) were isolated by the sequential sieving technique and stimulated with Lp(a) in different concentration and time course. The DNA synthesis of the cells was measured by [3H] thymidine incorporation for detecting the proliferation. The expression of all the three members of MAPK family, including ERK1/ERK2, JNK, and p38, and their phosphorylation were detected by Western blotting.
Lp(a) could induce a significant dose-dependent proliferation of HMCs. The 3H-TdR incorporation was 1.64+/-0.31, 1.69+/-0.48, 3.59+/-0.68 (P<0.01), 4.14+/-0.78 (P<0.01), and 4.05+/-0.55 (P<0.01) (10(3) cpm) at the Lp(a) concentration of 0, 5, 10, 25, and 50 microg/ml, respectively. Lp(a) induced an increase in ERK1/ERK2 phosphorylation between 5 and 60 minutes, and in JNK phosphorylation between 15 and 30 minutes after incubating with HMCs, whereas the level of p38 and its phosphorylation was not changed.
Lp(a) could stimulate the proliferation of HMCs by activiating the phosphorylation of ERK1/ERK2 and JNK MAPK signaling pathway, whereas p38 pathway had no effect on the Lp(a)-induced HMC proliferation, which indicated that three MAPKs seem to be distinctly involved in the effect. In particular, it also provides the evidence that Lp(a) may act as one of the major endogenous modulators for mitogenic signaling response and cell proliferation within the glomerulus.
系膜细胞增生是人类和实验性肾小球疾病中早期的关键组织病理学发现。高脂血症和脂蛋白在肾小球中的沉积通常与系膜细胞增生有关，并在肾小球疾病的发展中起着重要的病理生物学作用。细胞质有丝分裂原激活蛋白激酶（MAPK）的激活，主要包括细胞外信号调节蛋白激酶（ERK）、c-Jun 氨基末端激酶（JNK）和 p38，已被认为可转位入核并激活与细胞生长和增殖相关的各种转录因子和原癌基因。脂蛋白（a）[Lp（a）]已被证明能刺激系膜细胞增殖，但 Lp（a）信号转导事件尚未被描述。本研究的目的是探讨 Lp（a）诱导细胞增殖的信号转导途径，并为 Lp（a）参与系膜细胞增殖的细胞内信号转导途径提供证据。
采用密度梯度超速离心和色谱法从接受低密度脂蛋白（LDL）-血浆置换治疗的患者中分离 Lp（a）。通过连续筛网技术分离人系膜细胞（HMCs），并在不同浓度和时间进程中用 Lp（a）刺激。用[3H]胸腺嘧啶核苷掺入法测定细胞的 DNA 合成，以检测增殖。通过 Western 印迹检测 MAPK 家族的所有三个成员（包括 ERK1/ERK2、JNK 和 p38）及其磷酸化的表达。
Lp（a）可诱导 HMC 产生明显的浓度依赖性增殖。Lp（a）浓度为 0、5、10、25 和 50μg/ml 时，[3H]TdR 掺入量分别为 1.64+/-0.31、1.69+/-0.48、3.59+/-0.68（P<0.01）、4.14+/-0.78（P<0.01）和 4.05+/-0.55（P<0.01）（103 cpm）。Lp（a）孵育 5 至 60 分钟后，ERK1/ERK2 磷酸化增加，孵育 15 至 30 分钟后 JNK 磷酸化增加，而 p38 及其磷酸化水平没有变化。
Lp（a）可通过激活 ERK1/ERK2 和 JNK MAPK 信号通路来刺激 HMC 增殖，而 p38 通路对 Lp（a）诱导的 HMC 增殖没有影响，这表明三种 MAPK 似乎都参与了这一作用。特别是，这也为 Lp（a）可能作为肾小球内有丝分裂信号反应和细胞增殖的主要内源性调节剂之一提供了证据。
