Gutman C R, Strittmatter W J, Weisgraber K H, Matthew W D
Department of Neurobiology, Duke University Medical Center, Durham, North Carolina 27710, USA.
J Neurosci. 1997 Aug 15;17(16):6114-21. doi: 10.1523/JNEUROSCI.17-16-06114.1997.
Expression of apolipoprotein E (apoE) and ciliary neurotrophic factor (CNTF), a pleiotropic neuron survival factor, increases in the CNS in response to injury. Although CNTF is believed to act as a survival factor after injury in the CNS, the functions of apoE in the CNS remain mainly unknown. Similarities between apoE and CNTF, including coinciding patterns of postinjury expression, extracellular localization, homologous tertiary structure, and ability to form homodimers led us to examine the possibility that apoE and CNTF directly associate and thereby facilitate the neurotrophic activity of CNTF. We identified two binding interactions between apoE and CNTF: (1) reversible binding of both the apoE3 and apoE4 isoforms to CNTF under nondenaturing conditions, and (2) a higher avidity, SDS-stable binding of apoE3 with CNTF. Purified lipid-free apoE, as well as apoE in cerebrospinal fluid, binds CNTF. We demonstrate here that the survival-promoting activity of CNTF on cultured hippocampal neurons is potentiated by apoE. In the absence of apoE, survival of hippocampal neurons with 1 ng/ml CNTF was 20% above control survival values. In contrast, in the presence of apoE, survival of hippocampal neurons with 1 ng/ml CNTF was 40% above control survival values. These data, which indicate a novel function for apoE in the nervous system, support the hypothesis that apoE secreted locally at sites of injury can facilitate neural repair by promoting the activity of certain growth factors, in particular CNTF.
载脂蛋白E（apoE）和睫状神经营养因子（CNTF，一种多效性神经元存活因子）的表达会在中枢神经系统（CNS）因损伤而升高。尽管人们认为CNTF在中枢神经系统损伤后起到存活因子的作用，但apoE在中枢神经系统中的功能仍主要未知。apoE与CNTF之间存在相似之处，包括损伤后表达模式一致、细胞外定位、同源三级结构以及形成同二聚体的能力，这促使我们研究apoE与CNTF直接结合从而促进CNTF神经营养活性的可能性。我们确定了apoE与CNTF之间的两种结合相互作用：（1）在非变性条件下，apoE3和apoE4异构体均可与CNTF可逆结合；（2）apoE3与CNTF具有更高的亲和力且在SDS中稳定结合。纯化的无脂apoE以及脑脊液中的apoE均可与CNTF结合。我们在此证明，apoE可增强CNTF对培养的海马神经元的促存活活性。在没有apoE的情况下，1 ng/ml CNTF条件下海马神经元的存活率比对照存活率高20%。相比之下，在有apoE的情况下，1 ng/ml CNTF条件下海马神经元的存活率比对照存活率高40%。这些数据表明apoE在神经系统中具有新功能，支持了这样一种假说，即损伤部位局部分泌的apoE可通过促进某些生长因子（特别是CNTF）的活性来促进神经修复。
