Functional analysis of variant BDNF (Val66Met)

 描述(申请人提供)：现在已经被广泛接受，儿童和青春期大脑回路的结构和生化变化会影响以后生活中的学习、记忆和功能回路。BDNF前结构域中常见的人类单核苷酸多态(SNP)导致66密码子上的甲硫氨酸替换，为BDNF在学习和记忆改变中的作用提供了深入的见解，特别是在与恐惧相关的过程中。到目前为止的体外研究表明，这种SNP作为一种功能缺失突变，损害了BDNF的分泌。因此，在人类和转基因小鼠中发现的这种SNP的异常被归因于基于成熟BDNF生物利用度降低的功能丧失模型。原脑源性神经营养因子蛋白分解后产生的分离前结构域的潜在功能(S)仍然是未知的。在这里，我们提供了证据表明，Met原结构域以一种活性依赖的方式分泌，作为一个独立的配体，并通过激活另一组受体p75NTR和SorCS2来诱导对成熟的BDNF的拮抗生物学作用。最近，我们在BDNF Met敲入小鼠身上取得了两项关键发现，表明Met前域影响特定脑回路的成熟，导致基于恐惧的学习功能障碍，这在BDNF缺乏(BDNF+/-小鼠)中并不明显。我们将直接检验这一假设，即人类BDNF的Met前域是一个生物活性配体，可以诱导形态神经元重构，并解释这种SNP对恐惧电路和功能的重大影响。我们将确定Met前域信号通过p75/SorCS2共同受体复合体改变培养神经元中神经元形态并影响海马区和前额叶皮质之间发育中的恐惧回路的机制。最后，我们将确定在过渡到青春期的恐惧调节的“敏感期”期间，Met前域在恐惧消退相关行为中的影响。总而言之，这些研究旨在研究BDNF SNP可能影响大脑功能的另一种潜在机制。测试的假说代表了对一种关键的大脑生长因子的生物学行为的重大重新概念。

 DESCRIPTION (provided by applicant): It is now well-accepted that structural and biochemical alterations in brain circuitry during childhood and adolescence can affect learning, memory, and functional circuitry later in life. A common human single nucleotide polymorphism (SNP) in the BDNF prodomain that leads to valise-to-methionine substitution at codon 66 has provided insights into the role of BDNF in altered learning and memory, especially in the realm of fear-related processes. In vitro studies to date have suggested that this SNP acts as a loss of function mutation that impairs BDNF secretion. Thus, the abnormalities found in humans and knock-in mice with this SNP have been attributed to a loss of function model based on decreased bioavailability of mature BDNF. The potential function(s) of the isolated prodomain generated after proteolysis of proBDNF remain cryptic. Here, we provide evidence that the Met prodomain is secreted in an activity-dependent manner, acts as an independent ligand, and elicits antagonistic biological actions to mature BDNF, by activating an alternate set of receptors, p75NTR and SorCS2. Recently, we have made two key findings using the BDNF Met knock-in mouse that suggest that the Met prodomain affects the maturation of a specific brain circuit, leading to functional impairments in fear- based learning that is not evident with BDNF deficiency (BDNF+/- mice). We will directly test the hypothesis that the human Met prodomain of BDNF is a biologically active ligand that induces morphological neuronal remodeling, and explains the significant impact of this SNP on fear circuitry and function. We will identify the mechanisms by which Met prodomain signals through a p75/SorCS2 co-receptor complex to alter neuronal morphology in cultured neurons and affect the developing fear circuitry between the hippocampus and prefrontal cortex. Finally, we will determine the impact of the Met prodomain in fear extinction-related behaviors during a "sensitive period" for fear regulation during the transition into adolescence. Collectively, these studies are designed to investigate an additional potential mechanism by which the BDNF SNP may impact brain function. The hypotheses tested represent a significant reconceptualization of the biological actions of a key brain growth factor.