A Dual Role of Activin-like kinase 5 (ALK5)-mediated TGF Beta Signaling in Adult Neurogenesis

项目摘要 成年哺乳动物大脑中新的神经元是通过一个称为成年神经发生和成年神经再生的过程增加的。 神经发生在学习和记忆的功能结果中起关键作用。两个已知的壁龛之一， 成年神经发生是海马齿状回（DG）的亚颗粒区（SGZ）。已知 TGF-β信号传导在发育过程中对神经发生至关重要，而其在成人神经发生中的作用仍然存在。 不清楚由于TGF-β基因敲除小鼠早期新生小鼠的致死表型， TGF-β信号在成人神经发生中的作用一直是研究的挑战。TGF-β在体内的慢性递送抑制 然而，通过敲除I型受体（Alk 5）抑制TGF-β信号传导在成熟和成熟的神经发生中是不可能的。 不成熟的神经元也导致受损的成年神经发生。此外，药理学调节 在以前的研究中，TGF-β信号传导影响多种细胞类型，包括已知的神经元和小胶质细胞。 在调节成人神经发生中起间接作用。因此，要理解精确的自主 在成体神经发生的不同阶段，如增殖， 分化、成熟和迁移，成体神经干细胞特异性和诱导性基因调控模型 是必要的。为了规避该领域的这些挑战，我们已经产生了NSC特异性TGF-β受体类型。 I型（Alk 5）或II型（TβRII）诱导型敲除（iKO）小鼠，这使我们能够更具体地研究这是如何发生的。 信号通路影响成体NSC和下游后代。我们实验室的初步数据显示， SB-431542对TGF-β信号传导的药理学抑制增加了成体神经干的增殖 细胞（NSCs）的增殖，而用TGF-β处理则抑制其增殖。这暗示了TGF-β信号在调节细胞凋亡中的作用。 抑制成体神经干细胞的增殖。此外，我们从NestincreER-Alk 5获得的初步体内数据 iKO小鼠表明TGF-β信号传导对于SGZ中NSC的成熟和迁移是重要的。我们， 因此，假设TGF-β信号在抑制增殖的神经源性级联反应中具有双重作用， 同时支持未成熟和成熟神经元的成熟和迁移。目标 本研究的主要目的是确定TGF-β信号转导在调节细胞凋亡中的确切功能和机制。 成年神经发生的不同阶段，并确定在每个过程中不同的靶基因。尽管先前 研究提供了TGF-β信号传导影响成人神经发生的证据，但结果相互矛盾 因为已知TGF-β信号传导以高度环境依赖的方式起作用。具有所述特异性 我们的体内小鼠模型，这一建议将提供新的见解的细胞和机制的过程 与成人神经发生有关

Project Summary New neurons are added in the adult mammalian brain by a process known as adult neurogenesis and adult neurogenesis is a key player in functional outcomes for learning and memory. One of the two known niches of adult neurogenesis is the subgranular zone (SGZ) of the dentate gyrus (DG) in the hippocampus. It is known that TGF-β signaling is crucial for neurogenesis during development while its role in adult neurogenesis remains unclear. Due to the lethal phenotype in early neonatal mice of the global TGF-β knockout mice, the precise role of TGF-β signaling in adult neurogenesis has been challenging to study. Chronic delivery of TGF-β in vivo inhibits neurogenesis; however, inhibition of TGF-β signaling via knockout of the type I receptor (Alk5) in mature and immature neurons also leads to compromised adult neurogenesis. Additionally, pharmacological modulation of TGF-β signaling in previous studies affect multiple cells types including neurons and microglia which are known to have an indirect role in regulating adult neurogenesis. Therefore, to understand the precise autonomous requirement of TGF-β signaling in the process of adult neurogenesis during different stages such as proliferation, differentiation, maturation, and migration, adult neural stem cell specific and inducible gene modulation models are needed. To circumvent these challenges in the field, we have generated NSC- specific TGF-β receptor type I (Alk5) or type II (TβRII) inducible knockout (iKO) mice which allows us to more specifically investigate how this signaling pathway affects adult NSCs and downstream progeny. Preliminary data from our lab shows in vitro pharmacological inhibition of TGF-β signaling with SB-431542 increases the proliferation of adult neural stem cell (NSCs) while treatment with TGF-β inhibits the proliferation. This implicates TGF-β signaling in playing an inhibitory role in the proliferation of adult NSCs. Additionally, our preliminary in vivo data from NestincreER-Alk5 iKO mice suggests TGF-β signaling is important for the maturation and migration of NSCs in the SGZ. We, therefore, hypothesize a dual role of TGF-β signaling in the neurogenic cascade which inhibits the proliferation of NSCs while simultaneously supporting maturation and migration in immature and mature neurons. The goal of this current study is to determine the precise functions and mechanisms of TGF-β signaling in regulation of adult neurogenesis through different stages and identify distinct target genes in each process. Although previous studies provide evidence of TGF-β signaling influencing adult neurogenesis, there are conflicting results throughout the field as TGF-β signaling is known to act in a highly context-dependent manner. With the specificity of our in vivo mouse models, this proposal will provide novel insight on the cellular and mechanistic processes involved with adult neurogenesis.