Geriatric Research, Education, and Clinical Center and Research Service, Bruce W. Carter Veterans Affairs Medical Center, Miami, FL 33125, USA.
Mol Cell Neurosci. 2012 Feb;49(2):138-48. doi: 10.1016/j.mcn.2011.10.008. Epub 2011 Oct 26.
Due to the limitations of neural stem cells to repair neuronal damage in the human brain, alternative approaches of repair using autologous adult stem cells have been examined for direct cell-replacement, or paracrine mediated neuroprotective effects. Human bone marrow-derived stromal cells (hMSCs) are a heterogeneous adult stem cell population with diverse immunomodulatory properties and the potential to differentiate into cells characteristic of all three germ layers. hMSCs are a renewable source of progenitor cells suitable for cell-based tissue repair. The marrow isolated adult multilineage inducible (MIAMI) cells developed by our laboratory are a developmentally immature homogeneous subpopulation of hMSCs that maintain self-renewal potential during ex vivo expansion, efficient differentiation capacity into neuron-like cells in vitro, as well as direct in vivo neuroprotection and functional recovery in animal models of neurological diseases. We now address the early signaling mechanisms regulating the neuron-like differentiation of MIAMI cells in vitro, in response to activation of the neurotrophic tyrosine-kinase receptor, type 3 (NTRK3) via neurotrophin 3 (NT3). We molecularly characterize a novel role for Rac1b mediating the neurogenic potential of MIAMI cells. Rac1b had an overall negative modulatory effect on the NT3-stimulated Mek1/2-Erk1/2 signaling pathway, proneuronal gene expression and neurite-like extensions. Rac1b was required for NT3-stimulated cell proliferation of MIAMI cells, yet was found to repress CCND1 and CCNB1 mRNA expression independent of NT3 stimulation, suggesting a dual neurotrophin dependent/independent function. Differential levels of Rac1b activity in hMSCs may explain the apparent contradictory reports regarding their neurogenic potential. These findings demonstrate the in vitro neurogenic potential of hMSCs as governed by Rac1b during NT3 stimulation.
由于神经干细胞在修复人类大脑神经元损伤方面的局限性，因此已经研究了使用自体成体干细胞的替代修复方法，以实现直接细胞替代或旁分泌介导的神经保护作用。人骨髓基质细胞（hMSC）是一种异质性的成体干细胞群体，具有多种免疫调节特性，并具有分化为所有三个胚层特征细胞的潜力。hMSC 是一种可再生的祖细胞来源，适合用于基于细胞的组织修复。我们实验室开发的骨髓分离的多谱系诱导（MIAMI）细胞是 hMSC 中一种发育不成熟的同质亚群，在体外扩增过程中保持自我更新潜力，能够有效地分化为神经元样细胞，并且在神经疾病动物模型中具有直接的体内神经保护和功能恢复作用。我们现在研究了调节 MIAMI 细胞体外神经元样分化的早期信号机制，这些机制是对神经营养性酪氨酸激酶受体 3（NTRK3）通过神经营养因子 3（NT3）的激活做出的反应。我们从分子水平上确定了 Rac1b 在调节 MIAMI 细胞神经发生潜能中的新作用。Rac1b 对 NT3 刺激的 Mek1/2-Erk1/2 信号通路、前体细胞基因表达和神经突样延伸具有总体负调节作用。Rac1b 是 MIAMI 细胞 NT3 刺激增殖所必需的，但发现其独立于 NT3 刺激可抑制 CCND1 和 CCNB1mRNA 的表达，表明其具有神经营养素依赖/非依赖的双重功能。hMSC 中 Rac1b 活性的差异水平可能解释了其神经发生潜能的明显矛盾报道。这些发现表明，在 NT3 刺激下，hMSC 的体外神经发生潜能受 Rac1b 调节。
