Laboratory of Molecular Neurobiology, Medical Biochemistry and Biophysics, Karolinska Institute, Scheeleväg 1, Stockholm, Sweden.
Stem Cells. 2012 May;30(5):865-75. doi: 10.1002/stem.1049.
Secreted Frizzled related proteins (sFRPs) are a family of proteins that modulate Wnt signaling, which in turn regulates multiple aspects of ventral midbrain (VM) and dopamine (DA) neuron development. However, it is not known which Wnt signaling branch and what aspects of midbrain DA neuron development are regulated by sFRPs. Here, we show that sFRP1 and sFRP2 activate the Wnt/planar-cell-polarity/Rac1 pathway in DA cells. In the developing VM, sFRP1 and sFRP2 are expressed at low levels, and sFRP1-/- or sFRP2-/- mice had no detectable phenotype. However, compound sFRP1-/-;sFRP2-/- mutants revealed a Wnt/PCP phenotype similar to that previously described for Wnt5a-/- mice. This included an anteroposterior shortening of the VM, a lateral expansion of the Shh domain and DA lineage markers (Lmx1a and Th), as well as an accumulation of Nurr1+ precursors in the VM. In vitro experiments showed that, while very high concentrations of SFRP1 had a negative effect on cell survival, low/medium concentrations of sFRP1 or sFRP2 promoted the DA differentiation of progenitors derived from primary VM cultures or mouse embryonic stem cells (ESCs), mimicking the effects of Wnt5a. We thus conclude that the main function of sFRP1 and sFRP2 is to enhance Wnt/PCP signaling in DA cells and to regulate Wnt/PCP-dependent functions in midbrain development. Moreover, we suggest that low-medium concentrations of sFRPs may be used to enhance the DA differentiation of ESCs and improve their therapeutic application.
分泌型卷曲相关蛋白（sFRPs）是一类调节 Wnt 信号的蛋白，而 Wnt 信号又调节中脑腹侧（VM）和多巴胺（DA）神经元发育的多个方面。然而，目前尚不清楚 sFRPs 调节的是 Wnt 信号的哪个分支以及中脑 DA 神经元发育的哪些方面。在这里，我们表明 sFRP1 和 sFRP2 在 DA 细胞中激活 Wnt/平面细胞极性/Rac1 通路。在发育中的 VM 中，sFRP1 和 sFRP2 表达水平较低，sFRP1-/-或 sFRP2-/-小鼠没有可检测到的表型。然而，sFRP1-/-;sFRP2-/-杂合子突变体显示出类似于以前描述的 Wnt5a-/-小鼠的 Wnt/PCP 表型。这包括 VM 的前后缩短、Shh 结构域和 DA 谱系标记物（Lmx1a 和 Th）的侧向扩张，以及 Nurr1+前体在 VM 中的积累。体外实验表明，尽管非常高浓度的 SFRP1 对细胞存活有负面影响，但低/中浓度的 sFRP1 或 sFRP2 促进源自原代 VM 培养物或小鼠胚胎干细胞（ESCs）的祖细胞的 DA 分化，模拟了 Wnt5a 的作用。因此，我们得出结论，sFRP1 和 sFRP2 的主要功能是增强 DA 细胞中的 Wnt/PCP 信号，并调节中脑发育中 Wnt/PCP 依赖的功能。此外，我们建议低/中浓度的 sFRPs 可用于增强 ESCs 的 DA 分化，并改善其治疗应用。
