Department of Molecular Genetics, University of Toronto, Donnelly Centre Rm 1110, 160 College Street, Toronto, ON, M5S 3E1, Canada.
Institute of Medical Science, University of Toronto, Toronto, ON, M5S 1A8, Canada.
Stem Cell Res Ther. 2021 Oct 30;12(1):560. doi: 10.1186/s13287-021-02630-0.
The adult mammalian retina does not have the capacity to regenerate cells lost due to damage or disease. Therefore, retinal injuries and blinding diseases result in irreversible vision loss. However, retinal stem cells (RSCs), which participate in retinogenesis during development, persist in a quiescent state in the ciliary epithelium (CE) of the adult mammalian eye. Moreover, RSCs retain the ability to generate all retinal cell types when cultured in vitro, including photoreceptors. Therefore, it may be possible to activate endogenous RSCs to induce retinal neurogenesis in vivo and restore vision in the adult mammalian eye.
To investigate if endogenous RSCs can be activated, we performed combinatorial intravitreal injections of antagonists to BMP and sFRP2 proteins (two proposed mediators of RSC quiescence in vivo), with or without growth factors FGF and Insulin. We also investigated the effects of chemically-induced N-methyl-N-Nitrosourea (MNU) retinal degeneration on RSC activation, both alone and in combination withthe injected factors. Further, we employed inducible Msx1-Cre genetic lineage labeling of the CE followed by stimulation paradigms to determine if activated endogenous RSCs could migrate into the retina and differentiate into retinal neurons.
We found that in vivo antagonism of BMP and sFRP2 proteins induced CE cells in the RSC niche to proliferate and expanded the RSC population. BMP and sFRP2 antagonism also enhanced CE cell proliferation in response to exogenous growth factor stimulation and MNU-induced retinal degeneration. Furthermore, Msx1-Cre genetic lineage tracing revealed that CE cells migrated into the retina following stimulation and/or injury, where they expressed markers of mature photoreceptors and retinal ganglion cells.
Together, these results indicate that endogenous adult mammalian RSCs may have latent regenerative potential that can be activated by modulating the RSC niche and hold promise as a means for endogenous retinal cell therapy to repair the retina and improve vision.
成年哺乳动物的视网膜没有能力再生因损伤或疾病而丧失的细胞。因此，视网膜损伤和致盲性疾病导致不可逆转的视力丧失。然而，在发育过程中参与视网膜发生的视网膜干细胞（RSCs）在成年哺乳动物眼睛的睫状上皮（CE）中处于静止状态。此外，当在体外培养时，RSCs 保留生成所有视网膜细胞类型的能力，包括光感受器。因此，有可能激活内源性 RSCs，在体内诱导视网膜神经发生并恢复成年哺乳动物眼睛的视力。
为了研究内源性 RSCs 是否可以被激活，我们进行了组合性玻璃体内注射 BMP 和 sFRP2 蛋白的拮抗剂（两种体内 RSC 静止的假定介质），并与或不与 FGF 和胰岛素等生长因子一起注射。我们还研究了化学诱导的 N-甲基-N-亚硝基脲（MNU）视网膜变性对 RSC 激活的影响，单独和与注射因子一起作用。此外，我们采用诱导型 Msx1-Cre 基因谱系标记 CE，然后进行刺激方案，以确定激活的内源性 RSCs 是否可以迁移到视网膜并分化为视网膜神经元。
我们发现，体内拮抗 BMP 和 sFRP2 蛋白诱导 RSC 龛位中的 CE 细胞增殖，并扩大了 RSC 群体。BMP 和 sFRP2 拮抗剂还增强了 CE 细胞对外源性生长因子刺激和 MNU 诱导的视网膜变性的增殖反应。此外，Msx1-Cre 基因谱系追踪显示，CE 细胞在刺激和/或损伤后迁移到视网膜，在那里它们表达成熟光感受器和视网膜神经节细胞的标志物。
总之，这些结果表明，内源性成年哺乳动物 RSCs 可能具有潜在的再生潜能，可以通过调节 RSC 龛位来激活，并有望成为内源性视网膜细胞治疗的一种手段，以修复视网膜并改善视力。
