| Summary: | 博士 === 國立陽明大學 === 生化暨分子生物研究所 === 102 === Stroke is a leading cause of death and disability worldwide and lacking effective treatment to improve its recovery. Over the past two decades, despite several adjuvant therapies such as immunotherapy and neuroprotective agents have been shown effective in animal models, numerous clinical trials fail due to the complicated pathophysiologic mechanisms of ischemic stroke. The current notion of stroke recovery attests the benefits of combinational therapy, which requires intimate interaction between neural and vascular systems. Several lines of evidence indicate that post-stroke neurogenesis-induced migration of neuroblasts occurs within an angiogenesis niche. Thus, neovascularization plays an important role for neurogenesis after stroke. The optimization of neovascularization is deemed an important strategy for promoting recovery after stroke.
The availability of fetal-type human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) marks as a milestone in stem cell therapies, aside from basic feature of differentiating into tissues distinct from their origin in vitro and in vivo, owing to their fascinating properties, such as non-invasive harvest, higher proliferation potential and greater efficacy of induced pluripotent stem cells (iPSCs) production, compared with adult-type MSCs. Although xenotransplantation of hUC-MSCs through the multiple mechanisms of action involved in complicated brain remodeling is recognized as a potential source for stroke therapy, the precise cellular and molecular mechanisms underlying the beneficial outcomes remain to be investigated. There is a growing concern regarding the rejection and alteration of genetic code using this xenograft approach. Besides, legislative and social ethical doubts have limited hUC-MSCs to use in basic research.
Except for fewer ethical concerns, mouse primary cell culture provides an important platform to elucidate the cellular and molecular mechanisms of the phenomena for its relatively easy sampling and gene manipulation, as well as allogeneic transplantation mimicry. As a result, a novel strain of MSC from mouse umbilical cord was successfully isolated, expanded, characterized, and was proved to be capable of sustained self-renewal for up to 7 months (over 50 passages) without overt changes in morphology and doubling time. They were capable of multipotent differentiation into mesodermal and neuroectodermal lineage cells in vitro and hematopoietic lineage cells in vivo has been identified. Despite cell surface markers which are quite similar to MSCs isolated from other tissue origins, as well as hUC-MSCs, mUC-MSCs revealed a substantially higher degree of differentiation and shorter doubling time as compared with hUC-MSCs. mUC-MSCs also possess therapeutic potential against three disease related models, including hematopoietic reconstitution, acute hepatic failure and focal ischemic stroke induced by middle cerebral artery occlusion (MCAo). Transplantation of mUC-MSCs increased the survival rate in mice subjected to sub-lethal -irradiation or acute hepatic failure. Intracerebral administration of mUC-MSCs into ischemic brain not only significantly reduced the infarct volume (63% vs. 47%), but also improved neurological behavior (a 1.6-fold increase in gait swing speed) compared with the control.
We further investigated the mechanisms involved in mUC-MSCs–mediated therapeutic effects after ischemic stroke. The results showed that allogeneic transplantation of mUC-MSCs rapidly enhanced the neovascularization within three days post-MCAo as compared with the control. Interestingly, the transplanted mUC-MSCs simultaneously up-regulated SDF-1α via autonomous secretion of mUC-MSCs and stimulated microenvironment, which increased the homing of the peripheral blood- and BM-derived cells into ischemic cortex. Moreover, the dramatic up-regulation of SDF-1α was associated to the augmentation of F4/80, a macrophage/microglia marker, and promoted the alternative activation of M2 phenotype along with an increase in markers of Arginase-1 and CD206, as well as IL-10. The switch from M1 to M2 phenotype was attributed to neovascularization after injury. The perivascular engraftment of mUC-MSCs expressing pericyte marker PDGFR in vivo, as well as the vasculogenesis- promoting potential after co-culture with HUVECs in vitro implicated that mUC-MSCs might serve as pericytes to facilitate neovascularization. The synergistic effect on the expression level of genes, including IL-4, IL-6, and Galectin-3, after co-assembly with HUVECs and mUC-MSCs might be associated with the enhanced neovascularization and regulation of macrophages/microglia polarization.
The full spectrum of pathophysiology after stroke is complex along with various cell types for recovery. Establishment of mUC-MSCs provides not only a more primitive and easily available source for basic and preclinical stem cell research, but also sheds more light on the interplay between molecular components and cellular microenvironment when allogeneic transplantation into ischemic brain. Therefore, a better understanding of MSCs may broaden our insights into the development of more effective cell therapy regimens.
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