Migration and differentiation of myogenic precursors following transplantation into the developing rat brain

Muscle-derived stem cells in peripheral nerve regeneration: reality or illusion?

Owing to the complicated and time-consuming regenerative process, the repair of injured peripheral nerves depends largely on ongoing stem-cell therapy. Decades ago, researchers successfully isolated and identified muscle-derived stem cells (MDSCs) and discovered their potential for multidifferentiation. MDSCs play an important role in trauma repair associated with neuromuscular and vascular injury by simultaneously promoting tissue regrowth via direct differentiation and systematic secretion under physiological conditions. However, the isolation, culture, induction and application of MDSCs require further methodological analysis before clinical application. In this review, we comprehensively discuss the challenges associated with neural regeneration and reviewed the progress of stem cell based regenerative medicine, in an effort to realize the potential of MDSCs in nerve regeneration.

Single-cell RNA sequencing identifies distinct mouse medial ganglionic eminence cell types

Many subtypes of cortical interneurons (CINs) are found in adult mouse cortices, but the mechanism generating their diversity remains elusive. We performed single-cell RNA sequencing on the mouse embryonic medial ganglionic eminence (MGE), the major birthplace for CINs, and on MGE-like cells differentiated from embryonic stem cells. Two distinct cell types were identified as proliferating neural progenitors and immature neurons, both of which comprised sub-populations. Although lineage development of MGE progenitors was reconstructed and immature neurons were characterized as GABAergic, cells that might correspond to precursors of different CINs were not identified. A few non-neuronal cell types were detected, including microglia. In vitro MGE-like cells resembled bona fide MGE cells but expressed lower levels of Foxg1 and Epha4. Together, our data provide detailed understanding of the embryonic MGE developmental program and suggest how CINs are specified.

The role of engineering approaches in analysing cancer invasion and metastasis

In the past decade, novel materials, probes and tools have enabled fundamental and applied cancer researchers to take a fresh look at the complex problem of tumour invasion and metastasis. These new tools, which include imaging modalities, controlled but complex in vitro culture conditions, and the ability to model and predict complex processes in vivo, represent an integration of traditional with novel engineering approaches; and their potential effect on quantitatively understanding tumour progression and invasion looks promising.

Cloned myogenic cells can transdifferentiate in vivo into neuron-like cells

Background

The question of whether intact somatic cells committed to a specific differentiation fate, can be reprogrammed in vivo by exposing them to a different host microenvironment is a matter of controversy. Many reports on transdifferentiation could be explained by fusion with host cells or reflect intrinsic heterogeneity of the donor cell population.

Methodology/Principal Findings

We have tested the capacity of cloned populations of mouse and human muscle progenitor cells, committed to the myogenic pathway, to transdifferentiate to neurons, following their inoculation into the developing brain of newborn mice. Both cell types migrated into various brain regions, and a fraction of them gained a neuronal morphology and expressed neuronal or glial markers. Likewise, inoculated cloned human myogenic cells expressed a human specific neurofilament protein. Brain injected donor cells that expressed a YFP transgene controlled by a neuronal specific promoter, were isolated by FACS. The isolated cells had a wild-type diploid DNA content.

Conclusions

These and other results indicate a genuine transdifferentiation phenomenon induced by the host brain microenvironment and not by fusion with host cells. The results may potentially be relevant to the prospect of autologous cell therapy approach for CNS diseases.

Fate of amnion-derived stem cells transplanted to the fetal rat brain: migration, survival and differentiation

We have recently characterized a stem cell population isolated from the rodent amniotic membrane termed amnion-derived stem cells (ADSCs). In vitro ADSCs differentiate into cell types representing all three embryonic layers, including neural cells. In this study we evaluated the neuroectodermal potential of ADSCs in vivo after in utero transplantation into the developing rat brain. A clonal line of green fluorescent protein-expressing ADSCs were infused into the telencephalic ventricles of the developing embryonic day 15.5 rat brain. At E17.5 donor cells existed primarily as spheres in the ventricles with subsets fused to the ventricular walls, suggesting a mode of entry into the brain parenchyma. By E21.5 green fluorescent protein (GFP) ADSCs migrated to a number of brain regions. Examination at postnatal time points revealed that donor ADSCs expressed vimentin and nestin. Subsets of transplanted ADSCs attained neuronal morphologies, although there was no immunohistochemical evidence of neural or glial differentiation. Some donor cells migrated around blood vessels and differentiated into putative endothelial cells. Donor ADSCs transplanted in utero were present in recipients into adulthood with no evidence of immunological rejection or tumour formation. Long-term survival may suggest utility in the treatment of disorders where differentiation to a neural cell type is not required for clinical benefit.

MCP-1 deficiency causes altered inflammation with impaired skeletal muscle regeneration

We examined the role of MCP-1, a potent chemotactic and activating factor for macrophages, in perfusion, inflammation, and skeletal muscle regeneration post-ischemic injury. MCP-1-/- or C57Bl/6J control mice [wild-type (WT)] underwent femoral artery excision (FAE). Muscles were collected for histology, assessment of tissue chemokines, and activity measurements of lactate dehydrogenase (LDH) and myeloperoxidase. In MCP-1-/- mice, restoration of perfusion was delayed, and LDH and fiber size, indicators of muscle regeneration, were decreased. Altered inflammation was observed with increased neutrophil accumulation in MCP-1-/- versus WT mice at Days 1 and 3 (P< or =0.003), whereas fewer macrophages were present in MCP-1-/- mice at Day 3. As necrotic tissue was removed in WT mice, macrophages decreased (Day 7). In contrast, macrophage accumulation in MCP-1-/- was increased in association with residual necrotic tissue and impaired muscle regeneration. Consistent with altered inflammation, neutrophil chemotactic factors (keratinocyte-derived chemokine and macrophage inflammatory protein-2) were increased at Day 1 post-FAE. The macrophage chemotactic factor MCP-5 was increased significantly in WT mice at Day 3 compared with MCP-1-/- mice. However, at post-FAE Day 7, MCP-5 was significantly elevated in MCP-1-/- mice versus WT mice. Addition of exogenous MCP-1 did not induce proliferation in murine myoblasts (C2C12 cells) in vitro. MCP-1 is essential for reperfusion and the successful completion of normal skeletal muscle regeneration after ischemic tissue injury. Impaired muscle regeneration in MCP-1-/- mice suggests an important role for macrophages and MCP-1 in tissue reparative processes.

Fat accumulation with altered inflammation and regeneration in skeletal muscle of CCR2-/- mice following ischemic injury

Chemokines recruit inflammatory cells to sites of injury, but the role of the CC chemokine receptor 2 (CCR2) during regenerative processes following ischemia is poorly understood. We studied injury, inflammation, perfusion, capillary formation, monocyte chemotactic protein-1 (MCP-1) levels, muscle regeneration, fat accumulation, and transcription factor activation in hindlimb muscles of CCR2-/- and wild-type (WT) mice following femoral artery excision (FAE). In both groups, muscle injury and restoration of vascular perfusion were similar. Nevertheless, edema and neutrophil accumulation were significantly elevated in CCR2-/- compared with WT mice at day 1 post-FAE and fewer macrophages were present at day 3. MCP-1 levels in post-ischemic calf muscle of CCR2-/- animals were significantly elevated over baseline through 14 days post-FAE and were higher than WT mice at days 1, 7, and 14. In addition, CCR2-/- mice exhibited impaired muscle regeneration, decreased muscle fiber size, and increased intermuscular adipocytes with similar capillaries/mm(2) postinjury. Finally, the transcription factors, MyoD and signal transducers of and activators of transcription-3 (STAT3), were significantly increased above baseline but did not differ significantly between groups at any time point post-FAE. These findings suggest that increases in MCP-1, and possibly, MyoD and STAT3, may modulate molecular signaling in CCR2-/- mice during inflammatory and regenerative events. Furthermore, alterations in neutrophil and macrophage recruitment in CCR2-/- mice may critically alter the normal progression of downstream regenerative events in injured skeletal muscle and may direct myogenic precursor cells in the regenerating milieu toward an adipogenic phenotype.

Transplantation of Human Umbilical Cord Blood-Derived Adherent Progenitors Into the Developing Rodent Brain

The results of several recent studies suggest that human umbilical cord blood (HUCB)-derived cells have the potential to undergo neural differentiation both in vitro and in vivo. Transplantation into the embryonic ventricular zone provides a unique opportunity to study the migration and differentiation of nonneural somatic progenitor cells in response to instructive cues within the developing neuroepithelium. We isolated an adherently growing population of HUCB-derived cells expressing CD13, CD29, CD49e, CD71, CD73, CD166, Flk-1, and vimentin but lacking CD34 and CD45. On transplantation into the ventricles of embryonic day 16.5 rat embryos, these cells formed subventricular clusters that extended into a variety of host brain regions, including striatum, cortex, hippocampus, thalamus, hypothalamus, tectum, pons, and cerebellum. Donor cells identified with an antibody to human nuclei or human-specific DNA in situ hybridization maintained expression of their original marker antigens and showed no expression of the neural markers MAP2 and NeuN (neurons), GFAP (astrocytes), and CNP (oligodendrocytes). In contrast to grafted primary neural cells, they remained largely confined to subventricular clusters with little evidence for intraparenchymal integration. Thus, the neurogenic environment of the embryonic ventricular zone does not promote the elaboration of a neural phenotype in HUCB-derived cells.

Multi-germ layer lineage central nervous system repair: nerve and vascular cell generation by embryonic stem cells transplanted in the injured brain

OBJECT

To restore proper function to a damaged central nervous system (CNS) through transplantation, it is necessary to replace both neural and nonneural elements that arise from different germ layers in the embryo. Mounting evidence indicates the importance of signals related to vasculogenesis in governing neural proliferation and differentiation in early CNS development. Here, the authors examined whether embryonic stem cell (ESC)-derived progenitors can selectively generate both neural and endothelial cells after transplantation in the damaged CNS.

METHODS

Injections of 20 nmol N-methyl-D-aspartate created a unilateral striatal injury in 7-day-old rats. One week postinjury, murine ESCs, neural-induced with retinoic acid, were transplanted into the injured striatum. Histological staining, laser confocal microscopy, and transmission electron microscopy of grafted ESCs were performed 1 week posttransplantation.

CONCLUSIONS

Transplanted ESCs differentiated into neural cells, which segregated into multiple pools and formed neurons that conformed to host cytoarchitecture. The ESCs also generated endothelial cells, which integrated with host cells to form chimeric vasculature. The combination of ESC pluripotentiality and multiple germ layer differentiation provides a new conceptual framework for CNS repair.

Umbilical cord blood stem cells

The umbilical cord contains a rich source of haematopoietic stem cells that can be used to reconstitute the blood system and can easily be extracted and cryopreserved, thus allowing for the establishment of HLA-typed stem cell banks. Recently, it has been demonstrated that umbilical cord stem cells have the potential to give rise to non-haematopoietic cells, such as bone, neural and endothelial cells. It is not clear whether these multipotential cells are mesenchymal-like cells or blood cells. Currently, the number of these specialized cells capable of undergoing the differentiation process into non-haematopoietic cells is low and remains a block to the clinical development of umbilical cord stem cells for non-haematopoietic cell therapy. Further research will allow us to overcome these hurdles. This expanded potential for umbilical cord stem cells might replace embryonic stem cells and other fetal cells for some cell and tissue therapies.