Brain as the Sea of Marrow

MICROFLUIDIC PATTERNING ENGRAVED BY THE DIRECT-WRITE CO2 LASER MICROMACHINING FOR CELL COCULTURE

Cells respond dynamically to their microenvironment with biochemical, mechanical, and topological cues. Microfluidic patterned cells and biological molecules are promising methods for evaluating the interactions among cells, signals, and substrates. In this study, direct-write CO 2 laser micromachining to engrave microchannels onto polydimethylsiloxane using 60% laser power from 12 W resource is introduced. The microfluidic channels are applied to pattern NIH 3T3 cell fibroblasts, neuron cells from the brain tissue of embryonic mice and mesenchymal stem cells (MSCs) from mice expressing a green fluorescent protein. The patterned cells are organized at a width of 500 μm and separated by a width of 600 μm. MSCs and neuron cells were microfluidic patterned and cocultured at the same time to provide access for evaluating transdifferentiated MSCs after coculture with neuron cells. We study microfluidic patterned cells with laser engraved channels to evaluate the migration of proliferated cells, cross-talk between adjacent cells, induction from secreted factors, and documented the plasticity of cell behavior on the well-defined boundaries of seeded cells.

Evaluation of transdifferentiation from mesenchymal stem cells to neuron-like cells using microfluidic patterned co-culture system

We design a microfluidic patterned co-culture system for mouse mesenchymal stem cells (mMSCs) and neural cells to demonstrate the paracrine effects produced by the neural cells in facilitating the transdifferentiation from mMSCs to neuron-like cells. Neural cells and mMSC are orderly patterned in the microfluidic co-culturing system without direct cell contact. This configuration provides us to calculate the percentage of neural marker transdifferentiated by mMSCs easily. We obtain higher transdifferentiated ratio of mMSC in the microfluidic co-culturing system (beta III tubulin: 67%; glial fibrillary acidic protein (GFAP): 86.2%) as compared with the traditional transwell co-culturing system (beta III tubulin: 59.8%; GFAP: 52.0%), which is similar to the spontaneous neural marker expression in the undifferentiated MSCs (beta III tubulin: 47.5%; GFAP: 60.1%). Furthermore, mMSCs expressing green fluorescent protein and neural cells expressing red fluorescent protein were also used in our co-culture system to demonstrate the rarely occurring or observed cell fusion phenomenon. The results show that the co-cultured neural cells increased the transdifferentiation efficiency of mMSCs from soluble factors secreted by neural cells.

EGF and bFGF pre-treatment enhances neural specification and the response to neuronal commitment of MIAMI cells

AIMS

Multipotent mesenchymal stromal cells raise great interest for regenerative medicine studies. Some MSC subpopulations have the potential to undergo neural differentiation, including marrow isolated adult multilineage inducible (MIAMI) cells, which differentiate into neuron-like cells in a multi-step neurotrophin 3-dependent manner. Epidermal and basic fibroblast growth factors are often used in neuronal differentiation protocols for MSCs, but with a limited understanding of their role. In this study, we thoroughly assessed for the first time the capacity of these factors to enhance the neuronal differentiation of MSCs.

MATERIALS AND METHODS

We have characterized MIAMI cell neuronal differentiation program in terms of stem cell molecule expression, cell cycle modifications, acquisition of a neuronal morphology and expression of neural and neuronal molecules in the absence and presence of an EGF-bFGF pre-treatment.

RESULTS

EGF-bFGF pre-treatment down-regulated the expression of stemness markers Oct4A, Notch1 and Hes5, whereas neural/neuronal molecules Nestin, Pax6, Ngn2 and the neurotrophin receptor tyrosine kinase 1 and 3 were up-regulated. During differentiation, a sustained Erk phosphorylation in response to NT3 was observed, cells began to exit from the cell cycle and exhibit increased neurite-like extensions. In addition, neuronal β3-tubulin and neurofilament expression was increased; an effect mediated via the Erk pathway. A slight pre-oligodendrocyte engagement was noted, and no default neurotransmitter phenotype was observed. Overall, mesodermal markers were unaffected or decreased, while neurogenic/adipogenic PPARγ2 was increased.

CONCLUSION

EGF and bFGF pre-treatment enhances neural specification and the response to neuronal commitment of MIAMI cells, further increasing their potential use in adult cell therapy of the nervous system.

Electrophysiological and contractile evidence of the ability of human mesenchymal stromal cells to correct vascular malfunction in rats after ionizing irradiation

The effect of intravenous administration of human mesenchymal stromal stem cells (hMSC) has been evaluated by means of large-conductance calcium-dependent potassium channel (BK(Ca)) activity measurements in thoracic aorta smooth muscle cells (SMC) obtained from non-fatal whole-body irradiated rats, using the patch clamp technique in whole-cell modification, and the standard acetylcholine (ACh) test to evaluate functional endothelium integrity using SM contractile recordings. Myofilament calcium sensitivity was estimated using simultaneous contractile recordings versus [Ca(2+)](i). Arterial blood was measured in intact and irradiated rats before and after hMSC administration. Stimulation of isolated SMC from the control group of animals with depolarizing voltage steps showed that outward K(+) currents sensitive to the BK(Ca) inhibitor paxilline were expressed. Outward currents in SMC obtained from irradiated animals were significantly reduced on the 30th day of post-irradiation. Irradiation led to a significant elevation in arterial blood pressure and reduced ACh-induced relaxation responses in irradiated rats as compared with the control group. Simultaneous measurements of contractile force and [Ca(2+)](i) showed that myofilament Ca(2+) sensitivity had increased following irradiation. Intravenously injected hMSC effectively restored BK(Ca) current and the amplitude of ACh-induced endothelium-dependent vasodilatation in vascular tissues obtained from post-irradiated rats. SMC obtained from irradiated rats treated with hMSC demonstrated a significantly increased paxilline-sensitive component of outward potassium currents, indicating that BK(Ca) activity had been restored. hMSC administration normalized increased blood pressure and myofilament Ca(2+) sensitivity in irradiated animals. When administered to healthy rats, hMSC were without effects on either of these. This study does not provide any immunohistochemical proof of hMSC engraftment in the host rats. PCR analysis showed that hMSCs were negative for hematopoietic cell markers and positive for hMSC markers. There were no clinical signs of graft-versus-host disease throughout the experimental period of 30 days. The data obtained suggest that hMSC demonstrate a clearly expressed ability to normalize vascular function damaged following irradiation, i.e. to reduce an elevated arterial blood pressure and myofilament Ca(2+) sensitivity, and to repair BK(Ca) function and endothelium-dependent relaxation in vascular tissues obtained from irradiated animals. Thus, hMSC seem to be worthwhile therapeutic approach in cases of ionizing irradiation accident or radiation beam therapy.

Effects of plating density and culture time on bone marrow stromal cell characteristics

OBJECTIVE

Bone marrow stromal cells (MSC) are multipotent adult stem cells that have emerged as promising candidates for cell therapy in disorders including cardiac infarction, stroke, and spinal cord injury. While harvesting methods used by different laboratories are relatively standard, MSC culturing protocols vary widely. This study is aimed at evaluating the effects of initial plating density and total time in culture on proliferation, cell morphology, and differentiation potential of heterogeneous MSC cultures and more homogeneous cloned subpopulations.

MATERIALS AND METHODS

Rat MSC were plated at 20, 200, and 2000 cells/cm(2) and grown to 50% confluency. The numbers of population doublings and doubling times were determined within and across multiple passages. Changes in cell morphology and differentiation potential to adipogenic, chondrogenic, and osteogenic lineages were evaluated and compared among early, intermediate, and late passages, as well as between heterogeneous and cloned MSC populations.

RESULTS

We found optimal cell growth at a plating density of 200 cells/cm(2). Cultures derived from all plating densities developed increased proportions of flat cells over time. Assays for chondrogenesis, osteogenesis, and adipogenesis showed that heterogeneous MSC plated at all densities sustained the potential for all three mesenchymal phenotypes through at least passage 5; the flat subpopulation lost adipogenic and chondrogenic potential.

CONCLUSION

Our findings suggest that the initial plating density is not critical for maintaining a well-defined, multipotent MSC population. Time in culture, however, affects cell characteristics, suggesting that cell expansion should be limited, especially until the specific characteristics of different MSC subpopulations are better understood.

Preparation of neural progenitors from bone marrow and umbilical cord blood

The bone marrow is clearly much more than a reservoir of stem cells that repopulates blood cell lineages throughout life. The marrow also contains nonhematopoietic stem cells, which are much more versatile than previously appreciated. These nonhematopoietic stem/progenitor cells are found in the bone marrow stromal cell (BMSC) population. BMSCs also are known as colony-forming unit fibroblasts and mesenchymal stem cells (MSCs). MSCs also can be generated from umbilical cord blood and other tissues. MSCs have been shown to express properties of neuroectodermal cells in vitro by many researchers and in vivo after transplantation into the brain and spinal cord. Many investigators have developed variations on the original method described 6 years ago for the preparation of neural progenitors from BMSCs. We bring up to date the materials and procedures used to prepare BMSCs from bone marrow and from human umbilical cord blood for the induction of neural progenitor cells and subsequent differentiation into neurons and glia.

Combining motor training with transplantation of rat bone marrow stromal cells does not improve repair or recovery in rats with thoracic contusion injuries

Previous studies have demonstrated that either transplantation of bone marrow stromal cells (MSC) or physical exercise regimens can elicit limited functional recovery following spinal cord injury, presumably through different mechanisms. The present study examined whether transplantation of MSC derived from transgenic Fischer alkaline phosphatase (AP) rats, in combination with exercise, would have synergistic effects leading to recovery of function that is greater than either alone. Adult female Sprague-Dawley rats received a moderate thoracic contusion injury and were divided into three groups: operated controls (Op-Control), MSC transplant recipients (MSC), and MSC transplant recipients plus exercise (MSC+Ex). Nine days after contusion, a Vitrogen matrix +/-one million MSC was injected into the lesion site in all animals. Immunosuppression with high doses of Cyclosporine A, required for MSC survival, was provided for all animals. Passive hindlimb exercise on motorized bicycles was applied 1 h/day, 3 days/week to the MSC+Ex group. A battery of behavioral tests was performed weekly to assess motor and sensory functions in all 3 groups for 12 weeks. Morphological evaluation included MSC survival, evidence of axonal growth into grafts, phenotypic analysis of MSC, and lesion/transplant size. The weight of the medial gastrocnemius muscle, a hindlimb muscle activated during stance, was used to identify extent of atrophy. No differences in motor recovery were found among the three groups. MSC survived 3 months after transplantation, indicating that the immunosuppression treatment was successful. The extent of survival was variable, and there was no correlation between MSC survival and behavioral scores. The matrix persisted, filling the lesion cavity, and some axons grew into the lesion/matrix but to a similar extent in all groups. There was no difference in lesion/matrix size among groups, indicating no neuroprotective effect on the host provided by the treatments. Immunocytochemical analysis provided no evidence that MSC differentiated into neurons, astrocytes or oligodendrocytes. Muscle mass of the medial gastrocnemius was diminished in the Op-Control group indicating significant atrophy, but was partially preserved in both the MSC and MSC+Ex groups. Our results indicate that combining the beneficial effects of rat MSC and this exercise protocol was not sufficient to enhance behavioral recovery.

Neural stem-like cell line derived from a nonhematopoietic population of human umbilical cord blood

The ability of stem and progenitor cells to proliferate and differentiate into other lineages is widely viewed as a characteristic of stem cells. Previously, we have reported that cells from a CD34(-) (nonhematopoietic) adherent subpopulation of human cord blood can acquire a feature of multipotential neural progenitors in vitro. In the present study, using these cord blood-derived stem cells, we have established a clonal cell line termed HUCB-NSCs (human umbilical cord blood-neural stem cells) that expresses several neural antigens and has been grown in culture for more than 60 passages. During this time, HUCB-NSCs retained their growth rate, the ability to differentiate into neuronal-, astrocyte-, and oligodendrocyte-like cells and displayed a stable karyotype. DNA microarray analysis of HUCB-NSCs revealed enhanced expression of selected genes encoding putative stem and progenitor cell markers when compared to other mononuclear cells. dBcAMP-induced HUCBNSCs were further differentiated into more advanced neuronal cells. This is the first report of the establishment and characterization of a nontransformed HUCB-NSC line that can be grown continuously in a monolayer culture and induced to terminal differentiation. These cells should further our understanding of the regulatory mechanisms involved in NSC self-renewal and differentiation.

Recovery of function following grafting of human bone marrow-derived stromal cells into the injured spinal cord

This study evaluates functional recovery after transplanting human bone marrow-derived stromal cells (BMSCs) into contusion models of spinal cord injury (SCI). The authors used a high-throughput process to expand BMSCs and characterized them by flow cytometry, ELISA, and gene expression. They found that BMSCs secrete neurotrophic factors and cytokines with therapeutic potential for cell survival and axon growth. In adult immune-suppressed rats, mild, moderate, or severe contusions were generated using the MASCIS impactor. One week following injury, 0.5 to 1 x 106 BMSCs were injected into the lesioned spinal cord; control animals received vehicle injection. Biweekly behavioral tests included the Basso, Beattie, and Bresnahan Locomotor Rating Scale (BBB), exploratory rearing, grid walking, and thermal sensitivity. Animals receiving moderate contusions followed by BMSC grafts showed significant behavioral recovery in BBB and rearing tests when compared to controls. Animals receiving BMSC grafts after mild or severe contusion showed trends toward improved recovery. Immunocytochemistry identified numerous axons passing through the injury in animals with BMSC grafts but few in controls. BMSCS were detected at 2 weeks after transplantation; however, at 11 weeks very few grafted cells remained. The authors conclude that BMSCs show potential for repairing SCI. However, the use of carefully characterized BMSCs improved transplantation protocols ensuring BMSC, survival, and systematic motor and sensory behavioral testing to identify robust recovery is imperative for further improvement.

Neural transdifferentiation of mesenchymal stem cells--a critical review

The classic concept of stem cell differentiation can be illustrated as driving into a series of one-way streets, where a given stem cell through generations of daughter cells becomes correspondingly restricted and committed towards a definitive lineage with fully differentiated cells as end points. According to this concept, tissue-derived adult stem cells can only give rise to cells and cell lineages found in the natural, specified tissue of residence. During the last few years it has, however, been reported that under certain experimental conditions adult stem cells may lose their tissue or germ layer-specific phenotypes and become reprogrammed to transdifferentiate into cells of other germ layers and tissues. The transdifferentiation process is referred to as "stem cell plasticity". Mesenchymal stem cells, present in various tissues, including bone marrow, have--besides differentiation into bone, cartilage, smooth muscle and skeletal muscle--also been reported to transdifferentiate into skin, liver and brain cells (neurons and glia). Conversely, neural stem cells have been reported to give rise to blood cells. The actual occurrence of transdifferentiation is currently much debated, but would have immense clinical potential in cell replacement therapy and regenerative medicine. Controlled neural differentiation of human mesenchymal stem cells might thus become an important source of cells for cell therapy of neurodegenerative diseases, since autologous adult mesenchymal stem cells are more easily harvested and effectively expanded than corresponding neural stem cells. This article provides a critical review of the reports of neural transdifferentiation of mesenchymal stem cells, and proposes a set of criteria to be fulfilled for validation of transdifferentiation.

Axon growth and recovery of function supported by human bone marrow stromal cells in the injured spinal cord exhibit donor variations

Bone marrow stromal cells (MSC) are non-hematopoietic support cells that can be easily derived from bone marrow aspirates. Human MSC are clinically attractive because they can be expanded to large numbers in culture and reintroduced into patients as autografts or allografts. We grafted human MSC derived from aspirates of four different donors into a subtotal cervical hemisection in adult female rats and found that cells integrated well into the injury site, with little migration away from the graft. Immunocytochemical analysis demonstrated robust axonal growth through the grafts of animals treated with MSC, suggesting that MSC support axonal growth after spinal cord injury (SCI). However, the amount of axon growth through the graft site varied considerably between groups of animals treated with different MSC lots, suggesting that efficacy may be donor-dependent. Similarly, a battery of behavioral tests showed partial recovery in some treatment groups but not others. Using ELISA, we found variations in secretion patterns of selected growth factors and cytokines between different MSC lots. In a dorsal root ganglion explant culture system, we tested efficacy of conditioned medium from three donors and found that average axon lengths increased for all groups compared to control. These results suggest that human MSC produce factors important for mediating axon outgrowth and recovery after SCI but that MSC lots from different donors vary considerably. To qualify MSC lots for future clinical application, such notable differences in donor or lot-lot efficacy highlight the need for establishing adequate characterization, including the development of relevant efficacy assays.

Induction of bone marrow stromal cells to neurons: differentiation, transdifferentiation, or artifact?

Differentiation of stem cells toward a neuronal lineage normally involves a gradually progressive restriction in developmental potential and is regulated by a diverse set of specific and temporally precise genetic events. However, recent studies have indicated that both rodent and human bone marrow stromal cells (MSCs) can be rapidly (within minutes to hours) induced to differentiate into neurons in vitro by relatively simple chemical means (using beta-mercaptoethanol [BME] or dimethylsulfoxide [DMSO] and butylated hydroxyanisol [BHA]; Woodbury et al. [ 2000] J. Neurosci. Res. 61:364-370). The ability to transdifferentiate an easily accessible cell source into neurons could have substantial potential for promoting neural repair. We therefore explored the potential of simple chemical methods to transdifferentiate other cell types, including primary rat fibroblasts, primary human keratinocytes, HEK293 cells, rat PC-12 cells, and as positive control rat bone marrow stromal (BMS) cells. Surprisingly, all cells except for keratinocytes adopted at least partial "neuron-like" pyramidal cell morphology with fine-cellular extensions resembling neurites upon stimulation with BME or DMSO/BHA. However, time-lapse microscopy indicated that the chemical exposure of MSCs did not result in new neurite growth but rather cellular shrinkage, with retraction of the majority of existing cell extensions, leaving only few, fine neurite-like processes. To determine whether the chemically induced transdifferentiation resulted from simple cellular toxicity, MSCs were exposed to various stressors, including detergents, high-molarity sodium chloride, and extremes of pH. In all cases, cellular shrinkage and adoption of pseudoneuronal morphology were observed. Concomitantly with cellular shrinkage, apparent increases in immunolabeling for the neuronal markers NSE and NeuN were detected in the cell soma that could not be confirmed by RT-PCR. Furthermore, blockade of protein synthesis with cycloheximide did not prevent cells from adopting "neuron-like" morphology after chemical induction. Thus, morphological changes and increases in immunolabeling for certain cellular markers upon "chemical induction" of MSCs are likely the result of cellular toxicity, cell shrinkage, and changes in the cytoskeleton and do not represent regulated steps in a complicated cellular differentiation process.