Pluripotent hemopoietic stem cells in mice and humans

Recruitment by SDF-1α of CD34-positive cells involved in sciatic nerve regeneration

Object

Increased integration of CD34+ cells in injured nerve significantly promotes nerve regeneration, but this effect can be counteracted by limited migration and short survival of CD34+ cells. SDF-1α and its receptor mediate the recruitment of CD34+ cells involved in the repair mechanism of several neurological diseases. In this study, the authors investigate the potentiation of CD34+ cell recruitment triggered by SDF-1α and the involvement of CD34+ cells in peripheral nerve regeneration.

Methods

Peripheral nerve injury was induced in 147 Sprague-Dawley rats by crushing the left sciatic nerve with a vessel clamp. The animals were allocated to 3 groups: Group 1, crush injury (controls); Group 2, crush injury and local application of SDF-1α recombinant proteins; and Group 3, crush injury and local application of SDF-1α antibody. Electrophysiological studies and assessment of regeneration markers were conducted at 4 weeks after injury; neurobehavioral studies were conducted at 1, 2, 3, and 4 weeks after injury. The expression of SDF-1α, accumulation of CD34+ cells, immune cells, and angiogenesis factors in injured nerves were evaluated at 1, 3, 7, 10, 14, 21, and 28 days after injury.

Results

Application of SDF-1α increased the migration of CD34+ cells in vitro, and this effect was dose dependent. Crush injury induced the expression of SDF-1α, with a peak of 10–14 days postinjury, and this increased expression of SDF-1α paralleled the deposition of CD34+ cells, expression of VEGF, and expression of neurofilament. These effects were further enhanced by the administration of SDF-1α recombinant protein and abolished by administration of SDF-1α antibody. Furthermore, these effects were consistent with improvement in measures of neurological function such as sciatic function index, electrophysiological parameters, muscle weight, and myelination of regenerative nerve.

Conclusions

Expression of SDF-1α facilitates recruitment of CD34+ cells in peripheral nerve injury. The increased deposition of CD34+ cells paralleled significant expression of angiogenesis factors and was consistent with improvement of neurological function. Utilization of SDF-1α for enhancing the recruitment of CD34+ cells involved in peripheral nerve regeneration may be considered as an alternative treatment strategy in peripheral nerve disorders.

Biological treatment strategies for disc degeneration: potentials and shortcomings

Recent advances in molecular biology, cell biology and material sciences have opened a new emerging field of techniques for the treatment of musculoskeletal disorders. These new treatment modalities aim for biological repair of the affected tissues by introducing cell-based tissue replacements, genetic modifications of resident cells or a combination thereof. So far, these techniques have been successfully applied to various tissues such as bone and cartilage. However, application of these treatment modalities to cure intervertebral disc degeneration is in its very early stages and mostly limited to experimental studies in vitro or in animal studies. We will discuss the potential and possible shortcomings of current approaches to biologically cure disc degeneration by gene therapy or tissue engineering. Despite the increasing number of studies examining the therapeutic potential of biological treatment strategies, a practicable solution to routinely cure disc degeneration might not be available in the near future. However, knowledge gained from these attempts might be applied in a foreseeable future to cure the low back pain that often accompanies disc degeneration and therefore be beneficial for the patient.

Fibronectin and laminin enhance engraftibility of cultured hematopoietic stem cells

To test the hypothesis that extracellular matrix (ECM) components maintain stem cell property, murine bone marrow (BM) cells were expanded in fibronectin and laminin coated plate in the presence of cytokines. We observed significant phenotypic and functional improvement of expanded cells. In 10 days, 800-fold expansion of colony-forming unit-granulocyte erythrocyte monocyte megakaryocyte (CFU-GEMM) was observed in the cultured cells. No apparent activation of cell cycle was observed, but CD29 and very late antigen-4 (VLA-4) expression was increased, as compared to the normal BM cells. A fraction of the expanded cells became verapamil sensitive, suggesting upregulation of multi-drug resistant gene(s), as found in the primitive hematopoietic stem cells (HSCs). Competitive repopulation assay confirmed that HSCs compartment was amplified during culture. Overall, our study clearly demonstrated that ex vivo culture of murine HSCs in the presence of fibronectin and laminin resulted in expansion of primitive stem cells and improvement in the marrow engraftibility.

Increased mobilization of c-kit+ Sca-1+ Lin- (KSL) cells and colony-forming units in spleen (CFU-S) following de novo formation of a stem cell niche depends on dynamic, but not stable, membranous ossification

Stem cells are thought to inhabit in a unique microenvironment, known as "niche," in which they undergo asymmetric cell divisions that results in reproducing both stem cells and progenies to maintain various tissues throughout life. The cells of osteoblastic lineage have been identified as a key participant in regulating the number of hematopoietic stem cells (HSCs). HSCs receive their regulatory messages from the microenvironment in the bone marrow. This would account for a reason why the localization of hematopoiesis is usually restricted in the bone marrow. To clarify the above possibility we employed a cell implantation-based strategy with a unique osteoblast cell line (KUSA-A1) derived from a C3H/He mouse. The implantation of KUSA-A 1 cells resulted in the generation of ectopic bones in the subcutaneous tissues of the athymic BALB/c nu/nu mice. Subsequently the mice obtained a greater amount of the bone marrow than normal mice, and they showed an increased number of HSCs. These results indicate that the newly generated osteoblasts-derived ectopic bones are responsible for the increase in the number of the HSC population. Furthermore, the increased number of HSCs directly correlates with both the magnitude of dynamic osteogenic process and the size of the newly generated bone or "niche."

CD34+ corneal stromal cells are bone marrow-derived and express hemopoietic stem cell markers

Previous studies have suggested that corneal stromal keratocytes express the CD34 antigen. We wished to investigate CD34 antigen expression in normal mouse cornea using dual- and triple-staining techniques. Whole-mount preparations of mouse and rat corneas were examined with confocal microscopy using single, dual, or triple immunostaining to study their morphology, phenotype, and distribution. Single-cell suspensions from normal mouse corneas were also prepared and analyzed by flow cytometry. After short-term culture of corneal stromal explants, nonadherent cells were harvested and cytospins were prepared and stained for different markers. Combined staining for F-actin and leukocyte differentiation markers clearly showed that the corneal stroma contains a population of CD45(+) resident bone marrow-derived cells, whereas most cells were CD45-F-actin(+) keratocytes. A significant proportion (two thirds) of CD45(+) cells in the normal corneal stroma expressed CD34(+), whereas no CD45(-) cells (i.e., keratocytes) coexpressed CD34. In addition, CD34(+) cells were CD11c(-) and CD11b(+). Fewer than 10% of the CD34(+) cells also coexpressed Sca-1(+), but no CD34(+) cells coexpressed major histocompatibility complex (MHC) class II(+). In contrast, the remaining population of CD45(+)CD34(-) cells in the corneal stroma expressed CD11b, MHC class II(+) but not CD11c and were found mostly in the anterior and peripheral part of stroma. These cells are in intimate contact with corneal keratocytes, which stained only for F-actin and were negative for all leukocyte markers. Very few CD45(+) cells expressed the B220 marker, suggesting a plasmacytoid dendritic cell phenotype. Flow cytometry analyses confirmed the morphometric data showing that 68% of CD45(+) cells coexpress CD34 and CD11b, whereas 22% are CD11b(+)CD34(-).We conclude that the normal mouse cornea contains two populations of bone marrow-derived leukocytes, both of which are distinct from stromal keratocytes. The larger population resembles CD34(+) hemopoietic stem cells, whereas the smaller population are CD34(-)CD11b(+) MHC class II(+) macrophages. A very small percentage comprises plasmacytoid dendritic cells.

Adult human hematopoietic stem cells produce neurons efficiently in the regenerating chicken embryo spinal cord

Hematopoietic stem cells (HSCs) have been proposed as a potential source of neural cells for use in repairing brain lesions, but previous studies indicate a low rate of neuronal differentiation and have not provided definite evidence of neuronal phenotype. To test the neurogenic potential of human HSCs, we implanted CD34+ HSCs from adult human bone marrow into lesions of the developing spinal cord in the chicken embryo and followed their differentiation by using immunohistochemistry, retrograde labeling, and electrophysiology. We find that human cells derived from the implanted population express the neuronal markers NeuN and MAP2 at substantially higher rates than previously reported. We also find that these cells exhibit neuronal cytoarchitecture, extend axons into the ventral roots or several segments in length within the spinal white matter, are decorated with synaptotagmin+ and GABA+ synaptic terminals, and exhibit active membrane properties and spontaneous synaptic potentials characteristic of functionally integrated neurons. Neuronal differentiation is accompanied by loss of CD34 expression. Careful examination with confocal microscopy reveals no signs of heterokaryons, and human cells never express a chicken-specific antigen, suggesting that fusion with host chicken cells is unlikely. We conclude that the microenvironment in the regenerating spinal cord of the chicken embryo stimulates substantial proportions of adult human HSCs to differentiate into full-fledged neurons. This may open new possibilities for a high-yield production of neurons from a patient's own bone marrow.

Biologic strategies for the therapy of intervertebral disc degeneration

Recent advances in tissue engineering have led to promising new approaches for the biologic treatment of disc degeneration. At present, there is no effective therapy for disc degeneration, a condition which results in large healthcare and socio-economic costs. This article will examine the current approaches used in biologic therapies for disc degeneration, including cell-based tissue engineering, gene therapy and the application of mesenchymal stem cells, and discuss their therapeutic potential, as demonstrated in animal models and experimental studies to date.

Mixed bone marrow or mixed stem cell transplantation for prevention or treatment of lupus-like diseases in mice

Scientific analyses fortified by interpretations of immunodeficiency diseases as 'experiments of nature' have revealed the specific immune systems to be comprised of T cells subserving cell-mediated immunities plus B cells and plasma cells which produce and secrete antibodies. These two separate cellular systems regularly interact with each other to produce a coordinated defense which permits mammals to live within a sea of microorganisms that threaten the integrity and the survival of individuals. We have shown that bone marrow transplantation (BMT) can be used as a form of cellular engineering to construct or reconstruct the immune systems and cure otherwise fatal severe combined immunodeficiency. When severe aplastic anemia complicated the first BMT which was performed to cure a fatal severe combined immunodeficiency, a second BMT cured for the first time a complicating severe aplastic anemia. Subsequently, BMT has been used effectively to treat some 75 otherwise fatal diseases such as resistant leukemias, lymphomas, inborn errors of metabolism, and genetic anomalies of the hematopoietic development such as sickle cell anemia, thalassemia, congenital neutropenias, and many other diseases. More recently, we have employed BMT in mice both to cure and cause autoimmunities, and, together, these experiments showed that autoimmunities actually reside in the hematopoietic stem cells. We have also found that mixed BMT or mixed hematopoietic stem cell transplantation (HSCT) can be used to prevent and cure the most complex autoimmunities such as those occurring in BXSB mice and in (NZW x BXSB)F1 W/BF1 mice. Untreated, the former develop fulminating lethal glomerulonephritis plus numerous humoral autoimmunities. Mice of the (W/B)F1 strain develop autoimmune thrombocytopenic purpura, coronary vascular disease with myocardial infarction, glomerulonephritis, and numerous autoantibodies. All of these abnormalities are prevented or cured by mixed syngeneic (autoimmune) plus allogeneic (normal healthy) BMT or mixed peripheral blood HSCT. Thus, the most complex autoimmune diseases can be prevented or cured in experimental animals by mixed syngeneic plus allogeneic BMT or HSCT which produce stable mixed chimerism as a form of cellular engineering.

Phenotypic and immunologic characteristics of docetaxel-mobilized peripheral blood stem cells in mice

Effective mobilization of peripheral blood stem cells is vital for transplantation of patients after high-dose chemotherapy and provides a convenient source of stem cells for genetic engineering and other studies, but optimal mobilization strategies have not been defined. Recent studies show that in the presence of recombinant human granulocyte colony-stimulating factor (rhG-CSF), docetaxel (DXT) is an effective mobilization agent. This study was performed to evaluate the phenotype and immunologic properties of DXT-mobilized stem cells. Administration of DXT + rhG-CSF to normal C57Bl/6 mice induced a 75-fold increase in blood hematopoietic progenitors and a significant increase in both CD3(+) (T cell) and DX5(+) [natural killer (NK)] cells when compared to untreated mice. The cytotoxicity of DXT + rhG-CSF-mobilized cell populations against YAC-1 and B16F10 cell lines was not significantly different from that of untreated mice. When compared to cyclophosphamide + rhG-CSF, DXT + rhG-CSF-mobilized cell populations yielded a greater number of T and NK cells, with significantly higher cytotoxic effector function. These results suggest that DXT + rhG-CSF-mobilized PBSCs retain potent immunologic capacity with a high number of the functional cellular subsets than those normally present in peripheral blood, which may be important in maintaining the antitumor immunity after transplantation.

Recent advances in disc cell biology

STUDY DESIGN

There have been many advances over the past decade in understanding and experimentally modulating biologic aspects of intervertebral disc cell function. An overview of the current state of this biologic research is presented.

OBJECTIVES

To provide clinicians with a review of important recent advances in biologic studies of the disc and their implications for potential disc therapies.

SUMMARY OF BACKGROUND DATA

Historically, anatomic, biochemical, radiologic, and biomechanical studies of the intervertebral disc formed the foundation on which our understanding of disc function was built. Magnetic resonance imaging techniques that allowed viewing of soft tissue components of the disc further advanced imaging capabilities.

METHODS

Recent publications are reviewed.

RESULTS

Experimental approaches over the past decade have enabled researchers to look more critically at disc cell function. This is important because disc cell function produces the extracellular matrix components of the disc, which, in turn, shape the disc's subsequent physiologic and biomechanical functions. New approaches to the study of disc cell function, methods to manipulate disc cells, studies of intact discs and disc nutrition, vertebral endplate structure and function, tissue engineering, gene therapy, and the potential of stem cells in disc therapy are reviewed and discussed.

CONCLUSIONS

Many believe that disc degeneration has a cellular basis. New research is helping us better understand healthy, aging, and degenerating discs. Modern methods to manipulate and modulate disc cell function open exciting and challenging new therapeutic possibilities for future biologic treatments of disc degeneration.