Hematopoietic bone marrow cells participate in endothelial, but not epithelial or mesenchymal cell renewal in adult rats

The extent to which bone marrow (BM) contributes to physiological cell renewal is still controversial. Using the marker human placental alkaline phosphatase (ALPP) which can readily be detected in paraffin and plastic sections by histochemistry or immunohistochemistry, and in ultrathin sections by electron microscopy after pre-embedding staining, we examined the role of endogenous BM in physiological cell renewal by analysing tissues from lethally irradiated wild-type inbred Fischer 344 (F344) rats transplanted (BMT) with unfractionated BM from ALPP-transgenic F344 rats ubiquitously expressing the marker. Histochemical, immunohistochemical and immunoelectron microscopic analysis showed that the proportion of ALPP+ capillary endothelial cells (EC) profoundly increased from 1 until 6 months after BMT in all organs except brain and adrenal medulla. In contrast, pericytes and EC in large blood vessels were ALPP–. Epithelial cells in kidney, liver, pancreas, intestine and brain were recipient-derived at all time-points. Similarly, osteoblasts, chondrocytes, striated muscle and smooth muscle cells were exclusively of recipient origin. The lack of mesenchymal BM-derived cells in peripheral tissues prompted us to examine whether BMT resulted in engraftment of mesenchymal precursors. Four weeks after BMT, all haematopoietic BM cells were of donor origin by flow cytometric analysis, whereas isolation of BM mesenchymal stem cells (MSC) failed to show engraftment of donor MSC. In conclusion, our data show that BM is an important source of physiological renewal of EC in adult rats, but raise doubt whether reconstituted irradiated rats are an apt model for BM-derived regeneration of mesenchymal cells in peripheral tissues

Mesenchymal Stem Cells in a Transgenic Mouse Model of Multiple System Atrophy: Immunomodulation and Neuroprotection

Mesenchymal stem cells (MSC) are currently strong candidates for cell-based therapies. They are well known for their differentiation potential and immunoregulatory properties and have been proven to be potentially effective in the treatment of a large variety of diseases, including neurodegenerative disorders. Currently there is no treatment that provides consistent long-term benefits for patients with multiple system atrophy (MSA), a fatal late onset α-synucleinopathy. Principally neuroprotective or regenerative strategies, including cell-based therapies, represent a powerful approach for treating MSA. In this study we investigated the efficacy of intravenously applied MSCs in terms of behavioural improvement, neuroprotection and modulation of neuroinflammation in the (PLP)-αsynuclein (αSYN) MSA model.MSCs were intravenously applied in aged (PLP)-αSYN transgenic mice. Behavioural analyses, defining fine motor coordination and balance capabilities as well as stride length analysis, were performed to measure behavioural outcome. Neuroprotection was assessed by quantifying TH neurons in the substantia nigra pars compacta (SNc). MSC treatment on neuroinflammation was analysed by cytokine measurements (IL-1α, IL-2, IL-4, IL-5, IL-6, IL-10, IL-17, GM-CSF, INFγ, MCP-1, TGF-β1, TNF-α) in brain lysates together with immunohistochemistry for T-cells and microglia. Four weeks post MSC treatment we observed neuroprotection in the SNc, as well as downregulation of cytokines involved in neuroinflammation. However, there was no behavioural improvement after MSC application.To our knowledge this is the first experimental approach of MSC treatment in a transgenic MSA mouse model. Our data suggest that intravenously infused MSCs have a potent effect on immunomodulation and neuroprotection. Our data warrant further studies to elucidate the efficacy of systemically administered MSCs in transgenic MSA models

From tendon to nerve: a MSC for all seasons

The potential of mesenchymal stem cells (MSCs) to regenerate damaged tissue is well documented, as this specialized progenitor cell type exhibits superior cellular properties, and would allow medical as well as ethical limitations to be overcome. By now, MSCs have been successfully introduced in manifold experimental approaches within the newly defined realm of Regenerative Medicine. Advanced methods for in vitro cell expansion, defined induction of distinct differentiation processes, 3-dimensional culture on specific scaffold material, and tissue engineering approaches have been designed, and many clinical trials not only have been launched, but recently could be completed. To date, most of the MSC-based therapeutic approaches have been executed to address bone, cartilage, or heart regeneration; further, prominent studies have shown the efficacy of ex vivo expanded and infused MSCs to countervail graft-versus-host disease. Yet more fields of application emerge in which MSCs unfold beneficial effects, and presently, therapies that effectively ameliorate nonhealing conditions after tendon or spinal cord injury are, courtesy of scientific research, forging ahead to the clinical trial stage

Controversial Issue: Is it safe to employ mesenchymal stem cells in cell-based therapies?

The prospective clinical use of multipotent mesenchymal stromal stem cells (MSC) holds enormous promise for the treatment of a large number of degenerative and age-related diseases. However, the challenges and risks for cell-based therapies are multifaceted. The risks for patients receiving stem cells, which have been expanded in vitro in the presence of xenogenic compounds, can hardly be anticipated and methods for the culture and manipulation of “safe” MSC ex vivo are being investigated. During in vitro expansion, stem cells experience a long replicative history and are thus subject to damage from intracellular and extracellular influences. While murine MSC are prone to cellular transformation in culture, human MSC do not transform. One reason for this striking difference is that during long-term culture, human MSC finally become replicatively senescent. In consequence, this greatly restricts their proliferation and differentiation efficiency. It however also limits the yield of sufficient numbers of cells needed for therapy. Another issue is to eliminate contamination of expanding cells with serumbound pathogenic agents in order to reduce the risks for infection. A recent technical advancement, which applies human serum platelet lysates as an alternative source for growth factors and essential supplements, allows the unimpaired proliferation of MSC in the absence of animal sera. Here, we present an update regarding cellular senescence of MSC and recent insights concerning potential risks associated with their clinical use

Leptin receptor/CD295 is upregulated on primary human mesenchymal stem cells of advancing biological age and distinctly marks the subpopulation of dying cells

During the lifetime of an adult organism, stem cells face extrinsic and intrinsic aging. Mesenchymal stem cells (MSC) can be expanded in culture, and the proliferation potential of individual cell isolates before growing senescent appear to be dependent on fitness and age of the donor, respectively. To date no molecular markers are available, which specifically reflect the degree of cellular aging in a population of MSC. Employing a genomic approach, we noticed that the gene encoding leptin receptor (also termed OBR) is differentially regulated in MSC derived from aged donors as well as in MSC that had been stressed due to cultivation under hyperoxic conditions. We further observed that the leptin receptor transcript levels in primary MSC isolates are inversely correlated with the prospective number of generations that are ahead of these cells in culture, i.e., the number of population doublings that will occur in long term culture prior to cessation of growth due to replicative senescence. The MSC subpopulation, which exhibited distinctly elevated levels of leptin receptor or CD295 at the cell surface, is indistinguishable from dying cells. Considered together with the observation that primary MSC derived from healthy individuals showed proliferation capacities that declined at differentially increasing rates, we concluded that attenuation of MSC proliferation potential during aging greatly relies on the strictly increasing withdrawal of cells due to cell death

Changes of the Functional Capacity of Mesenchymal Stem Cells due to Aging or Age-Associated Disease – Implications for Clinical Applications and Donor Recruitment

In contrast to stem cells of embryonic origin, autologous tissue-specific stem cells are easier to introduce into the clinical practice. In this context however, molecular and cellular changes, which alter tissue-specific stem cell properties with age, are of particular interest, since elderly patients represent the main target group for cellbased therapies. The clinical use of mesenchymal stem cells is an emerging field, especially because this stem cell type appears to be amenable for the treatment of a large number of diseases, such as non-healing bone defects and fractures, inflammatory relieve during arthritis, and the repair of suspensory ligament tears. More than that, mesenchymal stem cells provoke effective immune suppression in the context of graft-versus-host disease. Here, we present a comprehensive overview of the recent findings with special attention to age-related changes of mesenchymal stem cells properties and the consequential impact involved on tissue regeneration and repair, together with the current perception concerning their therapeutic application potential as well as challenges associated with their clinical use