The lack of the influence of various species of Mycoplasma spp. on canine semen quality.

Mycoplasmas colonize fish, reptiles, birds and mammals, being commensals or causing diseases, sometimes severe in ruminants, swine, poultry, or wildlife animals. So far, 15 species of canine Mycoplasma spp. have been described. Conflicting results have been presented regarding the pathogenicity of Mycoplasma spp. Although many virulence factors of these bacteria have been described, they still require attention. The main aim of our study was to evaluate the presence of known canine Mycoplasmas in the male reproductive tract of clinically healthy dogs. The second aim was to check if Mycoplasma spp. cause any abnormalities in semen quality that could have further consequences and to propose the schemes for managing the carriers. 83.3% of examined dogs were Mycoplasma spp. -positive dogs, and most of them were the carriers of more than one species. Six dogs had azoospermic ejaculates. The total spermatozoa numbers were similar in Mycoplasma -positive and negative groups. Motility was slightly higher in Mycoplasma spp.-negative group, but the difference was not statistically significant. There was no significant difference in semen characteristics between the carriers and Mycoplasma spp.-negative dogs. Neither the individual species nor the number of species strains had a significant effect on sperm morphological parameters as well as viability. Semen quality parameters are not correlated with the species found on the prepuce. Over 70% Mycoplasma spp.- positive dogs have more than one species of this bacteria. Despite finding mycoplasmas in azoospermic dogs, we suggest that they were not the cause of infertility. Mycoplasma spp. could be a part of normal microbiota in canine prepuce in individuals without any clinical signs.

Stability of Pattern Formation in Systems with Dynamic Source Regions.

We explain the principles of gene expression pattern stabilization in systems of interacting, diffusible morphogens, with dynamically established source regions. Using a reaction-diffusion model with a step-function production term, we identify the phase transition between low-precision indeterminate patterning and the phase in which a traveling, well-defined contact zone between two domains is formed. Our model analytically explains single- and two-gene domain dynamics and provides pattern stability conditions for all possible two-gene regulatory network motifs.

Small-molecule inhibitor - tyrphostin AG1296 regulates proliferation, survival and migration of rhabdomyosarcoma cells.

Rhabdomyosarcoma (RMS) is the most commonly occurring malignant soft tissue tumor in children. Despite improving its treatment methods, the current outcome in the advanced stages of this tumor is not satisfactory. RMS cells are characterized by abnormal cellular signaling due to the changes in the activity of the tyrosine kinases. Thus, substances blocking the mitogenic signal transmitted by receptors with tyrosine kinase activity raise hopes for inhibition of the uncontrolled cell growth. In this study, we examined the anticancer activity of tyrphostin AG1296, a tyrosine kinase inhibitor that binds to the intracellular domain of the PDGF (platelet-derived growth factor) receptor in human RMS alveolar and embryonal cell lines. We have discovered that tyrphostin AG1296 completely inhibited cell proliferation and effectively inhibited cell viability. Tyrphostin AG1296 induced apoptosis of the RMS cells and significantly inhibited their migration. Additionally, investigated inhibitor slightly inhibited expression of AKT and phosphorylation of ERK in alveolar RMS cells. Importantly, the inhibitor exerted also potent effects on the nanomechanical properties and cytoskeleton organization of RMS cells. To conclude, tyrphostin AG1296 is a promising compound in the treatment of alveolar RMS. Undoubtedly, a better knowledge of receptor pathomechanism of tyrosine kinases may contribute to developing new, more effective ways of RMS treatment.

Effective one-component model of binary mixture: molecular arrest induced by the spatially correlated stochastic dynamics.

Spatially correlated noise (SCN), i.e. the thermal noise that affects neighbouring particles in a similar manner, is ubiquitous in soft matter systems. In this work, we apply the over-damped SCN-driven Langevin equations as an effective, one-component model of the dynamics in dense binary mixtures. We derive the thermodynamically consistent fluctuation-dissipation relation for SCN to show that it predicts the molecular arrest resembling the glass transition, i.e. the critical slow-down of dynamics in the disordered phases. We show that the mechanism of singular dissipation is embedded in the dissipation matrix, accompanying SCN. We are also able to identify the characteristic length of collective dissipation, which diverges at critical packing. This novel physical quantity conveniently describes the difference between the ergodic and non-ergodic dynamics. The model is fully analytically solvable, one-dimensional and admits arbitrary interactions between the particles. It qualitatively reproduces several different modes of arrested disorder encountered in binary mixtures, including e.g. the re-entrant arrest. The model can be effectively compared to the mode coupling theory.

Microwave-assisted synthesis and characterization of novel chitosan-based biomaterials for pelvic organ prolapse treatment.

Pelvic organ disorders affect up to one in four women in the United States. The prevalence of pelvic organ prolapse (POP) is increasing with each year, particularly in the setting of prolonged life expectancy and an aging population. Current treatment approaches, including polypropylene monofilaments are associated with numerous painful and worrisome side-effects. Therefore, scientists are looking for new solutions. A promising alternative to the current treatment is tissue engineering, which can be utilized to re-create support to the vagina and pelvic organs. Tissue engineering requires the use of three-dimensional scaffolds, derived from biocompatible materials. Chitosan is a natural polymer, obtained from shellfish exoskeletons. It is known for its biodegradability, lack of cytotoxicity and non-pyrogenicity. Due to the presence of free hydroxyl and amino groups, it may undergo various modifications. In this paper, we describe a new type of chitosan-based biomaterials, which can be used as a new alternative scaffold that may provide support to prolapse organs. The chitosan scaffold was obtained under microwave radiation using multifunctional amino and organic acids. We discuss the scaffold's characteristics, with an emphasis on its chemical structure and morphology. Fourier transform infrared spectroscopy (FT-IR) analysis confirmed cross-linking processes with preservation of free amino groups. Moreover, mechanical durability, the stability and swelling ability of the scaffolds in a simulated body fluid were investigated. All of the prepared scaffolds demonstrated very good antioxidant activity and biodegradability. Importantly, the biocompatibility of chitosan scaffolds was examined on human vaginal VK2/E6E7 cell line. No evidence of toxicity was documented, and the cells maintained their presence on the studied materials. These results allude to the lack of toxicity of the scaffolds, and indicate that chitosan-based scaffold should be further investigated in in vivo studies as they may be a promising alternative treatment to pelvic organ prolapse.

Mesenchymal Stem Cells as a Salvage Treatment for Severe Refractory Graft-vs-Host Disease in Children After Bone Marrow Transplantation.

Application of mesenchymal stem cells (MSC) enables a novel approach to the therapy of graft- vs-host disease (GVHD) after hematopoietic stem cell transplantation. Herein we present our preliminary experience with the use of allogeneic bone marrow‒derived MSC in 9 pediatric patients after hematopoietic transplantation complicated by severe acute or chronic GVHD (aGVHD, cGVHD) resistant to steroids and second-line immunosuppressants. The MSC therapy was applied concurrently with immunosuppressive treatment in 5 patients as a single infusion, in four patients as 2-6 infusions. The median dose of cells per infusion was 1.9 × 106/kg of recipient body weight (range, 0.1-6.5 × 106/kg). The median quantity of cells applied to patients was 1.2 × 106/kg (range, 0.2-30.9 × 106/kg). We did not observe any adverse symptoms of MSC therapy. Overall, partial, or complete remission (PR and CR, respectively) was obtained in 56% of patients after the first MSC infusions, and 44% after completing therapy. In those with skin involvement 50% achieved permanent CR, 38% in those with gastrointestinal manifestations, and 33% in those with liver GVHD. Three patients with overlap syndrome had amelioration, but none had permanent remission. Long-term improvement after consecutive MSC doses was observed in 3 patients. In the 4- to 8-year follow-up, 3 patients are alive and 2 have attained permanent remission. Six patients died during follow-up: 4 with aGVHD and 2 with infectous complications. Co-treatment of streoid-resistant GVHD with MSC and conventional immunosuppression can improve the outcome, although therapy regimens remain to be established.

Recent advances in the role of AMP-activated protein kinase in metabolic reprogramming of metastatic cancer cells: targeting cellular bioenergetics and biosynthetic pathways for anti-tumor treatment.

Growing data indicate that tumor progression and metastasis is dependent on the reprograming of cellular metabolism. Rapidly growing cancer cells undergo metabolic stress in a harsh microenvironment. AMP-activated protein kinase (AMPK) is an energy sensing factor that regulates bioenergetics and biosynthetic pathways within the cell, but its role under metastasis is in dispute. The best studied phenotype of cancer cells is aerobic glycolysis (the Warburg effect), an increased catabolism of glucose to lactate. However, glycolysis and mitochondrial oxidative phosphorylation may operate simultaneously in cancer cells. Many tumors may switch between these pathways accordingly to the current requirements. The alterations in metabolism of cancer cells combined with the overexpression of oncogenes (c-Myc) and transcription factors (Hypoxia-inducible factor 1a) confer a great advantage to malignant cells to avoid reactive oxygen species induced apoptosis. The determination of the role of AMPK network in metabolic reprogramming of metastatic cancer cells may help to identify the selective molecular targets for efficient anti-cancer therapies. In this review, we discuss the implications of AMPK activation in metabolic reprogramming of cancer cells and we present several potential therapeutic strategies targeting cancer cell metabolism. AMPK activator, biguanide metformin, either alone or in combination with other drugs, may selectively modulate signaling pathways, expresses the chemopreventive potential and can be used in current anti-cancer approaches. However, the ambiguous data suggest that the activation of AMPK may induce multiple effects and thus potential therapeutic anti-cancer approach should be carefully considered in relation to metabolic network of cancer cell signaling and other determinants such tumor stage and origin as well.

Thermodynamically consistent Langevin dynamics with spatially correlated noise predicting frictionless regime and transient attraction effect.

While the origins of temporal correlations in Langevin dynamics have been thoroughly researched, the understanding of spatially correlated noise (SCN) is rather incomplete. In particular, very little is known about the relation between friction and SCN. In this article, starting from the microscopic, deterministic model, we derive the analytical formula for the spatial correlation function in the particle-bath interactions. This expression shows that SCN is the inherent component of binary mixtures, originating from the effective (entropic) interactions. Further, employing this spatial correlation function, we postulate the thermodynamically consistent Langevin equation driven by the Gaussian SCN and calculate the adequate fluctuation-dissipation relation. The thermodynamical consistency is achieved by introducing the spatially variant friction coefficient, which can be also derived analytically. This coefficient exhibits a number of intriguing properties, e.g., the singular behavior for certain types of interactions. Eventually, we apply this new theory to the system of two charged particles in the presence of counter-ions. Such particles interact via the screened-charge Yukawa potential and the inclusion of SCN leads to the emergence of the anomalous frictionless regime. In this regime the particles can experience active propulsion leading to the transient attraction effect. This effect suggests a nonequilibrium mechanism facilitating the molecular binding of the like-charged particles.

Characterization of morphology and resistance to Blumeria graminis of winter triticale monosomic addition lines with chromosome 2D of Aegilops tauschii.

KEY MESSAGE: Allocation of the chromosome 2D of Ae. tauschii in triticale background resulted in changes of its organization, what is related to varied expression of genes determining agronomically important traits. Monosomic alien addition lines (MAALs) are crucial for transfer of genes from wild relatives into cultivated varieties. This kind of genetic stocks is used for physical mapping of specific chromosomes and analyzing alien genes expression. The main aim of our study is to improve hexaploid triticale by transferring D-genome chromatin from Aegilops tauschii × Secale cereale (2n = 4x = 28, DDRR). In this paper, we demonstrate the molecular cytogenetics analysis and SSR markers screening combined with phenotype analysis and evaluation of powdery mildew infection of triticale monosomic addition lines carrying chromosome 2D of Ae. tauschii. We confirmed the inheritance of chromosome 2D from the BC2F4 to the BC2F6 generation of triticale hybrids. Moreover, we unveiled a high variable region on the short arm of chromosome 2D, where chromosome rearrangements were mapped. These events had direct influence on plant height of hybrids what might be connected with changes at Rht8 loci. We obtained 20 semi-dwarf plants of BC2F6 generation carrying 2D chromosome with the powdery mildew resistance, without changes in spike morphology, which can be used in the triticale breeding programs.

Transmission of the Aegilops ovata chromosomes carrying gametocidal factors in hexaploid triticale (×Triticosecale Wittm.) hybrids.

The main aim of this work was to induce the chromosome rearrangements between Aegilops ovata (UUMM) and hexaploid triticale (AABBRR) by expression of the gametocidal factor located on the chromosome 4M. The Aegilops ovata × Secale cereale (UUMMRR) amphiploids and triticale 'Moreno' were used to produce hybrids by reciprocal crosses. Chromosome dynamics was observed in subsequent generations of hybrids during mitotic metaphase of root meristems and first metaphase of meiosis of pollen mother cells. Chromosomes were identified by genomic in situ hybridisation (GISH) and fluorescence in situ hybridisation (FISH) using pTa71, pTa791, pSc119.2 and pAs1 DNA probes. It has been shown that the origin of the genetic background had an influence on Aegilops chromosome transmission. Moreover, it has been reported that the preferential transmission of chromosome 4M appeared during both androgenesis and gynogenesis. It is also hypothesised that the expression of the triticale Gc gene suppressor had an influence on the semi-fertility of hybrids but did not inhibit the chromosome rearrangements. This paper also describes the double haploid production, which enabled to obtain plants with two identical copies of triticale chromosomes with translocations of Aegilops chromatin segments.

Allocation of the S-genome chromosomes of Aegilops variabilis Eig. carrying powdery mildew resistance in triticale (× Triticosecale Wittmack).

It has been hypothesized that the powdery mildew adult plant resistance (APR) controlled by the Pm13 gene in Aegilops longissima Schweinf. & Muschl. (S(l)S(l)) has been evolutionary transferred to Aegilops variabilis Eig. (UUSS). The molecular marker analysis and the visual evaluation of powdery mildew symptoms in Ae. variabilis and the Ae. variabilis × Secale cereale amphiploid forms (2n = 6x = 42, UUSSRR) showed the presence of product that corresponded to Pm13 marker and the lower infection level compared to susceptible model, respectively. This study also describes the transfer of Ae. variabilis Eig. (2n = 4x = 28, U(v)U(v)S(v)S(v)) chromosomes, carrying powdery mildew resistance, into triticale (× Triticosecale Wittm., 2n = 6x = 42, AABBRR) using Ae. variabilis × S. cereale amphiploid forms. The individual chromosomes of Ae. variabilis, triticale 'Lamberto' and hybrids were characterized by genomic and fluorescence in situ hybridization (GISH/FISH). The chromosome configurations of obtained hybrid forms were studied at first metaphase of meiosis of pollen mother cells (PMCs) using GISH. The statistical analysis showed that the way of S-genome chromosome pairing and transmission to subsequent hybrid generations was diploid-like and had no influence on chromosome pairing of triticale chromosomes. The cytogenetic study of hybrid forms were supported by the marker-assisted selection using Pm13 marker and visual evaluation of natural infection by Blumeria graminis, that allowed to select the addition or substitution lines of hybrids carrying chromosome 3S(v) which were tolerant to the powdery mildew infection.

Non-Gaussian polymers described by alpha-stable chain statistics: Model, effective interactions in binary mixtures, and application to on-surface separation.

The Gaussian chain model is the classical description of a polymeric chain, which provides analytical results regarding end-to-end distance, the distribution of segments around the mass center of a chain, coarse-grained interactions between two chains and effective interactions in binary mixtures. This hierarchy of results can be calculated thanks to the α stability of the Gaussian distribution. In this paper we show that it is possible to generalize the model of Gaussian chain to the entire class of α-stable distributions, obtaining the analogous hierarchy of results expressed by the analytical closed-form formulas in the Fourier space. This allows us to establish the α-stable chain model. We begin with reviewing the applications of Levy flights in the context of polymer sciences, which include: chains described by the heavy-tailed distributions of persistence length; polymers adsorbed to the surface; and the chains driven by a noise with power-law spatial correlations. Further, we derive the distribution of segments around the mass center of the α-stable chain and construct the coarse-grained interaction potential between two chains. These results are employed to discuss the model of binary mixture consisting of the α-stable chains. In what follows, we establish the spinodal decomposition condition generalized to the mixtures of the α-stable polymers. This condition is further applied to compare the on-surface phase separation of adsorbed polymers (which are known to be described with heavy-tailed statistics) with the phase separation condition in the bulk. Finally, we predict the four different scenarios of simultaneous mixing and demixing in the two- and three-dimensional systems.

Analytical theory of effective interactions in binary colloidal systems of soft particles.

While density functional theory with integral equations techniques are very efficient tools in the numerical analysis of complex fluids, analytical insight into the phenomenon of effective interactions is still limited. In this paper, we propose a theory of binary systems that results in a relatively simple analytical expression combining arbitrary microscopic potentials into effective interaction. The derivation is based on translating a many-particle Hamiltonian including particle-depletant and depletant-depletant interactions into the occupation field language, which turns the partition function into multiple Gaussian integrals, regardless of what microscopic potentials are chosen. As a result, we calculate the effective Hamiltonian and discuss when our formula is a dominant contribution to the effective interactions. Our theory allows us to analytically reproduce several important characteristics of systems under scrutiny. In particular, we analyze the following: the effective attraction as a demixing factor in the binary systems of Gaussian particles, the screening of charged spheres by ions, which proves equivalent to Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, effective interactions in the binary mixtures of Yukawa particles, and the system of particles consisting of both a repulsive core and an attractive/repulsive Yukawa interaction tail. For this last case, we reproduce the "attraction-through-repulsion" and "repulsion-through-attraction" effects previously observed in simulations.

The decreased metastatic potential of rhabdomyosarcoma cells obtained through MET receptor downregulation and the induction of differentiation.

Rhabdomyosarcoma (RMS) is the most common type of pediatric soft tissue sarcoma. The MET receptor has an important role in the biology of RMS, and its overexpression and hyperactivation correlate with the metastatic ability of RMS. Consequently, interfering with MET expression or functionality may constitute a sound strategy for reducing the progression and metastatic potential of RMS. Our study reveals that downregulation of the MET receptor leads to changes in the morphology of ARMS cell in vivo. Tumors acquire a spindle shape that is characteristic of muscle fibers. Inhibition of MET expression or function leads to (i) a decreased expression of the early myogenic marker MyoD, (ii) a decreased ability of ARMS cells to metastasize to bone marrow cavities, (iii) downregulation of CXCR4 receptor expression and (iv) a decreased migration of MET-depleted cells towards gradients of HGF and SDF-1. Finally, we demonstrate that in vitro differentiation of alveolar RMS cells decreases their metastatic behavior by reducing both the expression of the MET and CXCR4 receptors and their migratory response to HGF and SDF-1. These findings suggest that blockers of MET receptor function and inducers of RMS cells differentiation may be clinically useful for reducing the aggressiveness and metastatic potential of RMS and may have significant implications for its treatment.

Polymer unfolding and motion synchronization induced by spatially correlated noise.

The problem of a spatially correlated noise affecting a complex system is studied in this paper. We present a comprehensive analysis of a two-dimensional model polymer chain, driven by the spatially correlated Gaussian noise, for which we have varied the amplitude and the correlation length. The chain model is based on a bead-spring approach, enriched with a global Lennard-Jones potential and angular interactions. We show that spatial correlations in the noise inhibit the chain geometry dynamics, enhancing the preservation of the polymer shape. This is supported by the analysis of correlation functions of both the module length and angles between neighboring modules, which have been measured for the noise amplitude ranging over three orders of magnitude. Moreover, we have observed the correlation length dependent bead motion synchronization and the spontaneous polymer unfolding, resulting from an interplay between chain potentials and the spatially structured noise.

The presence of B7-H4+ macrophages and CD25+CD4+ and FOXP3+ regulatory T cells in the microenvironment of nasal polyps - a preliminary report.

The nasal polyp (NP) seems to represent the end-stage of longstanding inflammation in patients with chronic rhinosinusitis. The aim of our study has been to evaluate the presence of two regulatory cell populations in the microenvironment of NP: CD4+CD25high Foxp3+ (Treg) cells and B7-H4-expressing macrophages. Treg cells are actively able to inhibit T lymphocytes, while the population of B7-H4-expressing macrophages has recently been described as characterized by a regulatory function similar to that of Treg cells. For our study, we evaluated 14 NP tissue samples. The samples were divided into two main groups, eosinophilic (NP) and lymphocytic (NP), according to the predominant type of immune cell infiltration. The presence of Treg cells and B7-H4 positive macrophages in the samples was analyzed by FACS. Treg cells and B7-H4-expressing macrophages were identified in all the examined nasal polyps. The percentages of both Treg cells and of B7H4 positive cells found in the eosinophilic nasal polyps were higher than those found in the lymphocytic nasal polyps. Treg cells and B7H4+ macrophage subpopulations were present in the NP microenvironment and the alterations in their percentages were related to a distinct pattern of immune cell infiltration.

High anti tumor activity against rhabdomyosarcoma cells and low normal cells cytotoxicity of heat shock protein 90 inhibitors, with special emphasis on 17-[2-(pyrrolidin-1-yl)ethyl]-aminno-17-demethoxygeldanamycin.

Rhabdomyosarcoma is a highly metastatic tumor, mostly observed in children and adolescence. When diagnosed at early stages it is mostly curable. However, in advanced or metastatic stages the 5-years survival rate is below 20%. Thus, new treatment strategies for this tumor are needed. In this paper we showed that HSP90 inhibitors, geldanamycin and its analogs, can profoundly affect proliferation of rhabdomyosarcoma cells. We also showed that blocking of HSP90 function induces apoptosis of tumor cells and downregulates expression of anti apoptotic protein AKT. Cells exposed to geldanamycin and its analogs exhibit strong reduction of MET receptor expression and subsequent inhibition of HGF-dependent tumor cells migration and invasion. Interestingly, at concentrations sufficient to block tumor cells growth and motility, the 17AEP-GA, 17AAG and 17DMAP-GA were not toxic or only slightly toxic toward normal hematopoietic, mesenchymal and endothelial cells. This could be due to low HSP90 expression both at mRNA and protein level in these cells. Collectively, our findings suggest that blocking HSP90 action through geldanmycins could be in the future a part of new therapeutic strategies in rhabdomyosarcoma treatment.

A population of very small embryonic-like (VSEL) CXCR4(+)SSEA-1(+)Oct-4+ stem cells identified in adult bone marrow.

By employing multiparameter sorting, we identified in murine bone marrow (BM) a homogenous population of rare (approximately 0.02% of BMMNC) Sca-1(+)lin(-)CD45- cells that express by RQ-PCR and immunohistochemistry markers of pluripotent stem cells (PSC) such as SSEA-1, Oct-4, Nanog and Rex-1. The direct electronmicroscopical analysis revealed that these cells are small (approximately 2-4 microm), posses large nuclei surrounded by a narrow rim of cytoplasm, and contain open-type chromatin (euchromatin) that is typical for embryonic stem cells. In vitro cultures these cells are able to differentiate into all three germ-layer lineages. The number of these cells is highest in BM from young (approximately 1-month-old) mice and decreases with age. It is also significantly diminished in short living DBA/2J mice as compared to long living B6 animals. These cells in vitro respond strongly to SDF-1, HGF/SF and LIF and express CXCR4, c-met and LIF-R, respectively, and since they adhere to fibroblasts they may be coisolated with BM adherent cells. We hypothesize that this population of Sca-1(+)lin(-)CD45- very small embryonic-like (VSEL) stem cells is deposited early during development in BM and could be a source of pluripotent stem cells for tissue/organ regeneration.

Cells enriched in markers of neural tissue-committed stem cells reside in the bone marrow and are mobilized into the peripheral blood following stroke.

The concept that bone marrow (BM)-derived cells participate in neural regeneration remains highly controversial and the identity of the specific cell type(s) involved remains unknown. We recently reported that the BM contains a highly mobile population of CXCR4+ cells that express mRNA for various markers of early tissue-committed stem cells (TCSCs), including neural TCSCs. Here, we report that these cells not only express neural lineage markers (beta-III-tubulin, Nestin, NeuN, and GFAP), but more importantly form neurospheres in vitro. These neural TCSCs are present in significant amounts in BM harvested from young mice but their abundance and responsiveness to gradients of motomorphogens, such as SDF-1, HGF, and LIF, decreases with age. FACS analysis, combined with analysis of neural markers at the mRNA and protein levels, revealed that these cells reside in the nonhematopoietic CXCR4+/Sca-1+/lin-/CD45 BM mononuclear cell fraction. Neural TCSCs are mobilized into the peripheral-blood following stroke and chemoattracted to the damaged neural tissue in an SDF-1-CXCR4-, HGF-c-Met-, and LIF-LIF-R-dependent manner. Based on these data, we hypothesize that the postnatal BM harbors a nonhematopoietic population of cells that express markers of neural TCSCs that may account for the beneficial effects of BM-derived cells in neural regeneration.

Stem cell plasticity revisited: CXCR4-positive cells expressing mRNA for early muscle, liver and neural cells 'hide out' in the bone marrow.

It has been suggested that bone marrow (BM)-derived hematopoietic stem cells transdifferentiate into tissue-specific stem cells (the so-called phenomenon of stem cell plasticity), but the possibility of committed tissue-specific stem cells pre-existing in BM has not been given sufficient consideration. We hypothesized that (i) tissue-committed stem cells circulate at a low level in the peripheral blood (PB) under normal steady-state conditions, maintaining a pool of stem cells in peripheral tissues, and their levels increase in PB during stress/tissue injury, and (ii) they could be chemoattracted to the BM where they find a supportive environment and that the SDF-1-CXCR4 axis plays a prominent role in the homing/retention of these cells to BM niches. We performed all experiments using freshly isolated cells to exclude the potential for 'transdifferentiation' of hematopoietic stem or mesenchymal cells associated with in vitro culture systems. We detected mRNA for various early markers for muscle (Myf-5, Myo-D), neural (GFAP, nestin) and liver (CK19, fetoprotein) cells in circulating (adherent cell-depleted) PB mononuclear cells (MNC) and increased levels of expression of these markers in PB after mobilization by G-CSF (as measured using real-time RT-PCR). Furthermore, SDF-1 chemotaxis combined with real-time RT-PCR analysis revealed that (i) these early tissue-specific cells reside in normal murine BM, (ii) express CXCR4 on their surface and (iii) can be enriched (up to 60 x) after chemotaxis to an SDF-1 gradient. These cells were also highly enriched within purified populations of murine Sca-1(+) BM MNC as well as of human CD34(+)-, AC133(+)- and CXCR4-positive cells. We also found that the expression of mRNA for SDF-1 is upregulated in damaged heart, kidney and liver. Hence our data provide a new perspective on BM not only as a home for hematopoietic stem cells but also a 'hideout' for already differentiated CXCR4-positive tissue-committed stem/progenitor cells that follow an SDF-1 gradient, could be mobilized into PB, and subsequently take part in organ/tissue regeneration.