Bone marrow-derived cells: A potential approach for the treatment of xerostomia

Transplantations of bone marrow-derived cells (BMDCs) are traditionally used for hematologic diseases, but there are increasing numbers of clinical trials using BMDC treatments for non-hematologic disorders, including autoimmune diseases. BMDCs are recently reported to improve organ functions. This paper will review available reports supporting the role of BMDCs in reducing xerostomia (i.e. re-establishing salivary gland functions) due to head and neck irradiation for cancer therapies and in Sj?gren's syndrome. There are reports that BMDCs provide a beneficial effect on the saliva production. BMDCs positively affect blood vessels stability and regeneration in irradiated salivary glands. Also, BMDCs provide an immunomodulatory activity in mice with Sj?gren's-like disease. While the exact mechanisms by which BMDCs improve organ functions remain controversial, there is preliminary evidence that a combination of them (such as cell transdifferentiation, vasculogenesis, and paracrine effect) occur in salivary glands.     

Adult stem cells: seing is not being

Recent unexpected observations in adult rodents that stem/progenitor cells located in the bone marrow, but also in other tissues, could, after their transplantation to an irradiated host contribute to the regeneration of damaged organs such as brain, liver, pancreas or muscle, have raised much hope for future therapeutic applications. These data have also initially been interpreted as a proof of a possible transdifferentiation or plasticity of adult stem cells located in these tissues. Additional experiments rigorously analyzed have tempered initial enthusiasm, by showing that if marrow cells do migrate in damaged muscles and liver, their contribution to organ repair is low, and in some cases, explained by cell fusion. Nevertheless, among bone marrow cells, two categories of stem cells now emerge that have a potentially tremendous interest in cell therapy, if we succeed in understanding how to purify, amplify and differentiate these more efficiently and reproducibly.     

成体干细胞的可塑性:横向分化还是细胞融合?

近年来研究显示成体干细胞(adult stem cells)具有可塑性(plasticity),不仅可以生成它们所在组织的成熟细胞,而且在特定环境下能分化成其他组织类型细胞,这种跨系或跨胚层分化现象称为横向分化或转分化(transdifferentiation)。横向分化已为成体干细胞的研究和临床应用包括组织器官损伤的修复提供了新的思路和应用前景。然而,最近的一些研究进展又引出不同的解释,即成体干细胞的可塑性是由于细胞融合(cellfusion)的结果。在此,就成体干细胞的可塑性、横向分化、细胞融合等方面研究作一综述。     

Neurogenin3 Activation Is Not Sufficient to Direct Duct-to-Beta Cell Transdifferentiation in the Adult Pancreas

It remains controversial whether adult pancreatic ducts harbor facultative beta cell progenitors. Because neurogenin3 (Ngn3) is a key determinant of pancreatic endocrine cell neogenesis during embryogenesis, many studies have also relied upon Ngn3 expression as evidence of beta cell neogenesis in adults. Recently, however, Ngn3 as a marker of adult beta cell neogenesis has been called into question by reports of Ngn3 expression in fully-developed beta cells. Nevertheless, direct evidence as to whether Ngn3 activation in adult pancreatic duct cells may lead to duct-to-beta cell transdifferentiation is lacking. Here we studied two models of Ngn3 activation in adult pancreatic duct cells (low-dose alloxan treatment and pancreatic duct ligation) and lineage-traced Ngn3-activated duct cells by labeling them through intraductal infusion with a cell-tagging dye, CFDA-SE No dye-labeled beta cells were found during the follow-up in either model, suggesting that activation of Ngn3 in duct cells is not sufficient to direct their transdifferentiation into beta cells. Therefore, Ngn3 activation in duct cells is not a signature for adult beta cell neogenesis.     

成体干细胞向肝细胞分化

成体干细胞跨越胚层限制分化为其他胚层来源的细胞,对揭示不同胚层细胞间相互分化的生物学意义和机制具有重要学术价值,并可以为临床细胞移植治疗开辟新的途径,从而成为当前研究的热点之一。综述了近年来肝源性卵圆细胞、成肝细胞、骨髓源干细胞和其他成体干细胞跨越分化为肝细胞的研究现状与进展,以及卵圆细胞、成肝细胞等的分离鉴定,表面标志、生物学特征和跨越分化机制,并对成体干细胞在肝脏疾病细胞治疗上的应用前景作了展望。     

IGF-I increases bone marrow contribution to adult skeletal muscle and enhances the fusion of myelomonocytic precursors

Muscle damage has been shown to enhance the contribution of bone marrow-derived cells (BMDCs) to regenerating skeletal muscle. One responsible cell type involved in this process is a hematopoietic stem cell derivative, the myelomonocytic precursor (MMC). However, the molecular components responsible for this injury-related response remain largely unknown. In this paper, we show that delivery of insulin-like growth factor I (IGF-I) to adult skeletal muscle by three different methods-plasmid electroporation, injection of genetically engineered myoblasts, and recombinant protein injection-increases the integration of BMDCs up to fourfold. To investigate the underlying mechanism, we developed an in vitro fusion assay in which co-cultures of MMCs and myotubes were exposed to IGF-I. The number of fusion events was substantially augmented by IGF-I, independent of its effect on cell survival. These results provide novel evidence that a single factor, IGF-I, is sufficient to enhance the fusion of bone marrow derivatives with adult skeletal muscle.     

Caspase-2-Dependent Dendritic Cell Death, Maturation, and Priming of T Cells in Response to Brucella abortus Infection

Smooth virulent Brucella abortus strain 2308 (S2308) causes zoonotic brucellosis in cattle and humans. Rough B. abortus strain RB51, derived from S2308, is a live attenuated cattle vaccine strain licensed in the USA and many other countries. Our previous report indicated that RB51, but not S2308, induces a caspase-2-dependent apoptotic and necrotic macrophage cell death. Dendritic cells (DCs) are professional antigen presenting cells critical for bridging innate and adaptive immune responses. In contrast to Brucella-infected macrophages, here we report that S2308 induced higher levels of apoptotic and necrotic cell death in wild type bone marrow-derived DCs (WT BMDCs) than RB51. The RB51 and S2308-induced BMDC cell death was regulated by caspase-2, indicated by the minimal cell death in RB51 and S2308-infected BMDCs isolated from caspase-2 knockout mice (Casp2KO BMDCs). More S2308 bacteria were taken up by Casp2KO BMDCs than wild type BMDCs. Higher levels of S2308 and RB51 cells were found in infected Casp2KO BMDCs compared to infected WT BMDCs at different time points. RB51-infected wild type BMDCs were mature and activated as shown by significantly up-regulated expression of CD40, CD80, CD86, MHC-I, and MHC-II. RB51 induced the production of cytokines TNF-α, IL-6, IFN-γ and IL12/IL23p40 in infected BMDCs. RB51-infected WT BMDCs also stimulated the proliferation of CD4(+) and CD8(+) T cells compared to uninfected WT BMDCs. However, the maturation, activation, and cytokine secretion are significantly impaired in Casp2KO BMDCs infected with RB51 or Salmonella (control). S2308-infected WT and Casp2KO BMDCs were not activated and could not induce cytokine production. These results demonstrated that virulent smooth strain S2308 induced more apoptotic and necrotic dendritic cell death than live attenuated rough vaccine strain RB51; however, RB51, but not its parent strain S2308, induced caspase-2-mediated DC maturation, cytokine production, antigen presentation, and T cell priming.     

Transdifferentiation, Metaplasia and Tissue Regeneration

Transdifferentiation is defined as the conversion of one cell type to another. It belongs to a wider class of cell type transformations called metaplasias which also includes cases in which stem cells of one tissue type switch to a completely different stem cell. Numerous examples of transdifferentiation exist within the literature. For example, isolated striated muscle of the invertebrate jellyfish (Anthomedusae) has enormous transdifferentiation potential and even functional organs (e.g., tentacles and the feeding organ (manubrium)) can be generated in vitro. In contrast, the potential for transdifferentiation in vertebrates is much reduced, at least under normal (nonpathological) conditions. But despite these limitations, there are some well-documented cases of transdifferentiation occurring in vertebrates. For example, in the newt, the lens of the eye can be formed from the epithelial cells of the iris. Other examples of transdifferentiation include the appearance of hepatic foci in the pancreas, the development of intestinal tissue at the lower end of the oesophagus and the formation of muscle, chondrocytes and neurons from neural precursor cells. Although controversial, recent results also suggest the ability of adult stem cells from different embryological germlayers to produce differentiated cells e.g., mesodermal stem cells forming ecto- or endodermally-derived cell types. This phenomenon may constitute an example of metaplasia. The current review examines in detail some well-documented examples of transdifferentiation, speculates on the potential molecular and cellular mechanisms that underlie the switches in phenotype, together with their significance to organogenesis and regenerative medicine.Key Words: transdifferentiation, metaplasia, tissue regeneration, stem cells, plasticity, reprogramming, regenerative medicine     

Transdifferentiation,Metaplasia and Tissue Regeneration

Transdifferentiation is defined as the conversion of one cell type to another. It belongs to a wider class of cell type transformations called metaplasias which also includes cases in which stem cells of one tissue type switch to a completely different stem cell. Numerous examples of transdifferentiation exist within the literature. For example, isolated striated muscle of the invertebrate jellyfish (Anthomedusae) has enormous transdifferentiation potential and even functional organs (e.g. tentacles and the feeding organ (manubrium) can be generated in-vitro. In contrast, the potential for transdifferentiation in vertebrates is much reduced, at least under normal (non-pathological) conditions. But despite these limitations, there are some well-documented cases of transdifferentiation occurring in vertebrates. For example, in the newt, the lens of the eye can be formed from the epithelial cells of the iris. Other examples of transdifferentiation include the appearance of hepatic foci in the pancreas, the development of intestinal tissue at the lower end of the oesophagus and the formation of muscle, chondrocytes and neurons from neural precursor cells. Although controversial, recent results also suggest the ability of adult stem cells from different embryological germlayers to produce differentiated cells e.g. mesodermal stem cells forming ecto- or endodermally-derived cell types. This phenomenon may constitute an example of metaplasia. The current review examines in detail some well-documented examples of transdifferentiation, speculates on the potential molecular and cellular mechanisms that underlie the switches in phenotype, together with their significance to organogenesis and regenerative medicine.     

Switching from bone marrow-derived neurons to epithelial cells through dedifferentiation and translineage redifferentiation

While the ability of stem cells to switch lineages has been suggested, the route(s) through which this may happen is unclear. To date, the best characterized adult stem cell population considered to possess transdifferentiation capacity is BM-MSCs (bone marrow mesenchymal stem cells). We investigated whether BM-MSCs that had terminally differentiated into the neural or epithelial lineage could be induced to transdifferentiate into the other phenotype in vitro. Our results reveal that neuronal phenotypic cells derived from adult rat bone marrow cells can be switched to epithelial phenotypic cells, or vice versa, by culture manipulation allowing the differentiated cells to go through, first, dedifferentiation and then redifferentiation to another phenotype. Direct transdifferentiation from differentiated neuronal or epithelial phenotype to the other differentiated phenotype cannot be observed even when appropriate culture conditions are provided. Thus, dedifferentiation appears to be a prerequisite for changing fate and differentiating into a different lineage from a differentiated cell population.     

Inductive effect of the eye tissues of adult clawed toads on the gastrula ectoderm

The inducing influence of adult eye tissues on the early gastrula ectoderm was studied in vitro. Both retina and pigment epithelium induced in the early gastrula ectoderm similar spectra of cell types, including nervous tissue, retina, pigment epithelium, lentoids, ectomesenchyme, and melanophores. It is suggested that the correspondence of these cell types with those arising at a spontaneous transdifferentiation of the isolated retina and pigment epithelium cells in vitro or at the induction of the early gastrula ectoderma by archencephalic endomesoderm during the normal development can be accounted for by that in these eye cells molecular determinants appeared as a result of induction and maintaina the stability of their differentiation and their potencies to transdifferentiation in vitro being reproduced during the lifetime of these cells.     

How to make pancreatic beta cells--prospects for cell therapy in diabetes

One promising approach for the cure of diabetes is the replacement of lost insulin-expressing beta cells by cell or regenerative therapy. The recent development of an effective islet transplantation procedure has focused attention on the limiting supply of beta cells. Various sources for new beta cells are therefore being considered, including embryonic stem cells, adult stem cells and transdifferentiation of certain types of differentiated cells, so far with limited success. The major physiological mechanism for adult beta cell formation was recently shown to be beta cell proliferation. This finding underscores the potential use of terminally differentiated beta cells as a starting material for enhancement of beta cell mass.     

A new paradigm in cell therapy for diabetes: Turning pancreatic α‐cells into β‐cells

Cell therapy means treating diseases with the body's own cells. One of the cell types most in demand for therapeutic purposes is the pancreatic β‐cell. This is because diabetes is one of the major healthcare problems in the world. Diabetes can be treated by islet transplantation but the major limitation is the shortage of organ donors. To overcome the shortfall in donors, alternative sources of pancreatic β‐cells must be found. Potential sources include embryonic or adult stem cells or, from existing β‐cells. There is now a startling new addition to this list of therapies: the pancreatic α‐cell. Thorel and colleagues recently showed that under circumstances of extreme pancreatic β‐cell loss, α‐cells may serve to replenish the insulin‐producing compartment. This conversion of α‐cells to β‐cells represents an example of transdifferentiation. Understanding the molecular basis for transdifferentiation may help to enhance the generation of β‐cells for the treatment of diabetes.     

The relative efficiency of acquisition of MHC:peptide complexes and cross-presentation depends on dendritic cell type

Intercellular exchange of MHC molecules has been reported between many cells, including professional and nonprofessional APCs. This phenomenon may contribute to T cell immunity to pathogens. In this study, we addressed whether the transfer of MHC class I:peptide complexes between cells plays a role in T cell responses and compare this to conventional cross-presentation. We observed that dsRNA-matured bone marrow-derived dendritic cells (BMDCs) acquired peptide:MHC complexes from other BMDCs either pulsed with OVA(257-264) peptide, soluble OVA, or infected with a recombinant adenovirus expressing OVA. In addition, BMDCs were capable of acquiring MHC:peptide complexes from epithelial cells. Spleen-derived CD8alpha(+) and CD8alpha(-) dendritic cells (DCs) also acquired MHC:peptide complexes from BMDCs pulsed with OVA(257-264) peptide. However, the efficiency of acquisition by these ex vivo derived DCs is much lower than acquisition by BMDC. In all cases, the acquired MHC:peptide complexes were functional in that they induced Ag-specific CD8(+) T cell proliferation. The efficiency of MHC transfer was compared with cross-presentation for splenic CD8alpha(+) and CD8alpha(-) as well as BMDCs. CD8alpha(+) DCs were more efficient at inducing T cell proliferation when they acquired Ag via cross-presentation, the opposite was observed for BMDCs and splenic CD8alpha(-) DCs. We conclude from these observations that the relative efficiency of MHC transfer vs cross-presentation differs markedly between different DC subsets.     

精原干细胞的生命历程

精原干细胞是动物体内的一种成体干细胞,在睾丸微环境中可以像胚胎干细胞一样具有增殖、分化潜能。近年来借助于各种细胞学技术,人们对精原干细胞在不同睾丸微环境中的分化和发育状况进行了深入研究,睾丸内不同种类细胞间的相互作用以及特定微环境对干细胞转分化的影响,已成为本领域的热点核心内容。将从精原干细胞生命历程的角度讨论该过程中所取得的研究成果和存在的问题。     

Delivery and tracking of therapeutic cell preparations for clinical cardiovascular applications

Experimental observations suggesting adult stem cell plasticity and cross-lineage transdifferentiation have underpinned the investigation of cell therapy for cardiovascular disease. Many challenges still face the full realization of cardiovascular regenerative medicine. This brief review will highlight some of these, with emphasis on the choice of cell preparation, route of cell delivery and tracking of delivered cells.     

Cardiomyocyte differentiation from embryonic and adult stem cells

In recent years multiple reports indicating that embryonic as well as adult stem cells can differentiate to cardiomyocytes have ignited discussions on whether these stem cells could lead to new therapies for patients with heart disease. Recent developments have been made in the generation of cardiomyocytes from both embryonic and adult stem cells, and progress towards clinical applications in patients with heart failure has been made. Nevertheless, controversies surrounding safety and transdifferentiation issues will need to be overcome before these stem cell approaches can reach their full potential.     

Systemic administration of bone marrow‐derived cells leads to better uterine engraftment than use of uterine‐derived cells or local injection

Stem cells are recruited to the uterus where they differentiate into endometrial cells and have been suggested as potential therapy for uterine injury such as Asherman's syndrome. However, it is unknown whether local intrauterine injection may result in better stem cell engraftment of the uterus compared with systemic administration, and whether uterine‐derived cells (UDCs) may confer an advantage over BM‐derived cells (BMDCs). Mice underwent local injury to a single uterine horn. Green fluorescent protein (GFP)‐expressing BMDCs, UDCs or saline (control) were injected either intravenously or locally (uterine lumen) into wild‐type recipients. Two or 3 weeks post‐transplant, uterine tissues were collected for fluorescence‐activated cell sorting (FACS) and immunohistochemistry/immunofluorescence studies. Mice injected intravenously with BMDCs or UDCs had increased GFP⁺ cells recruitment to the non‐injured or injured uterus compared to those injected locally. No significant differences were noted in GFP⁺ cell recruitment to the injured versus non‐injured horn. In addition, systemic injection of BMDCs led to greater recruitment of GFP⁺ cells at 2 weeks and 3 weeks compared with UDCs. Immunohistochemical staining demonstrated that GFP⁺ cells were found in stroma but not in epithelium or blood vessels. Immunofluorescence analysis revealed that GFP⁺ cells were mostly CD45‐negative, and negative for CD31 and cytokeratin, confirming their stromal identity. In conclusion, the systemic route of administration results in better recruitment of BMDCs or UDCs to the injured uterus than local injection. In addition, BMDCs recruitment to the uterus is greater than UDCs. These findings inform the development of stem cell‐based therapies targeting the uterus.