Local signals in stem cell-based bone marrow regeneration

Colonic Tuft Cells: The Less-Recognized Therapeutic Targets in Inflammatory Bowel Disease and Colorectal Cancer

Tuft cells are more than guardian chemosensory elements of the digestive tract. They produce a variety of immunological effector molecules in response to stimulation; moreover, they are essential for defense against protozoa and nematodes. Beyond the description of their characteristics, this review aims to elucidate the potential pathogenic and therapeutic roles of colonic tuft cells in inflammatory bowel disease and colorectal cancer, focusing on their primarily immunomodulatory action. Regarding inflammatory bowel disease, tuft cells are implicated in both maintaining the integrity of the intestinal epithelial barrier and in tissue repair and regeneration processes. In addition to maintaining intestinal homeostasis, they display complex immune-regulatory functions. During the development of colorectal cancer, tuft cells can promote the epithelial-to-mesenchymal transition, alter the gastrointestinal microenvironment, and modulate both the anti-tumor immune response and the tumor microenvironment. A wide variety of their biological functions can be targeted for anti-inflammatory or anti-tumor therapies; however, the adverse side effects of immunomodulatory actions must be strictly considered.

Network analysis to explore the pharmacological mechanism of Shenmai injection in treating granulocytopenia and evidence-based medicine approach validation

BACKGROUND

Shenmai injection is frequently utilized in China to clinically treat granulocytopenia in oncology patients following chemotherapy. Despite this, the drug's therapeutic benefits remain a topic of contention, and its active components and potential treatment targets have yet to be established. The present study utilizes a network pharmacology approach to investigate the drug's active ingredients and possible therapeutic targets, and to evaluate the effectiveness of Shenmai injection in treating granulocytopenia through meta-analysis.

METHODS

In our subject paper, we utilized the TCMID database to investigate the active ingredients present in red ginseng and ophiopogon japonicus. To further identify molecular targets, we employed SuperPred, as well as OMIM, Genecards, and DisGeNET databases. Our focus was on targets associated with granulocytopenia. The DAVID 6.8 database was utilized to perform gene ontology functional enrichment analysis and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis. Additionally, a protein-protein interaction network was established. The resulting "drug-key component-potential target-core pathway" network was used to predict the mechanism of action of Shenmai injection in the treatment of granulocytopenia. In order to evaluate the quality of the studies included in our analysis, we utilized the Cochrane Reviewers' Handbook. We then conducted a meta-analysis of the clinical curative effect of Shenmai injection for granulocytopenia, utilizing the Cochrane Collaboration's RevMan 5.3 software.

RESULTS

After conducting a thorough screening, the study identified 5 primary ingredients of Shenmai injection - ophiopogonoside a, β-patchoulene, ginsenoside rf, ginsenoside re, and ginsenoside rg1-that can potentially target 5 essential proteins: STAT3, TLR4, PIK3CA, PIK3R1, and GRB2. Additionally, Kyoto Encyclopedia of Genes and Genomes pathway analysis revealed that Shenmai injection can be beneficial in treating granulocytopenia by interacting with pathways such as HIF-1 signaling, T-cell receptor signaling, PI3K-Akt signaling, chemokine signaling, and FoxO signaling. The results of meta-analysis indicate that the treatment group exhibited superior performance in terms of both efficiency and post-treatment leukocyte count when compared to the control group.

CONCLUSION

In summary, studies in network pharmacology demonstrate that Shenmai injection exerts an impact on granulocytopenia via various components, targets, and mechanisms. Additionally, evidence-based studies provide strong support for the effectiveness of Shenmai injection in preventing and treating granulocytopenia.

A novel strategy to reveal clinical advantages and molecular mechanism of aidi injection in the treatment of pancreatic cancer based on network meta-analysis and network pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

Pancreatic cancer is a common malignancy worldwide due to its poor prognosis and high mortality rate. It is clinically proven that the combination of chemotherapeutic drugs and Traditional Chinese Medicine injections (TCMIs) significantly improves the therapeutic effect.

AIM OF THE STUDY

To evaluate the efficacy and clinical benefits of TCMIs in combination with chemotherapy in the treatment of pancreatic cancer and to explore the mechanism of clinical advantage of Aidi injection.

METHODS

Randomized controlled trials (RCTs) were searched in databases by NMA before December 29, 2020. WinBUGS 1.4, Stata 14.0, and R 4.0.4 software were used for calculations. All results were expressed as odds ratios and 95% credible intervals. Through the network pharmacology method, the chemical components and their targets, as well as the disease targets were further analyzed. And then, biological experiments were integrated to verify the results of network pharmacology analysis. (PROSPERO ID: CRD42021283559).

RESULTS

A total of 33 RCTs with 8 TCMIs and 2011 patients were included. The results of NMA showed that Aidi injection can significantly improve the clinical efficacy (OR = 0.34, 95%CI: 0.16-0.74), and the clinical advantage was that it can significantly alleviate the leukopenia and thrombocytopenia caused by chemotherapy (OR = 5.65, 95%CI: 1.18-28.13). A total of 23 chemical compounds and 280 potential targets for Aidi injection were obtained from the online databases. Among them, there were 22 compounds, 50 targets and 211 signaling pathways closely related to leukopenia. Five genes were predicted to be core targets of ADI in alleviating leukopenia, and 2 of them (TP53 and VEGFA) were confirmed by biological experiments as regulatory targets of ADI in the treatment of PC.

CONCLUSIONS

In conclusion, TCMIs in combination with chemotherapy, can improve clinical efficacy and safety in the treatment of pancreatic cancer. However, the overall evidence base is low, and large samples with multi-center RCTs are still needed to support further research findings. Aidi injection can alleviate leukopenia mainly by intervening in oxidative stress, regulating cell proliferation and apoptosis, and regulating the inflammatory response. The combined application of NMA, network pharmacology, and biological experiments provides a reference for clinical evaluation and mechanism of action exploration of other drugs.

Hematopoietic stem and progenitor cell signaling in the niche

Hematopoietic stem and progenitor cells (HSPCs) are responsible for lifelong maintenance of hematopoiesis through self-renewal and differentiation into mature blood cell lineages. Traditional models hold that HSPCs guard homeostatic function and adapt to regenerative demand by integrating cell-autonomous, intrinsic programs with extrinsic cues from the niche. Despite the biologic significance, little is known about the active roles HSPCs partake in reciprocally shaping the function of their microenvironment. Here, we review evidence of signals emerging from HSPCs through secreted autocrine or paracrine factors, including extracellular vesicles, and via direct contact within the niche. We also discuss the functional impact of direct cellular interactions between hematopoietic elements on niche occupancy in the context of leukemic infiltration. The aggregate data support a model whereby HSPCs are active participants in the dynamic adaptation of the stem cell niche unit during development and homeostasis, and under inflammatory stress, malignancy, or transplantation.

The lncRNA MCF2L-AS1 controls osteogenic differentiation by regulating miR-33a

Bone homeostasis is maintained by balanced osteoblast-mediated tissue production and osteoclast-mediated tissue destruction, and is disrupted in pathological conditions such as osteoporosis. The mechanisms underlying osteogenic differentiation of bone marrow mesenchymal stem cells, which is critical to bone homeostasis, are not completely clear, despite extensively studies. Long noncoding RNAs (lncRNAs) have recently emerged as novel therapeutic targets in various diseases. However, the expression pattern and biological function of lncRNAs in osteogenic differentiation remain unclear. In this study, we aimed to determine the role of lncRNAs in osteogenic differentiation of human bone marrow mesenchymal stem cells. We found high lncRNA MCF2L-AS1 expression in human bone marrow mesenchymal stem cells, and used bioinformatics analysis to analyze its function. MCF2L-AS1 knockdown induced inhibition of osteoblast differentiation. Silencing of MCF2L-AS1 increased the expression of miR-33a and subsequently inhibited Runx2 expression at the post-transcriptional level. Moreover, MCF2L-AS1 directly interacted with miR-33a, and downregulation of miR-33a efficiently reversed the suppression of Runx2 induced by MCF2L-AS1 short hairpin RNA (shRNA). Thus, MCF2L-AS1 positively regulated the expression of Runx2 by sponging miR-33a, and promoted osteogenic differentiation in BMSCs. Our results indicated that the lncRNA MCF2L-AS1 plays a critical role in the osteogenic differentiation of BMSCs, and targeting lncRNA MCF2L-AS1 could be a promising strategy to promote osteogenic differentiation.

Gene therapy and cell therapy for the management of radiation damages to healthy tissues: Rationale and early results

Nowadays, ionizing radiations have numerous applications, especially in medicine for diagnosis and therapy. Pharmacological radioprotection aims at increasing detoxification of free radicals. Radiomitigation aims at improving survival and proliferation of damaged cells. Both strategies are essential research area, as non-contained radiation can lead to harmful effects. Some advances allowing the comprehension of normal tissue injury mechanisms, and the discovery of related predictive biomarkers, have led to developing several highly promising radioprotector or radiomitigator drugs. Next to these drugs, a growing interest does exist for biotherapy in this field, including gene therapy and cell therapy through mesenchymal stem cells. In this review article, we provide an overview of the management of radiation damages to healthy tissues via gene or cell therapy in the context of radiotherapy. The early management aims at preventing the occurrence of these damages before exposure or just after exposure. The late management offers promises in the reversion of constituted late damages following irradiation.

Prevention of perinatal nicotine-induced bone marrow mesenchymal stem cell myofibroblast differentiation by augmenting the lipofibroblast phenotype

Perinatal nicotine exposure drives the differentiation of alveolar lipofibroblasts (LIFs), which are critical for lung injury repair, to myofibroblasts (MYFs), which are the hallmark of chronic lung disease. Bone marrow-derived mesenchymal stem cells (BMSCs) are important players in lung injury repair; however, how these cells are affected with perinatal nicotine exposure and whether these can be preferentially driven to a lipofibroblastic phenotype are not known. We hypothesized that perinatal nicotine exposure would block offspring BMSCs lipogenic differentiation, driving these cells toward a MYF phenotype. Since peroxisome proliferator activated-receptor γ (PPARγ) agonists can prevent nicotine-induced MYF differentiation of LIFs, we further hypothesized that the modulation of PPARγ expression would inhibit nicotine's myogenic effect on BMSCs. Sprague Dawley dams were perinatally administered nicotine (1 mg/kg bodyweight) with or without the potent PPARγ agonist rosiglitazone (RGZ), both administered subcutaneously. At postnatal day 21, BMSCs were isolated and characterized morphologically, molecularly, and functionally for their lipogenic and myogenic potentials. Perinatal nicotine exposure resulted in decreased oil red O staining, triolein uptake, expression of PPARγ, and its downstream target gene adipocyte differentiation-related protein by BMSCs, but enhanced α-smooth muscle actin and fibronectin expression, and activated Wnt signaling, all features indicative of their inhibited lipogenic, but enhanced myogenic potential. Importantly, concomitant treatment with RGZ virtually blocked all of these nicotine-induced morphologic, molecular, and functional changes. Based on these data, we conclude that BMSCs can be directionally induced to differentiate into the lipofibroblastic phenotype, and PPARγ agonists can effectively block perinatal nicotine-induced MYF transdifferentiation, suggesting a possible molecular therapeutic approach to augment BMSC's lung injury/repair potential.

Oral Chinese Herbal Medicine as an Adjuvant Treatment for Chemotherapy, or Radiotherapy, Induced Myelosuppression: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Objective

Myelosuppression is a common side effect in cancer patients receiving chemotherapy or radiotherapy. Chinese herbal medicine (CHM) has shown promise in alleviating myelosuppression.

Method

We searched for randomized controlled trials (RCTs) from seven databases without language restriction. We included RCTs in adults, in which hematological toxicity was measured according to WHO criteria and control group underwent chemotherapy and/or radiotherapy and the treatment group was given oral CHM.

Results

We searched 1021 articles from the date of databases inception to October 7, 2016. We selected 14 articles for the final analysis. Pooled data showed that CHM significantly decreased the suppression rate of leukocytes, neutrophils, hemoglobin, and platelets compared with the control group, particularly in grade III-IV toxicity (leukocytes: RR = 0.43, 95% CI = 0.33–0.56; neutrophils: RR = 0.39, 95% CI = 0.27–0.58; hemoglobin: RR = 0.33, 95% CI = 0.18–0.61; platelets: RR = 0.61, 95% CI = 0.39–0.95).

Conclusions

CHM as an adjuvant can alleviate myelosuppression induced by chemotherapy or radiotherapy, reduce grade III-IV toxicity, and maintain therapeutic dose and treatment cycle. However, due to heterogeneity and publication bias, the results should be interpreted with caution and validated by conducting strictly designed multicenter RCTs of high quality and large scale.

Characterization and angiogenic potential of human neonatal and infant thymus mesenchymal stromal cells

Resident mesenchymal stromal cells (MSCs) are involved in angiogenesis during thymus regeneration. We have previously shown that MSCs can be isolated from enzymatically digested human neonatal and infant thymus tissue that is normally discarded during pediatric cardiac surgical procedures. In this paper, we demonstrate that thymus MSCs can also be isolated by explant culture of discarded thymus tissue and that these cells share many of the characteristics of bone marrow MSCs. Human neonatal thymus MSCs are clonogenic, demonstrate exponential growth in nearly 30 population doublings, have a characteristic surface marker profile, and express pluripotency genes. Furthermore, thymus MSCs have potent proangiogenic behavior in vitro with sprout formation and angiogenic growth factor production. Thymus MSCs promote neoangiogenesis and cooperate with endothelial cells to form functional human blood vessels in vivo. These characteristics make thymus MSCs a potential candidate for use as an angiogenic cell therapeutic agent and for vascularizing engineered tissues in vitro.

Heterogeneous functions of perinatal mesenchymal stromal cells require a preselection before their banking for clinical use

Perinatal sources of mesenchymal stromal cells (MSCs) have raised growing interest because they are readily and widely available with minimal ethical/legal issues and can easily be stored for allogeneic settings. In addition, perinatal tissues are known to be important in mediating the fetomaternal tolerance of pregnancy, which confer upon perinatal-MSCs (P-MSCs) a particular interest in immunomodulation. It has been recently shown that it is possible to deeply modify the secreted factor profiles of MSCs with different cytokine stimuli such as interferon gamma or tumor necrosis factor alpha to license MSCs for a better immunosuppresive potential. Therefore, we aimed to compare adult bone marrow-MSCs with MSCs from perinatal tissues (cord blood, umbilical cord, amnion, and chorion) on their in vitro immunological and stromacytic efficiencies under different priming conditions. Our results showed that P-MSCs had a potential to modulate the in vitro immune response and be useful for hematopoietic progenitor cell ex vivo expansion. However, we showed contrasted effects of cytokine priming embedded in an important between-donor variability. In conclusion, our study highlights the importance to elaborate predicitive in vitro tests to screen between-donor variability of perinatal tissues for banking allogeneic standardized MSCs.

Are bone marrow regenerative cells ideal seed cells for the treatment of cerebral ischemia?

Bone marrow cells for the treatment of ischemic brain injury may depend on the secretion of a large number of neurotrophic factors. Bone marrow regenerative cells are capable of increasing the secretion of neurotrophic factors. In this study, after tail vein injection of 5-fluorouracil for 7 days, bone marrow cells and bone marrow regenerative cells were isolated from the tibias and femurs of rats, and then administered intravenously via the tail vein after focal cerebral ischemia. Immunohistological staining and reverse transcription-PCR detection showed that transplanted bone marrow cells and bone marrow regenerative cells could migrate and survive in the ischemic regions, such as the cortical and striatal infarction zone. These cells promote vascular endothelial cell growth factor mRNA expression in the ischemic marginal zone surrounding the ischemic penumbra of the cortical and striatal infarction zone, and have great advantages in promoting the recovery of neurological function, reducing infarct size and promoting angiogenesis. Bone marrow regenerative cells exhibited stronger neuroprotective effects than bone marrow cells. Our experimental findings indicate that bone marrow regenerative cells are preferable over bone marrow cells for cell therapy for neural regeneration after cerebral ischemia. Their neuroprotective effect is largely due to their ability to induce the secretion of factors that promote vascular regeneration, such as vascular endothelial growth factor.

CD11a is essential for normal development of hematopoietic intermediates

The process of lymphopoiesis begins in the bone marrow (BM) and requires multiple cellular intermediates. For T cell production, lymphoid progenitors exit the BM and home to the thymus where maturation and selection ensue. These processes are dependent on a number of factors, including chemokines and adhesion molecules. Although the β2 integrin CD11a plays an important role in the migration of lymphocytes to lymph nodes, the role of CD11a in T cell development is largely undefined. Our studies now show that, in CD11a(-/-) mice, thymic cellularity was decreased and early T cell development was partially impaired. Remarkably, CD11a was critical for generation of common lymphoid progenitors (CLPs) and lymphoid-primed multipotent progenitors. However, in intact CD11a(-/-) mice, peripheral B and T cell subsets were only modestly altered, suggesting that compensatory mechanisms were operating. In contrast, competitive BM-reconstitution assays revealed an essential role for CD11a in the generation of thymocytes and mature T and B cells. This defect was linked to the requirement for CD11a in the development of CLPs. Furthermore, our results identified CLPs, and not lymphoid-primed multipotent progenitors, as the requisite CD11a-dependent precursor for lymphocyte development. Thus, these findings established a key role for CD11a in lymphopoiesis.

Hematopoietic effects and mechanisms of Fufang e׳jiao jiang on radiotherapy and chemotherapy-induced myelosuppressed mice

ETHNOPHARMACOLOGICAL RELEVANCE

Fufang e׳jiao jiang (FEJ), which has been widely used in clinic to replenish qi (vital energy) and nourish blood, is a famous traditional Chinese medicine formula made up of Colla corii asini (donkey-hide gelatin prepared by stewing and concentrating from the hide of Equus asinus Linnaeus.), Radix codonopsis pilosulae (the root of Codonopsis pilosula (Franch.) Nannf.), Radix ginseng rubra (the steamed and dried root of Panax ginseng C.A. Mey.), Fructus crataegi (the fruit of Crataegus pinnatifida Bunge) and Radix rehmanniae preparata (the steamed and sun dried tuber of Rehmannia glutinosa (Gaertn.) Libosch. ex Fisch. & C.A. Mey.). The present study aimed to investigate the hematopoietic effects of FEJ on myelosuppressed mice induced by radiotherapy and chemotherapy systematically and to explore the underlying hematopoietic regulation mechanisms.

METHODS

The myelosuppressed mouse model was induced by (60)Co radiation, cyclophosphamide and chloramphenicol. FEJ was then administered by i.g. at the dosages of 5, 10, or 20 mL/kg·d for 10d. The numbers of blood cells from peripheral blood and bone marrow nucleated cells (BMNC) were counted. Body weight and the thymus and spleen indices were also measured. The numbers of hemopoietic progenitor cells and colony-forming unit-fibroblast (CFU-F) were measured in vitro. The ratio of hematopoietic stem cells (HSC) in BMNC, cell cycle and apoptosis of BMNC were determined by flow cytometry. The histology of femoral bone was examined by H&E staining. The levels of transforming growth factor-β (TGF-β), tumor necrosis factor-α (TNF-α), erythropoietin (EPO), granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3) and interleukin-6 (IL-6) in serum were measured by ELISA. IL-1β, IL-3, IL-6 mRNA levels in spleen were detected by real-time quantitative PCR (RT-qPCR). In addition, bone marrow stromal cells (BMSC) were cultured in vitro followed by treatment with different doses of FEJ (2.5, 5, 10 μL/mL) for 48 h. Then the levels of cytokines (IL-6, SCF, GM-CSF) in the conditioned media and their mRNA levels in BMSC were determined by ELISA and RT-qPCR, respectively.

RESULTS

FEJ could significantly increase the numbers of peripheral blood cells and BMNC, and reverse the loss of body weight and the atrophy of thymus and spleen in a dose-dependent manner. The quantities of hemopoietic progenitor cells and CFU-F in bone marrow were also significantly increased in a dose-dependent manner after FEJ administration. A high-dose FEJ of 20 mL/kg·d could significantly increase the ratio of HSC in BMNC, promote bone marrow cells entering the proliferative cycle phase (S+G2/M) and prevent cells from proceeding to the apoptotic phase. FEJ could also improve the femoral bone marrow morphology. Furthermore, FEJ could increase the levels of GM-CSF and IL-3 and reduce the level of TGF-β in serum, and enhance the expressions of IL-1β and IL-3 mRNA in spleen. Lastly, the levels of cytokines (IL-6, SCF, GM-CSF) in the conditioned media and their mRNA levels in BMSC were elevated after treatment with FEJ.

CONCLUSIONS

FEJ was clearly confirmed to promote the recovery of bone marrow hemopoietic function in a myelosuppressed mouse model, which may be attributed to (i) improving bone marrow hematopoietic microenvironment; (ii) facilitating the cell proliferation and preventing BMNC from apoptosis; (iii) stimulating the expressions of IL-1β, IL-3, IL-6, SCF and GM-CSF and inhibiting the expression of TGF-β.

Introduction to stem cells and regenerative medicine

Stem cells are a population of undifferentiated cells characterized by the ability to extensively proliferate (self-renewal), usually arise from a single cell (clonal), and differentiate into different types of cells and tissue (potent). There are several sources of stem cells with varying potencies. Pluripotent cells are embryonic stem cells derived from the inner cell mass of the embryo and induced pluripotent cells are formed following reprogramming of somatic cells. Pluripotent cells can differentiate into tissue from all 3 germ layers (endoderm, mesoderm, and ectoderm). Multipotent stem cells may differentiate into tissue derived from a single germ layer such as mesenchymal stem cells which form adipose tissue, bone, and cartilage. Tissue-resident stem cells are oligopotent since they can form terminally differentiated cells of a specific tissue. Stem cells can be used in cellular therapy to replace damaged cells or to regenerate organs. In addition, stem cells have expanded our understanding of development as well as the pathogenesis of disease. Disease-specific cell lines can also be propagated and used in drug development. Despite the significant advances in stem cell biology, issues such as ethical controversies with embryonic stem cells, tumor formation, and rejection limit their utility. However, many of these limitations are being bypassed and this could lead to major advances in the management of disease. This review is an introduction to the world of stem cells and discusses their definition, origin, and classification, as well as applications of these cells in regenerative medicine.

Recovery from radiation-induced bone marrow damage by HSP25 through Tie2 signaling

PURPOSE

Whole-body radiation therapy can cause severe injury to the hematopoietic system, and therefore it is necessary to identify a novel strategy for overcoming this injury.

METHODS AND MATERIALS

Mice were irradiated with 4.5 Gy after heat shock protein 25 (HSP25) gene transfer using an adenoviral vector. Then, peripheral blood cell counts, histopathological analysis, and Western blotting on bone marrow (BM) cells were performed. The interaction of HSP25 with Tie2 was investigated with mouse OP9 and human BM-derived mesenchymal stem cells to determine the mechanism of HSP25 in the hematopoietic system.

RESULTS

HSP25 transfer increased BM regeneration and reduced apoptosis following whole-body exposure to ionizing radiation (IR). The decrease in Tie2 protein expression that followed irradiation of the BM was blocked by HSP25 transfer, and Tie2-positive cells were more abundant among the BM cells of HSP25-transferred mice, even after IR exposure. Following systemic RNA interference of Tie2 before IR, HSP25-mediated radioprotective effects were partially blocked in both mice and cell line systems. Stability of Tie2 was increased by HSP25, a response mediated by the interaction of HSP25 with Tie2. IR-induced tyrosine phosphorylation of Tie2 was augmented by HSP25 overexpression; downstream events in the Tie2 signaling pathway, including phosphorylation of AKT and EKR1/2, were also activated.

CONCLUSIONS

HSP25 protects against radiation-induced BM damage by interacting with and stabilizing Tie2. This may be a novel strategy for HSP25-mediated radioprotection in BM.

Activated expression of the chemokine Mig after chemotherapy contributes to chemotherapy-induced bone marrow suppression and lethal toxicity

Alterations in gene expression after chemotherapy may potentially help to identify mediators that induce suppression or regeneration in bone marrow. This paper reports our observation that the expression of the chemokine monokine induced by IFN-γ (Mig) and its receptor CXCR3 was significantly activated in mice after treatment with the chemotherapeutic agent 5-fluorouracil (5-FU). The neutralization of antibodies against the activated Mig increased the survival rate and accelerated BM recovery after chemotherapy. In addition, elevation of Mig plasma levels after 5-FU treatment corresponded with increased mortality. The cell cycle-inhibiting effect of the prophylactic administration of Mig protected hematopoietic progenitor cells (HPCs) from 1-β-d-arabinofuranosylcytosine in spleen colony assays and enhanced the irradiated recipients' survival. In CXCR3(-/-) mice, Mig did not propagate BM suppression, indicating that the suppressive effect of Mig is dependent on CXCR3. On the one hand, Mig stimulated p70 S6K and Erk1/2 pathways in mesenchymal stroma cells, inhibiting mesenchymal stroma cell-dependent HPC expansion. Moreover, Mig suppressed the STAT5 pathway in HPCs, inhibiting leukocyte differentiation. Our results strongly suggest that Mig contributes to the acute lethal toxicity arising from 5-FU administration. Neutralization of Mig may offer new strategies to alleviate BM toxicity with potentially dramatic implications for chemotherapy.

Deregulation of the CXCL12/CXCR4 axis in methotrexate chemotherapy-induced damage and recovery of the bone marrow microenvironment

Cancer chemotherapy disrupts the bone marrow (BM) microenvironment affecting steady-state proliferation, differentiation and maintenance of haematopoietic (HSC) and stromal stem and progenitor cells; yet the underlying mechanisms and recovery potential of chemotherapy-induced myelosuppression and bone loss remain unclear. While the CXCL12/CXCR4 chemotactic axis has been demonstrated to be critical in maintaining interactions between cells of the two lineages and progenitor cell homing to regions of need upon injury, whether it is involved in chemotherapy-induced BM damage and repair is not clear. Here, a rat model of chemotherapy treatment with the commonly used antimetabolite methotrexate (MTX) (five once-daily injections at 0.75 mg/kg/day) was used to investigate potential roles of CXCL12/CXCR4 axis in damage and recovery of the BM cell pool. Methotrexate treatment reduced marrow cellularity, which was accompanied by altered CXCL12 protein levels (increased in blood plasma but decreased in BM) and reduced CXCR4 mRNA expression in BM HSC cells. Accompanying the lower marrow CXCL12 protein levels (despite its increased mRNA expression in stromal cells) was increased gene and protein levels of metalloproteinase MMP-9 in bone and BM. Furthermore, recombinant MMP-9 was able to degrade CXCL12 in vitro. These findings suggest that MTX chemotherapy transiently alters BM cellularity and composition and that the reduced cellularity may be associated with increased MMP-9 expression and deregulated CXCL12/CXCR4 chemotactic signalling.

Identification of hub genes related to the recovery phase of irradiation injury by microarray and integrated gene network analysis

BACKGROUND

Irradiation commonly causes long-term bone marrow injury charactertized by defective HSC self-renewal and a decrease in HSC reserve. However, the effect of high-dose IR on global gene expression during bone marrow recovery remains unknown.

METHODOLOGY

Microarray analysis was used to identify differentially expressed genes that are likely to be critical for bone marrow recovery. Multiple bioinformatics analyses were conducted to identify key hub genes, pathways and biological processes.

PRINCIPAL FINDINGS

1) We identified 1302 differentially expressed genes in murine bone marrow at 3, 7, 11 and 21 days after irradiation. Eleven of these genes are known to be HSC self-renewal associated genes, including Adipoq, Ccl3, Ccnd1, Ccnd2, Cdkn1a, Cxcl12, Junb, Pten, Tal1, Thy1 and Tnf; 2) These 1302 differentially expressed genes function in multiple biological processes of immunity, including hematopoiesis and response to stimuli, and cellular processes including cell proliferation, differentiation, adhesion and signaling; 3) Dynamic Gene Network analysis identified a subgroup of 25 core genes that participate in immune response, regulation of transcription and nucleosome assembly; 4) A comparison of our data with known irradiation-related genes extracted from literature showed 42 genes that matched the results of our microarray analysis, thus demonstrated consistency between studies; 5) Protein-protein interaction network and pathway analyses indicated several essential protein-protein interactions and signaling pathways, including focal adhesion and several immune-related signaling pathways.

CONCLUSIONS

Comparisons to other gene array datasets indicate that global gene expression profiles of irradiation damaged bone marrow show significant differences between injury and recovery phases. Our data suggest that immune response (including hematopoiesis) can be considered as a critical biological process in bone marrow recovery. Several critical hub genes that are key members of significant pathways or gene networks were identified by our comprehensive analysis.

Delivery of progenitors to the thymus limits T-lineage reconstitution after bone marrow transplantation

T-cell production depends on the recruitment of hematopoietic progenitors into the thymus. T cells are among the last of the hematopoietic lineages to recover after bone marrow transplantation (BMT), but the reasons for this delay are not well understood. Under normal physiologic conditions, thymic settling is selective and either CCR7 or CCR9 is required for progenitor access into the thymus. The mechanisms of early thymic reconstitution after BMT, however, are unknown. Here we report that thymic settling is briefly CCR7/CCR9-independent after BMT but continues to rely on the selectin ligand PSGL-1. The CCR7/CCR9 independence is transient, and by 3 weeks after BMT these receptors are again strictly required. Despite the normalization of thymic settling signals, the rare bone marrow progenitors that can efficiently repopulate the thymus are poorly reconstituted for at least 4 weeks after BMT. Consistent with reduced progenitor input to the thymus, intrathymic progenitor niches remain unsaturated for at least 10 weeks after BMT. Finally, we show that thymic recovery is limited by the number of progenitors entering the thymus after BMT. Hence, T-lineage reconstitution after BMT is limited by progenitor supply to the thymus.

The effect of prolonged whole-body cryostimulation treatment with different amounts of sessions on chosen pro- and anti-inflammatory cytokines levels in healthy men

Cryotherapy is used in the early treatment of acute injuries (sprains, strains, fractures) yet only a few papers discuss the possible influence of whole-body cryostimulation on inflammation mechanisms or immunology. It is postulated that cold exposure can have an immunostimulating effect related to enhanced noradrenaline response and can be connected with paracrine effects. The aim of this study was to examine the effect of different sequences of whole-body cryostimulations on the level of pro- and anti-inflammatory cytokines in healthy individuals. The research involved 45 healthy men divided into three groups. The groups were subjected to 5, 10 or 20, 3-minute long whole-body cryostimulations each day at -130°C. Blood was collected for analysis before the stimulations, after completion of the whole series, and 2 weeks after completion of the series, for the examination of any long-term effect. The analysis of results showed that in response to cryostimulation, the level of ani-inflammatory cytokines IL-6 and IL-10 increased while Il-1α cytokine level decreased. It seems that the most advantageous sequence was the series of 20 cryostimulations due to the longest lasting effects of stimulation after the completion of the whole series of treatments.

Proteomic definitions of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are pluripotent cells isolated from the bone marrow and various other organs. They are able to proliferate and self-renew, as well as to give rise to progeny of at least the osteogenic, chondrogenic, and adipogenic lineages. Despite this functional definition, MSCs can also be defined by their expression of a distinct set of cell surface markers. In the current paper, studies investigating the proteome of human MSCs are reviewed with the aim to identify common protein markers of MSCs. The proteomic analysis of MSCs revealed a distinct set of proteins representing the basic molecular inventory, including proteins for (i) cell surface markers, (ii) the responsiveness to growth factors, (iii) the reuse of developmental signaling cascades in adult stem cells, (iv) the interaction with molecules of the extracellular matrix, (v) the expression of genes regulating transcription and translation, (vi) the control of the cell number, and (vii) the protection against cellular stress.

Mesenchymal stem cell differentiation and roles in regenerative medicine

Adult stem cells with multi or unipotent differentiation potential are present in almost all tissues of adult organisms. The main function of these stem cells is to support normal repair and rejuvenation of diseased and aging tissues. Mesenchymal stem cells (MSCs) isolated from the bone marrow have the potential to differentiate into multiple connective tissues. Advancements in understanding tissue specific differentiation of MSCs in conjunction with global genomic and proteomic profiling of MSCs have not only provided insights into their biology but also made MSC based clinical trials a reality for treating various debilitating diseases and genetic disorders. The emerging evidence that MSCs are immunosuppressive makes them an even more attractive candidate for regenerative medicine as rejections of transplants by the recipient could be a limiting step for moving the stem cells based therapies from "bedside to bed side." To a large extent the therapeutic potential of MSCs is attributed to their differentiation ability. The fate and commitment of MSCs are regulated by various instructive signals from their immediate vicinity or microenvironment, which comprises many biological molecules (soluble and insoluble) and biomechanical forces. These biochemical and biophysical factors play a pivotal role in determining the efficacy of MSC differentiation and their contribution to the repair process. In this review, we discuss the characteristics of MSCs, their differentiation potential toward different skeletal tissues (cartilage and bone), and their emerging role in regenerative medicine.

Paracrine effects of mesenchymal stem cells in cisplatin-induced renal injury require heme oxygenase-1

Multipotent mesenchymal stem cells (MSC) have become a popular and promising therapeutic approach in many clinical conditions. MSC are beneficial in animal models of acute kidney injury (AKI), by mediating differentiation-independent paracrine properties, and have prompted ongoing clinical trials to evaluate the safety and efficacy of MSC. Heme oxygenase-1 (HO-1) is induced in response to stress including AKI and has important anti-apoptotic, anti-inflammatory, and proangiogenic properties in these settings. We therefore examined whether HO-1 plays a role in the beneficial effects of MSC in AKI. We isolated MSC from bone marrow of age-matched HO-1+/+ and HO-1-/- mice. Our studies indicate that while differentiation of MSC into osteo- and adipocytic lineages did not differ between cells isolated from HO-1+/+ and HO-1-/- mice, MSC from HO-1-/- mice had significantly lower angiogenic potential. Moreover, HO-1-/- MSC demonstrated reduced expression and secretion of several important growth and proangiogenic factors (stromal cell-derived factor-1, vascular endothelial growth factor-A, and hepatocyte growth factor) compared with MSC derived from HO-1+/+ mice. In addition, conditioned medium of HO-1+/+ MSC rescued functional and morphological changes associated with cisplatin-induced AKI, while the HO-1-/--conditioned medium was ineffectual. Our studies indicate that HO-1 plays an important role in MSC-mediated protection. The results expand understanding of the renoprotective effects of MSC and may provide novel strategies to better utilize MSC in various disease models.

Prevention and mitigation of acute death of mice after abdominal irradiation by the antioxidant N-acetyl-cysteine (NAC)

Gastrointestinal (GI) injury is a major cause of acute death after total-body exposure to large doses of ionizing radiation, but the cellular and molecular explanations for GI death remain dubious. To address this issue, we developed a murine abdominal irradiation model. Mice were irradiated with a single dose of X rays to the abdomen, treated with daily s.c. injection of N-acetyl-l-cysteine (NAC) or vehicle for 7 days starting either 4 h before or 2 h after irradiation, and monitored for up to 30 days. Separately, mice from each group were assayed 6 days after irradiation for bone marrow reactive oxygen species (ROS), ex vivo colony formation of bone marrow stromal cells, and histological changes in the duodenum. Irradiation of the abdomen caused dose-dependent weight loss and mortality. Radiation-induced acute death was preceded not only by a massive loss of duodenal villi but also, surprisingly, abscopal suppression of stromal cells and elevation of ROS in the nonirradiated bone marrow. NAC diminished these radiation-induced changes and improved 10- and 30-day survival rates to >50% compared with <5% in vehicle-treated controls. Our data establish a central role for abscopal stimulation of bone marrow ROS in acute death in mice after abdominal irradiation.

Effect of Notch activation on the regenerative response to acute renal failure

Episodes of acute renal failure (ARF) are not always fully reversible and may lead to chronic disease, due in part to an inadequate regenerative response. The Notch signaling pathway is involved in determining cell fate during development, and tissue maintenance and repair in adult organs. The purpose of this study was to examine the role of the Notch pathway in renal regeneration following ARF. Kidney injury, induced by ischemia-reperfusion, resulted in early activation of the Notch pathway, as evidenced by increased expression of Notch1 and Notch2 intracellular domain (cleaved Notch). The effect of exogenous administration of the Notch ligand Delta-like-4 (DLL4) on recovery from ARF was then studied. Rats were pretreated by intraperitoneal injection of DLL4 or vehicle control. Two days following the last DLL4 dose, ARF was induced by bilateral renal artery clamping for 45 min followed by reperfusion. The severity of renal injury was similar in DLL4 and control rats. Renal recovery was facilitated by DLL4 treatment, as evidenced by faster return of serum creatinine to baseline by 48 h in DLL4-treated rats as against 5 days in vehicle-treated control rats. Cell proliferation was higher in the DLL4-treated group. In conclusion, activation of the Notch pathway occurs following ARF. Pretreatment with the Notch ligand DLL4 enhanced recovery from ARF and represents a potential novel therapeutic option for regenerating the injured kidney.

Hibernating myocardium: pathophysiology, diagnosis, and treatment

Comprehensive management of patients with chronic ischemic disease is a critically important component of clinical practice. Cardiac myocytes have the potential to adapt to limited flow conditions by adjusting contractile function, reducing metabolism, conserving resources, and preserving myocardial integrity to cope with an oxygen and (or) nutrition shortage. A prime metabolic feature of cardiac myocytes affected by chronic ischemia is the return to a fetal gene pattern with predominance of carbohydrates as the substrate for energy. Structural adaptation with multiple intracellular changes is part of the remodeling process in hibernating myocardium. Transmural heterogeneity, which defines the pattern of injury in ventricular cardiomyocytes and the response to chronic ischemia, is a multifactorial process originating from functional, metabolic, and flow differences in subendocardial and subepicardial regions. Autophagy is typically activated in hibernating myocardium and has been identified as a prosurvival mechanism. Chronic ischemia is associated with changes in the number, size, and distribution of gap junctions and may give rise to conduction disturbances and arrhythmogenesis. Differentiation between viable and nonviable myocardium by assessing sensitivity of inotropic reserve is a crucial diagnostic tool that is correlated with the prognosis and outcome for improved contractility after restoration of blood perfusion in afflicted myocardium.Reliable and accurate diagnosis of ischemic, scar, and viable tissues is critical for recover strategies. Although early surgical reinstitution of blood flow is most effective in restoring physiologic function of the hibernating myocardium, several new approaches offer promising alternatives. Among others, vascular endothelial growth factor and fibroblast growth factor-2 (FGF-2), especially its lo-FGF-2 isoform, have been shown to be effective in rapid neovascularization. Substances such as statins, resveratrol, some hormones, and omega-3 fatty acids can improve recovery effect in chronically underperfused hearts. For patients with drug-refractory ischemia, intramyocardial transplantation of stem cells into predefined areas of the heart can enhance vascularization and have beneficial effects on cardiac function. This review of ischemic injury, its heterogeneity, accurate diagnosis, and newer methods of treatment, shows there is much information and tremendous hope for better management of patients with coronary heart disease.

Pharmacokinetics and pharmacogenomics in esophageal cancer chemoradiotherapy

Esophageal cancer is one of the most lethal malignancies. Surgical resection of the tumor from the primary site has been the standard treatment, especially for localized squamous cell carcinoma, but considerable clinical efforts during the last decade have resulted in novel courses of treatment. These options include chemoradiotherapy, consisting of a continuous infusion of 5-fluorouracil (5-FU), cisplatin (CDDP), and concurrent radiation. Given the substantial inter- and/or intra-individual variation in clinical outcome, future improvements will likely require the incorporation of a novel anticancer drug, pharmacokinetically guided administration of CDDP or 5-FU, and identification of potential responders by patient genetic profiling prior to treatment. In this review, the latest information on incidence, risk factors, biomarkers, therapeutic strategies, and the pharmacokinetically guided or genotype-guided administration of CDDP and 5-FU is summarized for future individualization of esophageal cancer treatment.

Hyaluronan substratum induces multidrug resistance in human mesenchymal stem cells via CD44 signaling

Little information is available concerning multidrug resistance (MDR) in mesenchymal stem cells, although several studies have reported that MDR is associated with hyaluronan in neoplastic cells. We have evaluated whether a hyaluronan-coated surface modulates MDR in placenta-derived human mesenchymal stem cells (PDMSCs). We have found that PDMSCs cultured on a tissue-culture polystyrene surface coated with 30 microg/cm(2) hyaluronan are more resistant than control PDMSCs to doxorubicin. Inhibiting PI3K/Akt signaling has shown that the PI3K/Akt pathway modulates both P-glycoprotein activity and doxorubicin resistance. In addition, 10 microM verapamil dramatically suppresses the doxorubicin resistance induced by the hyaluronan-coated surface, indicating that P-glycoprotein activity is necessary for MDR. We have further found that PDMSCs treated with CD44 small interfering RNA (siRNA) and grown on a polystyrene surface coated with 30 microg/cm(2) hyaluronan have fewer P-glycoprotein(+) cells and lower CD44 expression levels (less than 60% in both cases) than PDMSCs not treated with CD44 siRNA and grown on the hyaluronan-coated surface. Moreover, treatment with CD44 siRNA suppresses the hyaluronan-substratum-induced doxorubicin resistance. We conclude that a hyaluronan substratum induces MDR in PDMSCs through CD44 signaling.

VEGF G-1154A is predictive of severe acute toxicities during chemoradiotherapy for esophageal squamous cell carcinoma in Japanese patients

This study was conducted to evaluate the association between systemic exposure to 5-fluorouracil (5-FU) and genetic polymorphisms of vascular endothelial growth factor (VEGF) with clinical outcomes to a 5-FU/cisplatin-based chemoradiotherapy in Japanese patients with esophageal squamous cell carcinoma (ESCC). Forty-nine patients with ESCC (I/II/III/IVa = 11/9/17/7, with 5 postoperative recurrences) were enrolled into this study. One course of treatment consisted of protracted venous infusions of 5-FU (400 mg/m2/24 hr for day 1-5 and 8-12) and cisplatin (40 mg/m2/3 hr on day 1 and 8), and radiation (2 Gy/day on day 1-5, 8-12, and 15-19); a second course was repeated after a 2 week interval. A total of eight measurements of the plasma concentration of 5-FU were made per patient to evaluate its systemic exposure as area under the concentration time curve for 480 hours (AUC480h), and VEGF genotypes of T-1498C, G-1154A, C-634G, C-7T, C936T, and G1612A were evaluated. The mean value of AUC480h in the patients with a complete response was 58.7 +/- 16.8 mg*h/L, which was higher than that in the others, 49.0 +/- 10.9 mg*h/L (P = 0.029), whereas no such association was found for severe acute toxicities. VEGF genotype was not associated with the clinical response, whereas VEGF G-1154A resulted in severe acute leukopenia (P = 0.042) and severe acute cheilitis (P = 0.025). In conclusion, VEGF G-1154A was a predictor of severe acute toxicities during 5-FU/cisplatin-based chemoradiotherapy in Japanese ESCC patients, whereas the AUC480h value of 5-FU was predictive of the clinical response.

Hyaluronan substratum holds mesenchymal stem cells in slow-cycling mode by prolonging G1 phase

We examined, in vitro, whether hyaluronan induces slow cycling in placenta-derived mesenchymal stem cells (PDMSCs) by comparing cell growth on a hyaluronan-coated surface with cell growth on a tissue-culture polystyrene surface. The hyaluronan-coated surface significantly downregulated the proliferation of PDMSCs, more of which were maintained in the G(0)/G(1) phases than were cells on the tissue-culture polystyrene surface. Both PKH-26 labeling and BrdU incorporation assays showed that most PDMSCs grown on a hyaluronan-coated surface duplicated during cultivation indicating that the hyaluronan-coated surface did not inhibit PDMSCs from entering the cell cycle. Mitotic synchronization showed that the G(1)-phase transit was prolonged in PDMSCs growing on a hyaluronan-coated surface. Increases in p27(Kip1) and p130 were the crucial factors that allowed hyaluronan to lengthen the G(1) phase. Thus, hyaluronan might be a promising candidate for maintaining stem cells in slow-cycling mode by prolonging their G(1)-phase transit.

Inhibition of gluconeogenesis in primary hepatocytes by stromal cell-derived factor-1 (SDF-1) through a c-Src/Akt-dependent signaling pathway

Hepatic gluconeogenesis is elevated in diabetes and a major contributor to hyperglycemia. Stromal cell-derived factor-1 (SDF-1) is a chemokine and an activator of Akt. In this study, we tested the hypothesis that SDF-1 suppresses hepatic gluconeogenesis through Akt. Our results from isolated primary hepatocytes show that SDF-1alpha and SDF-1beta inhibited glucose production via gluconeogenesis and reduced transcript levels of key gluconeogenic genes glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK). Additionally, SDF-1alpha and SDF-1beta both inhibited activation of the PEPCK promoter. In examining the mechanism by which SDF-1 inhibits gluconeogenesis, we found that SDF-1 promoted phosphorylation of Akt, FoxO1, and c-Src, but did not activate insulin receptor substrate-1-like insulin. Blockade of Akt activation by LY294002, FoxO1 translocation by constitutively nuclear FoxO1 mutant, or c-Src activation by the chemical inhibitor PP2, respectively, blunted SDF-1 suppression of gluconeogenesis. Finally, our results show that knocking down the level of SDF-1 receptor CXCR4 mRNA blocked SDF-1 suppression of gluconeogenesis. Together, our results demonstrate that SDF-1 is capable of inhibiting gluconeogenesis in primary hepatocytes through a signaling pathway distinct from the insulin signaling.

Skeletal stem cells: phenotype, biology and environmental niches informing tissue regeneration

Advances in our knowledge of the biology of skeletal stem cells, together with an increased understanding of the regeneration of normal tissue offer exciting new therapeutic approaches in musculoskeletal repair. Skeletal stem cells from various adult tissues such as bone marrow can be identified and isolated based on their expression of a panel of markers associated with smooth muscle cells, pericytes and endothelial cells. Thus, skeletal stem cell-like populations within bone marrow may share a common perivascular stem cell niche within the microvascular network. To date, the environmental niche that nurtures and maintains the stromal stem cell at different anatomical sites remains poorly understood. However, an understanding of the osteogenic and perivascular niches will inform identification of the key growth factors, matrix constituents and physiological conditions that will enhance the ex vivo amplification and differentiation of osteogenic stem cells to mimic native tissue critical for tissue repair. This review will examine skeletal stem cell biology, the advances in our understanding of the skeletal and perivascular niche and interactions therein and the opportunities to harness that knowledge for musculoskeletal regeneration.

Isolation and characterization of CD146+ multipotent mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) represent a bone marrow (BM) population, classically defined by five functional properties: extensive proliferation, ability to differentiate into osteoblasts, chondrocytes, adipocytes, and stromal cells-supporting hematopoiesis. However, research progress in this area has been hampered by lack of suitable markers and standardized procedures for MSC isolation. We have isolated a CD146(+) multipotent MSC population from 20 human BM donors displaying the phenotype of self-renewing osteoprogenitors; an extensive 12-week proliferation; and the ability to differentiate in osteoblasts, chondrocytes, adipocytes, and stromal cells supporting hematopoiesis. Furthermore, the CD146(+) MSCs secrete a complex combination of growth factors (GFs) controlling hematopoietic stem cells (HSCs) function, while providing a >2-log increase in the long-term culture (LTC) colony output in 8-week LTC over conventional assays. The hematopoietic stromal function exhibited by the MSCs was further characterized by manipulating LTCs with the chemical inhibitors Imatinib or SU-5416, targeting two GF receptors (GFRs), KIT or VEGFR2/1, respectively. Both treatments similarly impaired LTC colony output, indicating key roles for these two GF/GFR interactions to support LTC-initiating cell activity. CD146(+) MSCs may thus represent a tool to explore the MSC-HSC cross-talk in an in vitro surrogate model for HSC "niches," and for regenerative therapy studies. In addition, the MSC microRNA (miRNA) expression profile was analyzed by microarrays in both basic conditions and chondrogenic differentiation. Our analysis revealed that several miRNAs are modulated during chondrogenesis, and many of their putative targets are genes involved in chondrogenic differentiation.

Therapeutic pathways of adult stem cell repair

The use of adult stem cells as therapeutic agents to treat disease has become increasingly prevalent. During the last decade, isolated and expanded stem and progenitor cells have demonstrated the capacity to differentiate into multiple cell types. Early optimism that in vitro differentiation capacity would translate into in vivo tissue regeneration has lessened and identifying the mechanisms that underlie the benefit of stem cell repair is an emerging area of investigation. This review considers several of the pathways and mechanisms required for adult stem cell repair. These mechanisms include the mobilization and the homing of stem cells to sites of injury, immunomodulatory effect of stem cells, and the association of stem cells with increased vascularization of injured tissue. These data suggest that the unique properties of adult stem cells can be utilized to treat a wide variety of diseases that cannot be treated with existing pharmacological agents, and prompt new paradigms for the bio-pharmacokinetics of biological expressed by efficacious stem cells.

Notch signaling regulates regeneration in the avian retina

The chicken retina is capable of limited regeneration. In response to injury, some Müller glia proliferate and de-differentiate into progenitor cells. However, most of these progenitors fail to differentiate into neurons. The Notch pathway is upregulated during retinal regeneration in both fish and amphibians. Since the Notch signaling pathway maintains cells in a progenitor state during development, we hypothesized that a persistently active Notch pathway might prevent a more successful regeneration in the chick retina. We found that Notch signaling components are upregulated in the proliferating progenitors. We also found that blocking the Notch pathway while Müller glia are de-differentiating into progenitor cells prohibits regeneration; conversely, blocking the Notch pathway after the progenitors have been generated from the Müller glia caused a significant increase in the percentage of new neurons. Thus, Notch signaling appears to play two distinct roles during retinal regeneration. Initially, Notch activity is necessary for the de-differentiation/proliferation of Müller glia, while later it inhibits the differentiation of the newly generated progenitor cells.

Fibroblast growth factor-2 and cardioprotection

Boosting myocardial resistance to acute as well as chronic ischemic damage would ameliorate the detrimental effects of numerous cardiac pathologies and reduce the probability of transition to heart failure. Experimental cardiology has pointed to ischemic and pharmacological pre- as well as post-conditioning as potent acute cardioprotective manipulations. Additional exciting experimental strategies include the induction of true regenerative and/or angiogenic responses to the damaged heart, resulting in sustained structural and functional beneficial effects. Fibroblast growth factor-2 (FGF-2), an endogenous multifunctional protein with strong affinity for the extracellular matrix and basal lamina and well-documented paracrine, autocrine and intracellular modes of action, has been shown over the years to exert acute and direct pro-survival effects, irrespectively of whether it is administered before, during or after an ischemic insult to the heart. FGF-2 is also a potent angiogenic protein and a crucial agent for the proliferation, expansion, and survival of several cell types including those with stem cell properties. Human clinical trials have pointed to a good safety record for this protein. In this review, we will present a case for the low molecular weight isoform of fibroblast growth factor-2 (lo-FGF-2) as a very promising therapeutic agent to achieve powerful acute as well as sustained benefits for the heart, due to its cytoprotective and regenerative properties.

Nothing but skin and bone

Skin and bone - what comes to mind at hearing this phrase? While certainly a metaphor for disease, it also defines two very different tissues, one a flexible and contiguous outer covering, the other a morphologically diverse hard tissue distributed at over 200 sites in the body. As the accompanying series of Reviews highlights, these tissues are indeed diverse, but there are also surprising similarities. Skin is the interface between the internal organs and the environment, and as such plays a crucial role in the body's defense mechanism. The skin and its many appendages are responsible for functions as diverse as epidermal barrier and defense, immune surveillance, UV protection, thermoregulation, sweating, lubrication, pigmentation, the sensations of pain and touch, and, importantly, the protection of various stem cell niches in the skin. Bone serves a number of purposes: it provides protection for vital organs, a lever for locomotion, a reservoir for calcium, and the site of adult hematopoiesis. The tissue is composed of osteoblasts, osteoclasts, and their individual precursors plus a complex mixture of mesenchymal, myeloid, and lymphoid cells in the marrow space. Finally, the endothelial microenvironment provides nutrition and is a conduit for the influx and emigration of cells that impact bone biology in several important ways. This Review series guides the reader through these various facets of 2 diverse, yet interdependent, tissues.

Kidney side population reveals multilineage potential and renal functional capacity but also cellular heterogeneity

Side population (SP) cells in the adult kidney are proposed to represent a progenitor population. However, the size, origin, phenotype, and potential of the kidney SP has been controversial. In this study, the SP fraction of embryonic and adult kidneys represented 0.1 to 0.2% of the total viable cell population. The immunophenotype and the expression profile of kidney SP cells was distinct from that of bone marrow SP cells, suggesting that they are a resident nonhematopoietic cell population. Affymetrix expression profiling implicated a role for Notch signaling in kidney SP cells and was used to identify markers of kidney SP. Localization by in situ hybridization confirmed a primarily proximal tubule location, supporting the existence of a tubular "niche," but also revealed considerable heterogeneity, including the presence of renal macrophages. Adult kidney SP cells demonstrated multilineage differentiation in vitro, whereas microinjection into mouse metanephroi showed that SP cells had a 3.5- to 13-fold greater potential to contribute to developing kidney than non-SP main population cells. However, although reintroduction of SP cells into an Adriamycin-nephropathy model reduced albuminuria:creatinine ratios, this was without significant tubular integration, suggesting a humoral role for SP cells in renal repair. The heterogeneity of the renal SP highlights the need for further fractionation to distinguish the cellular subpopulations that are responsible for the observed multilineage capacity and transdifferentiative and humoral activities.