Bone marrow-derived cells contribute to pulmonary vascular remodeling in hypoxia-induced pulmonary hypertension

STUDY OBJECTIVE: In these days, it was reported that bone marrow (BM) cells might take part in the remodeling of some systemic vascular diseases; however, it remains unknown whether the BM cells were involved in the vascular remodeling of pulmonary arteries and the progression of pulmonary hypertension (PH). The purpose of this study was to investigate whether BM-derived cells contribute to pulmonary vascular remodeling in hypoxia-induced PH. MATERIALS AND METHODS: To investigate the role of BM-derived cells, we transplanted the whole BM of enhanced green fluorescent protein (GFP)-transgenic mice to the lethally irradiated syngeneic mice (n = 30). After 8 weeks, chimera mice were exposed to consistent hypoxia using a hypoxic chamber (10% O(2)) for up to 4 or 8 weeks (10 mice per group). After hemodynamics and the ratio of right ventricular (RV) weight to left ventricle (LV) weight, RV/(LV + septum [S]), were measured, histologic and immunofluorescent staining were performed. RESULTS: BM-transplanted mice showed a high chimerism (mean [+/- SEM], 91 +/- 2.3%). RV systolic pressure and the RV/(LV + S) ratio increased significantly with time in PH mice, indicating RV hypertrophy. Marked vascular remodeling including medial hypertrophy and adventitial proliferation was observed in the pulmonary arteries of PH mice. Strikingly, a number of GFP(+) cells were observed at the pulmonary arterial wall, including the adventitia, in hypoxia-induced PH mice, while very few cells were observed in the control mice. Metaspectrometer measurements using confocal laser scanning microscopy confirmed that this green fluorescence was produced by GFP, suggesting that these GFP(+) cells were mobilized from the BM. Most of them expressed alpha-smooth muscle actin, a smooth muscle cell, or myofibroblast phenotype, and contributed to the pulmonary vascular remodeling. A semiquantitative polymerase chain reaction of the GFP gene revealed that the BM-derived GFP-positive cells in the PH group were observed more than eightfold as often compared with the control mice. CONCLUSION: The BM-derived cells mobilize to the hypertensive pulmonary arteries and contribute to the pulmonary vascular remodeling in hypoxia-induced PH mice.     

Bone marrow-derived cells contribute to infarct remodelling

OBJECTIVE: The paradigm that cardiac myocytes are non-proliferating and terminally differentiated cells has recently been challenged by several studies reporting the ability of bone marrow-derived cells (BMC) to transdifferentiate into cardiomyocytes. However, these results are controversial and could not be reproduced by others. Therefore, we studied the contribution and potential transdifferentiation of BMC into different cell types during the remodelling process in mouse hearts with experimental myocardial infarction. METHODS: Mice (C57BL/6J) were sublethally irradiated, and BM from enhanced green fluorescent protein (eGFP)-transgenic mice was transplanted. Coronary artery ligation was performed 3 months later. The hearts were studied 7 days (n=13) and 21 days (n=12) after infarction. Immunohistochemical staining was performed using antibodies against titin, connexin 43, vimentin, SMemb alpha-smooth muscle actin, CD45, CD34, F4/80, BS-1, CD31, and eGFP. Sections were analyzed using fluorescence and confocal laser microscopy. RESULTS: Success of BM transplantation was confirmed by FACS analysis. Occlusion of the coronary artery resulted in infarct sizes of 41+/-6% of the left ventricle. CD45+/eGFP+ inflammatory cells were found frequently after 7 days and to a lesser degree after 21 days. In 25 examined hearts, only 3 eGFP-positive cardiomyocytes were found. However, numerous BMC-derived fibroblasts and myofibroblasts were found in the infarct area. BMC contributed to scar tissue neoangiogenesis but not to angiogenesis in the periinfarct and remote zones. CONCLUSION: Transdifferentiation of BMC into viable cardiomyocytes is a negligible event in normal repair processes after myocardial damage. BMC-derived fibroblasts and myofibroblasts as well as neoangiogenesis significantly contribute to post-infarction scar formation and might be important in scar tissue remodelling.     

Bone marrow-derived lung epithelial cells

Bone marrow-derived cells can take on the phenotype of epithelial cells and express epithelial-specific genes in multiple organs. Here, we focus on recent data on the appearance of marrow-derived epithelial cells in the adult lung. These findings have garnered significant skepticism because in most cases marrow-derived epithelial cells are very rare, the marrow cell of origin is not known, the techniques for detection have needed improvement, and there seem to be multiple mechanisms by which this occurs. Recent studies have focused on these concerns. Once these important concerns are addressed, further studies on the function(s) of these cells will need to be performed to determine whether this engraftment has any clinical significance-either beneficial or detrimental.     

Bone marrow-derived proangiogenic cells in pancreatic cancer

Tumor-derived signals systemically induce an angiogenic switch that allows cancer cells to survive and grow. However, the vascular network in tumors is not well organized and fails to meet metabolic needs to maintain tissue homeostasis, resulting in significant hypoxia. Among various tumors, pancreatic ductal adenocarcinoma (PDAC) typically develops in an unusually disordered microenvironment, which contributes to its highly aggressive behavior. Since anti-vascular endothelial growth factor (VEGF) (Avastin) has failed to demonstrate a survival benefit in PDAC, we need to re-visit the basic biology of this disease and understand what makes it so refractory to the anti-angiogenic approaches that are clinically effective in other neoplasms. To address this issue, we specifically focused on the process of neovascularization where bone marrow-derived cells (BMDCs) play a role during pancreatic tumorigenesis. We have identified subsets of BMDCs that regulate key processes during development of the neovessels through paracrine Hedgehog signaling. Considering the importance of systemic responses occurring in tumor bearing hosts, we are currently using genetically engineered mice, which spontaneously develop PDAC, Pdx1-Cre;LSL-Kras(G12D);p53(lox/+) strain, to clarify critical events that can trigger aberrant angiogenesis in pancreatic cancer. These studies allow us to provide insights into the cellular and molecular mechanisms of pancreatic tumorigenesis and have an implication for the design of therapies against this difficult disease.     

Bone marrow-derived immune cells mediate sensitization to liver injury in a myeloid differentiation factor 88-dependent fashion

Toll-like receptors (TLRs) expressed on both immune cells and hepatocytes recognize microbial danger signals and regulate immune responses. Previous studies showed that TLR9 and TLR2 mediate Propionibacterium acnes-induced sensitization to lipopolysaccharide-triggered acute liver injury in mice. Ligand-specific activation of TLR2 and TLR9 are dependent on the common TLR adaptor, myeloid differentiation factor 88 (MyD88). Here, we dissected the role of MyD88 in parenchymal and bone marrow (BM)-derived cells in liver sensitization. Using chimeric mice with green fluorescent protein-expressing BM cells, we identified that P. acnes-induced liver inflammatory foci are of BM origin. Chimeras with MyD88-deficient BM showed no inflammatory foci after P. acnes or TLR2+TLR9 challenge, suggesting that recruitment of inflammatory cells to the liver required MyD88 expression in BM-derived cells. Further, selective MyD88 deficiency in parenchymal cells in mice with wild-type BM failed to prevent inflammatory cell infiltration. These results demonstrate that MyD88 in immune cells rather than in liver parenchymal cells plays an important role in inflammatory cell recruitment and liver injury.     

Bone marrow-derived cells and stem cells in lung repair

Although it has been many years since publication of the first peer-reviewed studies showing that bone marrow (BM)-derived cells can become mature-appearing epithelial cells, we still know very little regarding the mechanisms, kinetics, cells, and potential clinical utility or pathology associated with this phenomenon. The initial discovery of BM-derived epithelial cells (BMDE) in the liver was published by Petersen and colleagues (Petersen BE, Bowen WC, Patrene KD, Mars WM, Sullivan AK, Murase N, Boggs SS, Greenberger JS, Goff JP. Bone marrow as a potential source of hepatic oval cells. Science 1999;284:1168-1170). Since that time, BMDE were identified in the skin, eye, GI tract, kidney, and the lung. Surprisingly, once several laboratories started to examine the effects of BM cells after tissue injury, BM-derived cells of different types were found to decrease tissue injury and enhance tissue repair, often without engraftment of marrow-derived epithelial cells. Thus, the potentially beneficial effects of BM-derived cells in some tissue microenvironments may be unrelated to differentiation into nonhematopoietic cell types. Here, I focus on recent findings from my laboratory as well as several other laboratories on the effects of BM cells on lung damage, and BMDE in the lung, including tracheal epithelial cells, bronchiolar epithelial cells, and type II pneumocytes in the alveoli. Potential mechanisms underlying the appearance of marrow-derived epithelial cells, and the role of tissue damage are discussed.     

Bone marrow-derived mesenchymal stromal cells for the repair of central nervous system injury

Transplantation of bone marrow-derived mesenchymal stromal cells (MSCs) into the injured brain or spinal cord may provide therapeutic benefit. Several models of central nervous system (CNS) injury have been examined, including that of ischemic stroke, traumatic brain injury and traumatic spinal cord injury in rodent, primate and, more recently, human trials. Although it has been suggested that differentiation of MSCs into cells of neural lineage may occur both in vitro and in vivo, this is unlikely to be a major factor in functional recovery after brain or spinal cord injury. Other mechanisms of recovery that may play a role include neuroprotection, creation of a favorable environment for regeneration, expression of growth factors or cytokines, vascular effects or remyelination. These mechanisms are not mutually exclusive, and it is likely that more than one contribute to functional recovery. In light of the uncertainty surrounding the fate and mechanism of action of MSCs transplanted into the CNS, further preclinical studies with appropriate animal models are urgently needed to better inform the design of new clinical trials.     

Bone marrow-derived cells can acquire renal stem cells properties and ameliorate ischemia-reperfusion induced acute renal injury

ABSTRACT: BACKGROUND: Bone marrow (BM) stem cells have been reported to contribute to tissue repair after kidney injury model. However, there is no direct evidence so far that BM cells can trans-differentiate into renal stem cells. METHODS: To investigate whether BM stem cells contribute to repopulate the renal stem cell pool, we transplanted BM cells from transgenic mice, expressing enhanced green fluorescent protein (EGFP) into wild-type irradiated recipients. Following hematological reconstitution and ischemia-reperfusion (I/R), Sca-1 and c-Kit positive renal stem cells in kidney were evaluated by immunostaining and flow cytometry analysis. Moreover, granulocyte colony stimulating factor (G-CSF) was administrated to further explore if G-CSF can mobilize BM cells and enhance trans-differentiation efficiency of BM cells into renal stem cells. RESULTS: BM-derived cells can contribute to the Sca-1+ or c-Kit+ renal progenitor cells population, although most renal stem cells came from indigenous cells. Furthermore, G-CSF administration nearly doubled the frequency of Sca-1+ BM-derived renal stem cells and increased capillary density of I/R injured kidneys. CONCLUSIONS: These findings indicate that BM derived stem cells can give rise to cells that share properties of renal resident stem cell. Moreover, G-CSF mobilization can enhance this effect.     

Bone marrow-derived stem cells and respiratory disease

Adult bone marrow contains a number of discrete populations of progenitor cells, including endothelial, mesenchymal, and epithelial progenitor cells and fibrocytes. In the context of a range of diseases, endothelial progenitor cells have been reported to promote angiogenesis, mesenchymal stem cells are potent immunosuppressors but can also contribute directly to tissue regeneration, and fibrocytes have been shown to induce tissue fibrosis. This article provides an overview of the basic biology of these different subsets of progenitor cells, reporting their distinct phenotypes and functional activities. The differences in their secretomes are highlighted, and the relative role of cellular differentiation vs paracrine effects of progenitor cells is considered. The article reviews the literature examining the contribution of progenitor cells to the pathogenesis of respiratory disease, and discusses recent studies using bone marrow progenitor cells as stem cell therapies in the context of pulmonary hypertension, COPD, and asthma.     

Bone marrow-derived stem cells and "plasticity"

Studies describing plasticity of somatic stem cells have become a focus of interest because clinical applications in the treatment of degenerative diseases would be at hand. In particular, bone marrow-derived cells and their potential to contribute to skeletal and cardiac muscle, liver, neurons and epithelium have recently been studied extensively. Nevertheless, results of these studies have not always been consistent with each other, and yet it remains to be resolved whether plasticity of adult stem cells truly exists. This review will discuss the role of bone marrow-derived stem cells in the field of experimental and clinical plasticity studies. Observations compatible with the concept of stem cell plasticity will be weighed against limitations of the experimental systems employed.     

Bone marrow-derived cells and tumor growth: contribution of bone marrow-derived cells to tumor micro-environments with special focus on mesenchymal stem cells

Research has provided evidence that tumor growth depends on the interaction of tumor cells with stromal cells, as already suggested in 1889 by Paget. Experimental and clinical studies have revealed that tumor stromal cells can be derived from bone marrow (BM)-derived progenitor cells, such as mesenchymal stem cells (MSCs), which can be mobilized into the circulation and incorporate into tumor micro-environments. Many observations indicate that, in the tumor micro-environment, MSCs have several tumor growth promoting functions, including expression of growth factors, promotion of tumor vessel formation and creation of tumor stem cell niches. This review will discuss the currently known tumor growth promoting BM-derived cells and focus on the role of MSCs in modulating tumor micro-environments. In addition, we will discuss the potential of inhibiting BM-derived cells and their utilization as cellular vehicles for selective delivery of cancer therapeutics as additional strategies in the treatment of cancer.     

Bone marrow-derived cells in ocular neovascularization: contribution and mechanisms

Ocular neovascularization often leads to severe vision loss. The role of bone marrow-derived cells (BMCs) in the development of ocular neovascularization, and its significance, is increasingly being recognized. In this review, we discuss their contribution and the potential mechanisms that mediate the effect of BMCs on the progression of ocular neovascularization. The sequence of events by which BMCs participate in ocular neovascularization can be roughly divided into four phases, i.e., mobilization, migration, adhesion and differentiation. This process is delicately regulated and liable to be affected by multiple factors. Cytokines such as vascular endothelial growth factor, granulocyte colony-stimulating factor and erythropoietin are involved in the mobilization of BMCs. Studies have also demonstrated a key role of cytokines such as stromal cell-derived factor-1, tumor necrosis factor-α, as well as vascular endothelial growth factor, in regulating the migration of BMCs. The adhesion of BMCs is mainly regulated by vascular cell adhesion molecule-1, intercellular adhesion molecule-1 and vascular endothelial cadherin. However, the mechanisms regulating the differentiation of BMCs are largely unknown at present. In addition, BMCs secrete cytokines that interact with the microenvironment of ocular neovascularization; their contribution to ocular neovascularization, especially choroidal neovascularization, can be aggravated by several risk factors. An extensive regulatory network is thought to modulate the role of BMCs in the development of ocular neovascularization. A comprehensive understanding of the involved mechanisms will help in the development of novel therapeutic strategies related to BMCs. In this review, we have limited the discussion to the recent progress in this field, especially the research conducted at our laboratory.     

Bone marrow-derived cells do not engraft into skeletal muscle microvasculature but promote angiogenesis after acute injury

The skeletal muscle is supported by a vast network of microvessels with the capacity to regenerate in response to injury. However, the dynamics of microvascular repair and the origin of reconstituted endothelial cells in the skeletal muscle are poorly understood. A growing body of literature exists to indicate bone marrow (BM)-derived cells engraft into regenerating vascular endothelium and muscle macrovasculature. Therefore, we investigated the extent of BM contribution to skeletal muscle microvasculature after acute injury. Because reporters and markers commonly used to trace donor BM cells are not endothelial specific but are also expressed by leukocytes, we generated novel BM chimeras utilizing Tie2-green fluorescent protein BM cells transplanted into CD31 and Caveolin-1 knockout recipients. In turn, we surveyed BM vascular contribution, not just by the presence of green fluorescent protein, but also CD31 and Caveolin-1, respectively. After stable BM reconstitution, chimera limb muscles were cardiotoxin (CTX) injured and examined 21 days post-injury for the presence of green fluorescent protein, CD31, and Caveolin-1. Acute muscle injury by CTX is characterized by initial microvasculature death followed by rapid endothelial regeneration within 14 days post-damage. Histological analysis of injured and uninjured contralateral limb muscles revealed a complete absence of BM engraftment in the muscle vasculature of wild-type and CD31/Caveolin-1 knockout chimeras. In contrast, F4/80(+) cells isolated from CTX-injured muscle, expressed endothelial-related markers and promoted angiogenesis in?vitro. Therefore, despite the absence of BM engraftment to regenerated skeletal muscle microvasculature, macrophages recruited after injury promote angiogenesis and, in turn, vascular regeneration.     

Bone marrow-derived cells: roles in solid tumor. Minireview

The role of cancer stem cells has been demonstrated for some cancers. Recently, research indicated that solid tumors may originate from bone marrow stem cells. Bone marrow-derived cells have recently been shown to contribute to stromal formation, especially angiogenesis and lymphvasculogenesis. Moreover, the interaction and the cell fusion between cancer cells and bone mesenchymal stem cells could enhance the aggregative ability of cancer cells. Bone marrow derived cells home to tumor-specific pre-metastatic sites to provide a permissive niche for incoming tumor cells. Since bone marrow-derived cells play an important role in carcinogenesis, angiogenesis and metastasis, bone marrow-derived cells are not only the tool for cancer therapy, but also the targets for cancer therapy.