Lnk deletion reinforces the function of bone marrow progenitors in promoting neovascularization and astrogliosis following spinal cord injury

Role of small molecules as drug candidates for reprogramming somatic cells into induced pluripotent stem cells: A comprehensive review

With the use of specific genetic factors and recent developments in cellular reprogramming, it is now possible to generate lineage-committed cells or induced pluripotent stem cells (iPSCs) from readily available and common somatic cell types. However, there are still significant doubts regarding the safety and effectiveness of the current genetic methods for reprogramming cells, as well as the conventional culture methods for maintaining stem cells. Small molecules that target specific epigenetic processes, signaling pathways, and other cellular processes can be used as a complementary approach to manipulate cell fate to achieve a desired objective. It has been discovered that a growing number of small molecules can support lineage differentiation, maintain stem cell self-renewal potential, and facilitate reprogramming by either increasing the efficiency of reprogramming or acting as a genetic reprogramming factor substitute. However, ongoing challenges include improving reprogramming efficiency, ensuring the safety of small molecules, and addressing issues with incomplete epigenetic resetting. Small molecule iPSCs have significant clinical applications in regenerative medicine and personalized therapies. This review emphasizes the versatility and potential safety benefits of small molecules in overcoming challenges associated with the iPSCs reprogramming process.

Aquaporin 4 beyond a water channel; participation in motor, sensory, cognitive and psychological performances, a comprehensive review

Aquaporin 4 (AQP4) is a protein highly expressed in the central nervous system (CNS) and peripheral nervous system (PNS) as well as various other organs, whose different sites of action indicate its importance in various functions. AQP4 has a variety of essential roles beyond water homeostasis. In this article, we have for the first time summarized different roles of AQP4 in motor and sensory functions, besides cognitive and psychological performances, and most importantly, possible physiological mechanisms by which AQP4 can exert its effects. Furthermore, we demonstrated that AQP4 participates in pathology of different neurological disorders, various effects depending on the disease type. Since neurological diseases involve a spectrum of dysfunctions and due to the difficulty of obtaining a treatment that can simultaneously affect these deficits, it is therefore suggested that future studies consider the role of this protein in different functional impairments related to neurological disorders simultaneously or separately by targeting AQP4 expression and/or polarity modulation.

Intravenous injection of adult human bone marrow mesenchymal stromal cells attenuates spinal cord ischemia/reperfusion injury in a murine aortic arch crossclamping model

OBJECTIVE

We sought to investigate the efficacy of human bone marrow mesenchymal stem/stromal cell (hBM-MSC) in a murine spinal cord ischemia/reperfusion (SCIR) model.

METHODS

C57BL/6J mice were subjected to SCIR by crossclamping the aortic arch and left subclavian artery for 5.5 minutes. Two hours after reperfusion, hBM-MSCs (hBM-MSC group) or phosphate-buffered saline (control group) were intravenously injected without immunosuppressant. Hindlimb motor function was assessed until day 28 after reperfusion using the Basso Mouse Scale (BMS). The lumbar spinal cord was harvested at hour 24 and day 28, and the histologic number of NeuN-positive motor neurons in 3 cross-sections of each lumbar spinal cord and the gene expression were evaluated.

RESULTS

BMS score was 0 throughout the study period in all control mice. BMS score was significantly greater in the hBM-MSC group than the control group from hour 8 (P < .05) to day 28 (P < .01). The numbers of motor neurons at hour 24 (P < .01) and day 28 (P < .05) were significantly preserved in the hBM-MSC group than the control group. mRNA expression levels of proinflammatory cytokines were significantly lower (P < .05), and those of insulin-like growth factor-1 (P < .01) and proangiogenic factors (P < .05) were significantly greater in the hBM-MSC group than the control group at hour 24.

CONCLUSIONS

hBM-MSC therapy may attenuate SCIR injury by preserving motor neurons, at least in part, through inhibition of proinflammatory cytokines and upregulation of proangiogenic factors in the reperfusion-injured spinal cord.

Tissue-specific endothelial cells: a promising approach for augmentation of soft tissue repair in orthopedics

Biologics are playing an increasingly significant role in the practice of modern medicine and surgery in general and orthopedics in particular. Cell-based approaches are among the most important and widely used modalities in orthopedic biologics, with mesenchymal stem cells and other multi/pluripotent cells undergoing evaluation in numerous preclinical and clinical studies. On the other hand, fully differentiated endothelial cells (ECs) have been found to perform critical roles in homeostasis of visceral tissues through production of an adaptive panel of so-called "angiocrine factors." This newly discovered function of ECs renders them excellent candidates for novel approaches in cell-based biologics. Here, we present a review of the role of ECs and angiocrine factors in some visceral tissues, followed by an overview of current cell-based approaches and a discussion of the potential applications of ECs in soft tissue repair.

Transplantation of Hematopoietic Stem Cells Promotes Functional Improvement Associated with NT-3-MEK-1 Activation in Spinal Cord-Transected Rats

Transected spinal cord injury (SCT) is a devastating clinical disease that strongly affects a patient’s daily life and remains a great challenge for clinicians. Stem-cell therapy has been proposed as a potential therapeutic modality for SCT. To investigate the effects of hematopoietic stem cells (HSCs) on the recovery of structure and function in SCT rats and to explore the mechanisms associated with recovery, 57 adult Sprague-Dawley rats were randomly divided into sham (n = 15), SCT (n = 24), and HSC transplantation groups (n = 15). HSCs (passage 3) labeled by Hoechst 33342, were transplanted intraspinally into the rostral, scar and caudal sites of the transected lesion at 14 days post-operation. Both in vitro and in vivo, HSCs exhibited a capacity for cell proliferation and differentiation. Following HSC transplantation, the animals’ Basso, Beattie, and Bresnahan (BBB). locomotion scale scores increased significantly between weeks 4 and 24 post-SCT, which corresponded to an increased number of 5-hydroxytryptamine (5-HT) fibers and oligodendrocytes. The amount of astrogliosis indicated by immunohistochemical staining, was markedly decreased. Moreover, the decreased expression of neurotrophin- 3 (NT-3) and mitogen-activated protein kinase kinase-1 (MEK-1) after SCT was effectively restored by HSC transplantation. The data from the current study indicate that intraspinally administered HSCs in the chronic phase of SCT results in an improvement in neurological function. Further, the results indicate that intraspinally administered HSCs benefit the underlying mechanisms involved in the enhancement of 5-HT-positive fibers and oligogenesis, the suppression of excessive astrogliosis and the upregulation of NT3-regulated MEK-1 activation in the spinal cord. These crucial findings reveal not only the mechanism of cell therapy, but may also contribute to a novel therapeutic target for the treatment of spinal cord injury (SCI).

The Use of Endothelial Progenitor Cells for the Regeneration of Musculoskeletal and Neural Tissues

Endothelial progenitor cells (EPCs) derived from bone marrow and blood can differentiate into endothelial cells and promote neovascularization. In addition, EPCs are a promising cell source for the repair of various types of vascularized tissues and have been used in animal experiments and clinical trials for tissue repair. In this review, we focused on the kinetics of endogenous EPCs during tissue repair and the application of EPCs or stem cell populations containing EPCs for tissue regeneration in musculoskeletal and neural tissues including the bone, skeletal muscle, ligaments, spinal cord, and peripheral nerves. EPCs can be mobilized from bone marrow and recruited to injured tissue to contribute to neovascularization and tissue repair. In addition, EPCs or stem cell populations containing EPCs promote neovascularization and tissue repair through their differentiation to endothelial cells or tissue-specific cells, the upregulation of growth factors, and the induction and activation of endogenous stem cells. Human peripheral blood CD34(+) cells containing EPCs have been used in clinical trials of bone repair. Thus, EPCs are a promising cell source for the treatment of musculoskeletal and neural tissue injury.

Specific disruption of Lnk in murine endothelial progenitor cells promotes dermal wound healing via enhanced vasculogenesis, activation of myofibroblasts, and suppression of inflammatory cell recruitment

BACKGROUND

Although endothelial progenitor cells (EPCs) contribute to wound repair by promoting neovascularization, the mechanism of EPC-mediated wound healing remains poorly understood due to the lack of pivotal molecular targets of dermal wound repair.

METHODS AND RESULTS

We found that genetic targeting of the Lnk gene in EPCs dramatically enhances the vasculogenic potential including cell proliferation, migration, and tubule-like formation as well as accelerates in vivo wound healing, with a reduction in fibrotic tissue and improved neovascularization via significant suppression of inflammatory cell recruitment. When injected into wound sites, Lnk ^-/- EPCs gave rise to a significant number of new vessels, with remarkably increased survival of transplanted cells and decreased recruitment of cytotoxic T cells, macrophages, and neutrophils, but caused activation of fibroblasts in the wound-remodeling phase. Notably, in a mouse model of type I diabetes, transplanted Lnk ^-/- EPCs induced significantly better wound healing than Lnk ^+/+ EPCs did.

CONCLUSIONS

The specific targeting of Lnk may be a promising EPC-based therapeutic strategy for dermal wound healing via improvement of neovascularization but inhibition of excessive inflammation as well as activation of myofibroblasts during dermal tissue remodeling.

Angiogenic microspheres promote neural regeneration and motor function recovery after spinal cord injury in rats

This study examined sustained co-delivery of vascular endothelial growth factor (VEGF), angiopoietin-1 and basic fibroblast growth factor (bFGF) encapsulated in angiogenic microspheres. These spheres were delivered to sites of spinal cord contusion injury in rats, and their ability to induce vessel formation, neural regeneration and improve hindlimb motor function was assessed. At 2–8 weeks after spinal cord injury, ELISA-determined levels of VEGF, angiopoietin-1, and bFGF were significantly higher in spinal cord tissues in rats that received angiogenic microspheres than in those that received empty microspheres. Sites of injury in animals that received angiogenic microspheres also contained greater numbers of isolectin B4-binding vessels and cells positive for nestin or β III-tubulin (P < 0.01), significantly more NF-positive and serotonergic fibers, and more MBP-positive mature oligodendrocytes. Animals receiving angiogenic microspheres also suffered significantly less loss of white matter volume. At 10 weeks after injury, open field tests showed that animals that received angiogenic microspheres scored significantly higher on the Basso-Beattie-Bresnahan scale than control animals (P < 0.01). Our results suggest that biodegradable, biocompatible PLGA microspheres can release angiogenic factors in a sustained fashion into sites of spinal cord injury and markedly stimulate angiogenesis and neurogenesis, accelerating recovery of neurologic function.

Lnk is an important modulator of insulin-like growth factor-1/Akt/peroxisome proliferator-activated receptor-gamma axis during adipogenesis of mesenchymal stem cells

Adipogenic differentiation of mesenchymal stem cells (MSCs) is critical for metabolic homeostasis and nutrient signaling during development. However, limited information is available on the pivotal modulators of adipogenic differentiation of MSCs. Adaptor protein Lnk (Src homology 2B3 [SH2B3]), which belongs to a family of SH2-containing proteins, modulates the bioactivities of different stem cells, including hematopoietic stem cells and endothelial progenitor cells. In this study, we investigated whether an interaction between insulin-like growth factor-1 receptor (IGF-1R) and Lnk regulated IGF-1-induced adipogenic differentiation of MSCs. We found that wild-type MSCs showed greater adipogenic differentiation potential than Lnk^–/– MSCs. An ex vivo adipogenic differentiation assay showed that Lnk^–/– MSCs had decreased adipogenic differentiation potential compared with wild-type MSCs. Interestingly, we found that Lnk formed a complex with IGF-1R and that IGF-1 induced the dissociation of this complex. In addition, we observed that IGF-1-induced increase in the phosphorylation of Akt and mammalian target of rapamycin was triggered by the dissociation of the IGF-1R–Lnk complex. Expression levels of a pivotal transcription factor peroxisome proliferator-activated receptor gamma (PPAR-γ) and its adipogenic target genes (LPL and FABP4) significantly decreased in Lnk^–/– MSCs. These results suggested that Lnk adaptor protein regulated the adipogenesis of MSCs through the IGF-1/Akt/PPAR-γ pathway.

Recent Progress in Endothelial Progenitor Cell Culture Systems: Potential for Stroke Therapy

Endothelial progenitor cells (EPCs) participate in endothelial repair and angiogenesis due to their abilities to differentiate into endothelial cells and to secrete protective cytokines and growth factors. Consequently, there is considerable interest in cell therapy with EPCs isolated from peripheral blood to treat various ischemic injuries. Quality and quantity-controlled culture systems to obtain mononuclear cells enriched in EPCs with well-defined angiogenic and anti-inflammatory phenotypes have recently been developed, and increasing evidence from animal models and clinical trials supports the idea that transplantation of EPCs contributes to the regenerative process in ischemic organs and is effective for the therapy of ischemic cerebral injury. Here, we briefly describe the general characteristics of EPCs, and we review recent developments in culture systems and applications of EPCs and EPC-enriched cell populations to treat ischemic stroke.

Administration of microRNA-210 promotes spinal cord regeneration in mice

STUDY DESIGN

Experimental animal study of treatment of spinal cord injury (SCI).

OBJECTIVE

To investigate the therapeutic effects of administering microRNA-210 (miR-210) to promote angiogenesis in a mouse SCI model.

SUMMARY OF BACKGROUND DATA

Despite many previous studies regarding SCI, there is no established treatment in clinical practice. miRNAs have attracted immense attention because of their crucial role in human disease, and they have been proposed as potential new therapeutic targets for SCI.

METHODS

At specific times after administration, mice were analyzed by several methods to examine the distribution of miR-210, histological angiogenesis and neurogenesis, functional recovery from SCI, and the expression levels of target genes of miR-210.

RESULTS

After injection of miR-210 into the lesion of the injured spinal cord, expression of endogenous miR-210 increased until 6 days after injection. The administration of miR-210 promoted angiogenesis and astrogliosis, and improved functional recovery after SCI compared with the noninjected controls. Furthermore, the area made up of axons and myelin in the spinal cord tissues caudal to the injury site was larger in mice injected with miR-210 than those of the controls. Apoptotic cell death was lower in mice administered miR-210. After administration of miR-210, the expressions of protein-tyrosine phosphate 1B and ephrin-A3, both gene targets of miR-210, were downregulated at the protein level and protein-tyrosine phosphate 1B expression was also downregulated at the transcriptional level.

CONCLUSION

MiR-210 might contribute to spinal cord repair by promoting angiogenesis via the inhibition of protein-tyrosine phosphate 1B and ephrin-A3.

LEVEL OF EVIDENCE

N/A.

Aquaporin-4 mitigates retrograde degeneration of rubrospinal neurons by facilitating edema clearance and glial scar formation after spinal cord injury in mice

Atrophy of upper motor neurons hampers axonal regeneration and functional recovery following spinal cord injury (SCI). Apart from the severity of primary injury, a series of secondary pathological damages including spinal cord edema and glial scar formation affect the fate of injured upper motor neurons. The aquaporin-4 (AQP4) water channel plays a critical role in water homeostasis and migration of astrocytes in the central nervous system, probably offering a new therapeutic target for protecting against upper motor neuron degeneration after SCI. To test this hypothesis, we examined the effect of AQP4 deficiency on atrophy of rubrospinal neurons after unilateral rubrospinal tract transection at the fourth cervical level in mice. AQP4 gene knockout (AQP4-/-) mice exhibited high extent of spinal cord edema at 72 h after lesion compared with wild-type littermates. AQP4-/- mice showed impairments in astrocyte migration toward the transected site with a greater lesion volume at 1 week after surgery and glial scar formation with a larger cyst volume at 6 weeks. More severe atrophy and loss of axotomized rubrospinal neurons as well as axonal degeneration in the rubrospinal tract rostral to the lesion were observed in AQP4-/- mice at 6 weeks after SCI. AQP4 expression was downregulated at the lesioned spinal segment at 3 days and 1 week after injury, but upregulated at 6 weeks. These results demonstrated that AQP4 not only mitigates spinal cord damage but also ameliorates retrograde degeneration of rubrospinal neurons by promoting edema clearance and glial scar formation after laceration SCI. This finding supports the notion that AQP4 may be a promising therapeutic target for SCI.

Inhibitory effect of glyceollins on vasculogenesis through suppression of endothelial progenitor cell function

SCOPE

Endothelial progenitor cells (EPCs) are derived from hematopoietic stem cells, and have the ability to differentiate into mature endothelial cells and contribute to neovascularization. Glyceollins are a type of phytoalexin produced in soybeans under stress conditions. The aim of this study is to determine the effect of glyceollin treatment on EPCs during early tumor vasculogenesis.

METHODS AND RESULTS

We found that glyceollin treatment significantly decreased the number of EPC colony-forming units in human cord blood-derived AC133⁺ cells and mouse bone-marrow-derived c-Kit⁺/Sca-1⁺/Lin⁻ cells. Glyceollin treatment diminished the number of lineage-committed EPC cells in a dose-dependent manner (1-20 μM). Glyceollin treatment inhibited EPC migration, tube formation and the mRNA expression of angiopoietin-1 (Ang-1), Tie-2, stromal-derived factor-1 (SDF-1), C-X-C-chemokine receptor-4 (CXCR4), and endothelial nitric oxide synthase (eNOS) in cultured EPCs. Glyceollin treatment suppressed activation of Akt, Erk, and eNOS induced by SDF-1α or vascular endothelial growth factor (VEGF). Treatment with 10 mg/kg glyceollins significantly reduced the number of tumor-induced circulating EPCs and the incorporation of EPCs into neovessels in bone marrow transplanted mice.

CONCLUSION

These results suggest that glyceollins inhibit the function of EPCs in tumor neovascularization. Glyceollins from soybean elicitation could be beneficial in prevention of cancer development via vasculogenesis.

A small interfering RNA targeting Lnk accelerates bone fracture healing with early neovascularization

Lnk, an intracellular adapter protein, is expressed in hematopoietic cell lineages, which has recently been proved as an essential inhibitory signaling molecule for stem cell self-renewal in the stem cell factor-c-Kit signaling pathway with enhanced hematopoietic and osteogenic reconstitution in Lnk-deficient mice. Moreover, the therapeutic potential of hematopoietic stem/endothelial progenitor cells (EPCs) for fracture healing has been demonstrated with mechanistic insight into vasculogenesis/angiogenesis and osteogenesis enhancement in the fracture sites. We report here, Lnk siRNA-transfected endothelial commitment of c-kit+/Sca-1+/lineage- subpopulations of bone marrow cells have high EPC colony-forming capacity exhibiting endothelial markers, VE-Cad, VEGF and Ang-1. Lnk siRNA-transfected osteoblasts also show highly osteoblastic capacity. In vivo, locally transfected Lnk siRNA could successfully downregulate the expression of Lnk at the fracture site up to 1 week, and radiological and histological examination showed extremely accelerated fracture healing in Lnk siRNA-transfected mice. Moreover, Lnk siRNA-transfected mice exhibited sufficient therapeutic outcomes with intrinstic enhancement of angiogenesis and osteogenesis, specifically, the mice demonstrated better blood flow recovery in the sites of fracture. In our series of experiments, we clarified that a negatively regulated Lnk system contributed to a favorable circumstance for fracture healing by enhancing vasculogenesis/angiogenesis and osteogenesis. These findings suggest that downregulation of Lnk system may have the clinical potential for faster fracture healing, which contributes to the reduction of delayed unions or non-unions.

Ex-vivo expanded human blood-derived CD133+ cells promote repair of injured spinal cord

Human blood-derived CD133(+) cell populations, which are believed to represent a hematopoietic/endothelial progenitor fraction, have the ability to promote the repair of injured spinal cord in animal models. However, the mechanisms by which CD133(+) cell transplantation promotes spinal cord regeneration remain to be clarified. Another possible hurdle on the way to clinical applicability of these cells is their scarce representation in the overall population of mononuclear cells. We therefore analyzed and compared ex-vivo expanded human cord blood derived CD133(+) cells with freshly isolated CD133(+) cells as well as corresponding CD133(-) control mononuclear cells in respect to their ability to promote spinal cord repair using in vitro assays and cell transplantation into a mouse spinal cord injury model. In vitro, expanded cells as well as fresh CD133(+) cells formed endothelial progenitor cell (EPC) colonies, whereas CD133(-) cells formed no EPC colonies. In vivo, the administration of fresh CD133(+) and expanded cells enhanced angiogenesis, astrogliosis, axon growth and functional recovery after injury. In contrast, the administration of CD133(-) cells failed to promote axon growth and functional recovery, but moderately enhanced angiogenesis and astrogliosis. In addition, high-dose administration of expanded cells was highly effective in the induction of regenerative processes at the injured spinal cord.

Contribution of bone marrow-derived endothelial progenitor cells to neovascularization and astrogliosis following spinal cord injury

Spinal cord injury causes initial mechanical damage, followed by ischemia-induced, secondary degeneration, worsening the tissue damage. Although endothelial progenitor cells (EPCs) have been reported to play an important role for pathophysiological neovascularization in various ischemic tissues, the EPC kinetics following spinal cord injury have never been elucidated. In this study, we therefore assessed the in vivo kinetics of bone marrow-derived EPCs by EPC colony-forming assay and bone marrow transplantation from Tie2/lacZ transgenic mice into wild-type mice with spinal cord injury. The number of circulating mononuclear cells and EPC colonies formed by the mononuclear cells peaked at day 3 postspinal cord injury. Bone marrow transplantation study revealed that bone marrow-derived EPCs recruited into the injured spinal cord markedly increased at day 7, when neovascularization and astrogliosis drastically occurred in parallel with axon growth in the damaged tissue. To elucidate further the contribution of EPCs to recovery after spinal cord injury, exogenous EPCs were systemically infused immediately after the injury. The administered EPCs were incorporated into the injured spinal cord and accelerated neovascularization and astrogliosis. These findings suggest that bone marrow-derived EPCs may contribute to the tissue repair by augmenting neovascularization and astrogliosis following spinal cord injury.

The Lnk adaptor protein: a key regulator of normal and pathological hematopoiesis

The development and function of blood cells are regulated by specific growth factors/cytokines and their receptors' signaling pathways. In this way, these factors influence cell survival, proliferation and differentiation of hematopoietic cells. Central to this positive and/or negative control are the adaptor proteins. Since their identification 10 years ago, members of the Lnk adaptor protein family have proved to be important activators and/or inhibitors in the hematopoietic, immune and vascular system. In particular, the generation of animal and cellular models for the Lnk and APS proteins has helped establish the physiological role of these molecules through the identification of their specific signaling pathways and the characterization of their binding partners. Moreover, the recent identification of mutations in the LNK gene in myeloproliferative disorders, as well as the correlation of a single nucleotide polymorphism on LNK with hematological, immune and vascular diseases have suggested its involvement in the pathophysiology of these malignancies. The latter findings have thus raised the possibility of addressing Lnk signaling for the treatment of certain human diseases. This review therefore describes the pathophysiological role of this adaptor protein in hematological malignancies and the potential benefits of Lnk therapeutic targeting.

Magnetic field-based delivery of human CD133⁺ cells promotes functional recovery after rat spinal cord injury

STUDY DESIGN

Experimental animal study of spinal cord injury (SCI), using a cell delivery system.

OBJECTIVE

To investigate the therapeutic effects of transplantation of peripheral blood-derived CD133 cells, with a magnetic delivery system in a rat SCI model.

SUMMARY OF BACKGROUND DATA

There are no reports on intrathecal transplantation of peripheral blood-derived CD133 cells, with a magnetic cell delivery system to treat SCI.

METHODS

Magnetically isolated peripheral blood-derived CD133 cells were used as the cell source. Contusion SCI was induced by an Infinite Horizon impactor in athymic nude rats. CD133 cells or phosphate-buffered saline was administered via a lumbar puncture immediately after SCI, and a magnetic field was applied to rats for 30 minutes. Animals were analyzed at specific times after transplantation by several methods to examine cell tracking, functional recovery, and histological angiogenesis and neurogenesis.

RESULTS

A combination of cell transplantation and application of a magnetic field at the site of injury caused significant functional recovery. Transplantation of the cells alone in the absence of the magnetic field showed no effect beyond that observed in control rats.

CONCLUSION

The combination of intrathecal transplantation of CD133 cells and application of a magnetic field at the site of injury is a possible therapeutic strategy to treat rat SCI and may therefore find application in clinical settings.

Adaptor protein LNK is a negative regulator of brain neural stem cell proliferation after stroke

Ischemic stroke causes transient increase of neural stem and progenitor cell (NSPC) proliferation in the subventricular zone (SVZ), and migration of newly formed neuroblasts toward the damaged area where they mature to striatal neurons. The molecular mechanisms regulating this plastic response, probably involved in structural reorganization and functional recovery, are poorly understood. The adaptor protein LNK suppresses hematopoietic stem cell self-renewal, but its presence and role in the brain are poorly understood. Here we demonstrate that LNK is expressed in NSPCs in the adult mouse and human SVZ. Lnk(-/-) mice exhibited increased NSPC proliferation after stroke, but not in intact brain or following status epilepticus. Deletion of Lnk caused increased NSPC proliferation while overexpression decreased mitotic activity of these cells in vitro. We found that Lnk expression after stroke increased in SVZ through the transcription factors STAT1/3. LNK attenuated insulin-like growth factor 1 signaling by inhibition of AKT phosphorylation, resulting in reduced NSPC proliferation. Our findings identify LNK as a stroke-specific, endogenous negative regulator of NSPC proliferation, and suggest that LNK signaling is a novel mechanism influencing plastic responses in postischemic brain.

LNK (SH2B3) is a key regulator of integrin signaling in endothelial cells and targets α-parvin to control cell adhesion and migration

Focal adhesion (FA) formation and disassembly play an essential role in adherence and migration of endothelial cells. These processes are highly regulated and involve various signaling molecules that are not yet completely identified. Lnk [Src homology 2-B3 (SH2B3)] belongs to a family of SH2-containing proteins with important adaptor functions. In this study, we showed that Lnk distribution follows that of vinculin, localizing Lnk in FAs. Inhibition of Lnk by RNA interference resulted in decreased spreading, whereas sustained expression dramatically increases the number of focal and cell-matrix adhesions. We demonstrated that Lnk expression impairs FA turnover and cell migration and regulates β1-integrin-mediated signaling via Akt and GSK3β phosphorylation. Moreover, the α-parvin protein was identified as one of the molecular targets of Lnk responsible for impaired FA dynamics and cell migration. Finally, we established the ILK protein as a new molecular partner for Lnk and proposed a model in which Lnk regulates α-parvin expression through its interaction with ILK. Collectively, our results underline the adaptor Lnk as a novel and effective key regulator of integrin-mediated signaling controlling endothelial cell adhesion and migration.

Abnormal tumor vasculatures and bone marrow-derived pro-angiogenic cells in cancer

Tumor-derived factors affect the stroma of cancer tissue by activating pro-angiogenic signals. One of the key components of this response is the mobilization of the pro-angiogenic cells from bone marrow (BM), which contribute to the development of abnormal tumor vasculature. Evidence is accumulating that the pro-angiogenic cells derived from BM are involved in the physiological processes of tissue repair and wound healing. However, vascular structure in cancer tissue is impaired, resulting in the formation of chaotic neo-vessels and hypoxic microenvironments. Ultimately, these structural and functional abnormalities result in the limited delivery of chemotherapeutic agents and create regions of metabolic derangement, both of which enhance resistance to chemotherapy. In spite of recent advances in targeted therapy using anti-vascular agents, clinical results from studies using individual agents have unsatisfactory, necessitating the combinatorial use of anti-cancer drugs and a targeting agent. We suggest the possibility of a new therapeutic approach in which aberrant tumor vessels are normalized by BM-derived pro-angiogenic cells, and the delivery of anti-cancer drugs is maximized. In this review, we focus on the current understanding of the structure and function of tumor vessels, and an alternative approach to the repair of abnormal tumor vasculature by the use of BM-derived pro-angiogenic cells. This approach may improve both the delivery and the efficacy of anti-cancer drugs by restoring aberrant tumor vascularization and hypoxia.

Development of serum-free quality and quantity control culture of colony-forming endothelial progenitor cell for vasculogenesis

Quantitative and qualitative impairment of endothelial progenitor cells (EPCs) limits the efficacy of autologous cell therapy in patients with cardiovascular diseases. Here, we developed a serum-free quality and quantity control culture system for colony-forming EPCs to enhance their regenerative potential. A culture with serum-free medium containing stem cell factor, thrombopoietin, vascular endothelial growth factor, interleukin-6, and Flt-3 ligand was determined as optimal quality and quantity culture (QQc) in terms of the most vasculogenic colony-forming EPC expansion, evaluated by the newly established EPC colony formation assay. The QQc of umbilical cord blood-CD133(+) cells for 7 days produced a 52.9-fold increase in total cell number and 3.28-fold frequency in definitive EPC colony development, resulting in a 203.9-fold increase in estimated total definitive EPC colony number in vitro. Pre- or post-QQc cells were intramyocardially transplanted into nude rats with myocardial infarction (MI). Echocardiographic and micromanometer-tipped conductance catheter examinations 28 days post-MI revealed significant preservation of left ventricular (LV) function in rats receiving pre- or post-QQc cells compared with those receiving phosphate-buffered saline. Assessments of global LV contractility indicated a dose-dependent effect of pre- or post-QQc cells and the superior potency of post-QQc cells over pre-QQc cells. Furthermore, immunohistochemistry showed more abundant formation of both human and rat endothelial cells and cardiomyocytes in the infarcted myocardium following transplantation of post-QQc cells compared with pre-QQc cells. Our optimal serum-free quality and quantity culture may enhance the therapeutic potential of EPCs in both quantitative and qualitative aspects for cardiovascular regeneration.

Improved culture-based isolation of differentiating endothelial progenitor cells from mouse bone marrow mononuclear cells

Numerous endothelial progenitor cell (EPC)-related investigations have been performed in mouse experiments. However, defined characteristics of mouse cultured EPC have not been examined. We focused on fast versus slow adherent cell population in bone marrow mononuclear cells (BMMNCs) in culture and examined their characteristics. After 24 h-culture of BMMNCs, attached (AT) cells and floating (FL) cells were further cultured in endothelial differentiation medium separately. Immunological and molecular analyses exhibited more endothelial-like and less monocyte/macrophage-like characteristics in FL cells compared with AT cells. FL cells formed thick/stable tube and hypoxia or shear stress overload further enhanced these endothelial-like features with increased angiogenic cytokine/growth factor mRNA expressions. Finally, FL cells exhibited therapeutic potential in a mouse myocardial infarction model showing the specific local recruitment to ischemic border zone and tissue preservation. These findings suggest that slow adherent (FL) but not fast attached (AT) BMMNCs in culture are EPC-rich population in mouse.

Diabetes alters subsets of endothelial progenitor cells that reside in blood, bone marrow, and spleen

Circulating endothelial progenitor cells (EPCs) derived from the bone marrow (BM) participate in maintaining endothelial integrity and vascular homeostasis. Reduced EPC number and function result in vascular complications in diabetes. EPCs are a population of cells existing in various differentiation stages, and their cell surface marker profiles change during the process of mobilization and maturation. Hence, a generally accepted marker combination and a standardized protocol for the quantification of EPCs remain to be established. To determine the EPC subsets that are affected by diabetes, we comprehensively analyzed 32 surface marker combinations of mouse peripheral blood (PB), BM, and spleen cells by multicolor flow cytometry. Ten subsets equivalent to previously reported mouse EPCs significantly declined in number in the PB of streptozotocin-induced diabetic mice, and this reduction was reversed by insulin treatment. The PI(-)Lin(-)c-Kit(-)Sca-1(+)Flk-1(-)CD34(-)CD31(+) EPC cluster, which can differentiate into mature endothelial cells in vitro, was the highest population in the PB, BM, and spleen and occurred 61 times more in the spleen than in the PB. The cell number significantly decreased in the BM as well as in the PB but paradoxically increased in the spleen under diabetic conditions. Insulin treatment reversed the decrease of EPC subsets in the BM and PB and reversed their increase in spleen. A similar tendency was observed in some of the major cell populations in db/db mice. To the best of our knowledge, we are the first to report spatial population changes in mouse EPCs by diabetes in the blood and in the BM across the spleen. Diminished circulating EPC supply by diabetes may be ascribed to impaired EPC production in the BM and to decreased EPC mobilization from the spleen, which may contribute to vascular dysfunction in diabetic conditions.

Methodological Development of a Clonogenic Assay to Determine Endothelial Progenitor Cell Potential

The precise and conceptual insight of circulating endothelial progenitor cell (EPC) kinetics is hampered by the absence of an assay system capable of evaluating the EPC differentiation cascade. An assay system for EPC colony formation was developed to delineate circulating EPC differentiation. EPC colony-forming assay using semisolid medium and single or bulk CD133 + cells from umbilical cord blood exhibited the formation of two types of attaching cell colonies made of small or large cells featuring endothelial lineage potential and properties, termed small EPC colony-forming units and large EPC colony-forming units, respectively. In vitro and in vivo assays of each EPC colony-forming unit cell revealed a differentiation hierarchy from small EPC to large EPC colonies, indicating a primitive EPC stage with highly proliferative activity and a definitive EPC stage with vasculogenic properties, respectively. Experimental comparison with a conventional EPC culture assay system disclosed EPC colony-forming unit cells differentiate into noncolony-forming early EPC. The fate analysis of single CD133 + cells into the endothelial and hematopoietic lineage was achieved by combining this assay system with a hematopoietic progenitor assay and demonstrated the development of colony-forming EPC and hematopoietic progenitor cells from a single hematopoietic stem cell. EPC colony-forming assay permits the determination of circulating EPC kinetics from single or bulk cells, based on the evaluation of hierarchical EPC colony formation. This assay further enables a proper exploration of possible links between the origin of EPC and hematopoietic stem cells, representing a novel and powerful tool to investigate the molecular signaling pathways involved in EPC biology.

The adaptor Lnk (SH2B3): an emerging regulator in vascular cells and a link between immune and inflammatory signaling

A better knowledge of the process by which inflammatory extracellular signals are relayed from the plasma membrane to specific intracellular sites is a key step to understand how inflammation develops and how it is regulated. This review focuses on Lnk (SH2B3) a member, with SH2B1 and SH2B2, of the SH2B family of adaptor proteins that influences a variety of signaling pathways mediated by Janus kinase and receptor tyrosine kinases. SH2B adaptor proteins contain conserved dimerization, pleckstrin homology, and SH2 domains. Initially described as a regulator of hematopoiesis and lymphocyte differentiation, Lnk now emerges as a key regulator in hematopoeitic and non hematopoeitic cells such as endothelial cells (EC) moderating growth factor and cytokine receptor-mediated signaling. In EC, Lnk is a negative regulator of TNF signaling that reduce proinflammatory phenotype and prevent EC from apoptosis. Lnk is a modulator in integrin signaling and actin cytoskeleton organization in both platelets and EC with an impact on cell adhesion, migration and thrombosis. In this review, we discuss some recent insights proposing Lnk as a key regulator of bone marrow-endothelial progenitor cell kinetics, including the ability to cell growth, endothelial commitment, mobilization, and recruitment for vascular regeneration. Finally, novel findings also provided evidences that mutations in Lnk gene are strongly linked to myeloproliferative disorders but also autoimmune and inflammatory syndromes where both immune and vascular cells display a role. Overall, these studies emphasize the importance of the Lnk adaptor molecule not only as prognostic marker but also as potential therapeutic target.

CD34+ cells represent highly functional endothelial progenitor cells in murine bone marrow

Background

Endothelial progenitor cells (EPCs) were shown to have angiogenic potential contributing to neovascularization. However, a clear definition of mouse EPCs by cell surface markers still remains elusive. We hypothesized that CD34 could be used for identification and isolation of functional EPCs from mouse bone marrow.

Methodology/Principal Findings

CD34⁺ cells, c-Kit⁺/Sca-1⁺/Lin⁻ (KSL) cells, c-Kit⁺/Lin⁻ (KL) cells and Sca-1⁺/Lin⁻ (SL) cells were isolated from mouse bone marrow mononuclear cells (BMMNCs) using fluorescent activated cell sorting. EPC colony forming capacity and differentiation capacity into endothelial lineage were examined in the cells. Although CD34⁺ cells showed the lowest EPC colony forming activity, CD34⁺ cells exhibited under endothelial culture conditions a more adherent phenotype compared with the others, demonstrating the highest mRNA expression levels of endothelial markers vWF, VE-cadherin, and Flk-1. Furthermore, a dramatic increase in immediate recruitment of cells to the myocardium following myocardial infarction and systemic cell injection was observed for CD34⁺ cells comparing with others, which could be explained by the highest mRNA expression levels of key homing-related molecules Integrin β2 and CXCR4 in CD34⁺ cells. Cell retention and incorporation into the vasculature of the ischemic myocardium was also markedly increased in the CD34⁺ cell-injected group, giving a possible explanation for significant reduction in fibrosis area, significant increase in neovascularization and the best cardiac functional recovery in this group in comparison with the others.

Conclusion

These findings suggest that mouse CD34⁺ cells may represent a functional EPC population in bone marrow, which could benefit the investigation of therapeutic EPC biology.