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

Bone Marrow Nucleated Cells and Bone Marrow-Derived CD271+ Mesenchymal Stem Cell in Treatment of Encephalopathy and Drug-Resistant Epilepsy

The broad spectrum of brain injuries in preterm newborns and the plasticity of the central nervous system prompts us to seek solutions for neurodegeneration to prevent the consequences of prematurity and perinatal problems. The study aimed to evaluate the safety and efficacy of the implantation of autologous bone marrow nucleated cells and bone marrow mesenchymal stem cells in different schemes in patients with hypoxic-ischemic encephalopathy and immunological encephalopathy. Fourteen patients received single implantation of bone marrow nucleated cells administered intrathecally and intravenously, followed by multiple rounds of bone marrow mesenchymal stem cells implanted intrathecally, and five patients were treated only with repeated rounds of bone marrow mesenchymal stem cells. Seizure outcomes improved in most cases, including fewer seizures and status epilepticus and reduced doses of antiepileptic drugs compared to the period before treatment. The neuropsychological improvement was more frequent in patients with hypoxic-ischemic encephalopathy than in the immunological encephalopathy group. Changes in emotional functioning occurred with similar frequency in both groups of patients. In the hypoxic-ischemic encephalopathy group, motor improvement was observed in all patients and the majority in the immunological encephalopathy group. The treatment had manageable toxicity, mainly mild to moderate early-onset adverse events. The treatment was generally safe in the 4-year follow-up period, and the effects of the therapy were maintained after its termination.

The Endometrial Stem/Progenitor Cells and Their Niches

Endometrial stem/progenitor cells are a type of stem cells with the ability to self-renew and differentiate into multiple cell types. They exist in the endometrium and form niches with their neighbor cells and extracellular matrix. The interaction between endometrial stem/progenitor cells and niches plays an important role in maintaining, repairing, and regenerating the endometrial structure and function. This review will discuss the characteristics and functions of endometrial stem/progenitor cells and their niches, the mechanisms of their interaction, and their roles in endometrial regeneration and diseases. Finally, the prospects for their applications will also be explored.

Endometrial and placental stem cells in successful and pathological pregnancies

The endometrium is a dynamic tissue that undergoes extensive remodeling during the menstrual cycle and further gets modified during pregnancy. Different kinds of stem cells are reported in the endometrium. These include epithelial stem cells, endometrial mesenchymal stem cells, side population stem cells, and very small embryonic-like stem cells. Stem cells are also reported in the placenta which includes trophoblast stem cells, side population trophoblast stem cells, and placental mesenchymal stem cells. The endometrial and placental stem cells play a pivotal role in endometrial remodeling and placental vasculogenesis during pregnancy. The dysregulation of stem cell function is reported in various pregnancy complications like preeclampsia, fetal growth restriction, and preterm birth. However, the mechanisms by which it does so are yet elusive. Herein, we review the current knowledge of the different type of stem cells involved in pregnancy initiation and also highlight how their improper functionality leads to pathological pregnancy.

Beyond brain injury biomarkers: chemoattractants and circulating progenitor cells as biomarkers of endogenous rehabilitation effort in preterm neonates with encephalopathy

Introduction

Preclinical work and studies in adults have shown that endogenous regeneration efforts that involve mobilization of progenitor cells take place after brain injury. However, kinetics of endogenous circulating progenitor cells (CPCs) in preterm neonates is not well described, particularly their possible role regarding brain injury and regeneration. We aimed to assess the kinetics of CPCs in neonates with encephalopathy of prematurity in relation to brain injury biomarkers, chemoattractants and relevant antenatal and postanal clinical factors, in an effort to outline the related pathophysiology.

Materials and methods

47 preterm neonates (of 28-33 weeks GA) were enrolled: 31 newborns with no or minimal brain injury (grade I IVH) and 16 prematures with encephalopathy (grade III or IV IVH, PVL or infarct). Peripheral blood samples obtained on days 1, 3, 9, 18 and 45 after birth were analyzed using flow cytometry, focusing on EPCs (early and late Endothelial Progenitor Cells), HSCs (Hematopoietic Stem Cells) and VSELs (Very Small Embryonic-Like Stem Cells). At the same time-points serum levels of S100B, Neuron-specific Enolase (NSE), Erythropoietin (EPO), Insulin-like growth factor-1 (IGF-1) and SDF-1 were also measured. Neonates were assessed postnatally with brain MRI, and with Bayley III developmental test at 2 years of corrected age.

Results

Preterms with brain injury proved to have significant increase of S100B and NSE, followed by increase of EPO and enhanced mobilization mainly of HSCs, eEPCs and lEPCs. IGF-1 was rather decreased in this group of neonates. IGF-1 and most CPCs were intense decreased in cases of antenatal or postnatal inflammation. S100B and NSE correlated with neuroimaging and language scale in Bayley III test, providing good prognostic ability.

Conclusion

The observed pattern of CPCs' mobilization and its association with neurotrophic factors following preterm brain injury indicate the existence of an endogenous brain regeneration process. Kinetics of different biomarkers and associations with clinical factors contribute to the understanding of the related pathophysiology and might help to early discriminate neonates with adverse outcome. Timely appropriate enhancement of the endogenous regeneration effort, when it is suppressed and insufficient, using neurotrophic factors and exogenous progenitor cells might be a powerful therapeutic strategy in the future to restore brain damage and improve the neurodevelopmental outcome in premature infants with brain injury.

Therapeutic effect of transplantation of human bone marrow‑derived mesenchymal stem cells on neuron regeneration in a rat model of middle cerebral artery occlusion

Human bone marrow-derived mesenchymal stromal cells (hBMSCs) have been revealed to be beneficial for the regeneration of tissues and cells in several diseases. The present study aimed to elucidate the mechanisms underlying the effect of hBMSC transplantation on neuron regeneration in a rat model of middle cerebral artery occlusion (MCAO). The hBMSCs were isolated, cultured and identified. A rat model of MCAO was induced via the modified Longa method. Neurological severity scores (NSS) were adopted for the evaluation of neuronal function in the model rats after cell transplantation. Next, the expression levels of nestin, β-III-tubulin (β-III-Tub), glial fibrillary acidic protein (GFAP), HNA and neuronal nuclear antigen (NeuN) were examined, as well as the positive expression rates of human neutrophil alloantigen (HNA), nestin, NeuN, β-III-Tub and GFAP. The NSS, as well as the mRNA and protein expression of nestin, decreased at the 1st, 2nd, 4 and 8th weeks, while the mRNA and protein expression of NeuN, β-III-Tub and GFAP increased with time. In addition, after treatment, the MCAO rats showed decreased NSS and mRNA and protein expression of nestin, but elevated mRNA and protein expression of NeuN, β-III-Tub and GFAP at the 2nd, 4 and 8th weeks, and decreased positive expression of HNA and nestin with enhanced expression of NeuN, β-III-Tub and GFAP. Therefore, the present findings demonstrated that hBMSC transplantation triggered the formation of nerve cells and enhanced neuronal function in a rat model of MCAO.

Repair of Peripheral Nerve Sensory Impairments via the Transplantation of Bone Marrow Neural Tissue-Committed Stem Cell-Derived Sensory Neurons

The present study aimed to investigate the efficacy of transplantation of bone marrow neural tissue-committed stem cell-derived sensory neuron-like cells for the repair of peripheral nerve sensory impairments in rats. Bone marrow was isolated and cultured to obtain the neural tissue-committed stem cells (NTCSCs), and the differentiation of these cells into sensory neuron-like cells was induced. Bone marrow mesenchymal stem cells (BMSCs), bone marrow NTCSCs, and bone marrow NTCSC-derived sensory neurons (NTCSC-SNs) were transplanted by microinjection into the L4 and L5 dorsal root ganglions (DRGs) in an animal model of sensory defect. On the 2nd, 4th, 8th, and 12th week after the transplantation, the effects of the three types of stem cells on the repair of the sensory functional defect were analyzed via behavioral observation, sensory function evaluation, electrophysiological examination of the sciatic nerve, and morphological observation of the DRGs. The results revealed that the transplanted BMSCs, NTCSCs, and NTCSC-SNs were all able to repair the sensory nerves. In addition, the effect of the NTCSC-SNs was significantly better than that of the other two types of stem cells. The general posture and gait of the animals in the sensory defect model exhibited evident improvement over time. Plantar temperature sensitivity and pain sensitivity gradually recovered, and the sensation latency was reduced, with faster sensory nerve conduction velocity. Transplantation of NTCSC-SNs can improve the repair of peripheral nerve sensory defects in rats.

Pre-conditioning with Remote Photobiomodulation Modulates the Brain Transcriptome and Protects Against MPTP Insult in Mice

Transcranial photobiomodulation (PBM), which involves the application of low-intensity red to near-infrared light (600-1100 nm) to the head, provides neuroprotection in animal models of various neurodegenerative diseases. However, the absorption of light energy by the human scalp and skull may limit the utility of transcranial PBM in clinical contexts. We have previously shown that targeting light at peripheral tissues (i.e. "remote PBM") also provides protection of the brain in an MPTP mouse model of Parkinson's disease, suggesting remote PBM might be a viable alternative strategy for overcoming penetration issues associated with transcranial PBM. This present study aimed to determine an effective pre-conditioning regimen of remote PBM for inducing neuroprotection and elucidate the molecular mechanisms by which remote PBM enhances the resilience of brain tissue. Balb/c mice were irradiated with 670-nm light (4 J/cm² per day) targeting dorsum and hindlimbs for 2, 5 or 10 days, followed by injection of the parkinsonian neurotoxin MPTP (50 mg/kg) over two consecutive days. Despite no direct irradiation of the head, 10 days of pre-conditioning with remote PBM significantly attenuated MPTP-induced loss of midbrain tyrosine hydroxylase-positive dopaminergic cells and mitigated the increase in FOS-positive neurons in the caudate-putamen complex. Interrogation of the midbrain transcriptome by RNA microarray and pathway enrichment analysis suggested upregulation of cell signaling and migration (including CXCR4⁺ stem cell and adipocytokine signaling), oxidative stress response pathways and modulation of the blood-brain barrier following remote PBM. These findings establish remote PBM preconditioning as a viable neuroprotective intervention and provide insights into the mechanisms underlying this phenomenon.

Novel View on Umbilical Cord Blood and Maternal Peripheral Blood-an Evidence for an Increase in the Number of Circulating Stem Cells on Both Sides of the Fetal-Maternal Circulation Barrier

Umbilical cord blood (UCB) is a rich source of stem cells, including hematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs), endothelial progenitors cells (EPCs), and very small embryonic-like stem cells (VSELs). These cells most likely are mobilized into UCB in response to hypoxia and delivery stress. We have hypothesized that they may play a role in repairing certain tissue/organ injuries that occur in the newborn child after delivery. Here we asked whether delivery also mobilizes stem cells into maternal blood, as the mother also experiences hypoxia and several types of internal tissue injuries, particularly in the reproductive tract. We observed that the number of HSCs, MSCs, EPCs, and VSELs increases in maternal blood at 24 h after physiological delivery (n = 17). Based on this observation, we propose that delivery stress is associated with an increase in the number of circulating stem cells, not only on the fetal side but also on the maternal side of the fetal–maternal circulatory barrier.

Neural Stem Cells Derived Directly from Adipose Tissue

Neural stem cells (NSCs) are characterized as self-renewing cell populations with the ability to differentiate into the multiple tissue types of the central nervous system. These cells can differentiate into mature neurons, astrocytes, and oligodendrocytes. This category of stem cells has been shown to be a promisingly effective treatment for neurodegenerative diseases and neuronal injury. Most treatment studies with NSCs in animal models use embryonic brain-derived NSCs. This approach presents both ethical and feasibility issues for translation to human patients. Adult tissue is a more practical source of stem cells for transplantation therapies in humans. Some adult tissues such as adipose tissue and bone marrow contain a wide variety of stem cell populations, some of which have been shown to be similar to embryonic stem cells, possessing many pluripotent properties. Of these stem cell populations, some are able to respond to neuronal growth factors and can be expanded in vitro, forming neurospheres analogous to cells harvested from embryonic brain tissue. In this study, we describe a method for the collection and culture of cells from adipose tissue that directly, without going through intermediates such as mesenchymal stem cells, results in a population of NSCs that are able to be expanded in vitro and be differentiated into functional neuronal cells. These adipose-derived NSCs display a similar phenotype to those directly derived from embryonic brain. When differentiated into neurons, cells derived from adipose tissue have spontaneous spiking activity with network characteristics similar to that of neuronal cultures.

Stem cells, pluripotency and glial cell markers in peripheral blood of bipolar patients on long-term lithium treatment

BACKGROUND

We investigated the effect of long-term lithium treatment on very-small embryonic-like stem cells (VSELs) and the mRNA expression of pluripotency and glial markers, in peripheral blood, in patients with bipolar disorder (BD).

METHODS

Fifteen BD patients (aged 53±7years) not treated with lithium, with duration of illness >10years, 15 BD patients (aged 55±6years) treated with lithium for 8-40years (mean 16years) and 15 control subjects (aged 50±5years) were included. The number of VSELs was measured by flow cytometric analysis. Assessment of the mRNA levels of pluripotency markers (Oct-4, Sox 2 and Nanog) and glial markers (glial fibrillary acidic protein - GFAP, Olig1 and Olig2) was performed, using the Real-time quantitative reverse transcription PCR.

RESULTS

In BD patients not taking lithium, the number of VSELs was significantly higher than in control subjects and correlated with the duration of illness. The expression of pluripotency markers was significantly higher than in the controls and correlated with the number of VSELs. The mRNA levels of the Olig1 and Olig 2 were higher than in the controls and those of the GFAP were higher than in patients receiving lithium. In lithium-treated BD patients the number of VSELs was similar to controls and correlated negatively with the duration of lithium treatment and serum lithium concentration. The mRNA levels of Oct-4, Sox-2, GFAP and Olig1 were not different from controls. The mRNA expression of Nanog was significantly higher and correlated with the number of VSELs. The mRNA expression of Olig 2 was higher than in the BD patients not taking lithium.

CONCLUSION

Long-term treatment with lithium may suppress the activation of regenerative processes by reducing the number of VSELs circulating in PB. These cells, in BD patients not treated with lithium, may provide a new potential biological marker of the illness and its clinical progress. The higher expression of peripheral mRNA markers in BD patients may involve ongoing inflammatory process, compensatory mechanisms and regenerative responses. Long-term lithium treatment may attenuate these mechanisms, especially in relation to the transcription factors Oct-4, Sox-2, GFAP and Olig1.

Mobilization of Peripheral Blood Stem Cells and Changes in the Concentration of Plasma Factors Influencing their Movement in Patients with Panic Disorder

In this paper we examined whether stem cells and factors responsible for their movement may serve as new biological markers of anxiety disorders. The study was carried out on a group of 30 patients diagnosed with panic disorder (examined before and after treatment), compared to 30 healthy individuals forming the control group. We examined the number of circulating HSCs (hematopoetic stem cells) (Lin−/CD45 +/CD34 +) and HSCs (Lin−/CD45 +/AC133 +), the number of circulating VSELs (very small embryonic-like stem cells) (Lin−/CD45−/CD34 +) and VSELs (Lin−/CD45−/AC133 +), as well as the concentration of complement components: C3a, C5a and C5b-9, SDF-1 (stromal derived factor) and S1P (sphingosine-1-phosphate). Significantly lower levels of HSCs (Lin−/CD45 +/AC133 +) have been demonstrated in the patient group compared to the control group both before and after treatment. The level of VSELs (Lin−/CD45−/CD133 +) was significantly lower in the patient group before treatment as compared to the patient group after treatment.

The levels of factors responsible for stem cell movement were significantly lower in the patient group compared to the control group before and after treatment. It was concluded that the study of stem cells and factors associated with their movement can be useful in the diagnostics of panic disorder, as well as differentiating between psychotic and anxiety disorders.

Valproic acid enforces the priming effect of sphingosine-1 phosphate on human mesenchymal stem cells

Engraftment and homing of mesenchymal stem cells (MSCs) are modulated by priming factors including the bioactive lipid sphingosine-1-phosphate (S1P), by stimulating CXCR4 receptor signaling cascades. However, limited in vivo efficacy and the remaining priming molecules prior to administration of MSCs can provoke concerns regarding the efficiency and safety of MSC priming. Here, we showed that valproic acid (VPA), a histone deacetylase inhibitor, enforced the priming effect of S1P at a low dosage for human umbilical cord-derived MSCs (UC-MSCs). A DNA-methylation inhibitor, 5-azacytidine (5-Aza), and VPA increased the expression of CXCR4 in UC-MSCs. In particular, UC-MSCs primed with a suboptimal dose (50 nM) of S1P in combination with 0.5 mM VPA (VPA+S1P priming), but not 1 µM 5-Aza, significantly improved the migration activity in response to stromal cell-derived factor 1 (SDF-1) concomitant with the activation of both MAPKp42/44 and AKT signaling cascades. Both epigenetic regulatory compounds had little influence on cell surface marker phenotypes and the multi-potency of UC-MSCs. In contrast, VPA+S1P priming of UC-MSCs potentiated the proliferation, colony forming unit-fibroblast, and anti-inflammatory activities, which were severely inhibited in the case of 5-Aza treatment. Accordingly, the VPA+S1P-primed UC-MSCs exhibited upregulation of a subset of genes related to stem cell migration and anti-inflammation response. Thus, the present study demonstrated that VPA enables MSC priming with S1P at a low dosage by enhancing their migration and other therapeutic beneficial activities. This priming strategy for MSCs may provide a more efficient and safe application of MSCs for treating a variety of intractable disorders.

The effect of long-term lithium treatment of bipolar disorder on stem cells circulating in peripheral blood

OBJECTIVES

To investigate the effect of long-term lithium treatment on very small embryonic-like stem cells (VSELs), haematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs) circulating in peripheral blood (PB), in bipolar disorder (BD).

METHODS

The study included 15 BD patients (aged 55 ± 6 years) treated with lithium for 8-40 years (mean 16 years), 15 BD patients (aged 53 ± 7 years) with duration of illness >10 years, who had never received lithium, and 15 healthy controls (aged 50 ± 5 years). The VSELs, HSCs, MSCs and EPCs were measured by flow cytometric analysis.

RESULTS

In BD subjects not taking lithium the number of CD34⁺VSELs was significantly higher, and MSCs and EPCs numerically higher, than in control subjects and the number of CD34⁺VSELs correlated with the duration of illness. In lithium-treated patients these values were similar to controls and the number of CD34⁺VSELs correlated negatively with the duration of lithium treatment and serum lithium concentration.

CONCLUSIONS

Long-term treatment with lithium may suppress the activation of regenerative processes by reducing the number of VSELs circulating in PB. These cells, in BD patients not treated with lithium, may provide a new potential biological marker of the illness and its clinical progress.

Modification of Bone Marrow Stem Cells for Homing and Survival During Cerebral Ischemia

Over the last decade, major advances have been made in stem cell-based therapy for ischemic stroke, which is one of the leading causes of death and disability worldwide. Various stem cells from bone marrow, such as mesenchymal stem cells (MSCs), hematopoietic stem cells (HSCs), and endothelial progenitor cells (EPCs), have shown therapeutic potential for stroke. Concomitant with these exciting findings are some fundamental bottlenecks that must be overcome in order to accelerate their clinical translation, including the low survival and engraftment caused by the harsh microenvironment after transplantation. In this chapter, strategies such as gene modification, hypoxia/growth factor preconditioning, and biomaterial-based methods to improve cell survival and homing are summarized, and the potential strategies for their future application are also discussed.

Is Immunomodulation a Principal Mechanism Underlying How Cell-Based Therapies Enhance Stroke Recovery?

Inflammation within the brain and in peripheral tissues contributes to brain injury following ischemic stroke. Therapeutic modulation of the inflammatory response has been actively pursued as a novel stroke treatment approach for decades, without success. In recent years, extensive studies support the high potential for cell-based therapies to become a new treatment modality for stroke and other neurological disorders. In this review, we explore different types of cellular therapies and discuss how they modulate central and peripheral inflammatory processes after stroke. Apart from identifying potential targets for cell therapy, we also discuss paracrine and immunomodulatory mechanisms of cell therapy.

Stem Cell Therapy for Interstitial Cystitis/Bladder Pain Syndrome

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a disease characterized by pelvic pain, usually with urinary frequency. These symptoms make patients suffer from a poor quality of life. However, there is still a lack of consensus on the pathophysiology and curable treatment of IC/BPS. We have reviewed several candidates for the pathophysiology of this disease and also treatments that have been used. Although several oral medications, bladder instillation therapies, fulguration for Hunner's lesion, and hydrodistention have been tried as IC/BPS treatments, their outcomes have not been satisfactory. As the application of stem cell therapy is expanding into the urologic field, innovative strategies have been tested with animal models of IC/BPS and have shown promising therapeutic effects for reversing the symptoms of this disorder. Although several concerns about stem cell sources and their safety should be addressed before initiating human clinical trials, we introduce stem cell therapy as a valuable future treatment approach for IC/BPS.

Migration of Bone Marrow-Derived Very Small Embryonic-Like Stem Cells toward An Injured Spinal Cord

OBJECTIVE

Bone marrow (BM) is one of the major hematopoietic organs in postnatal life that consists of a heterogeneous population of stem cells which have been previously described. Recently, a rare population of stem cells that are called very small embryonic-like (VSEL) stem cells has been found in the BM. These cells express several developmental markers of pluri- potent stem cells and can be mobilized into peripheral blood (PB) in response to tissue injury. In this study we have attempted to investigate the ability of these cells to migrate toward an injured spinal cord after transplantation through the tail vein in a rat model.

MATERIALS AND METHODS

In this experimental study, VSELs were isolated from total BM cells using a fluorescent activated cell sorting (FACS) system and sca1 and stage specific embryonic antigen (SSEA-1) antibodies. After isolation, VSELs were cultured for 7 days on C2C12 as the feeder layer. Then, VSELs were labeled with 1,1´-dioctadecyl-3,3,3´,3´- tetramethylindocarbocyanine perchlorate (DiI) and transplanted into the rat spinal cord injury (SCI) model via the tail vein. Finally, we sought to determine the presence of VSELs in the lesion site.

RESULTS

We isolated a high number of VSELs from the BM. After cultivation, the VSELs colonies were positive for SSEA-1, Oct4 and Sca1. At one month after transplantation, real-time polymerase chain reaction analysis confirmed a significantly increased expres- sion level of Oct4 and SSEA-1 positive cells at the injury site.

CONCLUSION

VSELs have the capability to migrate and localize in an injured spinal cord after transplantation.

Cell Therapy with G-CSF-Mobilized Stem Cells in a Rat Osteoarthritis Model

G-CSF-mobilized peripheral blood stem cells (gm-PBSCs) offer a convenient cell source for treatment of hematopoietic and vascular disorders. Whether gm-PBSCs provide beneficial effects on skeleton diseases, such as osteoarthritis (OA), remains unknown. This study was undertaken to address the hypothesis that gm-PBSCs promote articular regeneration in OA. Here we studied the effect of single-dose intra-articular injection of gm-PBSCs from male donors delivered in hyaluronic acid (HA) on papain-induced OA in the knee joints of female Sprague—Dawley (SD) rats. Contralateral OA knee joints received single-dose HA alone and served as vehicle controls. We evaluated the histologic changes in glycosaminoglycan, type II collagen, type X collagen, modified Mankin score, and cell apoptosis rate in the articular cartilage of rat knees. We demonstrated that gm-PBSCs were mobilized to the peripheral blood via G-CSF infusion for 5 days in SD rats with increasing CD34+ percentage up to 55-fold. We showed that gm-PBSCs inhibit progression of papain-induced OA via reducing articular surface irregularity, fibrillation, and erosion, preventing cellular necrosis and loss of chondrogenic proteins, such as glycosaminoglycan and type II collagen, at both 3 and 6 weeks after treatment. Moreover, gm-PBSCs reduced modified Mankin scores and cellular apoptosis rates compared with HA alone. Our findings demonstrate that HA plus gm-PBSCs, rather than HA alone, inhibits progression of OA in rats in vivo. Thus, intra-articular injection of gm-PBSCs is a convenient protocol for treating OA with consistent beneficial effects.

The Therapeutic Effects of Human Mesenchymal Stem Cells Primed with Sphingosine-1 Phosphate on Pulmonary Artery Hypertension

Stem cell (SC) therapy has become a potential treatment modality for pulmonary artery hypertension (PAH), but the efficacy of human SC and priming effects have not yet been established. The mobilization and homing of hematopoietic stem cells (HSCs) are modulated by priming factors that include a bioactive lipid, sphingosine-1-phosphate (S1P), which stimulates CXCR4 receptor kinase signaling. Here, we show that priming human mesenchymal stem cells (MSCs) with S1P enhances their therapeutic efficacy in PAH. Human MSCs, similar to HSCs, showed stronger chemoattraction to S1P in transwell assays. Concomitantly, MSCs treated with 0.2 μM S1P showed increased phosphorylation of both MAPKp42/44 and AKT protein compared with nonprimed MSCs. Furthermore, S1P-primed MSCs potentiated colony forming unit-fibroblast, anti-inflammatory, and angiogenic activities of MSCs in culture. In a PAH animal model induced by subcutaneously injected monocrotaline, administration of human cord blood-derived MSCs (hCB-MSCs) or S1P-primed cells significantly attenuated the elevated right ventricular systolic pressure. Notably, S1P-primed CB-MSCs, but not unprimed hCB-MSCs, also elicited a significant reduction in the right ventricular weight ratio and pulmonary vascular wall thickness. S1P-primed MSCs enhanced the expression of several genes responsible for stem cell trafficking and angiogenesis, increasing the density of blood vessels in the damaged lungs. Thus, this study demonstrates that human MSCs have potential utility for the treatment of PAH, and that S1P priming increases the effects of SC therapy by enhancing cardiac and vascular remodeling. By optimizing this protocol in future studies, SC therapy might form a basis for clinical trials to treat human PAH.

Continuous improvement after multiple mesenchymal stem cell transplantations in a patient with complete spinal cord injury

Interruption of spinal cord (SC) continuity leads to functional loss below the lesion level. The purpose of this study was to evaluate the safety and efficacy of bone marrow nucleated cell (BMNC) and multiple mesenchymal stem cell (MSC) transplantations in spinal cord injury (SCI). A patient with total SC interruption at the Th2-3 level underwent experimental therapy with BMNC and MSC transplantations followed with intensive neurorehabilitation treatment. At admission, 6 h after SCI, the patient was scored ASIA A, had a Th1 sensation level, paraplegia with sphincter palsy, and was without the ability to control trunk movement. Neurophysiology examination showed bilateral axonal damage to the motor and sensory neural fibers with no motor unit potentials or peripheral motor nerve conduction in the lower extremities. The standard therapy had been applied and had not produced any positive results. The patient was treated with autologous BMNCs injected intravenously (3.2×10(9)) and intrathecally (0.5×10(9)) 10 weeks after the SCI and with five rounds of MSCs every 3-4 months (1.3-3.65×10(7)) administered via lumbar puncture. Total number of transplanted MSC cells during the course of treatment was 1.54×10(8). There were no complications related to transplantations and no side effects related to the therapy during 2 years of treatment. The ASIA score improved from A to C/D (from 112 to 231 points). The sensation level expanded from Th1 to L3-4, and the patient's ability to control the body trunk was fully restored. Bladder filling sensation, bladder control, and anal sensation were also restored. Muscle strength in the left lower extremities improved from plegia to deep paresis (1 on the Lovett scale). The patient's ability to move lower extremities against gravity supported by the movements in quadriceps was restored. The patient gained the ability to stand in a standing frame and was able to walk with the support of hip and knee ortheses. Magnetic resonance imaging (MRI) revealed that at the Th2/Th3 level, where the hemorrhagic necrosis was initially observed, small tissue structures appeared. Our results suggest that repeated intrathecal infusions of MSCs might have the potential to produce clinically meaningful improvements for SCI patients.

Circulating cells contribute to cardiomyocyte regeneration after injury

RATIONALE

The contribution of bone marrow-borne hematopoietic cells to the ischemic myocardium has been documented. However, a pivotal study reported no evidence of myocardial regeneration from hematopoietic-derived cells. The study did not take into account the possible effect of early injury-induced signaling as the test mice were parabiotically paired to partners immediately after surgery-induced myocardial injury when cross-circulation has not yet developed.

OBJECTIVE

To re-evaluate the role of circulating cells in the injured myocardium.

METHODS AND RESULTS

By combining pulse-chase labeling and parabiosis model, we show that circulating cells derived from the parabiont expressed cardiac-specific markers in the injured myocardium. Genetic fate mapping also revealed that circulating hematopoietic cells acquired cardiac cell fate by means of cell fusion and transdifferentiation.

CONCLUSIONS

These results suggest that circulating cells participate in cardiomyocyte regeneration in a mouse model of parabiosis when the circulatory system is fully developed before surgery-induced heart injury.

Optimization of pre-transplantation conditions to enhance the efficacy of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are considered a potential tool for cell based regenerative therapy due to their immunomodulatory property, differentiation potentials, trophic activity as well as large donor pool. Poor engraftment and short term survival of transplanted MSCs are recognized as major limitations which were linked to early cellular ageing, loss of chemokine markers during ex vivo expansion, and hyper-immunogenicity to xeno-contaminated MSCs. These problems can be minimized by ex vivo expansion of MSCs in hypoxic culture condition using well defined or xeno-free media i.e., media supplemented with growth factors, human serum or platelet lysate. In addition to ex vivo expansion in hypoxic culture condition using well defined media, this review article describes the potentials of transient adaptation of expanded MSCs in autologous serum supplemented medium prior to transplantation for long term regenerative benefits. Such transient adaptation in autologous serum supplemented medium may help to increase chemokine receptor expression and tissue specific differentiation of ex vivo expanded MSCs, thus would provide long term regenerative benefits.

IGF-1 enhances cell proliferation and survival during early differentiation of mesenchymal stem cells to neural progenitor-like cells

BACKGROUND

There has been increasing interest recently in the plasticity of mesenchymal stem cells (MSCs) and their potential to differentiate into neural lineages. To unravel the roles and effects of different growth factors in the differentiation of MSCs into neural lineages, we have differentiated MSCs into neural lineages using different combinations of growth factors. Based on previous studies of the roles of insulin-like growth factor 1 (IGF-1) in neural stem cell isolation in the laboratory, we hypothesized that IGF-1 can enhance proliferation and reduce apoptosis in neural progenitor-like cells (NPCs) during differentiation of MSCs into NCPs.We induced MSCs differentiation under four different combinations of growth factors: (A) EGF + bFGF, (B) EGF + bFGF + IGF-1, (C) EGF + bFGF + LIF, (D) EGF + bFGF + BDNF, and (E) without growth factors, as a negative control. The neurospheres formed were characterized by immunofluorescence staining against nestin, and the expression was measured by flow cytometry. Cell proliferation and apoptosis were also studied by MTS and Annexin V assay, respectively, at three different time intervals (24 hr, 3 days, and 5 days). The neurospheres formed in the four groups were then terminally differentiated into neuron and glial cells.

RESULTS

The four derived NPCs showed a significantly higher expression of nestin than was shown by the negative control. Among the groups treated with growth factors, NPCs treated with IGF-1 showed the highest expression of nestin. Furthermore, NPCs derived using IGF-1 exhibited the highest cell proliferation and cell survival among the treated groups. The NPCs derived from IGF-1 treatment also resulted in a better yield after the terminal differentiation into neurons and glial cells than that of the other treated groups.

CONCLUSIONS

Our results suggested that IGF-1 has a crucial role in the differentiation of MSCs into neuronal lineage by enhancing the proliferation and reducing the apoptosis in the NPCs. This information will be beneficial in the long run for improving both cell-based and cell-free therapy for neurodegenerative diseases.

Stem cell transplantation for neuroprotection in stroke

Stem cell-based therapies for stroke have expanded substantially over the last decade. The diversity of embryonic and adult tissue sources provides researchers with the ability to harvest an ample supply of stem cells. However, the optimal conditions of stem cell use are still being determined. Along this line of the need for optimization studies, we discuss studies that demonstrate effective dose, timing, and route of stem cells. We recognize that stem cell derivations also provide uniquely individual difficulties and limitations in their therapeutic applications. This review will outline the current knowledge, including benefits and challenges, of the many current sources of stem cells for stroke therapy.

Evidence that the population of quiescent bone marrow-residing very small embryonic/epiblast-like stem cells (VSELs) expands in response to neurotoxic treatment

The concept that bone marrow (BM)-derived cells may participate in neural regeneration remains controversial, and the identity of the specific cell type(s) involved remains unknown. We recently reported that the adult murine BM contains a highly mobile population of Sca-1⁺Lin⁻CD45⁻ cells known as very small embryonic/epiblast-like stem cells (VSELs) that express several markers of pluripotency such as Oct-4. In the BM microenvironment, these cells are kept quiescent because of epigenetic modification of certain paternally imprinted genes. However, as reported, these cells can be mobilized in mice in an experimental model of stroke and express several genes involved in neurogenesis while circulating in peripheral blood (PB). In the current work, we employed a model of toxic brain damage, which is induced by administration of kainic acid, to see not only whether VSELs can be mobilized into PB in response to this neurotoxin, but, more importantly, whether they proliferate and expand in BM tissue. We report here for the first time that brain damage leads to activation and expansion of the BM pool of quiescent VSELs, which precedes their subsequent egress into PB. Harnessing these cells in neural tissue regeneration is currently one of the challenges in regenerative medicine.

A module of human peripheral blood mononuclear cell transcriptional network containing primitive and differentiation markers is related to specific cardiovascular health variables

Peripheral blood mononuclear cells (PBMCs), including rare circulating stem and progenitor cells (CSPCs), have important yet poorly understood roles in the maintenance and repair of blood vessels and perfused organs. Our hypothesis was that the identities and functions of CSPCs in cardiovascular health could be ascertained by analyzing the patterns of their co-expressed markers in unselected PBMC samples. Because gene microarrays had failed to detect many stem cell-associated genes, we performed quantitative real-time PCR to measure the expression of 45 primitive and tissue differentiation markers in PBMCs from healthy and hypertensive human subjects. We compared these expression levels to the subjects' demographic and cardiovascular risk factors, including vascular stiffness. The tested marker genes were expressed in all of samples and organized in hierarchical transcriptional network modules, constructed by a bottom-up approach. An index of gene expression in one of these modules (metagene), defined as the average standardized relative copy numbers of 15 pluripotency and cardiovascular differentiation markers, was negatively correlated (all p<0.03) with age (R² = −0.23), vascular stiffness (R² = −0.24), and central aortic pressure (R² = −0.19) and positively correlated with body mass index (R² = 0.72, in women). The co-expression of three neovascular markers was validated at the single-cell level using mRNA in situ hybridization and immunocytochemistry. The overall gene expression in this cardiovascular module was reduced by 72±22% in the patients compared with controls. However, the compactness of both modules was increased in the patients' samples, which was reflected in reduced dispersion of their nodes' degrees of connectivity, suggesting a more primitive character of the patients' CSPCs. In conclusion, our results show that the relationship between CSPCs and vascular function is encoded in modules of the PBMCs transcriptional network. Furthermore, the coordinated gene expression in these modules can be linked to cardiovascular risk factors and subclinical cardiovascular disease; thus, this measure may be useful for their diagnosis and prognosis.

Preliminary study of autologous bone marrow nucleated cells transplantation in children with spinal cord injury

The objective of this study was to assess the safety and efficacy of transplanting bone marrow nucleated cells (BMNCs) to treat children with complete interruption of spinal cord (SC) continuity. The present study was conducted from 2005 to 2011. The inclusion criteria were a magnetic resonance imaging-confirmed complete interruption of SC continuity and no improvement in neurological status within 6 months after standard therapy. Bone marrow was isolated from the iliac ala and submitted to BMNC isolation. Subsequently, the cell suspension was administered into the SC cavity and intravenously. In total, 18 of 19 intraspinal and intravenous BMNC transplantation procedures performed caused no adverse events. One case was connected with transient bradycardia. The experimental therapy showed no late complications in the 1- to 6-year follow-up evaluation period. Neurological improvement was observed in two patients who received multiple implantations. One patient demonstrated improved superficial sensation from Th3 to Th12/L1 and a restored bladder-filling sensation. In the other case, superficial sensation was improved from C2 to C5, and the respiratory drive, the swallowing reflex, and tongue movements were restored. Spasticity and quality of life were improved in three of five patients. In addition, skin pressure ulcers healed and did not recur. Our preliminary results demonstrate the safety and feasibility of BMNC transplantation in children with complete SC injury. The results indicate that a certain degree of neurological and quality-of-life improvement can be attained by children with chronic complete SC injury who receive multiple BMNC implantations.

Novel evidence for enhanced stem cell trafficking in antipsychotic-naïve subjects during their first psychotic episode

In this study, we tested the novel hypothesis that stem cells and those factors that modulate their trafficking may be biological markers for acute psychosis. Twenty-eight subjects during their first nonaffective psychotic episode were investigated before and after antipsychotic treatment and were compared with 35 healthy controls (CG); the psychotic group (PG) was divided into "schizophrenic" (SG) and "non-schizophrenic" (NG) subgroups. We examined the number of circulating Lin(-)/CD45(-)/CD34(+) and Lin(-)/CD45(-)/CD133(+) very small embryonic-like stem cells (VSELs), which express markers of the neural lineage, and also the plasma levels of factors that modulate their trafficking: the C3a, C5a, and C5b-9 activated complement cascade components, stromal-derived factor 1, and sphingosine-1-phosphate (S1P). We found that the mean numbers of Lin(-)/CD45(-)/CD34(+) VSELs and the plasma levels of S1P prior to treatment differ between the CG and PG and that these cells express markers of neural lineage. The number of Lin(-)/CD45(-)/CD133(+) VSELs in peripheral blood differed between the SG and NG prior to treatment. Using logistic regression analysis, we found that C3a and S1P are the best predictors of risk and are potential markers for the first psychotic episode. Furthermore, in the SG, the number of circulating Lin(-)/CD45(-)/CD34(+) VSELs and the S1P plasma level are the best predictors of risk and are proposed as novel markers for the first "schizophrenic" episode of psychosis.

Do pluripotent stem cells exist in adult mice as very small embryonic stem cells?

Very small embryonic-like stem cells (VSELs) isolated from bone marrow (BM) have been reported to be pluripotent. Given their nonembryonic source, they could replace blastocyst-derived embryonic stem cells in research and medicine. However, their multiple-germ-layer potential has been incompletely studied. Here, we show that we cannot find VSELs in mouse BM with any of the reported stem cell potentials, specifically for hematopoiesis. We found that: (1) most events within the "VSEL" flow-cytometry gate had little DNA and the cells corresponding to these events (2) could not form spheres, (3) did not express Oct4, and (4) could not differentiate into blood cells. These results provide a failure to confirm the existence of pluripotent VSELs.

Perioperative release of pro-regenerative biochemical signals from human renal allografts subjected to ischemia-reperfusion injury

Complement-derived molecules modulate the intensity of renal ischemia-reperfusion injury and may lead to the generation of biochemical signals [such as stromal-derived factor-1 (SDF-1) or sphingosine-1-phosphate (S1P)], which stimulate tissue/organ regeneration after injury. We tested the association between perioperative C5b-9/membrane attack complex (MAC) levels and intensified erythrocyte lysis, and asked whether significant changes in the levels of pro-regenerative substances occur during the early phase of renal allograft reperfusion. Seventy-five recipients were enrolled and divided into the early, slow, and delayed graft function (DGF) groups. Perioperative blood samples were collected from the renal vein during consecutive minutes of reperfusion. Extracellular hemoglobin (eHb), albumin (plasma S1P transporter), 8-iPF2α-III isoprostane, SDF-1 and S1P concentrations were measured. Throughout the reperfusion period, erythrocyte lysis intensified and was most pronounced in the DGF group. However, perioperative eHb levels did not correlate significantly with C5b-9/MAC values, but rather with the intensity of oxidative stress. No significant changes were observed in S1P, its plasma transporter (albumin) or SDF-1 levels, which were relatively low in all groups throughout the reperfusion period. Our study therefore demonstrates that no known biochemical signal for bone marrow-derived stem cell mobilization is released from human renal allografts to the periphery during the early phase of reperfusion.

CD133 Expression Strongly Correlates with the Phenotype of Very Small Embryonic-/Epiblast-Like Stem Cells

CD133 antigen (prominin-1) is a useful cell surface marker of very small embryonic-like stem cells (VSELs). Antibodies against it, conjugated to paramagnetic beads or fluorochromes, are thus powerful biological tools for their isolation from human umbilical cord blood, mobilized peripheral blood, and bone marrow. VSELs are described with the following characteristics: (1) are slightly smaller than red blood cells; (2) display a distinct morphology, typified by a high nuclear/cytoplasmic ratio and an unorganized euchromatin; (3) become mobilized during stress situations into peripheral blood; (4) are enriched in the CD133(+)Lin(-)CD45(-) cell fraction in humans; and (5) express markers of pluripotent stem cells (e.g., Oct-4, Nanog, and stage-specific embryonic antigen-4). The most recent in vivo data from our and other laboratories demonstrated that human VSELs exhibit some characteristics of long-term repopulating hematopoietic stem cells and are at the top of the hierarchy in the mesenchymal lineage. However, still more labor is needed to characterize better at a molecular level these rare cells.

Erythropoietin modulates the structure of bone morphogenetic protein 2-engineered cranial bone

The ideally engineered bone should have similar structural and functional properties to the native tissue. Although structural integrity is critical for functional bone regeneration, we know less about modulating the structural properties of the engineered bone elicited by bone morphogenetic protein (BMP) than efficacy and safety. Erythropoietin (Epo), a primary erythropoietic hormone, has been used to augment blood transfusion in orthopedic surgery. However, the effects of Epo on bone regeneration are not well known. Here, we determined the role of Epo in BMP2-induced bone regeneration using a cranial defect model. Epo administration improved the quality of BMP2-induced bone and more closely resembled natural cranial bone with a higher bone volume (BV) fraction and lower marrow fraction when compared with BMP2 treatment alone. Epo increased red blood cells (RBCs) in peripheral blood and also increased hematopoietic and mesenchymal stem cell (MSC) populations in bone marrow. Consistent with our previous work, Epo increased osteoclastogenesis both in vitro and in vivo. Results from a metatarsal organ culture assay suggested that Epo-promoted osteoclastogenesis contributed to angiogenesis because angiogenesis was blunted when osteoclastogenesis was blocked by alendronate (ALN) or osteoprotegerin (OPG). Earlier calcification of BMP2-induced temporary chondroid tissue was observed in the Epo+BMP group compared to BMP2 alone. We conclude that Epo significantly enhanced the outcomes of BMP2-induced cranial bone regeneration in part through its actions on osteoclastogenesis and angiogenesis.

Human very small embryonic-like cells generate skeletal structures, in vivo

Human very small embryonic-like (hVSEL) cells are a resident population of multipotent stem cells in the bone marrow involved in the turnover and regeneration of tissues. The levels of VSEL cells in blood are greatly increased in response to injury, and they have been shown to repair injured tissues. Adult hVSEL cells, SSEA-4(+)/CD133(+)/CXCR4(+)/Lin(-)/CD45(-), express the pluripotency markers (Oct-4 and Nanog) and may be able to differentiate into cells from all 3 germ lineages. hVSEL cells isolated from blood by apheresis following granulocyte-colony-stimulating factor mobilization were fractionated and enriched by elutriation and fluorescence activated cell sorting. Collagen sponge scaffolds containing 2,000-30,000 hVSEL cells were implanted into cranial defects generated in SCID mice. Analysis by microcomputed tomography showed that a cell population containing VSEL cells produced mineralized tissue within the cranial defects compared with controls at 3 months. Histologic studies showed significant bone formation and cellular organization within the defects compared with cellular or scaffold controls alone. Antibodies to human leukocyte antigens demonstrated that the newly generated tissues were of human origin. Moreover, human osteocalcin was identified circulating in the peripheral blood. There was evidence that some level of hVSEL cells migrated away from the defect site, using quantitative real-time polymerase chain reaction to detect for human-specific Alu sequences. This study demonstrates that hVSEL cells are able to generate human bone tissue in a mouse model of skeletal repair. These studies lay the foundation for future cell-based regenerative therapies for osseous and connective tissue disorders, including trauma and degenerative conditions, such as osteoporosis, fracture repair, and neoplastic repair.

Stem cell research, repairing, and regeneration medicine

Stem cell research has become one of the hot points in the medical field, including wound healing, repairing, or regeneration medicine, because stem cells have the characteristics of self-renewal and differentiating into multiple types of total specialized cells of the body. The researchers involved in stem cell research hope that they can use this skill to one day create tissues or even organs instead of treating damaged tissues or organs in severe injury or in terminal-stage diseases, thus prolonging the life of patients and improving their quality of the life. But it is still a long way ahead with many difficulties to overcome to realize this dream. In this article, the authors discuss some problems in this special field.

Circulating mesenchymal stem cells microparticles in patients with cerebrovascular disease

Preclinical and clinical studies have shown that the application of CD105⁺ mesenchymal stem cells (MSCs) is feasible and may lead to recovery after stroke. In addition, circulating microparticles are reportedly functional in various disease conditions. We tested the levels of circulating CD105⁺ microparticles in patients with acute ischemic stroke. The expression of CD105 (a surface marker of MSCs) and CXCR4 (a CXC chemokine receptor for MSC homing) on circulating microparticles was evaluated by flow cytometry of samples from 111 patients and 50 healthy subjects. The percentage of apoptotic CD105 microparticles was determined based on annexin V (AV) expression. The relationship between serum levels of CD105⁺/AV⁻ microparticles, stromal cells derived factor-1α (SDF-1α), and the extensiveness of cerebral infarcts was also evaluated. CD105⁺/AV⁻ microparticles were higher in stroke patients than control subjects. Correlation analysis showed that the levels of CD105⁺/AV⁻ microparticles increased as the baseline stroke severity increased. Multivariate testing showed that the initial severity of stroke was independently associated with circulating CD105⁺/AV⁻ microparticles (OR, 1.103 for 1 point increase in the NIHSS score on admission; 95% CI, 1.032–1.178) after adjusting for other variables. The levels of CD105⁺/CXCR4⁺/AV⁻ microparticles were also increased in patients with severe disability (r = 0.192, p = 0.046 for NIHSS score on admission), but were decreased with time after stroke onset (r = −0.204, p = 0.036). Risk factor profiles were not associated with the levels of circulating microparticles or SDF-1α. In conclusion, our data showed that stroke triggers the mobilization of MSC-derived microparticles, especially in patients with extensive ischemic stroke.

A comparison of stem cells for therapeutic use

A critical comparison of the attributes of several types of stem cells is presented, with particular emphasis on properties that are critical for the application of these cells for therapeutic purposes. The importance of an autologous source of pluripotent stem cells is stressed. It is apparent that two sources currently exist for non-embryonic pluripotent stem cells--very small embryonic-like stem cells (VSELs) and induced pluripotent stem cells (iPS). The impact of the emerging iPS research on therapy is considered.

The use of chemokine receptor agonists in stem cell mobilization

INTRODUCTION

Pharmacological mobilization has been exploited as a means to obtain hematopoietic stem progenitor cells (HSPCs) for hematopoietic reconstitution. HSPCs mobilized from bone marrow into peripheral blood (PB) are a preferred source of stem cells for transplantation, because they are easily accessible and evidence indicates that they engraft faster after transplantation than HSPCs directly harvested from bone marrow (BM) or umbilical cord blood (UCB).

AREAS COVERED

Since chemokine-chemokine receptor axes are involved in retention of HSPCs in the BM microenvironment, chemokine receptor agonists have been proposed as therapeutics to facilitate the mobilization process. These compounds include agonists of the CXCR4 receptor expressed on HSPCs (CTCE-0021 and ATI-2341) or chemokines binding to chemokine receptors expressed on granuclocytes and monocytes (e.g., CXCL2, also known as the growth-related oncogene protein-beta (Gro-β); CCL3, also known as macrophage inflammatory protein-1α (MIP-1α); or CXCL8, also known as IL-8) could be employed alone or in combination with other mobilizing agents (e.g., G-CSF or Plerixafor (AMD3100)). We discuss the current state of knowledge about chemokine receptor agonists and the rationale for their application in mobilization protocols.

EXPERT OPINION

Evidence is accumulating that CXCR4 receptor agonists could be employed alone or with other agents as mobilizing drugs. In particular they may provide an alternative for patients that are poor mobilizers.

The role of innate immunity in trafficking of hematopoietic stem cells-an emerging link between activation of complement cascade and chemotactic gradients of bioactive sphingolipids

Hematopoietic stem and progenitor cells (HSPCs) circulate under steady-state conditions at detectable levels in peripheral blood (PB). The phenomenon of enforced release of HSPCs from BM into PB is called mobilization and may be envisioned as a danger-sensing response mechanism triggered by hypoxia or mechanical- or infection-induced tissue damage and is a part of stress response. It is unquestionable that the a-chemokine stromal derived factor-1 (SDF-1)-CXCR4 axis plays crucial role in retention of HSPCs in BM. However, all factors that direct mobilization of HSPCs into PB and homing back to the BM or their allocation to damaged organs are not characterized very well. In this chapter we will present mounting evidence that elements of innate immunity such as complement cascade (CC) cleavage fragments (e.g., C3a and C5a), granulocytes, generation of membrane attack complex (MAC) together with sphingosine-1 phosphate (S1P) orchestrate HSPC mobilization. On other hand some other bioactive lipids e.g., ceramide-1-phosphate (C1P) that is released from damaged/"leaky" cells in BM after myeloablative conditioning for transplant may play an opposite important role in homing of HSPCs to BM. Finally, the chemotactic activity of all chemoattractants for HSPCs including SDF-1, S1P and C1P is enhanced in presence of CC cleavage fragments (e.g., C3a) and MAC that is a final product of CC activation.

Enumeration of very small embryonic-like stem cells in peripheral blood

In addition to hematopoietic stem and progenitor cells (HSPCs) also other types of stem cells (e.g., -mesenchymal stem cells [MSCs], endothelial progenitor cells [EPCs], and very small embryonic-like stem cells [VSELs]) circulate under steady-state conditions at detectable levels in peripheral blood (PB), with their numbers increasing in response to stress, inflammation, tissue organ injury (e.g., heart infarct, stroke, or colitis), or mobilizing agents (e.g., granulocyte colony-stimulating factor; G-CSF). This mobilization process may be envisioned as a danger-sensing response mechanism triggered by hypoxia or mechanical- or infection-induced tissue damage that recruits into peripheral blood various types of stem cells that play a role not only in immune surveillance but also in organ/tissue regeneration. Thus, stem cells circulating in PB could be envisioned as "cellular paramedics" that are involved in immune surveillance (HSPCs) or -tissue/organ rejuvenation (MSCs, EPCs, VSELs). In this chapter we focus on detection and enumeration of VSELs circulating in human PB, which are circulating in steady-state conditions or after administration of G-CSF or as a consequence of various pathological events.

Stem Cells are mobilized from the bone marrow into the peripheral circulation in response to retinal pigment epithelium damage--a pathophysiological attempt to induce endogenous regeneration

PURPOSE

Stem cell regeneration of damaged tissue has recently been reported in many different organs. Here, we investigated the mobilization of different stem/progenitor cell (SPC) populations into the peripheral blood (PB), their subsequent homing to the injured retina (IR) and contribution to its regeneration in a retinal pigment epithelium (RPE) damage model induced by sodium iodate (NaIO(3)).

METHODS

Mobilization of SPCs was evaluated by flow cytometry. SPCs distribution in IR was assessed using bone marrow (BM)-derived GFP(+)Lin(-) cells transplanted intravenously into NaIO(3)-treated C57Bl/6 mice. The quantity of the chemokine SDF-1 in PB and IR was measured by ELISA and qRT-PCR, respectively. Apoptosis (TUNEL assay), cell proliferation (PCNA analysis) as well as functional retinal activity (electroretinogram) were examined at several time points after NaIO(3) administration.

RESULTS

Mobilization of SPCs along with the highest cell proliferation and massive apoptosis within IR were observed on the third day after NaIO(3) administration. Similarly, donor GFP(+)Lin(-) cells were detected in the retina as soon as day 4 after NaIO(3) injection. Plasma levels of SDF-1 did not differ significantly in mice exposed to NaIO(3) compared to healthy controls, however mRNA for SDF-1 was overexpressed locally in IR. Functional retinal recovery was not achieved.

CONCLUSION

Our study provides evidence that BM SPCs egress into PB and home to the injured retina, but are not capable of restoring its function. These results indicate that if the range of retinal destruction is profound, endogenous regeneration is ineffective and may ultimately require adjuvant therapeutic transplantation of specific SPCs subpopulations.

The great migration of bone marrow-derived stem cells toward the ischemic brain: therapeutic implications for stroke and other neurological disorders

Accumulating laboratory studies have implicated the mobilization of bone marrow (BM)-derived stem cells in brain plasticity and stroke therapy. This mobilization of bone cells to the brain is an essential concept in regenerative medicine. Over the past ten years, mounting data have shown the ability of bone marrow-derived stem cells to mobilize from BM to the peripheral blood (PB) and eventually enter the injured brain. This homing action is exemplified in BM stem cell mobilization following ischemic brain injury. Various BM-derived cells, such as hematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs), endothelial progenitor cells (EPCs) and very small embryonic-like cells (VSELs) have been demonstrated to exert therapeutic benefits in stroke. Here, we discuss the current status of these BM-derived stem cells in stroke therapy, with emphasis on possible cellular and molecular mechanisms of action that mediate the cells' beneficial effects in the ischemic brain. When possible, we also discuss the relevance of this therapeutic regimen in other central nervous system (CNS) disorders.

A novel perspective on stem cell homing and mobilization: review on bioactive lipids as potent chemoattractants and cationic peptides as underappreciated modulators of responsiveness to SDF-1 gradients

Hematopoietic stem progenitor cells (HSPCs) respond robustly to α-chemokine stromal-derived factor-1 (SDF-1) gradients, and blockage of CXCR4, a seven-transmembrane-spanning G(αI)-protein-coupled SDF-1 receptor, mobilizes HSPCs into peripheral blood. Although the SDF-1-CXCR4 axis has an unquestionably important role in the retention of HSPCs in bone marrow (BM), new evidence shows that, in addition to SDF-1, the migration of HSPCs is directed by gradients of the bioactive lipids sphingosine-1 phosphate and ceramide-1 phosphate. Furthermore, the SDF-1 gradient may be positively primed/modulated by cationic peptides (C3a anaphylatoxin and cathelicidin) and, as previously demonstrated, HSPCs respond robustly even to very low SDF-1 gradients in the presence of priming factors. In this review, we discuss the role of bioactive lipids in stem cell trafficking and the consequences of HSPC priming by cationic peptides. Together, these phenomena support a picture in which the SDF-1-CXCR4 axis modulates homing, BM retention and mobilization of HSPCs in a more complex way than previously envisioned.

Growth factors in ischemic stroke

Data from pre-clinical and clinical studies provide evidence that colony-stimulating factors (CSFs) and other growth factors (GFs) can improve stroke outcome by reducing stroke damage through their anti-apoptotic and anti-inflammatory effects, and by promoting angiogenesis and neurogenesis. This review provides a critical and up-to-date literature review on CSF use in stroke. We searched for experimental and clinical studies on haemopoietic GFs such as granulocyte CSF, erythropoietin, granulocyte-macrophage colony-stimulating factor, stem cell factor (SCF), vascular endothelial GF, stromal cell-derived factor-1α and SCF in ischemic stroke. We also considered studies on insulin-like growth factor-1 and neurotrophins. Despite promising results from animal models, the lack of data in human beings hampers efficacy assessments of GFs on stroke outcome. We provide a comprehensive and critical view of the present knowledge about GFs and stroke, and an overview of ongoing and future prospects.

Bone marrow stem cell mobilization in stroke: a 'bonehead' may be good after all!

Mobilizing bone cells to the head, astutely referred to as 'bonehead' therapeutic approach, represents a major discipline of regenerative medicine. The last decade has witnessed mounting evidence supporting the capacity of bone marrow (BM)-derived cells to mobilize from BM to peripheral blood (PB), eventually finding their way to the injured brain. This homing action is exemplified in BM stem cell mobilization following ischemic brain injury. Here, I review accumulating laboratory studies implicating the role of therapeutic mobilization of transplanted BM stem cells for brain plasticity and remodeling in stroke.

Transcriptional landscape of bone marrow-derived very small embryonic-like stem cells during hypoxia

Background

Hypoxia is a ubiquitous feature of many lung diseases and elicits cell-specific responses. While the effects of hypoxia on stem cells have been examined under in vitro conditions, the consequences of in vivo oxygen deprivation have not been studied.

Methods

We investigated the effects of in vivo hypoxia on a recently characterized population of pluripotent stem cells known as very small embryonic-like stem cells (VSELs) by whole-genome expression profiling and measuring peripheral blood stem cell chemokine levels.

Results

We found that exposure to hypoxia in mice mobilized VSELs from the bone marrow to peripheral blood, and induced a distinct genome-wide transcriptional signature. Applying a computationally-intensive methodology, we identified a hypoxia-induced gene interaction network that was functionally enriched in a diverse array of programs including organ-specific development, stress response, and wound repair. Topographic analysis of the network highlighted a number of densely connected hubs that may represent key controllers of stem cell response during hypoxia and, therefore, serve as putative targets for altering the pathophysiologic consequences of hypoxic burden.

Conclusions

A brief exposure to hypoxia recruits pluripotent stem cells to the peripheral circulation and actives diverse transcriptional programs that are orchestrated by a selective number of key genes.

Identification and isolation from either adult human bone marrow or G-CSF-mobilized peripheral blood of CD34(+)/CD133(+)/CXCR4(+)/ Lin(-)CD45(-) cells, featuring morphological, molecular, and phenotypic characteristics of very small embryonic-like (VSEL) stem cells

OBJECTIVE

Recently, we demonstrated that normal human bone marrow (hBM)-derived CD34(+) cells, released into the peripheral blood after granulocyte colony-stimulating factor mobilization, contain cell subpopulations committed along endothelial and cardiac differentiation pathways. These subpopulations could play a key role in the regeneration of post-ischemic myocardial lesion after their direct intracardiac delivery. We hypothesized that these relevant cells might be issued from very small embryonic-like stem cells deposited in the BM during ontogenesis and reside lifelong in the adult BM, and that they could be mobilized into peripheral blood by granulocyte colony-stimulating factor.

MATERIALS AND METHODS

Samples of normal hBM and leukapheresis products harvested from cancer patients after granulocyte colony-stimulating factor mobilization were analyzed and sorted by multiparameter flow cytometry strategy. Immunofluorescence and reverse transcription quantitative polymerase chain reaction assays were performed to analyze the expression of typical pluripotent stem cells markers.

RESULTS

A population of CD34(+)/CD133(+)/CXCR4(+)/Lin(-) CD45(-) immature cells was first isolated from the hBM or from leukapheresis products. Among this population, very small (2-5 μm) cells expressing Oct-4, Nanog, and stage-specific embryonic antigen-4 at protein and messenger RNA levels were identified.

CONCLUSIONS

Our study supports the hypothesis that very small embryonic-like stem cells constitute a "mobile" pool of primitive/pluripotent stem cells that could be released from the BM into the peripheral blood under the influence of various physiological or pathological stimuli. In order to fully support that hBM- and leukapheresis product-derived very small embryonic-like stem cells are actually pluripotent, we are currently testing their ability to differentiate in vitro into cells from all three germ layers.

Intermittent hypoxia mobilizes bone marrow-derived very small embryonic-like stem cells and activates developmental transcriptional programs in mice

BACKGROUND

obstructive sleep apnea is a prevalent disorder associated with cognitive dysfunction and cardiovascular and metabolic morbidity and is characterized by recurrent episodes of hypoxia during sleep. Bone marrow-derived very small embryonic-like (VSEL) pluripotent stem cells represent a recruitable pool that may play an important role in organ repair after injury. We hypothesized that exposure to intermittent hypoxia (IH) can mobilize VSELs from the bone marrow (BM) to peripheral blood (PB) in mice and can activate distinct transcriptional programs.

METHODS

adult mice were exposed to IH or normoxia for 48 hours. VSELs were sorted from BM and PB using flow cytometry. Plasma levels of stem cell chemokines, stromal cell derived factor-1 (SDF-1), hepatocyte growth factor (HGF), and leukemia inhibitory factor (LIF) were measured. Transcriptional profiling of VSELs was performed, and differentially expressed genes were mapped to enriched functional categories and genetic networks.

RESULTS

exposure to IH elicited migration of VSELs from BM to PB and elevations in plasma levels of chemokines. More than 1100 unique genes were differentially expressed in VSELs in response to IH. Gene Ontology and network analysis revealed the activation of organ-specific developmental programs among these genes.

CONCLUSIONS

exposure to IH mobilizes VSELs from the BM to PB and activates distinct transcriptional programs in VSELs that are enriched in developmental pathways, including central nervous system development and angiogenesis. Thus, VSELs may serve as a reserve mobile pool of pluripotent stem cells that can be recruited into PB and may play an important role in promoting end-organ repair during IH.