Endothelial Progenitor Cells Promote Astrogliosis following Spinal Cord Injury through Jagged1-Dependent Notch Signaling

Cytokine polarized, alternatively activated bone marrow neutrophils drive axon regeneration

The adult central nervous system (CNS) possesses a limited capacity for self-repair. Severed CNS axons typically fail to regrow. There is an unmet need for treatments designed to enhance neuronal viability, facilitate axon regeneration and ultimately restore lost neurological functions to individuals affected by traumatic CNS injury, multiple sclerosis, stroke and other neurological disorders. Here we demonstrate that both mouse and human bone marrow neutrophils, when polarized with a combination of recombinant interleukin-4 (IL-4) and granulocyte colony-stimulating factor (G-CSF), upregulate alternative activation markers and produce an array of growth factors, thereby gaining the capacity to promote neurite outgrowth. Moreover, adoptive transfer of IL-4/G-CSF-polarized bone marrow neutrophils into experimental models of CNS injury triggered substantial axon regeneration within the optic nerve and spinal cord. These findings have far-reaching implications for the future development of autologous myeloid cell-based therapies that may bring us closer to effective solutions for reversing CNS damage.

Endothelial progenitor cell-derived exosomes promote anti-inflammatory macrophages via SOCS3/JAK2/STAT3 axis and improve the outcome of spinal cord injury

BACKGROUND

Macrophage in the spinal cord injury (SCI) area imparts a chronic pro-inflammation effect that challenges the recovery of SCI. Previously, endothelial progenitor cell-produced exosomes (EPC-EXOs) have been noticed to facilitate revascularization and inflammation control after SCI. However, their effects on macrophage polarization remained unclear. This study aimed to investigate the EPC-EXOs' role in macrophage polarization and reveal its underlying mechanism.

METHODS

We extracted the macrophages and EPC from the bone marrow suspension of C57BL/L mice by centrifugation. After cell identification, the EPC-EXOs were collected by ultra-high-speed centrifugation and exosome extraction kits and identified by transmission electron microscopy and nanoparticle tracking analysis. Then, macrophages were cultured with EPC-EXOs in different concentrations. We labeled the exosome to confirm its internalization by macrophage and detected the macrophage polarization marker level both in vitro and in vivo. We further estimated EPC-EXOs' protective effects on SCI by mice spinal cord tissue H&E staining and motor behavior evaluation. Finally, we performed RT-qPCR to identify the upregulated miRNA in EPC-EXOs and manipulate its expression to estimate its role in macrophage polarization, SOCS3/JAK2/STAT3 pathway activation, and motor behavior improvement.

RESULTS

We found that EPC-EXOs decreased the macrophages' pro-inflammatory marker expression and increased their anti-inflammatory marker expression on the 7 and 14 days after SCI. The spinal cord H&E staining results showed that EPC-EXOs raised the tissue-sparing area rate significantly after 28 days of SCI and the motor behavior evaluation indicated an increased BMS score and motor-evoked potential by EPC-EXOs treatment after SCI. The RT-qPCR assay identified that miR-222-3P upregulated in EPC-EXOs and its miRNA-mimic also decreased the pro-inflammatory macrophages and increased the anti-inflammatory macrophages. Additionally, miR-222-3P mimic activated the SOCS3/JAK2/STAT3 pathway, and SOCS3/JAK2/STAT3 pathway inhibition blocked miR-2223P's effects on macrophage polarization and mouse motor behavior.

CONCLUSION

Comprehensively, we discovered that EPC-EXOs-derived miR-222-3p affected macrophage polarization via SOCS3/JAK2/STAT3 pathway and promoted mouse functional repair after SCI, which reveals EPC-EXOs' role in modulation of macrophage phenotype and will provide a novel interventional strategy to induce post-SCI recovery.

Transplanting Human Neural Stem Cells with ≈50% Reduction of SOX9 Gene Dosage Promotes Tissue Repair and Functional Recovery from Severe Spinal Cord Injury

Neural stem cells (NSCs) derived from human pluripotent stem cells (hPSCs) are considered a major cell source for reconstructing damaged neural circuitry and enabling axonal regeneration. However, the microenvironment at the site of spinal cord injury (SCI) and inadequate intrinsic factors limit the therapeutic potential of transplanted NSCs. Here, it is shown that half dose of SOX9 in hPSCs-derived NSCs (hNSCs) results in robust neuronal differentiation bias toward motor neuron lineage. The enhanced neurogenic potency is partly attributed to the reduction of glycolysis. These neurogenic and metabolic properties retain after transplantation of hNSCs with reduced SOX9 expression in a contusive SCI rat model without the need for growth factor-enriched matrices. Importantly, the grafts exhibit excellent integration properties, predominantly differentiate into motor neurons, reduce glial scar matrix accumulation to facilitate long-distance axon growth and neuronal connectivity with the host as well as dramatically improve locomotor and somatosensory function in recipient animals. These results demonstrate that hNSCs with half SOX9 gene dosage can overcome extrinsic and intrinsic barriers, representing a powerful therapeutic potential for transplantation treatments for SCI.

Mesenchymal stem cell and endothelial progenitor cells coinjection improves LPS-induced lung injury via Tie2 activation and downregulation of the TLR4/MyD88 pathway

Sepsis is one of the most important complications of infection with a high mortality rate. Recently, cell therapy has been widely used to reduce the symptoms of sepsis. It has been previously reported that mesenchymal stem cell (MSC) and endothelial progenitor cells (EPC) therapy have beneficial effects in experimental models of sepsis. The effects of coculture of MSC and EPC have not yet been used to treat sepsis. Therefore, the aim of this study was to investigate the therapeutic potential of EPC + MSC coculture on the residual effects of sepsis in a lipopolysaccharide (LPS)-induced mice model. Coinjections of EPC + MSC significantly enhanced the survival rate of LPS-induced mice, decreased concentrations of pro-inflammatory cytokines, and increased the level of anti-inflammatory cytokine. The LPS-induced mice that were treated with EPC + MSC showed a notable reduction in pulmonary edema, hepatic enzymes, and C-reactive protein level compared with the control group. Our results showed that coinjection of EPC + MSC up and downregulates Tie2 and TLR4/MyD88 signaling pathways in LPS-induced mice, respectively. Also, in vitro study showed that viability, adhesion, and migration in coculture cells is significantly decreased after being induced with 10 μg/ml LPS. Our results showed that LPS impaired the functional activity of the cocultured EPC + MSC via upregulation of the TLR4/MyD88 signaling pathway, which may be associated with decreased pTie2/Tie2 expression. In conclusion, coinjection of EPC and MSC modulated the TLR4/MyD88 signaling pathway that leads to reduce the inflammatory response. This study may provide promising results for the introduction of cocultured cells to manage infectious diseases and balance the immune response through immune regulatory function.

The interaction of Notch and Wnt signaling pathways in vertebrate regeneration

Regeneration is an evolutionarily conserved process in animal kingdoms, however, the regenerative capacities differ from species and organ/tissues. Mammals possess very limited regenerative potential to replace damaged organs, whereas non-mammalian species usually have impressive abilities to regenerate organs. The regeneration process requires proper spatiotemporal regulation from key signaling pathways. The canonical Notch and Wnt signaling pathways, two fundamental signals guiding animal development, have been demonstrated to play significant roles in the regeneration of vertebrates. In recent years, increasing evidence has implicated the cross-talking between Notch and Wnt signals during organ regeneration. In this review, we summarize the roles of Notch signaling and Wnt signaling during several representative organ regenerative events, emphasizing the functions and molecular bases of their interplay in these processes, shedding light on utilizing these two signaling pathways to enhance regeneration in mammals and design legitimate therapeutic strategies.

GDNF rescues the fate of neural progenitor grafts by attenuating Notch signals in the injured spinal cord in rodents

Neural progenitor cell (NPC) transplantation is a promising strategy for the treatment of spinal cord injury (SCI). In this study, we show that injury-induced Notch activation in the spinal cord microenvironment biases the fate of transplanted NPCs toward astrocytes in rodents. In a screen for potential clinically relevant factors to modulate Notch signaling, we identified glial cell-derived neurotrophic factor (GDNF). GDNF attenuates Notch signaling by mediating delta-like 1 homolog (DLK1) expression, which is independent of GDNF's effect on cell survival. When transplanted into a rodent model of cervical SCI, GDNF-expressing human-induced pluripotent stem cell-derived NPCs (hiPSC-NPCs) demonstrated higher differentiation toward a neuronal fate compared to control cells. In addition, expression of GDNF promoted endogenous tissue sparing and enhanced electrical integration of transplanted cells, which collectively resulted in improved neurobehavioral recovery. CRISPR-induced knockouts of the DLK1 gene in GDNF-expressing hiPSC-NPCs attenuated the effect on functional recovery, demonstrating that this effect is partially mediated through DLK1 expression. These results represent a mechanistically driven optimization of hiPSC-NPC therapy to redirect transplanted cells toward a neuronal fate and enhance their integration.

Comparative gene expression profiling between optic nerve and spinal cord injury in Xenopus laevis reveals a core set of genes inherent in successful regeneration of vertebrate central nervous system axons

BACKGROUND

The South African claw-toed frog, Xenopus laevis, is uniquely suited for studying differences between regenerative and non-regenerative responses to CNS injury within the same organism, because some CNS neurons (e.g., retinal ganglion cells after optic nerve crush (ONC)) regenerate axons throughout life, whereas others (e.g., hindbrain neurons after spinal cord injury (SCI)) lose this capacity as tadpoles metamorphose into frogs. Tissues from these CNS regions (frog ONC eye, tadpole SCI hindbrain, frog SCI hindbrain) were used in a three-way RNA-seq study of axotomized CNS axons to identify potential core gene expression programs for successful CNS axon regeneration.

RESULTS

Despite tissue-specific changes in expression dominating the injury responses of each tissue, injury-induced changes in gene expression were nonetheless shared between the two axon-regenerative CNS regions that were not shared with the non-regenerative region. These included similar temporal patterns of gene expression and over 300 injury-responsive genes. Many of these genes and their associated cellular functions had previously been associated with injury responses of multiple tissues, both neural and non-neural, from different species, thereby demonstrating deep phylogenetically conserved commonalities between successful CNS axon regeneration and tissue regeneration in general. Further analyses implicated the KEGG adipocytokine signaling pathway, which links leptin with metabolic and gene regulatory pathways, and a novel gene regulatory network with genes regulating chromatin accessibility at its core, as important hubs in the larger network of injury response genes involved in successful CNS axon regeneration.

CONCLUSIONS

This study identifies deep, phylogenetically conserved commonalities between CNS axon regeneration and other examples of successful tissue regeneration and provides new targets for studying the molecular underpinnings of successful CNS axon regeneration, as well as a guide for distinguishing pro-regenerative injury-induced changes in gene expression from detrimental ones in mammals.

Curcumin attenuates hypoxia/reoxygenation‑induced cardiomyocyte injury by downregulating Notch signaling

Recovery of the blood supply is the most effective treatment against ischemic heart disease; however, it is also a major cause of myocardial ischemia/reperfusion injury in clinical therapy. Curcumin has been reported to possess beneficial effects against hypoxia/reoxygenation (H/R)-induced cardiomyocyte injury by regulating cell proliferation, apoptosis and antioxidant enzyme activity. The aim of the present study was to investigate the molecular mechanisms underlying the effects of curcumin on H/R-injured cardiomyocytes. H9C2 cardiomyocytes were pretreated with curcumin, and then cultured under H/R conditions. The viability of H9C2 cells was measured using a Cell Counting kit-8 assay, and the levels of intracellular lactate dehydrogenase (LDH), malondialdehyde (MDA) and superoxide dismutase (SOD) were measured to assess cell injury. Levels of reactive oxygen species (ROS) and apoptosis were evaluated by flow cytometry. The expression levels of Notch intracellular domain (NICD) and numerous downstream genes were analyzed via reverse transcription-quantitative polymerase chain reaction and western blotting. The results revealed that curcumin protected H9C2 cells against H/R-induced injury, reversing the H/R-induced increases in LDH and MDA levels, and decreases in SOD levels. ROS levels in H/R-induced cells were also significantly downregulated by curcumin treatment (P<0.01), and the apoptotic rate was significantly decreased from 15.13% in the H/R group to 7.7% in the H/R + curcumin group (P<0.01). The expression levels of NICD, hairy and enhancer of split (Hes)-1, Hes-5 and hairy/enhancer-of-split related with YRPW motif protein 1 (Hey-1) were significantly decreased in H/R-treated cells following curcumin treatment. Treatment with Jagged1 attenuated the effects of curcumin on cell viability, ROS levels and apoptosis; the Notch pathway was also reactivated. The present study indicated that there was a role for the Notch pathway in the protective effects of curcumin against H/R-induced cardiomyocyte injury, suggesting that downregulation of the Notch pathway may alleviate H/R-induced injury in H9C2 cells.

Astrocyte-derived Jagged-1 mitigates deleterious Notch signaling in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a late-onset devastating degenerative disease mainly affecting motor neurons. Motor neuron degeneration is accompanied and aggravated by oligodendroglial pathology and the presence of reactive astrocytes and microglia. We studied the role of the Notch signaling pathway in ALS, as it is implicated in several processes that may contribute to this disease, including axonal retraction, microgliosis, astrocytosis, oligodendrocyte precursor cell proliferation and differentiation, and cell death. We observed abnormal activation of the Notch signaling pathway in the spinal cord of SOD1^G93A mice, a well-established model for ALS, as well as in the spinal cord of patients with sporadic ALS (sALS). This increased activation was particularly evident in reactive GFAP-positive astrocytes. In addition, one of the main Notch ligands, Jagged-1, was ectopically expressed in reactive astrocytes in spinal cord from ALS mice and patients, but absent in resting astrocytes. Astrocyte-specific inactivation of Jagged-1 in presymptomatic SOD1^G93A mice further exacerbated the activation of the Notch signaling pathway and aggravated the course of the disease in these animals without affecting disease onset. These data suggest that aberrant Notch signaling activation contributes to the pathogenesis of ALS, both in sALS patients and SOD1^G93A mice, and that it is mitigated in part by the upregulation of astrocytic Jagged-1.

Protective effect of epigenetic silencing of CyclinD1 against spinal cord injury using bone marrow-derived mesenchymal stem cells in rats

This study focuses on the protective effect of epigenetic silencing of CyclinD1 against spinal cord injury (SCI) using bone marrow-derived mesenchymal stem cells (BMSCs) in rats. Eighty-eight adult female Wistar rats were randomly assigned into the sham group, the control group, the si-CyclinD1 + BMSCs group and the BMSCs group. CyclinD1 protein and mRNA expressions after siRNA transfection were detected by Western blotting and qRT-PCR. The siRNA-CyclinD1 BMSCs were transplanted into rats in the si-CyclinD1 + BMSCs group using stereotaxic method 6 hr after SCI. Hindlimb locomotor performance was determined using inclined plane test and Basso-Beattie-Bresnahan (BBB) locomotor rating scale. Expressions of glial fibrillary acidic protein (GFAP) and nerve growth factor (NGF) were detected by immunohistochemistry. Inclined plane and BBB scores in the control, si-CyclinD1 + BMSCs, and BMSCs groups were significantly lower than the sham group, but these scores were evidently decreased in the control group and increased in the si-CyclinD1 + BMSCs group compared with the BMSCs group. The repair degree of spinal cord tissues of rats in the si-CyclinD1 + BMSCs group was obvious than the BMSCs group. GFAP and NGF protein expressions were markedly decreased in the control, si-CyclinD1 + BMSCs and BMSCs groups when compared with the sham group. GFAP- and NGF-positive cells were significantly increased in the si-CyclinD1 + BMSCs group while decreased in the control group. Our study provides evidence that epigenetic silencing of CyclinD1 using BMSCs might accelerate the repair of SCI in rats.

Activation of the Notch-1 signaling pathway may be involved in intracerebral hemorrhage-induced reactive astrogliosis in rats

OBJECTIVE Reactive astrogliosis, a key feature that is characterized by glial proliferation, has been observed in rat brains after intracerebral hemorrhage (ICH). However, the mechanisms that control reactive astrogliosis formation remain unknown. Notch-1 signaling plays a critical role in modulating reactive astrogliosis. The purpose of this paper was to establish whether Notch-1 signaling is involved in reactive astrogliosis after ICH. METHODS ICH was induced in adult male Sprague-Dawley rats via stereotactic injection of autologous blood into the right globus pallidus. N-[ N-(3,5-difluorophenacetyl)-l-alanyl]- S-phenylglycine t-butyl ester (DAPT) was injected into the lateral ventricle to block Notch-1 signaling. The rats' brains were perfused to identify proliferating cell nuclear antigen (PCNA)-positive/GFAP-positive nuclei. The expression of GFAP, Notch-1, and the activated form of Notch-1 (Notch intracellular domain [NICD]) and its ligand Jagged-1 was assessed using immunohistochemical and Western blot analyses, respectively. RESULTS Notch-1 signaling was upregulated and activated after ICH as confirmed by an increase in the expression of Notch-1 and NICD and its ligand Jagged-1. Remarkably, blockade of Notch-1 signaling with the specific inhibitor DAPT suppressed astrocytic proliferation and GFAP levels caused by ICH. In addition, DAPT improved neurological outcome after ICH. CONCLUSIONS Notch-1 signaling is a critical regulator of ICH-induced reactive astrogliosis, and its blockage may be a potential therapeutic strategy for hemorrhagic injury.

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.

Overexpression of Jagged1 Ameliorates Aged Rat-Derived Endothelial Progenitor Cell Functions and Improves Its Transfusion Efficiency for Rat Balloon-Induced Arterial Injury

BACKGROUND

Endothelial progenitor cell (EPC) has significant age-dependent alterations in properties, but the role of Jagged1 in aging-induced decline of EPC functions remains unclear.

METHODS

2- and 20-month old healthy male Sprague-Dawley rats were used in present study. Jagged1 gene transfection was performed in EPC isolated from aged (AEPC) and young rats (YEPC), respectively. Experiments were divided into 4 groups: (1) pIRES2-EGFP (PE) group, (2) PE-combined N-[N-(3, 5-difluoro-phenacetyl)-1- alany1]-S-phenyglycine t-butyl ester (DAPT) (PE + D) group, (3) pIRES2 EGFP-Jagged1 (PEJ) group, and (4) PEJ combined DAPT (PEJ + D) group. Notch molecules were detected by real-time quantitative polymerase chain reaction or Western blotting. CD34, CD133, CD45, and KDR markers were detected by flow cytometry. EPC migration and proliferation were detected with a modified Boyden chamber and 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay, respectively; the tube formation ability was assayed by in vitro angiogenesis kit; EPC transfusion after Jagged1 gene transfection was performed in rat carotid artery injury models.

RESULTS

Jagged1 gene transfection effectively activates notch-signaling pathway. Compared with PE groups, overexpression of Jagged1 significantly promoted AEPC functions including proliferation, migration, the tube formation ability, and cell differentiation, these effects could be reasonably diminished by DAPT. In vivo study demonstrated that Jagged1 overexpressing also significantly promoted AEPC homing to the vascular injury sites and decreases the neointima formation after vascular injury.

CONCLUSIONS

Overexpression of Jagged1 ameliorates aged rat-derived EPC functions and increases its transfusion efficiency for balloon-induced rat arterial injury.

Jagged-1 Signaling in the Bone Marrow Microenvironment Promotes Endothelial Progenitor Cell Expansion and Commitment of CD133+ Human Cord Blood Cells for Postnatal Vasculogenesis

Notch signaling is involved in cell fate decisions during murine vascular development and hematopoiesis in the microenvironment of bone marrow. To investigate the close relationship between hematopoietic stem cells and human endothelial progenitor cells (EPCs) in the bone marrow niche, we examined the effects of Notch signals [Jagged-1 and Delta-like ligand (Dll)-1] on the proliferation and differentiation of human CD133+ cell-derived EPCs. We established stromal systems using HESS-5 murine bone marrow cells transfected with human Jagged-1 (hJagged-1) or human Dll-1 (hDll-1). CD133+ cord blood cells were co-cultured with the stromal cells for 7 days, and then their proliferation, differentiation, and EPC colony formation was evaluated. We found that hJagged-1 induced the proliferation and differentiation of CD133+ cord blood EPCs. In contrast, hDll-1 had little effect. CD133+ cells stimulated by hJagged-1 differentiated into CD31+/KDR+ cells, expressed vascular endothelial growth factor-A, and showed enhanced EPC colony formation compared with CD133+ cells stimulated by hDll-1. To evaluate the angiogenic properties of hJagged-1- and hDll-1-stimulated EPCs in vivo, we transplanted these cells into the ischemic hindlimbs of nude mice. Transplantation of EPCs stimulated by hJagged-1, but not hDll-1, increased regional blood flow and capillary density in ischemic hindlimb muscles. This is the first study to show that human Notch signaling influences EPC proliferation and differentiation in the bone marrow microenvironment. Human Jagged-1 induced the proliferation and differentiation of CD133+ cord blood progenitors compared with hDll-1. Thus, hJagged-1 signaling in the bone marrow niche may be used to expand EPCs for therapeutic angiogenesis.

Wnt3a is critical for endothelial progenitor cell-mediated neural stem cell proliferation and differentiation

The present study aimed to determine whether co-culture with bone marrow‑derived endothelial progenitor cells (EPCs) affects the proliferation and differentiation of spinal cord-derived neural stem cells (NSCs), and to investigate the underlying mechanism. The proliferation and differentiation of the NSCs were evaluated by an MTT cell proliferation and cytotoxicity assay, and immunofluorescence, respectively. The number of neurospheres and the number of β‑tubulin III‑positive cells were detected by microscopy. The wingless‑type MMTV integration site family, member 3a (Wnt3a)/β-catenin signaling pathway was analyzed by western blot analysis and reverse transcription‑quantitative polymerase chain reaction to elucidate the possible mechanisms of EPC‑mediated NSC proliferation and differentiation. The results revealed that co‑culture with EPCs significantly induced NSC proliferation and differentiation. In addition, co‑culture with EPCs markedly induced the expression levels of Wnt3a and β‑catenin and inhibited the phosphorylation of glycogen synthase kinase 3β (GSK‑3β). By contrast, Wnt3a knockdown using a short hairpin RNA plasmid in the EPCs reduced EPC‑mediated NSC proliferation and differentiation, accompanied by inhibition of the EPC‑mediated expression of β‑catenin, and its phosphorylation and activation of GSK‑3β. Taken together, the findings of the present study demonstrated that Wnt3a was critical for EPC‑mediated NSC proliferation and differentiation.

Pushing Forward: Remyelination as the New Frontier in CNS Diseases

The evolutionary acquisition of myelin sheaths around large caliber axons in the central nervous system (CNS) represented a milestone in the development of vertebrate higher brain function. Myelin ensheathment of axons enabled saltatory conduction and thus accelerated information processing. However, a number of CNS diseases harm or destroy myelin and oligodendrocytes (myelin-producing cells), ultimately resulting in demyelination. In the adult CNS, new oligodendrocytes can be generated from a quiescent pool of precursor cells, which - upon differentiation - can replace lost myelin sheaths. The efficiency of this spontaneous regeneration is limited, which leads to incomplete remyelination and residual clinical symptoms. Here, we discuss CNS pathologies characterized by white matter degeneration and regeneration and highlight drugs that could potentially serve as remyelination therapies.

Evidence for proangiogenic cellular and humoral systemic response in patients with acute onset of spinal cord injury

CONTEXT/OBJECTIVE

Traumatic spinal cord injury (SCI) leads to disruption of local vasculature inducing secondary damage of neural tissue. Circulating endothelial progenitor cells (EPCs) play an important role in post-injury regeneration of vasculature, whereas endothelial cells (ECs) reflect endothelial damage.

METHODS

Twenty patients with SCI were assessed during the first 24 hours, at day 3, and day 7 post-injury and compared to 25 healthy subjects. We herein investigated EPC and EC counts by flow cytometry as well as the levels of soluble factors (SDF-1, HGF, VEGF, Ang2, EGF, endoglin, PLGF, FGF-2, ET-1, BDNF, IGF-1) regulating their migration and proangiogenic function. To better characterize peripheral blood (PB) cells, global gene expression profiles of PB-derived cells were determined using genome-wide RNA microarray technology.

RESULTS

We found significantly higher EPC (CD34(+)/CD133(+)/VEGFR2(+)) as well as EC (VEGFR2(+)) count in PB of patients with SCI within 7 days post-injury and the increased HGF, ET-1, Ang2, EGF, and PLGF plasma levels. Global gene expression analysis revealed considerably lower expression of genes associated with both innate and adaptive immune response in PB cells in patients.

CONCLUSION

Collectively, our findings demonstrate that SCI triggers bone marrow-derived EPC mobilization accompanied by increased circulating EC numbers. Significant changes in both chemoattractive and proangiogenic cytokines plasma levels occurring rapidly after SCI suggest their role in SCI-related regenerative responses to injury. Broadened knowledge concerning the mechanisms governing of human organism response to the SCI might be helpful in developing effective therapeutic strategies.

Activation of the Notch signaling pathway promotes neurovascular repair after traumatic brain injury

The Notch signaling pathway plays a key role in angiogenesis and endothelial cell formation, but it remains unclear whether it is involved in vascular repair by endothelial progenitor cells after traumatic brain injury. Therefore, in the present study, we controlled the Notch signaling pathway using overexpression and knockdown constructs. Activation of the Notch signaling pathway by Notch1 or Jagged1 overexpression enhanced the migration, invasiveness and angiogenic ability of endothelial progenitor cells. Suppression of the Notch signaling pathway with Notch1 or Jagged1 siRNAs reduced the migratory capacity, invasiveness and angiogenic ability of endothelial progenitor cells. Activation of the Notch signaling pathway in vivo in a rat model of mild traumatic brain injury promoted neurovascular repair. These findings suggest that the activation of the Notch signaling pathway promotes blood vessel formation and tissue repair after brain trauma.

Thickness-controllable electrospun fibers promote tubular structure formation by endothelial progenitor cells

Controlling the thickness of an electrospun nanofibrous scaffold by altering its pore size has been shown to regulate cell behaviors such as cell infiltration into a three-dimensional (3D) scaffold. This is of great importance when manufacturing tissue-engineering scaffolds using an electrospinning process. In this study, we report the development of a novel process whereby additional aluminum foil layers were applied to the accumulated electrospun fibers of an existing aluminum foil collector, effectively reducing the incidence of charge buildup. Using this process, we fabricated an electrospun scaffold with a large pore (pore size >40 μm) while simultaneously controlling the thickness. We demonstrate that the large pore size triggered rapid infiltration (160 μm in 4 hours of cell culture) of individual endothelial progenitor cells (EPCs) and rapid cell colonization after seeding EPC spheroids. We confirmed that the 3D, but not two-dimensional, scaffold structures regulated tubular structure formation by the EPCs. Thus, incorporation of stem cells into a highly porous 3D scaffold with tunable thickness has implications for the regeneration of vascularized thick tissues and cardiac patch development.

Spinal cord regeneration

Three theories of regeneration dominate neuroscience today, all purporting to explain why the adult central nervous system (CNS) cannot regenerate. One theory proposes that Nogo, a molecule expressed by myelin, prevents axonal growth. The second theory emphasizes the role of glial scars. The third theory proposes that chondroitin sulfate proteoglycans (CSPGs) prevent axon growth. Blockade of Nogo, CSPG, and their receptors indeed can stop axon growth in vitro and improve functional recovery in animal spinal cord injury (SCI) models. These therapies also increase sprouting of surviving axons and plasticity. However, many investigators have reported regenerating spinal tracts without eliminating Nogo, glial scar, or CSPG. For example, many motor and sensory axons grow spontaneously in contused spinal cords, crossing gliotic tissue and white matter surrounding the injury site. Sensory axons grow long distances in injured dorsal columns after peripheral nerve lesions. Cell transplants and treatments that increase cAMP and neurotrophins stimulate motor and sensory axons to cross glial scars and to grow long distances in white matter. Genetic studies deleting all members of the Nogo family and even the Nogo receptor do not always improve regeneration in mice. A recent study reported that suppressing the phosphatase and tensin homolog (PTEN) gene promotes prolific corticospinal tract regeneration. These findings cannot be explained by the current theories proposing that Nogo and glial scars prevent regeneration. Spinal axons clearly can and will grow through glial scars and Nogo-expressing tissue under some circumstances. The observation that deleting PTEN allows corticospinal tract regeneration indicates that the PTEN/AKT/mTOR pathway regulates axonal growth. Finally, many other factors stimulate spinal axonal growth, including conditioning lesions, cAMP, glycogen synthetase kinase inhibition, and neurotrophins. To explain these disparate regenerative phenomena, I propose that the spinal cord has evolved regenerative mechanisms that are normally suppressed by multiple extrinsic and intrinsic factors but can be activated by injury, mediated by the PTEN/AKT/mTOR, cAMP, and GSK3b pathways, to stimulate neural growth and proliferation.

Myeloid-Specific Blockade of Notch Signaling by RBP-J Knockout Attenuates Spinal Cord Injury Accompanied by Compromised Inflammation Response in Mice

The outcome of spinal cord injury (SCI) is determined by both neural cell-intrinsic survival pathways and tissue microenvironment-derived signals. Macrophages dominating the inflammatory responses in SCI possess both destructive and reparative potentials, according to their activation status. Notch signaling is involved in both cell survival and macrophage-mediated inflammation, but a comprehensive role of Notch signaling in SCI has been elusive. In this study, we compared the effects of general Notch blockade by a pharmaceutical γ-secretase inhibitor (GSI) and myeloid-specific Notch signal disruption by recombination signal binding protein Jκ (RBP-J) knockout on SCI. The administration of Notch signal inhibitor GSI resulted in worsened hind limb locomotion and exacerbated inflammation. However, mice lacking RBP-J, the critical transcription factor mediating signals from all four mammalian Notch receptors, in myeloid lineage displayed promoted functional recovery, attenuated glial scar formation, improved neuronal survival and axon regrowth, and mitigated inflammatory response after SCI. These benefits were accompanied by enhanced AKT activation in the lesion area after SCI. These findings demonstrate that abrogating Notch signal in myeloid cells ameliorates inflammation response post-SCI and promotes functional recovery, but general pharmaceutical Notch interception has opposite effects. Therefore, clinical intervention of Notch signaling in SCI needs to pinpoint myeloid lineage to avoid the counteractive effects of global inhibition.

Influence of the extracellular matrix on endogenous and transplanted stem cells after brain damage

The limited regeneration capacity of the adult central nervous system (CNS) requires strategies to improve recovery of patients. In this context, the interaction of endogenous as well as transplanted stem cells with their environment is crucial. An understanding of the molecular mechanisms could help to improve regeneration by targeted manipulation. In the course of reactive gliosis, astrocytes upregulate Glial fibrillary acidic protein (GFAP) and start, in many cases, to proliferate. Beside GFAP, subpopulations of these astroglial cells coexpress neural progenitor markers like Nestin. Although cells express these markers, the proportion of cells that eventually give rise to neurons is limited in many cases in vivo compared to the situation in vitro. In the first section, we present the characteristics of endogenous progenitor-like cells and discuss the differences in their neurogenic potential in vitro and in vivo. As the environment plays an important role for survival, proliferation, migration, and other processes, the second section of the review describes changes in the extracellular matrix (ECM), a complex network that contains numerous signaling molecules. It appears that signals in the damaged CNS lead to an activation and de-differentiation of astrocytes, but do not effectively promote neuronal differentiation of these cells. Factors that influence stem cells during development are upregulated in the damaged brain as part of an environment resembling a stem cell niche. We give a general description of the ECM composition, with focus on stem cell-associated factors like the glycoprotein Tenascin-C (TN-C). Stem cell transplantation is considered as potential treatment strategy. Interaction of transplanted stem cells with the host environment is critical for the outcome of stem cell-based therapies. Possible mechanisms involving the ECM by which transplanted stem cells might improve recovery are discussed in the last section.

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.

Regenerative medicine in orthopedics using cells, scaffold, and microRNA

Cells, scaffold, and growth factors are crucially important in regenerative medicine and tissue engineering. Progress in science and technology has enabled development of these three factors, with basic research being applied clinically. In the past decade, we have investigated tissue regeneration in animal models of musculoskeletal disorders by using cells, scaffold, and delivery systems which has been relatively easy to apply and develop in clinical settings. Moreover, microRNA (miRNA), which are important in biological processes and in the pathogenesis of human diseases, have been used in research on regenerative medicine. For the cell source, we focused on mesenchymal stem cells (MSC) and CD34(+) and CD133(+) cells as endothelial progenitor cells for regeneration of musculoskeletal organs. These cells are accessible and safe. For less invasive and more effective therapy, we developed a novel cell-delivery system using magnetic force to accumulate cells at a desired site. Furthermore, administration of synthetic miRNA could enhance tissue regeneration. In our studies, use of these cells combined with a cell-delivery system, miRNA, scaffold, and cytokines has led to effective regeneration of musculoskeletal tissues including cartilage, bone, ligaments, muscle, peripheral nerves, and spinal cord. The current and future objective is more effective and less invasive cell-based therapy with spatial control of transplanted cells by use of an external magnetic force. Analysis of efficiency, safety, and the mechanism of tissue regeneration by cells, scaffold, and miRNA will lead to more promising regenerative medicine, involving the development of a new generation of therapy. This review will focus on our regenerative medicine research, which focuses on clinical application of cells, scaffold, and miRNA.

Notch signaling pathway is activated in motoneurons of spinal muscular atrophy

Spinal muscular atrophy (SMA) is a neurodegenerative disease produced by low levels of Survival Motor Neuron (SMN) protein that affects alpha motoneurons in the spinal cord. Notch signaling is a cell-cell communication system well known as a master regulator of neural development, but also with important roles in the adult central nervous system. Aberrant Notch function is associated with several developmental neurological disorders; however, the potential implication of the Notch pathway in SMA pathogenesis has not been studied yet. We report here that SMN deficiency, induced in the astroglioma cell line U87MG after lentiviral transduction with a shSMN construct, was associated with an increase in the expression of the main components of Notch signaling pathway, namely its ligands, Jagged1 and Delta1, the Notch receptor and its active intracellular form (NICD). In the SMNΔ7 mouse model of SMA we also found increased astrocyte processes positive for Jagged1 and Delta1 in intimate contact with lumbar spinal cord motoneurons. In these motoneurons an increased Notch signaling was found, as denoted by increased NICD levels and reduced expression of the proneural gene neurogenin 3, whose transcription is negatively regulated by Notch. Together, these findings may be relevant to understand some pathologic attributes of SMA motoneurons.

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.