Roles of activated astrocytes in bone marrow stromal cell proliferation and differentiation

The delivery of miR-21a-5p by extracellular vesicles induces microglial polarization via the STAT3 pathway following hypoxia-ischemia in neonatal mice

Extracellular vesicles (EVs) from mesenchymal stromal cells (MSCs) have previously been shown to protect against brain injury caused by hypoxia-ischemia (HI). The neuroprotective effects have been found to relate to the anti-inflammatory effects of EVs. However, the underlying mechanisms have not previously been determined. In this study, we induced oxygen-glucose deprivation in BV-2 cells (a microglia cell line), which mimics HI in vitro, and found that treatment with MSCs-EVs increased the cell viability. The treatment was also found to reduce the expression of pro-inflammatory cytokines, induce the polarization of microglia towards the M2 phenotype, and suppress the phosphorylation of selective signal transducer and activator of transcription 3 (STAT3) in the microglia. These results were also obtained in vivo using neonatal mice with induced HI. We investigated the potential role of miR-21a-5p in mediating these effects, as it is the most highly expressed miRNA in MSCs-EVs and interacts with the STAT3 pathway. We found that treatment with MSCs-EVs increased the levels of miR-21a-5p in BV-2 cells, which had been lowered following oxygen-glucose deprivation. When the level of miR-21a-5p in the MSCs-EVs was reduced, the effects on microglial polarization and STAT3 phosphorylation were reduced, for both the in vitro and in vivo HI models. These results indicate that MSCs-EVs attenuate HI brain injury in neonatal mice by shuttling miR-21a-5p, which induces microglial M2 polarization by targeting STAT3.

Regulating Endogenous Neural Stem Cell Activation to Promote Spinal Cord Injury Repair

Spinal cord injury (SCI) affects millions of individuals worldwide. Currently, there is no cure, and treatment options to promote neural recovery are limited. An innovative approach to improve outcomes following SCI involves the recruitment of endogenous populations of neural stem cells (NSCs). NSCs can be isolated from the neuroaxis of the central nervous system (CNS), with brain and spinal cord populations sharing common characteristics (as well as regionally distinct phenotypes). Within the spinal cord, a number of NSC sub-populations have been identified which display unique protein expression profiles and proliferation kinetics. Collectively, the potential for NSCs to impact regenerative medicine strategies hinges on their cardinal properties, including self-renewal and multipotency (the ability to generate de novo neurons, astrocytes, and oligodendrocytes). Accordingly, endogenous NSCs could be harnessed to replace lost cells and promote structural repair following SCI. While studies exploring the efficacy of this approach continue to suggest its potential, many questions remain including those related to heterogeneity within the NSC pool, the interaction of NSCs with their environment, and the identification of factors that can enhance their response. We discuss the current state of knowledge regarding populations of endogenous spinal cord NSCs, their niche, and the factors that regulate their behavior. In an attempt to move towards the goal of enhancing neural repair, we highlight approaches that promote NSC activation following injury including the modulation of the microenvironment and parenchymal cells, pharmaceuticals, and applied electrical stimulation.

Preconditioning of bone marrow mesenchymal stem cells with hydrogen sulfide improves their therapeutic potential

Bone marrow mesenchymal stem cells (BMSCs) transplantation has shown great promises for treating various brain diseases. However, poor viability of transplanted BMSCs in injured brain has limited the therapeutic efficiency. Hypoxia-ischemic injury is one of major mechanisms underlying the survival of transplanted BMSCs. We investigated the mechanism of preconditioning of BMSCs with hydrogen sulfide (H2S), which has been proposed as a novel therapeutic strategy for hypoxia-ischemic injury. In this study, we demonstrated that preconditioning of NaHS, a H2S donor, effectively suppressed hypoxia-ischemic-induced apoptosis whereby the rise in Bax/Bcl-2 ratio. Further analyses revealed Akt and ERK1/2 pathways were involved in the protective effects of NaHS. In addition, NaHS preconditioning increased secretion of BDNF and VEGF in BMSCs. Consistent with in vitro data, transplantation of NaHS preconditioned BMSCs in vivo further enhanced the therapeutic effects of BMSCs on neuronal injury and neurological recovery, associated with increased vessel density and upregulation of BDNF and VEGF in the ischemic tissue. These findings suggest that H2S could enhance the therapeutic effects of BMSCs. The underlying mechanisms might be due to enhanced capacity of BMSCs and upregulation of protective cytokines in the hypoxia tissue.

Fimbria-fornix (FF)-transected hippocampal extracts induce the activation of astrocytes in vitro

Hippocampus is one of the neurogenesis areas in adult mammals, but the function of astrocytes in this area is still less known. In our previous study, the fimbria-fornix (FF)-transected hippocampal extracts promoted the proliferation and neuronal differentiation of radial glial cells in vitro. To explore the effects of hippocampal extracts on gliogenesis, the hippocampal astrocytes were treated by normal or ff-transected hippocampal extracts in vitro. The cells were immunostained by brain lipid-binding protein (BLBP), nestin, and SOX2 to assess their state of activation. The effects of astrocyte-conditioned medium on the neuronal differentiation of hippocampal neural stem cells (NSCs) were also investigated. After treatment of FF-transected hippocampal extracts, the number of BLBP, nestin, and Sox-positive cells were obviously more than the cells which treated by normal hippocampal extracts, these cells maintained a state of activation and the activated astrocyte-conditioned medium also promoted the differentiation of NSCs into more neurons. These findings suggest that the astrocytes can be activated by FF-transected hippocampal extracts and these activated cells also can promote the neuronal differentiation of hippocampal NSCs in vitro.

Characterization of in vitro cultured bone marrow and adipose tissue-derived mesenchymal stem cells and their ability to express neurotrophic factors

MSCs (mesenchymal stem cells) have attracted attention as a promising tool for regenerative medicine and transplantation therapy. MSCs exert neuroprotective effects by secreting a number of factors in vitro and in vivo. Similar characteristics are found in ADSCs (adipose-derived stem cells) and BMSCs (bone marrow stromal cells). Multipotent capability, easy accessibility and rapid proliferation of ADSCs have been established. Our main objective was to compare cell viability, growth rate, expression of neurotrophic factors and nestin genes in ADSCs and BMSCs. Cell doubling time and proliferation rate indicate that ADSCs has a higher proliferation rate than BMSCs. ADSCs and BMSCs express a similar pattern of CD71 and CD90 markers. Nestin immunostaining showed that ADSCs and BMSCs are immunopositive. The expression of neurotrophic factors genes in ADSCs proved similar to that of BMSCs genes. Thus adipose tissue stem cells with a high proliferation rate can express nestin and neurotrophic factor genes. Therefore ADSCs may be useful in future cell replacement therapies and help improve neurodegenerative diseases.

Effect of cyclic strain on cardiomyogenic differentiation of rat bone marrow derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) are a potential source of material for the generation of tissue-engineered cardiac grafts because of their ability to transdifferentiate into cardiomyocytes after chemical treatments or co-culture with cardiomyocytes. Cardiomyocytes in the body are subjected to cyclic strain induced by the rhythmic heart beating. Whether cyclic strain could regulate rat bone marrow derived MSC (rBMSC) differentiation into cardiomyocyte-like lineage was investigated in this study. A stretching device was used to generate the cyclic strain for rBMSCs. Cardiomyogenic differentiation was evaluated using quantitative real-time reverse transcription polymerase chain reaction (RT-PCR), immunocytochemistry and western-blotting. The results demonstrated that appropriate cyclic strain treatment alone could induce cardiomyogenic differentiation of rBMSCs, as confirmed by the expression of cardiomyocyte-related markers at both mRNA and protein levels. Furthermore, rBMSCs exposed to the strain stimulation expressed cardiomyocyte-related markers at a higher level than the shear stimulation. In addition, when rBMSCs were exposed to both strain and 5-azacytidine (5-aza), expression levels of cardiomyocyte-related markers significantly increased to a degree suggestive of a synergistic interaction. These results suggest that cyclic strain is an important mechanical stimulus affecting the cardiomyogenic differentiation of rBMSCs. This provides a new avenue for mechanistic studies of stem cell differentiation and a new approach to obtain more committed differentiated cells.

Cytoprotective effects of melatonin on astroglial cells subjected to palmitic acid treatment in vitro

Melatonin, an endogenously produced neurohormone secreted mainly by the pineal gland, has a variety of physiological functions and neuroprotective effects. Saturated fatty acids (SFAs) have been known to induce neurotoxicity and oxidative stress in central nervous system injuries and neurodegenerative pathologies. However, the effect of melatonin on SFAs-induced cytotoxicity in astroglial cells, if any, has remained to be explored. This study reports that in primary cultured astroglial cells, melatonin significantly attenuated palmitic acid (PA)-induced cytotoxicity in a concentration- and time-dependent manner. Additionally, melatonin effectively suppressed PA-induced reactive oxygen species generation and prevented PA-induced apoptosis whereby the rise in Bax/Bcl-2 ratio and caspase-3 activation in astroglial cells was inhibited. However, it did not appear to exert an obvious effect on PA-induced intracellular calcium overload. Luzindole, a nonselective melatonin receptor antagonist, attenuated melatonin's promotion effect of cell survival and Stat3 phosphorylation, indicating that melatonin exerts its protective property in astroglial cells, at least in part, through the activation of membrane receptors and then Stat3 signaling pathway. Finally, melatonin had an inhibitory effect on the pro-inflammatory cytokine gene expression. The results suggest that melatonin may be an effective cytoprotective agent against PA-based cytotoxicity through modulating cell survival and inflammatory response in astroglial cells.

High glucose-induced expression of inflammatory cytokines and reactive oxygen species in cultured astrocytes

Astrocyte activation plays important roles both in physiological and pathological process in the CNS. In the latter, the process is further aggravated by hyperglycemia, leading to diabetes complications of CNS. We report here that high glucose (HG) treatment stimulated astrocytic morphological alteration coupled with changes in glial fibrillary acidic protein (GFAP) and vimentin expression. Additionally, HG upregulated the expression of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), interleukin-1β (IL-1β), interleukin-4 (IL-4), and vascular endothelial growth factor (VEGF); however, its effects on transforming growth factor-β (TGF-β) expression were not evident. HG treatment induced increased production of reactive oxygen species (ROS) as well as activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and signal transducer and activator transcription 3 (STAT 3). HG-induced expression of TNF-α, IL-6, IL-1β, IL-4, and VEGF was blocked by ROS scavenger and inhibitors specific for NF-κB and STAT 3, respectively. The results suggest that the aforementioned multiple inflammatory cytokines and mediators that may be linked to the pathogenesis of the diabetes complications of CNS are induced by HG via the key signaling pathways.

Stromal cell-derived factor-1 significantly induces proliferation, migration, and collagen type I expression in a human periodontal ligament stem cell subpopulation

BACKGROUND

The pivotal role of chemokine stromal cell-derived factor-1 (SDF-1) in bone marrow mesenchymal stem cells recruitment and tissue regeneration has already been reported. However, its roles in human periodontal ligament stem cells (PDLSCs) remain unknown. PDLSCs are regarded as candidates for periodontal tissue regeneration and are used in stem cell-based periodontal tissue engineering. The expression of chemokine receptors on PDLSCs and the migration of these cells induced by chemokines and their subsequent function in tissue repair may be a crucial procedure for periodontal tissue regeneration.

METHODS

PDL tissues were obtained from clinically healthy premolars extracted for orthodontic reasons and used to isolate single-cell colonies by the limited-dilution method. Immunocytochemical staining was used to detect the expression of the mesenchymal stem cell marker STRO-1. Differentiation potentials were assessed by alizarin-red staining and oil-red O staining. The expression of SDF-1 receptor CXCR4 was evaluated by real-time polymerase chain reaction (PCR) and immunocytochemical staining. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and bromodeoxyuridine incorporation assay were used to determine the viability and proliferation of the PDLSC subpopulation. Expression of collagen type I and alkaline phosphatase was detected by real-time PCR to determine the effect of SDF-1 on cells differentiation.

RESULTS

Twenty percent of PDL single-cell colonies expressed STRO-1 positively, and this specific subpopulation was positive for CXCR4 and formed minerals and lipid vacuoles after 4 weeks induction. SDF-1 significantly increased proliferation and stimulated the migration of this PDLSC subpopulation at concentrations between 100 and 400 ng/mL. CXCR4 neutralizing antibody could block cell proliferation and migration, suggesting that SDF-1 exerted its effects on cells through CXCR4. SDF-1 promoted collagen type I level significantly but had little effect on alkaline phosphatase level.

CONCLUSION

SDF-1 may have the potential of promoting periodontal tissue regeneration by the mechanism of guiding PDLSCs to destructive periodontal tissue, promoting their activation and proliferation and influencing the differentiation of these stem cells.

Roles of activated astrocyte in neural stem cell proliferation and differentiation

Recent studies demonstrated that the molecules secreted from astrocytes play important roles in the cell fate determination of neural stem cells (NSCs). However, the exact molecules involved and its possible mechanisms in the process remain largely unknown. In this study, astrocyte-conditioned medium (ACM) obtained from astrocytes unstimulated or stimulated by lipopolysaccharide was prepared to treat NSCs. The results showed that both the proliferation and differentiation of NSCs treated with stimulated ACMs were significantly increased compared with those treated with unstimulated ACM. Interleukin-6 (IL-6) antibody neutralization of the ACMs decreased NSC proliferation and astrogliogenesis, while NSC neurogenesis was increased. In contrast, recombinant IL-6 cytokine increased NSC proliferation and astrogliogenesis, but decreased neurogenesis. Furthermore, the expression of phosphorylated signal transducer and activator of transcription 3 (p-stat3) protein as well as serial of basic helix-loop-helix transcription factors (bHLH) mRNA in NSCs exposed to stimulated ACMs significantly increased, respectively. The expression levels of p-stat3 protein and bHLH mRNA of NSCs were significantly altered after adding anti-IL-6 antibody or recombinant IL-6, respectively. The data suggest that IL-6 secreted from activated astrocytes participates in ACM-induced proliferation and differentiation of NSCs via the phosphorylation of stat3 signals and the expression of bHLH transcription factors.

Peripheral nerve regeneration using autologous porcine skin-derived mesenchymal stem cells

Porcine skin-derived mesenchymal stem cells (pSMSCs) were evaluated on their biological MSC characterizations and differentiation into mesenchymal lineages, along with in vitro and in vivo neural inductions. Isolated pSMSCs showed plate-adherent growth, expression of various MSC-marker proteins and transcriptional factors, and differentiation potential into mesenchymal lineages. Neuron-like cell morphology and various neural markers were highly detected at 6 h and 24 h after in vitro neural induction of pSMSCs, but their neuron-like characteristics disappeared as induction time extended to 48 and 72 h. To evaluate the in vivo peripheral nerve regeneration potential of pSMSCs, a total of 5 × 10(6) autologous pSMSCs labelled with tracking dye, supplemented with fibrin glue scaffold and collagen tubulization, were transplanted into the peripheral nerve defected miniature pigs. At 2 and 4 weeks after cell transplantation, well-preserved transplanted cells and remarkable in vivo nerve regeneration, including histologically complete nerve bundles, were observed in the regenerated nerve tissues. Moreover, S-100 protein and p75 nerve growth factor receptor were more highly detected in regenerated nerve fibres compared to non-cell grafted control fibres. These results suggest that autologous pSMSCs transplanted with fibrin glue scaffold can induce prominent nerve regeneration in porcine peripheral nerve defect sites.

Interaction between lung cancer cells and astrocytes via specific inflammatory cytokines in the microenvironment of brain metastasis

The incidence of brain metastasis is increasing, however, little is known about molecular mechanism responsible for lung cancer-derived brain metastasis and their development in the brain. In the present study, brain pathology was examined in an experimental model system of brain metastasis as well as in human brain with lung cancer metastasis. In an experimental model, after 3–6 weeks of intracardiac inoculation of human lung cancer-derived (HARA-B) cells in nude mice, wide range of brain metastases were observed. The brain sections showed significant increase in glial fibrillary acidic protein (GFAP)-positive astrocytes around metastatic lesions. To elucidate the role of astrocytes in lung cancer proliferation, the interaction between primary cultured mouse astrocytes and HARA-B cells was analyzed in vitro. Co-cultures and insert-cultures demonstrated that astrocytes were activated by tumor cell-oriented factors; macrophage migration inhibitory factor (MIF), interleukin-8 (IL-8) and plasminogen activator inhibitor-1 (PAI-1). Activated astrocytes produced interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and interleukin-1 β (IL-1β), which in turn promoted tumor cell proliferation. Semi-quantitative immunocytochemistry showed that increased expression of receptors for IL-6 and its subunits gp130 on HARA-B cells. Receptors for TNF-α and IL-1β were also detected on HARA-B cells but down-regulated after co-culture with astrocytes. Insert-culture with astrocytes also stimulated the proliferation of other lung cancer-derived cell lines (PC-9, QG56, and EBC-1). These results suggest that tumor cells and astrocytes stimulate each other and these mutual relationships may be important to understand how lung cancer cells metastasize and develop in the brain.