Kaori Suyama

Delayed accumulation of activated macrophages and inhibition of remyelination after spinal cord injury in an adult rodent model

OBJECT Inhibition of remyelination is part of the complex problem of persistent dysfunction after spinal cord injury (SCI), and residual myelin debris may be a factor that inhibits remyelination. Phagocytosis by microglial cells and by macrophages that migrate from blood vessels plays a major role in the clearance of myelin debris. The object of this study was to investigate the mechanisms underlying the failure of significant remyelination after SCI. METHODS The authors investigated macrophage recruitment and related factors in rats by comparing a contusion model (representing contusive SCI with residual myelin debris and failure of remyelination) with a model consisting of chemical demyelination by lysophosphatidylcholine (representing multiple sclerosis with early clearance of myelin debris and remyelination). The origin of infiltrating macrophages was investigated using mice transplanted with bone marrow cells from green fluorescent protein-transfected mice. The changes in levels of residual myelin debris and the infiltration of activated macrophages in demyelinated lesions were investigated by immunostaining at 2, 4, and 7 days postinjury. To investigate various factors that might be involved, the authors also investigated gene expression of macrophage chemotactic factors and adhesion factors. RESULTS Activated macrophages coexpressing green fluorescent protein constituted the major cell population in the lesions, indicating that the macrophages in both models were mainly derived from the bone marrow, and that very few were derived from the intrinsic microglia. Immunostaining showed that in the contusion model, myelin debris persisted for a long period, and the infiltration of macrophages was significantly delayed. Among the chemotactic factors, the levels of monocyte chemoattractant protein-1 and granulocyte-macrophage colony-stimulating factor were lower in the contusion model at 2 and 4 days postinjury. CONCLUSIONS The results suggest that the delayed infiltration of activated macrophages is related to persistence of myelin debris after contusive SCI, resulting in the inhibition of remyelination.

Overexpression of GRP78 protects glial cells from endoplasmic reticulum stress

Endoplasmic reticulum (ER) stress induces apoptotic cell death by causing the accumulation of structurally abnormal proteins. The 78-kDa glucose-regulated protein (GRP78) is an ER chaperone that regulates protein folding in the ER and has been suggested to contribute to cell survival. Using the rat C6 glioma cell line and flow cytometry, we assessed GRP78 expression following tunicamycin- and glutamate-induced ER stress. The results showed that GRP78 expression is upregulated following ER stress and has protective effects on injured glial cells. Annexin V and propidium iodide labeling revealed cells transiently expressing GRP78 prior to injury were protected against high-concentrations of tunicamycin and glutamate within 72 h. Our findings support the hypothesis that GRP78 inhibits cell death associated with ER stress.

Efficacy of the coadministration of granulocyte colony-stimulating factor and stem cell factor in the activation of intrinsic cells after spinal cord injury in mice

OBJECT Granulocyte colony-stimulating factor (G-CSF) is a hematopoietic cytokine that induces undifferentiated stem cells from the bone marrow (BM) into the peripheral blood. Stem cell factor (SCF) is also a hematopoietic cytokine that stimulates the differentiation and proliferation of neural stem cells and has neuroprotective effects. In cerebrally infarcted mice, the combination of G-CSF and SCF promotes the differentiation of BM-derived cells into neural cells, stimulates the proliferation of intrinsic neural stem cells, and improves motor function. The object of this study was to investigate the effects of these cytokines on BM stem cells, intrinsic cells, and motor function recovery in spinal cord-injured mice. METHODS For marking BM-derived cells, the authors induced contusive spinal cord injury in mice transplanted with BM cells from green fluorescent protein (GFP)-transgenic mice after whole-body irradiation. These mice were treated with G-CSF and SCF in the subacute injury phase. Bromodeoxyuridine (BrdU) was injected into these mice to label proliferating cells. The cell numbers and phenotype of the BM-derived cells were evaluated, and the change in intrinsic cells (proliferation, accumulation, and differentiation) was noted using immunohistological analysis at 4 weeks postinjury (wpi). A behavior analysis was conducted until 12 wpi using the Basso, Beattie, Bresnahan locomotor rating scale. RESULTS In the SCF + G-CSF group, improvement in hindlimb motor function was significantly greater than in the SCF group, G-CSF group, and sham-treatment (vehicle) group after 8 wpi. At 4 wpi, the number of GFP+ BM-derived cells induced in the lesion did not significantly differ between groups. At 4 wpi, the authors evaluated perilesional GFP− intrinsic spinal cord cells. The number of GFP− and F4/80+ cells was significantly greater in the SCF + G-CSF group than in the other 3 groups. As compared with the sham group, the number of NG2+/BrdU+ cells was significantly increased in the SCF + G-CSF group. CONCLUSIONS In this study, the combined administration of SCF and G-CSF in traumatic spinal cord injury not only improved motor function, but also induced the accumulation of intrinsic microglia and the active proliferation of intrinsic oligodendrocyte precursor cells.

Contribution of IL-12/IL-35 common subunit p35 to maintaining the testicular immune privilege.

The testis is an organ with immune privilege. The comprehensive blood–testis barrier formed by Sertoli cells protects autoimmunogenic spermatozoa and spermatids from attack by the body’s immune system. The interleukin (IL)-6/IL-12 family cytokines IL-12 (p35/p40), IL-23 (p19/p40), IL-27 (p28/Epstein-Barr virus−induced gene 3 [EBI3]), and IL-35 (p35/EBI3) play critical roles in the regulation of various immune responses, but their roles in testicular immune privilege are not well understood. In the present study, we investigated whether these cytokines are expressed in the testes and whether they function in the testicular immune privilege by using mice deficient in their subunits. Expression of EBI3 was markedly increased at both mRNA and protein levels in the testes of 10- or 12-week-old wild-type mice as compared with levels in 2-week-old mice, whereas the mRNA expression of p40 was markedly decreased and that of p35 was conserved between these two groups. Lack of EBI3, p35, and IL-12 receptor β2 caused enhanced infiltration of lymphocytes into the testicular interstitium, with increased interferon-γ expression in the testes and autoantibody production against mainly acrosomal regions of spermatids. Spermatogenic disturbance was more frequently observed in the seminiferous tubules, especially when surrounded by infiltrating lymphocytes, of these deficient mice than in those of wild-type mice. In particular, p35-deficient mice showed the most severe spermatogenic disturbance. Immunohistochemical analyses revealed that endothelial cells and peritubular cells in the interstitium were highly positive for p35 at both ages, and CD163+ resident macrophages positive for p35 and EBI3, possibly producing IL-35, were also detected in the interstitium of 12-week-old mice but not those of 2-week-old mice. These results suggest that p35 helps in maintaining the testicular immune privilege, in part in an IL-35-dependent manner.

GRP78 Suppresses Lipid Peroxidation and Promotes Cellular Antioxidant Levels in Glial Cells following Hydrogen Peroxide Exposure

Oxidative stress, caused by the over production of reactive oxygen species (ROS), has been shown to contribute to cell damage associated with neurotrauma and neurodegenerative diseases. ROS mediates cell damage either through direct oxidation of lipids, proteins and DNA or by acting as signaling molecules to trigger cellular apoptotic pathways. The 78 kDa glucose-regulated protein (GRP78) is an ER chaperone that has been suggested to protect cells against ROS-induced damage. However, the protective mechanism of GRP78 remains unclear. In this study, we used C6 glioma cells transiently overexpressing GRP78 to investigate the protective effect of GRP78 against oxidative stress (hydrogen peroxide)-induced injury. Our results showed that the overexpression of GRP78 significantly protected cells from ROS-induced cell damage when compared to non-GRP78 overexpressing cells, which was most likely due to GRP78-overexpressing cells having higher levels of glutathione (GSH) and NAD(P)H:quinone oxidoreductase 1 (NQO1), two antioxidants that protect cells against oxidative stress. Although hydrogen peroxide treatment increased lipid peroxidation in non-GRP78 overexpressing cells, this increase was significantly reduced in GRP78-overexpressing cells. Overall, these results indicate that GRP78 plays an important role in protecting glial cells against oxidative stress via regulating the expression of GSH and NQO1.

Endoplasmic reticulum stress response in the rat contusive spinal cord injury model-susceptibility in specific cell types

Study design:Focus group studyObjective:To investigate cell-specific endoplasmic reticulum (ER) stress reactions in contusive spinal cord by evaluating the expression of the glucose-regulated protein 78 (GRP78) and C/EBP homologous transcription factor protein (CHOP) using immunohistochemical staining.Setting:Data were analysed at Tokai University School of Medicine in Japan.Methods:The authors generated rat spinal cord injury (SCI) models using an IH-Impactor (100 kdyne(LI), 200 kdyne (HI)). Rats were killed at 1, 3, 5, 7 and 14 days post operation (dpo). Spinal cord sections were prepared and the expression ratio of GRP78 and CHOP was evaluated in oligodendrocyte precursor cells (OPCs) (NG2+), oligodendrocytes (OLs) (APC+), neurons (NeuN+) and astrocytes (GFAP+) using double immunohistochemical staining. We examined an area 8 mm distal from SCI-epicenter.Results:Compared with the sham group, both injured groups had higher GRP78 expression ratio in contused spinal cord at 1 dpo. GRP78 expression ratio was highest in GFAP+ cells of both groups, and lowest in NG2+ cells. Although GRP78 was expressed strongly immediately after SCI in the both groups, increased CHOP expression was observed only in the HI group. The CHOP expression in NG2+ cells was significantly higher than that observed in GFAP+ cells at 5 dpo.Conclusion:Although the ER stress response contributes to cell survival in the low-stress SCI conditions, the ER stress response induces an apoptotic cascade in high-stress SCI conditions. The ER response varies according to cell type, with the highest observed in astrocytes, and the lowest observed in oligodendrocyte precursor cells.

Circadian factors BMAL1 and RORα control HIF-1α transcriptional activity in nucleus pulposus cells: implications in maintenance of intervertebral disc health

BMAL1 and RORα are major regulators of the circadian molecular oscillator. Since previous work in other cell types has shown cross talk between circadian rhythm genes and hypoxic signaling, we investigated the role of BMAL1 and RORα in controlling HIF-1-dependent transcriptional responses in NP cells that exist in the physiologically hypoxic intervertebral disc. HIF-1-dependent HRE reporter activity was further promoted by co-transfection with either BMAL1 or RORα. In addition, stable silencing of BMAL1 or inhibition of RORα activity resulted in decreased HRE activation. Inhibition of RORα also modulated HIF1α-TAD activity. Interestingly, immunoprecipitation studies showed no evidence of BMAL1, CLOCK or RORα binding to HIF-1α in NP cells. Noteworthy, stable silencing of BMAL1 as well as inhibition of RORα decreased expression of select HIF-1 target genes including VEGF, PFKFB3 and Eno1. To delineate if BMAL1 plays a role in maintenance of disc health, we studied the spinal phenotype of BMAL1-null mice. The lumbar discs of null mice evidenced decreased height, and several parameters associated with vertebral trabecular bone quality were also affected in nulls. In addition, null animals showed a higher ratio of cells to matrix in NP tissue and hyperplasia of the annulus fibrosus. Taken together, our results indicate that BMAL1 and RORα form a regulatory loop in the NP and control HIF-1 activity without direct interaction. Importantly, activities of these circadian rhythm molecules may play a role in the adaptation of NP cells to their unique niche.

Effect of amiloride on endoplasmic reticulum stress response in the injured spinal cord of rats

After traumatic spinal cord injury (SCI), endoplasmic reticulum (ER) stress exacerbates secondary injury, leading to expansion of demyelination and reduced remyelination due to oligodendrocyte precursor cell (OPC) apoptosis. Although recent studies have revealed that amiloride controls ER stress and leads to improvement in several neurological disorders including SCI, its mechanism is not completely understood. Here, we used a rat SCI model to assess the effects of amiloride on functional recovery, secondary damage expansion, ER stress‐induced cell death and OPC survival. Hindlimb function in rats with spinal cord contusion significantly improved after amiloride administration. Amiloride significantly decreased the expression of the pro‐apoptotic transcription factor CHOP in the injured spinal cord and significantly increased the expression of the ER chaperone GRP78, which protects cells against ER stress. In addition, amiloride treatment led to a significant decrease in ER stress‐induced apoptosis and a significant increase of NG2‐positive OPCs in the injured spinal cord. Furthermore, in vitro experiments performed to investigate the direct effect of amiloride on OPCs revealed that amiloride reduced CHOP expression in OPCs cultured under ER stress. These results suggest that amiloride controls ER stress in SCI and inhibits cellular apoptosis, contributing to OPC survival. The present study suggests that amiloride may be an effective treatment to reduce ER stress‐induced cell death in the acute phase of SCI.

Amiloride Promotes Oligodendrocyte Survival and Remyelination after Spinal Cord Injury in Rats

After spinal cord injury (SCI), secondary injury results in an expanding area of glial cell apoptosis. Oligodendrocyte precursor cells (OPCs) actively proliferate after SCI, but many of these cells undergo apoptosis. One of the factors that exacerbates secondary injury is endoplasmic reticulum (ER) stress. In this study, we tested the effects of amiloride treatment on the fate of OPCs during secondary injury in rats. Amiloride is an FDA-approved diuretic for treating hypertension, which in rats enhances ER stress response and suppresses the apoptosis of glial cells after SCI. A severe contusive SCI was induced in Sprague-Dawley rats using an infinite horizon (IH)-impactor (200 kdyne). Beginning 24 h after SCI, 10 mg/kg of amiloride or phosphate buffered saline (PBS) was intraperitoneally administered daily for a period of 14 days. At 7, 14, 28, and 56 days after SCI, animals were subsequently euthanized in order to analyze the injured spinal cord. We labeled proliferating OPCs and demonstrated that amiloride treatment led to greater numbers of OPCs and oligodendrocytes in the injured spinal cord. Increased myelin basic protein (MBP) expression levels were observed, suggesting that increased numbers of mature oligodendrocytes led to improved remyelination, significantly improving motor function recovery.

Sciatic nerve regeneration by transplantation of in vitro differentiated nucleus pulposus progenitor cells

AIM To assess the applicability of mouse intervertebral disc-derived nucleus pulposus (NP) progenitor cells as a cell source for sciatic nerve regeneration. MATERIALS & METHODS P0-Cre/Floxed-EGFP-transgenic mouse-derived NP progenitor cells were differentiated to Schwann-like cells in conventional induction medium. Schwann-like cells were subsequently transplanted into a mouse model of sciatic nerve transection, and nerve regeneration assessed by immunohistochemistry, electron microscopy and functional walking track analysis and heat stimulus reflex. RESULTS & CONCLUSION NP progenitor cells differentiated into Schwann-like cells. Transplantation of these cells promoted myelinated axon formation, morphology restoration and nerve function improvement. NP progenitor cells have the capacity to differentiate into neuronal cells and are candidates for peripheral nerve regeneration therapy.