Upregulation of the HLH Id gene family in neural progenitors and glial cells of the rat spinal cord following contusion injury

Quercetin prevents the ferroptosis of OPCs by inhibiting the Id2/transferrin pathway

Spinal cord injury (SCI) is a destructive neurological disorder that causes impaired mobility, sensory, and autonomic dysfunctions. The loss of oligodendrocyte progenitor cells (OPCs), which can differentiate into mature oligodendrocytes and re-myelinate damaged axons, is related to poorer recovery for SCI patients. However, inhibiting OPCs loss has always been a difficult problem to overcome. In this study, we demonstrated the anti-ferroptosis effects of quercetin as a mechanism in erastin-induced OPC ferroptosis. Quercetin ameliorated erastin-induced ferroptosis in OPCs, as indicated by decreased iron concentration, reactive oxygen species (ROS) production, and increased content of glutathione (GSH) as well as more normal mitochondria morphology. Compared with erastin-induced OPCs, the myelin basic protein (MBP)-positive myelin and NF200-positive axonal was remarkably increased in quercetin-treated OPCs. Furthermore, quercetin ameliorated the erastin-induced ferroptosis as well as the myelin and axon loss of OPCs by downregulating transferrin. Transfected OPCs with transferrin overexpression plasmids significantly abrogated the protective role of quercetin in OPC ferroptosis. Using ChIP-qPCR, a direct interaction of transferrin with its upstream gene Id2 was found. The overexpression of Id2 reversed the effect of quercetin on OPC ferroptosis. In vivo study found that quercetin greatly decreased the area of injury, and enhanced the BBB score after SCI. Furthermore, in the SCI model, quercetin significantly downregulated Id2 and transferrin expression, while significantly up-regulated GPX4 and PTGS2 expression. In conclusion, quercetin prevents the ferroptosis of OPCs by inhibiting the Id2/transferrin pathway. These findings highlight quercetin as an anti-ferroptosis agent for the treatment or prevention of spinal cord injury.

Id proteins: emerging roles in CNS disease and targets for modifying neural stemcell behavior

Neural stem/progenitor cells (NSPCs) are found in the adult brain and spinal cord, and endogenous or transplanted NSPCs contribute to repair processes and regulate immune responses in the CNS. However, the molecular mechanisms of NSPC survival and integration as well as their fate determination and functionality are still poorly understood. Inhibitor of DNA binding (Id) proteins are increasingly recognized as key determinants of NSPC fate specification. Id proteins act by antagonizing the DNA-binding activity of basic helix-loop-helix (bHLH) transcription factors, and the balance of Id and bHLH proteins determines cell fate decisions in numerous cell types and developmental stages. Id proteins are central in responses to environmental changes, as they occur in CNS injury and disease, and cellular responses in adult NSPCs implicate Id proteins as prime candidates for manipulating stemcell behavior. Here, we outline recent advances in understanding Id protein pleiotropic functions in CNS diseases and propose an integrated view of Id proteins and their promise as potential targets in modifying stemcell behavior to ameliorate CNS disease.

Integrated analysis of competing endogenous RNA (ceRNA) networks in subacute stage of spinal cord injury

This study aims to investigate the genetic and epigenetic mechanisms involved in the pathogenesis of subacute stage of spinal cord injury (SCI). Gene-expression datasets associated with SCI were downloaded from the Gene Expression Omnibus (GEO) database, and differential expression analyses were performed in order to identify differentially expressed genes (DEGs). Multiple network types were constructed and analyzed, including protein-protein-interaction (PPI) network, miRNA-target network, lncRNA-associated competing endogenous RNA (ceRNA) network, and miRNA-transcription factor (TF)-target network. Cluster analyses were performed to identify significant modules. To verify the prediction accuracy of the in-silico identified molecules, qRT-PCR experiments were conducted. The results depicted the Ywhae gene as the hub gene with the highest degree in the PPI network. The ceRNA network identified specific genes (Flna, ID3, and HK2), miRNAs (miR-16-5p, miR-1958, and miR-185-5p), and lncRNAs (Neat1, Xist, and Malat1) as playing critical regulating roles in the pathological mechanisms of SCI. The miRNA-TF-gene interaction network identified four important TFs (Sp1, Trp53, Jun, and Rela). The miRNA-gene-TF interaction loops from the significant modules indicated that miR-325-3p can interact with the Asah1 gene and TF-Sp1 by forming a closed loop. The qRT-PCR experiments verified four selected genes (Flna, ID3, HK2, and Ywhae) and two selected TFs (Jun, and Sp1) as significantly up-regulated following SCI. The results indicated that four genes (Flna, ID3, HK2, and Ywhae), four transcription factors (Sp1, Trp53, Jun, and RelA), two miRNAs (miR-16-5p and miR-325-3p), and three lncRNAs (Neat1, Xist, and Malat1) are likely to be involved in the molecular mechanisms underlying the subacute stage of SCI. These findings uncover putative pathogenic mechanisms involved in SCI and might bear translation significance for future research towards therapeutic development.

Myelin status and oligodendrocyte lineage cells over time after spinal cord injury: What do we know and what still needs to be unwrapped?

Spinal cord injury (SCI) affects over 17,000 individuals in the United States per year, resulting in sudden motor, sensory and autonomic impairments below the level of injury. These deficits may be due at least in part to the loss of oligodendrocytes and demyelination of spared axons as it leads to slowed or blocked conduction through the lesion site. It has long been accepted that progenitor cells form new oligodendrocytes after SCI, resulting in the acute formation of new myelin on demyelinated axons. However, the chronicity of demyelination and the functional significance of remyelination remain contentious. Here we review work examining demyelination and remyelination after SCI as well as the current understanding of oligodendrocyte lineage cell responses to spinal trauma, including the surprisingly long-lasting response of NG2+ oligodendrocyte progenitor cells (OPCs) to proliferate and differentiate into new myelinating oligodendrocytes for months after SCI. OPCs are highly sensitive to microenvironmental changes, and therefore respond to the ever-changing post-SCI milieu, including influx of blood, monocytes and neutrophils; activation of microglia and macrophages; changes in cytokines, chemokines and growth factors such as ciliary neurotrophic factor and fibroblast growth factor-2; glutamate excitotoxicity; and axon degeneration and sprouting. We discuss how these changes relate to spontaneous oligodendrogenesis and remyelination, the evidence for and against demyelination being an important clinical problem and if remyelination contributes to motor recovery.

Expression profiling of Aldh1l1-precursors in the developing spinal cord reveals glial lineage-specific genes and direct Sox9-Nfe2l1 interactions

Developmental regulation of gliogenesis in the mammalian CNS is incompletely understood, in part due to a limited repertoire of lineage-specific genes. We used Aldh1l1-GFP as a marker for gliogenic radial glia and later-stage precursors of developing astrocytes and performed gene expression profiling of these cells. We then used this dataset to identify candidate transcription factors that may serve as glial markers or regulators of glial fate. Our analysis generated a database of developmental stage-related markers of Aldh1l1+ cells between murine embryonic day 13.5-18.5. Using these data we identify the bZIP transcription factor Nfe2l1 and demonstrate that it promotes glial fate under direct Sox9 regulatory control. Thus, this dataset represents a resource for identifying novel regulators of glial development.

Gene expression profile of glioblastoma peritumoral tissue: an ex vivo study

The gene expression pattern of glioblastoma (GBM) is well documented but the expression profile of brain adjacent to tumor is not yet analysed. This may help to understand the oncogenic pathway of GBM development. We have established the genome-wide expression profiles of samples isolated from GBM tumor mass, white matter adjacent to tumor (apparently free of tumor cells), and white matter controls by using the Affymetrix HG-U133 arrays. Array-CGH (aCGH) was also performed to detect genomic alterations. Among genes dysregulated in peritumoral white matter, 15 were over-expressed, while 42 were down-regulated when compared to white matter controls. A similar expression profile was detected in GBM cells. Growth, proliferation and cell motility/adhesion-associated genes were up-regulated while genes involved in neurogenesis were down-regulated. Furthermore, several tumor suppressor genes along with the KLRC1 (a member of natural killer receptor) were also down-regulated in the peritumoral brain tissue. Several mosaic genomic lesions were detected by aCGH, mostly in tumor samples and several GBM-associated mosaic genomic lesions were also present in the peritumoral brain tissue, with a similar mosaicism pattern. Our data could be explained by a dilution of genes expressed from tumor cells infiltrating the peritumour tissue. Alternatively, these findings could be substained by a relevant amount of “apparently normal” cells presenting a gene profile compatible with a precancerous state or even “quiescent” cancer cells. Otherwise, the recurrent tumor may arise from both infiltrating tumor cells and from an interaction and recruitment of apparently normal cells in the peritumor tissue by infiltrating tumor cells.

ID2: A negative transcription factor regulating oligodendroglia differentiation

Remyelination of the central nervous system in multiple sclerosis patients is often incomplete. Remyelination depends on normal oligodendrogenesis and the differentiation of oligodendrocyte precursor cells (OPC) into mature oligodendrocytes (OL). Inhibitor of DNA binding (ID), a transcription factor, is thought to inhibit oligodendrogenesis and the differentiation of OPC. This Mini-Review aims to reveal the roles of and mechanisms used by IDs (mainly ID2) in this process. An interaction between ID2 and retinoblastoma tumor suppressor is responsible for the cell cycle transition from G1 to S. The translocation of ID2 between the nucleus and cytoplasm is regulated by E47 and OLIG. An interaction between ID2 and OLIG mediates the inhibitory effects of bone morphogenic proteins and G protein-coupled receptor 17 on oligodendroglia differentiation. ID2 expression is regulated by Wnt and histone deacetylases during the differentiation of OPC. ID4, another member of the ID family, functions similarly to ID2 in regulating the differentiation of OPC. The main difference is that ID4 is essential for oligodendrogenesis, whereas ID2 is nonessential. This could have important implications for demyelinating diseases, and interfering with these pathways might represent a viable therapeutic approach for these diseases.

Differential gene induction by genetic and ligand-mediated activation of the Sonic hedgehog pathway in neural stem cells

Sonic hedgehog (Shh), a secreted morphogen and mitogen, is essential for nervous system development and neural stem cell (NSC) self-renewal. As the intracellular signal transduction of Shh in NSCs is largely unknown, we sought to characterize pathway targets using ligand stimulation and genetic models of activation. NSCs haploinsufficient for Patched (Ptc), a receptor repressive to Shh signaling, showed enhanced proliferation of a magnitude similar to Shh-treated wild-type (Wt) NSCs. Analysis of the Gli zinc-finger transcription factors, primary mediators of Shh activity, demonstrated differential induction between models of pathway activation. Gli1 was significantly induced in Wt NSCs exposed to Shh, whereas Gli2 was elevated and Gli1 expression did not change in Ptc(+/-) NSCs. Other Shh targets (Nmyc, Id factors) were induced under both conditions of pathway activation. Interestingly, Shh-treated Ptc(+/-) NSCs induced expression of Gli1 but failed to increase proliferation, suggesting that the NSCs may have reached a physiologic plateau in proliferative capacity. Thus, our data demonstrate that Ptc(+/-) mice have an expanded progenitor cell niche in vivo and that NSCs maintain a cell-intrinsic increase in basal proliferation in vitro that is sustained by a Gli transduction signature distinct from that of exogenous Shh stimulation. Additionally, Ptc(+/-) NSCs maintain tight control over mitosis and do not further augment proliferation in the presence of mitogenic stimulation.

Genomic Loci Modulating the Retinal Transcriptome in Wound Healing

Purpose

The present study predicts and tests genetic networks that modulate gene expression during the retinal wound-healing response.

Methods

Upstream modulators and target genes were defined using meta-analysis and bioinformatic approaches. Quantitative trait loci (QTLs) for retinal acute phase genes (Vazquez-Chona et al. 2005) were defined using QTL analysis of CNS gene expression (Chesler et al. 2005). Candidate modulators were defined using computational analysis of gene and motif sequences. The effect of candidate genes on wound healing was tested using animal models of gene expression.

Results

A network of early wound-healing genes is modulated by a locus on chromosome 12. The genetic background of the locus altered the wound-healing response of the retina. The C57BL/6 allele conferred enhanced expression of neuronal marker Thy1 and heat-shock-like crystallins, whereas the DBA/2J allele correlated with greater levels of the classic marker of retinal stress, glial fibrillary acidic protein (GFAP). Id2 and Lpin1 are candidate upstream modulators as they strongly correlated with the segregation of DBA/2J and C57BL/6 alleles, and their dosage levels correlated with the enhanced expression of survival genes ( Thy1 and crystallin genes).

Conclusion

We defined a genetic network associated with the retinal acute injury response. Using genetic linkage analysis of natural transcript variation, we identified regulatory loci and candidate modulators that control transcript levels of acute phase genes. Our results support the convergence of gene expression profiling, QTL analysis, and bioinformatics as a rational approach to discover molecular pathways controlling retinal wound healing.

Differential RIP antigen (CNPase) expression in peripheral ensheathing glia

The RIP monoclonal antibody is commonly used to identify oligodendrocytes. Recently, the RIP antigen was identified as 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase), a known non-compact myelin protein [Watanabe, M., Sakurai, Y., Ichinose, T., Aikawa, Y., Kotani, M., Itoh, K., 2006. Monoclonal antibody Rip specifically recognizes 2',3'-cyclic nucleotide 3'-phosphodiesterase in oligodendrocytes. J. Neurosci. Res. 84, 525-533]. In the present study we characterize normal and axotomy-induced changes in RIP immunoreactivity in peripheral glia. In myelinating Schwann cells, RIP demarcated paranodal regions of myelinated axons and clearly defined Schmidt-Lantermann incisures. Surprisingly, RIP immunoreactivity was not confined to myelinating glia. Robust RIP immunoreactivity was present in Remak bundles in mixed nerves and in sympathetic ganglia and grey rami. Following peripheral nerve injury, RIP immunoreactivity was redistributed diffusely throughout de-differentiating Schwann cell cytoplasm. In uninjured rats, low levels of RIP immunoreactivity were detectable in satellite cells surrounding dorsal root ganglion (DRG) neurons and in terminal Schwann cells at neuromuscular junctions. This pattern suggested a correlation between RIP immunoreactivity and the amount of axon-glial contact. We therefore injured the L5 spinal nerve to induce sympathetic sprouting and pericellular basket formation in the DRG, and asked whether relatively RIP-negative satellite glia, which normally contact only neuronal somata, would upregulate the RIP antigen upon contact with sprouting sympathetic axons. All perineuronal sympathetic sprouts infiltrated heavily RIP-immunoreactive satellite cell sheaths. RIP immunoreactivity was absent from placode-derived olfactory ensheathing glia, indicating that the relationship between axon-glial contact and RIP-immunoreactivity is restricted to peripheral ensheathing glia of the neural crest-derived Schwann cell lineage.

Requirement for Id1 in opioid-induced oligodendrogenesis in cultured adult rat hippocampal progenitors

Growth factors and peptides playing important roles during early development of the central nervous system have also been shown to maintain their regulation of cell genesis in the adult brain. We have previously described that endogenous opioids, expressed in the developing hippocampus, regulate proliferation and differentiation in the adult rat hippocampus. The aim of this study was to investigate the effects of the opioid beta-endorphin on gene expression and glial differentiation in cultures of adult rat hippocampal progenitors (AHPs). Changes in gene expression after stimulation of AHPs with beta-endorphin for 48 h were investigated using cDNA arrays. Confirmation experiments verified that stimulation with beta-endorphin increased the mRNA levels of myelin basic protein, glutathione S-transferase pi, c-junD and rab16 (P < 0.05), genes that are associated with oligodendrogenesis. Furthermore, beta-endorphin increased the levels of Id1, but not Id3, mRNA on the arrays. Incubation of AHPs with beta-endorphin resulted in a threefold increase in oligodendrogenesis (P < 0.01) but no significant change in astrogliogenesis. No effect on oligodendrogenesis was observed in the presence of the opioid antagonist naloxone. Coincubation of beta-endorphin with Id1 antisense oligonucleotides for 10 days also entirely blocked the induced oligodendrogenesis in our AHP cultures. Moreover, a subpopulation of AHPs (25%) showed nuclear expression of the proneural transcriptional activator Mash1 that was reduced to approximately 5% of the cells when exposed to beta-endorphin. We suggest a requirement for Id1 in opioid-induced oligodendrogenesis in cultured AHPs possibly acting on opioid-responsive AHPs expressing the proneural transcriptional activator Mash1.

Cell proliferation and replacement following contusive spinal cord injury

After spinal cord injury (SCI), about 50% of the oligodendrocytes and astrocytes in the residual white matter at the injury site are lost by 24 h. However, chronically after SCI, the density of oligodendrocytes is normal. Previous studies have shown that the adult rat spinal cord contains a pool of proliferating glial progenitors whose progeny could help restore cell density after injury. To study proliferation in response to injury, we performed SCI on adult female rats at the T8 level, using a standardized contusion model. Animals received bromodeoxyuridine (BrdU) injections during the first week after SCI, and were perfused within 2 h for acute studies, and at 6 weeks for chronic studies. The tissue was analyzed using immunohistochemical detection of BrdU and cell marker antigens. We demonstrate that cell proliferation in the residual white matter is increased at 1-7 days after SCI, peaking on day 3. Dividing cells include oligodendrocytes, astrocytes, microglia/macrophages, and a high proportion of NG2(+) glial precursors. By 6 weeks, some cells that had been labeled 2-4 days after SCI were still present. Double immunohistochemistry showed that while very few of these cells expressed NG2 or the microglia/macrophage marker OX42, about 50% expressed CC1 or glial fibrillary acidic protein (GFAP), markers of mature oligodendrocytes and astrocytes, respectively. The post-injury environment represented by residual white matter is thus permissive to the differentiation of glial precursors. Cells that are stimulated to divide during the first week after SCI develop chronically into mature phenotypes that replace macroglia lost after injury.

Characterisation of transverse slice culture preparations of postnatal rat spinal cord: preservation of defined neuronal populations

Spinal cord injury induces degenerative and regenerative processes and complex interactions of neurons with non-neuronal cells. In order to develop an in vitro tool for the investigation of such processes, we prepared and characterised spinal cord slice cultures (SCSC) from Wistar rats (p0-12). SCSC were sustained in vitro up to 12 days and characterised by immunohistochemistry. Calbindin+ neurons, distributed across the entire gray matter, were visible also after longer culture periods. NeuN+ neurons were best preserved in the dorsal horn whereas large NeuN+ and choline acetyltransferase+ motoneurons in the ventral horn vanished after 3 days in vitro. Nestin immunoreactivity was found in animals of all age groups, either in cells interspersed in the ependymal lining around the central canal or in cells resembling protoplasmic astrocytes. Glial fibrillary acidic protein+ astrocytes, initially restricted to the white matter, invaded the gray matter of SCSC early during the culture period. Microglial cells, stained by Griffonia simplicifolia isolectin B4, were rapidly activated in the dorsal tract and in the gray matter but declined in number with time. SCSC derived from p0 or p3 animals showed a better preservation of the cytoarchitecture than cultures derived from older animals. In summary, SCSC undergo degenerative changes, but they contain defined neuronal populations, the cytoarchitecture is partially preserved and the glial reaction is limited.

Inhibitors of DNA binding in neural cell proliferation and differentiation

Id proteins function as negative regulators of bHLH transcription factors by disrupting the homo- and/or hetero-dimerization of bHLH-bHLH transcription factors. Recent data from in vitro and in vivo studies have revealed the complex biological functions of Id proteins in the regulation of cell differentiation, the cell cycle, and cell survival. Several advances in the understanding of Id-regulated neurogenesis have been made. Basically, Id proteins are positive regulators of neural cell proliferation, are required for neural cell cycle progression, and also play a role in the timing of oligodendroglial differentiation. Here we summarize recent findings regarding the regulation of Id proteins in neural cells and discuss the possible mechanisms of Id-regulated neurogenesis.

Spinal cord contusion models

Most human spinal cord injuries involve contusions of the spinal cord. Many investigators have long used weight-drop contusion animal models to study the pathophysiology and genetic responses of spinal cord injury. All spinal cord injury therapies tested to date in clinical trial were validated in such models. In recent years, the trend has been towards use of rats for spinal cord injury studies. The MASCIS Impactor is a well-standardized rat spinal cord contusion model that produces very consistent graded spinal cord damage that linearly predicts 24-h lesion volumes, 6-week white matter sparing, and locomotor recovery in rats. All aspects of the model, including anesthesia for male and female rats, age rather than body weight criteria, and arterial blood gases were empirically selected to enhance the consistency of injury.