Expression of p27kip1 and Skp2 in the adult spinal cord following sciatic nerve injury

Blocking the Spinal Fbxo3/CARM1/K+ Channel Epigenetic Silencing Pathway as a Strategy for Neuropathic Pain Relief

Many epigenetic regulators are involved in pain-associated spinal plasticity. Coactivator-associated arginine methyltransferase 1 (CARM1), an epigenetic regulator of histone arginine methylation, is a highly interesting target in neuroplasticity. However, its potential contribution to spinal plasticity-associated neuropathic pain development remains poorly explored. Here, we report that nerve injury decreased the expression of spinal CARM1 and induced allodynia. Moreover, decreasing spinal CARM1 expression by Fbxo3-mediated CARM1 ubiquitination promoted H3R17me2 decrement at the K+ channel promoter, thereby causing K+ channel epigenetic silencing and the development of neuropathic pain. Remarkably, in naïve rats, decreasing spinal CARM1 using CARM1 siRNA or a CARM1 inhibitor resulted in similar epigenetic signaling and allodynia. Furthermore, intrathecal administration of BC-1215 (a novel Fbxo3 inhibitor) prevented CARM1 ubiquitination to block K+ channel gene silencing and ameliorate allodynia after nerve injury. Collectively, the results reveal that this newly identified spinal Fbxo3-CARM1-K+ channel gene functional axis promotes neuropathic pain. These findings provide essential insights that will aid in the development of more efficient and specific therapies against neuropathic pain.

Endothelin-1 stimulates expression of cyclin D1 and S-phase kinase-associated protein 2 by activating the transcription factor STAT3 in cultured rat astrocytes

Brain injury-mediated induction of reactive astrocytes often leads to glial scar formation in damaged brain regions. Activation of signal transducer and activator of transcription 3 (STAT3), a member of the STAT family of transcription factors, plays a pivotal role in inducing reactive astrocytes and glial scar formation. Endothelin-1 (ET-1) is a vasoconstrictor peptide, and its levels increase in brain disorders and promote astrocytic proliferation through ETB receptors. To clarify the mechanisms underlying ET-1-mediated astrocytic proliferation, here we examined its effects on STAT3 in cultured rat astrocytes. ET-1 treatment stimulated Ser-727 phosphorylation of STAT3 in the astrocytes, but Tyr-705 phosphorylation was unaffected, and ET-induced STAT3 Ser-727 phosphorylation was reduced by the ET_B antagonist BQ788. ET-1 stimulated STAT3 binding to its consensus DNA-binding motifs. Monitoring G₁/S phase cell cycle transition through bromodeoxyuridine (BrdU) incorporation, we found that ET-1 increases BrdU incorporation into the astrocytic nucleus, indicating cell cycle progression. Of note, STAT3 chemical inhibition (with stattic or 5,15-diphenyl-porphine (5,15-DPP)) or siRNA-mediated STAT3 silencing reduced ET-induced BrdU incorporation. Moreover, ET-1 increased astrocytic expression levels of cyclin D1 and S-phase kinase-associated protein 2 (SKP2), which were reduced by stattic, 5,15-DPP, and STAT3 siRNA. ChIP-based PCR analysis revealed that ET-1 promotes the binding of SAT3 to the 5'-flanking regions of rat cyclin D1 and SKP2 genes. Our results suggest that STAT3-mediated regulation of cyclin D1 and SKP2 expression underlies ET-induced astrocytic proliferation.

FOXO3a/p27kip1 expression and essential role after acute spinal cord injury in adult rat

FOXO3a (Forkhead Class box O3a), as an important direct target of the phosphatidylinositol 3-kinase (PI3K)/protein B (Akt) pathway, which regulates the cell survival and the cell-cycle progression. Recent reports showed that FOXO3a could inhibit cell-cycle progression at the G1/S transition by controlling transcription of the cyclin-dependent kinase inhibitor p27(kip1) , which is also a key regulator of the mammalian neurogenesis. To elucidate the expression and role of FOXO3a in nervous system lesion and repair, we performed an acute spinal cord contusion injury (SCI) model in adult rats, which showed a temporal-spatial expression pattern of FOXO3a. Temporally, FOXO3a protein level significantly reduced day 3 after injury, and following FOXO3a down-regulation, p27(kip1) protein and mRNA levels were also decreased after injury. Spatially, decreased levels of FOXO3a and p27(kip1) were predominant in astrocytes, which were regenerating axons and largely proliferated after injury. Furthermore in vitro, Western blot analysis, RT-PCR, and immunofluorescence staining analysis demonstrated the relationship between FOXO3a and p27(kip1) in primary astrocytes. FOXO3a modulated the cell cycle by transcriptional regulation of p27(kip1) in astrocytes. Administration of the PI3K pharmacological inhibitor LY294002 abrogated this effect by regulating FOXO3a and p27(kip1) expression and subcellular localization. These results suggest that decreased levels of FOXO3a and p27(kip1) in spinal cord are involved in axonal regeneration and the proliferation of glial cells after SCI.

FoxM1 involvement in astrocyte proliferation after spinal cord injury in rats

The Forkhead box M1 (FoxM1) protein is a proliferation-associated transcription factor that plays a key role in controlling both the G1/S and G2/M transitions of the cell cycle and regulates transcription of cell cycle genes, including cyclin-dependent kinase inhibitors p27(kip1) and p21(waf1/cip1). The expression levels of FoxM1 directly correlated with the proliferation index, cancer survival, genomic instability rate, and microvessel density, and inversely correlated with apoptosis. Furthermore, FoxM1 is determined to play a role in tissue repair following injury in the lungs and liver. However, the signaling of FoxM1, involved in its expression and its role in central nervous system lesion and repair is poorly known. In this study, we performed a spinal cord injury (SCI) model in adult Sprague-Dawley rats and investigated the dynamic changes and role of FoxM1 expression in the spinal cord. Western blot analysis revealed that FoxM1 was lowly presented in normal spinal cord. It gradually increased, reached a peak at day 3, and then declined to basal levels at 14 days after spinal cord injury. Immunohistochemistry further confirmed that FoxM1 was expressed at low levels in gray and white matters in normal condition and increased after SCI. Double immunofluorescence staining showed that FoxM1was co-expressed with NeuN (neuronal marker) and GFAP (astrocytic marker), and FoxM1 expression was increased predominantly in astrocytes after injury, which were regenerating axons and largely proliferated after injury. Furthermore, co-immunoprecipitation studies demonstrated increased interactions among FoxM1, Skp2, and p27(kip1) in the spinal cord after injury. Taken together, these results provide new insights into the molecular mechanisms underlying astrocyte proliferation during SCI and suggest that FoxM1 might play crucial roles in CNS pathophysiology after SCI.

Peripheral nerve injury induces down-regulation of Foxo3a and p27kip1 in rat dorsal root ganglia

FOXO3a, as a forkhead transcription factor, can control cell cycle through transcriptionally down-regulating p27(kip1) level, which is a key regulator of the mammalian cell cycle and a good candidate to regulate multiple aspects of neurogenesis. To elucidate their expression and function in nervous system lesion and repair, we performed an acute sciatic nerve crush model and studied differential expressions of Foxo3a and p27(kip1) in lumbar dorsal root ganglia. Temporally, Foxo3a protein level was reduced 1 day after injury, and following Foxo3a down-regulation, p27(kip1) mRNA and protein levels were also decreased after injury. Spatially, decreased levels of Foxo3a and p27(kip1) were predominant in neurons and glial cells, which were regenerating axons and largely proliferated after injury, respectively. Together with previous reports, we hypothesized decreased levels of Foxo3a and p27(kip1) in lumbar dorsal root ganglia were implicated in axonal regeneration and the proliferation of glial cells after sciatic nerve injury.