P75NTR Exacerbates SCI-induced Mitochondrial Damage and Neuronal Apoptosis Depending on NTRK3.

OBJECTIVE: The aim of the study was to investigate the mechanism by which p75 neurotrophin receptor (p75NTR) affects mitochondrial damage and neuronal apoptosis in spinal cord injury (SCI). METHODS: After the establishment of SCI rat models, short hairpin (sh) RNA of p75NTR and control sh-RNA were injected into SCI rats, respectively. On days 1, 7 and 21 after SCI, the severity of SCI and cell apoptosis in SCI rats were determined as well as the recovery of hind limb performance and p75NTR expression. After spinal cord neurons were transfected with p75NTR overexpression plasmid or empty plasmid vector or cotransfected with overexpression plasmids of p75NTR and neurotrophic tyrosine receptor kinase3 (NTRK3), the expression levels of p75NTR and NTRK3 were quantified. Moreover, we detected the apoptosis and proliferation rates of the neurons in addition to the levels of reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) in the neurons. The binding between p75NTR and NTRK3 was confirmed via Co-immunoprecipitation (Co-IP). RESULTS: The rat spinal cords in the Model group were notably damaged after SCI accompanied by increased apoptosis and decreased locomotor function. The expression of p75NTR was significantly upregulated after SCI. The aforementioned injuries were remarkably ameliorated in response to injection of sh-p75NTR. p75NTR overexpression induced mitochondrial damage and neuronal apoptosis in spinal cord neurons, while the promotive effects were perturbed by NTRK3 overexpression. Furthermore, p75NTR directly bound to and downregulated NTRK3. CONCLUSION: Both in vivo and in vitro experiments showed that p75NTR aggravates mitochondrial damage and neuronal apoptosis in SCI through downregulating NTRK3.

Cerebrospinal fluid-contacting neurons affect the expression of endogenous neural progenitor cells and the recovery of neural function after spinal cord injury.

OBJECTIVE: To explore the relationship between cerebrospinal fluid-contacting neurons (CSF-cNs) and endogenous neural progenitor cells (ENPCs) and whether CSF-cNs are involved in nerve repair after spinal cord injury (SCI). METHODS: Cholera toxin B-horseradish peroxidase complex (CB-HRP) and cholera toxin B conjugated with saporin (CB-SAP) were injected into the lateral ventricles of spinal cord injured rats to mark and destroy the CSF-cNs. Then the rats in the experimental group were injured by SCI. Observe the content and co-expression of CSF-cNs and ENPCs in rats of each group, and observe the recovery of motor function after SCI in each group. RESULTS: After the destruction of CSF-cNs, the number of ENPCs decreased significantly in the long term after the surgery, and the recovery of motor function also deteriorated as compared to the group with intact CSF-cNs. Meanwhile some cells in the spinal cord express both the biological marker of CSF-cNs and ENPCs. CONCLUSION: This study shows that the population of ENPCs and motor function recovery in SCI rats declined after the destruction of CSF-cNs, suggesting that CSF-cNs affect the ENPCs population and may be involved in the recovery of neural function after SCI.

TNFAIP8 influences the motor function in mice after spinal cord injury (SCI) through meditating inflammation dependent on AKT.

Spinal cord injury (SCI) is a devastating disease and causes tissue loss and neurologic dysfunction, contributing to high morbidity and disability among human. However, the underlying molecular mechanisms still remain unclear. Tumor necrosis factor-α-induced protein 8 (TNFAIP8) is a member of the TNFAIP8/TIPE family, and has been implicated in different diseases associated with inflammation, infection, and immunity. Nevertheless, its effects on SCI have not been well investigated. In our study, we found time course of TNFAIP8 following SCI in mice, along with time-dependent increases of pro-inflammatory cytokines. The in vitro results confirmed the up-regulation of TNFAIP8 induced by lipopolysaccharide (LPS). Subsequently, we found that reducing TNFAIP8 by transfection with its specific siRNA (siTNFAIP8) markedly alleviated cell viability and inflammatory response caused by LPS in mouse microglial BV2 cells. Importantly, LPS-enhanced activation of inhibitor of κBα/nuclear factor-κB (IκBα/NF-κB) and phosphoinositide 3-kinase/serine-threonine kinase (PI3K/AKT) signaling pathways was considerably blunted by siTNFAIP8. Intriguingly, our results further showed that siTNFAIP8-restrained inflammation and IκBα/NF-κB in LPS-stimulated BV2 cells were almost abolished by the pre-treatment of AKT activator SC-79, demonstrating that TNFAIP8-regulated inflammatory response was largely dependent on AKT activation. Then, the in vivo studies were performed using the wild type (WT) and TNFAIP8-knockout (KO) mice with or without SCI operation. Results showed that TNFAIP8-KO mice exhibited improved neuron injury and locomotor function along with decreased microglial activity. Furthermore, compared with the WT/SCI mice, the expression of pro-inflammatory cytokines in spinal cords was markedly down-regulated by TNFAIP8-deficiency through blocking IκBα/NF-κB and PI3K/AKT signaling pathways. Taken together, these findings elucidated the novel role of TNFAIP8 in regulating SCI via the AKT signaling, and thus TNFAIP8 may be served as a promising therapeutic target for SCI treatment.

3-Iodothyronamine Acting through an Anti-Apoptotic Mechanism Is Neuroprotective Against Spinal Cord Injury in Rats.

This study aims to show how 3-iodothyronamine (T1AM) protects against spinal cord injury (SCI) in rats. We randomly divided adult female Sprague-Dawley rats (N=54) into three equal groups: (1) untreated control (n=18) (2) T1AM (n=18) (3) T1AM+EPPTB (n=18). The clamp method was used to produce SCI at the T10 segment, and the following data were collected 3, 5, and 7 days after the injury plus treatment. The mean BBB scores of both the control and T1AM+EPPTB groups were 1.5±0.5, 3.5±0.5, and 4.5±0.5 on days 3, 5, and 7 after SCI, respectively, whereas those for the T1AM group were 3.3±0.5, 5.3±0.5, and 7.5±0.5, a significant difference from the first two groups mentioned on each day (all P values <0.05). Although HE staining indicated that all three groups displayed neuronal degeneration and necrosis, disorganized spinal cord tissue structure, proliferation of glial cells, and spinal cord porosis, the damage was less in the T1AM group than in the other two groups. The number of apoptotic cells gradually increased in all three groups. However, while the mean numbers of apoptotic cells in the control (9.8%±2.6%, 14.2%±5.9%, 57.2%±15.1%) and T1AM+EPPTB groups (9.1%±3.0%, 13.4%±6.3%, 57.4%±11.1%) on days 3, 5, and 7, respectively, were not significantly different from each other, those in the T1AM group (2.3%±1.4%, 7.6%±1.8%, 36.1%±9.9%) were significantly lower than those in both the other groups at each time point (all P values <0.05). Thus, T1AM is involved in the apoptosis pathway through stimulation of TAAR1. The T1AM-TAAR1 interaction decreased spinal cord neuron apoptosis, reduced secondary SCI, and promoted hind limb motor function recovery in rats with SCI.