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.

Bone Microthrombus Promotes Bone Loss in Iron Accumulation Rats.

In the present study, we investigated the changes of the coagulation state, bone microthrombus, microvascular bed and bone density levels in iron accumulation rats. Meanwhile,the effect of anticoagulation therapy on bone mineral density was further investigated. We established two groups: a control (Ctrl) group and an iron intervention (FAC) group. Changes in coagulation function, peripheral blood cell counts, bone microthrombus, bone vessels and bone mineral density were compared between the two groups. We designed the non-treatment group and treatment group to study the changes of bone mineral density by preventing microthrombus formation with the anticoagulant fondaparinux. We found that the fibrinogen and D-dimer contents were significantly higher, whereas the thrombin time (TT) and prothrombin time (PT) were significantly shorter in the FAC group. After ink staining, the microvascular bed in the FAC group was significantly reduced compared with that in the Ctrl group. HE and Martius Scarlet Blue (MSB) staining showed microthrombus in the bone marrow of the iron accumulation rats. Following anticoagulation therapy, the bone microcirculation vascular bed areas in the treatment group rats were significantly increased. Furthermore, the bone mineral density was increased in the treatment group compared with that in the non-treatment group. Through experiments, we found that the blood in iron accumulation rat was relatively hypercoagulable; moreover, there was microthrombus in the bone marrow, and the bone vascular bed was reduced. Additionally, anticoagulation was helpful for improving bone microcirculation, reducing microthrombus and decreasing bone loss.

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.