Small interfering RNA directed against CTMP reduces acute traumatic brain injury in a mouse model by activating Akt

Abstract

Objective:

Protein kinase B (PKB/Akt), which is phosphorylated and activated by upstream activators, exerts critical neuroprotective effects by phosphorylating downstream targets after traumatic brain injury (TBI). Studies on the regulation of Akt will be crucial for our understanding of neuronal survival. The goal of this study is to investigate the effects of carboxyl-terminal modulator protein (CTMP) on phosphorylation of Akt and neurological function in a mouse model of TBI.

Methods:

Traumatic brain injury in mice was performed by a controlled cortical impact device. The expression of Akt, phospho-Akt, and CTMP was examined in the injured cortices by immunohistochemistry and Western blot analysis. To determine the effects of CTMP, small interfering RNAs (siRNAs) directed against CTMP were injected in mice with TBI, and the expression of phosphorylated Akt and neurological function were evaluated.

Results:

Phospho-Akt significantly increased at 4 hours post-TBI in the nucleus (P < 0·01) and remained at high levels until 72 hours after TBI, as shown by Western blot analysis. In the cytosol, the expression of phospho-Akt reached its peak at 4 hours post-TBI, but decreased markedly at 24 hours and maintained below pre-TBI levels until 72 hours post-TBI. Interestingly, the expression of CTMP significantly increased 4 hours after TBI (P < 0·01) and sustained those levels until 72 hours without dramatic changes. Treatment with CTMP siRNA effectively augmented the phosphorylation of Akt and significantly improved the neurological functional recovery up to 28 days post-TBI.

Conclusion:

We conclude that Akt is phosphorylated and translocated to nucleus after TBI to exert neuroprotective effects. However, CTMP is simultaneously triggered to inhibit the phosphorylation of Akt. Inhibition of CTMP by siRNA improves the recovery of neurological functions after TBI.     

NLRP3 deficiency ameliorates neurovascular damage in experimental ischemic stroke

Although the innate immune response to induce postischemic inflammation is considered as an essential step in the progression of cerebral ischemia injury, the role of innate immunity mediator NLRP3 in the pathogenesis of ischemic stroke is unknown. In this study, focal ischemia was induced by middle cerebral artery occlusion in NLRP3^−/−, NOX2^−/−, or wild-type (WT) mice. By magnetic resonance imaging (MRI), Evans blue permeability, and electron microscopic analyses, we found that NLRP3 deficiency ameliorated cerebral injury in mice after ischemic stroke by reducing infarcts and blood–brain barrier (BBB) damage. We further showed that the contribution of NLRP3 to neurovascular damage was associated with an autocrine/paracrine pattern of NLRP3-mediated interleukin-1β (IL-1β) release as evidenced by increased brain microvessel endothelial cell permeability and microglia-mediated neurotoxicity. Finally, we found that NOX2 deficiency improved outcomes after ischemic stroke by mediating NLRP3 signaling. This study for the first time shows the contribution of NLRP3 to neurovascular damage and provides direct evidence that NLRP3 as an important target molecule links NOX2-mediated oxidative stress to neurovascular damage in ischemic stroke. Pharmacological targeting of NLRP3-mediated inflammatory response at multiple levels may help design a new approach to develop therapeutic strategies for prevention of deterioration of cerebral function and for the treatment of stroke.     

Capillary transit time heterogeneity and flow-metabolism coupling after traumatic brain injury

Most patients who die after traumatic brain injury (TBI) show evidence of ischemic brain damage. Nevertheless, it has proven difficult to demonstrate cerebral ischemia in TBI patients. After TBI, both global and localized changes in cerebral blood flow (CBF) are observed, depending on the extent of diffuse brain swelling and the size and location of contusions and hematoma. These changes vary considerably over time, with most TBI patients showing reduced CBF during the first 12 hours after injury, then hyperperfusion, and in some patients vasospasms before CBF eventually normalizes. This apparent neurovascular uncoupling has been ascribed to mitochondrial dysfunction, hindered oxygen diffusion into tissue, or microthrombosis. Capillary compression by astrocytic endfeet swelling is observed in biopsies acquired from TBI patients. In animal models, elevated intracranial pressure compresses capillaries, causing redistribution of capillary flows into patterns argued to cause functional shunting of oxygenated blood through the capillary bed. We used a biophysical model of oxygen transport in tissue to examine how capillary flow disturbances may contribute to the profound changes in CBF after TBI. The analysis suggests that elevated capillary transit time heterogeneity can cause critical reductions in oxygen availability in the absence of ‘classic'' ischemia. We discuss diagnostic and therapeutic consequences of these predictions.     

Acellular spinal cord scaffold seeded with bone marrow stromal cells protects tissue and promotes functional recovery in spinal cord‐injured rats

Therapy using scaffolds seeded with stem cells plays an important role in repair of spinal cord injury (SCI), with the transplanted cells differentiating into nerve cells to replace the lost tissue while releasing neurotrophic factors that contribute to repair following SCI and enhance the function of the damaged nervous system. The present study investigated the ability to extend the survival time of bone marrow stromal cells (BMSCs) to restore the damaged spinal cord and improve functional recovery by grafting acellular spinal cord (ASC) scaffold seeded or not with BMSCs in a rat model of acute hemisected SCI. BBB scores revealed that treatment with BMSCs seeded into ASC scaffold led to an obvious improvement in motor function recovery compared with treatment with ASC scaffold alone or untreated controls. This improvement was evident at 2 and 8 weeks after surgery (P < 0.05). When BMSCs labeled with 5‐bromodeoxyuridine were implanted together with ASC scaffold into the injured sites, they differentiated into glial cells, and some BMSCs could be observed within the graft by immunofluorescent staining at 8 weeks after implantation. Evaluation of caspase‐3 activation suggested that the graft group was able to reduce apoptosis compared with SCI alone at 8 weeks after operation (P < 0.05). This study suggests that ASC scaffolds have the ability to enhance BMSC survival and improve differentiation and could also reduce native damaged nerve tissue apoptosis, thus protecting host tissue as well as improving functional recovery after implantation. © 2013 Wiley Periodicals, Inc.     

Granulocyte colony‐stimulating factor improves neuron survival in experimental spinal cord injury by regulating nucleophosmin‐1 expression

Granulocyte colony‐stimulating factor (G‐CSF) and its related mechanisms were investigated to assess the potential for this factor to exert neuroprotective effects against spinal cord injury in mice. Recombinant human granulocyte colony‐stimulating factor (rhG‐CSF) was injected into mice spinal cord hemisection models. Locomotor activity was assessed by using the Basso‐Bettie‐Bresnahan scale. Neurons isolated from spinal cords were cultured in vitro and used in a neuronal mechanical injury model. Three treatment groups were compared with this model, 1) G‐CSF, 2) G‐CSF + NSC348884 (a nucleophosmin 1‐specific inhibitor), and 3) NSC348884. Immunofluorescence staining and Western blotting were performed to analyze the expression of G‐CSF and nucleophosmin 1 (Npm1). TUNEL staining was performed to analyze apoptosis after G‐CSF treatment. We found that the G‐CSF receptor (G‐CSFR) and Npm1 were expressed in neurons and that Npm1 expression was induced after G‐CSF treatment. G‐CSF inhibited neuronal apoptosis. NSC348884 induced p53‐dependent cell apoptosis and partially blocked the neuroprotective activity of G‐CSF on neurons in vitro. G‐CSF promoted locomotor recovery and demonstrated neuroprotective effects in an acute spinal cord injury model. The mechanism of G‐CSF's neuroprotection may be related in part to attenuating neuronal apoptosis by NPM1. © 2014 Wiley Periodicals, Inc.     

ApoE mimetic ameliorates motor deficit and tissue damage in rat spinal cord injury

Apolipoprotein E (apoE), a plasma protein responsible for transporting lipid and cholesterol, modulates responses of the central nervous system to injury. Small peptides derived from the receptor‐binding region of apoE can simulate some important bioactivities of apoE holoprotein and offer neuroprotection against brain injury. We tested whether COG1410, an apoE‐mimetic peptide, provides protection in a rat model of spinal cord injury (SCI). Traumatic injury was created at T8 by a cortical impact device. Injured rats were randomized to four treatment groups: vehicle, 0.15, 0.3, or 0.6 mg/kg COG1410; sham surgery rats received vehicle. Basso, Beattie, Bresnahan neurological score was evaluated prior to injury and at 1, 3, 7, and 14 days after injury. Histological changes were evaluated at 14 days. All injured rats lost body weight during the first week following injury. Body weight recovery was significantly improved in rats treated with COG1410. Mechanical impact resulted in severe motor deficit, and most animals had a BBB score of 0–1 at 24 hours postinjury. COG1410‐treated rats showed significantly improved functional recovery and ameliorated motor deficit at 14 days postinjury. Histological analysis showed that COG1410 groups had a significantly reduced lesion size at the site of injury, a larger preserved luxol fast blue‐stained area, and more visible neurons in the surrounding area of injury. Microglial activation was also significantly suppressed. These findings indicate that this apoE mimetic effectively improved neurological and histological outcome following SCI in rats, and the effect was associated with inhibition of microglial activation. © 2014 Wiley Periodicals, Inc.     

Sex differences in circadian timing systems: Implications for disease

Virtually every eukaryotic cell has an endogenous circadian clock and a biological sex. These cell-based clocks have been conceptualized as oscillators whose phase can be reset by internal signals such as hormones, and external cues such as light. The present review highlights the inter-relationship between circadian clocks and sex differences. In mammals, the suprachiasmatic nucleus (SCN) serves as a master clock synchronizing the phase of clocks throughout the body. Gonadal steroid receptors are expressed in almost every site that receives direct SCN input. Here we review sex differences in the circadian timing system in the hypothalamic–pituitary–gonadal axis (HPG), the hypothalamic–adrenal–pituitary (HPA) axis, and sleep–arousal systems. We also point to ways in which disruption of circadian rhythms within these systems differs in the sexes and is associated with dysfunction and disease. Understanding sex differentiated circadian timing systems can lead to improved treatment strategies for these conditions.