MicroRNA-133b Dysregulation in a Mouse Model of Cervical Contusion Injury.

Our previous research studies have demonstrated the role of microRNA133b (miR133b) in healing the contused spinal cord when administered either intranasally or intravenously 24 h following an injury. While our data showed beneficial effects of exogenous miR133b delivered within hours of a spinal cord injury (SCI), the kinetics of endogenous miR133b levels in the contused spinal cord and rostral/caudal segments of the injury were not fully investigated. In this study, we examined the miR133b dysregulation in a mouse model of moderate unilateral contusion injury at the fifth cervical (C5) level. Between 30 min and 7 days post-injury, mice were euthanized and tissues were collected from different areas of the spinal cord, ipsilateral and contralateral prefrontal motor cortices, and off-targets such as lung and spleen. The endogenous level of miR133b was determined by RT-qPCR. We found that after SCI, (a) most changes in miR133b level were restricted to the injured area with very limited alterations in the rostral and caudal parts relative to the injury site, (b) acute changes in the endogenous levels were predominantly specific to the lesion site with delayed miR133b changes in the motor cortex, and (c) ipsilateral and contralateral hemispheres responded differently to unilateral SCI. Our results suggest that the therapeutic window for exogenous miR133b therapy begins earlier than 24 h post-injury and potentially lasts longer than 7 days.

Intranasal Delivery of miR133b in a NEO100-Based Formulation Induces a Healing Response in Spinal Cord-Injured Mice.

Despite important advances in the pre-clinical animal studies investigating the neuroinhibitory microenvironment at the injury site, traumatic injury to the spinal cord remains a major problem with no concrete response. Here, we examined whether (1) intranasal (IN) administration of miR133b/Ago2 can reach the injury site and achieve a therapeutic effect and (2) NEO100-based formulation of miR133b/Ago2 can improve effectiveness. 24 h after a cervical contusion, C57BL6 female mice received IN delivery of miR133b/Ago2 or miR133b/Ago2/NEO100 for 3 days, one dose per day. The pharmacokinetics of miR133b in the spinal cord lesion was determined by RT-qPCR. The role of IN delivery of miR133b on motor function was assessed by the grip strength meter (GSM) and hanging tasks. The activity of miR133b at the lesion site was established by immunostaining of fibronectin 1 (FN1), a miR133b target. We found that IN delivery of miR133b/Ago2 (1) reaches the lesion scar and co-administration of miR133b with NEO100 facilitated the cellular uptake; (2) enhanced the motor function and addition of NEO100 potentiated this effect and (3) targeted FN1 expression at the lesion scar. Our results suggest a high efficacy of IN delivery of miR133b/Ago2 to the injured spinal cord that translates to improved healing with NEO100 further potentiating this effect.

Intravenous delivery of microRNA-133b along with Argonaute-2 enhances spinal cord recovery following cervical contusion in mice.

BACKGROUND CONTEXT: Acute spinal cord injury (SCI) is a devastating condition for which spine decompression and stabilization of injury remains the only therapy available in the clinical setup. However, fibrous scar formation during the healing process significantly impairs full recovery. MicroRNAs (miRs) are small noncoding RNAs that regulate gene expression by binding to target mRNA(s) and initiating translational repression or mRNA degradation. It has been reported that microRNA-133b (miR133b) is highly expressed in regenerating neurons following a SCI in zebrafish, and lentiviral delivery of miR133b at the time of SCI in mice resulted in improved functional recovery. PURPOSE: The aim of this study was to investigate whether intravenous delivery of miR133b enhances spinal cord recovery when administered 24 hours following a cervical contusion injury in mice. STUDY DESIGN: This is an experimental animal study of acute SCI, investigating the effect of miR133b on spinal cord recovery by targeting scar lesion formation. The approach involved setting an acute SCI in mice, which was followed 24 hours later by intravenous co-delivery of miR133b and Argonaute 2 (Ago2), a protein involved in miRNA stabilization. Readouts of the impact of this intervention included analysis of RNA and protein expression at the lesion site, in particular with regard to markers of scar tissue formation, and determination of motor function recovery by the grip strength meter task. METHODS: C57BL6 female mice between 6 and 8 weeks of age were tested. The injury model employed was a unilateral moderate contusion at the cervical fifth level. Twenty-four hours following the injury, the authors co-delivered miR133b, or scrambled miRNA as negative control, along with Ago2 for 3 consecutive days, one dose per day via tail-vein injection. They first investigated the level of miR133b in the spinal cord and in spinal cord lesion after a single dose of injection. Next, they determined the efficacy of miR133b and/or Ago2 delivery in regulating gene and protein expression at the lesion site. Finally, they established the role of miR133b and/or Ago2 in enhancing forelimb gripping recovery as assessed by the grip strength meter task for 8 weeks post-SCI. RESULTS: Intravenous delivery of miR133b and/or Ago2 targeted the microenvironment at the lesion site and prevented the increased expression of certain extracellular matrix proteins (ECM), in particular collagen type 1 alpha 1 and tenascin N, which are known to have a key role in scar formation. It also reduced microglia and/or macrophage recruitment to the lesion site. Functional recovery in mice treated with miR133b and/or Ago2 started around 2 weeks postinjury and continued to improve over time, whereas mice in the control group displayed significantly poorer recovery. CONCLUSIONS: Our data indicate therapeutic activity of intravenous miR133b and/or Ago2 treatment, possibly via decreasing ECM protein expression and macrophage recruitment at the lesion site, thereby minimizing detrimental fibrous scar formation. CLINICAL SIGNIFICANCE: There is an urgent medical need for better treatments of SCIs. Based on our findings in a preclinical model, the miR133b and/or Ago2 system specifically targets fibrous scar formation, a barrier in neuronal regrowth, by remodeling ECM molecules at the injury site. Prevention of scar formation is critical to improved outcomes of treatment. Of note, delivery of miR133b and/or Ago2 was initiated 24 hours after traumatic impact, thus indicating a fairly long window of opportunity providing more time and flexibility for therapeutic intervention. Intravenous miR133b may become a beneficial therapeutic strategy to treat patients with acute SCI.

Conditional genetic deletion of PTEN after a spinal cord injury enhances regenerative growth of CST axons and motor function recovery in mice.

Previous studies indicate that conditional genetic deletion of phosphatase and tensin homolog (PTEN) in neonatal mice enhances the ability of axons to regenerate following spinal cord injury (SCI) in adults. Here, we assessed whether deleting PTEN in adult neurons post-SCI is also effective, and whether enhanced regenerative growth is accompanied by enhanced recovery of voluntary motor function. PTEN(loxP/loxP) mice received moderate contusion injuries at cervical level 5 (C5). One group received unilateral injections of adeno-associated virus expressing CRE (AAV-CRE) into the sensorimotor cortex; controls received a vector expressing green fluorescent protein (AAV-GFP) or injuries only (no vector injections). Forelimb function was tested for 14weeks post-SCI using a grip strength meter (GSM) and a hanging task. The corticospinal tract (CST) was traced by injecting mini-ruby BDA into the sensorimotor cortex. Forelimb gripping ability was severely impaired immediately post-SCI but recovered slowly over time. The extent of recovery was significantly greater in PTEN-deleted mice in comparison to either the AAV-GFP group or the injury only group. BDA tract tracing revealed significantly higher numbers of BDA-labeled axons in caudal segments in the PTEN-deleted group compared to control groups. In addition, in the PTEN-deleted group, there were exuberant collaterals extending from the main tract rostral to the lesion and into and around the scar tissue at the injury site. These results indicate that PTEN deletion in adult mice shortly post-SCI can enhance regenerative growth of CST axons and forelimb motor function recovery.

Histone deacetylase inhibitors preserve white matter structure and function during ischemia by conserving ATP and reducing excitotoxicity.

The importance of white matter (WM) injury to stroke pathology has been underestimated in experimental animal models and this may have contributed to the failure to translate potential therapeutics into the stroke clinic. Histone deacetylase (HDAC) inhibitors are neuroprotective and also promote neurogenesis. These properties make them ideal candidates for stroke therapy. In a pure WM tract (isolated mouse optic nerve), we show that pan- and class I-specific HDAC inhibitors, administered before or after a period of oxygen and glucose deprivation (OGD), promote functional recovery of axons and preserve WM cellular architecture. This protection correlates with the upregulation of an astrocyte glutamate transporter, delayed and reduced glutamate accumulation during OGD, preservation of axonal mitochondria and oligodendrocytes, and maintenance of ATP levels. Interestingly, the expression of HDACs 1, 2, and 3 is localized to astrocytes, suggesting that changes in glial cell gene transcription and/or protein acetylation may confer protection to axons. Our findings suggest that a therapeutic opportunity exists for the use of HDAC inhibitors, targeting mitochondrial energy regulation and excitotoxicity in ischemic WM injury.

Metabolic vulnerability disposes retinal ganglion cell axons to dysfunction in a model of glaucomatous degeneration.

We tested the hypothesis that glaucoma disrupts electrophysiological conduction properties and axon function in optic nerve as a function of intraocular pressure (IOP) levels and age in the DBA/2J mouse model of glaucoma. The amplitude and the integral of electrical signals evoked along the axons decreased considerably by 6 months of age as a function of increasing IOP levels. At young ages, raised IOP was directly associated with increased vulnerability to metabolic challenge. Changes in the physiological function of the optic nerves were accentuated with aging, leading to loss of compound action potential in an entire population of fibers: small, slow conducting axons. This loss was accompanied with loss of small fiber axon counts and declining metabolic reserve by demonstrating IOP-dependent ATP decrease in mouse optic nerves. These data shed light on a novel potential mechanism of glaucoma pathology whereby increased IOP and declining metabolic capacity lead to axon liability and eventually dysfunction and loss.

Sulforaphane protects astrocytes against oxidative stress and delayed death caused by oxygen and glucose deprivation.

Oxidative stress is an important molecular mechanism of astrocyte injury and death following ischemia/reperfusion and may be an effective target of intervention. One therapeutic strategy for detoxifying the many different reactive oxygen and nitrogen species that are produced under these conditions is induction of the Phase II gene response by the use of chemicals or conditions that promote the translocation of the transcriptional activating factor NRF2 from the cytosol to the nucleus, where it binds to genomic antioxidant response elements. This study tested the hypothesis that pre- or post-treatment of cultured cortical astrocytes with sulforaphane, an alkylating agent known to activate the NRF2 pathway of gene expression protects against death of astrocytes caused by transient exposure to O(2) and glucose deprivation (OGD). Rat cortical astrocytes were exposed to 5 muM sulforaphane either 48 h prior to, or for 48 h after a 4-h period of OGD. Both pre- and post-treatments significantly reduced cell death at 48 h after OGD. Immunostaining for 8-hydroxy-2-deoxyguanosine, a marker of DNA/RNA oxidation, was reduced at 4 h reoxygenation with sulforaphane pretreatment. Sulforaphane exposure was followed by an increase in cellular and nuclear NRF2 immunoreactivity. Moreover, sulforaphane also increased the mRNA, protein level, and enzyme activity of NAD(P)H/Quinone Oxidoreductase1, a known target of NRF2 transcriptional activation. We conclude that sulforaphane stimulates the NRF2 pathway of antioxidant gene expression in astrocytes and protects them from cell death in an in vitro model of ischemia/reperfusion.

Postischemic oxidative stress promotes mitochondrial metabolic failure in neurons and astrocytes.

Oxidative stress and mitochondrial dysfunction have been closely associated in many subcellular, cellular, animal, and human studies of both acute brain injury and neurodegenerative diseases. Our animal models of brain injury caused by cardiac arrest illustrate this relationship and demonstrate that both oxidative molecular modifications and mitochondrial metabolic impairment are exacerbated by reoxygenation of the brain using 100% ventilatory O(2) compared to lower levels that maintain normoxemia. Numerous molecular mechanisms may be responsible for mitochondrial dysfunction caused by oxidative stress, including oxidation and inactivation of mitochondrial proteins, promotion of the mitochondrial membrane permeability transition, and consumption of metabolic cofactors and intermediates, for example, NAD(H). Moreover, the relative contribution of these mechanisms to cell injury and death is likely different among different types of brain cells, for example, neurons and astrocytes. In order to better understand these oxidative stress mechanisms and their relevance to neurologic disorders, we have undertaken studies with primary cultures of astrocytes and neurons exposed to O(2) and glucose deprivation and reoxygenation and compared the results of these studies to those using a rat model of neonatal asphyxic brain injury. These results support the hypothesis that release and or consumption of mitochondrial NAD(H) is at least partially responsible for respiratory inhibition, particularly in neurons.

Hyperoxia promotes astrocyte cell death after oxygen and glucose deprivation.

Astrocyte dysfunction and death accompany cerebral ischemia/reperfusion and possibly compromise neuronal survival. Animal studies indicate that neuronal death, neurologic injury, and oxidative molecular modifications are worse in animals exposed to hyperoxic compared to normoxic ventilation during reperfusion after global cerebral ischemia. It is unknown, however, whether ambient O2 affects brain cell survival using in vitro ischemia paradigms where mechanisms of injury to specific cell types can be more thoroughly investigated. This study tested the hypothesis that compared with the supraphysiological level of 20% O2 normally used in cell culture, lower, more physiological O2 levels protect astrocytes from death following oxygen and glucose deprivation. Primary rat cortical astrocytes were cultured under either 7 or 20% O2, exposed to O2, and glucose deprivation for 4 h, and then exposed to normal medium under either 7 or 20% O2. Cell death and 3-nitrotyrosine and 8-hydroxy-2-deoxyguanosine immunoreactivities were assessed at different periods of reoxygenation. Astrocytes exposed to low levels of O2 during reoxygenation undergo less death and exhibit lower levels of protein nitration and nucleic acid oxidation when compared with those under high levels of O2 during reoxygenation. These results support the hypothesis that the 20% O2 normally used in cell culture exacerbates astrocyte death and oxidative stress in an in vitro ischemia/reperfusion model compared to levels that more closely approximate those that exist in vivo.