Electrical stimulation of olfactory bulb downregulates RGMa expression after ischemia/reperfusion injury in rats

Knockdown of RGMA improves ischemic stroke via Reprogramming of Neuronal Metabolism

Neuronal energy metabolism dysregulation is involved in various pathologies of Ischemia-reperfusion (I/R), yet the role of RGMA in neuronal metabolic reprogramming has not been reported. In this study, we found that RGMA expression significantly increased after I/R, and compared to control mice, mice with MCAO/R showed an increase in glycolytic metabolic products and the expression of glycolytic pathway proteins. Furthermore, RGMA levels are closely related to neuronal energy metabolism. We discovered that knockdown of RGMA can shift neuronal energy metabolism towards oxidative phosphorylation and the pentose phosphate pathway, thereby protecting mice from ischemic reperfusion injury. Mechanistically, knockdown of RGMA can downregulate PGK1 expression, reducing the increase in glycolytic flux following ischemia reperfusion. Moreover, we found that knockdown of RGMA can reduce the interaction between USP10 and PGK1, thus affecting the ubiquitination degradation of PGK1. In summary, our data suggest that RGMA may regulate neuronal energy metabolism by inhibiting the USP10-mediated deubiquitination of PGK1, thus protecting it from I/R injury. This study provides new ideas for clarifying the intrinsic mechanism of neuronal damage after I/R.

Managing Post-traumatic Olfactory Disorders

Purpose of Review

This study aims to summarize and critically review recent literature on management of post-traumatic olfactory dysfunction (PTOD) with emphasis on the diagnostic procedure and treatment options.

Recent Findings

Magnetic resonance imaging and olfactory testing are the basis of the diagnostic procedure. Time of diagnosis is critical as the most improvement occurs within the first year after trauma. Olfactory training and oral steroids seem to be a relatively evidence-based therapeutic option but with non-optimal results. Surgery has a limited place in the management of PTOD. Promising future options could be the development of olfactory implants and transplantation of olfactory epithelium or stem cells.

Summary

PTOD management is challenging as it has several pathogenetic mechanisms and relatively poor prognosis. Patients with olfactory impairment and head trauma have diminished quality of life, and increased risk for harmful events and development of depression. Thus, clinicians should not only focus to therapeutic options but equally to appropriate counseling to their patients in order to decrease risks of personal injury and improve their daily life.

Cholesterol synthesis inhibition promotes axonal regeneration in the injured central nervous system

Neuronal regeneration in the injured central nervous system is hampered by multiple extracellular proteins. These proteins exert their inhibitory action through interactions with receptors that are located in cholesterol rich compartments of the membrane termed lipid rafts. Here we show that cholesterol-synthesis inhibition prevents the association of the Neogenin receptor with lipid rafts. Furthermore, we show that cholesterol-synthesis inhibition enhances axonal growth both on inhibitory -myelin and -RGMa substrates. Following optic nerve injury, lowering cholesterol synthesis with both drugs and siRNA-strategies allows for robust axonal regeneration and promotes neuronal survival. Cholesterol inhibition also enhanced photoreceptor survival in a model of Retinitis Pigmentosa. Our data reveal that Lovastatin leads to several opposing effects on regenerating axons: cholesterol synthesis inhibition promotes regeneration whereas altered prenylation impairs regeneration. We also show that the lactone prodrug form of lovastatin has differing effects on regeneration when compared to the ring-open hydroxy-acid form. Thus the association of cell surface receptors with lipid rafts contributes to axonal regeneration inhibition, and blocking cholesterol synthesis provides a potential therapeutic approach to promote neuronal regeneration and survival in the diseased Central Nervous System. SIGNIFICANCE STATEMENT: Statins have been intensively used to treat high levels of cholesterol in humans. However, the effect of cholesterol inhibition in both the healthy and the diseased brain remains controversial. In particular, it is unclear whether cholesterol inhibition with statins can promote regeneration and survival following injuries. Here we show that late stage cholesterol inhibition promotes robust axonal regeneration following optic nerve injury. We identified distinct mechanisms of action for activated vs non-activated Lovastatin that may account for discrepancies found in the literature. We show that late stage cholesterol synthesis inhibition alters Neogenin association with lipid rafts, thereby i) neutralizing the inhibitory function of its ligand and ii) offering a novel opportunity to promote CNS regeneration and survival following injuries.

Expression and regulation of miR-449a and AREG in cerebral ischemic injury

Rodent focal ischemia models are widely used to mimic and examine human strokes. To the best of our knowledge, no investigation has systematically examined the expression changes of microRNA (miR)-449a and Amphiregulin (AREG) as well as their biological relationship during middle cerebral artery occlusion (MCAO) and oxygen and glucose deprivation/reperfusion (OGD/R). The present study examined the histological and behavioral outcomes of MCAO and the function of miR-449a and AREG in cerebral ischemic injury. Rats were subjected to 2 h MCAO, which was followed by reperfusion. miR-449a and AREG were examined in the injury tissues of MCAO rats and the OGD/R cell line by reverse transcription-quantitative polymerase chain reaction. Protein expressions of AREG in the injury tissues of MCAO rats was measured using an immunohistochemistry and the protein expression levels of AREG, epidermal growth factor receptor (EGFR), phosphatidylinositol 3-kinase (PI3K)/ protein kinase B (Akt) and the phosphorylation level of Akt (p-Akt) were analyzed by western blotting. Cell apoptosis was examined following the knock down and subsequent overexpression of AREG in a human OGD/R neuronal cell line by small interfering RNAs (siRNAs) and plasmid transfection. Luciferase reporter assays were used to validate the target of miR-449a. The expression changes and regulatory mechanisms of miR-449a and AREG in an ischemia/reperfusion (I/R) injury model were examined in vivo and in vitro. The neurological deficit score, brain edema volume, cerebral infarct area, and the number of apoptosis cells in ischemic rats were all markedly elevated, than that in the control rats. The expression of miR-449a was decreased and AREG was increased in the MCAO rats and human OGD/R neuronal cell line. miR-449a inhibition or AREG overexpression in OGD/R cells resulted in a significant decrease in apoptotic cells, and AREG was revealed to be one of the direct targets of miR-449a. Molecular recovery was observed following transfection with miR-449a mimics and AREG knockdown in an OGD/R model in vitro. The present study demonstrated that miR-449a was downregulated while AREG was upregulated in cerebral ischemic injury, and the recovery of neurological function can be obtained following the overexpression of miR-449a and the knockdown of AREG in an I/R injury model. miR-449a functions in ischemic stroke via directly targeting AREG. These findings suggest a novel mechanism involving in cerebral I/R injury model and may aid investigators in gaining a deeper understanding of strokes in a clinical setting.

Targeting Smox Is Neuroprotective and Ameliorates Brain Inflammation in Cerebral Ischemia/Reperfusion Rats

Spermine oxidase (Smox) is a member of the polyamine oxidases and has been demonstrated to be involved in ischemic brain damage. In this study, we found that Smox expression was increased in a rat middle cerebral artery occlusion (MCAO) model and in cultured primary neurons after oxygen-glucose deprivation and reoxygenation (OGD/R). Smox downregulation by the adeno-associated virus RNA interference system significantly reduced the MCAO-induced brain infarct volume and neurological deficits and decreased neuronal apoptosis and inflammatory reactions. In addition, significant microglial activation and increased IL-6 and TNF-α expression were observed in microglia treated with supernatant from neurons after OGD/R. However, a significant reduction in microglial activation as well as IL-6 and TNF-α expression was observed in microglia treated with supernatant from Smox downregulated neurons after OGD/R. Therefore, the results indicated that Smox is an important mediator of cerebral ischemia injury and may be a therapeutic target for cerebral ischemia patients.

Adenoviral vector-induced silencing of RGMa attenuates blood-brain barrier dysfunction in a rat model of MCAO/reperfusion

BACKGROUND

Repulsive guidance molecule A (RGMa) is implicated in focal cerebral ischemia-reperfusion (I/R) injury, but its mechanisms are still largely unknown. This work focused on the effects of RGMa on the blood-brain barrier (BBB) after focal cerebral I/R injury.

METHODS

Sprague-Dawley (SD) rats were randomly divided into four groups: sham, middle cerebral artery occlusion (MCAO)/reperfusion (I/R), MCAO/reperfusion administered recombinant adenovirus expressing sh-con (I/R + sh-con) and MCAO/reperfusion administered recombinant adenovirus expressing sh-RGMa (I/R + sh-RGMa) groups. Infarct volume, brain edema and neurological scores were evaluated at 3 day after reperfusion. Evens blue leakage and transmission electron microscopy was performed. And the expression level of claudin-5 and ZO-1, CDC-42 and PAK-1, RGMa were detected by western blot.

RESULTS

Compared with I/R or I/R + sh-con groups, I/R + sh-RGMa group showed smaller infarction volume, attenuated brain edema, improved neurological scores and better BBB integrity, such as reduced Evans blue leakage and ultra-structural change. We also observed improved BBB function followed by down-regulation of MMP-9 and up-regulation of claudin-5 and ZO-1 in the I/R + sh-RGMa group. In addition, up-regulation of the CDC-42 and PAK-1 in the I/R + sh-RGMa group was obtained.

CONCLUSIONS

RGMa may be involved in I/R injury associated with BBB dysfunction via the CDC-42/PAK-1 signal pathway and may be a promising therapeutic target for I/R injury.

Targeting repulsive guidance molecule A to promote regeneration and neuroprotection in multiple sclerosis

Repulsive guidance molecule A (RGMa) is a potent inhibitor of neuronal regeneration and a regulator of cell death, and it plays a role in multiple sclerosis (MS). In autopsy material from progressive MS patients, RGMa was found in active and chronic lesions, as well as in normal-appearing gray and white matter, and was expressed by cellular meningeal infiltrates. Levels of soluble RGMa in the cerebrospinal fluid were decreased in progressive MS patients successfully treated with intrathecal corticosteroid triamcinolone acetonide (TCA), showing functional improvements. In vitro, RGMa monoclonal antibodies (mAbs) reversed RGMa-mediated neurite outgrowth inhibition and chemorepulsion. In animal models of CNS damage and MS, RGMa antibody stimulated regeneration and remyelination of damaged nerve fibers, accelerated functional recovery, and protected the retinal nerve fiber layer as measured by clinically relevant optic coherence tomography. These data suggest that targeting RGMa is a promising strategy to improve functional recovery in MS patients.

Uncoupling Neogenin association with lipid rafts promotes neuronal survival and functional recovery after stroke

The dependence receptor Neogenin and its ligand, the repulsive guidance molecule a (RGMa), regulate apoptosis and axonal growth in the developing and the adult central nervous system (CNS). Here, we show that this pathway has also a critical role in neuronal death following stroke, and that providing RGMa to neurons blocks Neogenin-induced death. Interestingly, the Neogenin pro-death function following ischemic insult depends on Neogenin association with lipid rafts. Thus, a peptide that prevents Neogenin association with lipid rafts increased neuronal survival in several in vitro stroke models. In rats, a pro-survival effect was also observed in a model of ocular ischemia, as well as after middle cerebral artery occlusion (MCAO). Treatments that prevented Neogenin association with lipid rafts improved neuronal survival and the complexity of the neuronal network following occlusion of the middle artery. Toward the development of a treatment for stroke, we developed a human anti-RGMa antibody that also prevents Neogenin association with lipid rafts. We show that this antibody also protected CNS tissue from ischemic damage and that its application resulted in a significant functional improvement even when administrated 6 h after artery occlusion. Thus, our results draw attention to the role of Neogenin and lipid rafts as potential targets following stroke.

Decreased levels of repulsive guidance molecule A in association with beneficial effects of repeated intrathecal triamcinolone acetonide application in progressive multiple sclerosis patients

Repeated intrathecal application of the sustained release steroid triamcinolone acetonide is beneficial in progressive multiple sclerosis patients. Its putative regenerative effect may involve regulation of the repulsive guidance molecule A synthesis. This protein inhibits axonal regeneration and functional recovery. Objectives were to demonstrate the efficacy of four triamcinolone applications every other day in association with repulsive guidance molecule A levels in cerebrospinal fluid. Clinical evaluation was performed at baseline and on each day after a triamcinolone administration in 25 progressive multiple sclerosis patients. Repulsive guidance molecule A concentrations were determined before each triamcinolone application by western blot analysis with quantification. Clinical scores for multiple sclerosis improved, and the maximum walking distance and speed ameliorated in 17 patients. Repulsive guidance molecule A levels declined in these responders. The remaining patients showed no prompt clinical benefit and no decrease of repulsive guidance molecule A concentrations. Decline of repulsive guidance molecule A may reflect regeneration and functional recovery by triamcinolone in progressive multiple sclerosis patients.

Preventive and therapeutic effects of ginsenoside Rb1 for neural injury during cerebral infarction in rats

To examine the preventive and therapeutic effects of ginsenoside Rb1 for neural injury during cerebral infarction, we used a middle cerebral artery occlusion (MCAO) model in rats to investigate the effects of ginsenoside Rb1 with Edaravone as a control. Ginsenoside Rb1 was given to the rats by intragastric administration either before or after the MCAO surgery to study its preventive and therapeutic effects. Ginsenoside Rb1-treated rats had a smaller infarct volume than the positive control. Interleukin-1 (IL-1), brain-derived neurotrophic factor (BDNF), tumor necrosis factor-α (TNF-α), neurofilament (NF) and growth associated protein-43 (GAP-43) were measured to determine brain damage and the recovery of nerves. These findings suggest that ginsenoside Rb1 has neuroprotective effects in rats, and the protection efficiency is higher than Edaravone. The protective mechanism is different from Edaravone. The preventive ability of ginsenoside Rb1 is higher than its repair ability in neuroprotection in vivo.

Effective neuroprotection by ischemic postconditioning is associated with a decreased expression of RGMa and inflammation mediators in ischemic rats

Whether ischemic postconditioning (IPC) can significantly alleviate ischemic injury hinges on the appropriate measure. In this study, the expression RGMa and IL-1β, IL-6 are investigated to estimate the therapeutic benefits of various postconditioning strategies after cerebral ischemia/reperfusion. The study consists of the sham-operated group and five treatment groups: ischemia/reperfusion (I/R), two proximate ischemic postconditioning (IPC-S and IPC-M), remote postconditioning (RIPC) and delayed postconditioning (DIPC) groups. We find that rats in IPC and RIPC groups exhibit significantly less neural deficit and lower infarct volume than that in I/R and DIPC groups after ischemia/reperfusion. Moreover, in ischemic cortex and hippocampus, the mRNA level of RGMa is much lower in IPC and RIPC groups. Immunohistochemical analysis indicates that the expression of RGMa, IL-1β and IL-6 are reduced in IPC and RIPC groups (especially in IPC-S group). Furthermore, neurofilament staining reveals that the rats in IPC and RIPC groups have less axonal injury than that in I/R and DIPC groups. Our studies suggest that the optimal strategy to attenuate cerebral ischemia/reperfusion is achieved by early, short-term, and multiple cycles of proximal IPC. The cerebral protective effect of IPC may be associated with the decreased expression of RGMa and inflammation mediators.

Minocycline promotes axonal regeneration through suppression of RGMa in rat MCAO/reperfusion model

Minocycline has been recently implicated in protection against focal cerebral ischemia reperfusion (I/R), but the protective effects on neurobehavioral abnormalities remains contradictory. In the present study, we investigate whether minocycline improves axonal regeneration and neurological function recovery by inhibiting the expression of the repulsive guidance molecular A (RGMa) after focal cerebral ischemia reperfusion. Male Sprague-Dawley (SD) rats were subjected to occlusion of the right middle cerebral artery (MCAO) for 2 h and 3 mg kg⁻¹ minocycline was injected intravenously immediately after reperfusion twice a day for 14 days. The staircase test and modified neurological severity score (mNSS) were performed to evaluate functional outcome and blood-brain barrier (BBB) permeability was assessed by Evan's blue dye extravasation (EB) at the expected time point. The expression of RGMa in ischemic cortex was measured by immunohistochemical staining and Western blot 2 weeks after MCAO. Neurofilament protein 200 (NF-200) immunohistochemical staining was used to assess axonal damage. Treatment with minocycline at a dose of 3 mg kg⁻¹ via the caudal vein significantly reduced the extravasation of EB, elevated mNSS and improved forelimb motor function as assessed by the staircase test when compared to the I/R group (P < 0.05). Moreover, axonal regrowth was enhanced in the minocycline treatment group when compared to the I/R group (P < 0.05). In addition, minocycline significantly reduced the expression of RGMa protein 2 weeks after MCAO as assessed by both immunostaining and Western blot. Our studies suggest that early minocycline treatment promotes neurological functional recovery and axonal regeneration in rats after MCAO, which might be mediated by down-regulating RGMa expression.

RNA interference against repulsive guidance molecule A improves axon sprout and neural function recovery of rats after MCAO/reperfusion

Repulsive guidance molecule a (RGMa) is a neurite growth inhibitor that is of great interest in the study of CNS neuronal regeneration. We adopted RNA interference (RNAi) as a means of suppressing the expression of RGMa and observed the improvement in axonal regeneration and neurological function of rats after cerebral ischemic injury. Recombinant adenovirus rAd5-shRNA-RGMa was constructed and prepared for animal experimentation. RGMa and neurofilament protein 200 (NF200) in the ischemic cortex and ipsilateral hippocampus were detected by reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry. The ischemic regions were examined by triphenyltetrazolium chloride (TTC) staining and the newborn neurite branches by Biotinylated Dextran Amine (BDA) neuronal tracing. Behavior tests were adopted to evaluate neurologic function recovery. Results showed RGMa was down-regulated and axonal growth was improved in the RNAi treated group (P<0.01). The number of axonal sprouts of corticospinal tract from the uninjured side to the ischemic side in the RNAi treated group was increased (P<0.01). Behavior test scores in the RNAi treated group were significantly better than other groups after 6 weeks (P<0.01). RGMa in rat brains after middle cerebral artery occlusion (MCAO) can be down-regulated by RNAi successfully, which may lead to improved axonal growth and neural anatomy plasticity, as well as neuron functional recovery.