Upregulated neuregulin-1 protects against optic nerve injury by regulating the RhoA/cofilin/F-actin axis.

OBJECTIVE: In recent years, the roles of Neuregulin-1 (NRG-1) in optic nerve injury and retinal cells have been investigated. However, the molecular mechanism by which NRG-1 affects optic nerve injury remains elusive and merits deeper exploration. Hence, this study examined the specific function of NRG-1 in the RhoA/cofilin/F-actin axis in optic nerve injury. METHODS: Retinal cells were isolated and identified for subsequent experimental uses. Reverse transcription quantitative polymerase chain reaction and Western blot assays were performed to measure NRG-1 expression in retinal cells which were cultured under elevated pressure. TUNEL staining was used to detect the cell apoptosis rate, and Western blot assay was performed to detect the expression of related genes. The axon growth was examined by immunofluorescence. The effects of NRG-1 on RhoA activity, cofilin phosphorylation, and F-actin were detected by Western blot assay. In other studies we established a rat model of acute optic nerve injury, and tested for beneficial effects of NRG-1 in vivo. RESULTS: High expression of NRG-1 was evident in the retinal tissues of rats with optic nerve injury. Overexpressing NRG-1 successfully inhibited RhoA activity and the phosphorylation of cofilin and promoted F-actin expression. In cell experiments, overexpressed NRG-1 suppressed the apoptosis of retinal cells and promoted axon growth through the RhoA/cofilin/F-actin axis. In animal experiments, overexpressed NRG-1 relieved retinal injury. CONCLUSION: Our results strongly suggest that overexpressed NRG-1 is highly effective in the protection of normal optic nerve function by suppressing RhoA activity and the phosphorylation of cofilin and rescuing F-actin function.

The Whole Lateral Type of the Sphenoethmoidal Cell and Its Relevance to Endoscopic Sinus Surgery.

BACKGROUND: The sphenoethmoidal cell and the sphenoid sinus (SS) show great similarity in endoscopy and imaging. Hence, it is important to accurately identify the sphenoethmoidal cell preoperatively to prevent injury of the nerve and artery during endoscopic surgery. The aim of the present study was to investigate a special type of sphenoethmoidal cell. METHODS: A total of 365 inpatients whose paranasal sinus computed tomography (CT) was collected and reviewed from May 2018 to September 2019 were included. The anatomical imaging characteristics of the sphenoethmoidal cell were observed. RESULTS: A special type of the sphenoethmoidal cell was found on 9 sides in 730 sides (1.3%), according to its extension to the SS. Unlike Onodi cell (49.6%) and Jinfeng cell (1.3%), this cell simultaneously extends toward the superolateral, lateral, and inferolateral regions of the SS and is simultaneously closely attached to the optic canal and the maxillary nerve. Presently, this cell is named as the whole lateral type of the sphenoethmoidal cell, and the SS is located at the medial or inferomedial of it. CONCLUSIONS: When evaluating the paranasal sinus CT preoperatively, attention must be paid to the possibility of the whole lateral type of sphenoethmoidal cell appearing, not just Onodi cell, extending into the SS.

Treatment with GDF15, a TGFß superfamily protein, induces protective effect on retinal ganglion cells.

Growth differentiation factor 15 (GDF15) is a protein belonging to the transforming growth factor beta (TGF-ß) superfamily. The precursor GDF15 is cleaved and activated as a mature GDF15 by protease. GDF15 has been detected in the aqueous humor of the primary open angle glaucoma patients, however the localization and the effect on the retinal ganglion cells (RGCs) are still unknown. Thus, the purpose of this study was to elucidate the effect of GDF15 on mouse optic nerve crush (ONC) model and primary culture of rat RGCs. Immunostaining showed that the GDF15 was in the ganglion cell layer (GCL), and colocalized with GFAP-positive cells in the GCL and the optic nerve. Western blotting analysis showed that the mature GDF15 was upregulated in the retina and the optic nerve after the ONC. Intravitreal injection of GDF15 suppressed RGCs loss of the ONC model mice in vivo. The neurites length of the primary culture of rat RGCs were increased by mature GDF15 treatment. In addition, the neurotrophic effect of GDF15 was canceled by RET inhibitor treatment. These findings indicate that GDF15 has neuroprotective effect on RGCs via GFRAL-RET pathway. Therefore, GDF15 may be one of novel therapeutic targets in RGC degenerative diseases.

Surgical Treatment and Visual Outcomes of Adult Orbital Roof Fractures.

BACKGROUND: Fractures of the orbital roof require high-energy trauma and have been linked to high rates of neurologic and ocular complications. However, there is a paucity of literature exploring the association between injury, management, and visual prognosis. METHODS: The authors performed a 3-year retrospective review of orbital roof fracture admissions to a Level I trauma center. Fracture displacement, comminution, and frontobasal type were ascertained from computed tomographic images. Pretreatment characteristics of operative orbital roof fractures were compared to those of nonoperative fractures. Risk factors for ophthalmologic complications were assessed using univariable/multivariable regression analyses. RESULTS: In total, 225 patients fulfilled the inclusion criteria. Fractures were most commonly nondisplaced [n = 118 (52.4 percent)] and/or of type II frontobasal pattern (linear vault involving) [n = 100 (48.5 percent)]. Eight patients underwent open reduction and internal fixation of their orbital roof fractures (14.0 percent of displaced fractures). All repairs took place within 10 days from injury. Traumatic optic neuropathy [n = 19 (12.3 percent)] and retrobulbar hematoma [n = 11 (7.1 percent)] were the most common ophthalmologic complications, and led to long-term visual impairment in 51.6 percent of cases. CONCLUSIONS: Most orbital roof fractures can be managed conservatively, with no patients in this cohort incurring long-term fracture-related complications or returning for secondary treatment. Early fracture treatment is safe and may be beneficial in patients with vertical dysmotility, globe malposition, and/or a defect surface area larger than 4 cm2. Ophthalmologic prognosis is generally favorable; however, traumatic optic neuropathy is major cause of worse visual outcome in this population. CLINICAL QUESTION/LEVEL OF EVIDENCE: Risk, III.

Differential susceptibility of retinal ganglion cell subtypes in acute and chronic models of injury and disease.

Retinal ganglion cells (RGCs) are a heterogeneous population of neurons, comprised of numerous subtypes that work synchronously to transmit visual information to the brain. In blinding disorders such as glaucoma, RGCs are the main cell type to degenerate and lead to loss of vision. Previous studies have identified and characterized a variety of RGC subtypes in animal models, although only a handful of studies demonstrate the differential loss of these RGC subtypes in response to disease or injury. Thus, efforts of the current study utilized both chronic (bead occlusion) and acute (optic nerve crush, ONC) rat models to characterize disease response and differential loss of RGC subtypes. Bead occlusion and ONC retinas demonstrated significant RGC loss, glial reactivity and apoptosis compared to control retinas. Importantly, bead occlusion and ONC retinas resulted in differential subtype-specific loss of RGCs, with a high susceptibility for alpha- and direction selective-RGCs and preferential survival of ipRGCs. Results of this study serve as an important foundation for future experiments focused on the mechanisms resulting in the loss of RGCs in optic neuropathies, as well as the development of targeted therapeutics for RGC subtype-specific neuroprotection.

Protective Efficacy of a Dietary Supplement Based on Forskolin, Homotaurine, Spearmint Extract, and Group B Vitamins in a Mouse Model of Optic Nerve Injury.

Glaucoma is a multifactorial blinding disease with a major inflammatory component ultimately leading to apoptotic retinal ganglion cell (RGC) death. Pharmacological treatments lowering intraocular pressure can help slow or prevent vision loss although the damage caused by glaucoma cannot be reversed. Recently, nutritional approaches have been evaluated for their efficacy in preventing degenerative events in the retina although mechanisms underlying their effectiveness remain to be elucidated. Here, we evaluated the efficacy of a diet supplement consisting of forskolin, homotaurine, spearmint extract, and vitamins of the B group in counteracting retinal dysfunction in a mouse model of optic nerve crush (ONC) used as an in vivo model of glaucoma. After demonstrating that ONC did not affect retinal vasculature by fluorescein angiography, we determined the effect of the diet supplement on the photopic negative response (PhNR) whose amplitude is strictly related to RGC integrity and is therefore drastically reduced in concomitance with RGC death. We found that the diet supplementation prevents the reduction of PhNR amplitude (p < 0.001) and concomitantly counteracts RGC death, as in supplemented mice, RGC number assessed immunohistochemically is significantly higher than that in non-supplemented animals (p < 0.01). Major determinants of the protective efficacy of the compound are due to a reduction of ONC-associated cytokine secretion leading to decreased levels of apoptotic markers that in supplemented mice are significantly lower than in non-supplemented animals (p < 0.001), ultimately causing RGC survival and ameliorated visual dysfunction. Overall, our data suggest that the above association of compounds plays a neuroprotective role in this mouse model of glaucoma thus offering a new perspective in inflammation-associated neurodegenerative diseases of the inner retina.

RETRACTED: Arbutin attenuates hydrogen peroxide-induced oxidative injury through regulation of microRNA-29a in retinal ganglion cells.

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Editor-in-Chief as panels from Figures 1D, 2E and 4E appear similar to each other. Given the comments of Dr Elisabeth Bik regarding this article "As previously described by Christopher …, the Western blot bands in all 400+ papers are all very regularly spaced and have a smooth appearance in the shape of a dumbbell or tadpole, without any of the usual smudges or stains", the journal requested the authors to provide the raw data. However, the authors were not able to fulfil this request.

Neuroprotective Effects of HSF1 in Retinal Ischemia-Reperfusion Injury.

Purpose: Retinal ischemia, a common cause of several vision-threatening diseases, contributes to the death of retinal neurons, particularly retinal ganglion cells (RGCs). Heat shock transcription factor 1 (HSF1), a stress-responsive protein, has been shown to be important in response to cellular stress stimuli, including ischemia. This study is to investigate whether HSF1 has a role in retinal neuronal injury in a mouse model of retinal ischemia-reperfusion (IR). Methods: IR was induced by inserting an infusion needle into the anterior chamber of the right eye and elevating a saline reservoir connected to the needle to raise the intraocular pressure to 110 mm Hg for 45 minutes. HSF1, Hsp70, molecules in the endoplasmic reticulum (ER) stress branches, tau phosphorylation, inflammatory molecules, and RGC injury were determined by immunohistochemistry, Western blot, or quantitative PCR. Results: HSF1 expression was significantly increased in the retina 6 hours after IR. Using our novel transgenic mice carrying full-length human HSF gene, we demonstrated that IR-induced retinal neuronal apoptosis and necroptosis were abrogated 12 hours after IR. RGCs and their function were preserved in the HSF1 transgenic mice 7 days after IR. Mechanistically, the beneficial effects of HSF1 may be mediated by its induction of chaperone protein Hsp70 and alleviation of ER stress, leading to decreased tau phosphorylation and attenuated inflammatory response 12 to 24 hours after IR. Conclusions: These data provide compelling evidence that HSF1 is neuroprotective against retinal IR injury, and boosting HSF1 expression may be a beneficial strategy to limit neuronal degeneration in retinal diseases.

Endoscopic Endonasal Removal of Primary/Recurrent Meningiomas in the Medial Optic Canal: Surgical Technique and Long-Term Visual Outcome.

BACKGROUND: Tuberculum sellae meningiomas frequently extend into the optic canals, which leads to a progressive longitudinal visual loss. Therefore, in addition to tumor removal, unroofing and exploration inside the optic canal are important procedures. OBJECTIVE: To perform endoscopic endonasal tumor removal with optic canal decompression for small primary or recurrent meningiomas associated with a progressive visual loss at the inferior-medial optic canal, which corresponded to a blind corner in the ipsilateral pterional/subfrontal approach. METHODS: We retrospectively reviewed 2 cases of primary meningiomas that arose in the inferior-medial optic canal and 4 recurrent cases from the remnant inside the medial optic canal that had previously undergone craniotomy for tuberculum sellae meningiomas, and were treated by the endoscopic endonasal approach. RESULTS: All tumors were detectable and could be removed without manipulation of the affected optic nerve. The average maximum diameter of the tumor was 8.4 mm (range: 5-12 mm). Two patients who had a long history of progressive visual disturbance and papillary atrophy did not recover from severe visual disturbances postoperatively. However, others showed considerable improvement, maintaining postoperative visual function during follow-up. There were no postoperative complications. CONCLUSION: Endoscopic endonasal approach has several advantages for meningiomas in the medial optic canal and associated with progressive visual disturbance. In surgery of tuberculum sellae meningiomas, optic canal decompression and exploration inside the optic canal are important procedures to avoid symptomatic recurrence, which may be facilitated by the endoscopic endonasal approach. Papillary atrophy and duration of visual deterioration are predictive factors for postoperative visual outcomes.

PR1P ameliorates neurodegeneration through activation of VEGF signaling pathway and remodeling of the extracellular environment.

Neurodegenerative diseases affect millions of people worldwide. Optic neuropathies are the most commonly occurring neurodegenerative diseases, characterized by progressive retinal ganglion cell (RGC) degeneration. We recently reported that Prominin-1, a protein found on the surface of stem cells, interacts with VEGF and enhances its activity. VEGF is known to have various protective roles in the nervous system. Subsequently, we have developed a 12-mer peptide derived from Prominin-1, named PR1P, and investigated its effects on neuronal survival of damaged RGCs in a rat model of optic nerve crush (ONC). PR1P prevented RGC apoptosis resulting in improvement of retinal function in the rat ONC model. PR1P treatment significantly increased phosphorylation of ERK and AKT and expression its downstream proteins c-fos and Egr-1 in the retina. Additionally, PR1P beneficially increased the MMP-9/TIMP-1 ratio and promoted glial activation in the retina of ONC rats. Thus, PR1P displayed neuroprotective effects through enhanced VEGF-driven neuronal survival and reconstruction of the extracellular environment in ONC model. Our data indicate that PR1P may be a promising new clinical candidate for the treatment of neurodegenerative diseases.

Three-dimensional biomimetic head model as a platform for thermal testing of protective goggles for prevention of eye injuries.

BACKGROUND: The rate of eye injury is steadily rising during military conflicts of the century, with thermal burns being the most common type of injury to the eyes. The present study focuses on assessing the heat resistance properties of military protective goggles using three-dimensional (3D) finite element head modeling fitted with the tested protective gear. METHODS: A computational thermal impact was applied onto a 3D biomimetic human head model fitted with two goggle models - sports (Type 1) and square (Type 2). The resultant temperature of the eye tissues and the thermal injury thresholds were calculated by using the modeling, hence allowing to determine the protective efficacy of the goggles objectively, in a standardized, quantitative and cost-effective manner. FINDINGS: Both types of goggles had a dramatic protective effect on the eyes. The specific goggle geometry had no notable effect on the level of protection to the inner tissues against the thermal insult. At the skin level goggles reduced temperatures by ~64% under the impact zone, with only a mild difference (10 °C) between the goggles. INTERPRETATION: Little limitations on the shape and geometry of goggles were observed and any structure of goggles can provide an adequate protection against a thermal insult (per se) to inner cranial tissues, assuming the lenses are wide and thick enough to block direct skin contact of the heat insult. It was shown that our 3D biomimetic human head model provides a practical and cost-effective tool for determining the performance level of goggles with different attributed (i.e., shapes and thermal properties).

AAV2-mediated GRP78 Transfer Alleviates Retinal Neuronal Injury by Downregulating ER Stress and Tau Oligomer Formation.

Purpose: Retinal ganglion cell (RGC) death following axonal injury occurring in traumatic optic neuropathy (TON) causes irreversible vision loss. GRP78 is a molecular chaperone that enhances protein folding and controls activation of endoplasmic reticulum (ER) stress pathways. This study determined whether adeno-associated virus (AAV)-mediated gene transfer of GRP78 protected RGCs from death in a mouse model of TON induced by optic nerve crush (ONC). Methods: ONC was induced by a transient crush of optic nerve behind the eye globe. AAV was used to deliver genes into retina. Molecules in the ER stress branches, tau oligomers, and RGC injury were determined by immunohistochemistry or Western blot. Results: Among tested AAV serotypes, AAV2 was the most efficient for delivering genes to RGCs. Intravitreal delivery of AAV2-GRP78 markedly attenuated ER stress and RGC death 3 days after ONC, and significantly improved RGC survival and function 7 days after ONC. Protein aggregation is increased during ER stress and aggregated proteins such as tau oligomers are key players in neurodegenerative diseases. AAV2-GRP78 alleviated ONC-induced increases in tau phosphorylation and oligomerization. Furthermore, tau oligomers directly induced RGC death, and blocking tau oligomers with tau oligomer monoclonal antibody (TOMA) attenuated ONC-induced RGC loss. Conclusion: These data indicate that the beneficial effect of AAV2-GRP78 is partially mediated by the reduction of misfolded tau, and provide compelling evidence that gene therapy with AAV2-GRP78 or immunotherapy with TOMA offers novel therapeutic approaches to alleviate RGC loss in TON.

Effects of Pycnogenol on cisplatin-induced optic nerve injury: an experimental study.

AIM: To determine the effects of Pycnogenol on cisplatin-induced optic nerve damage. MATERIAL AND METHOD: Totally 18 albino Wistar male rats were assigned into three groups, with six rats in each group as follows: healthy controls (HC group), only cisplatin (2.5 mg/kg) administered group (CIS group) and Pycnogenol (40 mg/kg) + cisplatin (2.5 mg/kg) administered group (PYC group). We analyzed the levels of malondialdehyde (MDA) as a marker of lipid peroxidation and oxidative stress, total glutathione (tGSH) as a marker of antioxidant status, nuclear factor-kappa B (NF-κB) and tumor necrosis factor alpha (TNF-α) as inflammatory markers, total oxidative status (TOS) and total antioxidant status (TAS) on eye tissue together with histopathological evaluation of optic nerve in an experimental model. RESULTS: In CIS group MDA, TOS, TNF-α and NF-κB levels were statistically significantly higher (p < 0.001) than HC group while tGSH and TAS levels were significantly lower (p < 0.001). On the other hand, in PYC group MDA, TOS, TNF-α and NF-κB levels were statistically significantly lower (p < 0.001) than CIS group while tGSH and TAS levels were significantly higher (p < 0.001). CONCLUSION: Pycnogenol pretreatment was highly effective in preventing augmentation of cisplatin-induced oxidative stress and inflammation in eye tissue.

Långvarigt Trendelenburgs läge kan orsaka ögonskador - Kortad operationstid i tippat läge och justering av tippningsvinkeln kan minska risken.

Risk of optic nerve injury after prolonged Trendelenburg's position Postoperative loss of vision due to acute ischaemic optic nerve injury is a rare complication following pelvic surgery. A steep Trendelenburg's position of the patient, high intraabdominal pressure and a long operative time in Trendelenburg's position are recognised risk factors associated with robot-assisted pelvic surgery. This manuscript presents the underlying pathophysiologic mechanism. Practical tips and tricks for prevention are discussed.

Optic neuropathy after anterior communicating artery aneurysm clipping: 3 cases and techniques to address a correctable pitfall.

Brain shifts following microsurgical clip ligation of anterior communicating artery (ACoA) aneurysms can lead to mechanical compression of the optic nerve by the clip. Recognition of this condition and early repositioning of clips can lead to reversal of vision loss. The authors identified 3 patients with an afferent pupillary defect following microsurgical clipping of ACoA aneurysms. Different treatment options were used for each patient. All patients underwent reexploration, and the aneurysm clips were repositioned to prevent clip-related compression of the optic nerve. Near-complete restoration of vision was achieved at the last clinic follow-up visit in all 3 patients. Clip ligation of ACoA aneurysms has the potential to cause clip-related compression of the optic nerve. Postoperative visual examination is of utmost importance, and if any changes are discovered, reexploration should be considered as repositioning of the clips may lead to resolution of visual deterioration.

Hydrogen Sulfide Protects Retinal Ganglion Cells Against Glaucomatous Injury In Vitro and In Vivo.

Purpose: Hydrogen sulfide (H2S) is recognized as a novel third signaling molecule and gaseous neurotransmitter. Recently, cell protective properties within the central nervous and cardiovascular system have been proposed. Our purpose was to analyze the expression and neuroprotective effects of H2S in experimental models of glaucoma. Methods: Elevated IOP was induced in Sprague-Dawley rats by means of episcleral vein cauterization. After 7 weeks, animals were killed and the retina was analyzed with label-free mass spectrometry. In vitro, retinal explants were exposed to elevated hydrostatic pressure or oxidative stress (H2O2), with and without addition of a slow-releasing H2S donor Morpholin-4-ium-methoxyphenyl-morpholino-phosphinodithioate (GYY4137). In vivo, GYY4137 was injected intravitreally in animals with acute ischemic injury or optic nerve crush. Brn3a+ retinal ganglion cells (RGCs) were counted in retinal flat mounts and compared. Optical coherence tomography (OCT) was performed to examine the vessels. Comparisons were made by t-test and ANOVA (P < 0.05). Results: IOP elevation caused significant RGC loss (P < 0.001); 3-mercaptosulfurtransferase, an H2S producing enzyme, showed a 3-fold upregulation within the retina after IOP elevation. GYY4137 protected RGCs against elevated pressure and oxidative stress in vitro depending on the concentration used (P < 0.005). In vivo, intravitreal administration of GYY4137 preserved RGCs from acute ischemic injury and optic nerve crush (P < 0.0001). Retinal vessel diameters enlarged after intravitreal GYY4137 injection (P < 0.0001). Conclusions: H2S is specifically regulated in experimental glaucoma. By scavenging reactive oxygen species and dilating retinal vessels, H2S may protect RGCs from pressure and oxidative stress-induced RGC loss in vitro and in vivo. Therefore, H2S might be a novel neuroprotectant in glaucoma.

Attenuation of Axonal Degeneration by Calcium Channel Inhibitors Improves Retinal Ganglion Cell Survival and Regeneration After Optic Nerve Crush.

Axonal degeneration is one of the initial steps in many traumatic and neurodegenerative central nervous system (CNS) disorders and thus a promising therapeutic target. A focal axonal lesion is followed by acute axonal degeneration (AAD) of both adjacent axon parts, before proximal and distal parts follow different degenerative fates at later time points. Blocking calcium influx by calcium channel inhibitors was previously shown to attenuate AAD after optic nerve crush (ONC). However, it remains unclear whether the attenuation of AAD also promotes consecutive axonal regeneration. Here, we used a rat ONC model to study the effects of calcium channel inhibitors on axonal degeneration, retinal ganglion cell (RGC) survival, and axonal regeneration, as well as the molecular mechanisms involved. Application of calcium channel inhibitors attenuated AAD after ONC and preserved axonal integrity as visualized by live imaging of optic nerve axons. Consecutively, this resulted in improved survival of RGCs and improved axonal regeneration at 28 days after ONC. We show further that calcium channel inhibition attenuated lesion-induced calpain activation in the proximity of the crush and inhibited the activation of the c-Jun N-terminal kinase pathway. Pro-survival signaling via Akt in the retina was also increased. Our data thus show that attenuation of AAD improves consecutive neuronal survival and axonal regeneration and that calcium channel inhibitors could be valuable tools for therapeutic interventions in traumatic and degenerative CNS disorders.

Calculation of an Optic Nerve Injury Risk Profile Before Sphenoid Sinus Surgery.

OBJECTIVES: Our objective was to analyze variations in the optic nerve (ON) course and surrounding structures in an effort to construct an optic nerve injury risk profile before endoscopic intranasal sphenoidal, or endoscopic endonasal transphenoidal, skull-base surgery, and eventually to construct and formulate a common classification by combining the known classes. The authors used computed tomography (CT) toward this end. METHODS: The authors retrospectively reviewed 200 consecutive CT scans (400 sides) of the paranasal sinuses. The pneumatization of the anterior clinoid process, the relationships of the ONs to the sphenoidal sinuses, and ON dehiscence were evaluated. The authors then created a formula by which risk profiles can be constructed for patients for whom sphenoid or parasellar surgery is planned. RESULTS: Pneumatization of the anterior clinoid process was evident in 28.25%. Dehiscence of the bony wall of the ON was evident in 9.5%. The ON course lay adjacent to the sphenoidal sinus, causing sinus wall indentation, in 23%. Cumulative optic nerve injury risk scoring showed that, radiologically, surgery on 8.5% and 1.5% of sphenoid sinuses described here carried severe or critical risk of ON injury, respectively. CONCLUSIONS: Head-and-neck surgeons and neurosurgeons should be aware of variations in ON course. The authors composed an optic nerve injury risk classification category based on the sum of individual weights of each of these classes. Reductions in ON injuries require careful evaluation of potential variant anatomies. Preoperative CT scans must be meticulously reviewed to avoid ON injury.

siRNA-Mediated Knockdown of the mTOR Inhibitor RTP801 Promotes Retinal Ganglion Cell Survival and Axon Elongation by Direct and Indirect Mechanisms.

PURPOSE: To investigate, using in vivo and in vitro models, retinal ganglion cell (RGC) neuroprotective and axon regenerative effects and underlying mechanisms of siRTP801, a translatable small-interfering RNA (siRNA) targeting the mTOR negative regulator RTP801. METHODS: Adult rats underwent optic nerve (ON) crush (ONC) followed by intravitreal siRTP801 or control siRNA (siEGFP) every 8 days, with Brn3a+ RGC survival, GFAP+ reactive gliosis, and GAP43+ regenerating axons analyzed immunohistochemically 24 days after injury. Retinal cultures, prepared from uninjured animals or 5 days after ONC to activate retinal glia, were treated with siRTP801/controls in the presence/absence of rapamycin and subsequently assessed for RGC survival and neurite outgrowth, RTP801 expression, glial responses, and mTOR activity. Conditioned medium was analyzed for neurotrophin titers by ELISA. RESULTS: Intravitreal siRTP801 enabled 82% RGC survival compared to 45% with siEGFP 24 days after ONC, correlated with greater GAP43+ axon regeneration at 400 to 1200 µm beyond the ONC site, and potentiated the reactive GFAP+ Müller glial response. In culture, siRTP801 had a direct RGC neuroprotective effect, but required GFAP+ activated glia to stimulate neurite elongation. The siRTP801-induced neuroprotection was significantly reduced, but not abolished, by rapamycin. The siRTP801 potentiated the production and release of neurotrophins NGF, NT-3, and BDNF, and prevented downregulation of RGC mTOR activity. CONCLUSIONS: The RTP801 knockdown promoted RGC survival and axon elongation after ONC, without increasing de novo regenerative sprouting. The neuroprotection was predominantly direct, with mTORC1-dependent and -independent components. Enhanced neurite/axon elongation by siRTP801 required the presence of activated retinal glia and was mediated by potentiated secretion of neurotrophic factors.

Low-dose carbon monoxide inhalation protects neuronal cells from apoptosis after optic nerve crush.

Glaucomatous optic neuropathy, including axonal degeneration and apoptotic death of retinal ganglion cells (RGCs), eventually leads to irreversible visual impairment. Carbon monoxide (CO) acts as a therapeutic agent against neural injury via its anti-apoptotic effect. Here we hypothesized that low-dose CO inhalation can protect RGCs in a rat model of optic nerve crush (ONC). ONC was performed on adult male Sprague Dawley rats to imitate glaucomatous optic damage. Low-dose CO (250 ppm) or air was inhaled for 1 h immediately after ONC, and all the tests were carried out 2 weeks later. Flash visual evoked potentials (FVEP) and pupil light relax (PLR) were recorded for the assessment of visual function. RGC density was evaluated by hematoxylin and eosin staining and Fluorogold labeling. Retinal apoptotic process was assessed by TUNEL staining and caspase-3 activity measurement. Low-dose CO treatment significantly ameliorated the abnormalities of FVEP and PLR induced by ONC. As expected, the RGC density was increased remarkably by CO inhalation after the glaucomatous optic nerve insult. Moreover, CO treatment after ONC significantly decreased the number of TUNEL-positive cells in ganglion cell layer and attenuated the retinal caspase-3 activity. Low-dose CO inhalation protects RGCs from optic nerve injury via inhibiting caspase-3 dependent apoptosis.