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Published in final edited form as: Exp Eye Res. 2017 Oct 12;167:25–30. doi: 10.1016/j.exer.2017.10.012

Relationship between Sigma-1 receptor and BDNF in the visual system

Barbara A Mysona 1,2,3, Jing Zhao 1,2,3, Sylvia Smith 1,2,3, Kathryn E Bollinger 1,2,3
PMCID: PMC5757370  NIHMSID: NIHMS920758  PMID: 29031856

Abstract

Glaucoma is an incurable optic neuropathy characterized by dysfunction and death of retinal ganglion cells (RGCs). Brain derived neurotrophic factor (BDNF) is an essential neurotrophin that supports RGC function and survival. Despite BDNF’s importance, our knowledge of molecular mechanisms that modulate BDNF processing and secretion is incomplete. Sigma-1 receptor (S1R) is associated with increased BDNF in hippocampus and with BDNF secretion by brain-derived astrocytes and neuronal cell lines. Much less is known about the relationship between S1R and BDNF in the visual system. Here, we examine how S1R activation and deletion alter expression of mature BDNF (mBDNF) and proBDNF in retina and cultured optic nerve head (ONH) astrocytes. For S1R activation, the S1R agonist (+)-pentazocine (PTZ, 0.5 mg/kg) was administered by intraperitoneal injection to C57BL/6J mice, 3 times per week, for 5 weeks. Expression of proBDNF and mBDNF was also examined in S1R knockout and age-matched C57BL/6J mice. In vitro, cultured ONH astrocytes were treated with 3μM PTZ for 24 hours followed by collection of media and ONH astrocyte lysates. Results showed that treatment with (+)-PTZ increased mBDNF protein in both retina and hippocampus. In contrast, S1R deletion was associated with retinal mBDNF deficits. In ONH astrocytes S1R agonist (+)-PTZ significantly increased levels of secreted BDNF and proBDNF in cell lysates. These findings support a role for S1R in the modulation of BDNF levels within the retina and optic nerve head. Treatment with S1R agonists might provide benefit in diseases such as glaucoma by increasing BDNF levels from endogenous sources.

Keywords: BDNF, retina, optic nerve head astrocytes, glaucoma

1.0 Introduction

Glaucoma is an incurable optic neuropathy and second leading cause of blindness worldwide (Quigley and Broman, 2006). Glaucoma is characterized by the death and dysfunction of retinal ganglion cells (RGCs), the final output neurons of the retina. RGC axons leave the retina at the optic nerve head (ONH) where they form the optic nerve and project to the brain. The most common risk factors for glaucoma are aging and elevated intraocular pressure (IOP) (Friedman et al., 2004; Worley and Grimmer-Somers, 2011). Because lowering IOP is currently the only treatment strategy for slowing glaucoma-induced degeneration (Gordon et al., 2002; Heijl et al., 2002; Kass et al., 2002), a great need exists to identify novel targets that will protect RGCs. Development of these new therapies depends, in part, upon expanding our understanding of molecular mechanisms that regulate expression and secretion of brain derived neurotrophic factor (BDNF), a critical factor for RGC function and survival (reviewed by (Johnson et al., 2009; Mysona BA, 2017)).

The study of BDNF within the visual system is complicated by the presence of multiple forms and sources of BDNF. BDNF is synthesized as a precursor protein, proBDNF (30–35 kD), that is proteolytically cleaved and processed to form mature BDNF (mBDNF, 14 kD) (Kolbeck et al., 1994; Suter et al., 1991; Teng et al., 2010). This cleavage occurs either intracellularly in the endoplasmic reticulum (ER) and golgi (Seidah et al., 1996), or extracellularly (Lee et al., 2001; Pang et al., 2004). Whether a cell secretes proBDNF, mBDNF, or both varies with tissue, cell type, and culture conditions (Koshimizu et al., 2009; Matsumoto et al., 2008; Yang et al., 2009). In healthy retina, BDNF is produced endogenously by RGCs and glia (Avwenagha et al., 2006; Perez and Caminos, 1995; Vecino et al., 1998) or can enter the retina via retrograde transport from the brain via RGC axons (Pease et al., 2000; Quigley et al., 2000).

The link between S1R and BDNF first became evident when several selective serotonin uptake inhibitors used as anti-depressants were shown to bind S1R and to enhance BDNF expression and signaling (Larsen et al., 2008; Narita et al., 1996; Yagasaki et al., 2006). In addition, treatment with S1R specific agonists SA4503 (Matsuno et al., 1996) and PRE-084 (Su et al., 1991) enhances BDNF expression and signaling in hippocampal regions of the brain (Kikuchi-Utsumi and Nakaki, 2008; Xu et al., 2015). In neuroblastoma cell lines, S1R has been shown to act as a chaperone associated with enhanced secretion of mature BDNF (Fujimoto et al., 2012). Whether the relationship between S1R agonists and BDNF extends to other regions within the central nervous system (CNS) is uncertain. For example, the antidepressants imipramine and fluvoxamine both enhance BDNF signaling through a S1R dependent mechanism in cortex-derived neuronal cultures. However, chronic treatment with the S1R agonist, SA4503, did not increase BDNF protein in rodent cortex (Kikuchi-Utsumi and Nakaki, 2008; Larsen et al., 2008; Matsuno et al., 1996; Narita et al., 1996; Xu et al., 2015; Yagasaki et al., 2006). Given the importance of BDNF in supporting RGC health and function in the retina and the need for neuroprotective therapies in neurodegenerative diseases such as glaucoma, we were interested in investigating the relationship between S1R and BDNF in the visual system.

In this paper, we hypothesized that S1R modulates BDNF levels within the visual system. Effects of S1R activation and deletion were examined in vivo in retina and in vitro in ONH astrocyte cultures. Results of this study showed that in vivo, S1R activation by (+)-PTZ increased mBDNF protein in retina, whereas S1R deletion caused a mBDNF deficit. In vitro, (+)-PTZ treatment of ONH astrocyte cultures increased proBDNF levels within cell lysates and stimulated cellular secretion of BDNF. Together these findings suggest that an important relationship exists between S1R and BDNF within the retina and ONH. Treatment with S1R agonists might provide benefit in diseases such as glaucoma by increasing BDNF levels from endogenous sources.

2.0 Methods

2.1 Animals and injections

Experiments requiring animals adhered to the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research and the National Institutes of Health guide for the care and use of laboratory animals. C57BL/6J (The Jackson Laboratory, Bar Harbor, Maine) and S1R-KO mice (Wang et al., 2015), ages 4–18 months, were used in experiments. Mice were kept under controlled lighting conditions (12-h light: 12-h dark). A subset of C57BL/6J mice (4 months old) received intraperitoneal injection of (+)-PTZ (Sigma-Aldrich, St. Louis, MO) 0.5 mg/kg, every other day, 3 days per week, for 5 weeks. (+)-PTZ was dissolved initially in DMSO and diluted 1:10 with 0.01M phosphate buffered saline (PBS) and administered at the final dosage of 0.5mg/kg. In addition to mice, Sprague-Dawley rat breeder pairs (ENVIGO Laboratories, Indianapolis, IN) were maintained for the generation of 3–5 day old rat pups used in the isolation and culture of ONH astrocytes.

2.2 Collection of tissue

Following euthanasia by CO2, retina and hippocampus were removed and immediately frozen over dry ice and stored at −80°C until needed.

2.3 Western blot

Tissue and cells were lysed and sonicated in radioimmunoprecipitation assay (RIPA) buffer (Sigma-Aldrich) with Halt Protease Inhibitor Cocktail (Thermo Fisher Scientific, Waltham, MA) and 2 mM sodium orthovanadate (Sigma-Aldrich) phosphatase inhibitor. Lysates were centrifuged at 14,000g for 15 minutes. Protein concentration in the supernatant was measured using the Bio-Rad DC Protein assay (Bio-Rad, Hercules, CA). Proteins were separated by electrophoresis using SDS-polyacrylamide gel (PAGE). For mBDNF (14 kD) 15% SDS-PAGE or gradient (4–20%, Bio-Rad) gels were used. Gels were transferred to a nitrocellulose membrane (Thermo Fisher Scientific). Membranes were blocked with 5% nonfat milk in Tris-buffered saline-0.1%Tween 20 (TBST) for 15–30 min at room temperature and then incubated overnight at 4°C with primary antibody. After three washes in TBST, membranes were incubated for 1.5 hour with appropriate HRP-conjugated secondary antibody in 5% milk TBST solution at room temperature. Proteins were visualized by incubating with SuperSignal West Pico chemiluminescent substrate (Thermo Fisher Scientific) or Immoblion Western Chemiluminescent HRP substrate (EMD Millipore, Billerica, MA) and quantified by densitometry with ImageJ software (Schneider et al., 2012). Blots were stripped and re-probed for loading controls, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), β-actin, or γ-tubulin. Different loading controls were required as blots were sometimes cut to facilitate probing for proteins with different molecular weights from the same blot.

2.4 BDNF ELISA

Total BDNF levels in mouse tissue were quantified using Quantikine ELISA kit for total BDNF (R&D Systems, Minneapolis, MN) per the manufacturer’s instructions. For retina 50 μl of retinal lysate containing 30 μg of total protein was loaded for each condition. BDNF in rat ONH astrocyte cell culture media was quantified using RayBio Rat BDNF ELISA Kit (RayBiotech, Norcross, GA) per the manufacturer’s instructions.

2.5 Antibodies

Antibodies were purchased from manufacturers as follows: anti-ProBDNF (AGP-031) with blocking peptide (Alomone, Jeruselem, Israel); anti-actin and anti-γ-tubulin (Sigma-Aldrich); anti-BDNF(SC-546), anti-GAPDH (sc-365062), HRP-conjugated anti-rabbit, anti-goat, and anti-mouse IgG all from Santa Cruz Biotechnology, Dallas, TX; HRP-conjugated donkey anti-guinea pig (Jackson ImmunoResearch Laboratories, West Grove, PA), goat anti-rabbit Alexa-Fluor 546 (Invitrogen, Carlsbad, CA). S1R rabbit polyclonal antibody was raised from a peptide sequence generated by the laboratory of Dr. Sylvia Smith (Ola et al., 2002).

2.6 Rat ONH astrocyte culture

Primary ONH astrocytes were isolated and cultured from 3–5 day old Sprague Dawley rat pups as published previously by our group (Zhao J, under revision) per the protocol modified from Mandal (Mandal et al., 2010) and Beckel (Beckel et al., 2014). Briefly, after sacrifice, eyes were enucleated and ONH tissue dissected proximal to the sclera and digested for 15 minutes using 0.25% trypsin (Invitrogen) at 37°C. After washing, cells were spun and resuspended in growth media of Dulbecco’s modified Eagle’s medium DMEM/F12 (Invitrogen) containing 10% heat inactivated fetal bovine serum (FBS) (Atlanta Biologicals, Atlanta, GA), 1% penicillin/streptomycin and 1% Glutamax (Invitrogen) and 25ng/ml epidermal growth factor (EGF) (Sigma-Aldrich), and plated on 0.2% gelatin (Sigma-Aldrich) coated T75 cell-culture flasks. Cells were maintained in a humidified incubator containing 5% CO2 at 37°C. Cells were passaged after 7–10 days and were used between passages 2–5. Immunocytochemistry for GFAP was performed to confirm purity of ONH astrocyte cultures as published previously by our group (Zhao J, under revision).

2.7 ONH astrocyte cell treatment

For cell culture experiments, ONH astrocytes were seeded 250,000 cells per 25 cm2 filter flask and maintained for 3 days after which cells were washed 1x with serum free DMEM F-12 with 0.1% Penn-Strep and 1% glutamax and maintained in 4 ml of serum free media with or without treatment with (+)-PTZ (3μM) for 24 hours.

2.8 ONH astrocyte collection of media and cell lysates

After 24 hours, 3.5 ml media was collected and concentrated using Amicon Ultra-4 Centrifugal filters, Ultracel – 3K (EMD Millipore). For secreted BDNF, the concentrated media was analyzed by ELISA (RayBiotech) and normalized to protein content of the corresponding cell lysate. To collect lysates, ONH astrocytes were washed 1X with PBS then lysed in 100 μl of RIPA buffer prepared as described above for Western blot and stored at −80°C for further analysis. For ONH astrocyte studies, 6 experiments using ONH astrocytes from independent isolations were used.

2.9 Statistical analysis

Statistical analysis was performed with the aid of GraphPad Prism (Prism; GraphPad Software Inc. La Jolla, CA). For comparison of two groups the unpaired t test was used with Welch’s correction for unequal variances. For multiple comparisons of groups with a normal distribution and equal variances one-way ANOVA was used followed by Tukey-Kramer post hoc test. Significance was set at P<0.05.

3.0 Results

In this study, we hypothesized that S1R activation and deletion would have the opposite effects of increasing versus decreasing BDNF levels in the visual system. Administration of the S1R agonist (+)-PTZ was used to activate S1R. C57BL/6J mice (4 weeks old) were treated for five weeks with (+)-PTZ and compared to age-matched C57BL/6J (WT) controls (Figure 1A). At end of treatment, retina and hippocampus tissues were collected and lysates analyzed by Western blot to determine whether S1R activation caused changes in expression levels of mBDNF and proBDNF proteins. We began by examining the relative level of mBDNF in hippocampus of (+)-PTZ treated mice (Figure 1B) to provide a comparison with the published finding that treatment with the S1R agonist SA4503 (Kikuchi-Utsumi and Nakaki, 2008) increases levels of mBDNF in hippocampus. Our results also showed that treatment with the S1R agonist (+)-PTZ corresponded with a significant elevation of mBDNF in hippocampus (2.04 ± 0.44 fold increase) relative to WT controls.

Figure 1. S1R activation and deletion have opposite effects on retinal BDNF levels.

Figure 1

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A) Four month old C57BL/6J mice (WT) were treated for 5 weeks with (+)-PTZ (PTZ). B) (+)-PTZ treatment significantly increased mBDNF protein in hippocampus (n=6–11, * P < 0.05) and C) retina (n=10–17, ** P < 0.01). D) ProBDNF protein was unchanged by (+)-PTZ treatment in retina but E) S1R protein was significantly increased in (+)-PTZ treated retina (n=10–17, *** P < 0.001). F) Significant mBDNF deficits were detected in retinas of SR1-KO (KO) mice compared to WT (n=11–17, * P < 0.05) G) ProBDNF protein was similar in WT and KO retinas. H) Decreased total BDNF was detected by ELISA in retinas of 5–18 month KO mice compared to age-matched WT (n=9, * P < 0.05). For Western blot, representative bands show mBDNF and proBDNF from three different WT and KO mice relative to internal protein controls actin, γ-tubulin or GAPDH. Graphs show quantification of mBDNF, proBDNF, and S1R proteins in tissue lysates for all n.

Next we examined the relative levels of mBDNF, proBDNF, and S1R in the retinas of (+)-PTZ treated mice compared to WT controls. Similar to hippocampus, retinas of (+)-PTZ treated mice showed a significant increase in mBDNF (1.57 ± 0.20 fold increase) compared to untreated controls (Figure 1C). ProBDNF protein expression in retinas of (+)-PTZ treated mice was similar to that of controls (Figure 1D). However, S1R protein levels (Figure 1E) were significantly increased in retinas of (+)-PTZ treated mice (1.75 ± 0.14 fold change).

The finding that treatment with (+)-PTZ increased mBDNF in retina prompted us to examine the effect of S1R deletion on retinal BDNF levels. Relative levels of mBDNF and proBDNF were examined in WT and KO retinas of adult (5–6mo) mice. Western blot analysis showed that KO retinas had a significant deficit in mBDNF (0.57 ± 0.06 fold decrease). In contrast, proBDNF protein was similar in both KO and WT retinas (Figure 1F and 1G, respectively). We also investigated the level of total BDNF in KO and WT retinal lysates. For this experiment, age-matched KO and WT retinal lysates from adult mice (ages 6–18 months) were examined by ELISA. Results from the pooled analyses showed that total BDNF was significantly decreased in retinal lysates of KO mice (0.51 ± 0.11 fold change) compared with their WT counterparts (Figure 1H).

Finally, we used cultured primary ONH astrocytes to investigate the effect of (+)-PTZ treatment on S1R-mediated BDNF levels at the ONH. Cultured ONH astrocytes were strongly positive for GFAP (Figure 2A). ONH astrocyte cultures were treated with (+)-PTZ (3 μM) or vehicle alone for 24 hours, after which media was concentrated and analyzed by ELISA to determine the amount of total BDNF secreted. ONH astrocyte cell lysates were also collected and analyzed by western blot for mBDNF and proBDNF protein. Treatment with (+)-PTZ significantly increased secretion of total BDNF (1.72 ± 0.27 fold change) compared to vehicle treated control astrocytes (Figure 2C). This increase was accompanied by elevated proBDNF (1.75 ± 0.30 fold increase) in ONH astrocyte cell lysates (Figure 2D). No change was observed for mBDNF or S1R proteins in (+)-PTZ treated ONH astrocyte lysates compared to controls (Figures 2E, and 2F).

Figure 2. Treatment with S1R agonist (+)-PTZ modulates BDNF in ONH astrocytes.

Figure 2

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Cultures of ONH astrocytes are positive for A) GFAP (red), DAPI (blue) B) secondary only. C) Treatment for 24 hours with (+)-PTZ significantly increased secretion of total BDNF into the media as determined by ELISA (n=14–17, * P < 0.05). Western blot analysis showed corresponding significant increase of (E) proBDNF in ONHA cell lysates (n=10–14, * P < 0.05). Although D) mature BDNF, and F) S1R proteins showed no significant differences between control and (+)-PTZ treated ONH astrocyte lysates (n=9–15).

4.0 Discussion

The main finding of this study is that S1R activation and deletion exerted the opposite actions of increasing versus decreasing BDNF levels in the visual system. Treatment with the S1R agonist, (+)-PTZ, increased the level of mBDNF in mouse retina and hippocampus. These results are consistent with the findings of increased mBDNF in the hippocampi of mice treated with the S1R agonist, SA-4503 (Kikuchi-Utsumi and Nakaki, 2008). In addition, (+)-PTZ treatment of cultured primary ONH astrocytes caused these cells to increase secretion of total BDNF. We also found a corresponding increase in proBDNF protein in astrocyte lysates. Furthermore, consistent with S1R-mediated regulation of BDNF, analysis of retinas derived from S1R-KO mice showed BDNF deficits.

The discovery that S1R agonist, (+)-PTZ, increases mBDNF in retina has important implications for glaucoma treatment. BDNF supplementation delays RGC death in rodent models of ocular hypertension (Domenici et al., 2014; Ko et al., 2001; Valiente-Soriano et al., 2015). Treatment strategies that provide a long-term source of locally supplied BDNF by means of viral vectors (Martin et al., 2003) or BDNF overexpression in transgenic mice (Feng et al., 2016), may afford better protection of RGCs than simple intravitreal injection of BDNF (Ko et al., 2001). In addition, BDNF supplementation to both eye and visual cortex appear to provide better protection of RGCs than to the eye alone (Weber et al., 2010). A therapeutic strategy using an agonist for S1R has potential to systemically enhance BDNF levels. This is especially important in the visual system where sources of BDNF include both endogenous production within the retina and retrograde transport from the brain. This study provides proof of concept for the future testing of S1R agonists as a novel treatment in rodent models of glaucoma.

In contrast to treatment with the S1R agonist (+)-PTZ, S1R-KO mice had retinal BDNF deficits. BDNF deficits are associated with visual dysfunction (Gupta et al., 2014) and S1R-KO mice display an age associated optic neuropathy typified by RGC death and decreased visual function (Ha et al., 2011). Future studies should address whether the mBDNF deficit observed in our analyses is the cause of age-related RGC death and compromised visual function previously reported in S1R-KO animals (Ha et al., 2011).

The relationship between S1R and BDNF is particularly important at the ONH. The ONH is susceptible to glaucoma-induced injury (Johnson et al., 2000; Johnson et al., 2007) and BDNF deficits have been detected in this tissue (Gupta et al., 2014). Both lamina cribrosa cells and ONH astrocytes derived from human ONH have been shown to secrete BDNF (Lambert et al., 2001; Lambert et al., 2004). In rodents, the ONH astrocyte is the major supporting cell type at the ONH (Morrison et al., 1995; Sun et al., 2009). Because of the large number of animals required to generate sufficient ONH tissue for analysis, we investigated the relationship between S1R and BDNF in cultured ONH astrocytes isolated from rats (Zhao J, under revision).

Our results showed that stimulation of S1R with (+)-PTZ increased ONH astrocyte secretion of total BDNF with a corresponding increase of proBDNF protein within ONH astrocyte cell lysates. This finding is in accord with a recent study showing that S1R agonists stimulate the release of BDNF from a human astrocyte cell line (Dalwadi et al., 2017). S1R has the potential to mediate BDNF secretion via multiple mechanisms. S1R is associated with upregulation of BDNF transcription (Larsen et al., 2008) as well as with S1R mediated chaperone activity (Fujimoto et al., 2012). BDNF is well-known to be the subject of both transcriptional (Zheng et al., 2012) and post translational (Lu et al., 2005) regulation. Whether S1R-mediated increases in BDNF levels result from a direct effect on BDNF transcription or translation, or are secondary to S1R’s known role as a modulator of oxidative (Wang et al., 2015) and ER stress (Ha et al., 2014) is not known.

In conclusion, the results of this study support the existence of an important relationship between S1R and BDNF in the visual system. The finding that S1R activation and deletion had opposite effects of increasing versus decreasing mBDNF levels has important implications for glaucoma treatment. Treatment with S1R agonists might provide benefit by increasing mBDNF levels from endogenous sources. Further studies are required to determine whether S1R agonists are an effective neuroprotective treatment for glaucoma.

Highlights.

  • Treatment with (+)-PTZ increased mBDNF protein in both retina and hippocampus.

  • S1R deletion was associated with retinal mBDNF deficits.

  • S1R agonist (+)-PTZ significantly increased secreted BDNF and proBDNF in cell lysates of optic nerve head astrocytes.

  • These findings support a role for S1R in the modulation of BDNF levels within the retina and optic nerve head.

  • Treatment with S1R agonists might provide benefit in diseases such as glaucoma by increasing BDNF levels from endogenous sources.

Acknowledgments

We would like to acknowledge our funding sources.

Funding: This work was supported by the National Institutes for Health grant 5K08EY021758-05, the James and Jean Culver Vision Discovery Institute, an American Glaucoma Society Young Clinician Scientist Award to KEB, and Augusta University.

Footnotes

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References

  1. Avwenagha O, Bird MM, Lieberman AR, Yan Q, Campbell G. Patterns of expression of brain-derived neurotrophic factor and tyrosine kinase B mRNAs and distribution and ultrastructural localization of their proteins in the visual pathway of the adult rat. Neuroscience. 2006;140:913–928. doi: 10.1016/j.neuroscience.2006.02.056. [DOI] [PubMed] [Google Scholar]
  2. Beckel JM, Argall AJ, Lim JC, Xia J, Lu W, Coffey EE, Macarak EJ, Shahidullah M, Delamere NA, Zode GS, Sheffield VC, Shestopalov VI, Laties AM, Mitchell CH. Mechanosensitive release of adenosine 5′-triphosphate through pannexin channels and mechanosensitive upregulation of pannexin channels in optic nerve head astrocytes: a mechanism for purinergic involvement in chronic strain. Glia. 2014;62:1486–1501. doi: 10.1002/glia.22695. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Dalwadi DA, Kim S, Schetz JA. Activation of the sigma-1 receptor by haloperidol metabolites facilitates brain-derived neurotrophic factor secretion from human astroglia. Neurochemistry international. 2017 doi: 10.1016/j.neuint.2017.02.003. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Domenici L, Origlia N, Falsini B, Cerri E, Barloscio D, Fabiani C, Sanso M, Giovannini L. Rescue of retinal function by BDNF in a mouse model of glaucoma. PloS one. 2014;9:e115579. doi: 10.1371/journal.pone.0115579. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Feng L, Chen H, Yi J, Troy JB, Zhang HF, Liu X. Long-Term Protection of Retinal Ganglion Cells and Visual Function by Brain-Derived Neurotrophic Factor in Mice With Ocular Hypertension. Investigative ophthalmology & visual science. 2016;57:3793–3802. doi: 10.1167/iovs.16-19825. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Friedman DS, Wilson MR, Liebmann JM, Fechtner RD, Weinreb RN. An evidence-based assessment of risk factors for the progression of ocular hypertension and glaucoma. American journal of ophthalmology. 2004;138:S19–31. doi: 10.1016/j.ajo.2004.04.058. [DOI] [PubMed] [Google Scholar]
  7. Fujimoto M, Hayashi T, Urfer R, Mita S, Su TP. Sigma-1 receptor chaperones regulate the secretion of brain-derived neurotrophic factor. Synapse. 2012;66:630–639. doi: 10.1002/syn.21549. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Gordon MO, Beiser JA, Brandt JD, Heuer DK, Higginbotham EJ, Johnson CA, Keltner JL, Miller JP, Parrish RK, 2nd, Wilson MR, Kass MA. The Ocular Hypertension Treatment Study: baseline factors that predict the onset of primary open-angle glaucoma. Arch Ophthalmol. 2002;120:714–720. doi: 10.1001/archopht.120.6.714. discussion 829-730. [DOI] [PubMed] [Google Scholar]
  9. Gupta V, You Y, Li J, Golzan M, Klistorner A, van den Buuse M, Graham S. BDNF impairment is associated with age-related changes in the inner retina and exacerbates experimental glaucoma. Biochimica et biophysica acta. 2014;1842:1567–1578. doi: 10.1016/j.bbadis.2014.05.026. [DOI] [PubMed] [Google Scholar]
  10. Ha Y, Saul A, Tawfik A, Williams C, Bollinger K, Smith R, Tachikawa M, Zorrilla E, Ganapathy V, Smith SB. Late-onset inner retinal dysfunction in mice lacking sigma receptor 1 (sigmaR1) Investigative ophthalmology & visual science. 2011;52:7749–7760. doi: 10.1167/iovs.11-8169. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Ha Y, Shanmugam AK, Markand S, Zorrilla E, Ganapathy V, Smith SB. Sigma receptor 1 modulates ER stress and Bcl2 in murine retina. Cell Tissue Res. 2014;356:15–27. doi: 10.1007/s00441-013-1774-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Heijl A, Leske MC, Bengtsson B, Hyman L, Hussein M. Reduction of intraocular pressure and glaucoma progression: results from the Early Manifest Glaucoma Trial. Arch Ophthalmol. 2002;120:1268–1279. doi: 10.1001/archopht.120.10.1268. [DOI] [PubMed] [Google Scholar]
  13. Huang EJ, Reichardt LF. Trk receptors: roles in neuronal signal transduction. Annu Rev Biochem. 2003;72:609–642. doi: 10.1146/annurev.biochem.72.121801.161629. [DOI] [PubMed] [Google Scholar]
  14. Johnson EC, Deppmeier LM, Wentzien SK, Hsu I, Morrison JC. Chronology of optic nerve head and retinal responses to elevated intraocular pressure. Investigative ophthalmology & visual science. 2000;41:431–442. [PubMed] [Google Scholar]
  15. Johnson EC, Guo Y, Cepurna WO, Morrison JC. Neurotrophin roles in retinal ganglion cell survival: lessons from rat glaucoma models. Experimental eye research. 2009;88:808–815. doi: 10.1016/j.exer.2009.02.004. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Johnson EC, Jia L, Cepurna WO, Doser TA, Morrison JC. Global changes in optic nerve head gene expression after exposure to elevated intraocular pressure in a rat glaucoma model. Investigative ophthalmology & visual science. 2007;48:3161–3177. doi: 10.1167/iovs.06-1282. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Kass MA, Heuer DK, Higginbotham EJ, Johnson CA, Keltner JL, Miller JP, Parrish RK, 2nd, Wilson MR, Gordon MO. The Ocular Hypertension Treatment Study: a randomized trial determines that topical ocular hypotensive medication delays or prevents the onset of primary open-angle glaucoma. Arch Ophthalmol. 2002;120:701–713. doi: 10.1001/archopht.120.6.701. discussion 829-730. [DOI] [PubMed] [Google Scholar]
  18. Kikuchi-Utsumi K, Nakaki T. Chronic treatment with a selective ligand for the sigma-1 receptor chaperone, SA4503, up-regulates BDNF protein levels in the rat hippocampus. Neurosci Lett. 2008;440:19–22. doi: 10.1016/j.neulet.2008.05.055. [DOI] [PubMed] [Google Scholar]
  19. Ko ML, Hu DN, Ritch R, Sharma SC, Chen CF. Patterns of retinal ganglion cell survival after brain-derived neurotrophic factor administration in hypertensive eyes of rats. Neurosci Lett. 2001;305:139–142. doi: 10.1016/s0304-3940(01)01830-4. [DOI] [PubMed] [Google Scholar]
  20. Kolbeck R, Jungbluth S, Barde YA. Characterisation of neurotrophin dimers and monomers. Eur J Biochem. 1994;225:995–1003. doi: 10.1111/j.1432-1033.1994.0995b.x. [DOI] [PubMed] [Google Scholar]
  21. Koshimizu H, Kiyosue K, Hara T, Hazama S, Suzuki S, Uegaki K, Nagappan G, Zaitsev E, Hirokawa T, Tatsu Y, Ogura A, Lu B, Kojima M. Multiple functions of precursor BDNF to CNS neurons: negative regulation of neurite growth, spine formation and cell survival. Mol Brain. 2009;2:27. doi: 10.1186/1756-6606-2-27. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Lambert W, Agarwal R, Howe W, Clark AF, Wordinger RJ. Neurotrophin and neurotrophin receptor expression by cells of the human lamina cribrosa. Investigative ophthalmology & visual science. 2001;42:2315–2323. [PubMed] [Google Scholar]
  23. Lambert WS, Clark AF, Wordinger RJ. Effect of exogenous neurotrophins on Trk receptor phosphorylation, cell proliferation, and neurotrophin secretion by cells isolated from the human lamina cribrosa. Mol Vis. 2004;10:289–296. [PubMed] [Google Scholar]
  24. Larsen MH, Hay-Schmidt A, Ronn LC, Mikkelsen JD. Temporal expression of brain-derived neurotrophic factor (BDNF) mRNA in the rat hippocampus after treatment with selective and mixed monoaminergic antidepressants. European journal of pharmacology. 2008;578:114–122. doi: 10.1016/j.ejphar.2007.08.050. [DOI] [PubMed] [Google Scholar]
  25. Lee R, Kermani P, Teng KK, Hempstead BL. Regulation of cell survival by secreted proneurotrophins. Science. 2001;294:1945–1948. doi: 10.1126/science.1065057. [DOI] [PubMed] [Google Scholar]
  26. Lu B, Pang PT, Woo NH. The yin and yang of neurotrophin action. Nat Rev Neurosci. 2005;6:603–614. doi: 10.1038/nrn1726. [DOI] [PubMed] [Google Scholar]
  27. Mandal A, Shahidullah M, Delamere NA. Hydrostatic pressure-induced release of stored calcium in cultured rat optic nerve head astrocytes. Investigative ophthalmology & visual science. 2010;51:3129–3138. doi: 10.1167/iovs.09-4614. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Martin KR, Quigley HA, Zack DJ, Levkovitch-Verbin H, Kielczewski J, Valenta D, Baumrind L, Pease ME, Klein RL, Hauswirth WW. Gene therapy with brain-derived neurotrophic factor as a protection: retinal ganglion cells in a rat glaucoma model. Investigative ophthalmology & visual science. 2003;44:4357–4365. doi: 10.1167/iovs.02-1332. [DOI] [PubMed] [Google Scholar]
  29. Matsumoto T, Rauskolb S, Polack M, Klose J, Kolbeck R, Korte M, Barde YA. Biosynthesis and processing of endogenous BDNF: CNS neurons store and secrete BDNF, not pro-BDNF. Nat Neurosci. 2008;11:131–133. doi: 10.1038/nn2038. [DOI] [PubMed] [Google Scholar]
  30. Matsuno K, Nakazawa M, Okamoto K, Kawashima Y, Mita S. Binding properties of SA4503, a novel and selective sigma 1 receptor agonist. European journal of pharmacology. 1996;306:271–279. doi: 10.1016/0014-2999(96)00201-4. [DOI] [PubMed] [Google Scholar]
  31. Morrison J, Farrell S, Johnson E, Deppmeier L, Moore CG, Grossmann E. Structure and composition of the rodent lamina cribrosa. Experimental eye research. 1995;60:127–135. doi: 10.1016/s0014-4835(95)80002-6. [DOI] [PubMed] [Google Scholar]
  32. Mysona BAZJ, Bollinger KE. Role of BDNF/TrkB pathway in the visual system: therapeutic implications for glaucoma. Expert Review of Ophthalmology. 2017;12:69–81. doi: 10.1080/17469899.2017.1259566. [DOI] [PMC free article] [PubMed] [Google Scholar]
  33. Narita N, Hashimoto K, Tomitaka S, Minabe Y. Interactions of selective serotonin reuptake inhibitors with subtypes of sigma receptors in rat brain. European journal of pharmacology. 1996;307:117–119. doi: 10.1016/0014-2999(96)00254-3. [DOI] [PubMed] [Google Scholar]
  34. Ola MS, Moore P, Maddox D, El-Sherbeny A, Huang W, Roon P, Agarwal N, Ganapathy V, Smith SB. Analysis of sigma receptor (sigmaR1) expression in retinal ganglion cells cultured under hyperglycemic conditions and in diabetic mice. Brain Res Mol Brain Res. 2002;107:97–107. doi: 10.1016/s0169-328x(02)00444-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  35. Pang PT, Teng HK, Zaitsev E, Woo NT, Sakata K, Zhen S, Teng KK, Yung WH, Hempstead BL, Lu B. Cleavage of proBDNF by tPA/plasmin is essential for long-term hippocampal plasticity. Science. 2004;306:487–491. doi: 10.1126/science.1100135. [DOI] [PubMed] [Google Scholar]
  36. Pease ME, McKinnon SJ, Quigley HA, Kerrigan-Baumrind LA, Zack DJ. Obstructed axonal transport of BDNF and its receptor TrkB in experimental glaucoma. Investigative ophthalmology & visual science. 2000;41:764–774. [PubMed] [Google Scholar]
  37. Perez MT, Caminos E. Expression of brain-derived neurotrophic factor and of its functional receptor in neonatal and adult rat retina. Neurosci Lett. 1995;183:96–99. doi: 10.1016/0304-3940(94)11123-z. [DOI] [PubMed] [Google Scholar]
  38. Quigley HA, Broman AT. The number of people with glaucoma worldwide in 2010 and 2020. Br J Ophthalmol. 2006;90:262–267. doi: 10.1136/bjo.2005.081224. [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Quigley HA, McKinnon SJ, Zack DJ, Pease ME, Kerrigan-Baumrind LA, Kerrigan DF, Mitchell RS. Retrograde axonal transport of BDNF in retinal ganglion cells is blocked by acute IOP elevation in rats. Investigative ophthalmology & visual science. 2000;41:3460–3466. [PubMed] [Google Scholar]
  40. Rodriguez-Tebar A, Dechant G, Barde YA. Binding of brain-derived neurotrophic factor to the nerve growth factor receptor. Neuron. 1990;4:487–492. doi: 10.1016/0896-6273(90)90107-q. [DOI] [PubMed] [Google Scholar]
  41. Schneider CA, Rasband WS, Eliceiri KW. NIH Image to ImageJ: 25 years of image analysis. Nature methods. 2012;9:671–675. doi: 10.1038/nmeth.2089. [DOI] [PMC free article] [PubMed] [Google Scholar]
  42. Seidah NG, Benjannet S, Pareek S, Chretien M, Murphy RA. Cellular processing of the neurotrophin precursors of NT3 and BDNF by the mammalian proprotein convertases. FEBS letters. 1996;379:247–250. doi: 10.1016/0014-5793(95)01520-5. [DOI] [PubMed] [Google Scholar]
  43. Su TP, Wu XZ, Cone EJ, Shukla K, Gund TM, Dodge AL, Parish DW. Sigma compounds derived from phencyclidine: identification of PRE-084, a new, selective sigma ligand. J Pharmacol Exp Ther. 1991;259:543–550. [PubMed] [Google Scholar]
  44. Sun D, Lye-Barthel M, Masland RH, Jakobs TC. The morphology and spatial arrangement of astrocytes in the optic nerve head of the mouse. J Comp Neurol. 2009;516:1–19. doi: 10.1002/cne.22058. [DOI] [PMC free article] [PubMed] [Google Scholar]
  45. Suter U, Heymach JV, Jr, Shooter EM. Two conserved domains in the NGF propeptide are necessary and sufficient for the biosynthesis of correctly processed and biologically active NGF. EMBO J. 1991;10:2395–2400. doi: 10.1002/j.1460-2075.1991.tb07778.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  46. Teng HK, Teng KK, Lee R, Wright S, Tevar S, Almeida RD, Kermani P, Torkin R, Chen ZY, Lee FS, Kraemer RT, Nykjaer A, Hempstead BL. ProBDNF induces neuronal apoptosis via activation of a receptor complex of p75NTR and sortilin. J Neurosci. 2005;25:5455–5463. doi: 10.1523/JNEUROSCI.5123-04.2005. [DOI] [PMC free article] [PubMed] [Google Scholar]
  47. Teng KK, Felice S, Kim T, Hempstead BL. Understanding proneurotrophin actions: Recent advances and challenges. Dev Neurobiol. 2010;70:350–359. doi: 10.1002/dneu.20768. [DOI] [PMC free article] [PubMed] [Google Scholar]
  48. Valiente-Soriano FJ, Nadal-Nicolas FM, Salinas-Navarro M, Jimenez-Lopez M, Bernal-Garro JM, Villegas-Perez MP, Agudo-Barriuso M, Vidal-Sanz M. BDNF Rescues RGCs But Not Intrinsically Photosensitive RGCs in Ocular Hypertensive Albino Rat Retinas. Investigative ophthalmology & visual science. 2015;56:1924–1936. doi: 10.1167/iovs.15-16454. [DOI] [PubMed] [Google Scholar]
  49. Vecino E, Caminos E, Ugarte M, Martin-Zanca D, Osborne NN. Immunohistochemical distribution of neurotrophins and their receptors in the rat retina and the effects of ischemia and reperfusion. Gen Pharmacol. 1998;30:305–314. doi: 10.1016/s0306-3623(97)00361-3. [DOI] [PubMed] [Google Scholar]
  50. Wang J, Shanmugam A, Markand S, Zorrilla E, Ganapathy V, Smith SB. Sigma 1 receptor regulates the oxidative stress response in primary retinal Muller glial cells via NRF2 signaling and system xc(−), the Na(+)-independent glutamate-cystine exchanger. Free radical biology & medicine. 2015;86:25–36. doi: 10.1016/j.freeradbiomed.2015.04.009. [DOI] [PMC free article] [PubMed] [Google Scholar]
  51. Weber AJ, Viswanathan S, Ramanathan C, Harman CD. Combined application of BDNF to the eye and brain enhances ganglion cell survival and function in the cat after optic nerve injury. Investigative ophthalmology & visual science. 2010;51:327–334. doi: 10.1167/iovs.09-3740. [DOI] [PMC free article] [PubMed] [Google Scholar]
  52. Worley A, Grimmer-Somers K. Risk factors for glaucoma: what do they really mean? Aust J Prim Health. 2011;17:233–239. doi: 10.1071/PY10042. [DOI] [PubMed] [Google Scholar]
  53. Xu Q, Ji XF, Chi TY, Liu P, Jin G, Gu SL, Zou LB. Sigma 1 receptor activation regulates brain-derived neurotrophic factor through NR2A-CaMKIV-TORC1 pathway to rescue the impairment of learning and memory induced by brain ischaemia/reperfusion. Psychopharmacology. 2015;232:1779–1791. doi: 10.1007/s00213-014-3809-6. [DOI] [PubMed] [Google Scholar]
  54. Yagasaki Y, Numakawa T, Kumamaru E, Hayashi T, Su TP, Kunugi H. Chronic antidepressants potentiate via sigma-1 receptors the brain-derived neurotrophic factor-induced signaling for glutamate release. The Journal of biological chemistry. 2006;281:12941–12949. doi: 10.1074/jbc.M508157200. [DOI] [PubMed] [Google Scholar]
  55. Yang J, Siao CJ, Nagappan G, Marinic T, Jing D, McGrath K, Chen ZY, Mark W, Tessarollo L, Lee FS, Lu B, Hempstead BL. Neuronal release of proBDNF. Nat Neurosci. 2009;12:113–115. doi: 10.1038/nn.2244. [DOI] [PMC free article] [PubMed] [Google Scholar]
  56. Zhao J, MB, Gonsalvez GB, Smith SB, Bollinger KE. Sigma 1 receptor regulates ERK activation and promotes survival of optic nerve head astrocytes. PloS one. doi: 10.1371/journal.pone.0184421. under revision. (under revieion) [DOI] [PMC free article] [PubMed] [Google Scholar]
  57. Zheng F, Zhou X, Moon C, Wang H. Regulation of brain-derived neurotrophic factor expression in neurons. International journal of physiology, pathophysiology and pharmacology. 2012;4:188–200. [PMC free article] [PubMed] [Google Scholar]

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