Does elevated intraocular pressure reduce retinal TRKB-mediated survival signaling in experimental glaucoma?

Ying Guo, Elaine Johnson, William Cepurna, Lijun Jia, Jennifer Dyck, John Morrison

Research output: Contribution to journalArticle

32 Citations (Scopus)

Abstract

Reduced retrograde transport of neurotrophins (NT) and their receptors has been hypothesized to contribute directly to retinal ganglion cell (RGC) loss in glaucoma. However, strategies of supplementing NT and NT receptors have failed to avert ultimate RGC death in experimental glaucoma. This study examines the response of major components of the NT system and their interacting proteins in a rat glaucoma model. Unilateral chronic intraocular pressure (IOP) elevation was produced by episcleral vein injection of hypertonic saline (N = 99). Retinas were collected and grouped by extent of optic nerve injury. Quantitative reverse transcription PCR, western blot analysis and immunohistochemistry were used to determine mRNA and protein levels and protein localization. Out of three RGC-specific Brn3 proteins (Brn3a, b, and c), only Brn3a was significantly downregulated at the message level to 35 ± 4% of fellow values with the severest nerve injury. With IOP elevation, no significant alterations were found in retinal mRNA levels for BDNF, NGF, NT-4/5 or NT-3. The abundance of mature retinal BDNF protein was not significantly affected by elevated IOP, while proBDNF protein decreased linearly with increasing injury grade (r2 = 0.50). In retinas with the severest nerve injury, TrkB and TrkC receptor mRNA levels significantly declined to 67 ± 9% and 44 ± 5% of fellow values, respectively. However, the levels of TRKB protein and its phosphorylated form were unchanged. Message level for p75NTR was linearly upregulated up to 219 ± 26% with increasing injury (r2 = 0.46), but no alteration was detected at protein level. The mRNA expression of p75NTR apoptosis adaptor proteins NADE, NRIF, and Lingo1 were significantly downregulated in retinas with the greatest nerve injury. A positive correlation was found between injury extent and message levels for Jun (r2 = 0.23) as well as Junb (r2 = 0.27), and RGC labeling of activated JUN protein increased. Atf3 mRNA levels demonstrated a positive linear correlation to the extent of injury (r2 = 0.53), resulting in a nearly five-fold increase (482 ± 76%) in eyes with the greatest nerve damage. Among downstream pro-survival signaling components, Erk5 mRNA expression was linearly upregulated (r2 = 0.32) up to 157 ± 15% of fellow values in retinas with the severest nerve injury (p 2 = 0.12). Bcl-xl mRNA levels in the most severely injured retinas were significantly reduced to 83 ± 7% by elevated IOP exposure. Message levels for Erk1/2, Akt1-3 or Bcl2 appeared unaffected. Elevated IOP did not alter mRNA levels of pro-apoptotic Bim, Bax, or p53. This study demonstrates that elevated IOP exposure does not result in a dramatic decrease in retinal levels of either BDNF or its receptor, TrkB. It shows that the responses of NT pathways to elevated IOP are complex, particularly with regard to the role of p75NTR and Atf3. A better understanding of the roles of these proteins in IOP-induced injury is likely to suggest informed strategies for neuroprotection in glaucoma.

Original languageEnglish (US)
Pages (from-to)921-933
Number of pages13
JournalExperimental Eye Research
Volume89
Issue number6
DOIs
StatePublished - Dec 2009

Fingerprint

Intraocular Pressure
Glaucoma
Messenger RNA
Wounds and Injuries
Retinal Ganglion Cells
Proteins
Retina
Brain-Derived Neurotrophic Factor
Nerve Growth Factors
trkB Receptor
Nerve Growth Factor Receptors
trkC Receptor
Down-Regulation
Optic Nerve Injuries
Neurotrophin 3
Nerve Growth Factor
Reverse Transcription
Veins
Cell Death
Western Blotting

Keywords

  • Atf3
  • experimental glaucoma
  • IOP elevation
  • neurotrophin
  • p75
  • Trk receptor

ASJC Scopus subject areas

  • Ophthalmology
  • Sensory Systems
  • Cellular and Molecular Neuroscience

Cite this

Does elevated intraocular pressure reduce retinal TRKB-mediated survival signaling in experimental glaucoma? / Guo, Ying; Johnson, Elaine; Cepurna, William; Jia, Lijun; Dyck, Jennifer; Morrison, John.

In: Experimental Eye Research, Vol. 89, No. 6, 12.2009, p. 921-933.

Research output: Contribution to journalArticle

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abstract = "Reduced retrograde transport of neurotrophins (NT) and their receptors has been hypothesized to contribute directly to retinal ganglion cell (RGC) loss in glaucoma. However, strategies of supplementing NT and NT receptors have failed to avert ultimate RGC death in experimental glaucoma. This study examines the response of major components of the NT system and their interacting proteins in a rat glaucoma model. Unilateral chronic intraocular pressure (IOP) elevation was produced by episcleral vein injection of hypertonic saline (N = 99). Retinas were collected and grouped by extent of optic nerve injury. Quantitative reverse transcription PCR, western blot analysis and immunohistochemistry were used to determine mRNA and protein levels and protein localization. Out of three RGC-specific Brn3 proteins (Brn3a, b, and c), only Brn3a was significantly downregulated at the message level to 35 ± 4{\%} of fellow values with the severest nerve injury. With IOP elevation, no significant alterations were found in retinal mRNA levels for BDNF, NGF, NT-4/5 or NT-3. The abundance of mature retinal BDNF protein was not significantly affected by elevated IOP, while proBDNF protein decreased linearly with increasing injury grade (r2 = 0.50). In retinas with the severest nerve injury, TrkB and TrkC receptor mRNA levels significantly declined to 67 ± 9{\%} and 44 ± 5{\%} of fellow values, respectively. However, the levels of TRKB protein and its phosphorylated form were unchanged. Message level for p75NTR was linearly upregulated up to 219 ± 26{\%} with increasing injury (r2 = 0.46), but no alteration was detected at protein level. The mRNA expression of p75NTR apoptosis adaptor proteins NADE, NRIF, and Lingo1 were significantly downregulated in retinas with the greatest nerve injury. A positive correlation was found between injury extent and message levels for Jun (r2 = 0.23) as well as Junb (r2 = 0.27), and RGC labeling of activated JUN protein increased. Atf3 mRNA levels demonstrated a positive linear correlation to the extent of injury (r2 = 0.53), resulting in a nearly five-fold increase (482 ± 76{\%}) in eyes with the greatest nerve damage. Among downstream pro-survival signaling components, Erk5 mRNA expression was linearly upregulated (r2 = 0.32) up to 157 ± 15{\%} of fellow values in retinas with the severest nerve injury (p 2 = 0.12). Bcl-xl mRNA levels in the most severely injured retinas were significantly reduced to 83 ± 7{\%} by elevated IOP exposure. Message levels for Erk1/2, Akt1-3 or Bcl2 appeared unaffected. Elevated IOP did not alter mRNA levels of pro-apoptotic Bim, Bax, or p53. This study demonstrates that elevated IOP exposure does not result in a dramatic decrease in retinal levels of either BDNF or its receptor, TrkB. It shows that the responses of NT pathways to elevated IOP are complex, particularly with regard to the role of p75NTR and Atf3. A better understanding of the roles of these proteins in IOP-induced injury is likely to suggest informed strategies for neuroprotection in glaucoma.",
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