Tackling Glaucoma from within the Brain: An Unfortunate Interplay of BDNF and TrkB

PLoS One. 2015 Nov 11;10(11):e0142067. doi: 10.1371/journal.pone.0142067. eCollection 2015.

Abstract

According to the neurotrophin deprivation hypothesis, diminished retrograde delivery of neurotrophic support during an early stage of glaucoma pathogenesis is one of the main triggers that induce retinal ganglion cell (RGC) degeneration. Therefore, interfering with neurotrophic signaling seems an attractive strategy to achieve neuroprotection. Indeed, exogenous neurotrophin administration to the eye has been shown to reduce loss of RGCs in animal models of glaucoma; however, the neuroprotective effect was mostly insufficient for sustained RGC survival. We hypothesized that treatment at the level of neurotrophin-releasing brain areas might be beneficial, as signaling pathways activated by target-derived neurotrophins are suggested to differ from pathways that are initiated at the soma membrane. In our study, first, the spatiotemporal course of RGC degeneration was characterized in mice subjected to optic nerve crush (ONC) or laser induced ocular hypertension (OHT). Subsequently, the well-known neurotrophin brain-derived neurotrophic factor (BDNF) was chosen as the lead molecule, and the levels of BDNF and its high-affinity receptor, tropomyosin receptor kinase B (TrkB), were examined in the mouse retina and superior colliculus (SC) upon ONC and OHT. Both models differentially influenced BDNF and TrkB levels. Next, we aimed for RGC protection through viral vector-mediated upregulation of collicular BDNF, thought to boost the retrograde neurotrophin delivery. Although the previously reported temporary neuroprotective effect of intravitreally delivered recombinant BDNF was confirmed, viral vector-induced BDNF overexpression in the SC did not result in protection of the RGCs in the glaucoma models used. These findings most likely relate to decreased neurotrophin responsiveness upon vector-mediated BDNF overexpression. Our results highlight important insights concerning the complexity of neurotrophic factor treatments that should surely be considered in future neuroprotective strategies.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Brain / drug effects
  • Brain / metabolism*
  • Brain-Derived Neurotrophic Factor / genetics
  • Brain-Derived Neurotrophic Factor / metabolism*
  • Brain-Derived Neurotrophic Factor / pharmacology
  • Disease Models, Animal
  • Glaucoma / metabolism*
  • Glaucoma / pathology
  • HEK293 Cells
  • Humans
  • Intraocular Pressure / drug effects
  • Mice
  • Nerve Crush
  • Ocular Hypertension / metabolism
  • Ocular Hypertension / pathology
  • Optic Nerve Injuries / metabolism
  • Optic Nerve Injuries / pathology
  • Receptor, trkB / genetics
  • Receptor, trkB / metabolism*
  • Retinal Ganglion Cells / drug effects
  • Retinal Ganglion Cells / metabolism
  • Retinal Ganglion Cells / pathology
  • Up-Regulation

Substances

  • Brain-Derived Neurotrophic Factor
  • Receptor, trkB

Grants and funding

Eline Dekeyster is supported by a Ph.D. fellowship of the Research Foundation Flanders (FWO). This study was also supported by the Flemisch Institute for the Promotion of Scientific Research (IWT) [SBO Optobrain 110086], and the Belgian Fonds for Research in Ophtalmology (FRO).