Macroglia-derived thrombospondin 2 regulates alterations of presynaptic proteins of retinal neurons following elevated hydrostatic pressure

PLoS One. 2017 Sep 27;12(9):e0185388. doi: 10.1371/journal.pone.0185388. eCollection 2017.

Abstract

Many studies on retinal injury and repair following elevated intraocular pressure suggest that the survival ratio of retinal neurons has been improved by various measures. However, the visual function recovery is far lower than expected. The homeostasis of retinal synapses in the visual signal pathway is the key structural basis for the delivery of visual signals. Our previous studies found that complicated changes in the synaptic structure between retinal neurons occurred much earlier than obvious degeneration of retinal ganglion cells in rat retinae. The lack of consideration of these earlier retinal synaptic changes in the rescue strategy may be partly responsible for the limited visual function recovery with the types of protective methods for retinal neurons used following elevated intraocular pressure. Thus, research on the modulatory mechanisms of the synaptic changes after elevated intraocular pressure injury may give new light to visual function rescue. In this study, we found that thrombospondin 2, an important regulator of synaptogenesis in central nervous system development, was distributed in retinal macroglia cells, and its receptor α2δ-1 was in retinal neurons. Cell cultures including mixed retinal macroglia cells/neuron cultures and retinal neuron cultures were exposed to elevated hydrostatic pressure for 2 h. The expression levels of glial fibrillary acidic protein (the marker of activated macroglia cells), thrombospondin 2, α2δ-1 and presynaptic proteins were increased following elevated hydrostatic pressure in mixed cultures, but the expression levels of postsynaptic proteins were not changed. SiRNA targeting thrombospondin 2 could decrease the upregulation of presynaptic proteins induced by the elevated hydrostatic pressure. However, in retinal neuron cultures, elevated hydrostatic pressure did not affect the expression of presynaptic or postsynaptic proteins. Rather, the retinal neuron cultures with added recombinant thrombospondin 2 protein upregulated the level of presynaptic proteins. Finally, gabapentin decreased the expression of presynaptic proteins in mixed cultures by blocking the interaction of thrombospondin 2 and α2δ-1. Taken together, these results indicate that activated macroglia cells may participate in alterations of presynaptic proteins of retinal neurons following elevated hydrostatic pressure, and macroglia-derived thrombospondin 2 may modulate these changes via binding to its neuronal receptor α2δ-1.

MeSH terms

  • Animals
  • Calcium Channels / metabolism
  • Carrier Proteins / metabolism
  • Cells, Cultured
  • Disks Large Homolog 4 Protein
  • Glial Fibrillary Acidic Protein / metabolism
  • Homer Scaffolding Proteins / metabolism
  • Humans
  • Hydrostatic Pressure*
  • Intracellular Signaling Peptides and Proteins / metabolism
  • Membrane Proteins / metabolism
  • Neuroglia / metabolism*
  • Presynaptic Terminals / metabolism*
  • Rats, Sprague-Dawley
  • Retinal Neurons / metabolism*
  • Synapsins / metabolism
  • Synaptophysin / metabolism
  • Thrombospondins / metabolism*

Substances

  • Cacna2d2 protein, rat
  • Calcium Channels
  • Carrier Proteins
  • Disks Large Homolog 4 Protein
  • Dlg4 protein, rat
  • Glial Fibrillary Acidic Protein
  • Homer Scaffolding Proteins
  • Intracellular Signaling Peptides and Proteins
  • Membrane Proteins
  • Synapsins
  • Synaptophysin
  • Thrombospondins
  • gephyrin
  • thrombospondin 2

Grants and funding

This study was supported by National Natural Science Foundation of China (No. 81400399, NO.81371011). www.nsfc.gov.cn; the Project of Innovation-driven Plan of Central South University (NO. 2015CXS022). http://www.csu.edu.cn; National Key Technologies Research and Development Program of China (No. 2012BAK14B03). http://program.most.gov.cn. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.