Valproic acid-mediated neuroprotection and regeneration in injured retinal ganglion cells.
OBJECTIVE
Valproic acid (VPA) has been demonstrated to have neuroprotective effects in neurodegenerative conditions. VPA inhibits histone-deacetylases (HDAC) and delays apoptosis in degenerating neurons. The authors investigated whether VPA delays retinal ganglion cell (RGC) death and enhances axonal regeneration after optic nerve crush (ONC). Furthermore, potential molecular targets involved in VPA-mediated protection were analyzed.


METHODS
ONC was performed on the left eye of rats, which received VPA or Ringer's solution subcutaneously (SC; 300 mg/kg twice daily) or intravitreally (single postlesional injection). Densities of fluorogold-labeled RGC were analyzed in retinal flatmounts after 5 or 8 days. Retinal tissue was also harvested and processed to quantify axon growth in retinal explants; evaluate caspase-3 activity; analyze transcription factor cAMP response element binding protein (CREB); and determine acetylated histone 3 and 4, as well as phosphorylated extracellular signal-regulated kinase (pERK) 1/2.


RESULTS
Five and 8 days after ONC, 93% and 58% RGC survived after subcutaneous VPA treatment in comparison to Ringer's solution (62% and 37% viable RGC), respectively (P < 0.001). Likewise, a single intravitreal injection of VPA immediately after injury significantly delayed apoptosis in RGC (P = 0.0016). Injured RGC treated with VPA showed better regeneration of their axons in culture (196 axons/explant) than the crushed controls receiving Ringer (115 axons/explant). RGC axons of the right control eyes regenerated more after VPA treatment. VPA-mediated neuroprotection and neuroregeneration were accompanied by decreased caspase-3 activity, CREB induction, pERK1/2 activation, but not by altered histone-acetylation.


CONCLUSIONS
VPA provided neuroprotection and axonal regrowth after ONC. Alterations were observed in several pathways; however, the precise mechanism of VPA-mediated protection is not yet fully understood.
Biermann
Julia
J
University Eye Hospital Freiburg, Freiburg im Breisgau, Germany. julia.biermann@uniklinik-freiburg.de
Grieshaber
Philippe
P
Goebel
Ulrich
U
Martin
Gottfried
G
Thanos
Solon
S
Di Giovanni
Simone
S
Lagrèze
Wolf Alexander
WA
D000818:Animals; D001369:Axons / Q000502:physiology*; D015153:Blotting, Western; D050882:CREB-Binding Protein / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D002452:Cell Count; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D024202:Electrophoretic Mobility Shift Assay; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006657:Histones / Q000378:metabolism; D008297:Male; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D048053:Mitogen-Activated Protein Kinase 6 / Q000378:metabolism; D018696:Neuroprotective Agents / Q000494:pharmacology*; D020221:Optic Nerve Injuries / Q000473:pathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012038:Regeneration / Q000187:drug effects*; D012165:Retinal Ganglion Cells / Q000166:cytology / Q000502:physiology*; D014635:Valproic Acid / Q000494:pharmacology*
D004791:Enzyme Inhibitors; D006657:Histones; D018696:Neuroprotective Agents; D014635:Valproic Acid; D050882:CREB-Binding Protein; C494365:Crebbp protein, rat; D048052:Mitogen-Activated Protein Kinase 3; D048053:Mitogen-Activated Protein Kinase 6; D053148:Caspase 3