Epac and the high affinity rolipram binding conformer of PDE4 modulate neurite outgrowth and myelination using an in vitro spinal cord injury model.
OBJECTIVE
cAMP and pharmacological inhibition of PDE4, which degrades it, are promising therapeutic targets for the treatment of spinal cord injury (SCI). Using our previously described in vitro SCI model, we studied the mechanisms by which cAMP modulators promote neurite outgrowth and myelination using enantiomers of the PDE4-specific inhibitor rolipram and other modulators of downstream signalling effectors.


METHODS
Rat mixed neural cell myelinating cultures were cut with a scalpel and treated with enantiomers of the PDE4-specific inhibitor rolipram, Epac agonists and PKA antagonists. Neurite outgrowth, density and myelination were assessed by immunocytochemistry and cytokine levels analysed by qPCR.


RESULTS
Inhibition of the high-affinity rolipram-binding state (HARBS), rather than the low-affinity rolipram binding state (LARBS) PDE4 conformer promoted neurite outgrowth and myelination. These effects were mediated through the activation of Epac and not through PKA. Expression of the chemokine CXCL10, known to inhibit myelination, was markedly elevated in astrocytes after Rho inhibition and this was blocked by inhibition of Rho kinase or PDE4.


CONCLUSIONS
PDE4 inhibitors targeted at the HARBS conformer or Epac agonists may provide promising novel targets for the treatment of SCI. Our study demonstrates the differential mechanisms of action of these compounds, as well as the benefit of a combined pharmacological approach and highlighting potential promising targets for the treatment of SCI. These findings need to be confirmed in vivo.
Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, UK.
S D
SD
Boomkamp
M A
MA
McGrath
M D
MD
Houslay
S C
SC
Barnett
D000111:Acetylcysteine / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004917:Erythromycin / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D009413:Nerve Fibers, Myelinated / Q000187:drug effects* / Q000473:pathology; D016501:Neurites / Q000187:drug effects* / Q000473:pathology; D058988:Phosphodiesterase 4 Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D011485:Protein Binding / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D020889:Rolipram / Q000494:pharmacology* / Q000627:therapeutic use; D013119:Spinal Cord Injuries / Q000188:drug therapy / Q000473:pathology
D058988:Phosphodiesterase 4 Inhibitors; D004917:Erythromycin; C057513:erythromycin propionate-N-acetylcysteinate; D020889:Rolipram; D000111:Acetylcysteine
Epac; PDE4; cAMP; myelination; neurite outgrowth; spinal cord injury