title: Inhibiting cortical protein kinase A in spinal cord injured rats enhances efficacy of rehabilitative training.
abstract: Elevated levels of the second messenger molecule cyclic adenosine monophosphate (cAMP) are often associated with neuron sprouting and neurite extension (i.e., neuroplasticity). Phosphokinase A (PKA) is a prominent downstream target of cAMP that has been associated with neurite outgrowth. We hypothesized that rehabilitative motor training following spinal cord injuries promotes neuroplasticity via PKA activation. However, in two independent experiments, inhibition of cortical PKA using Rp-cAMPS throughout rehabilitative training robustly increased functional recovery and collateral sprouting of injured corticospinal tract axons, an indicator of neuroplasticity. Consistent with these in vivo findings, using cultured STHdh neurons, we found that Rp-cAMPS had no effect on the phosphorylation of CREB (cAMP response element-binding protein), a prominent downstream target of PKA, even with the concomitant application of the adenylate cyclase agonist forskolin to increase cAMP levels. Conversely, when cAMP levels were increased using the phosphodiesterase inhibitor IBMX, Rp-cAMPS potently inhibited CREB phosphorylation. Taken together, our results suggest that an alternate cAMP dependent pathway was involved in increasing CREB phosphorylation and neuroplasticity. This idea was supported by an in vitro neurite outgrowth assay, where inhibiting PKA did enhance neurite outgrowth. However, when PKA inhibition was combined with inhibition of EPAC2 (exchange protein directly activated by cAMP), another downstream target of cAMP in neurons, neurite outgrowth was significantly reduced. In conclusion, blocking PKA in cortical neurons of spinal cord injured rats increases neurite outgrowth of the lesioned corticospinal tract fibres and the efficacy of rehabilitative training, likely via EPAC.
authors.affiliation: Neuroscience and Mental Health Institute, University of Alberta, Edmonton T6G 2E1, Canada.
authors.forename: David
authors.initials: D
authors.lastname: Wei
authors.affiliation: Department of Physical Therapy, University of Alberta, Edmonton T6G 2E1, Canada.
authors.forename: Caitlin
authors.initials: C
authors.lastname: Hurd
authors.affiliation: Neuroscience and Mental Health Institute, University of Alberta, Edmonton T6G 2E1, Canada; Department of Pharmacology, University of Alberta, Edmonton T6G 2E1, Canada.
authors.forename: Danny
authors.initials: D
authors.lastname: Galleguillos
authors.affiliation: Division of Anatomy, University of Alberta, Edmonton T6G 2E1, Canada.
authors.forename: Jyoti
authors.initials: J
authors.lastname: Singh
authors.affiliation: Neuroscience and Mental Health Institute, University of Alberta, Edmonton T6G 2E1, Canada.
authors.forename: Keith K
authors.initials: KK
authors.lastname: Fenrich
authors.affiliation: Neuroscience and Mental Health Institute, University of Alberta, Edmonton T6G 2E1, Canada; Division of Anatomy, University of Alberta, Edmonton T6G 2E1, Canada.
authors.forename: Christine A
authors.initials: CA
authors.lastname: Webber
authors.affiliation: Neuroscience and Mental Health Institute, University of Alberta, Edmonton T6G 2E1, Canada; Department of Pharmacology, University of Alberta, Edmonton T6G 2E1, Canada.
authors.forename: Simonetta
authors.initials: S
authors.lastname: Sipione
authors.affiliation: Neuroscience and Mental Health Institute, University of Alberta, Edmonton T6G 2E1, Canada; Department of Physical Therapy, University of Alberta, Edmonton T6G 2E1, Canada. Electronic address: kfouad@ualberta.ca.
authors.forename: Karim
authors.initials: K
authors.lastname: Fouad
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D050882:CREB-Binding Protein / Q000378:metabolism; D002461:Cell Line, Transformed / Q000378:metabolism / Q000473:pathology; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000201:enzymology* / Q000378:metabolism; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004195:Disease Models, Animal; D005260:Female; D005727:Ganglia, Spinal / Q000166:cytology; D017628:Microglia / Q000378:metabolism / Q000473:pathology; D016501:Neurites / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011712:Pyramidal Tracts / Q000378:metabolism; D051381:Rats; D011917:Rats, Inbred Lew; D020127:Recovery of Function / Q000502:physiology; D013119:Spinal Cord Injuries / Q000473:pathology* / Q000534:rehabilitation*; D013873:Thionucleotides / Q000378:metabolism
chemical_list: D010726:Phosphodiesterase Inhibitors; D013873:Thionucleotides; C016957:adenosine-3',5'-cyclic phosphorothioate; D000242:Cyclic AMP; D050882:CREB-Binding Protein; C494365:Crebbp protein, rat; D017868:Cyclic AMP-Dependent Protein Kinases; D015056:1-Methyl-3-isobutylxanthine
keywords: PKA; Single pellet grasping; Spinal cord injury; cAMP