Citron kinase regulates axon growth through a pathway that converges on cofilin downstream of RhoA.
Axon regeneration in the adult central nervous system (CNS) is prevented by inhibitory molecules present in myelin, which bind to a receptor complex that leads to downstream RhoGTP activation and axon growth cone collapse. Here, we compared expression of Citron kinase (Citron-K), a target molecule of RhoGTP in non-regenerating dorsal root ganglion neurons (DRGN) after dorsal column (DC) injury, and in regenerating DRGN after either sciatic nerve (SN) injury or preconditioning SN+DC lesion models. We show by microarray that Citron-K mRNA levels in DRGN of a non-regenerating DC injury model were elevated 2-fold compared to those of intact control DRGN. Conversely, Citron-K levels were reduced by 2 and 2.4-fold at 10 days post lesion in the regenerating SN and preconditioning SN+DC lesion models, respectively, compared to levels in control intact DRGN. Western blotting and immunohistochemistry confirmed these observations and localised Citron-K immunostaining to both DRGN and satellite glia. In dissociated, adult rat DRG cell cultures, 80% knockdown of Citron-K, in the presence of inhibitory concentrations of CNS myelin extract (CME), promoted significant disinhibited DRGN neurite outgrowth, only when cells were stimulated with neurotrophic factors. The levels of RhoGTP remained unchanged after Citron-K knockdown in the presence of CME while enhanced cofilin levels correlated with disinhibited DRGN neurite outgrowth. This observation suggests that Citron-K plays a role in axon growth downstream of Rho activation. We conclude that Citron-K regulates actin polymerisation downstream of RhoA and may offer a potentially novel therapeutic approach for promoting CNS axon regeneration.
Ahmed
Zubair
Z
Neuropharmacology and Neurobiology Section, School of Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham B15 2TT, UK. z.ahmed.1@bham.ac.uk
Douglas
Michael R
MR
Read
Martin L
ML
Berry
Martin
M
Logan
Ann
A
D000199:Actins / Q000378:metabolism; D000818:Animals; D001369:Axons / Q000201:enzymology* / Q000502:physiology; D002478:Cells, Cultured; D051338:Cofilin 1 / Q000378:metabolism*; D004195:Disease Models, Animal; D015536:Down-Regulation / Q000235:genetics / Q000502:physiology; D020439:Growth Cones / Q000201:enzymology*; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000502:physiology*; D054461:Lim Kinases / Q000502:physiology; D008297:Male; D009416:Nerve Regeneration / Q000235:genetics / Q000502:physiology*; D058105:Polymerization; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*; D054460:rho-Associated Kinases / Q000502:physiology; D020742:rhoA GTP-Binding Protein / Q000378:metabolism*
D000199:Actins; C495812:Cfl1 protein, rat; D051338:Cofilin 1; D047908:Intracellular Signaling Peptides and Proteins; C115635:citron-kinase; D054461:Lim Kinases; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein