Current treatments to restore neurological deficits caused by axonal disconnection following central nervous system (CNS) injury are extremely limited. Protein phosphatase 2A (PP2A), one of the main serine-threonine phosphatases in mammalian cells, dephosphorylates collapsin response mediator protein-2 (CRMP2) in the developing CNS. In our study, we found that the major CNS inhibiting substrates, including chondroitin sulfate proteoglycans (CSPGs) and myelin associated glycoproteins (MAG), activated epidermal growth factor receptor (EGFR), but inactivated PP2A and downstream CRMP2. Both EGFR inactivation and PP2A activation promoted axon elongation in vitro in the presence of inhibitory substrates. EGFR blockage by AG1478 selectively attenuated the inactive form of PP2A in pY307 phosphorylation, thus increasing PP2A activity. EGFR activation by EGF attenuated PP2A activity, whereas mutation of Y307 to phenylalanine abolished the effect. Furthermore, PP2A activity was down-regulated immediately after spinal cord injury (SCI) in rats. Chronic application of d-erythro-sphingosine (DES), the PP2A agonist, to spinal cord-lesioned rats enhanced the activity of this phosphatase and dephosphorylated CRMP2 around the lesion. PP2A activation induced significant axon sprouting in the lesioned spinal cord and promoted function recovery after SCI. These findings suggest that PP2A works downstream of EGFR and dephosphorylates CRMP2 after CNS injury. Therefore, therapies targeting PP2A may be effective following SCI.
Keywords: Axon growth; CRMP2; EGFR; PP2A; Spinal cord injury; Y307 phosphorylation.
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