ErbB1 epidermal growth factor receptor is a valid target for reducing the effects of multiple inhibitors of axonal regeneration

Abstract

Pharmacological inhibitors of epidermal growth factor receptor (ErbB1) attenuate the ability of CNS myelin to inhibit axonal regeneration. However, it has been claimed that such effects are mediated by off-target interactions. We have tested the role of ErbB1 in axonal regeneration by culturing neurons from ErbB1 knockout mice in the presence of various inhibitors of axonal regeneration: CNS myelin, chondroitin sulfate proteoglycans (CSPG), fibrinogen or polyinosinic:polycytidylic acid (poly I:C). We confirmed that ErbB1 was activated in cultures of cerebellar granule cells exposed to inhibitors of axonal regeneration and that ErbB1 kinase inhibitors promoted neurite outgrowth under these conditions. In the presence of myelin, fibrinogen, CSPG and poly I:C ErbB1 −/− neurons grew longer neurites than neurons expressing ErbB1. Furthermore, inhibitors of ErbB1 kinase did not improve neurite outgrowth from ErbB1 −/− neurons, ruling out an off-target mechanism of action. ErbB1 kinase activity is therefore a valid target for promoting axonal elongation in the presence of many of the molecules believed to contribute to the failure of axonal regeneration in the injured CNS.

Sulf1 and Sulf2 expression in the nervous system and its role in limiting neurite outgrowth in vitro

“…We sought to use function-blocking antibodies to Sulf1 and Sulf2 (Gill et al, 2010(Gill et al, , 2011(Gill et al, , 2012 to test the effects of SULFs on neurite outgrowth from neurons cultured in the presence of CSPGs. Because there is an emerging body of evidence that the epidermal growth factor receptor (ErbB1) has a role in mediating responses from CSPGs and other molecules that inhibit neurite outgrowth in vitro and axonal regeneration in vivo (Erschbamer et al, 2007;Koprivica et al, 2005;Leinster et al, 2012), we also investigated the interactions of SULFs and ErbB1 in the responses of neurons to CSPGs.…”

ErbB2 blockade with Herceptin (trastuzumab) enhances peripheral nerve regeneration after repair of acute or chronic peripheral nerve injury

“…14,21 The ErbB family of receptors are known to regulate axon regeneration through soluble and axon-bound NRG acting through the ErbB2 receptor in addition to inhibitory regulation by activated Erb1 (EGFR). 14,17,21,32,33 We now demonstrate that the ErbB2 receptor may negatively regulate axonal outgrowth through its potential inhibitory association with the EGFR. This expanded role of ErbB2 emphasizes its function of integrating multiple signals for regeneration and remyelination and now possibly as a way to limit vigorous, inefficient sprouting at the repair site through the EGFR pathway.…”

“…An alternative mechanism that we examined was whether Herceptin blocked the normally strong binding and activation of the EGFR (also known as ErbB1), a recently identified inhibitor of axon regeneration. [30][31][32][33] This possibility was verified by the significant effect of Herceptin in reducing the EGFR phosphorylation on neurons proximal to the repair site in rats treated with Herceptin (see Fig 8). Blockade of this transactivation of inhibitory EGFR by ErbB2 provides an explanation for the paradoxical finding that Herceptin enhances peripheral nerve regeneration independent of NRG signaling.…”

“…Activated EGFR acts through mechanisms involving transactivation by an unknown factor. 32,33,42 Of note, transactivation of EGFR by ErbB2 elicits a strong and unique signal that can be blocked by in vitro application of antibodies directed at the ErbB2 receptor. 30,31,37,43 Last, EGFR and ErbB2 are both expressed on the surface of peripheral motor and sensory neurons as well as Schwann cells.…”

“…From a translational perspective, Herceptin is already US Food and Drug Administration-approved and is an established therapy for treating HER2/ErbB2-overexpressing breast cancer. 18,48,49 Based on the evidence presented in this study and the evidence suggesting the inhibitory function of neuronal EGFR activation on peripheral nerve regeneration, 32,33 it would be important to examine how other ErbB2 and EGFR inhibitors perform in similar animal and clinical models of peripheral nerve injury. Of note, dual EGFR and ErbB2 small molecule inhibitors such as afatinib and lapatinib are now available and can inhibit the activation of both receptors in an EGFR-ErbB2 heterodimer.…”