Beta1-integrin mediates myelin-associated glycoprotein signaling in neuronal growth cones

Eyleen Lk Goh,Ju Kim Young,Kenichiro Kuwako,John W Griffin,Marc Tessier-Lavigne,Guo-Li Ming,Zhigang He

doi:10.1186/1756-6606-1-10

Abstract

Several myelin-associated factors that inhibit axon growth of mature neurons, including Nogo66, myelin-associated glycoprotein (MAG) and oligodendrocyte myelin glycoprotein (OMgp), can associate with a common GPI-linked protein Nogo-66 receptor (NgR). Accumulating evidence suggests that myelin inhibitors also signal through unknown NgR-independent mechanisms. Here we show that MAG, a RGD tri-peptide containing protein, forms a complex with β1-integrin to mediate axonal growth cone turning responses of several neuronal types. Mutations that alter the RGD motif in MAG or inhibition of β1-integrin function, but not removal of NgRs, abolish these MAG-dependent events. In contrast, OMgp-induced repulsion is not affected by inhibition of b1-integrin function. We further show that MAG stimulates tyrosine phosphorylation of focal adhesion kinase (FAK), which in turn is required for MAG-induced growth cone turning. These studies identify β1-integrin as a specific mediator for MAG in growth cone turning responses, acting through FAK activation.

Highlights

Myelin-associated glycoprotein (MAG), a component of myelin in the central and peripheral nervous system, promotes neurite outgrowth during the embryonic development, but inhibits axonal regeneration in the adult nervous system [1,2,3,4,5,6,7,8,9]
To determine whether β1-integrin interacts with MAG, we treated cultured primary hippocampal neurons with recombinant MAG consisting of the MAG extracellular domain fused to human Fc, a fusion protein previously shown to potently regulate neurite outgrowth when present uniformly and induce growth cone turning responses when applied locally [2,12,13,39,40,41]
To further examine whether MAG directly interacts with β1-integrin, we purified recombinant protein of GST fused to the extracellular domain of β1-integrin

Summary

Introduction

Myelin-associated glycoprotein (MAG), a component of myelin in the central and peripheral nervous system, promotes neurite outgrowth during the embryonic development, but inhibits axonal regeneration in the adult nervous system [1,2,3,4,5,6,7,8,9]. Following damage to the adult CNS, disruption of the myelin sheath leads to the release in abundance of a soluble fragment containing the MAG extracellular domain, which possesses potent inhibitory activity for neurite outgrowth [10]. A receptor complex consisting of NgR, p75/TROY and Lingo-1 has been shown to mediate the inhibitory activities of three major myelin-associated inhibitors: MAG, Nogo (an extracellular domain of NogoA) and OMgp [11,12,13,14,15,16,17,18,19]. While certain classes of neurons from p75 knockout mice exhibit reduced responses to myelin inhibitors, several types of neurons lacking NgRs are still inhibited by these factors [20,21,22,23]. It is likely that an additional signaling mechanism is critical for transducing the signaling of MAG and possibly other myelin-associated inhibitors

Methods

Results

Conclusion