Accelerating axonal growth promotes motor recovery after peripheral nerve injury in mice
Chi Him Eddie Ma, Takao Omura, Enrique J. Cobos, Alban Latrémolière, Nader Ghasemlou, Gary J. Brenner, Ed van Veen, Lee Barrett, Tomokazu Sawada, Fuying Gao, Giovanni Coppola, Frank Gertler, Michael Costigan, Dan Geschwind, Clifford J. Woolf
Chi Him Eddie Ma, Takao Omura, Enrique J. Cobos, Alban Latrémolière, Nader Ghasemlou, Gary J. Brenner, Ed van Veen, Lee Barrett, Tomokazu Sawada, Fuying Gao, Giovanni Coppola, Frank Gertler, Michael Costigan, Dan Geschwind, Clifford J. Woolf
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Research Article

Accelerating axonal growth promotes motor recovery after peripheral nerve injury in mice

Abstract

Although peripheral nerves can regenerate after injury, proximal nerve injury in humans results in minimal restoration of motor function. One possible explanation for this is that injury-induced axonal growth is too slow. Heat shock protein 27 (Hsp27) is a regeneration-associated protein that accelerates axonal growth in vitro. Here, we have shown that it can also do this in mice after peripheral nerve injury. While rapid motor and sensory recovery occurred in mice after a sciatic nerve crush injury, there was little return of motor function after sciatic nerve transection, because of the delay in motor axons reaching their target. This was not due to a failure of axonal growth, because injured motor axons eventually fully re-extended into muscles and sensory function returned; rather, it resulted from a lack of motor end plate reinnervation. Tg mice expressing high levels of Hsp27 demonstrated enhanced restoration of motor function after nerve transection/resuture by enabling motor synapse reinnervation, but only within 5 weeks of injury. In humans with peripheral nerve injuries, shorter wait times to decompression surgery led to improved functional recovery, and, while a return of sensation occurred in all patients, motor recovery was limited. Thus, absence of motor recovery after nerve damage may result from a failure of synapse reformation after prolonged denervation rather than a failure of axonal growth.

Authors

Chi Him Eddie Ma, Takao Omura, Enrique J. Cobos, Alban Latrémolière, Nader Ghasemlou, Gary J. Brenner, Ed van Veen, Lee Barrett, Tomokazu Sawada, Fuying Gao, Giovanni Coppola, Frank Gertler, Michael Costigan, Dan Geschwind, Clifford J. Woolf

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Figure 2

mHsp25 colocalizes with actin in growth cone filopodia, and both its knockdown and inhibition of phosphorylation reduce neurite growth.

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mHsp25 colocalizes with actin in growth cone filopodia, and both its kno...
(A) High levels of mHsp25 are present in growth cones of adult DRG neurons, colocalizing with actin at the barbed end tips of filopodia (white arrowheads). Scale bar: 7.5 μm. Original magnification, ×250 (insets). (B) DRG neurons were transduced with lentiviral vectors containing a GFP reporter and either shRNAcontrol or shRNAmHsp25, and somata were stripped from their neurites after 7-day culture, replated, and allowed to grow for 17 hours. Knockdown of mHsp25 (GFP +ve, mHsp25 –ve; white arrows) reduced neurite length compared with that of nontransduced (GFP –ve, mHsp25 +ve; white arrowheads) neurons in the same culture or with neurons transduced with lenti-shRNAcontrol. Scale bar: 50 μm. (C) mHsp25 knockdown reduced neurite length of DRG neurons in C57BL/6 mice (where cell death increased) and Bax–/– mice (where cell death was prevented; Supplemental Figure 1B). (D) Total Hsp25 protein levels and phosphorylation on Ser15 and Ser86 increased in L4/5 DRGs 3 days after an ipsilateral (ipsi) SNT compared with those in contralateral (con) DRGs. Quantification of Western blots shows relative changes in mHsp25 and its 2 phosphorylation sites (fold change is relative to uninjured naive mice; mean ± SEM of triplicates; *P < 0.001, Student’s t test). (E and F) A peptide MK2 inhibitor that blocks phosphorylation of mHsp25 dose dependently reduced neurite growth (mean ± SEM of triplicates; *P < 0.001, 1-way ANOVA followed with post-hoc Newman-Keuls test in C and F). CTL, control. Scale bar: 250 μm.