The Journal of Neuroscience, December 1, 2002, 22(23):10408-10415
Metalloproteinase-Dependent Predegeneration In
Vitro Enhances Axonal Regeneration within Acellular Peripheral
Nerve Grafts
Craig A.
Krekoski,
Debbie
Neubauer,
James B.
Graham, and
David
Muir
Departments of Pediatrics (Neurology Division) and Neuroscience,
Evelyn F. and William L. McKnight Brain Institute, University of
Florida College of Medicine, Gainesville, Florida 32610-0296
Injury to peripheral nerve initiates a degenerative process
that converts the denervated nerve from a suppressive environment to
one that promotes axonal regeneration. We investigated the role of
matrix metalloproteinases (MMPs) in this degenerative process and
whether effective predegenerated nerve grafts could be produced
in vitro. Rat peripheral nerve explants were cultured for 1-7 d in various media, and their neurite-promoting activity was
assessed by cryoculture assay, in which neurons are grown directly on
nerve sections. The neurite-promoting activity of cultured nerves
increased rapidly and, compared with uncultured nerve, a maximum
increase of 72% resulted by 2 d of culture in the presence of
serum. Remarkably, the neurite-promoting activity of short-term
cultured nerves was also significantly better than nerves degenerated
in vivo. We examined whether in vitro
degeneration is MMP dependent and found that the MMP inhibitor
N-[(2R)-2(hydroxamidocarbonylmethyl)-4-methylpantanoyl]-L-tryptophan methylamide primarily blocked the degenerative increase in
neurite-promoting activity. In the absence of
hematogenic macrophages, MMP-9 was trivial, whereas elevated
MMP-2 expression and activation paralleled the increase in
neurite-promoting activity. MMP-2 immunoreactivity localized to Schwann
cells and the endoneurium and colocalized with gelatinolytic activity
as demonstrated by in situ zymography. Finally,
in vitro predegenerated nerves were tested as acellular grafts and, compared with normal acellular nerve grafts, axonal ingress
in vivo was approximately doubled. We conclude that
Schwann cell expression of MMP-2 plays a principal role in the
degenerative process that enhances the regeneration-promoting
properties of denervated nerve. Combined with their low immunogenicity,
acellular nerve grafts activated by in vitro
predegeneration may be a significant advancement for clinical nerve allografting.
Key words:
Wallerian degeneration; acellular nerve graft; MMP-2; Schwann cell; cryoculture; basal lamina; metalloproteinase; chondroitin
sulfate proteoglycan; axon regeneration; rat sciatic nerve
Copyright © 2002 Society for Neuroscience 0270-6474/02/222310408-08$05.00/0