title: Adjuvant neurotrophic factors in peripheral nerve repair with chondroitin sulfate proteoglycan-reduced acellular nerve allografts.
abstract: BACKGROUND
  Acellular nerve allografts are now standard tools in peripheral nerve repair because of decreased donor site morbidity and operative time savings. Preparation of nerve allografts involves several steps of decellularization and modification of extracellular matrix to remove chondroitin sulfate proteoglycans (CSPGs), which have been shown to inhibit neurite outgrowth through a poorly understood mechanism involving RhoA and extracellular matrix-integrin interactions. Chondroitinase ABC (ChABC) is an enzyme that degrades CSPG molecules and has been shown to promote neurite outgrowth after injury of the central and peripheral nervous systems. Variable results after ChABC treatment make it difficult to predict the effects of this drug in human nerve allografts, especially in the presence of native extracellular signaling molecules. Several studies have shown cross-talk between neurotrophic factor and CSPG signaling pathways, but their interaction remains poorly understood. In this study, we examined the adjuvant effects of nerve growth factor (NGF) and glial cell line-derived neurotrophic factor (GDNF) on neurite outgrowth postinjury in CSPG-reduced substrates and acellular nerve allografts.
  
  
  METHODS
  E12 chicken DRG explants were cultured in medium containing ChABC, ChABC + NGF, ChABC + GDNF, or control media. Explants were imaged at 3 d and neurite outgrowths measured. The rat sciatic nerve injury model involved a 1-cm sciatic nerve gap that was microsurgically repaired with ChABC-pretreated acellular nerve allografts. Before implantation, nerve allografts were incubated in NGF, GDNF, or sterile water. Nerve histology was evaluated at 5 d and 8 wk postinjury.
  
  
  RESULTS
  The addition of GDNF in vitro produced significant increase in sensory neurite length at 3 d compared with ChABC alone (P < 0.01), whereas NGF was not significantly different from control. In vivo adjuvant NGF produced increases in total myelinated axon count (P < 0.005) and motor axon count (P < 0.01), whereas significantly reducing IB4+ nociceptor axon count (P < 0.01). There were no significant differences produced by in vivo adjuvant GDNF.
  
  
  CONCLUSIONS
  This study provides initial evidence that CSPG-reduced nerve grafts may disinhibit the prosurvival effects of NGF in vivo, promoting motor axon outgrowth and reducing regeneration of specific nociceptive neurons. Our results support further investigation of adjuvant NGF therapy in CSPG-reduced acellular nerve grafts.
authors.affiliation: Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee; Department of Plastic Surgery, Vanderbilt University Medical Center, Nashville, Tennessee. Electronic address: Richard.b.boyer@vanderbilt.edu.
authors.forename: Richard B
authors.initials: RB
authors.lastname: Boyer
authors.affiliation: Department of Plastic Surgery, Vanderbilt University Medical Center, Nashville, Tennessee.
authors.forename: Kevin W
authors.initials: KW
authors.lastname: Sexton
authors.affiliation: Department of Plastic Surgery, Vanderbilt University Medical Center, Nashville, Tennessee.
authors.forename: Charles L
authors.initials: CL
authors.lastname: Rodriguez-Feo
authors.affiliation: Department of Plastic Surgery, Vanderbilt University Medical Center, Nashville, Tennessee.
authors.forename: Ratnam
authors.initials: R
authors.lastname: Nookala
authors.affiliation: Department of Plastic Surgery, Vanderbilt University Medical Center, Nashville, Tennessee.
authors.forename: Alonda C
authors.initials: AC
authors.lastname: Pollins
authors.affiliation: Department of Plastic Surgery, Vanderbilt University Medical Center, Nashville, Tennessee.
authors.forename: Nancy L
authors.initials: NL
authors.lastname: Cardwell
authors.affiliation: Vanderbilt Center for Science Outreach, Vanderbilt University, Nashville, Tennessee.
authors.forename: Keonna Y
authors.initials: KY
authors.lastname: Tisdale
authors.affiliation: Department of Plastic Surgery, Vanderbilt University Medical Center, Nashville, Tennessee.
authors.forename: Lillian B
authors.initials: LB
authors.lastname: Nanney
authors.affiliation: Department of Plastic Surgery, Vanderbilt University Medical Center, Nashville, Tennessee.
authors.forename: R Bruce
authors.initials: RB
authors.lastname: Shack
authors.affiliation: Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee; Department of Plastic Surgery, Vanderbilt University Medical Center, Nashville, Tennessee.
authors.forename: Wesley P
authors.initials: WP
authors.lastname: Thayer
mesh_terms: D064591:Allografts / Q000187:drug effects; D000818:Animals; D017024:Chemotherapy, Adjuvant; D002642:Chick Embryo; D011508:Chondroitin Sulfate Proteoglycans; D004353:Drug Evaluation, Preclinical; D005260:Female; D005727:Ganglia, Spinal / Q000187:drug effects; D051100:Glial Cell Line-Derived Neurotrophic Factor / Q000494:pharmacology / Q000627:therapeutic use*; D020932:Nerve Growth Factor / Q000494:pharmacology / Q000627:therapeutic use*; D016501:Neurites / Q000187:drug effects*; D059348:Peripheral Nerve Injuries / Q000188:drug therapy / Q000601:surgery*; D017207:Rats, Sprague-Dawley; D012584:Sciatic Nerve / Q000637:transplantation*
chemical_list: D011508:Chondroitin Sulfate Proteoglycans; D051100:Glial Cell Line-Derived Neurotrophic Factor; D020932:Nerve Growth Factor
keywords: Axotomy; CSPG; Chondroitin; Chondroitinase; GDNF; NGF; Nerve repair; Neurotrophic; P75; Sciatic