title: Temporal Changes in Cellular Repopulation and Collagen Fibril Remodeling and Regeneration After Allograft Anterior Cruciate Ligament Reconstruction: An Experimental Study Using Kusabira-Orange Transgenic Pigs.
abstract: Distinguishing recipient cells from donor ligament cells is difficult in the early graft-healing phase after anterior cruciate ligament (ACL) reconstruction. The ability to track the distribution and differentiation of recipient cells using genetically engineered transgenic (Tg) animals would have significant clinical and research effects on graft healing after ACL reconstruction.
  
  
  
  Kusabira-Orange Tg pigs may allow the tracking of recipient cells infiltrating the graft after ACL reconstruction. The repopulation of recipient cells within the graft would be apparent even in the early graft-healing phase when necrotic donor cells are still present.
  
  
  
  Descriptive laboratory study.
  
  
  
  In 17 genetically engineered Tg pigs, which carried the red fluorescent protein Kusabira-Orange, ACL reconstruction was performed on the right knee using a digital flexor tendon harvested from wild-type pigs. Tissue samples harvested at different time points were subjected to histological, immunohistochemical, and electron microscopic analyses.
  
  
  
  At 3 weeks postoperatively, recipient cells expressing red fluorescence embraced the graft and were infiltrating the central part of the graft. These cells with oval nuclei gradually infiltrated the gap of collagen fibers, losing their regular orientation. At 6 weeks, cellularity within the graft had doubled to match that of the native ACL, while acellular necrotic regions still existed centrally. Ubiquitous cellular distributions resembling the native ACL were observed at 24 weeks. Electron microscopic analysis showed that the mean collagen fibril diameter and density gradually decreased over 24 weeks.
  
  
  
  Genetically engineered pigs carrying the Kusabira-Orange gene were useful animal models for analyzing intrinsic and extrinsic cellular dynamics during the course of graft healing after ACL reconstruction. Cellular repopulation by recipient cells occurred in the very early stage, and the cellular distribution within the graft resembled that in the native ACL by 24 weeks, but the reconstructed graft had not restored the ultrastructure of the native ACL by that stage.
  
  
  
  In allograft ACL reconstruction in a pig model, cellular repopulation was completed by 24 weeks after surgery, but the collagen matrix had not resumed the ultrastructure of the native ACL. Surgeons should be aware that risks may remain with returning to sports activities at 24 weeks after surgery.
authors.affiliation: Department of Orthopaedic Surgery, Keio University School of Medicine, Tokyo, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Takeuchi
authors.affiliation: Department of Orthopaedic Surgery, Keio University School of Medicine, Tokyo, Japan y-niki@keio.jp.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Niki
authors.affiliation: International Institute for Bio-Resource Research, Meiji University, Kawasaki, Japan.
authors.forename: Hitomi
authors.initials: H
authors.lastname: Matsunari
authors.affiliation: International Institute for Bio-Resource Research, Meiji University, Kawasaki, Japan.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Umeyama
authors.affiliation: International Institute for Bio-Resource Research, Meiji University, Kawasaki, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nagashima
authors.affiliation: Department of Orthopaedic Surgery, Keio University School of Medicine, Tokyo, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Enomoto
authors.affiliation: Department of Orthopaedic Surgery, Keio University School of Medicine, Tokyo, Japan.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Toyama
authors.affiliation: Department of Orthopaedic Surgery, Keio University School of Medicine, Tokyo, Japan.
authors.forename: Morio
authors.initials: M
authors.lastname: Matsumoto
authors.affiliation: Department of Orthopaedic Surgery, Keio University School of Medicine, Tokyo, Japan.
authors.forename: Masaya
authors.initials: M
authors.lastname: Nakamura
mesh_terms: D064591:Allografts / Q000637:transplantation; D000818:Animals; D030801:Animals, Genetically Modified; D059549:Anterior Cruciate Ligament Reconstruction; D002450:Cell Communication; D049109:Cell Proliferation; D003094:Collagen / Q000378:metabolism*; D005109:Extracellular Matrix / Q000378:metabolism; D023421:Models, Animal; D034421:Sus scrofa; D013710:Tendons / Q000637:transplantation*; D014184:Transplantation, Homologous
chemical_list: D003094:Collagen
keywords: Kusabira-Orange; anterior cruciate ligament reconstruction; biology of ligament; cell/molecular biology; transgenic animal