title: Similar cellular migration patterns from niches in intervertebral disc and in knee-joint regions detected by in situ labeling: an experimental study in the New Zealand white rabbit.
abstract: BACKGROUND
  Potential stem cell niches (SNs) were recently reported in intervertebral discs (IVDs) and knee joints (KJs) in different mammals (located adjacent to the epiphyseal plate; EP). The aim here was to examine further possible cellular migration and migration directions of cells originating from niches possibly involved in regeneration of cartilaginous tissues in the IVD and in the KJ regions in adult mammals.
  
  
  METHODS
  In total, 33 rabbits were used in studies A through C. A. IVD cells were sorted; fluorescence-activated cell sorting (FACS) by size (forward scatter; ≤ 10 μm or >10 μm or GDF5+ cells (anti-GDF5 antibody). Sorted cells, labeled with cell tracer (carboxyfluorescein-diacetate-succinimidyl ester; CDFA-SE) were applied on IVD explants in vitro. Migrating cells/distance was evaluated by fluorescence- and confocal-microscopy (FC). B. DNA labeling was performed with BrdU (oral administration). Animals were killed (14 to 56 days), KJs collected, and BrdU+ cells visualized with immunohistochemistry (IHC)/anti-BrdU antibody in SN and articular cartilage (AC). C. Cell tracer: (Fe-nanoparticles: Endorem) were injected into SNs of IVDs (LI-LV) and KJs (tibia). Animals were killed after 2 to 6 weeks. Fe-labeled cells were traced by ferric-iron staining (Prussian blue reaction; Mallory method).
  
  
  RESULTS
  A. GDF5+ cells and ≤ 10-μm cells displayed the best migration capability in IVD explants. GDF5+ cells were detected at a tissue depth of 1,300 μm (16 days). B. BrdU+ cells were observed in early time points in niches of KJs, and at later time points in AC, indicating a gradual migration of cells. C. Fe+ cells were detected in IVDs; in annulus fibrosus (AF) in 11 of 12 animals and in nucleus pulposus (NP) in two of 12 animals. In AC (tibia), Fe+ cells were detected in six of 12 animals. In the potential migration route (PMR), from niches toward the IVD, Fe+ cells (three of 12 animals) and in PMR toward AC (KJs) (six of 12 animals) were detected.
  
  
  CONCLUSIONS
  Results indicate similar cellular migration patterns in cartilage regions (IVD and KJs) with migration from stem cell niche areas into the mature cartilaginous tissues of both the KJs and the IVD. These findings of a cellular migration pattern in mature cartilage are of interest from tissue-repair and engineering perspectives.
authors.forename: Helena
authors.initials: H
authors.lastname: Barreto Henriksson
authors.forename: Anders
authors.initials: A
authors.lastname: Lindahl
authors.forename: Eva
authors.initials: E
authors.lastname: Skioldebrand
authors.forename: Katarina
authors.initials: K
authors.lastname: Junevik
authors.forename: Carolina
authors.initials: C
authors.lastname: Tängemo
authors.forename: Johan
authors.initials: J
authors.lastname: Mattsson
authors.forename: Helena
authors.initials: H
authors.lastname: Brisby
mesh_terms: D000818:Animals; D001973:Bromodeoxyuridine / Q000737:chemistry / Q000378:metabolism; D002358:Cartilage, Articular / Q000166:cytology / Q000502:physiology; D002465:Cell Movement; D002478:Cells, Cultured; D004247:DNA / Q000737:chemistry; D005260:Female; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D007403:Intervertebral Disc / Q000166:cytology / Q000473:pathology*; D007719:Knee Joint / Q000166:cytology / Q000473:pathology*; D053768:Metal Nanoparticles / Q000737:chemistry; D011817:Rabbits; D012038:Regeneration; D000071250:Snail Family Transcription Factors; D055153:Stem Cell Niche; D013234:Stem Cells / Q000166:cytology; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D000071250:Snail Family Transcription Factors; D014157:Transcription Factors; D004247:DNA; D001973:Bromodeoxyuridine