title: Subcellular redistribution of la/SSB autoantigen during physiologic apoptosis in the fetal mouse heart and conduction system: a clue to the pathogenesis of congenital heart block.
abstract: OBJECTIVE
  In isolated congenital heart block, the mechanism by which maternal autoantibodies target the intracellular components of the Ro/La RNP complex is unclear. Previous studies have demonstrated that cultured fetal cardiac myocytes rendered apoptotic bind antibodies to 48-kd La/SSB. This study further investigated the subcellular distribution of the La antigen during apoptosis in the fetal mouse heart and conduction system.
  
  
  METHODS
  The atrioventricular (AV) node, AV bundle, and sinoatrial (SA) node were identified in serial sections prepared from paraffin blocks of normal mouse fetuses on days 15, 17, and 19 of gestation. Apoptosis was detected by TUNEL assay. Under confocal microscopy, fluorescent labeling of fragmented DNA in apoptotic cells was assessed by TUNEL, and La protein localization was visualized simultaneously using a murine monoclonal antibody or affinity-purified human polyclonal anti-La antibodies.
  
  
  RESULTS
  Apoptotic cells were detected in and at the periphery of the AV and SA nodes as well as in the fetal heart valve insertions and working myocardium. In contrast, no apoptosis was detected in the adult heart AV node or surrounding myocardium. As expected, the La antigen was predominantly immunolocalized to the nucleus in nonapoptotic cells. However, apoptotic cells showed a marked reduction of nuclear La and redistribution of La to the cytoplasm. High-resolution confocal microscopy revealed that in cells that had undergone apoptosis, La antigen asymmetrically clustered near the surface of TUNEL-positive nuclei and apoptotic bodies.
  
  
  CONCLUSIONS
  These data provide the first in vivo demonstration of the subcellular translocation of La autoantigen during apoptosis in the fetal heart and the conduction system under physiologic conditions. This observation supports the hypothesis that subcellular redistribution of La in the normally developing heart facilitates the binding of cognate maternal antibodies and subsequent tissue damage.
authors.affiliation: Flinders Medical Centre, Flinders University, Adelaide, Australia.
authors.forename: Hai B
authors.initials: HB
authors.lastname: Tran
authors.forename: Maria
authors.initials: M
authors.lastname: Ohlsson
authors.forename: Dimitra
authors.initials: D
authors.lastname: Beroukas
authors.forename: Jenny
authors.initials: J
authors.lastname: Hiscock
authors.forename: John
authors.initials: J
authors.lastname: Bradley
authors.forename: Jill P
authors.initials: JP
authors.lastname: Buyon
authors.forename: Tom P
authors.initials: TP
authors.lastname: Gordon
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000276:immunology*; D001324:Autoantigens / Q000032:analysis*; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D006327:Heart Block / Q000151:congenital / Q000209:etiology* / Q000473:pathology; D006329:Heart Conduction System / Q000737:chemistry* / Q000196:embryology / Q000473:pathology; D007112:Immunity, Maternally-Acquired; D020287:In Situ Nick-End Labeling; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D009206:Myocardium / Q000737:chemistry* / Q000276:immunology / Q000473:pathology; D011247:Pregnancy; D012261:Ribonucleoproteins / Q000032:analysis*; D000097585:SS-B Antigen
chemical_list: D001324:Autoantigens; D012261:Ribonucleoproteins; D000097585:SS-B Antigen