Mesangial factor V expression colocalized with fibrin deposition in IgA nephropathy.
BACKGROUND
Factor V in its active form (Va) plays a key role at the termination of the intrinsic coagulation pathway, serving as a membrane-bound cofactor for the conversion of prothrombin to thrombin by factor Xa. Cross-linked fibrin (XFb) is often observed in mesangial areas in active types of human glomerulonephritis. In this study, to clarify contribution of factor V in intramesangial coagulation, mesangial factor V expression and its relationship to mesangial proliferation and fibrin deposition in IgA nephropathy (IgAN) were investigated.


METHODS
Twenty-two patients with IgAN were studied. XFb was detected in renal biopsy specimens using anti-d-dimer antibody combined with plasmin exposure, and factor V was detected with rabbit antibody against human factor V. Double-labeling immunohistochemistry was used to investigate the relationship of the glomerular distribution of factor V to XFb. The relationship of factor V staining to the activity index or XFb deposition was evaluated. The expression of factor V mRNA was assessed by in situ hybridization in relationship to the antigen staining of alpha-smooth muscle actin (alpha-SMA). The ultrastructural distribution of factor V in glomeruli was studied by immunoelectron microscopy.


RESULTS
XFb and factor V were observed in the mesangium and along capillary loops in seven and nine specimens, respectively. Factor V had intense, frequent expression in the proliferating and necrotizing areas, showing a significant relationship to XFb (P < 0.05). Furthermore, XFb deposition and factor V expression were markedly correlated with disease activity (P = 0.005 and P = 0.008, respectively). By double-labeling experiments, XFb and factor V were often seen colocalized in mesangial areas of the glomeruli, which showed necrotizing lesions and/or intense cellular proliferation. By in situ hybridization, factor V mRNA was detected mainly in the mesangial cells, which were positive for alpha-SMA, and partly in the endothelial cells. By immunoelectron microscopy, factor V presence was confirmed in the mesangium and endothelium.


CONCLUSIONS
The present findings suggest that factor V is strongly expressed in mesangial cells in active IgAN accompanied with mesangial proliferation and may exert procoagulant activity, leading to intramesangial coagulation.
Department of Cardiovascular Medicine, Graduate School of Medicine, Kyoto University, Japan.
N
N
Liu
T
T
Ono
K
K
Suyama
F
F
Nogaki
K
K
Shirakawa
M
M
Maeda
T
T
Kawamura
T
T
Kamata
A
A
Oyama
E
E
Muso
S
S
Sasayama
D000199:Actins / Q000032:analysis; D000328:Adult; D001706:Biopsy; D003432:Cross-Linking Reagents / Q000032:analysis; D005165:Factor V / Q000032:analysis* / Q000378:metabolism; D005260:Female; D005337:Fibrin / Q000032:analysis*; D005920:Glomerular Mesangium / Q000737:chemistry* / Q000473:pathology / Q000648:ultrastructure; D005922:Glomerulonephritis, IGA / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D016253:Microscopy, Immunoelectron; D008875:Middle Aged
D000199:Actins; D003432:Cross-Linking Reagents; D005165:Factor V; D005337:Fibrin