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.
Liu
N
N
Department of Cardiovascular Medicine, Graduate School of Medicine, Kyoto University, Japan.
Ono
T
T
Suyama
K
K
Nogaki
F
F
Shirakawa
K
K
Maeda
M
M
Kawamura
T
T
Kamata
T
T
Oyama
A
A
Muso
E
E
Sasayama
S
S
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