DNA fragmentation in chronic glomerulonephritis: an immunohistological analysis

Experimental data suggest that apoptosis plays an important pathophysiological role in glomerulonephritis by restoring tissue structure after proliferation of intrinsic renal cells and infiltration of leukocytes. Relatively little is known of apoptosis in human glomerulonephritis, particularly in predicting renal function during follow-up.

In order to colocalize different markers for cell damage in renal tissue from patients with different forms of glomerulonephritis (GN), a series of semithin sections from 34 kidney biopsies were studied retrospectively. Normal kidney from a nephrectomy specimen with a small renal adenocarcinoma served as a control. DNA fragmentation, expression of tissue transglutaminase II, BAX and BCL-2 were visualized immunohistochemically. In some renal biopsies, immunohistochemical staining for activated caspase 3 was performed. Proinflammatory markers (C-reactive protein, leukocytes), serum creatinine, creatinine clearance, total proteinuria, albuminuria, alpha(1)-microglobulin and IgG excretion were determined at the time of biopsy. Serum creatinine and total proteinuria were assessed 6 and 12 months after renal biopsy.

Nuclei with different degrees of DNA fragmentation were mainly found in epithelial cells of tubules, but also in glomerular cells, regardless of the form of GN studied. Transglutaminase II expression was found only in cells with a strong staining for DNA fragmentation. DNA fragmentation localized to glomerular cells was more pronounced in proliferative than in non-proliferative forms of GN, being most abundant in patients with rapid progressive GN. Staining for activated caspase 3 in selected biopsies confirmed the presence of apoptosis. BAX and BCL-2 staining was detected within the same cells, but exhibited a different intracellular distribution. In proliferative GN, the extent of DNA damage in tubular epithelial cells significantly corresponds with the concentration of serum creatinine (p < 0.04) and with urinary excretion of alpha(1)-microglobulin (p < 0.01) at the time of biopsy. A significant correlation (p < 0.01) was seen between glomerular DNA fragmentation and follow-up total proteinuria 12 months after biopsy for proliferative forms of GN. The damaged glomerular area (e.g. mesangial sclerosis) significantly correlated with DNA fragmentation in proliferative, but not in nonproliferative GN at the time of biopsy. Furthermore, glomerular damaged showed a significant correlation with tubular DNA damage in proliferative GN.

In glomerular cells, apoptosis may be important for the clearance of proliferating cells whereas in tubules, cell damage showed dependence on the degree of tubular injury mediated by inflammation and/or proteinuria. Although the degree of apoptosis in tubular cells correlates with serum creatinine in proliferative GN at the time of biopsy, it is of limited use to predict future renal function.