Oligonephronia, not exuberant apoptosis, accounts for the development of glomerulosclerosis in the bcl-2 knockout mouse.

BACKGROUND

A main function attributed to B cell leukaemia/lymphoma 2 gene (bcL-2) is its ability to confer resistance against apoptosis. In bcl-2 deficient mice, extensive apoptosis occurs during abnormal nephrogenesis, and renal failure is found very quickly after birth. However, the underlying mechanisms remain poorly understood. The aim of the present study was to clarify whether the degenerative process in the kidneys seen after birth is based either on increased apoptosis of glomerular cells or on mechanisms independent from the genetic defect.

MATERIALS AND METHODS

Kidneys from 7-56-day-old bcl-2 knockout mice and wild-type litter mates were studied. Glomerular number, glomerular tuft volume, cell counts in 'non-sclerotic' glomeruli as well as the glomerular damage score were determined by histomorphometrical studies. Apoptosis was evaluated by morphological criteria and the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labelling (TUNEL)-technique.

RESULTS

The number of nephrons at birth was severely decreased in bcl-2 knockout mice compared to controls (<20%; P < 0.001). These nephrons undergo dramatic hypertrophy with an approximately 4-fold increase in volume (P < 0.001). In hypertrophic, but 'non-sclerotic' glomeruli, the number density of glomerular cells progressively declined with time (P<0.001). Starting with day 20, enlarged glomeruli developed sclerosis beginning with a segmental distribution, but quickly progressing to global sclerosis. Apoptosis was neither detected in non-sclerotic glomeruli nor in stages prior to fully established sclerosis. As shown by the glomerular damage score, post-natal degeneration of kidneys from bcl-2 knockout animals proceeded rapidly.

CONCLUSIONS

Bcl-2 knockout mice exhibit deficient nephrogenesis resulting in severe oligonephronia at birth. Post-partum development of glomerulosclerosis does not seem to be due to augmented apoptosis. The degenerative process appears to be based on a glomerular overload with increased mechanical stress to the filtration barrier, leading via glomerular hypertrophy, podocyte damage and formation of tuft adhesions to glomerulosclerosis.