REGULATION OF ORNITHINE DECARBOXYLASE IN THE KIDNEY OF AUTOIMMUNE MICE WITH THE LPR GENE

The lymphoproliferative lpr gene confers a lupus-like disease with lym phadenopathy, antinuclear antibody production, and glomerulonephritis in MRL-lpr/lpr mice. Upregulation of ornithine decarboxylase (ODC) act ivity and polyamine levels have been observed in the kidney and lympho id organs of this strain. Inhibition of ODC with 0.5-1.5% (w/v) difluo romethylornithine (DEMO) in drinking water prolonged life-span and ame liorated renal disease. Glomerulonephritis is a major cause of morbidi ty and mortality in human and murine lupus. In order to elucidate the mechanism(s) of ODC regulation in lupus nephritis, we characterized OD C at the protein and mRNA levels in 3 strains of autoimmune mice with the lpr genetic background (MRL-lpr/lpr, C3H-lpr/lpr and C57BL/6J-lpr/ lpr) using Western blotting, enzyme kinetics, turnover rate measuremen ts, Northern blot hybridization, and reverse transcription-polymerase chain reaction (RT-PCR). Normal BALB/c mice were used as a control. We found that ODC activity in the kidney of lpr strains was 4- to 6-fold higher than that of BALB/c mice. The intensity of the major ODC prote in band at 54 kD in Western blot was 4-fold higher in MRL-lpr/lpr and C3H-lpr/lpr kidney compared to that of BALB/c kidney. Putrescine level s were 2- to 4-fold higher in kidney of lpr strains than that of BALB/ c and DFMO-treated MRL-lpr/lpr mice. DFMO treatment significantly redu ced ODC activity and polyamine levels. The half-life of ODC enzyme in MRL-lpr/lpr, C3H-lpr/lpr; B6-lpr/lpr and BALB/c mouse kidneys was 15, 5, 8 and 23 min, respectively. There was no significant difference in the K-m, values of different strains, whereas V-max values differed si gnificantly. There was no difference in the level of SAMDC, another en zyme involved in the polyamine biosynthetic pathway, in various strain . Steady-state levels of ODC mRNA were lower in lpr strains compared t o that of BALB/c mouse. Our results suggest that the basis for up-regu lation of ODC is not at the transcriptional level, but may involve pos t-transcriptional modification(s) in lpr strains. The link between abe rrant regulation of ODC and the immunopathogenesis of murine lupus nep hritis indicates novel targets for lupus therapy.