nutlin-3a and Necrosis

Murine double minute (MDM)-2, an E3 ubiquitin ligase, promotes cancer cell survival and growth, by degrading the cell cycle regulator p53. Antagonism of MDM2 by the small-molecule cis-imidazoline nutlin analogs is under current study for cancer therapy. To test whether MDM2 also promotes regenerative cell growth, we determined the effects of nutlin-3a on tubule cell healing during postischemic acute kidney injury (AKI). Treatment with nutlin-3a impaired tubular cell regeneration during postischemic AKI in wild-type mice in a p53-dependent manner; however, MDM2 blockade also prevented tubular necrosis by suppressing sterile inflammation during the early postischemic phase. This effect also occurred in p53 knockout mice, indicating a second, proinflammatory, p53-independent role for MDM2 in AKI. In vitro experiments confirmed that MDM2 is required to induce mRNA expression and secretion of NFκB-dependent cytokines upon Toll-like receptor stimulation by enhanced binding of NFκB to cytokine promoter-binding sites. Thus, MDM2 links inflammation and epithelial healing during AKI. These additional biological functions need to be regarded when considering MDM2 inhibition therapy.

Topics: Acute Kidney Injury; Animals; Apoptosis; Cell Cycle Checkpoints; Cell Proliferation; Cells, Cultured; Cytokines; Disease Models, Animal; Gene Expression Regulation; Imidazoles; Inflammation; Inflammation Mediators; Injections, Intraperitoneal; Kidney Tubules; Mice; Mice, Inbred C57BL; Mice, Knockout; Necrosis; NF-kappa B; Piperazines; Proto-Oncogene Proteins c-mdm2; Regeneration; Reperfusion Injury; RNA, Messenger; Time Factors; Tumor Suppressor Protein p53; Wound Healing

Systemic lupus erythematosus (SLE) is a polyclonal autoimmune syndrome directed against multiple nuclear autoantigens. Although RNA and DNA seem to have identical immunostimulatory effects on systemic and intrarenal inflammation, each seems to differ with regard to the propensity to induce mitogenic effects such as lymphoproliferation. To identify potential mechanisms by which DNA specifically contributes to the pathogenesis of lupus nephritis, we stimulated cells with immunostimulatory DNA or RNA in vitro and used microarray to compare the transcriptomes of RNA- and DNA-induced genes. Immunostimulatory DNA, but not RNA, induced Mdm2, which is a negative regulator of p53. In vivo, we observed greater expression and activation of Mdm2 in the spleen and kidneys in a mouse model of lupus (MRL-Fas(lpr) mice) than healthy controls. Treatment of MRL-Fas(lpr) mice with the Mdm2 inhibitor nutlin-3a prevented nephritis and lung disease and significantly prolonged survival. Inhibition of Mdm2 reduced systemic inflammation and abrogated immune complex disease by suppressing plasma cells and the production of lupus autoantibodies. In addition, nutlin-3a suppressed the abnormal expansion of all T cell subsets, including CD3(+)CD4(-)CD8(-) T cells, which associated with attenuated systemic inflammation. However, inhibiting Mdm2 did not cause myelosuppression or affect splenic regulatory T cells, neutrophils, dendritic cells, or monocytes. Taken together, these data suggest that the induction of Mdm2 promotes the expansion of plasma cells and CD3(+)CD4(-)CD8(-) T cells, which cause autoantibody production and immune complex disease in MRL-Fas(lpr) mice. Antagonizing Mdm2 may have therapeutic potential in lupus nephritis.

Topics: Animals; Autoantibodies; CD4-Positive T-Lymphocytes; CD8-Positive T-Lymphocytes; Cytosol; DNA; Female; Gene Expression; Glomerular Mesangium; Imidazoles; Lupus Erythematosus, Systemic; Lupus Nephritis; Mice; Mice, Inbred MRL lpr; Necrosis; NIH 3T3 Cells; Piperazines; Plasma Cells; Proto-Oncogene Proteins c-mdm2; Spleen