Abstract: FR-PO369

Calcineurin A-Alpha regulation of Nox2 via NFκB Is Involved in Cyclosporine-Induced Nephrotoxicity

Session Information

Category: Chronic Kidney Disease (Non-Dialysis)

  • 308 CKD: Mechanisms of Tubulointerstitial Fibrosis

Authors

  • Cheriyan, Aswathy Miriam, Emory University, Atlanta, Georgia, United States
  • Hoover, Robert S., Emory University, Atlanta, Georgia, United States
  • Williams, Clintoria R., Emory University, Atlanta, Georgia, United States
Background

The calcineurin inhibitor cyclosporine (CsA) is an effective immunosuppressant and dramatically improved the outcomes of transplant patients. However, one long-term consequence of CsA and other calcineurin inhibitor treatments is nephrotoxicity attributed to oxidative damage. Calcineurin has two primary isoforms of the catalytic subunit - CnAα and CnAβ. The renal phenotype of CnAα-/- mice substantially mirrors CsA nephrotoxicity whereas CnAβ-/- mice do not. However, mechanisms downstream of CnAα that are involved in nephrotoxicity are poorly understood. Since NADPH oxidase-2 (Nox2) derived oxidative stress has been implicated in CsA nephrotoxicity, we hypothesized that inhibition of CnAα by CsA stimulates Nox2 upregulation and promotes oxidative stress.

Methods

To test this hypothesis, WT mice were administered CsA or vehicle alone daily for 6 weeks. Kidneys were then collected for analysis of CnAα isoform activity, Nox2 expression and ROS generation. In addition, Nox2 regulation was investigated in kidneys from CnAα-/-, CnAβ-/- and WT mice. Since Nox2 may be transcriptionally regulated via the NFκB pathway, fibroblasts derived from CnAα-/-, CnAβ-/- and WT mouse kidneys were treated with the NFκB inhibitor, caffeic acid phenethyl ester (CAPE).

Results

In WT mice, CnAα was the predominant isoform bound to calmodulin, consistent with previous in vitro findings showing that CnAα is the basally active isoform. CnAα-calmodulin association was disrupted with CsA treatment and was accompanied by enhanced Nox2 upregulation. Consistent with CsA inhibition of CnAα, Nox2 upregulation and ROS generation occurred only in CnAα-/- mice. Interestingly, NFκB but not NFAT activation was observed. In CnAα-/- renal fibroblasts, NFκB inhibition prevented Nox2 and ROS upregulation.

Conclusion

Our findings demonstrate that CnAα plays a key role in Nox2 regulation and ROS generation. Additionally, loss of CnAα activity, such as with CsA, promotes Nox2-mediated oxidative stress via an NFκB-dependent mechanism. These novel findings provide additional evidence of divergent CnA isoform signaling pathways. Therefore, selective targeting of CnAα and not CnAβ could improve the long-term outcomes of transplant patients.

Funding

  • NIDDK Support