Calcineurin Aβ Regulates NADPH Oxidase ( Nox) Expression and Activity via Nuclear Factor of Activated T Cells ( NFAT) in Response to High Glucose*

Background: Similar to its role in other organs, calcineurin is involved in kidney hypertrophy. However, downstream targets are not known. Results: The isoform of calcineurin (CnA) is required for hypertrophy and regulates Nox2 and Nox4 expression and function through NFAT. Conclusion: CnA and not CnA mediates hypertrophy in renal cells and is required for chronic ROS generation. Significance: Interaction of calcineurin and Nox signaling is essential for renal hypertrophy. Hypertrophy is an adaptive response that enables organs to appropriately meet increased functional demands. Previously, we reported that calcineurin (Cn) is required for glomerular and whole kidney hypertrophy in diabetic rodents (Gooch, J. L., Barnes, J. L., Garcia, S., and Abboud, H. E. (2003). Calcineurin is activated in diabetes and is required for glomerular hypertrophy and ECM accumulation. Am. J. Physiol. Renal Physiol. 284, F144-F154; Reddy, R. N., Knotts, T. L., Roberts, B. R., Molkentin, J. D., Price, S. R., and Gooch, J. L. (2011). Calcineurin A is required for hypertrophy but not matrix expansion in the diabetic kidney. J. Cell Mol. Med. 15, 414-422). Because studies have also implicated the reactive oxygen species-generating enzymes NADPH oxidases (Nox) in diabetic kidney responses, we tested the hypothesis that Nox and Cn cooperate in a common signaling pathway. First, we examined the role of the two main isoforms of Cn in hypertrophic signaling. Using primary kidney cells lacking a catalytic subunit of Cn (CnA(-/-) or CnA(-/-)), we found that high glucose selectively activates CnA, whereas CnA is constitutively active. Furthermore, CnA but not CnA mediates hypertrophy. Next, we found that chronic reactive oxygen species generation in response to high glucose is attenuated in CnA(-/-) cells, suggesting that Cn is upstream of Nox. Consistent with this, loss of CnA reduces basal expression and blocks high glucose induction of Nox2 and Nox4. Inhibition of nuclear factor of activated T cells (NFAT), a CnA-regulated transcription factor, decreases Nox2 and Nox4 expression, whereas NFAT overexpression increases Nox2 and Nox4, indicating that the CnA/NFAT pathway modulates Nox. These data reveal that the CnA/NFAT pathway regulates Nox and plays an important role in high glucose-mediated hypertrophic responses in the kidney.