Splice variants of neuronal nitric oxide synthase are present in the rat kidney

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Abstract
Decreased renal cortical neuronal NO synthase (nNOS) abundance/activity correlates with progression of chronic kidney disease (CKD) in a number of animal models. Western blotting with both N-terminal and C-terminal antibodies, immunoprecipitation, proteomics, RT-PCR and in situ hybridization were used to identify nNOS splice variants in the rat kidney. We have identified two nNOS proteins and transcripts in the rat kidney; nNOSalpha (approximately 160 kDa) and nNOSbeta (approximately 140 kDa), a catalytically active exon-2 deletion variant, lacking both the PDZ and protein inhibitor of nNOS (PIN) domains. We also report that nNOSbeta protein abundance is increased in the kidney at 11 weeks following 5/6th nephrectomy (5/6NX)-induced CKD while nNOSalpha protein abundance is diminished. The transcript data parallel the protein data in 5/6NX. By in situ hybridization, there is abundant nNOSalpha mRNA widely distributed throughout the normal kidney cortex, with very sparse nNOSbeta mRNA confined to a few proximal tubules. In a second injury model (6 weeks after 5/6 renal mass reduction by combined right kidney ablation and infarction of approximately 2/3 of the left kidney; 5/6 A/I), nNOSalpha mRNA almost disappears from the kidney cortex while nNOSbeta mRNA abundance increases in tubules and tubulo-interstitium. The renal cortical nNOSbeta protein is present in low abundance in the normal kidney and increases with injury, in an inverse pattern of change with the nNOSalpha.