In 2008, we discovered that intact kidneys produce large quantities of 2',3'-cAMP (a positional isomer of 3',5'-cAMP), that 2',3'-cAMP derives from mRNA degradation and that energy depletion massively increases renal 2',3'-cAMP biosynthesis. This was the FIRST documentation of endogenous 2',3'-cAMP in any organ, tissue or cell. This exciting discovery triggered an eureka moment: 2',3'-cAMP may be an unrecognized, but critically important, source of extracellular adenosine! We have now confirmed this hypothesis, and we refer to the production of 2',3'-cAMP, followed by its conversion to adenosine, via 2'-AMP and 3'-AMP, as the 2',3'- cAMP-Adenosine Pathway. The focus of this application is the role of 2',3'-cyclic nucleotide-3'- phosphodiesterase (CNPase) in the renal 2',3'-cAMP-adenosine pathway. CNPase is an enzyme that can convert 2',3'-cAMP to 2'-AMP and is the ONLY enzyme known to promote this reaction. Why do we think that renal CNPase is important? A recent report demonstrates that intracellular 2',3'-cAMP opens mitochondrial permeability transition pores (mPTPs), and it is well known that opening of mPTPs leads to apoptosis and necrosis. Moreover, many studies demonstrate that adenosine, via specific receptors, protects the kidney from ischemia/reperfusion injury. Therefore, CNPase should be renoprotective because it likely reduces the intracellular levels of an intracellular toxn (2',3'-cAMP) and concomitantly increases the extracellular levels of a protective metabolite (adenosine). The main goal of the present proposal is to quantify the importance of renal CNPase in regulating renal levels of 2',3'-cAMP and adenosine. We will employ a LC-MS/MS assay for the 2',3'-cAMP metabolome using a 13C-labeled internal standard to examine: 1) the metabolism of exogenous 2',3'-cAMP to 2'-AMP, 3'-AMP, adenosine and inosine by intact kidneys and renal cells from CNPase -/-, CNPase -/+ and CNPase +/+ mice;and 2) the metabolism of endogenous (triggered by energy depletion) 2',3'-cAMP to 2'-AMP, 3'-AMP, adenosine and inosine by intact kidneys and renal cells from CNPase -/-, CNPase -/+ and CNPase +/+ mice. If CNPase is involved in the renal metabolism of 2',3'-cAMP, then this should be reflected in the renal metabolome of exogenous and endogenous 2',3'-cAMP. Finally, we will quantify renal damage induced by ischemia/reperfusion injury in kidneys from CNPase -/-, CNPase -/+ and CNPase +/+ mice. If CNPase is involved in ridding cells of 2',3'-cAMP or increasing extracellular adenosine, then renal injury should be exacerbated in kidneys deficient in CNPase. Our hypothesis has several critically important implications: 1) Renal CNPase may be a key enzyme in protecting the kidneys from insults;2) Malfunction of this enzyme (because of disease or drugs) could explain why some patients develop acute or chronic renal failure in response to renal injury;and 3) Pharmacological or molecular manipulation of the 2',3'- cAMP-adenosine pathway may offer an effective approach to reducing the risk of acute and chronic renal failure, diseases which are costly, prevalent and life altering.
We hypothesize that 2',3'-cyclic nucleotide-3'-phosphodiesterase (CNPase) protects the kidneys from injury. Our hypothesis, if correct, has several critically important implications: 1) renal CNPase should be viewed as a key enzyme in protecting the kidneys from insults;2) malfunction of this enzyme (because of disease or drugs) could explain why some patients develop acute or chronic renal failure in response to renal injury;and 3) pharmacological or molecular manipulation of the 2',3'-cAMP-adenosine pathway may offer an effective approach to reducing the risk of acute and chronic renal failure, diseases which are costly, prevalent and life altering.
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