Production of Nitric Oxide, but Not Prostacyclin, Is Reduced in Klotho Mice

Abstract

ABSTRACT-A novel murine model of aging (kl /kl mice) has been developed by in vivo mutagenesis. We analyzed endothelial function in this strain. Ring preparations of the thoracic aorta were obtained from 6-to 9-week old wild-type (+ /+) and heterozygous (kl /+) klotho mice. The aortas of kl /+ mice showed an exaggerated contractile response to norepinephrine and attenuated vasodilator responses to acetylcholine and lecithinized superoxide dismutase (SOD) compared to + /+ mice. The response to sodium nitroprusside was unaltered in kl /+ mice. The contraction in response to norepinephrine was augmented by treatment with N G -nitro-L-arginine methyl ester (L-NAME, 10 -5 M) to a greater extent in + /+ mice than in kl /+ mice. Treatment with L-NAME abolished the vasodilator responses to both acetylcholine and lecithinized SOD. NO metabolites (NO2 -and NO3 -) and cGMP concentrations in the urine were significantly reduced in kl /+ mice compared to + /+ mice. However, the urinary excretion of 6-keto-prostaglandin F1= was unaltered. There was little immunostaining for NO synthase and vascular endothelial growth factor (VEGF) in the aorta of kl /+ mice. No immunostaining for NO synthase was noted in the aorta of kl /kl mice. The expression of the klotho gene product may have a role in the regulation of VEGF expression and is tightly linked to endothelial release of NO.

Competitive Interaction Between Fibroblast Growth Factor 23 And Asymmetric Dimethylarginine in Patients With CKD

“…Indeed, Klotho knockout mice 35,36 (i.e., animal models characterized by high plasma levels of FGF-23 37 ) do not express NO synthase in the vascular system and exhibit almost abolished response to acetylcholine, the strongest stimulant of NO activity. 36 Our findings show that ADMA has a variable influence on renal outcomes across the spectrum of FGF-23 values because it is associated with a higher risk for CKD progression only when FGF-23 levels are in the low-normal range (i.e., when the expression of NO synthase is not suppressed by FGF-23-Klotho). This possibility has biologic plausibility because the gene expression of NO synthase is almost entirely abolished when FGF-23 levels are elevated, such as in the Klotho knockout mice.…”

“…This possibility has biologic plausibility because the gene expression of NO synthase is almost entirely abolished when FGF-23 levels are elevated, such as in the Klotho knockout mice. 35,36 Therefore, in this situation minimal or no effect of ADMA on NO synthesis can be envisaged and vice versa. Thus, FGF-23 and ADMA act jointly rather than independently on NO-dependent mechanisms, impinging upon renal integrity and renal function.…”

“…Their competitive interaction can be seen as an experiment where we injected a fixed dose of ADMA at progressively increasing levels of FGF-23. Because high FGF-23-Klotho almost completely suppresses NO synthase, 35,36 ADMA at high FGF-23 levels has no effect on the risk of CKD progression, an outcome strongly influenced by the NO system. 24 The observation that in the MMKD cohort not only ADMA but also SDMA (i.e., a methylarginine that inhibits NO synthesis by reducing cellular L-arginine uptake) showed a competitive interaction with c-terminal FGF-23 adds circumstantial support to our interpretation that these interactions depend on the interference of FGF-23-Klotho with the NO system.…”

Serum FGF23 and Risk of Cardiovascular Events in Relation to Mineral Metabolism and Cardiovascular Pathology

“…We speculate that a possible mechanism could be an impaired renal response to hormonal action (i.e., FGF23 resistance). Indeed, this phenomenon is a cardinal feature of CKD and is mediated by reduced expression of the FGF23 coreceptor Klotho (27), which has been shown to preserve and protect vascular integrity through multiple independent mechanisms (14,(28)(29)(30)(31). It is further possible that other aspects of tubular dysfunction modulate cardiovascular risk independently of baseline eGFR; indeed, tubular injury could cause long-term interstitial fibrosis and secondary glomerular scarring, which translates into a more rapid loss of GFR and increased cardiovascular risk.…”

Protective effect of extracellular superoxide dismutase on endothelial function during aging

“…Reduction of mRNA expression of Klotho has been demonstrated in the liver of old rats (28). In Klotho-knockout mice, eNOS expression in vessels was undetectable (19,24). The mechanism for the relationship between Klotho and eNOS is not known.…”