Translational study of the fibroblast growth factor (FGF)-23-klotho axis in the setting of uremic cardiomyopathy: Specific role in calcium handling and ventricular rhythm.

• Autores: José Alberto Navarro García
• Directores de la Tesis: Gema Ruiz Hurtado (dir. tes.), María Fernández Velasco (dir. tes.)
• Lectura: En la Universidad Autónoma de Madrid ( España ) en 2020
• Idioma: inglés
• Número de páginas: 135
• Tribunal Calificador de la Tesis: Ana Belén Sanz Bartolomé (presid.), Javier Blanco Rivero (secret.), Marta Crespo Barrio (voc.), Ana Maria Gomez Garcia (voc.), Tarik Smani Hajami (voc.)
• Programa de doctorado: Programa de Doctorado en Biociencias Moleculares por la Universidad Autónoma de Madrid
• Menciones:
  • Internacional
• Calificación: Sobresaliente Cum Laude
• Materias:
  • Química
    • Bioquímica
• Enlaces
  • Tesis en acceso abierto en: Biblos-e Archivo
• Resumen

  • Background. Chronic kidney disease (CKD), especially dialysis-dependent CKD, is associated with an increased risk of cardiovascular disease (CVD) and mortality. The commonest cardiac events in CKD patients are heart failure and arrhythmias. CKD is associated with increased levels of fibroblast growth factor (FGF)-23 and decreased levels of klotho, both involved in the CKD-related mineral bone disorders. The aim of this work was to study the role of the FGF-23-klotho axis on cardiac dysfunction and alterations in ventricular rhythm in the setting of CKD.

    Methods and results. Circulating FGF-23 levels and alterations in ventricular rhythm were analyzed in a cohort of dialysis patients of Hospital 12 de Octubre. FGF-23 levels were associated with long QT in dialysis patients. The direct FGF-23 effects on cardiac rhythm were analyzed in healthy C57BL/6J mice in vivo. FGF-23 injection induced prolongation of QT interval in healthy mice. Acute in vitro FGF-23 (100 ng/mL) effects were assessed on excitation-contraction (EC)-coupling in adult ventricular isolated cardiomyocytes using patch-clamp and confocal microscopy techniques. FGF-23 also impaired Ca2+ handling by compromising systolic Ca2+ release and cellular contraction and increasing the occurrence of pro-arrhythmogenic Ca2+ events in adult ventricular cardiomyocytes via the calmodulin kinase type II (CaMKII)-dependent pathway. Preincubation with klotho prevented FGF-23 effects on Ca2+ handling. The impact of klotho on cardiac function and rhythm was studied using the klotho-deficiency (kl/kl) and 5/6 nephrectomy (Nfx) mice (both models of uremic cardiomyopathy characterized by increased FGF-23 and reduced klotho levels). In addition, two strategies to improve klotho availability were used for Nfx mice: chronic supply of recombinant klotho and klotho-overexpressing mice. Klotho deficiency and Nfx mice exhibited similar impaired Ca2+ handling characterized by cardiac dysfunction, electrical remodeling, increased pro-arrhythmogenic Ca2+ activity and long QT phenotype. These alterations were prevented in Nfx mice by enhancing klotho availability through exogenous chronic klotho-treatment or by endogenous klotho-overexpression. To decode the possible mechanisms responsible for Ca2+ mishandling, target proteins involved in Ca2+ dynamics as ryanodine receptor (RyR) or sarcoplasmic reticulum (SR)- Ca2+ adenosine triphosphatase 2a pump (SERCA2a) were analyzed using different biochemical approaches as quantitative real-time PCR, western blot or binding analysis. Increased RyR phosphorylation, RyR hyperactivity and decreased SERCA function were observed in in vitro and in vivo approaches.

    Conclusion. This Doctoral Thesis demonstrates that CKD uremic milieu characterized by high FGF-23 levels is involved in cardiac dysfunction and pro-arrhythmogenic events including the prolonged QT interval. This translational study highlights klotho as a new therapeutic strategy to prevent FGF-23 deleterious cardiac actions on cellular Ca2+ mishandling, electrical remodeling and prolongation of QT interval observed in uremic cardiomyopathy