Effects of Fibroblast Growth Factor 23 and aKlotho on adult cardiomyocytes – EFIKAC
Renal insufficiency is a frequent disorder affecting 10% of the population. It is associated with elevated risks of cardiovascular death at any stage of the disorder. The causes of the high cardiovascular morbidity remain uncertain and are only weakly associated with the traditional risk factors. In clinical studies elevated Fibroblast Growth Factor 23 (FGF23) plasma concentrations have been consistently associated with an increased risk of death even at the early stage of kidney disease. Few data obtained in animals suggest that intact-FGF23 could directly induce heart hypertrophy. FGF23 is a hormone-like FGF synthesized by osteocytes. It controls phosphate and vitamin D homeostasis. Its physiological effects are restricted to the kidney and the parathyroid gland. In the kidney FGF23 decreases calcitriol production, which consequently lowers intestinal phosphate absorption and inhibits phosphate reabsorption from urine in the renal proximal tubule. FGF23 plasma concentration increases at the very early stage of renal insufficiency in order to maintain normal serum phosphate concentration. Physiological FGF23 effects require the co-expression at the cell surface of a FGF receptor (FGFR) and aKlotho, a protein that acts as a co-receptor. aKlotho expression is restricted to few organs including the kidney and the parathyroid glands but in is absent in cardiomyocytes. A circulating form of aKlotho is present in the plasma. Its function is unknown. FGF23 can be cleaved in N and C-terminal peptides that have no physiological effect but could interfere with intact-FGF23 actions. Preliminary results obtained in collaboration by the two partners of this project have shown that intact-FGF23 can alter various functions of rat ventricular cardiomyocytes. These effects are mediated by a FGFR in the absence of aKlotho. The aim of this project is to further characterize the effects of intact FGF23 on cardiomyocyte and to determine if soluble aKlotho or the fragments of FGF23 can interfere with FGF23 effects on cardiomyocytes. In a first step we will perform experiments on primary culture of rat ventricular cardiomyocytes to determine if soluble aKlotho or FGF23 fragments alone can modify cardiomyocyte size, the kinetics of contraction, and calcium current transients. Using a proteomic platform we will assess the modifications of protein expression induced by the incubation of cardiomyocytes with soluble aKlotho or FGF23 fragments. We will check if aKlotho and FGF23 fragment can interfere with intact FGF23 action on cardiomyocytes. On the basis of the results obtained we will carry out in vivo experiments in rats with renal insufficiency to determine if overexpression of soluble aKlotho or FGF23 fragments alone or in combination could prevent intact FGF23 off-target effects on heart. aKlotho and FGF23 proteins will be expressed using adeno-associated viruses. We will measure heart conduction and functions using ECG, echocardiography, and cardiac MRI. We will perform histology analysis. We will check the occurrence of arrhythmia and heart performance with Langendorff apparatus. We will control if these treatments affect FGF23 function on phosphate and vitamin D homeostasis. Our result will determine if intact FGF23 can be a therapeutic target and if soluble aKlotho or FGF23 fragments can be used to design new therapeutic strategies to prevent the high rate of cardiovascular death observed in chronic kidney disease, which is a public health concern. Decreasing FGF23 concentration using blocking antibodies cannot be used to lower FGF23 effects on heart. In animals this strategy augments the mortality since it results in an increase in plasma phosphate concentration and subsequent vascular calcifications due to the suppression of the beneficial effect of intact FGF23 on the kidney to regulate phosphate homeostasis. This project aims at finding methods to prevent intact FGF23 action on heart without altering its effects on the kidney.
Monsieur Dominique Prié (Institut Necker Enfants Malades)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
INSERM UMRS 1180 Institut National de la Santé et de la Recherche Médicale
UPD-UMRS1151 Institut Necker Enfants Malades
Help of the ANR 469,975 euros
Beginning and duration of the scientific project: September 2016 - 36 Months