Expression of FGF23/KLOTHO system in human vascular tissue

https://doi.org/10.1016/j.ijcard.2011.08.850Get rights and content

Abstract

Background

Fibroblast growth factor (FGF)-23 levels have been associated with impaired vasoreactivity, increased arterial stiffness, and cardiovascular morbi-mortality, whereas a protective function of KLOTHO against endothelial dysfunction has been reported. Since expression of the FGF23–KLOTHO system in human vascular tissue remains unproved, we aimed to study the expression of FGF23, FGF receptors (FGFR) and KLOTHO in human aorta. In addition, we analyzed the FGF23–KLOTHO expression in occlusive coronary thrombi.

Methods

Thoracic aorta specimens from 44 patients underwent elective cardiac surgery, and thrombus material from 2 patients with acute coronary syndrome (ACS), were tested for FGF23–KLOTHO system expression.

Results

Expression of KLOTHO (mean expression level 4.85 ± 5.43, arbitrary units) and two of the three cognate FGFR (FGFR-1 and -3) were detected and confirmed by RT-PCR, sequencing and qRT-PCR. KLOTHO expression was confirmed within occlusive coronary thrombi from patients with ACS. However, expression of FGF23 and FGFR4 was not observed. We also detected the aortic expression of membrane-anchored A Desintegrin and Metalloproteinases (ADAM)-17, the enzyme responsible for the shedding of KLOTHO from the cell surface, and the anti-inflammatory cytokine interleukin (IL)-10. Interestingly, in aortic samples there was a direct association between KLOTHO mRNA levels and those of ADAM-17 and IL-10 (r = 0.54, P < 0.001; r = 0.51, P < 0.01, respectively).

Conclusions

Human vascular tissue expresses members of the FGF23–KLOTHO system, indicating that it can be a direct target organ for FGF23. In addition, KLOTHO expression is also detected in occlusive coronary thrombi. These findings suggest a putative role of FGF23–KLOTHO axis in human vascular pathophysiology and cardiovascular disease.

Introduction

Fibroblast growth factor (FGF)-23 is a recently discovered phosphaturic hormone synthesized and secreted by bone cells, mainly osteoblasts. This hormone acts primarily on the kidney, where it induces phosphaturia and suppresses vitamin D synthesis, regulating phosphate homeostasis [1]. FGF23 belongs to a subgroup of the FGF ligand superfamily called endocrine FGFs [2], [3], which, unlike paracrine and/or autocrine FGFs, posses differential features in their binding domains that allow them to enter into systemic circulation, but also determine them to require one or more cofactors to activate FGF receptors (FGFRs). Thus, FGF23 has very low affinity to FGFRs and it requires Klotho to bind and activate the cognate FGFRs under physiological concentration [4].

Since most tissues express FGFRs, presence of Klotho determines FGF23 target organs. The cognate FGFRs activated in the presence of transmembrane cofactor Klotho are FGFR1, 3 and 4 [5], [6], [7]. This represents a novel mechanism for confining target organs in redundant ligand–receptor interactions [2]. Until now, the organs described to express Klotho are distal convoluted tubules in the kidney, choroid plexus in the brain and also parathyroid gland, placenta, ovary, testis, small intestine, prostate, and sinoatrial node of the heart [8], [2], [5], [9], [10].

Recent studies have reported that higher serum FGF23 levels, even within the normal range, are independently associated with impaired vasoreactivity and increased arterial stiffness [11]. Moreover, in patients with stable coronary artery disease, higher FGF23 has been demonstrated to be independently associated with cardiovascular events and mortality [12]. On the other hand, secreted form of Klotho protein, formed by proteolytic cleavage on the cell surface by membrane-anchored A Desintegrin and Metalloproteinases (ADAM)-17 and -10, may also function as a humoral factor [13], and has been potentially related to protective mechanism against endothelial dysfunction by upregulating the anti-inflammatory cytokine interleukin-10 (IL-10) in vascular tissue [14]. Therefore, emerging evidence suggests that FGF23 and KLOTHO are factors potentially related to cardiovascular morbidity and mortality, raising the question whether FGF23–KLOTHO axis is involved in vascular pathology. Most of the works in this area have been done in vitro or in animal tissues, but the expression of FGF23, FGFRs and KLOTHO in human vascular tissue remains unproved. Therefore, we aimed to study the expression of members of the FGF23–KLOTHO axis in human aortic vascular tissue and also analyzed the expression of ADAM-17 and IL-10, factors related to KLOTHO functionality. In addition, we evaluated the expression of FGF23 and KLOTHO in coronary thrombi obtained from patients with acute coronary syndromes (ACS).

Section snippets

Patients

Thoracic aorta specimens were obtained from 44 consecutive patients (9 females, 35 males; mean age of 64.7 ± 9.3 years) who underwent elective cardiac surgery (coronary artery bypass surgery in 37 patients and replacement valvular surgery in 7 patients) at the Hospital Universitario de Canarias (Tenerife, Spain). Thrombus samples were collected using aspiration catheter from the site of coronary occlusion during primary percutaneous coronary intervention in two patients with ACS at the Cardiology

Expression of FGF23–KLOTHO axis components mRNA by RT-PCR

To analyze the expression of the components of the FGF23–KLOTHO axis (FGF23, KLOTHO and FGFRs) in human vascular tissue and thrombi, RT-PCR from cDNA reverse transcribed from extracted RNA was performed. FGF23 expression was not detected in any sample, whereas KLOTHO mRNA expression was demonstrated by obtaining an amplification product of the predicted size in all the specimens tested (Fig. 1). Regarding FGFRs, expression analysis in aortic tissue showed the presence of FGFR1, FGFR2 and FGFR3

Discussion

The main finding of the present study is to characterize the expression pattern of the components of the FGF23/KLOTHO system in human aortic vascular tissue. Specifically, our findings demonstrate the expression of KLOTHO and two cognate receptors for FGF23 (FGFR1 and FGFR3), whereas expression of FGF23 and FGFR4 was not detected. In addition, we also show that mRNA expression level of KLOTHO was direct and significantly correlated with expression levels of ADAM-17 and IL-10. Finally, we show

Acknowledgments

This study was funded by Fondo de Investigación Sanitaria, Instituto de Salud Carlos III, Ministerio de Sanidad y Consumo (Ref. PI 07/0870). The authors of this manuscript have certified that they comply with the Principles of Ethical Publishing in the International Journal of Cardiology.

References (37)

  • Y. Saito et al.

    In vivo klotho gene delivery protects against endothelial dysfunction in multiple risk factor syndrome

    Biochem Biophys Res Commun

    (2000)
  • H.L. Wang et al.

    A potential regulatory single nucleotide polymorphism in the promoter of the Klotho gene may be associated with essential hypertension in the Chinese Han population

    Clin Chim Acta

    (2010)
  • M. Riminucci et al.

    FGF-23 in fibrous dysplasia of bone and its relationship to renal phosphate wasting

    J Clin Invest

    (2003)
  • M. Kuro-o

    Overview of the FGF23–Klotho axis

    Pediatr Nephrol

    (2010)
  • X. Yu et al.

    Analysis of the biochemical mechanisms for the endocrine actions of fibroblast growth factor-23

    Endocrinology

    (2005)
  • I. Urakawa et al.

    Klotho converts canonical FGF receptor into a specific receptor for FGF23

    Nature

    (2006)
  • I.Z. Ben-Dov et al.

    The parathyroid is a target organ for FGF23 in rats

    J Clin Invest

    (2007)
  • M. Kuro-o et al.

    Mutation of the mouse klotho gene leads to a syndrome resembling ageing

    Nature

    (1997)
  • Cited by (85)

    • FGF23 and heart and vascular disease

      2021, Fibroblast Growth Factor 23
    View all citing articles on Scopus
    View full text