Tobias E. Larsson

Fibroblast growth factor-23 regulates parathyroid hormone and 1alpha-hydroxylase expression in cultured bovine parathyroid cells

Fibroblast growth factor-23 (FGF23) is a circulating factor that decreases serum levels of inorganic phosphate (Pi) as well as 1,25-dihydroxyvitamin D(3). Recent studies also suggest a correlation between serum levels of FGF23 and parathyroid hormone (PTH) in patients with chronic kidney disease. It is, however, unknown whether FGF23 directly modulates PTH expression, or whether the correlation is secondary to abnormalities in Pi and vitamin D metabolism. The objective of the current study was therefore to elucidate possible direct effects of FGF23 on bovine parathyroid cells in vitro. Treatment of parathyroid cells with a stabilized form of recombinant FGF23 (FGF23(R176Q)) induced a rise in early response gene-1 mRNA transcripts, a marker of FGF23 signaling. FGF23(R176Q) potently and dose-dependently decreased the PTH mRNA level within 12 h. In agreement, FGF23(R176Q) also decreased PTH secretion into conditioned media. In contrast, FGF23(R176Q) dose-dependently increased 1alpha-hydroxylase expression within 3 h. FGF23 (R176Q) did not affect cell viability nor induce apoptosis, whereas a small but significant increase in cell proliferation was found. We conclude that FGF23 is a negative regulator of PTH mRNA expression and secretion in vitro. Our data suggest that FGF23 may be a physiologically relevant regulator of PTH. This defines a novel function of FGF23 in addition to the previously established roles in controlling vitamin D and Pi metabolism.

Plasma parathyroid hormone and the risk of cardiovascular mortality in the community

Background— Diseases with elevated levels of parathyroid hormone (PTH) such as primary and secondary hyperparathyroidism are associated with increased incidence of cardiovascular disease and death. However, data on the prospective association between circulating PTH levels and cardiovascular mortality in the community are lacking. Methods and Results— The Uppsala Longitudinal Study of Adult Men (ULSAM), a community-based cohort of elderly men (mean age, 71 years; n=958), was used to investigate the association between plasma PTH and cardiovascular mortality. During follow-up (median, 9.7 years), 117 participants died of cardiovascular causes. In Cox proportional-hazards models adjusted for established cardiovascular risk factors (age, systolic blood pressure, diabetes, smoking, body mass index, total cholesterol, high-density lipoprotein cholesterol, antihypertensive treatment, lipid-lowering treatment, and history of cardiovascular disease), higher plasma PTH was associated with higher risk for cardiovascular mortality (hazard ratio for 1-SD increase in PTH, 1.38; 95% confidence interval, 1.18 to 1.60; P<0.001). This association remained essentially unaltered in participants without previous cardiovascular disease and in participants with normal PTH (<6.8 pmol/L) with no other signs of a disturbed mineral metabolism (normal serum calcium, 2.2 to 2.6 mmol/L; normal glomerular filtration rate, >50 mL · min−1 · 1.73 m−2 and without vitamin D deficiency, plasma 25-OH vitamin D >37.5 nmol/L). Interestingly, elevated plasma PTH (>5.27 pmol/L) accounted for 20% (95% confidence interval, 10 to 26) of the population-attributable risk proportion for cardiovascular mortality. Conclusions— Plasma PTH levels predict cardiovascular mortality in the community, even in individuals with PTH within the normal range. Further studies are warranted to evaluate the clinical implications of measuring PTH in cardiovascular risk prediction and to elucidate whether PTH is a modifiable risk factor.

Circulating fibroblast growth factor-23 is associated with vascular dysfunction in the community

OBJECTIVE Subjects with chronic kidney disease (CKD) are at higher risk for cardiovascular (CV) disease than the general population. These patients have elevated circulating levels of FGF23, which predict for increased mortality in CKD patients on hemodialysis. Since CV disease is a major cause of death in CKD, we investigated the association between FGF23 and vascular function. METHODS AND RESULTS We employed a community-based cohort of subjects aged 70, the PIVUS study (n=967), to investigate the relation between serum FGF23, endothelium function and arterial stiffness. Higher FGF23 was weakly associated with both impaired endothelium-dependent (beta=-0.08, p<0.05) and endothelium-independent (beta=-0.08, p<0.01) vasodilation. The association was stronger in subjects with eGFR> or =90mL/min/1.73m(2) (beta=-0.19 and beta=-0.22, respectively, p<0.001). In addition, higher FGF23 was associated with increased arterial stiffness exclusively in subjects with an age-adjusted impaired renal function (eGFR<60mL/min/1.73m(2)) (beta=0.26, p<0.001). All associations were independent of gender, biochemical covariates and established CV risk factors. CONCLUSIONS Higher serum FGF23 levels, even within the normal range, are independently associated with impaired vasoreactivity and increased arterial stiffness in the community. Additional studies are required to determine possible direct vascular effects of FGF23 and whether FGF23 is a modifiable CV risk factor.

Serum intact FGF23 associate with left ventricular mass, hypertrophy and geometry in an elderly population ☆

Fibroblast growth factor-23 (FGF23) is a hormonal regulator of circulating phosphate and vitamin D levels. Serum FGF23 is elevated in chronic kidney disease (CKD) and is a prognostic marker of poor outcomes, such as faster CKD progression and increased mortality in hemodialysis patients. Despite the high prevalence of cardiovascular disease in CKD, the relation between circulating FGF23 and cardiovascular risk factors, both in CKD and in the community, has not been studied in detail. We evaluated the relation between FGF23, left ventricular mass index (LVMI), hypertrophy (LVH) and LV geometry, employing the community-based PIVUS cohort. In total, 795 Swedish men and women aged 70 were included of which 164 had an age-adjusted diminished renal function (estimated glomerular filtration rate<60mL/min/1.73m(2)). FGF23 was positively associated with LVMI (beta=0.11, CI 0.01-0.18), with increased odds for the presence of LVH (OR 1.28, CI 1.09-1.51) and for concentric hypertrophy (OR 1.45, CI 1.19-1.77) in the whole population. All associations were stronger in subjects with eGFR<60mL/min/1.73m(2) (beta=0.30, CI 0.15-0.46 for LVMI; OR 1.86, CI 1.30-2.67 for the presence of LVH; OR 1.83, CI 1.17-2.85 and OR 1.87, CI 1.08-3.22 for concentric and eccentric hypertrophy, respectively). The results were essentially unaltered in multivariate models. In summary, elevated serum FGF23 levels, even within the normal range, are associated with increased LVMI and increased risk for the presence of LVH in elderly subjects. Additional longitudinal studies that evaluate the predictive power of FGF23 and whether FGF23 has additional clinical applications are needed.

Relationship between circulating FGF23 and total body atherosclerosis in the community

BACKGROUND Fibroblast growth factor-23 (FGF23) is a regulator of mineral metabolism and has been suggested to play a role in vascular calcification in chronic kidney disease (CKD). Data on the association between FGF23 and atherosclerosis, both in CKD and in the community, is limited. METHODS The total body atherosclerosis score (AS) was determined by a magnetic resonance imaging-based angiography in 306 elderly men and women, representing a subsample of the community-based PIVUS cohort. Subjects were divided into three categories based on AS: AS = 0, low AS and high AS. Serum FGF23 was measured using a two-site monoclonal antibody ELISA. RESULTS In continuous and multi-category regression models, higher FGF23 was associated with a significant increase in the odds of having a high AS (OR 1.43, CI 1.06-1.92 to OR 3.01, CI 1.52-5.99). This association was stronger in individuals with eGFR <60 mL/min/1.73 m(2) (n = 27), reaching a nearly 6-fold increase in the odds for a high AS in the upper FGF23 tertile (OR 5.64, CI 2.78-11.5). We found weaker support for a relationship between FGF23 and the presence of atherosclerosis as subjects in the highest FGF23 tertile had an increased risk for an AS > 0 in crude models (OR 1.93, CI 1.05-3.55), but this was not statistically significant in adjusted (OR 1.42, CI 0.74-1.72) models. CONCLUSIONS We provide novel evidence supporting an association between serum FGF23 and total body atherosclerosis in the community. Additional studies are warranted to determine the prospective relationship between FGF23 and atherosclerosis, and whether FGF23 is a modifiable cardiovascular risk factor.

Circulating Fibroblast Growth Factors as Metabolic Regulators—A Critical Appraisal

The circulating FGFs are a new group of proteins believed to function as classic hormones. With emphasis on human metabolism, we critically review current data, and propose that--although a number of questions remain--circulating FGF23 is pivotal in the control of phosphate and vitamin D metabolism, and may have additional systemic effects, particularly in chronic kidney disease; that FGF19 signaling is important for the regulation of bile acid metabolism, whereas its physiological role in promoting glucose and lipid metabolism is less well understood; and that the physiological role of circulating FGF21 in metabolic homeostasis warrants further investigation.

The Kidney Is the Principal Organ Mediating Klotho Effects

Klotho was discovered as an antiaging gene, and α-Klotho (Klotho) is expressed in multiple tissues with a broad set of biologic functions. Membrane-bound Klotho binds fibroblast growth factor 23 (FGF23), but a soluble form of Klotho is also produced by alternative splicing or cleavage of the extracellular domain of the membrane-bound protein. The relative organ-specific contributions to the levels and effects of circulating Klotho remain unknown. We explored these issues by generating a novel mouse strain with Klotho deleted throughout the nephron (Six2-KL(-/-)). Klotho shedding from Six2-KL(-/-) kidney explants was undetectable and the serum Klotho level was reduced by approximately 80% in Six2-KL(-/-) mice compared with wild-type littermates. Six2-KL(-/-) mice exhibited severe growth retardation, kyphosis, and premature death, closely resembling the phenotype of systemic Klotho knockout mice. Notable biochemical changes included hyperphosphatemia, hypercalcemia, hyperaldosteronism, and elevated levels of 1,25-dihydroxyvitamin D and Fgf23, consistent with disrupted renal Fgf23 signaling. Kidney histology demonstrated interstitial fibrosis and nephrocalcinosis in addition to absent dimorphic tubules. A direct comparative analysis between Six2-KL(-/-) and systemic Klotho knockout mice supports extensive, yet indistinguishable, extrarenal organ manifestations. Thus, our data reveal the kidney as the principal contributor of circulating Klotho and Klotho-induced antiaging traits.

Circulating Fibroblast Growth Factor-23 Is Associated With Fat Mass and Dyslipidemia in Two Independent Cohorts of Elderly Individuals

Objective—Disturbances in mineral metabolism define an increased cardiovascular risk in patients with chronic kidney disease. Fibroblast growth factor-23 (FGF23) is a circulating regulator of phosphate and vitamin D metabolism and has recently been implicated as a putative pathogenic factor in cardiovascular disease. Because other members of the FGF family play a role in lipid and glucose metabolism, we hypothesized that FGF23 would associate with metabolic factors that predispose to an increased cardiovascular risk. The goal of this study was to investigate the relationship between FGF23 and metabolic cardiovascular risk factors in the community. Methods and Results—Relationships between serum FGF23 and body mass index (BMI), waist circumference, waist-to-hip ratio, serum lipids, and fat mass were examined in 2 community-based, cross-sectional cohorts of elderly whites (Osteoporotic Fractures in Men Study: 964 men aged 75±3.2; Prospective Investigation of the Vasculature in Uppsala Seniors study: 946 men and women aged 70). In both cohorts, FGF23 associated negatively with high-density lipoprotein and apolipoprotein A1 (7% to 21% decrease per 1-SD increase in log FGF23; P<0.01) and positively with triglycerides (11% to 14% per 1-SD increase in log FGF23; P<0.01). A 1-SD increase in log FGF23 was associated with a 7% to 20% increase in BMI, waist circumference, and waist-to-hip ratio and a 7% to 18% increase in trunk and total body fat mass (P<0.01) as determined by whole-body dual x-ray absorptiometry. FGF23 levels were higher in subjects with the metabolic syndrome compared with those without (46.4 versus 41.2 pg/mL; P<0.05) and associated with an increased risk of having the metabolic syndrome (OR per 1-SD increase in log FGF23, 1.21; 95% CI, 1.04 to 1.40; P<0.05). Conclusion—We report for the first time on associations between circulating FGF23, fat mass, and adverse lipid metabolism resembling the metabolic syndrome, potentially representing a novel pathway(s) linking high FGF23 to an increased cardiovascular risk.

Higher fibroblast growth factor-23 increases the risk of all-cause and cardiovascular mortality in the community

Fibroblast growth factor-23 (FGF23), a regulator of mineral metabolism, has been linked to cardiovascular disease in chronic kidney disease. As community-based data of the longitudinal association between FGF23 and cardiovascular events are lacking, we investigated a possible relationship in 727 men of the Uppsala Longitudinal Study of Adult Men population-based cohort (mean age 77 years). During a median follow-up of 9.7 years, 110 participants died of cardiovascular causes. In Cox regression models adjusted for age and established cardiovascular risk factors, higher serum FGF23 was associated with a significantly increased risk for cardiovascular mortality (hazard ratio (HR) per increased s.d. of 1.36). This relationship remained significant, albeit attenuated, after adjustment for glomerular filtration rate (GFR) (HR 1.21). FGF23 was also associated with all-cause mortality, although the association was weaker than that with cardiovascular mortality, and it was nonsignificant in fully adjusted multivariate models. Spline analysis suggested a log-linear relationship between FGF23 and outcome. Participants with a combination of high FGF23 (>60 pg/ml), low GFR (<60 ml/min), and micro-/macro-albuminuria (albumin/creatinine ratio above 3 mg/ml) had an almost eightfold increased risk compared with participants without these abnormalities. Thus, a higher FGF23 level is associated with an increased cardiovascular mortality risk in the community. Clinical trials are needed to determine whether FGF23 is a modifiable risk factor.

Chronic Kidney Disease: A Clinical Model of Premature Aging

Premature aging is a process associated with a progressive accumulation of deleterious changes over time, an impairment of physiologic functions, and an increase in the risk of disease and death. Regardless of genetic background, aging can be accelerated by the lifestyle choices and environmental conditions to which our genes are exposed. Chronic kidney disease is a common condition that promotes cellular senescence and premature aging through toxic alterations in the internal milieu. This occurs through several mechanisms, including DNA and mitochondria damage, increased reactive oxygen species generation, persistent inflammation, stem cell exhaustion, phosphate toxicity, decreased klotho expression, and telomere attrition. Because recent evidence suggests that both increased local signaling of growth factors (through the nutrient-sensing mammalian target of rapamycin) and decreased klotho expression are important modulators of aging, interventions that target these should be tested in this prematurely aged population.