FGF23 and Klotho in Bone Mineralization in CKD

Katherine Wesseling Perry, MD MSCRAssociate Professor of Pediatrics

David Geffen School of Medicine at UCLA3/9/2019

Objectives

• 1. To understand the direct effects of FGF23 on mineral metabolism

• 2. To describe changes in FGF23 and Klotho levels in CKD

• 3. To understand complexities of the studies evaluating the direct effect of FGF23 and Klotho on bone in human CKD

FGF23: what it doesToo much: hypophosphatemic rickets

Too little: tumoral calcinosis

Is there a direct effect of FGF23 on bone?

FGF23: where it’s made

BoneCorrelation with blood levels (anuric):r=0.7; p

Klotho is expressed in osteocytes;Klotho null mice have osteoporosis

Kuro-o M et al Nature 1997

Rhee Y et al Bone 2011

Wild type Klotho-/-

Mineralization defects co-exist with increased FGF23 in early CKD

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CKD Stage2 3 4

Wesseling-Perry K et al CJASN 2013

Bone turnoverMineralization

Bone FGF23 (osteocytes/Bone Area)

OS/BS r = - 0.60, p

Direct effects of FGF23 and Klotho: confounding effects of 1,25D

Andrukhova O et al JBMR 2017

1,25D directly inhibits bone mineralization

Lieben L et al J Clin Invest 2012

FGF23 null fetuses have normal phosphate and skeletons

Ma Y et al Endocrinology 2017

Developmental change in receptors or a sign of very little effect on bone?

Klotho null fetuses also have normal skeletons

Ma Y et al Endocrinology 2017

Developmental change in receptors or a sign of very little effect on bone?

Forced FGF23 over-expression suppresses osteoblast

differentiation and mineralization

Wang H et al JBMR 2008

Osteocyte-specific Klotho deletion increases bone formation and mass

Komaba H et al Kidney Int 2017

Overexpression of Klotho inhibits mineralization of MC3T3 cells

Komaba H et al Kidney Int 2017

Exogenous FGF23 and Klotho together inhibit osteoblast

mineralization

Shalhoub V et al Calcif Tissue Int 2011

MC3T3.E1

FGF23 and Klotho inhibit osteoblastic Wnt signaling in CKD

Carillo-Lopez N et al Kidney Int 2016

Whole animal UMR106-01

UMR106-01

UMR106-01

Klotho is down-regulated in CKD bone; particularly in high phosphate

conditions

Komaba H et al Kidney Int 2017

CKD mimics the effect of Klotho-/-; there is no added

effect on bone

Komaba H et al Kidney Int 2017

Healthy controls 12

Dialysis patients 21

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1 week 2 weeks 3 weeks

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Primary osteoblasts from dialysis patients mineralize poorly in culture

Pereira RC et al Kidney Int 2018

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base 2 weeks

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Runx2

ControlCKD

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**Osteocalcin

base 2 weeks1 week

… this equates to defective maturation

Pereira RC Kidney Int 2018

Pereira RC et al Kidney Int 2018

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FGF23 (nm)

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ControlCKD

Phosphate, but not FGF23, plays a role in osteoblast maturation

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β-glycerol-phosphate (mM)

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Pereira RC Kidney Int 2018

DAPI FGF23 e11/gp38 merge

BMTB

BMTB

BMTB

BMTB

A

In human CKD, FGF23 is a marker of early osteocytes

Pereira RC et al Kidney Int 2018

A

#1

#2

#3

#4

FGF23

FGF2320.89

21.40

17.86

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FGF23-expressing osteocytes characterize early 2o mineralization

Pereira RC et al Kidney Int 2018

Summary• FGF23 and Klotho both affect phosphate and 1,25D and

both are regulated by 1,25D

• Klotho (and maybe FGF23+Klotho) may suppress osteoblast maturation

• While CKD bone disease mimics the effects of Klotho deficiency, primary human osteoblasts in vitro maintain intrinsic defects in maturation

• FGF23 may be a marker of early osteocytes in CKD bone

FGF23 and Klotho in Bone Mineralization in CKD ObjectivesFGF23: what it doesFGF23: where it’s madeKlotho is expressed in osteocytes;�Klotho null mice have osteoporosisMineralization defects co-exist with increased FGF23 in early CKDDirect effects of FGF23 and Klotho: confounding effects of 1,25D1,25D directly inhibits bone mineralizationFGF23 null fetuses have normal phosphate and skeletonsKlotho null fetuses also have normal skeletonsForced FGF23 over-expression suppresses osteoblast differentiation and mineralizationOsteocyte-specific Klotho deletion increases bone formation and massOverexpression of Klotho inhibits mineralization of MC3T3 cellsExogenous FGF23 and Klotho together inhibit osteoblast mineralizationFGF23 and Klotho inhibit osteoblastic Wnt signaling in CKDKlotho is down-regulated in CKD bone; particularly in high phosphate conditionsCKD mimics the effect of Klotho-/-; there is no added effect on boneSlide Number 18Slide Number 19Slide Number 20Slide Number 21Slide Number 22Summary