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Fibroblast growth factor 23 and α-Klotho co-dependent and independent functions

Quarles, L. Darryl

Current Opinion in Nephrology and Hypertension: January 2019 - Volume 28 - Issue 1 - p 16–25
doi: 10.1097/MNH.0000000000000467
HORMONES, AUTACOIDS, NEUROTRANSMITTERS AND GROWTH FACTORS: Edited by Mark Cooper and Merlin Thomas

Purpose of review The current review examines what is known about the FGF-23/α-Klotho co-dependent and independent pathophysiological effects, and whether FGF-23 and/or α-Klotho are potential therapeutic targets.

Recent findings FGF-23 is a hormone derived mainly from bone, and α-Klotho is a transmembrane protein. Together they form a trimeric signaling complex with FGFRs in target tissues to mediate the physiological functions of FGF-23. Local and systemic factors control FGF-23 release from osteoblast/osteocytes in bone, and circulating FGF-23 activates FGFR/α-Klotho complexes in kidney proximal and distal renal tubules to regulate renal phosphate excretion, 1,25 (OH)2D metabolism, sodium and calcium reabsorption, and ACE2 and α-Klotho expression. The resulting bone–renal–cardiac–immune networks provide a new understanding of bone and mineral homeostasis, as well as identify other biological effects FGF-23. Direct FGF-23 activation of FGFRs in the absence of α-Klotho is proposed to mediate cardiotoxic and adverse innate immune effects of excess FGF-23, particularly in chronic kidney disease, but this FGF-23, α-Klotho-independent signaling is controversial. In addition, circulating soluble Klotho (sKl) released from the distal tubule by ectodomain shedding is proposed to have beneficial health effects independent of FGF-23.

Summary Separation of FGF-23 and α-Klotho independent functions has been difficult in mammalian systems and understanding FGF-23/α-Klotho co-dependent and independent effects are incomplete. Antagonism of FGF-23 is important in treatment of hypophosphatemic disorders caused by excess FGF-23, but its role in chronic kidney disease is uncertain. Administration of recombinant sKl is an unproven therapeutic strategy that theoretically could improve the healt span and lifespan of patients with α-Klotho deficiency.

Division of Nephrology, Department of Medicine, College of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee, USA

Correspondence to L. Darryl Quarles, MD, UTMG Endowed Professor of Nephrology, Director, Division of Nephrology, Department of Medicine, Associate Dean for Research, College of Medicine, University of Tennessee Health Science Center, 956 Court Avenue, Suite B226, Memphis, TN 38163, USA . Tel: +1 448 1459; e-mail: dquarles@uthsc.edu

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