The bone is the major source of high circulating intact fibroblast growth factor-23 in acute murine polymicrobial sepsis induced by cecum ligation puncture

Abstract

Fibroblast growth factor-23 (FGF23), a bone-produced hormone, plays a critical role in mineral homeostasis. Human diseases associated with excessive intact circulating FGF23 (iFGF23) result in hypophosphatemia and low vitamin D hormone in patients with normal kidney function. In addition, there is accumulating evidence linking FGF23 with inflammation. Based on these studies and the frequent observation of hypophosphatemia among septic patients, we sought to elucidate further the relationship between FGF23 and mineral homeostasis in a clinically relevant murine polymicrobial sepsis model. Medium-severity sepsis was induced by cecum ligation puncture (CLP) in adult CD-1 mice of both sexes. Healthy CD-1 mice (without CLP) were used as controls. Forty-eight hours post-CLP, spontaneous urine was collected, and serum, organs and bones were sampled at necropsy. Serum iFGF23 increased ~20-fold in CLP compared to control mice. FGF23 protein concentration was increased in the bones, but not in spleen or liver of CLP mice. Despite the ~20-fold iFGF23 increase, we did not observe any significant changes in mineral homeostasis or parathyroid hormone levels in the blood of CLP animals. Urinary excretion of phosphate, calcium, and sodium remained unchanged in male CLP mice, whereas female CLP mice exhibited lower urinary calcium excretion, relative to healthy controls. In line with renal FGF23 resistance, expression of phosphate-, calcium- and sodium-transporting proteins did not show consistent changes in the kidneys of male and female CLP mice. Renal expression of the co-receptor αKlotho was downregulated in female, but not in male CLP mice. In conclusion, our data demonstrate that the dramatic, sex-independent rise in serum iFGF23 post-CLP was mainly caused by an upregulation of FGF23 secretion in the bone. Surprisingly, the upsurge in circulating iFGF23 did not alter humoral mineral homeostasis in the acutely septic mice. Hence, the biological function of elevated FGF23 in sepsis remains unclear and warrants further studies.

Bone homeostasis disorders increased the mortality of sepsis patients: A preliminary retrospective cohort study

“…They used rat sepsis model induced by cecal ligation and puncture (CLP) and found that rat femoral trabecular bone strength was reduced within 24 h and was associated with collagen reduction. J. Bayer et al ( 30 ) also used animal CLP induced sepsis model and proposed that the bone was the major source of high circulating intact fibroblast growth factor-23 in asepsis animal. A. Terashima ( 31 ) reviewed the role of bone cells in immune regulation during the course of infection and summarized that bone homeostasis played a crucial role in infection.…”

Mouse liver injury induces hepatic macrophage FGF23 production

“…Serum FGF23 has been shown to be increased in vivo by bacteria or bacterial products such as LPS [ 13 , 19 – 21 ]. The organ sources of FGF23 are unclear but have been attributed to spleen and bone [ 13 , 19 – 21 ] and not the liver [ 20 ].…”