Klotho and fibroblast growth factor 23 in cerebrospinal fluid in children

The fibroblast growth factor (FGF) 23/Klotho axis is a principal regulator of phosphate hemostasis and vitamin D metabolism, but limited data is available on its role in the central nervous system. Here, we investigate soluble α-Klotho (sKlotho) and C-terminal as well as intact FGF23 in cerebrospinal fluid (CSF) and plasma and their relationship to mineral metabolism parameters in humans. In 39 children aged 0.3-16.8 years undergoing lumbar puncture for the exclusion of inflammatory neurological disease, sKlotho and FGF23 were investigated by Western blot analysis, followed by ELISA quantification in CSF and plasma. The percentage of intrathecal synthesis of both proteins was calculated by measuring both the expected and observed CSF/plasma ratios of sKlotho and FGF23. The secreted (KL1) and cleaved (KL1+KL2) isoforms of sKlotho, and FGF23 were clearly detected in CSF in all subjects, although protein levels were lower compared to those of plasma samples (each p < 0.01). The intrathecal percentage of CSF sKlotho and FGF23 synthesis amounted to 98 and 99 %, respectively. CSF sKlotho levels were higher in boys than in girls (p < 0.01), and correlated positively with plasma C-terminal FGF23 concentrations (p < 0.05) and standardized height (p < 0.01). Importantly, there were no significant correlations between plasma and CSF levels of sKlotho or FGF23. Plasma sKlotho as well as C-terminal and intact FGF23, respectively, were associated with parameters of mineral metabolism These results provide evidence that cleaved and secreted sKlotho and FGF23 are present in CSF, mainly derived from brain and affected by sex, height, and mineral metabolism parameters in children. Nevertheless, the absence of significant associations between plasma and CSF levels of Klotho and FGF23, respectively, suggest that the regulation of Klotho and FGF23 may be different between organs secreting these hormones into blood and CSF.