The Effect of Intracerebroventricular Fibroblast Growth Factor 23 on gene expression in the Rats' Hypothalamus

Fibroblast growth factor 23 (FGF23) is a key regulator of systemic phosphate homeostasis, but also an interplay with glucose metabolism has been suggested. Several studies implicate a function of FGF23 in the brain, and indeed we have recently identified FGF23 protein in several brain areas in rats, such as the hypothalamus, third ventricle and choroid plexus. In the current study, we aimed to determine the effect of an intracerebroventricular (icv) injection of FGF23 in the third ventricle of rats on hypothalamic genes involved in glucose regulation. In addition, we assessed whether glycerol can be used safely for icv injections as glycerol is used as a stabilizing compound for FGF23 protein. Adult Wistar rats received an icv injection of recombinant rat FGF23 or vehicle. Dose dependent behavioral changes, suggestive of stress, were observed directly after infusion of FGF23. After 60 min animals were sacrificed and the arcuate nucleus, lateral hypothalamus and choroid plexus were isolated. In these brain regions gene expression was determined of the FGF23 receptor complex (FGFR1, Klotho), NPY, POMC, phosphate transporters (SLC20 and SLC34 families) and markers of cellular ER stress (ATF4 and the ratio of spliced/unspliced XBP1). We showed that glycerol is well tolerated as stabilizer for icv injections. In FGF23-treated animals, cellular ER stress markers were increased in the arcuate nucleus. FGF23 injection did not affect expression of its receptor complex, NPY, POMC, or phosphate transporters. Future studies are warranted to investigate the effect of FGF23 in the brain on the protein level and on neuronal activation.