Expression of fibroblast growth factor 23, vitamin D receptor, and sclerostin in bone tissue from hypercalciuric stone formers.
OBJECTIVE
Increased bone resorption, low bone formation, and abnormal mineralization have been described in stone formers with idiopathic hypercalciuria. It has been previously shown that the receptor activator of NF-κB ligand mediates bone resorption in idiopathic hypercalciuria (IH). The present study aimed to determine the expression of fibroblast growth factor 23 (FGF-23), vitamin D receptor (VDR), and sclerostin in bone tissue from IH stone formers.


METHODS
Immunohistochemical analysis was performed in undecalcified bone samples previously obtained for histomorphometry from 30 transiliac bone biopsies of idiopathic hypercalciuria stone-forming patients between 1992 and 2002 and 33 healthy individuals (controls). Serum parameters were obtained from their medical records.


RESULTS
Histomorphometry disclosed 21 IH patients with high and 9 IH patients with normal bone resorption. Importantly, eroded surfaces (ES/BS) from IH patients but not controls were significantly correlated with VDR immunostaining in osteoblasts (r=0.51; P=0.004), sclerostin immunostaining in osteocytes (r=0.41; P=0.02), and serum 1,25-dihydroxyvitamin D (r=0.55; P<0.01). Of note, both VDR and sclerostin immunostaining were significantly correlated with serum 1,25-dihydroxyvitamin D in IH patients (r=0.52; P=0.01 and r=0.53; P=0.02, respectively), although VDR and sclerostin expression did not differ between IH and controls. IH patients with high bone resorption exhibited a significantly stronger sclerostin immunostaining than IH patients with normal bone resorption. FGF-23 expression in osteocytes from IH patients did not differ from controls and was not correlated with any histomorphometric parameter.


CONCLUSIONS
These findings suggest the contribution of VDR and sclerostin, as well as 1,25-dihydroxyvitamin D, to increase bone resorption in idiopathic hypercalciuria but do not implicate FGF-23 in the bone alterations seen in these patients.
Nephrology Division, Federal University of São Paulo, São Paulo, Brazil; and.
Viviane Barcellos
VB
Menon
Nephrology Division, University of São Paulo, São Paulo, Brazil.
Rosa Maria Affonso
RM
Moysés
Nephrology Division, Federal University of São Paulo, São Paulo, Brazil; and.
Samirah Abreu
SA
Gomes
Nephrology Division, Federal University of São Paulo, São Paulo, Brazil; and.
Aluizio Barbosa
AB
de Carvalho
Nephrology Division, University of São Paulo, São Paulo, Brazil.
Vanda
V
Jorgetti
Nephrology Division, Federal University of São Paulo, São Paulo, Brazil; and ita.heilberg@gmail.com.
Ita Pfeferman
IP
Heilberg
D048868:Adaptor Proteins, Signal Transducing; D000328:Adult; D019485:Bone Morphogenetic Proteins / Q000032:analysis*; D001862:Bone Resorption / Q000378:metabolism / Q000503:physiopathology; D005260:Female; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000032:analysis*; D005819:Genetic Markers; D006801:Humans; D053565:Hypercalciuria / Q000175:diagnosis / Q000378:metabolism* / Q000503:physiopathology; D007085:Ilium / Q000737:chemistry* / Q000503:physiopathology; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D010006:Osteoblasts / Q000737:chemistry; D010011:Osteocytes / Q000737:chemistry; D018167:Receptors, Calcitriol / Q000032:analysis*; D012189:Retrospective Studies; D052878:Urolithiasis / Q000175:diagnosis / Q000378:metabolism* / Q000503:physiopathology; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood
D048868:Adaptor Proteins, Signal Transducing; D019485:Bone Morphogenetic Proteins; C000717427:FGF23 protein, human; D005819:Genetic Markers; D018167:Receptors, Calcitriol; C422903:SOST protein, human; C579457:VDR protein, human; D014807:Vitamin D; D005346:Fibroblast Growth Factors; C097949:1,25-dihydroxyvitamin D; D000089703:Fibroblast Growth Factor-23
FGF-23; VDR; hypercalciuria; immunohistochemistry; sclerostin