Tissue-Wide Expression of Genes Related to Vitamin D Metabolism and FGF23 Signaling following Variable Phosphorus Intake in Pigs

Calcium (Ca) and phosphorus (P) homeostasis is maintained by several regulators, including vitamin D and fibroblast growth factor 23 (FGF23), and their tissue-specific activation and signaling cascades. In this study, the tissue-wide expression of key genes linked to vitamin D metabolism (CYP2R1, CYP27A1, CYP27B1, CYP24A1, GC, VDR) and FGF23 signaling (FGF23, FGFR1-4, KL) were investigated in pigs fed conventional (trial 1) and divergent P diets (trial 2). The tissue set comprised kidney, liver, bone, lung, aorta, and gastrointestinal tract sections. Expression patterns revealed that non-renal tissues and cells (NRTC) express genes to form active vitamin D [1,25(OH)(2)D(3)] according to site-specific requirements. A low P diet resulted in higher serum calcitriol and increased CYP24A1 expression in the small intestine, indicating local suppression of vitamin D signaling. A high P diet prompted increased mRNA abundances of CYP27B1 for local vitamin D synthesis, specifically in bone. For FGF23 signaling, analyses revealed ubiquitous expression of FGFR1-4, whereas KL was expressed in a tissue-specific manner. Dietary P supply did not affect skeletal FGF23; however, FGFR4 and KL showed increased expression in bone at high P supply, suggesting regulation to balance mineralization. Specific NRTC responses influence vitamin D metabolism and P homeostasis, which should be considered for a thrifty but healthy P supply.