Simultaneous changes in the calcium-sensing receptor and the vitamin D receptor under the influence of calcium and calcitriol.
BACKGROUND
The regulatory mechanisms of parathyroid hormone (PTH) synthesis are complex, involving calcium, calcitriol, the calcium-sensing receptor (CaR) and the vitamin D receptor (VDR). In this study, the effects of calcium and calcitriol on the simultaneous expression of CaR and VDR mRNA and protein levels were assessed in parathyroid glands cultured in vitro.


METHODS
Parathyroid glands (N = 424) were removed and cultured for 24 h to study the effect of calcium on the CaR, VDR and PTH. In addition, the effect of calcitriol at low calcium concentrations (0.6 mM) on CaR and VDR levels was studied after 48 h of incubation. CaR, VDR and PTH mRNAs were measured by quantitative real-time PCR (qRT-PCR), and CaR and VDR protein levels were measured by immunohistochemistry.


RESULTS
PTH gene expression was reduced by high calcium concentration. No differences were found in the CaR mRNA levels among the different calcium concentrations tested (0.6 mM calcium: 100%; 1.2 mM calcium: 120%; 2.0 mM calcium: 112%; median values), but VDR gene expression rose when calcium increased (0.6 mM calcium: 100%; 1.2 mM calcium: 164%; 2.0 mM calcium: 195%; median values). Calcitriol increased both CaR (control: 100%; 10(-8) M calcitriol: 196%; median values) and VDR genes expression (control: 100%; 10(-8) M calcitriol: 176%; median values). The same findings were corroborated at protein levels for both CaR and VDR.


CONCLUSIONS
In parathyroid glands cultured in vitro, calcium up-regulates VDR but not CaR. Conversely, calcitriol up-regulates both VDR and CaR mRNAs and protein levels, even at low calcium concentrations.
Instituto Reina Sofía de Investigación, Hospital Universitario Central de Asturias, Universidad de Oviedo, Oviedo, Asturias, Spain.
Natalia
N
Carrillo-López
Daniel
D
Alvarez-Hernández
Ignacio
I
González-Suárez
Pablo
P
Román-García
Jose M
JM
Valdivielso
José Luis
JL
Fernández-Martín
Jorge B
JB
Cannata-Andía
D000818:Animals; D002117:Calcitriol / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D008297:Male; D023421:Models, Animal; D009924:Organ Culture Techniques; D010280:Parathyroid Glands / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D018167:Receptors, Calcitriol / Q000378:metabolism*; D044169:Receptors, Calcium-Sensing / Q000378:metabolism*; D015854:Up-Regulation
D010281:Parathyroid Hormone; D012333:RNA, Messenger; D018167:Receptors, Calcitriol; D044169:Receptors, Calcium-Sensing; D002117:Calcitriol; D002118:Calcium