Downregulation of parathyroid hormone receptor gene expression and osteoblastic dysfunction associated with skeletal resistance to parathyroid hormone in a rat model of renal failure with low turnover bone.
BACKGROUND
Adynamic bone disease (ABD), which is characterized by reduced bone formation and resorption, has become an increasingly common manifestation of bone abnormalities in patients with end-stage renal failure. It has been recognized that skeletal resistance to parathyroid hormone (PTH) underlies the pathogenesis of ABD; however, the mechanisms of such resistance remain unclear.


METHODS
We established a rat model simulating ABD under chronic renal failure conditions by thyroparathyroidectomy and partial nephrectomy (TPTx-Nx). TPTx-Nx rats were infused subcutaneously with a physiological dose of PTH. We analysed bone histomorphometric parameters and demonstrated gene expression using semi-quantitative reverse transcription-polymerase chain reaction.


RESULTS
Reduced bone formation was observed in this model, simulating ABD. The reduction was dependent on the degree of renal dysfunction. Bone formation rate was 6.4+/-2.7 microm3/m2/year in TPTx-5/6Nx rats and 22.7+/-7.2 microm3/m2/year in TPTx rats (P<0.05). Osteoblast surface was also significantly depressed (P<0.05) in TPTx-5/6Nx (3.8+/-2.7%) compared with TPTx rats (15.9+/-8.6). The expression of PTH/parathyroid hormone-related peptide (PTHrP) receptor and alkaline phosphatase genes was reduced significantly in TPTx-Nx compared with TPTx rats (P<0.05). Reduced bone formation in TPTx-Nx rats was ameliorated by intermittent injection of pharmacological doses of PTH.


CONCLUSIONS
Renal dysfunction without secondary hyperparathyroidism induces osteoblast dysfunction and reduces bone formation. Skeletal resistance to PTH develops in renal failure even at low or normal PTH levels, possibly through downregulation of PTH/PTHrP receptor and dysfunction of osteoblasts.
Iwasaki-Ishizuka
Yoshiko
Y
Department of Health Sciences, Oita University of Nursing and Health Sciences, Oita, 870-1201, Japan.
Yamato
Hideyuki
H
Nii-Kono
Tomoko
T
Kurokawa
Kiyoshi
K
Fukagawa
Masafumi
M
D000199:Actins / Q000097:blood; D000469:Alkaline Phosphatase / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D001842:Bone and Bones / Q000187:drug effects* / Q000378:metabolism* / Q000473:pathology; D017931:DNA Primers; D004195:Disease Models, Animal; D004351:Drug Resistance; D007262:Infusions, Intravenous; D007279:Injections, Subcutaneous; D007676:Kidney Failure, Chronic / Q000150:complications*; D008297:Male; D010006:Osteoblasts / Q000473:pathology*; D010281:Parathyroid Hormone / Q000008:administration & dosage / Q000627:therapeutic use*; D016133:Polymerase Chain Reaction; D051381:Rats; D017207:Rats, Sprague-Dawley; D044168:Receptor, Parathyroid Hormone, Type 1 / Q000235:genetics*; D013974:Thyroxine / Q000008:administration & dosage / Q000494:pharmacology
D000199:Actins; D017931:DNA Primers; D010281:Parathyroid Hormone; D044168:Receptor, Parathyroid Hormone, Type 1; D000469:Alkaline Phosphatase; D013974:Thyroxine