Angiotensin II increases parathyroid hormone-related protein (PTHrP) and the type 1 PTH/PTHrP receptor in the kidney

Angiotensin II (AngII) participates in the pathogenesis of kidney damage. Parathyroid hormone (PTH)-related protein (PTHrP), a vasodilator and mitogenic agent, is upregulated during renal injury. The aim of this study was to investigate the potential relation between AngII and PTHrP system in the kidney. Different methods were used to find that both rat mesangial and mouse tubuloepithelial cells express PTHrP and the type 1 PTH/PTHrP receptor (PTH1R). In these cells, AngII increased PTHrP mRNA and protein production. In contrast, PTH1R mRNA was increased in mesangial cells and downregulated in tubular cells, but its protein levels were unmodified in both cells. AT(1) antagonist, but not AT(2), abolished AngII effects on PTHrP/PTH1R. The in vivo effect of AngII was further investigated by systemic infusion (a low dose of 50 ng/kg per min) into normal rats. In controls, PTHrP immunostaining was mainly detected in renal tubules. In AngII-infused rats, PTHrP staining increased in renal tubules and appeared in the glomerulus and the renal vessels. After AngII infusion, PTHR1 staining was markedly increased in all these renal structures at day 3 but remained elevated only in tubules at day 7. The AT(1) antagonist, but not the AT(2), significantly diminished AngII-induced PTHrP and PTHR1 overexpression in the renal tissue, associated with a decrease in tubular damage and fibrosis. The results indicate that AngII regulates renal PTHrP/PTH1R system via AT(1) receptors. These findings demonstrate that PTHrP upregulation occurs in association with the mechanisms of AngII-induced kidney injury.     

PTH/PTHrP受体mRNA在血液透析患者成骨细胞中的表达

目的 了解PTH/PTHrP受体mRNA在维持性血液透析(HD)患者成骨细胞中的表达及钙离子拮抗剂(CCB)和骨化三醇对其影响。方法 21例随机分为HD试验组(8例)、骨化三醇治疗组(7例)及CCB治疗组(6例),并设置正常对照组(5例)。分别采取各例骨髓作成骨细胞培养。应用半定量RT-PCR方法观察各组成骨细胞的PTH/PTHrP受体mRNA表达。结果 与正常对照组比,HD患者PTH/PTHrP受体mRNA的表达下调(P<0.001),且与血中iPTH水平呈负相关(r=-0.673,P<0.001)。适量的骨化三醇可上调受体表达,而大剂量的骨化三醇可下调表达。CCB可上调HD患者的PTH/PTHrP受体表达。结论 HD患者成骨细胞PTH/PTHrP受体mRNA的表达下调。CCB上调PTH/PTHrP受体。适量的骨化三醇可以上调受体,而大剂量的骨化三醇抑制PTH和下调PTH/PTHrP受体。     

Down-regulation of human osteoblast PTH/PTHrP receptor mRNA in end-stage renal failure

BACKGROUND: Resistance to the action of parathyroid hormone (PTH) has been demonstrated in end-stage renal failure and is considered to be important in the pathogenesis of secondary hyperparathyroidism. The mechanism of resistance is unknown. However, altered regulation of cellular PTH/PTH-related protein (PTH/PTHrP) receptor (PTH1R) has been assumed to be important. METHODS: We have used in situ hybridization to examine PTH1R mRNA expression by osteoblasts in human bone and have compared the expression in high- and low-turnover renal bone disease, high-turnover nonrenal bone disease (healing fracture callus and Pagetic bone), and normal bone. Bone biopsies were formalin fixed, ethylenediaminetetraacetic acid decalcified, and paraffin wax embedded. A 1.8 kb PTH1R cDNA probe, labeled with 35S, was used, and the hybridization signal was revealed by autoradiography. The density of signal over osteoblasts was quantitated using a semiautomated Leica image analysis software package. RESULTS: The mean density of PTH1R mRNA signal over osteoblasts in renal high-turnover bone was only 36% of that found in nonrenal high-turnover bone (P < 0.05) and 51% of that found in normal bone (P < 0.05). Osteoblast PTH1R mRNA signal in adynamic bone from individuals with diabetes mellitus was 28% of normal bone (P < 0.05) and 54% of that found in renal high-turnover bone (P < 0.05). CONCLUSIONS: These results demonstrate a down-regulation of osteoblast PTH1R mRNA in end-stage renal failure in comparison to normal and high-turnover bone from otherwise healthy individuals, and provide an insight into the mechanisms of "skeletal resistance" to the actions of PTH.     

Chronic phosphorus supplementation decreases the expression of renal PTH/PTHrP receptor mRNA in rats

Dietary intake of high levels of phosphorus is known to increase serum levels of parathyroid hormone (PTH); however, how this increased serum PTH affects the action of PTH in major target tissues, particularly by kidney, remains unknown. In the present study, we therefore undertook to clarify this point in intact animals fed a high-P diet by examining various parameters of PTH action. Twelve weanling Wistar male rats were assigned randomly to two groups: a control group with dietary Ca:P = 1:1 and a high-P group (Ca:P = 1:3) fed the standard AIN-76 diet supplemented with P (0.5 and 1.5 g/100 g of diet). After 3 weeks of feeding, in the high-P diet group, we observed that serum Ca was lowered, without a difference in serum P, when compared to the control group. Excretion of urinary cAMP, an index of renal PTH action, was also decreased, with higher excretion of urinary P in those rats fed the high-P diet. In agreement with the decreased cAMP excretion, a clear reduction in PTH/PTH-related protein (PTHrP) receptor gene expression as estimated by Northern blotting was observed in the kidney, despite increased levels of serum PTH. Thus, the present study indicated that a high-P diet reduces PTH action in the kidney, though the serum PTH is increased.     

硝苯地平和罗钙全对尿毒症患者甲状旁腺素受体基因表达的影响

目的 观察钙通道阻滞剂硝苯地平和活性维生素Ｄ制剂罗钙全对尿毒症患者外周血单个核细胞（ＰＢＭＣ）上甲状旁腺素（ＰＴＨ）受体基因表达的影响。方法 ３０例非糖尿病常规血液透析患者随机分成硝苯地平组、罗钙全组和安慰剂组,治疗８周。应用逆转录－聚合酶链反应（ＲＴ－ＰＣＲ）方法检测用药前后ＰＢＭＣ上ＰＴＨ受体ｍＲＮＡ表达。结果 硝苯地平治疗能使尿毒症患者ＰＢＭＣ上ＰＴＨ受体ｍＲＮＡ的低表达显著上调（０．１４３     

Development of craniofacial structures in transgenic mice with constitutively active PTH/PTHrP receptor

Parathyroid hormone (PTH) and parathyroid hormone-related peptide (PTHrP) regulate calcium homeostasis, and PTHrP further regulates growth and development. A transgenic mouse carrying the constitutively active PTH/PTHrP receptor (HKrk-H223R) under the control of the mouse bone and odontoblast-specific alpha1(I) collagen promoter (Col1-caPPR) has been developed to demonstrate the complex actions of this mutant receptor in hard tissue formation. We have further characterized Col1-caPPR mice abnormalities in the craniofacial region as a function of development. Col1-caPPR mice exhibited a delay in embryonic bone formation, followed by expansion of a number of craniofacial bones including the maxilla and mandible, delay in tooth eruption and teratosis, and a disrupted temporomandibular joint (TMJ). These findings suggest that the Col1-caPPR mouse is a useful model for characterization of the downstream effects of the constitutively active receptor during development and growth, and as a model for development of treatments of human diseases with similar characteristics.     

肾脏病患者外周血淋巴细胞上甲状旁腺素受体的表达

目的　探讨人外周血淋巴细胞上有无甲状旁腺素（PTH）受体表达及其在肾脏疾病不同阶段的改变。方法应用RT-PCR方法观察各组患者淋巴细胞和肾脏组织中PTH受体mRNA表达。结果人淋巴细胞上可检出PTH受体基因表达；在慢性肾炎肾功能代偿期和尿毒症患者中均有不同程度下调，与肾功能损害密切相关，且与同组患者肾脏组织中PTH受体的改变相一致。结论肾功能减退时，患者淋巴细胞上PTH受体显著下调。     

Decrease in the expression of the type 1 PTH/PTHrP receptor (PTH1R) on chondrocytes in animals with osteoarthritis

Background  

To evaluate the expression of the type 1 PTH/PTHrP receptor (PTH1R) on chondrocytes from hyaline cartilage over the course of osteoarthritis (OA).     

肾脏病患者甲状旁腺素受体基因表达的研究

目的 探讨肾脏疾病不同阶段中甲状旁腺素(PTH)受体基因表达的变化及可能机制。方法 应用半定量RT/PCR方法观察各组患者肾穿刺或手术标本中PTH受体mRNA表达。结果 慢性肾炎肾功能正常、中度肾功能减退、尿毒症及急性肾衰患者均有不同程度PTH受体基因表达减少,且和肾脏损害密切相关。结论 在肾脏疾病进程中PTH受体下调明显早于肾功能、血PTH和钙磷的变化。     

Metabolic acidosis up-regulates PTH/PTHrP receptors in UMR 106-01 osteoblast-like cells

BACKGROUND: Metabolic acidosis results in skeletal demineralization by multiple mechanisms. One of these involves the inorganic phase of bone by which hydrogen ion is buffered by bone carbonate. In addition, the cellular components of bone participate by the induction and repression of several skeletal genes. Previous studies have suggested that the action of parathyroid hormone (PTH), a major regulator of bone turnover, might be altered by acidosis. The present studies were designed to test directly, in vitro, whether acidosis altered the effects of PTH in UMR 106-01 osteoblast-like cells. METHODS: Studies were conducted in confluent cultures of UMR 106-01 cells in modified Eagle's medium (MEM) with 5% fetal bovine serum (FBS) at pH values varying from 7.4 to 7.1 by addition of HCl. After time periods of 4 to 48 hours, cells were tested for cyclic AMP generation in response to PTH. PTH binding and PTH/PTHrP receptor mRNA levels were determined by radioligand binding assay and Northern analysis respectively. RESULTS: After 48 hours, decreases in pH from 7.4 to 7.1 resulted in a progressive increase in PTH-stimulated cyclic-AMP generation from 1978 +/- 294 to 4968 +/- 929 pmol/culture/5 min (P < 0.05). Basal cyclic AMP concentrations were unchanged. PTH binding increased 1.5- to twofold. Competitive inhibition binding revealed an increase in receptor number supported by up-regulation of PTH/PTHrP receptor mRNA up to twofold from control levels. CONCLUSIONS: These findings demonstrate that metabolic acidosis stimulates the response to PTH in UMR 106-01 osteoblast-like cells by a mechanism that involves an increase in the levels of PTH/PTHrP receptor mRNA. Thus, the skeletal response to acidosis that includes an increase in bone resorption may result, at least in part, from an increase in PTH/PTHrP receptors leading to an enhanced effect of PTH on bone.     

PTH/PTHrP receptor mRNA is down-regulated in epiphyseal cartilage growth plate of uraemic rats

PTH/PTHrP receptor mRNA is down-regulated in epiphyseal cartilagegrowth plate of uraemic rats. Growth retardation, hypocalcaemia,hyperphosphataemia, and skeletal resistance to the action ofPTH are well known features of advanced chronic renal failure(CRF). It has been suggested that the downregulation of renaland skeletal PTH receptors (PTH/PTHrP-R) could play an importantrole in the occurrence of these abnormalities. In the presentstudy, four uraemic (4 weeks after 5/6 nephrectomy) and fourcontrol (sham-operated) rats were analysed for PTH/PTHrP-R mRNAexpression at the proximal femoral and tibial growth platesby in situ hybridization. Uraemic rats had plasma biochemicalabnormalities of advanced CRF including high creatinine, phosphate,and PTH, and low calcium and calcitriol levels. The femoraland tibial bones of uraemic animals were shorter in length thanthose of control rats, and had reduced width and cellularityof the epiphyseal cartilage growth plate. Mean (±SD)tibia growth plate width was 152±30 µm in uraemicrats, compared with 170±35 µm in control rats.The difference was mostly due to a marked reduction of the zoneexpressing PTH/PTHrP-R (mature chondrocytes) which was 30±5µm in tibias from uraemic versus 44±10 µmin tibias from control rats. The hybridization signals of PTH/PTHrP-Rper individual cell were quantified on dark field images usinga computer-assisted image analysis system. The number of grainsin PTH/PTHrP-R positive cells was also decreased in uraemicrats, 103±13 compared with 123±14 arbitrary units(dark pixel density)/cell in control rats (P 0.005). In conclusion,these data indicate that rats with severe CRF and secondaryhyperparathyroidism have reduced epiphyseal cartil age PTH/PTHrP-RmRNA expression. This alteration may be relevant in the pathogenesisof growth retardation in uraemia.     

Expression of the PTH/PTHrP receptor in chondrogenic cells during the repair of full-thickness defects of articular cartilage

OBJECTIVE: We studied the accumulation of parathyroid hormone (PTH)/PTHrP receptor-positive mesenchymal cells using double immunohistochemistry and examined whether this correlated with the subsequent regeneration of 3-mm-diameter full-thickness defects of articular cartilage. MATERIALS AND METHODS: Cylindrical full-thickness articular cartilage defects (3 mm) were artificially created in the femoral trochlea of male adolescent Japanese white rabbits (n = 210) with a hand-drill. Recombinant human PTH(1-84) was then administered into the defect cavities with an osmotic pump for either 2 or 4 weeks post-injury. Following PTH treatment, the repair processes in the cartilage defects were histologically examined. Double immunostaining analyses for the PTH/PTH-related peptide (PTHrP) receptor and proliferating cell nuclear antigen (PCNA) in the regenerating tissues were then performed. RESULTS: Activation of PTH/PTHrP receptor signaling by hPTH(1-84) results in the inhibition of chondrogenic differentiation in full-thickness articular cartilage defects. At the conclusion of the 2-week PTH treatment, the defect cavities were filled with undifferentiated mesenchymal cells, which were similar to the controls. In addition, almost all of these cells localized at the center of the injuries were both PTH/PTHrP receptor- and PCNA-positive. In contrast, after prolonged PTH treatment for 4 weeks, there was no indication of a cartilaginous repair response and cells that had migrated to the defect cavities were found to have irreversibly lost expression of the PTH/PTHrP receptor. CONCLUSIONS: The chondrogenic capacity of cells that had migrated to the area of these defect cavities is closely associated with their ability to express the PTH/PTHrP receptor. Moreover, these cells maintain their chondrogenic potential within only a limited time-span of 2 weeks.