Parathyroid Cell Proliferation Research Articles

Parathyroid-Targeted Overexpression of Regulator of G-Protein Signaling 5 (RGS5) Causes Hyperparathyroidism in Transgenic Mice.

The relationship between impaired calcium sensing, dysregulated parathyroid hormone (PTH) secretion, and parathyroid cell proliferation in parathyroid neoplasia is not understood. We previously reported that a GTPase activating protein, regulator of G-protein signaling 5 (RGS5) is overexpressed in a subset of parathyroid tumors associated with primary hyperparathyroidism (PHPT) and that RGS5 can inhibit signaling from the calcium-sensing receptor (CASR). In vivo, we found that RGS5-null mice have abnormally low PTH levels. To gain a better understanding of the potential role of RGS5 overexpression in parathyroid neoplasia and PHPT and to investigate whether inhibition of CASR signaling can lead to parathyroid neoplasia, we created and characterized a transgenic mouse strain overexpressing RGS5 specifically in the parathyroid gland. These mice develop hyperparathyroidism, bone changes reflective of elevated PTH, and parathyroid neoplasia. Further, expression of exogenous RGS5 in normal human parathyroid cells results in impaired signaling from CASR and negative feedback on PTH secretion. These results provide evidence that RGS5 can modulate signaling from CASR and support a role for RGS5 in the pathogenesis of PHPT through inhibition of CASR signaling. © 2019 American Society for Bone and Mineral Research.

Gcm2 regulates the maintenance of parathyroid cells in adult mice

Glial cells missing homolog 2 (GCM2), a zinc finger-type transcription factor, is essential for the development of parathyroid glands. It is considered to be a master regulator because the glands do not form when Gcm2 is deficient. Remarkably, Gcm2 expression is maintained throughout the fetal stage and after birth. Considering the Gcm2 function in embryonic stages, it is predicted that Gcm2 maintains parathyroid cell differentiation and survival in adults. However, there is a lack of research regarding the function of Gcm2 in adulthood. Therefore, we analyzed Gcm2 function in adult tamoxifen-inducible Gcm2 conditional knockout mice. One month after tamoxifen injection, Gcm2-knockout mice showed no significant difference in serum calcium, phosphate, and PTH levels and in the expressions of calcium-sensing receptor (Casr) and parathyroid hormone (Pth), whereas Ki-67 positive cells were decreased and terminal deoxynucleotidyl transferase (TdT) dUTP Nick-End Labeling (TUNEL) positive cell number did not change, as compared with those of controls. Seven months after tamoxifen injection, Gcm2-knockout mice showed shrinkage of the parathyroid glands and fewer parathyroid cells. A significant decrease was noted in Casr- and Pth-expressing cells and serum PTH and Ca levels, whereas serum phosphate levels increased, as compared with those of controls. All our results concluded that a reduction of Gcm2 expression leads to a reduction of parathyroid cell proliferation, an increase in cell death, and an attenuation of parathyroid function. Therefore, we indicate that Gcm2 plays a prominent role in adult parathyroid cell proliferation and maintenance.

Parathyroidectomy in dialysis patients: Indications, methods, and consequences.

Secondary hyperparathyroidism, characterized by increased PTH synthesis and secretion, is often seen in advanced stages of chronic kidney disease. Excessive proliferation of parathyroid cells leads to the development of diffuse hyperplasia that subsequently progresses to nodular histology. Refractory hyperparathyroidism occurs when parathyroid glands fail to respond to medical therapy. Parathyroidectomy (PTX), surgical resection of parathyroid glands, is usually performed in cases of persistent serum levels of PTH above 1000pg/mL associated with hypercalcemia or when hyperparathyroidism is refractory to conservative therapy. Parathyroidectomy can be carried out using different procedures: subtotal PTX or total PTX with or without parathyroid autotransplantation. Parathyroid surgery may have undesirable consequences due to PTH oversuppression, such as the development of adynamic bone disease; hungry bone syndrome is quite common after this surgery. However, PTX improves survival and parameters of mineral metabolism. Parathyroidectomy needs to be considered in those patients with severe hyperparathyroidism with a poor response to pharmacological treatment and with distinct undesirable effects of PTH on bone and mineral metabolism parameters.

Sevelamer hydrochloride suppresses proliferation of parathyroid cells during the early phase of chronic renal failure in rats.

We examined the effects of sevelamer on parathyroid cell proliferation and secondary hyperparathyroidism in rats following induction of early-phase of chronic renal failure (CRF) by unilateral ureteral obstruction (UUO). For 5 days, rats in the control group received normal food, rats in the sevelamer group (SH) received control food plus 5% sevelamer, and rats in the low protein group (LP) received low protein food. Five rats of each group were killed at baseline (day 0). All other rats were given UUO, and five rats per group were killed on days 3, 7, 14, and 28 after UUO. Changes in body weight, serum phosphorus, calcium, intact-parathyroid hormone (i-PTH), creatinine (SCr), creatinine clearance rate (CCR), blood urea nitrogen (BUN), and 24-h urinary phosphorus were determined. Parathyroid tissues were removed for histological examination of proliferating cell nuclear antigen-positive (PCNA+) cells. Measurement of body weight, BUN, and SCr in the controls indicated successful establishment of this model of early-phase CRF. The controls also had remarkable proliferation of PCNA+ cells beginning on day 3, but this did not occur in the SH or LP groups. After 28 days, serum phosphorus had decreased more in the SH and LP groups than in the control group, and phosphorus excretion was much greater in the control group than in the SH and LP groups. The three groups had similar increases in serum i-PTH. Sevelamer rapidly lowered the serum phosphorus and inhibited the proliferation of PCNA+ cells in this experimental model of early-phase CRF.

NF-κB activation contributes to parathyroid cell proliferation in chronic kidney disease.

Secondary hyperparathyroidism is characterized by parathyroid gland (PG) hyperplasia, and excessive synthesis and secretion of parathyroid hormone (PTH). Reduced vitamin D receptor (VDR) density has shown to play an essential role in PG hyperplasia progression; nevertheless, its exact mechanism remains unclear. VDR has shown to suppress the inflammation mediator NF-κB-mediated gene transcription. The aim of this study is to examine whether NF-κB is involved in the pathogenesis of parathyroid hyperplasia. 35 PGs was obtained from 10 maintenance hemodialysis patients who underwent parathyroidectomy surgery. 5/6-nephrectomized rats fed with a high-phosphate diet were divided into four groups: (1) Nx + vehicle group, treated with vehicle; (2) Nx + PDTC prevention group, treated with NF-κB inhibitor PDTC for 2months; (3) Nx + PDTC therapy group, treated with PDTC for 1month; (4) Nx + calcitriol group, treated with activated vitamin D calcitriol for 1month. Ten sham-operated rats fed with normal-phosphate diet were used as a control group. Serum calcium, phosphorus, creatinine, Blood urea nitrogen (BUN), intact PTH and PG size in rats were measured. Proliferating cell nuclear antigen (PCNA), VDR, NF-κB of PGs were examined using immunohistochemistry and western blot. The activation of NF-κB pathway in the nodular hyperplasia gland was significantly increased compared with the diffuse hyperplasia gland found in hemodialysis patients. Markedly higher serum creatinine, BUN, phosphorus levels, serum iPTH levels and larger PGs were found in Nx rats fed with a high-phosphate diet compared to sham-operated rats. Also, PCNA levels and activation of NF-κB pathway in PGs were higher compared with the sham group, meanwhile the VDR levels decreased. Contrary, treating rats with PDTC and calcitriol notably reduced serum iPTH, expression of PCNA and activation of NF-κB pathway, and decreased the enlargement of PGs in those animals. NF-κB plays an important role in PG hyperplasia progression. VDR deficiency may be involved in the parathyroid gland hyperplasia through the activation of NF-κB pathway.

Persistent fibroblast growth factor 23 signalling in the parathyroid glands for secondary hyperparathyroidism in mice with chronic kidney disease

Secondary hyperparathyroidism, in which parathyroid hormone (PTH) is excessively secreted in response to factors such as hyperphosphataemia, hypocalcaemia, and low 1,25-dihydroxyvitamin D (1,25(OH)2D) levels, is commonly observed in patients with chronic kidney disease (CKD), and is accompanied by high levels of fibroblast growth factor 23 (FGF23). However, the effect of FGF23 on the parathyroid glands (PG) remains controversial. To bind to FGF receptors, FGF23 requires αKlotho, which is highly expressed in the PG. Here, we examined the effects of Fgfr1–3, αKlotho, or Fgfr1–4 ablation specifically in the PG (conditional knockout, cKO). When mice with early to mid-stage CKD with and without cKO were compared, plasma concentrations of calcium, phosphate, FGF23, and 1,25(OH)2D did not change significantly. In contrast, plasma PTH levels, which were elevated in CKD mice, were significantly decreased in cKO mice. PG from CKD mice showed augmentation of cell proliferation, which was significantly suppressed by cKO. Parathyroid tissue cultured for 4 days showed upregulation of PTH secretion and cell proliferation in response to FGF23. Both these effects were inhibited by cKO. These findings suggest that FGF23 is a long-term inducer of parathyroid cell proliferation and PTH secretion, and is one cause of secondary hyperparathyroidism in CKD.

Micro-RNAs in the parathyroid: a new portal in understanding secondary hyperparathyroidism.

Micro-RNAs (miRNAs) are important to the function of many cells including endocrine systems. We present the reported changes in miRNA profiles in parathyroid adenomas and carcinomas. We review the essential roles of parathyroid miRNAs to the response of the parathyroid to hypocalcemia and uremia. miRNA profiling in parathyroid adenomas and carcinomas revealed alterations in their miRNA expression. To study the function of miRNAs in the parathyroid, mice with parathyroid-specific deletion of dicer, the enzyme essential for miRNA maturation, were studied. Remarkably, the parathyroid-Dicer mice failed to increase serum parathyroid hormone (PTH) after acute hypocalcemia and in parathyroid organ cultures. Moreover, the parathyroid-Dicer mice had an impaired increase in serum PTH, PTH mRNA and parathyroid cell proliferation after both chronic hypocalcemia and uremia. In contrast, the response of the parathyroid- Dicer mice to hypercalcemia and a calcimimetic was intact. The stimulation of the parathyroid by hypocalcemia and uremia is miRNA dependent, as opposed to suppression of the parathyroid by hypercalcemia or a calcimimetic that is miRNA independent. miRNAs are essential for the generation of experimental secondary hyperparathyroidism and may be novel targets for its management in chronic kidney disease patients.

Modeling vitamin D insufficiency and moderate deficiency in adult mice via dietary cholecalciferol restriction

ABSTRACTPurpose: We sought to develop and characterize a model of human vitamin D nutritional insufficiency/deficiency in the adult mouse, which could have broad utility in examining health consequences of this common condition. Methods: Adult mice were fed diets containing cholecalciferol contents of 0.05 IU/g, 0.25 IU/g, 0.5 IU/g or 1.5 IU/g for four months. We studied induction of steady-state vitamin D insufficiency, and its consequences on primary cholecalciferol metabolite levels, calcium homeostasis, parathyroid physiology, and bone morphology. Results: All diets were well tolerated, without adverse effects on body weight. Diets containing 0.05 IU/g and 0.25 IU/g cholecalciferol significantly lowered serum 25-hydroxyvitamin D levels (median 25OHD, 10.5 ng/ml, and 21.6 ng/ml, respectively), starting as early as one month following initiation of the diets, maintained through the four-month experimental period. The 0.05 IU/g diet significantly decreased 1,25-dihydroxyvitamin D (1,25OH2D) levels (median, 78 pg/ml). Despite these decreased 25OHD and 1,25OH2D levels, the diets did not alter parathyroid gland morphology or parathyroid cell proliferation. There were no statistical differences in the serum total calcium and serum PTH levels among the various dietary groups. Furthermore, the 0.05 IU/g diet did not cause any alterations in the cortical and trabecular bone morphology, as determined by microCT. Conclusions: The dietary manipulations yielded states of vitamin D insufficiency or modest deficiency in adult mice, with no overtly detectable impact on parathyroid and bone physiology, and calcium homeostasis. This model system may be of value to study health effects of vitamin D insufficiency/deficiency especially on extraskeletal phenotypes such as cancer susceptibility or immune function.

Phosphorylation of Ribosomal Protein S6 Mediates Mammalian Target of Rapamycin Complex 1-Induced Parathyroid Cell Proliferation in Secondary Hyperparathyroidism.

Secondary hyperparathyroidism is characterized by increased serum parathyroid hormone (PTH) level and parathyroid cell proliferation. However, the molecular pathways mediating the increased parathyroid cell proliferation remain undefined. Here, we found that the mTOR pathway was activated in the parathyroid of rats with secondary hyperparathyroidism induced by either chronic hypocalcemia or uremia, which was measured by increased phosphorylation of ribosomal protein S6 (rpS6), a downstream target of the mTOR pathway. This activation correlated with increased parathyroid cell proliferation. Inhibition of mTOR complex 1 by rapamycin decreased or prevented parathyroid cell proliferation in secondary hyperparathyroidism rats and in vitro in uremic rat parathyroid glands in organ culture. Knockin rpS6(p-/-) mice, in which rpS6 cannot be phosphorylated because of substitution of all five phosphorylatable serines with alanines, had impaired PTH secretion after experimental uremia- or folic acid-induced AKI. Uremic rpS6(p-/-) mice had no increase in parathyroid cell proliferation compared with a marked increase in uremic wild-type mice. These results underscore the importance of mTOR activation and rpS6 phosphorylation for the pathogenesis of secondary hyperparathyroidism and indicate that mTORC1 is a significant regulator of parathyroid cell proliferation through rpS6.

Parathyroid-specific deletion of dicer-dependent microRNAs abrogates the response of the parathyroid to acute and chronic hypocalcemia and uremia

MicroRNAs (miRNAs) down-regulate gene expression and have vital roles in biology but their functions in the parathyroid are unexplored. To study this, we generated parathyroid-specific Dicer1 knockout (PT-Dicer(-/-) ) mice where parathyroid miRNA maturation is blocked. Remarkably, the PT-Dicer(-/-) mice did not increase serum parathyroid hormone (PTH) in response to acute hypocalcemia compared with the >5-fold increase in controls. PT-Dicer(-/-) glands cultured in low-calcium medium secreted 5-fold less PTH at 1.5 h than controls. Chronic hypocalcemia increased serum PTH >4-fold less in PT-Dicer(-/-) mice compared with control mice with no increase in PTH mRNA levels and parathyroid cell proliferation compared with the 2- to 3-fold increase in hypocalcemic controls. Moreover, uremic PT-Dicer(-/-) mice increased serum PTH and FGF23 significantly less than uremic controls. Therefore, stimulation of the parathyroid by both hypocalcemia and uremia is dependent upon intact dicer function and miRNAs. In contrast, the PT-Dicer(-/-) mice responded normally to activation of the parathyroid calcium-sensing receptor (Casr) by both hypercalcemia and a calcimimetic that decreases PTH secretion, demonstrating that they are dicer-independent. Therefore, miRNAs are essential for the response of the parathyroid to both acute and chronic hypocalcemia and uremia, the major stimuli for PTH secretion.

MicroRNA deregulation in parathyroid tumours suggests an embryonic signature.

Primary hyperparathyroidism is a common endocrine disorder caused by abnormal tumour parathyroid cell proliferation. Parathyroid tumours show a great variability both in clinical features, such as the severity of PTH secretion, the rate and the pattern of cell proliferation, and genetic background. Studies aiming to develop new diagnostic markers and therapeutic approaches need a deeper definition of this variability. Dysregulation of microRNAs (miRNAs) has been shown to play an essential role in the development and progression of cancer. MiRNAs are small noncoding RNAs that inhibit the translation and stability of messenger RNAs (mRNAs). Here, data about the miRNA expression pattern in parathyroid normal and tumour glands were reviewed. Though available data in parathyroid tumours are very limited, the expression pattern of a subset of specific miRNAs clearly discriminated parathyroid carcinomas from normal parathyroid glands and, more clinically relevant, from parathyroid adenomas. Investigation showed that parathyroid tumours were characterized by an embryonic expression pattern of miRNAs such as miR-296, or the miRNA clusters C19MC and miR-371-3, typically in stem cells committed to differentiation or during human embryonic development, respectively. Further, miRNA profiles were correlated with tumour aggressive behaviour. Moreover, the interaction with the oncosuppressor menin suggests that miRNAs might modulate the function of the known oncosuppressors or oncogenes involved in parathyroid tumourigenesis and thus overseeing the tumour phenotype. In conclusion, miRNAs might provide new diagnostic markers and new therapeutic approaches by developing molecular miRNA-targeted therapies for the cure of parathyroid tumours, whose unique option is surgery.

Value of GATA3 immunostaining in the diagnosis of parathyroid tumors.

GATA3 is a transcription factor that is involved in the embryonic development of the parathyroid glands and in adult parathyroid cell proliferation. The aim of this study is to investigate the expression of GATA3 in parathyroid tumors and to determine whether it could be used as an immunohistochemical marker for parathyroid differentiation in tumors. Immunoreactivity for GATA3 was nuclear and was demonstrated in all 10 hyperplastic parathyroid glands, 22 parathyroid adenomas, and 6 parathyroid carcinomas; whereas, all thyroid tumors, renal cell carcinomas, thymic epithelial tumors, and carcinoid tumors investigated for comparison purposes were negative for this marker. It is concluded that GATA3 is a very sensitive and relatively specific immunohistochemical marker for parathyroid differentiation that can assist in the differential diagnosis of parathyroid tumors.

PTH-C1: a rat continuous cell line expressing the parathyroid phenotype

The lack of a continuous cell line of epithelial parathyroid cells able to produce parathyroid hormone (PTH) has hampered the studies on in vitro evaluation of the mechanisms involved in the control of parathyroid cell function and proliferation. The PT-r cell line was first established from rat parathyroid tissue in 1987, but these cells were known to express the parathyroid hormone-related peptide (Pthrp) gene, but not the Pth gene. In an attempt to subclone the PT-r cell line, a rat parathyroid cell strain was isolated and named PTH-C1. During 3 years, in culture, PTH-C1 cells maintained an epithelioid morphology, displaying a diploid chromosome number, a doubling time around 15 h during the exponential phase of growth, and parathyroid functional features. PTH-C1 cell line produces PTH and expresses the calcium sensing receptor (Casr) gene and other genes known to be involved in parathyroid function. Most importantly, the PTH-C1 cells also exhibit an in vitro secretory response to calcium. Altogether these findings indicate the uniqueness of the PTH-C1 cell line as an in vitro model for cellular and molecular studies on parathyroid physiopathology.

Cinacalcet Induces Apoptosis in Parathyroid Cells in Patients with Secondary Hyperparathyroidism: Histological and Cytological Analyses

Background/Aims: Previous studies reported a reduction in parathyroid gland volume during treatment with cinacalcet in patients with secondary hyperparathyroidism (SHPT). However, it remains to be determined whether cinacalcet accelerates apoptosis of hyperplastic parathyroid cells in these patients. Methods: The study subjects were 16 hemodialysis patients who had undergone parathyroidectomy for severe SHPT. We compared the expression of the apoptotic marker TUNEL and the proliferative marker Ki67 by immunohistochemistry and the expression of CYP27B1 by quantitative real-time PCR in hyperplastic parathyroid glands from patients treated with cinacalcet (cinacalcet group; n = 8) and those not treated with cinacalcet (non-cinacalcet group; n = 8). We also examined the effect of cinacalcet on parathyroid cell death in in vitro cell culture with TUNEL staining, using parathyroid cells from SHPT patients. Results: Compared with the non-cinacalcet group, the expression of TUNEL was significantly increased but was accompanied with significantly increased Ki67 expression in the parathyroid glands from the cinacalcet group. In vitro examination showed dose- and time-dependent increases of apoptotic cells by adding cinacalcet into culture medium. We also found that the expression of CYP27B1 showed a three-fold increase in glands from the cinacalcet group compared to that of the non-cinacalcet group. Conclusion: Our data suggest that cinacalcet induces apoptosis of human parathyroid cells, but this effect may be overcome by more aggressive proliferation of parathyroid cells in patients with severe, cinacalcet-resistant SHPT.

A novel model of adenine-induced tubulointerstitial nephropathy in mice

BackgroundIn vivo models of uremia are important tools to study numerous aspects of acute and chronic kidney disease. Mouse models are pivotal because most genetically engineered animal models are mice, which allow dissecting the impact of selected target genes in renal failure. Adenine-based protocols to induce renal failure are available in rats, but have not been adapted in mice due to their reluctance to consume adenine. In the current paper we developed a novel method for induction of renal failure through dietary delivery of adenine mixed in a casein-based diet.ResultsAfter an induction phase, a stable model of renal impairment was obtained (target urea range 80–100 mg/dL), mimicking several aspects of chronic kidney disease - mineral and bone disorder including secondary hyperparathyroidism, bone abnormalities and pathological elevation of FGF23. No deaths occurred and the level of uremia was adaptable through adjustments of the adenine content, providing significant advantages compared to existing models. In an 8-week proof-of-concept study, renal histology showed mainly a tubulointerstitial damage with infiltrating leukocytes, interstitial edema and widening of the Bownman's space. Fibrosis was present in most animals as defined by histology and gene expression changes of fibrosis markers. Parathyroid cell proliferation was markedly increased but without signs of glandular hypertrophy. Skeletal histology showed increased trabecular bone and bone marrow adiposity whereas bone biomarkers (CTX and PINP) suggested higher bone formation, but surprisingly, lower bone resorption and perturbations in mineral metabolism.ConclusionsWe present a novel, non-surgical method for induction of renal failure in mice. This is an important complement to existing uremic models for pathophysiological studies in acute and chronic kidney disease, especially in terms of tubulointerstitial lesions.

Increased protein kinase A type Iα regulatory subunit expression in parathyroid gland adenomas of patients with primary hyperparathyroidism

Protein kinase A (PKA) regulatory subunit type Iα (RIα) is a major regulatory subunit that functions as an inhibitor of PKA kinase activity. We have previously demonstrated that elevated RIα expression is associated with diffuse-to-nodular transformation of hyperplasia in parathyroid glands of renal hyperparathyroidism. The aim of the current study was to determine whether or not RIα expression is increased in adenomas of primary hyperparathyroidism (PHPT), because monoclonal proliferation has been demonstrated in both adenomas and nodular hyperplasia. Surgical specimens comprising 22 adenomas and 11 normal glands, obtained from 22 patients with PHPT, were analyzed. Western blot and immunohistochemical analyses were employed to evaluate RIα expression. PKA activities were determined in several adenomas highly expressing RIα. RIα expression was also separately evaluated in chief and oxyphilic cells using the "Allred score" system. Expression of proliferating cell nuclear antigen (PCNA), a proliferation marker, was also immunohistochemically examined. Western blot analysis revealed that 5 out of 8 adenomas highly expressed RIα, compared with normal glands. PKA activity in adenomas was significantly less than in normal glands. Immunohistochemical analysis further demonstrated high expression of RIα in 20 out of 22 adenomas. In adenomas, the greater RIα expression and more PCNA positive cells were observed in both chief and oxyphilic cells. The present study suggested that high RIα expression could contribute to monoclonal proliferation of parathyroid cells by impairing the cAMP/PKA signaling pathway.

Comparisons of Parathyroid Klotho and FGFR1 Expression Between End-Stage Renal Disease Patients and Renal Transplant Recipients with Hyperparathyroidism

Recently, fibroblast growth factor 23 (FGF23), the phosphaturic hormone, has been ascertained to be increased in the patients with chronic kidney disease and end stage renal disease for a compensation of phosphate level. In parathyroid glands, FGF23 exerts its effect by binding to its cognate FGF receptor 1 (FGFR1) in the presence of its co-receptor Klotho, and FGF23 directly inhibit parathyroid hormone. However, in secondary hyperparathyroidism, ‘FGF23 resistance’ aggravates parathyroid cell proliferation. Tertiary hyperparathyroidism means the persistence of severe secondary hyperparathyroidism from dialysis into the post transplant period. We compared with expression of FGFR1 and Klotho in parathyroid tissue after parathryoidectomy owing to severe persistent hyperparathyroidism between renal allograft recipients and end stage renal disease patients. Methods: Hyperplastic parathyroid glands were obtained from dialysis patients and renal allograft recipients who underwent total parathyroidectomy with autotransplantation. We measured the expression of Klotho, FGFR1 by immunohistochemistry in 8 allograft recipients with persistent hyperparathyroidism after transplantation and 11 uremic patients with secondary hyperparathyroidism who underwent dialysis. Immunoreactivity was assessed semiquantitiatively. Results: FGFR1 expression in uremic patients was more decreased than that in renal allograft recipients (6.18 ± 7.26 vs. 3.00 ± 2.97 positive cell per area). But, Klotho expression was increased in uremic patients and renal allograft recipients compared with normal glands. Positive cell area of Klotho expression was 52.42 ± 16.63 % and 47.62 ± 14.04 % in uremic patients and renal allograft recipients. Klotho expression was decreased in renal allograft recipients compared with uremic patients, but there was not significant statistically. (P value 0.29) A significant positive correlation was observed between FGFR1 and serum phosphate level (r2= 0.410, P value 0.035), FGFR1 and serum calcium x phosphate products (r2= 0.509, P value 0.047) in renal allograft recipients. FGFR1 expression was found to be negatively correlated to serum creatinine. (r2= -0.819, P value 0.002). But, Klotho expression on parathyroid hyperplastic tissue in renal allograft recipients was not correlated to the serum phosphate, serum calcium, serum calcium x phosphate products, intact PTH and renal function. Conclusion: Klotho and FGFR1 expression is a discrepancy in hyperplastic glands from patients with secondary and tertiary hyperparathyroidism in this study. Expression of Klotho in parathyroid glands is not different with two groups, and the cause of this result may be explained a pleotrophic effect of Klotho protein. This result also suggested that change of FGFR1 expression in hyperplastic glands can explain ‘FGF23-resistance’ in secondary and tertiary hyperparathyroidism rather than Klotho parathyroid expression.

Vitamin D3: a helpful immuno-modulator

The active metabolite of vitamin D, 1α, 25-dihydroxyvitamin D3 [1,25(OH)(2) D3], is involved in calcium and phosphate metabolism and exerts a large number of biological effects. Vitamin D3 inhibits parathyroid hormone secretion, adaptive immunity and cell proliferation, and at the same time promotes insulin secretion, innate immunity and stimulates cellular differentiation. The role of vitamin D3 in immunoregulation has led to the concept of a dual function as both as an important secosteroid hormone for the regulation of body calcium homeostasis and as an essential organic compound that has been shown to have a crucial effect on the immune responses. Altered levels of vitamin D3 have been associated, by recent observational studies, with a higher susceptibility of immune-mediated disorders and inflammatory diseases. This review reports the new developments with specific reference to the metabolic and signalling mechanisms associated with the complex immune-regulatory effects of vitamin D3 on immune cells.

Role of Multifunctional Cell Cycle Modulators in Advanced Secondary Hyperparathyroidism

Long-term dialysis for patients with end stage renal disease leads to an unavoidable common complication, which is secondary hyperparathyroidism. Two histological patterns (nodular and diffuse hyperplasia) are detected, indicating that continuous uremia-related stimulation promotes parathyroid cell proliferation from diffuse to nodular growth. However, the key molecular mechanism is not fully understood, which narrows the range of therapeutic options for advanced secondary hyperparathyroidism. To address this issue, we utilized surgically resected normal and hyperplastic parathyroid glands to perform immunohistochemical analysis of a multifunctional cell cycle modulator, CCAAT enhancer binding protein (C/EBP)β. In contrast to normal parathyroid tissue and diffuse hyperplasia, the intensity of C/EBPβ staining was homogeneously increased in the parathyroid cells from nodules, along with a higher cyclin D1 labeling index (108.0 ± 19.5, mean ± SEM) and Ki-67 labeling index (31.70 ± 0.49). Normal and diffuse hyperplastic parathyroid glands had far fewer cyclin D1- and Ki-67-positive cells (P < 0.001). Immunofluorescent double staining showed abundant coexpression of Th235 (mitogen-activated protein kinase [MAPK] phosphorylation site) C/EBPβ, along with upregulation of cytoplasmic Ras in nodular hyperplasia. In conclusion, hyperplastic parathyroid cells in nodules have an autonomous proliferation mechanism similar to that of cancer, in which C/EBPβ is upregulated and phosphorylated to interact with the oncogenic Ras/MAPK pathway. C/EBPβ may be a novel target molecule for blocking the growth circuit that underlies parathyroid tumorigenesis in secondary hyperparathyroidism.

Cinacalcet HCl Suppresses Cyclin D1 Oncogene-Derived Parathyroid Cell Proliferation in a Murine Model for Primary Hyperparathyroidism

Cinacalcet HCl (cinacalcet) is a calcimimetic compound, which suppresses parathyroid (PTH) hormone secretion from parathyroid glands in both primary hyperparathyroidism (PHPT) and secondary hyperparathyroidism (SHPT). We previously reported the suppressive effect of cinacalcet on PTH secretion in vivo in a PHPT model mouse, in which parathyroid-targeted overexpression of the cyclin D1 oncogene caused chronic biochemical hyperparathyroidism and parathyroid cell hyperplasia. Although cinacalcet suppressed parathyroid cell proliferation in SHPT in 5/6-nephrectomized uremic rats, its effect on PHPT has not yet been determined. In this study, the effect of cinacalcet on parathyroid cell proliferation was analyzed in PHPT mice. Cinacalcet (1mg/g) was mixed into the rodent diet and orally administrated to 80-week-old PHPT mice for 10days before death. 5-Bromo-2'-deoxyuridine (BrdU, 6mg/day) was infused by an osmotic pump for 5days before death, followed by immunostaining of the thyroid-parathyroid complex using an anti-BrdU antibody to estimate parathyroid cell proliferation. Compared to untreated PHPT mice, cinacalcet significantly suppressed both serum calcium and PTH. The proportion of BrdU-positive cells to the total cell number in the parathyroid glands increased considerably in untreated PHPT mice (9.5±3.1%) compared to wild-type mice (0.7±0.1%) and was significantly suppressed by cinacalcet (1.2±0.2%). Cinacalcet did not affect apoptosis in the parathyroid cells of PHPT mice. These data suggest that cinacalcet suppressed both serum PTH levels and parathyroid cell proliferation in vivo in PHPT.