Vasoactive and proliferative effects of parathyroid hormone and parathyroid hormone-related peptide on human vascular smooth muscle

Parathyroid hormone-related protein serves as a prognostic indicator in oral squamous cell carcinoma

BACKGROUND

In our previous study, parathyroid hormone-like hormone (PTHLH) which encodes parathyroid hormone-related protein (PTHrP) was revealed to be up-regulated in oral squamous cell carcinoma (OSCC) compared with paired apparently normal surgical margins using microarray method. However, the function and prognostic indicators of PTHLH/PTHrP in OSCC remain obscure.

METHODS

The mRNA levels of PTHLH and its protein levels were investigated in 9 OSCC cell lines and in 36 paired OSCC specimens by real-time PCR and western blotting. The biological function of PTHLH/PTHrP was investigated using small interfering RNA (siRNA) in 3 OSCC cell lines, and immunohistochemistry was used to estimate the prognostic value of PTHrP in 101 patients with head and neck squamous cell carcinoma (HNSCC), including OSCC and oropharyngeal squamous cell carcinoma. Cell cycle was tested by flow cytometry and cell cycle related genes were investigated by western blotting and immunocytochemistry assay.

RESULTS

This study showed that the mRNA and protein levels of PTHLH in 9 OSCC cell lines were much higher than that in normal epithelial cells (P < 0.0001). In 36 paired OSCC tissues, PTHLH mRNA expressions were found higher in 32 OSCC tissues than that of paired apparently normal surgical margins (P = 0.0001). The results revealed that the down-regulation of PTHLH/PTHrP by siRNAs could reduce cell proliferation and inhibit plate and soft agar colony formation as well as affect the cell cycle of OSCC cells. The key proteins related to the cell cycle were changed by anti-PTHLH siRNA. The results showed that cyclin D1 and CDK4 expressions were significantly reduced in the cells transfected with anti-PTHLH siRNA. On the other hand, the expression of p21 was increased. The results also showed that high PTHrP level was associated with poor pathologic differentiation (P = 0.0001) and poor prognosis (P = 0.0003) in patients with HNSCC.

CONCLUSIONS

This study suggests that PTHLH/PTHrP is up-regulated in OSCCs. Therefore, PTHLH/PTHrP could play a role in the pathogenesis of OSCC by affecting cell proliferation and cell cycle, and the protein levels of PTHrP might serve as a prognostic indicator for evaluating patients with HNSCCs.

Increased plasminogen activator inhibitor-1, decreased tissue factor pathway inhibitor, and unchanged thrombin-activatable fibrinolysis inhibitor levels in patients with primary hyperparathyroidism

BACKGROUND AND OBJECTIVES

Primary hyperparathyroidism (PHPT) is associated with increased cardiovascular mortality and morbidity. Little is known about hemostatic features of patients with PHPT. To our knowledge, plasma tissue factor pathway inhibitor (TFPI) and thrombin-activatable fibrinolysis inhibitor (TAFI) levels in these patints have not been investigated. Therefore, the main purpose of this study was to evaluate the markers of endogenous coagulation/fibrinolysis, including TFPI and TAFI, and to investigate the relationships between serum calcium and PTH and these hemostatic parameters in patients with PHPT.

DESIGN AND METHODS

Twenty-four patients with PHPT and 20 age-, sex-, and-weight-matched healthy controls were included in the study. Tissue plasminogen activator (t-PA), tissue plasminogen activator inhibitor-1 (PAI-1), TFPI, and TAFI were measured. The relationships between serum calcium, phosphorus, and PTH and these hemostatic parameters were examinated.

RESULTS

Compared with the control subjects, t-PA, PAI-1, and PAI-1/t-PA ratios were significantly increased in patients with PHPT (P<0.0001), whereas TFPI levels were significantly decreased (P<0.0001). Plasma TAFI Ag levels did not significantly change in patients with PHPT compared with the controls. In patients with PHPT, serum phosphorus was negatively correlated with plasma PAI-1 Ag levels and PAI-1/t-PA ratio (r: -0.453, P<0.05; r: -0.580, P<0.01 respectively). There was a positive correlation between Cl/P ratio and plasma PAI-1 levels and PAI-1/t-PA ratio (r: 0.434, P<0.05; r: 0.528, P<0.05 respectively). iPTH was positively correlated with plasma PAI-1/t-PA ratio (r: 0.429, P<0.05).

INTERPRETATION AND CONCLUSIONS

In conclusion, we found some important differences in the hemostatic parameters between the patients with PHPT and healthy controls. Increased PAI-1, PAI-1/t-PA ratios and decreased TFPI levels in these patients represent a potential hypercoagulable and hypofibrinolytic state, which might augment the risk for atherosclerotic and atherothrombotic complications. This condition may contribute to the excess mortality due to cardiovascular disease seen in patients with PHPT.

Serum parathyroid hormone is associated with carotid intima-media thickness in postmenopausal women

OBJECTIVES

To test whether parathyroid hormone (PTH) might be related to the development of atherosclerosis in postmenopausal women, we measured serum levels of PTH, the carotid intima-media thickness (IMT), and other clinical and biochemical parameters.

METHODS

One hundred and seven postmenopausal women were recruited for this study. The serum level of PTH was measured by immunoradiometric assay, and carotid IMT was measured with high resolution B-mode ultrasonography.

RESULTS

On the basis of bivariate correlation analyses or unpaired t-tests, the body mass index (BMI), waist circumference, estimated glomerular filtration rate, and 25-hydroxyvitamin D were not associated with carotid IMT. In contrast, age (r = 0.414, p < 0.001), serum level of PTH (r = 0.304, p = 0.001), hypertension (p < 0.001), and hypercholesterolaemia (p = 0.004) were related to carotid IMT. On the basis of multiple regression analysis, the serum level of PTH (beta = 0.198, p = 0.029), as well as age (beta = 0.309, p = 0.001) and hypertension (beta = 0.262, p = 0.006), were independent predictors of carotid IMT.

CONCLUSIONS

Our results have demonstrated that serum PTH is an independent determinant of carotid IMT in postmenopausal women. This result suggests that serum PTH, even in the reference range, might be associated with the development of atherosclerosis or cardiovascular diseases in postmenopausal women. Further study is necessary in males and premenopausal women to fully elucidate the clinical significance of this finding.

Parathyroid hormone and the cardiovascular system

The classical actions of parathyroid hormone (PTH) are well recognized, but its effects on other target tissues, such as the cardiovascular system, are less appreciated. Several studies have evaluated the effects of PTH in patients with primary hyperparathyroidism in order to understand potential cardiovascular effects in terms of hypertension, cardiovascular mortality, left ventricular function, and endothelial function. We review these studies and evaluate the cellular mechanisms that may affect these outcomes.

The coronary effects of parathyroid hormone

OBJECTIVE

The aim of the present study was to characterize the role of the ATP-sensitive potassium channels (K(+)(ATP)) in the coronary dilator action of parathyroid hormone (PTH).

METHODS

Dose-response curves of intracoronary administrated PTH (0.15-1.33 nmol) were obtained in control phases and during continuous intracoronary administration of the K(+)(ATP) channel-selective antagonist glibenclamide (0.1-1.0 micromol/min) in dogs (n = 13).

RESULTS

Increments of integrated coronary conductance (excess coronary conductance) at PTH doses of 0.15 and 1.33 nmol were 1.17 versus 0.03 ml/mm Hg (p < 0.05) and 4.03 versus 0.94 ml/mm Hg (p < 0.05) in the control versus during maximal blockade, respectively.

CONCLUSION

The results indicate that the activation of K(+)(ATP) channels significantly contributes to the PTH-induced coronary vasodilation.

Parathyroid hormone has a prosclerotic effect on vascular smooth muscle cells

Although accelerated atherosclerosis and arteriosclerosis are common in patients with renal failure, the pathogenesis of these changes is poorly understood. Parathyroid hormone (PTH) levels are elevated in renal failure, and have been linked to uraemic vascular changes in some studies. We examined the in vitro effects of increasing doses of the 1-34 fragment of PTH on human aortic vascular smooth muscle cells (VSMCs). Factors examined were: (1) collagen production using tritiated hydroxyproline incorporation and transcription of procollagen alpha(1)(I) mRNA; (2) change in the surface area of collagen I lattices; (3) mRNA transcription of the collagen binding protein beta1 integrin; (4) proliferation using tritiated thymidine incorporation, and (5) methyl tetrazolium salt conversion to estimate live cell number after 5 days' exposure to PTH. PTH at a concentration of 200 pmol/l increased total collagen synthesis (188 +/- 25% of control, p < 0.01) as well as transcription of procollagen alpha(1)(I) mRNA (136 +/- 11% of control, p < 0.005). PTH also increased reorganisation of collagen I lattices (surface area 47 +/- 8% of well for control vs. 35.7 +/- 2.5 and 34.3 +/- 3.0% for PTH 100 and 200 pmol/l, respectively, p = 0.02) and upregulated beta1 integrin mRNA expression (160 +/- 20% of control at PTH concentration of 200 pmol/l, p < 0.05). PTH had no effect on VSMC proliferation or number at doses up to 200 pmol/l. In conclusion, PTH increases production and reorganisation of collagen by VSMCs in vitro. It is possible that more aggressive control of hyperparathyroidism in patients with renal failure may help to reduce the burden of cardiovascular disease in this patient population.

Fibrous dysplasia in the maxilla: possible mechanism of bone remodeling by calcitonin treatment

The long-term follow-up case of monostotic fibrous dysplasia of the maxilla in a 10-year-old girl is described with her endocrinologic data and therapeutic consequence of calcitonin administration in association with surgical interventions. The fibrous dysplasia tends to become more quiescent or static after skeletal growth ceases, but the causative has been still unknown to date. In this case reported changes of calciotropic hormones in the serum were well corresponding to the ceasing of the tumor growth at the puberty and reflected to the calcitonin administration. Although calcitonin has been applied to the fibrous dysplasia associated with McCune Albright syndrome, no histologic changes have been described after the calcitonin treatment. This report might be the first description of bone remodeling after the calcitonin treatment for the fibrous dysplasia of the maxilla in immature people. Data of this case may provide a clue to the pathogenesis of fibrous dysplasia. Surgical intervention can be performed after the local bone calcification by a calcitonin treatment, because of alleviation of vigorous hemorrhage by the bone remodeling.

Dual regulation of the parathyroid hormone (PTH)/PTH-related peptide receptor signaling by protein kinase C and beta-arrestins

We examined here the role of second messenger-dependent kinases and beta-arrestins in short-term regulation of the PTH receptor (PTHR) signaling. The inhibition of protein kinase C (PKC) in COS-7 cells transiently expressing PTHR, led to an approximately 2-fold increase in PTH-stimulated inositol phosphate (IP) and cAMP production. The inhibition of protein kinase A increased cAMP production 1.5-fold without affecting IP signaling. The effects of PKC inhibition on PTHR-mediated G(q) signaling were strongly decreased for a carboxy-terminally truncated PTHR (T480) that is phosphorylation deficient. PKC inhibition was associated with a decrease in agonist-stimulated PTHR phosphorylation and internalization without blocking PTH-dependent mobilization of beta-arrestin2 to the plasma membrane. Overexpression of beta-arrestins strongly decreased the PTHR-mediated IP signal, whereas cAMP production was impaired to a much lower extent. The regulation of PTH-stimulated signals by beta-arrestins was impaired for the truncated T480 receptor. Our data reveal mechanisms at, and distal to, the receptor regulating PTHR-mediated signaling pathways by second messenger-dependent kinases. We conclude that regulation of PTHR-mediated signaling by PKC and beta-arrestins are separable phenomena that both involve the carboxy terminus of the receptor. A major role for PKC and beta-arrestins in preferential regulation of PTHR-mediated G(q) signaling by independent mechanisms at the receptor level was established.