Cellular mechanism through which parathyroid hormone-related protein induces proliferation in arterial smooth muscle cells: definition of an arterial smooth muscle PTHrP/p27kip1 pathway

Intermittent parathyroid hormone enhances the healing of medication-related osteonecrosis of the jaw lesions in rice rats

Medication-related osteonecrosis of the jaw (MRONJ) is a potentially severe adverse event in patients treated with antiresorptives. Management of MRONJ is challenging, and no non-antibiotic, established medical treatment exists. Intermittent parathyroid hormone (iPTH) has been used off-label to treat MRONJ with favorable results. However, its medical efficacy has rarely been substantiated in clinical or preclinical experiments. Using a validated rice rat, infection-based model of MRONJ, we evaluated the effects of iPTH on established MRONJ. We hypothesize that iPTH contributes to MRONJ resolution by enhancing alveolar bone turnover and healing oral soft tissues. Eighty-four rice rats began a standard rodent chow diet at age 4 weeks to induce localized periodontitis. Rats were simultaneously randomized to receive saline (vehicle, VEH) or zoledronic acid (ZOL, 80 μg/kg IV) every 4 weeks. Oral exams were conducted bi-weekly to assign a gross quadrant grade (GQG, 0-4) to evaluate any lesion at the lingual aspect of the interdental space between maxillary molar (M2) and M3. 14 of 20 VEH-treated rice rats (70%) developed maxillary localized periodontitis with GQG 2-3 after 30 ± 10 weeks of saline. Additionally, 40 of 64 ZOL-treated rice rats with periodontitis developed MRONJ-like lesions after 30 ± 10 weeks of ZOL treatment. Rice rats with localized periodontitis or MRONJ-like lesions were treated with saline or iPTH (40 μg/kg) subcutaneously (SC) 3 times/week For 6 weeks until euthanasia. We found that iPTH -treated ZOL rats had a lower prevalence of MRONJ (p < 0.001), with lower severity extent of oral lesions (p = 0.003) and percentage of empty osteocyte lacunae (p < 0.001). ZOL rats treated with iPTH displayed a higher osteoblast surface (p < 0.001), more osteoblasts (p < 0.001), higher osteoclast surface (p < 0.001) and more osteoclasts (p = 0.002) at alveolar bone surfaces than ZOL/VEH rats. Greater gingival epithelial thickness and epithelial cell proliferation rate was found in the oral mucosa and gingiva of ZOL/PTH rats than in ZOL/VEH rats (p < 0.001). Our data suggest that iPTH is an efficacious non-operative medicinal therapy that accelerates oral healing and enhances the resolution of MRONJ lesions in ZOL-treated rice rats.

Nurses’ knowledge, attitudes, practice, and decision-making skills related to sepsis assessment and management

<b>Objectives</b>: The present study examines the critical care nurse’s knowledge, attitudes, practice (KAP), and decision-making related to early assessment and management of sepsis.<br /> <b>Methods</b>: This cross-sectional descriptive study utilized a convenience sample of 70 nurses working in a college hospital in the northern region of Jordan. Data were gathered employing a sepsis vignette and valid questionnaires via Google document. The nursing decision-making instrument and the knowledge, attitudes, and practice survey were utilized to assess nurses’ decision-making skills, knowledge, attitudes, and practice, respectively. Nurses’ sociodemographic/professional data, including gender, marital status, experience, education, and work environment, were also measured.<br /> <b>Result</b>: The participating nurses reported poor KAP, and analytical decision-making skills related to sepsis management. Experienced nurses and those with a master’s degree reported significantly better KAP, and intuitive decision-making skills than naïve and those with a bachelor’s degree. Nurses with analytical decision-making modes reported higher levels of knowledge, attitudes, and practice than nurses with intuitive or flexible analytical-intuitive decision-making modes.<br /> <b>Conclusion</b>: Poor decision-making skills, as well as knowledge, attitudes, and practice related to sepsis assessment and management, is a substantial problem that demands a productive re-evaluation of the current sepsis management practices. Boosting the knowledge and improving the practices on sepsis assessment and management through comprehensive educational programs and campaigns are necessary to improve nurses’ decision-making skills.

PTHrP induces STAT5 activation, secretory differentiation and accelerates mammary tumor development

BACKGROUND

Parathyroid hormone-related protein (PTHrP) is required for embryonic breast development and has important functions during lactation, when it is produced by alveolar epithelial cells and secreted into the maternal circulation to mobilize skeletal calcium used for milk production. PTHrP is also produced by breast cancers, and GWAS studies suggest that it influences breast cancer risk. However, the exact functions of PTHrP in breast cancer biology remain unsettled.

METHODS

We developed a tetracycline-regulated, MMTV (mouse mammary tumor virus)-driven model of PTHrP overexpression in mammary epithelial cells (Tet-PTHrP mice) and bred these mice with the MMTV-PyMT (polyoma middle tumor-antigen) breast cancer model to analyze the impact of PTHrP overexpression on normal mammary gland biology and in breast cancer progression.

RESULTS

Overexpression of PTHrP in luminal epithelial cells caused alveolar hyperplasia and secretory differentiation of the mammary epithelium with milk production. This was accompanied by activation of Stat5 and increased expression of E74-like factor-5 (Elf5) as well as a delay in post-lactation involution. In MMTV-PyMT mice, overexpression of PTHrP (Tet-PTHrP;PyMT mice) shortened tumor latency and accelerated tumor growth, ultimately reducing overall survival. Tumors overproducing PTHrP also displayed increased expression of nuclear pSTAT5 and Elf5, increased expression of markers of secretory differentiation and milk constituents, and histologically resembled secretory carcinomas of the breast. Overexpression of PTHrP within cells isolated from tumors, but not PTHrP exogenously added to cell culture media, led to activation of STAT5 and milk protein gene expression. In addition, neither ablating the Type 1 PTH/PTHrP receptor (PTH1R) in epithelial cells nor treating Tet-PTHrP;PyMT mice with an anti-PTH1R antibody prevented secretory differentiation or altered tumor latency. These data suggest that PTHrP acts in a cell-autonomous, intracrine manner. Finally, expression of PTHrP in human breast cancers is associated with expression of genes involved in milk production and STAT5 signaling.

CONCLUSIONS

Our study suggests that PTHrP promotes pathways leading to secretory differentiation and proliferation in both normal mammary epithelial cells and in breast tumor cells.

Parathyroid Hormone Induces Transition of Myofibroblasts in Arteriovenous Fistula and Increases Maturation Failure

CONTEXT

Arteriovenous fistula (AVF) maturation failure remains a clinical dilemma, and its pathobiology is largely unclear. Secondary hyperparathyroidism is a complication of chronic renal failure that is associated with cardiovascular disease. While parathyroid hormone (PTH) has a prosclerotic effect on vascular smooth muscle cells (VSMCs), its role in AVF maturation failure remained unknown.

OBJECTIVE

This work aimed to investigate the association between plasma PTH and AVF maturation.

METHODS

Patients receiving AVF creation were enrolled retrospectively. A mouse model of secondary hyperparathyroidism and aortocaval AVF was used to investigate the effect of PTH on an AVF lesion. A cell model of VSMCs treated with PTH in a pressurized culture system was used to disclose the signaling pathway underlying the effect of PTH on an AVF lesion.

RESULTS

In patients receiving AVF creation, higher PTH was associated with an increased risk for maturation failure. In a mouse model, vascular wall thickness and myofibroblasts of AVF significantly increased with higher PTH. When the same mice were treated with cinacalcet, AVF lesions were attenuated by suppression of PTH. A cell model showed that PTH increased the marker of myofibroblasts, integrin β6 subunit (ITGB6), via the phosphorylated protein kinase B pathway. Finally, in the same model of mice AVF, higher PTH also increased the expression of ITGB6 in the smooth muscle layer of AVF, suggesting the transition to myofibroblast.

CONCLUSION

Overall, our results suggest that higher PTH increased the risk of AVF maturation failure through increasing the transition of VSMCs to myofibroblasts. Lowering PTH may be a strategy to enhance AVF maturation.

Role of PTHrP nuclear localization and carboxyl terminus sequences in postnatal spinal cord development

Parathyroid hormone-related peptide (PTHrP) acts under physiological conditions to regulate normal development of several tissues and organs. The role of PTHrP in spinal cord development has not been characterized. Pthrp knock in (Pthrp KI) mice were genetically modified to produce PTHrP in which there is a deficiency of the nuclear localization sequence (NLS) and C-terminus. Using this genetically modified mouse model, we have characterized its effect on spinal cord development early postnatally. The spinal cords from Pthrp KI mice displayed a significant reduction in its length, weight, and cross-sectional area compared to wild-type controls. Histologically, there was a decreased development of neurons and glial cells that caused decreased cell proliferation and increased apoptosis. The neural stem cells (NSCs) cultures also revealed decreased cell proliferation and differentiation and increased apoptosis. The proposed mechanism of delayed spinal cord development in Pthrp KI mice may be due to alteration in associated pathways in regulation of cell-division cycles and apoptosis. There was significant downregulation of Bmi-1 and upregulation of cyclin-dependent kinase inhibitors p27, p21, and p16 in Pthrp KI animals. We conclude that NLS and C-terminus peptide segments of PTHrP play an important role in inhibiting cell apoptosis and stimulation of cellular proliferation necessary for normal spinal cord development.

Calcium-Sensing Receptor Promotes Breast Cancer by Stimulating Intracrine Actions of Parathyroid Hormone-Related Protein

Parathyroid hormone-related protein (PTHrP) contributes to the development and metastatic progression of breast cancer by promoting hypercalcemia, tumor growth, and osteolytic bone metastases, but it is not known how PTHrP is upregulated in breast tumors. Here we report a central role in this process for the calcium-sensing receptor, CaSR, which enables cellular responses to changes in extracellular calcium, through studies of CaSR-PTHrP interactions in the MMTV-PymT transgenic mouse model of breast cancer and in human breast cancer cells. CaSR activation stimulated PTHrP production by breast cancer cells in vitro and in vivo Tissue-specific disruption of the casr gene in mammary epithelial cells in MMTV-PymT mice reduced tumor PTHrP expression and inhibited tumor cell proliferation and tumor outgrowth. CaSR signaling promoted the proliferation of human breast cancer cell lines and tumor cells cultured from MMTV-PyMT mice. Further, CaSR activation inhibited cell death triggered by high extracellular concentrations of calcium. The actions of the CaSR appeared to be mediated by nuclear actions of PTHrP that decreased p27(kip1) levels and prevented nuclear accumulation of the proapoptotic factor apoptosis inducing factor. Taken together, our findings suggest that CaSR-PTHrP interactions might be a promising target for the development of therapeutic agents to limit tumor cell growth in bone metastases and in other microenvironments in which elevated calcium and/or PTHrP levels contribute to breast cancer progression. Cancer Res; 76(18); 5348-60. ©2016 AACR.

Treatment with intermittent PTH increases Wnt10b production by T cells in osteoporotic patients

We evaluated the effect of parathyroid hormone (PTH) on Wnt10b production by immune system cells in humans. We showed that bone anabolic effect of intermittent PTH treatment may be amplified by T cells through increased production of Wnt10b. Chronic increase in PTH as in primary hyperparathyroidism does not increase Wnt10b expression.

INTRODUCTION

The aim of this study is to assess the effect of PTH on Wnt10b production by immune system cells in humans. We assessed both the effect of intermittent PTH administration (iPTH) and of chronic PTH hypersecretion in primary hyperparathyroidism (PHP).

METHODS

Eighty-two women affected by post-menopausal osteoporosis were randomly assigned to treatment with calcium and vitamin D alone (22) or plus 1-84 PTH (42), or intravenous ibandronate (18). Wnt10b production by unfractioned blood nucleated cells and by T, B cells and monocytes was assessed by real-time RT-PCR and ELISA at baseline, 3, 6, 12 and 18 months of treatment. The effect of chronic elevation of PTH was evaluated in 20 patients affected by PHP at diagnosis and after surgical removal of parathyroid adenoma. WNT10b from both osteoporotic and PHP patients was compared to healthy subjects matched for age and sex.

RESULTS

iPTH increases Wnt10b production by T cells, whereas PHP does not. After surgical restoration of normal parathyroid function, WNT10b decreases, although it is still comparable with healthy subjects' level. Thus, chronic elevation of PTH does not significantly increase WNT10b production as respect to control.

CONCLUSIONS

This is the first work showing the effect of both intermittent and chronic PTH increase on Wnt10b production by immune system cells. We suggest that, in humans, T cells amplified the anabolic effect of PTH on bone, by increasing Wnt10b production, which stimulates osteoblast activity.

The p27 Pathway Modulates the Regulation of Skeletal Growth and Osteoblastic Bone Formation by Parathyroid Hormone-Related Peptide

Parathyroid hormone-related peptide (PTHrP) 1-84 knock-in mice (Pthrp KI) develop skeletal growth retardation and defective osteoblastic bone formation. To further examine the mechanisms underlying this phenotype, microarray analyses of differential gene expression profiles were performed in long bone extracts from Pthrp KI mice and their wild-type (WT) littermates. We found that the expression levels of p27, p16, and p53 were significantly upregulated in Pthrp KI mice relative to WT littermates. To determine whether p27 was involved in the regulation by PTHrP of skeletal growth and development in vivo, we generated compound mutant mice, which were homozygous for both p27 deletion and the Pthrp KI mutation (p27(-/-) Pthrp KI). We then compared p27(-/-) Pthrp KI mice with p27(-/-), Pthrp KI, and WT littermates. Deletion of p27 in Pthrp KI mice resulted in a longer lifespan, increased body weight, and improvement in skeletal growth. At 2 weeks of age, skeletal parameters, including length of long bones, size of epiphyses, numbers of proliferating cell nuclear antigen (PCNA)-positive chondrocytes, bone mineral density, trabecular bone volume, osteoblast numbers, and alkaline phosphatase (ALP)-, type I collagen-, and osteocalcin-positive bone areas were increased in p27(-/-) mice and reduced in both Pthrp KI and p27(-/-) Pthrp KI mice compared with WT mice; however, these parameters were increased in p27(-/-) Pthrp KI mice compared with Pthrp KI mice. As well, protein expression levels of PTHR, IGF-1, and Bmi-1, and the numbers of total colony-forming unit fibroblastic (CFU-f) and ALP-positive CFU-f were similarly increased in p27(-/-) Pthrp KI mice compared with Pthrp KI mice. Our results demonstrate that deletion of p27 in Pthrp KI mice can partially rescue defects in skeletal growth and osteoblastic bone formation by enhancing endochondral bone formation and osteogenesis. These studies, therefore, indicate that the p27 pathway may function downstream in the action of PTHrP to regulate skeletal growth and development.

Deficiency of the parathyroid hormone-related peptide nuclear localization and carboxyl terminal sequences leads to premature skin ageing partially mediated by the upregulation of p27

We previously reported that deficiency of the PTHrP nuclear localization sequence (NLS) and C-terminus in PTHrP knockin (PTHrP KI) mice resulted in premature ageing of skin. P27, a cyclin-dependent kinase inhibitor, was upregulated in PTHrP KI mice and acted as a downstream target of the PTHrP NLS to regulate the proliferation of vascular smooth muscle cells. To determine the effects of p27 deficiency on premature skin ageing of PTHrP KI mice, we compared the skin phenotypes of PTHrP KI mice to those of p27 knockout (p27(-/-) ) mice and to those of double homozygous p27-deficient and PTHrP KI (p27(-/-) PTHrP KI) mice at 2 weeks age. Compared with wild-type littermates, PTHrP KI mice displayed thinner skin and decreased subcutaneous fat and collagen fibres, decreased skin cell proliferation and increased apoptosis, higher expression of p27, p19 and p53 and lower expression of cyclin E and CDK2, and increased reactive oxygen species levels and decreased antioxidant capacity. Deficiency of p27 in the PTHrP KI mice at least in part corrected the skin premature ageing phenotype resulting in thicker skin and increased subcutaneous fat and collagen. These alternations were associated with higher expression of CDK2 and cyclin E, lower expression of p19 and p53, and enhanced antioxidant capacity with increased skin cell proliferation and inhibition of apoptosis. Our results indicate that the NLS and C-terminus of PTHrP play a critical role in preventing skin from premature ageing that is partially mediated by p27.

Involvement of ERK1/2, p38 MAPK, and PI3K/Akt signaling pathways in the regulation of cell cycle progression by PTHrP in colon adenocarcinoma cells

Parathyroid hormone-related peptide (PTHrP) is distributed in most fetal and adult tissues, and its expression correlates with the severity of colon carcinoma. Recently we obtained evidence that in Caco-2 cells, a cell line from human colorectal adenocarcinoma, exogenous PTHrP increases the number of live cells, via ERK1/2, p38 MAPK, and PI3-kinase and induces the expression of cyclin D1, a cell cycle regulatory protein. In this study, we further investigated the role of PTHrP in the regulation of the cell cycle progression in these intestinal cells. Flow cytometry analysis revealed that PTHrP treatment diminishes the number of cells in the G0/G1 phase and increases the number in both S and G2/M phases. The hormone increases the expression of CDK6 and diminishes the amount of negative cell cycle regulators p27Kip1, p15INK4B, and p53. However, PTHrP does not modify the expression of cyclin D3, CDK4, and p16INK4A. In addition, inhibitors of ERK1/2 (PD98059), p38 MAPK (SB203580), and PI3Kinase (LY294002) reversed PTHrP response in Caco-2 cells. Taken together, our results suggest that PTHrP positively modulates cell cycle progression and changes the expression of proteins involved in cell cycle regulation via ERK1/2, p38 MAPK, and PI3K signaling pathways in Caco-2 cells.

Functional roles of the nuclear localization signal of parathyroid hormone-related protein (PTHrP) in osteoblastic cells

PTHrP is an important regulator of bone remodelling, apparently by acting through several sequence domains. We here aimed to further delineate the functional roles of the nuclear localization signal (NLS) comprising the 88-107 amino acid sequence of PTHrP in osteoblasts. PTHrP mutants from a human PTHrP (-36/+139) cDNA (wild type) cloned into pcDNA3.1 plasmid with deletion (Δ) of the signal peptide (SP), NLS, T(107), or T107A replacing T(107) by A(107) were generated and stably transfected into osteoblastic MC3T3-E1 cells. In these cells, intracellular trafficking, cell proliferation and viability, as well as cell differentiation were evaluated. In these transfected cells, PTHrP was detected in the cytoplasm and also in the nucleus, except in the NLS mutant. Meanwhile, the PTH type 1 receptor (PTH1R) accumulates in the cytoplasm except for the ΔSP mutant in which the receptor remains at the cell membrane. PTHrP-wild type cells showed enhanced growth and viability, as well as an increased matrix mineralization, alkaline phosphatase activity, and osteocalcin gene expression; and these features were inhibited or abolished in ΔNLS or ΔT(107) mutants. Of note, these effects of PTHrP overexpression on cell growth and function were similarly decreased in the ΔSP mutant after PTH1R small interfering RNA transfection or by a PTH1R antagonist. The present in vitro findings suggest a mixed model for PTHrP actions on osteoblastic growth and function whereby this protein needs to be secreted and internalized via the PTH1R (autocrine/paracrine pathway) before NLS-dependent shuttling to the nucleus (intracrine pathway).

Parathyroid hormone-related protein is a mitogenic and a survival factor of mesangial cells from male mice: role of intracrine and paracrine pathways

Glomerulonephritis is characterized by the proliferation and apoptosis of mesangial cells (MC). The parathyroid-hormone related protein (PTHrP) is a locally active cytokine that affects these phenomena in many cell types, through either paracrine or intracrine pathways. The aim of this study was to evaluate the effect of both PTHrP pathways on MC proliferation and apoptosis. In vitro studies were based on MC from male transgenic mice allowing PTHrP-gene excision by a CreLoxP system. MC were also transfected with different PTHrP constructs: wild type PTHrP, PTHrP devoid of its signal peptide, or of its nuclear localization sequence. The results showed that PTHrP deletion in MC reduced their proliferation even in the presence of serum and increased their apoptosis when serum-deprived. PTH1R activation by PTHrP(1-36) or PTH(1-34) had no effect on proliferation but improved MC survival. Transfection of MC with PTHrP devoid of its signal peptide significantly increased their proliferation and minimally reduced their apoptosis. Overexpression of PTHrP devoid of its nuclear localization sequence protected cells from apoptosis without changing their proliferation. Wild type PTHrP transfection conferred both mitogenic and survival effects, which seem independent of midregion and C-terminal PTHrP fragments. PTHrP-induced MC proliferation was associated with p27(Kip1) down-regulation and c-Myc/E2F1 up-regulation. PTHrP increased MC survival through the activation of cAMP/protein kinase A and PI3-K/Akt pathways. These results reveal that PTHrP is a cytokine of multiple roles in MC, acting as a mitogenic factor only through an intracrine pathway, and reducing apoptosis mainly through the paracrine pathway. Thus, PTHrP appears as a probable actor in MC injuries.

c-myc and skp2 coordinate p27 degradation, vascular smooth muscle proliferation, and neointima formation induced by the parathyroid hormone-related protein

Parathyroid hormone-related protein (PTHrP) contains a classical bipartite nuclear localization signal. Nuclear PTHrP induces proliferation of arterial vascular smooth muscle cells (VSMC). In the arterial wall, PTHrP is markedly up-regulated in response to angioplasty and promotes arterial restenosis. PTHrP overexpression exacerbates arterial restenosis, and knockout of the PTHrP gene results in decreased VSMC proliferation in vivo. In arterial VSMC, expression of the cell cycle inhibitor, p27, rapidly decreases after angioplasty, and replacement of p27 markedly reduces neointima development. We have shown that PTHrP overexpression in VSMC leads to p27 down-regulation, mostly through increased proteosomal degradation. Here, we determined the molecular mechanisms through which PTHrP targets p27 for degradation. S-phase kinase-associated protein 2 (skp2) and c-myc, two critical regulators of p27 expression and stability, and neointima formation were up-regulated in PTHrP overexpression in VSMC. Normalization of skp2 or c-myc using small interfering RNA restores normal cell cycle and p27 expression in PTHrP overexpression in VSMC. These data indicate that skp2 and c-myc mediate p27 loss and proliferation induced by PTHrP. c-myc promoter activity was increased, and c-myc target genes involved in p27 stability were up-regulated in PTHrP overexpression in VSMC. In primary VSMC, PTHrP overexpression led to increased c-myc and decreased p27. Conversely, knockdown of PTHrP in primary VSMC from PTHrP(flox/flox) mice led to cell cycle arrest, p27 up-regulation, with c-myc and skp2 down-regulation. Collectively, these data describe for the first time the role of PTHrP in the regulation of skp2 and c-myc in VSMC. This novel PTHrP-c-myc-skp2 pathway is a potential target for therapeutic manipulation of the arterial response to injury.

Systemic and acute administration of parathyroid hormone-related peptide(1-36) stimulates endogenous beta cell proliferation while preserving function in adult mice

AIMS/HYPOTHESIS

A major focus in the treatment of diabetes is to identify factors that stimulate endogenous beta cell growth while preserving function. The first 36 amino acids of parathyroid hormone-related protein (PTHrP) are sufficient to enhance proliferation and function in rodent and human beta cells in vitro. This study examined whether acute and systemic administration of the amino-terminal PTHrP(1-36) peptide can achieve similar effects in rodent beta cells in vivo.

METHODS

Adult male mice were injected with 40, 80 or 160 μg of PTHrP(1-36) per kg body weight or with vehicle for 25 days. Glucose and beta cell homeostasis, as well as expression of differentiation markers and cell cycle genes were analysed.

RESULTS

All three doses of PTHrP(1-36) significantly enhanced beta cell proliferation in vivo at day 25, with 160 μg/kg PTHrP(1-36) increasing proliferation as early as day 5. Importantly, the two higher doses of PTHrP(1-36) caused a significant 30% expansion of beta cell mass, with a short-term improvement in glucose tolerance. PTHrP(1-36) did not cause hypercalcaemia, or change islet number, beta cell size, beta cell death or expression of differentiation markers. Analysis of islet G1/S cell cycle proteins revealed that chronic overabundance of PTHrP(1-139) in the beta cell significantly increased the cell cycle activator cyclin D2 and decreased levels of cyclin-dependent kinase 4 inhibitor (p16( Ink4a ) [Ink4a also known as Cdkn2a]), but acute treatment with PTHrP(1-36) did not.

CONCLUSIONS/INTERPRETATION

Acute and systemic administration of PTHrP(1-36) increases rodent beta cell proliferation and mass without negatively affecting function or survival. These findings highlight the future potential therapeutic effectiveness of this peptide under diabetes-related pathophysiological conditions.

Parathyroid hormone-related protein enhances human ß-cell proliferation and function with associated induction of cyclin-dependent kinase 2 and cyclin E expression

OBJECTIVE

Inducing human β-cell growth while enhancing function is a major goal in the treatment of diabetes. Parathyroid hormone-related protein (PTHrP) enhances rodent β-cell growth and function through the parathyroid hormone-1 receptor (PTH1R). Based on this, we hypothesized that PTH1R is expressed in human β-cells and that PTHrP has the potential to enhance human β-cell proliferation and/or function.

RESEARCH DESIGN AND METHODS

PTH1R expression, β-cell proliferation, glucose-stimulated insulin secretion (GSIS), and expression of differentiation and cell-cycle genes were analyzed in human islets transduced with adenoviral PTHrP constructs or treated with PTHrP peptides. The effect of overexpression of late G1/S cell cycle molecules was also assessed on human β-cell proliferation.

RESULTS

We found that human β-cells express PTH1R. More importantly, overexpression of PTHrP causes a significant approximately threefold increase in human β-cell proliferation. Furthermore, the amino terminus PTHrP(1-36) peptide is sufficient to increase replication as well as expression of the late G1/S cell-cycle proteins cyclin E and cyclin-dependent kinase 2 (cdk2) in human islets. Notably, PTHrP(1-36) also enhances GSIS. Finally, overexpression of cyclin E alone, but not cdk2, augments human β-cell proliferation, and when both molecules are expressed simultaneously there is a further marked synergistic increase in replication.

CONCLUSIONS

PTHrP(1-36) peptide enhances human β-cell proliferation as well as function, with associated upregulation of two specific cell-cycle activators that together can induce human β-cell proliferation several fold. The future therapeutic potential of PTHrP(1-36) for the treatment of diabetes is especially relevant given the complementary therapeutic efficacy of PTHrP(1-36) in postmenopausal osteoporosis.

Tumor necrosis factor-α regulates p27 kip expression and apoptosis in smooth muscle cells of human carotid plaques via forkhead transcription factor O1

Apoptosis of vascular smooth muscle cells (SMCs) is controlled by a balance between the effect of growth factors and cytokines, and is involved in plaque instability in advanced atherosclerotic lesions. Recently, we reported high levels of atheroma-associated cytokines, including tumor necrosis factor-α (TNF-α), in carotid plaques of symptomatic patients. These cytokines induce apoptosis of vascular SMCs, and thus could be responsible for plaque rupture, a clinically devastating event. In this study, we examined the effect of TNF-α on the cell cycle inhibitor p27(kip) and apoptosis of SMCs in human carotid plaques, and the underlying mechanism. Both Forkhead box subclass o1 (FoxO1) and p27(kip) were more strongly expressed in symptomatic than asymptomatic atherosclerotic plaques. TNF-α significantly induced the expression of FoxO1 in asymptomatic plaque SMCs in a dose- and time-dependent manner via JNK signaling pathway. TNF-α also induced phosphorylation of FoxO1, resulting in its cytoplasmic translocation/nuclear exclusion of transcription factors. The effect of TNF-α was blocked by the PI3K inhibitor, LY294002. Meanwhile, TNF-α not only induced the p27(kip) expression and cell cycle arrest in the G(0)-G(1) phase, but also enhanced caspase-3 activity and induced apoptosis in SMCs of asymptomatic plaques. However, the potential effect of TNF-α on the cell cycle inhibitor p27(kip) and apoptosis of SMCs was inhibited by siRNA against FoxO1 in asymptomatic patients. These data suggest the involvement of FoxO1 transcription factor in TNF-α-induced expression of a cell cycle regulatory protein and apoptosis of SMCs, thus regulating the stability of atherosclerotic plaques with carotid stenosis.

EBP50 inhibits the anti-mitogenic action of the parathyroid hormone type 1 receptor in vascular smooth muscle cells

Parathyroid hormone-related protein (PTHrP) and the parathyroid hormone type 1 receptor (PTH1R) are important regulators of vascular remodeling. PTHrP expression is associated to increased proliferation of vascular smooth muscle cells (VSMC). In contrast, signaling via the PTH1R inhibits cell growth. The mechanisms regulating the dual effect of PTHrP and PTH1R on VSMC proliferation are only partially understood. In this study we examined the role of the adaptor protein ezrin-radixin-moesin-binding phosphoprotein (EBP50) on PTH1R expression, trafficking, signaling and control of A10 cell proliferation. In normal rat vascular tissues, EBP50 was restricted to the endothelium with little expression in VSMC. EBP50 expression significantly increased in VSMC following angioplasty in parallel with PTHrP. Interestingly, PTHrP was able to induce EBP50 expression. In the clonal rat aortic smooth muscle cell line A10, EBP50 increased the recruitment of PTH1R to the cell membrane and delayed its internalization in response to PTHrP(1-36). This effect required an intact C-terminal motif in the PTH1R. In naïve A10 cells, PTHrP(1-36) stimulated cAMP production but not intracellular calcium release. In contrast, PTHrP(1-36) induced both cAMP and calcium signaling in A10 cells over-expressing EBP50. Finally, EBP50 attenuated the induction of p27(kip1) and the anti-proliferative effect of PTHrP(1-36). In summary, this study demonstrates the dynamic expression of EBP50 in vessels following injury and the effects of EBP50 on PTH1R function in VSMC. These findings highlight one of the mechanisms leading to increased VSMC proliferation and have important implication in the understanding of the molecular events leading to restenosis.

Endogenous parathyroid hormone-related protein regulates the expression of PTH type 1 receptor and proliferation of vascular smooth muscle cells

The PTH type 1 receptor (PTH1R) and PTHrP are expressed in vessels, where they contribute to regulating vascular smooth muscle cell (VSMC) function. Elevated PTHrP levels in VSMC are often associated with hyperplasia. In contrast, exogenous PTHrP, acting through the PTH1R, inhibits VSMC proliferation. In this study, we investigated the regulation of PTH1R expression by endogenous PTHrP and the associated effects on VSMC proliferation. Blocking binding of secreted PTHrP fragments to the PTH1R by treatment with either an antagonist or an antibody against PTHrP, and inhibition of PTHrP expression by small interfering RNA significantly increased PTH1R expression. Interestingly, treatment of the cells with a PTHrP analog (Bpa(1)-PTHrP) that activates the PTH1R without inducing its internalization had the same effect on receptor expression. To examine the association between receptor expression and the antiproliferative effect of N-terminal fragments of PTHrP, VSMC were treated with exogenous PTHrP (1-36) acutely and chronically to induce receptor down-regulation. Stimulation of VSMC with exogenous PTHrP (1-36) significantly reduced cell proliferation during the first 18 h of treatment but was no longer effective after 3 d, a time when PTH1R was down-regulated. In contrast, treatment with the noninternalizing agonist Bpa(1)-PTHrP strongly inhibited cell proliferation at all time points. In conclusion, our study show that PTHrP, after its intracellular processing and secretion, promotes down-regulation of the PTH1R in VSMC, thereby regulating cell proliferation in an auto/paracrine fashion. This regulatory mechanism may have important implication during vascular remodeling, in particular in the development of neointima after arterial injury, where PTHrP overexpression occurs.

Mutant parathyroid hormone-related protein, devoid of the nuclear localization signal, markedly inhibits arterial smooth muscle cell cycle and neointima formation by coordinate up-regulation of p15Ink4b and p27kip1

Arterial expression of PTH-related protein is markedly induced by angioplasty. PTH-related protein contains a nuclear localization signal (NLS). PTH-related protein mutants lacking the NLS (DeltaNLS-PTH-related protein) are potent inhibitors of arterial vascular smooth muscle cell (VSMC) proliferation in vitro. This is of clinical relevance because adenoviral delivery of DeltaNLS-PTH-related protein at angioplasty completely inhibits arterial restenosis in rats. In this study we explored the cellular mechanisms through which DeltaNLS-PTH-related protein arrests the cell cycle. In vivo, adenoviral delivery of DeltaNLS-PTH-related protein at angioplasty markedly inhibited VSMC proliferation as compared with angioplastied carotids infected with control adenovirus (Ad.LacZ). In vitro, DeltaNLS-PTH-related protein overexpression was associated with a decrease in phospho-pRb, and a G(0)/G(1) arrest. This pRb underphosphorylation was associated with stable levels of cdks 2, 4, and 6, the D and E cyclins, p16, p18, p19, and p21, but was associated with a dramatic decrease in cdk-2 and cdk4 kinase activities. Cyclin A was reduced, but restoring cyclin A adenovirally to normal did not promote cell cycle progression in DeltaNLS-PTH-related protein VSMC. More importantly, p15(INK4) and p27(kip1), two critical inhibitors of the G(1/S) progression, were markedly increased. Normalization of both p15(INK4b) and p27(kip1) by small interfering RNA knockdown normalized cell cycle progression. These data indicate that the changes in p15(INK4b) and p27(kip1) fully account for the marked cell cycle slowing induced by DeltaNLS-PTH-related protein in VSMCs. Finally, DeltaNLS-PTH-related protein is able to induce p15(INK4) and p27(kip1) expression when delivered adenovirally to primary murine VSMCs. These studies provide a mechanistic understanding of DeltaNLS-PTH-related protein actions, and suggest that DeltaNLS-PTH-related protein may have particular efficacy for the prevention of arterial restenosis.

Severe growth retardation and early lethality in mice lacking the nuclear localization sequence and C-terminus of PTH-related protein

Parathyroid hormone (PTH) plays a central role in the regulation of serum calcium and phosphorus homeostasis, while parathyroid hormone-related protein (PTHrP) has important developmental roles. Both peptides signal through the same G protein-coupled receptor, the PTH/PTHrP or PTH type 1 receptor (PTH1R). PTHrP, normally a secreted protein, also contains a nuclear localization signal (NLS) that in vitro imparts functionality to the protein at the level of the nucleus. We investigated this functionality in vivo by introducing a premature termination codon in Pthrp in ES cells and generating mice that express PTHrP (1-84), a truncated form of the protein that is missing the NLS and the C-terminal region of the protein but can still signal through its cell surface receptor. Mice homozygous for the knock-in mutation (Pthrp KI) displayed retarded growth, early senescence, and malnutrition leading postnatally to their rapid demise. Decreased cellular proliferative capacity and increased apoptosis in multiple tissues including bone and bone marrow cells were associated with altered expression and subcellular distribution of the senescence-associated tumor suppressor proteins p16(INK4a) and p21 and the oncogenes Cyclin D, pRb, and Bmi-1. These findings provide in vivo experimental proof that substantiates the biologic relevance of the NLS and C-terminal portion of PTHrP, a polypeptide ligand that signals mainly via a cell surface G protein-coupled receptor.

Hepatocyte growth factor enhances engraftment and function of nonhuman primate islets

OBJECTIVE

Adenoviral delivery of hepatocyte growth factor (HGF) to rodent islets improves islet graft survival and function, markedly reducing the number of islets required to achieve glucose control. Here, we asked whether these prior observations in rodent models extend to nonhuman primate (NHP) islets.

RESEARCH DESIGN AND METHODS

NHP islets were transduced with murine (Ad.mHGF) or human (Ad.hHGF) adenoviral HGF (Ad.HGF) at low multiplicity of infection and studied in vitro. To study the function of Ad.HGF-transduced NHP islets in vivo, a renal subcapsular marginal mass islet transplant model was developed in streptozotocin-induced diabetic NOD-SCID mice.

RESULTS

Baseline glucose values were 454.7 +/- 11.3 mg/dl (n = 7). Transplant of 500 NHP islet equivalents (IE) had only a marginal effect on blood glucose (369.1 +/- 9.7 mg/dl, n = 5). In striking contrast, 500 NHP IE transduced with Ad.mHGF promptly and continuously corrected blood glucose (142.0 +/- 6.2 mg/dl, n = 7) for the 6-week duration of the experiment. Unilateral nephrectomy resulted in an immediate return of glucose to baseline diabetic levels. Interestingly, adenoviral DNA, as well as mouse HGF (mHGF) mRNA derived from the adenovirus, were present for 42 days posttransplantation. Surprisingly, transplant of 500 IE with Ad.hHGF, as compared with Ad.mHGF, resulted in only marginal correction of blood glucose, suggesting that human HGF is less efficient than mHGF in this system.

CONCLUSIONS

These studies demonstrate that mHGF markedly improves islet transplant outcomes in the highest preclinical species examined to date. HGF has promise as an agent that can improve islet mass and function in transplant models and likely in other models of types 1 and 2 diabetes.

PTHrP promotes malignancy of human oral cancer cell downstream of the EGFR signaling

Parathyroid hormone-related protein (PTHrP) is detected in many aggressive tumors and involved in malignant conversion; however, the underlying mechanism remains obscure. Here, we identified PTHrP as a mediator of epidermal growth factor receptor (EGFR) signaling to promote the malignancies of oral cancers. PTHrP mRNA was abundantly expressed in most of the quiescent oral cancer cells, and was significantly upregulated by EGF stimulation via ERK and p38 MAPK. PTHrP silencing by RNA interference, as well as EGFR inhibitor AG1478 treatment, significantly suppressed cell proliferation, migration, and invasiveness. Furthermore, combined treatment of AG1478 and PTHrP knockdown achieved synergistic inhibition of malignant phenotypes. Recombinant PTHrP substantially promoted cell motility, and rescued the inhibition by PTHrP knockdown, suggesting the paracrine/autocrine function of PTHrP. These data indicate that PTHrP contributes to the malignancy of oral cancers downstream of EGFR signaling, and may thus provide a therapeutic target for oral cancer.