Rho and Rho kinase are involved in parathyroid hormone-stimulated protein kinase C alpha translocation and IL-6 promoter activity in osteoblastic cells

Advances in the molecular mechanisms of statins in regulating endothelial nitric oxide bioavailability: Interlocking biology between eNOS activity and L-arginine metabolism

Statins, inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A, are widely used to treat hypercholesterolemia. In addition, statins have been suggested to reduce the risk of cardiovascular events owing to their pleiotropic effects on the vascular system, including vasodilation, anti-inflammation, anti-coagulation, anti-oxidation, and inhibition of vascular smooth muscle cell proliferation. The major beneficial effect of statins in maintaining vascular homeostasis is the induction of nitric oxide (NO) bioavailability by activating endothelial NO synthase (eNOS) in endothelial cells. The mechanisms underlying the increased NO bioavailability and eNOS activation by statins have been well-established in various fields, including transcriptional and post-transcriptional regulation, kinase-dependent phosphorylation and protein-protein interactions. However, the mechanism by which statins affect the metabolism of L-arginine, a precursor of NO biosynthesis, has rarely been discussed. Autophagy, which is crucial for energy homeostasis, regulates endothelial functions, including NO production and angiogenesis, and is a potential therapeutic target for cardiovascular diseases. In this review, in addition to summarizing the molecular mechanisms underlying increased NO bioavailability and eNOS activation by statins, we also discuss the effects of statins on the metabolism of L-arginine.

ROCK (RhoA/Rho Kinase) Activation in Atrial Fibrillation: Molecular Pathways and Clinical Implications

Among the complex mechanisms of AF pathogenesis, intracellular calcium overload and oxidative stress play a major role, both triggered by inflammatory processes. The additional basic event taking place in AF is atrial fibrotic remodeling, again triggered by oxidative stress, which is determined by connexins rearrangement and differentiation of fibroblasts into active collagensecreting myofibroblasts. RhoA/ROCK system is the final pathway of a wide spectrum of molecular effectors such as Angiotensin II, platelet-derived growth factor, connective tissue growth factor and transforming growth factor β, that overall determine calcium dysregulation and pro-fibrotic remodeling. Both in experimental and clinical studies, RhoA/ROCK activation has been linked to superoxide ion production, fibrotic remodeling and connexins rearrangement, with important consequences for AF pathogenesis. ROCK pathway inhibition may therefore be a therapeutic or preventive target for special AF subgroups of patients.

Hypoxia-inducible factor signaling in vascular calcification in chronic kidney disease patients

Chronic kidney disease (CKD) affects approximately 15% of the adult population in high-income countries and is associated with significant comorbidities, including increased vascular calcifications which is associated with a higher risk for cardiovascular events. Even though the underlying pathophysiology is unclear, hypoxia-inducible factor (HIF) signaling appears to play a central role in inflammation, angiogenesis, fibrosis, cellular proliferation, apoptosis and vascular calcifications which is influenced by multiple variables such as iron deficiency anemia, serum phosphorus and calcium levels, fibroblast growth factor-23 (FGF-23) and Klotho. Along with the growing understanding of the pathology, potential therapeutic alternatives have emerged including HIF stabilizers and SGLT-2 inhibitors. The aim of this review is to discuss the role of HIF signaling in the pathophysiology of vascular calcification in CKD patients and to identify potential therapeutic approaches.

Parathyroid hormone

Parathyroid hormone is an essential regulator of extracellular calcium and phosphate. PTH enhances calcium reabsorption while inhibiting phosphate reabsorption in the kidneys, increases the synthesis of 1,25-dihydroxyvitamin D, which then increases gastrointestinal absorption of calcium, and increases bone resorption to increase calcium and phosphate. Parathyroid disease can be an isolated endocrine disorder or part of a complex syndrome. Genetic mutations can account for diseases of parathyroid gland formulation, dysregulation of parathyroid hormone synthesis or secretion, and destruction of the parathyroid glands. Over the years, a number of different options are available for the treatment of different types of parathyroid disease. Therapeutic options include surgical removal of hypersecreting parathyroid tissue, administration of parathyroid hormone, vitamin D, activated vitamin D, calcium, phosphate binders, calcium-sensing receptor, and vitamin D receptor activators to name a few. The accurate assessment of parathyroid hormone also provides essential biochemical information to properly diagnose parathyroid disease. Currently available immunoassays may overestimate or underestimate bioactive parathyroid hormone because of interferences from truncated parathyroid hormone fragments, phosphorylation of parathyroid hormone, and oxidation of amino acids of parathyroid hormone.

Different duration of parathyroid hormone exposure distinctively regulates primary response genes Nurr1 and RANKL in osteoblasts

Parathyroid hormone (PTH) exerts dual effects, anabolic or catabolic, on bone when administrated intermittently or continuously, via mechanisms that remain largely unknown. PTH binding to cells induces PTH-responsive genes including primary response genes (PRGs). PRGs are rapidly induced without the need for de novo protein synthesis, thereby playing pivotal roles in directing subsequent molecular responses. In this study, to understand the role of PRGs in mediating osteoblastic cellular responses to PTH, we investigated whether various durations of PTH differentially induce PRGs in primary osteoblasts and MC3T3-E1. Nurr1 and RANKL, PRGs known for their anabolic and catabolic roles in bone metabolism respectively, presented distinctive transient vs. sustained induction kinetics. Corroborating their roles, maximum induction of Nurr1 was sufficiently achieved by brief PTH in as little as 30 minutes and continued beyond that, while maximum induction of RANKL was achieved only by prolonged PTH over 4 hours. Our data suggested distinctive regulatory mechanisms for Nurr1 and RANKL: PKA-mediated chromatin rearrangement for transcriptional regulation of both PRGs and ERK-mediated transcriptional regulation for RANKL but not Nurr1. Lastly, we classified PRGs into two groups based on the induction kinetics: The group that required brief PTH for maximum induction included Nur77, cox-2, and Nurr1, all of which are reported to play roles in bone formation. The other group that required prolonged PTH for maximum induction included IL-6 and RANKL, which play roles in bone resorption. Together, our data suggested the crucial role of PRG groups in mediating differential osteoblastic cellular responses to intermittent vs. continuous PTH. Continued research into the regulatory mechanisms of PKA and ERK for PRGs will help us better understand the molecular mechanisms underlying the dual effects of PTH, thereby optimizing the current therapeutic use of PTH for osteoporosis.

Physiology of Parathyroid Hormone

Parathyroid hormone (PTH) is the major secretory product of the parathyroid glands, and in hypocalcemic conditions, can enhance renal calcium reabsorption, increase active vitamin D production to increase intestinal calcium absorption, and mobilize calcium from bone by increasing turnover, mainly but not exclusively in cortical bone. PTH has therefore found clinical use as replacement therapy in hypoparathyroidism. PTH also may have a physiologic role in augmenting bone formation, particularly in trabecular and to some extent in cortical bone. This action has been applied to the clinic to provide anabolic therapy for osteoporosis.

Elevated plasma interleukin-37 playing an important role in acute coronary syndrome through suppression of ROCK activation

OBJECTIVE

The plasma level of interleukin-37 is elevated in patients with acute coronary syndrome, however, its function during the onset and progress of the disease remains unclear. This study aimed to investigate the clinical significance of IL-37 in acute coronary syndrome and its underlying mechanism.

METHODS

124 patients with acute coronary syndrome and 40 healthy controls were recruited in this study. Plasma interleukin-37 levels were measured in 41 patients with ST elevation myocardial infarction (STEMI), 41 patients with non-STEMI, 42 patients with unstable angina, and 40 controls. Mortality was defined as an event.

RESULTS

In this study, the mean follow-up period was 824±306 days (2-1077 days). 22% (n=27) of patients died. The mortality rate was significantly lower in patients with interleukin-37 serum levels below the median (6.4 pg/mL) than those with interleukin-37 serum levels above 6.4 pg/mL at 36-month follow-up (16% vs. 24%, p=0.02, log rank X2=5.39). Highly concentration of the anti-inflammatory interleukin-37 exerted a protective effect by suppressing the activated Rho Kinase (ROCK) activity in the peripheral blood mononuclear cells in vivo and in vitro after ischemia/reperfusion injury and stimulation of the Rho activator, calpeptin.

CONCLUSIONS

The interleukin-37 level is significantly increased in acute coronary syndrome. Elevated baseline interleukin-37 levels in patients on admission are associated with poor outcomes. Thus, we propose that interleukin-37 could be a biomarker predictive of mortality in acute coronary syndrome. Moreover, this study reveals that the protective effect of interleukin-37 against atherosclerosis may involve the inhibition of ROCK activity.

RhoA/Rho-kinase activation promotes lung fibrosis in an animal model of systemic sclerosis

BACKGROUND

Systemic sclerosis (SSc) is a connective-tissue disease characterized by vascular injury, immune-system disorders, and excessive fibrosis of the skin and multiple internal organs. Recent reports found that RhoA/Rho-kinase (ROCK) pathway is implicated in various fibrogenic diseases. Intradermal injection of hypochlorous acid (HOCl)-generating solution induced inflammation, autoimmune activation, and fibrosis, mimicking the cutaneous diffuse form of SSc in humans. Our study aimed firstly to describe pulmonary inflammation and fibrosis induced by HOCl in mice, and secondly to determine whether fasudil, a selective inhibitor of ROCK, could prevent lung and skin fibroses in HOCl-injected mice.

METHODS

Female C57BL/6 mice received daily intradermal injection of hypochlorous acid (HOCl) for 6 weeks to induce SSc, with and without daily treatment with fasudil (30 mg·kg(-1)·day(-1)) by oral gavage.

RESULTS

HOCl intoxication induced significant lung inflammation (macrophages and neutrophils infiltration), and fibrosis. These modifications were prevented by fasudil treatment. Simultaneously, HOCl enhanced ROCK activity in lung and skin tissues. Inhibition of ROCK reduced skin fibrosis, expression of α-smooth-muscle actin and 3-nitrotyrosine, as well as the activity of ROCK in the fibrotic skin of HOCl-treated mice, through inhibition of phosphorylation of Smad2/3 and ERK1/2. Fasudil significantly decreased the serum levels of anti-DNA-topoisomerase-1 antibodies in mice with HOCl-induced SSc.

CONCLUSIONS

Our findings confirm HOCl-induced pulmonary inflammation and fibrosis in mice, and provide further evidence for a key role of RhoA/ROCK pathway in several pathological processes of experimental SSc. Fasudil could be a promising therapeutic approach for the treatment of SSc.

RhoA/Rho-Kinase in the Cardiovascular System

Twenty years ago, Rho-kinase was identified as an important downstream effector of the small GTP-binding protein, RhoA. Thereafter, a series of studies demonstrated the important roles of Rho-kinase in the cardiovascular system. The RhoA/Rho-kinase pathway is now widely known to play important roles in many cellular functions, including contraction, motility, proliferation, and apoptosis, and its excessive activity induces oxidative stress and promotes the development of cardiovascular diseases. Furthermore, the important role of Rho-kinase has been demonstrated in the pathogenesis of vasospasm, arteriosclerosis, ischemia/reperfusion injury, hypertension, pulmonary hypertension, and heart failure. Cyclophilin A is secreted by vascular smooth muscle cells and inflammatory cells and activated platelets in a Rho-kinase-dependent manner, playing important roles in a wide range of cardiovascular diseases. Thus, the RhoA/Rho-kinase pathway plays crucial roles under both physiological and pathological conditions and is an important therapeutic target in cardiovascular medicine. Recently, functional differences between ROCK1 and ROCK2 have been reported in vitro. ROCK1 is specifically cleaved by caspase-3, whereas granzyme B cleaves ROCK2. However, limited information is available on the functional differences and interactions between ROCK1 and ROCK2 in the cardiovascular system in vivo. Herein, we will review the recent advances about the importance of RhoA/Rho-kinase in the cardiovascular system.

Raloxifene Covalently Bonded to Titanium Implants by Interfacing with (3-Aminopropyl)-Triethoxysilane Affects Osteoblast-like Cell Gene Expression

Since Raloxifene, a drug used in osteoporosis therapy, inhibits the osteoclast functions but not osteoblast functions, it could improve the recovery during implant surgery. This preliminary report describes a simple method to link, through a covalent bond, Raloxifene to titanium by interfacing with (3-aminopropyl)-Triethoxysilane as assessed by the IR-FT and SEM. To evaluate the biological response of osteoblast-like cells to this implant, we compared expression gene profiling of cell cultures on Raloxifene conjugated implant and normal implant by DNA microarray. By using DNA microarrays containing 19,200 genes, we identified differently expressed genes in osteoblast-like cell line (MG-63). Surface Raloxifene conjugated implants have been shown to have a relevant importance in modifying cell response. This result could be an interesting starting point for the use of an immediate functional loading of implants.

Parathyroid hormone regulation of hypoxia-inducible factor signaling in osteoblastic cells

Osteoblasts perceive and respond to changes in their pericellular environment, including biophysical signals and oxygen availability, to elicit an anabolic or catabolic response. Parathyroid hormone (PTH) affects each arm of skeletal remodeling, with net anabolic or catabolic effects dependent upon duration of exposure. Similarly, the capacity of osteoblastic cells to perceive pericellular oxygen has a profound effect on skeletal mass and architecture, as mice expressing stable hypoxia-inducible factor (HIF)-1α and -2α demonstrate age-dependent increases in bone volume per tissue volume and osteoblast number. Further, HIF levels and signaling can be influenced in an oxygen-independent manner. Because the cellular mechanisms involved in PTH regulation of the skeleton remain vague, we sought whether PTH could influence HIF-1α expression and HIF-α-driven luciferase activity independently of altered oxygen availability. Using UMR106.01 mature osteoblasts, we observed that 100nM hPTH(1-34) decreased HIF-1α and HIF-responsive luciferase activity in a process involving heat shock protein 90 (Hsp90) and cyclic AMP but not intracellular calcium. Altering activity of the small GTPase RhoA and its effector kinase ROCK altered HIF-α-driven luciferase activity in the absence and presence of PTH. Taken together, these data introduce PTH as a regulator of oxygen-independent HIF-1α levels through a mechanism involving cyclic AMP, Hsp90, and the cytoskeleton.

2015 ATVB Plenary Lecture: translational research on rho-kinase in cardiovascular medicine

Rho-kinase (ROCKs) is an important downstream effector of the small GTP-binding protein Ras homolog gene family member A. There are 2 isoforms of ROCK, ROCK1 and ROCK2, and they have different functions in several vascular components. The Ras homolog gene family member A/ROCK pathway plays an important role in various fundamental cellular functions, including contraction, motility, proliferation, and apoptosis, whereas its excessive activity is involved in the pathogenesis of cardiovascular diseases. For the past 20 years, a series of translational research studies have demonstrated the important roles of ROCK in the pathogenesis of cardiovascular diseases. At the molecular and cellular levels, ROCK upregulates several molecules related to inflammation, thrombosis, and fibrosis. In animal experiments, ROCK plays an important role in the pathogenesis of vasospasm, arteriosclerosis, hypertension, pulmonary hypertension, and heart failure. Finally, at the human level, ROCK is substantially involved in the pathogenesis of coronary vasospasm, angina pectoris, hypertension, pulmonary hypertension, and heart failure. Furthermore, ROCK activity in circulating leukocytes is a useful biomarker for the assessment of disease severity and therapeutic responses in vasospastic angina, heart failure, and pulmonary hypertension. In addition to fasudil, many other ROCK inhibitors are currently under development for various indications. Thus, the ROCK pathway is an important novel therapeutic target in cardiovascular medicine.

P2X7-induced zeiosis promotes osteogenic differentiation and mineralization of postmenopausal bone marrow-derived mesenchymal stem cells

Polymorphisms of the P2X7 receptor have been associated with increased risk of fractures in postmenopausal women. Although both osteoblasts and osteoclasts express P2X7 receptors, their function in osteogenesis remains controversial. Here, we investigated the role of the P2X7 receptor on osteogenic differentiation and mineralization of bone marrow mesenchymal stem cell (BMSC) cultures from postmenopausal women (age 71±3 yr, n=18). We focused on the mechanisms related to intracellular [Ca(2+)]i oscillations and plasma membrane-dynamics. ATP, and the P2X7 agonist BzATP (100 μM), increased [Ca(2+)]i in parallel to the formation of membrane pores permeable to TO-PRO-3 dye uptake. ATP and BzATP elicited reversible membrane blebs (zeiosis) in 38 ± 1 and 70 ± 1% of the cells, respectively. P2X7-induced zeiosis was Ca(2+) independent, but involved phospholipase C, protein kinase C, and Rho-kinase activation. BzATP (100 μM) progressively increased the expression of Runx-2 and Osterix transcription factors by 452 and 226% (at d 21), respectively, alkaline phosphatase activity by 88% (at d 28), and mineralization by 329% (at d 43) of BMSC cultures in a Rho-kinase-dependent manner. In summary, reversible plasma membrane zeiosis involving cytoskeleton rearrangements due to activation of the P2X7-Rho-kinase axis promotes osteogenic differentiation and mineralization of BMSCs, thus providing new therapeutic targets for postmenopausal bone loss.

Breast cancer cell invasion mediated by Gα12 signaling involves expression of interleukins-6 and -8, and matrix metalloproteinase-2

Background

Recent studies on the involvement of the G12 family of heterotrimeric G proteins (Gα12 and Gα13, the products of the GNA12 and GNA13 genes, respectively) in oncogenic pathways have uncovered a link between G12 signaling and cancer progression. However, despite a well characterized role of Rho GTPases, the potential role of secreted factors in the capacity of G12 signaling to promote invasion of cancer cells is just beginning to be addressed.

Methods

MDA-MB-231 and MCF10A breast cancer cell lines were employed as a model system to explore the involvement of secreted factors in G12-stimulated cell invasion. Factors secreted by cells expressing dominant-active Gα12 were identified by protein array, and their involvement in breast cancer cell invasion was assessed through both RNAi-mediated knockdown and antibody neutralization approaches. Bioinformatics analysis of the promoter elements of the identified factors suggested NF-κB elements played a role in their enhanced expression, which was tested by chromatin immunoprecipitation.

Results

We found that signaling through the Gα12 in MDA-MB-231 and MCF10A breast cancer cell lines enhances expression of interleukins (IL)-6 and −8, and matrix metalloproteinase (MMP)-2, and that these secreted factors play a role in G12-stimulated cell invasion. Furthermore, the enhanced expression of these secreted factors was found to be facilitated by the activation of their corresponding promoters, where NF-κB seems to be one of the major regulators. Inhibition of IL-6 and IL-8, or MMP-2 activity significantly decreased Gα12-mediated cell invasion.

Conclusions

These studies confirm and extend findings that secreted factors contribute to the oncogenic potential of G12 signaling, and suggest potential therapeutic targets to control this process.

Small GTPase and regulation of inflammation response in atherogenesis

Small GTPases are key signal transducers from extracellular stimuli to the nucleus that regulate a variety of cellular responses, including changes in gene expression and cell adhesion and migration. Accumulating data have demonstrated that abnormal activation of these small GTPases plays a critical role in the atherosclerosis characterized by vascular abnormalities, especially endothelial dysfunction and inflammation. Here, we discuss the linkage between small GTPases, inflammation, and atherogenesis. First, small GTPases affect gene expression of inflammatory cytokines through proinflammatory signaling pathways, such as nuclear factor-κB, vascular cell adhesion molecule-1, intercellular adhesion molecule-1, interlukin-8, and monocyte chemoattractant protein-1. Then, these molecules regulate the vascular inflammation through cell adhesion and migration. In turn, small GTPases are also regulated by extracellular stimuli, such as L-selectin, thrombin, oxidized phospholipids, and interleukins. Thus, these inflammatory cytokines generate a vicious cycle for small GTPases and inflammatory responses in the atherogenesis.

Influence of ARHGEF3 and RHOA knockdown on ACTA2 and other genes in osteoblasts and osteoclasts

Osteoporosis is a common bone disease that has a strong genetic component. Genome-wide linkage studies have identified the chromosomal region 3p14-p22 as a quantitative trait locus for bone mineral density (BMD). We have previously identified associations between variation in two related genes located in 3p14-p22, ARHGEF3 and RHOA, and BMD in women. In this study we performed knockdown of these genes using small interfering RNA (siRNA) in human osteoblast-like and osteoclast-like cells in culture, with subsequent microarray analysis to identify genes differentially regulated from a list of 264 candidate genes. Validation of selected findings was then carried out in additional human cell lines/cultures using quantitative real-time PCR (qRT-PCR). The qRT-PCR results showed significant down-regulation of the ACTA2 gene, encoding the cytoskeletal protein alpha 2 actin, in response to RHOA knockdown in both osteoblast-like (P<0.001) and osteoclast-like cells (P = 0.002). RHOA knockdown also caused up-regulation of the PTH1R gene, encoding the parathyroid hormone 1 receptor, in Saos-2 osteoblast-like cells (P<0.001). Other findings included down-regulation of the TNFRSF11B gene, encoding osteoprotegerin, in response to ARHGEF3 knockdown in the Saos-2 and hFOB 1.19 osteoblast-like cells (P = 0.003–0.02), and down-regulation of ARHGDIA, encoding the Rho GDP dissociation inhibitor alpha, in response to RHOA knockdown in osteoclast-like cells (P<0.001). These studies identify ARHGEF3 and RHOA as potential regulators of a number of genes in bone cells, including TNFRSF11B, ARHGDIA, PTH1R and ACTA2, with influences on the latter evident in both osteoblast-like and osteoclast-like cells. This adds further evidence to previous studies suggesting a role for the ARHGEF3 and RHOA genes in bone metabolism.

Elevated rho-kinase activity as a marker indicating atherosclerosis and inflammation burden in polyvascular disease patients with concomitant coronary and peripheral arterial disease

BACKGROUND

Recent evidence suggests that Rho-kinase (ROCK) plays an important role in the pathogenesis of atherosclerosis and a marker of atherosclerotic burden. Polyvascular disease with concomitant peripheral arterial disease (PAD) and coronary artery disease (CAD) is common and associated with a worse prognosis. The aim of this study was to evaluate ROCK activity as a marker of polyvascular disease.

HYPOTHESIS

METHODS

We retrospectively analyzed patients undergoing coronary angiography at our institution between February 2009 and May 2009. Patients with only CAD (n = 40) defined by coronary artery stenosis of ≥50% by angiography, only PAD (n = 40) defined by an ankle brachial index (ABI) <0.9, and combined CAD/PAD (n = 40) were matched by age and sex to control patients (n = 40) without CAD or PAD. ROCK activity was determined by phosphorylation of the myosin binding subunit in leukocytes and then compared between each group. Multivariate analysis was used to determine independent predictors of polyvascular disease. Discriminative ability of elevated ROCK activity was assessed using receiver operator characteristics (ROC) curves.

RESULTS

Patients (age 68 ± 12 years, 79% male) with CAD, PAD, and CAD/PAD had a mean ABI of 1.08, 0.62, and 0.65, respectively, compared to 1.08 in the control group. There was an incremental increase in ROCK activity in patients with CAD (4.61 ± 2.11), PAD (4.27 ± 1.39), and CAD/PAD (5.96 ± 1.94) compared to control (2.40 ± 0.43) (all P < 0.05). ROCK activity (odds ratio: 4.53, 95% confidence interval: 1.26-6.30) was an independent predictor of polyvascular disease. The ROCK cutoff value of 4.85 had a sensitivity of 72.7% and a specificity of 65.7%, with an area under ROC curve of 0.71 for polyvascular disease.

CONCLUSIONS

Patients with concomitant peripheral and coronary arterial disease are associated with increased Rho-kinase activity. Rho-kinase activity may be a potential marker of atherosclerotic burden for patients with polyvascular disease.

Simvastatin prevents the induction of interleukin-6 gene expression by titanium particles in human osteoblastic cells

One of the most important complications of total joint arthroplasty is failure associated with periprosthetic osteolysis, a process mainly initiated by the biological response to wear-derived products from the biomaterials in service. The inflammatory mediator interleukin-6 (IL-6) plays a key role in the establishment and progression of aseptic loosening. Metal particles specifically up-regulate IL-6 production in bone-forming cells and implant-bone interfacial tissues. The use of statins has been recently associated with a significantly reduced risk of revision in patients that undergo total hip arthroplasty. We hypothesized that simvastatin (Simv) could modulate the osteoblastic response to titanium particles (Ti) by attenuating the production of IL-6. Pre-treatment of human osteoblastic cells with Simv down-regulated Ti particle-induced IL-6 gene expression at mRNA and protein levels. The effect of Simv on Ti-induced IL-6 production in osteoblastic cells could not be explained by inhibition of the internalization of metal particles. The mechanism involved in this down-regulation is based in the inhibition of the HMG-CoA/GGPP/RhoA/ROCK pathway, independently of Simv effects in the cholesterol synthesis. The cytokine-lowering property of Simv has been observed in Saos-2 cells and human primary osteoblasts (hOBs) exposed to Ti particles, and was further enhanced when hOBs were co-cultured with macrophages.

The guanine nucleotide exchange factor Vav2 is a negative regulator of parathyroid hormone receptor/Gq signaling

The parathyroid hormone receptor (PTHR) is a class B G protein-coupled receptor (GPCR) that mediates the endocrine and paracrine effects of parathyroid hormone and related peptides through the activation of phospholipase Cβ-, adenylyl cyclase-, mitogen-activated protein kinase-, and β-arrestin-initiated signaling pathways. It is currently not clear how specificity among these downstream signaling pathways is achieved. A possible mechanism involves adaptor proteins that affect receptor/effector coupling. In a proteomic screen with the PTHR C terminus, we identified vav2, a guanine nucleotide exchange factor (GEF) for Rho GTPases, as a PTHR-interacting protein. The core domains of vav2 bound to the intracellular domains of the PTHR independent of receptor activation. In addition, vav2 specifically interacted with activated Gα(q) but not with Gα(s) subunits, and it competed with PTHR for coupling to Gα(q). Consistent with its specific interaction with Gα(q), vav2 impaired G(q)-mediated inositol phosphate generation but not G(s)-mediated cAMP generation. This inhibition of G(q) signaling was specific for PTHR signaling, compared with other G(q)-coupled GPCRs. Moreover, the benefit for PTHR-mediated inositol phosphate generation in the absence of vav2 required the ezrin binding domain of Na(+)/H(+)-exchanger regulatory factor 1. Our results show that a RhoA GEF can specifically interact with a GPCR and modulate its G protein signaling specificity.

Fasudil, a Rho-kinase inhibitor, attenuates bleomycin-induced pulmonary fibrosis in mice

The mechanisms underlying the pathogenesis of idiopathic pulmonary fibrosis (IPF) involve multiple pathways, such as inflammation, epithelial mesenchymal transition, coagulation, oxidative stress, and developmental processes. The small GTPase, RhoA, and its target protein, Rho-kinase (ROCK), may interact with other signaling pathways known to contribute to pulmonary fibrosis. This study aimed to determine the beneficial effects and mechanisms of fasudil, a selective ROCK inhibitor, on bleomycin-induced pulmonary fibrosis in mice. Our results showed that the Aschcroft score and hydroxyproline content of the bleomycin-treated mouse lung decreased in response to fasudil treatment. The number of infiltrated inflammatory cells in the bronchoalveolar lavage fluid (BALF) was attenuated by fasudil. In addition, fasudil reduced the production of transforming growth factor-β1 (TGF-β1), connective tissue growth factor (CTGF), alpha-smooth muscle actin (α-SMA), and plasminogen activator inhibitor-1 (PAI-1) mRNA and protein expression in bleomycin-induced pulmonary fibrosis. These findings suggest that fasudil may be a potential therapeutic candidate for the treatment of pulmonary fibrosis.

Polymorphisms in the P2X7 receptor gene are associated with low lumbar spine bone mineral density and accelerated bone loss in post-menopausal women

The P2X7 receptor gene (P2RX7) is highly polymorphic with five previously described loss-of-function (LOF) single-nucleotide polymorphisms (SNP; c.151+1G>T, c.946G>A, c.1096C>G, c.1513A>C and c.1729T>A) and one gain-of-function SNP (c.489C>T). The purpose of this study was to determine whether the functional P2RX7 SNPs are associated with lumbar spine (LS) bone mineral density (BMD), a key determinant of vertebral fracture risk, in post-menopausal women. We genotyped 506 post-menopausal women from the Aberdeen Prospective Osteoporosis Screening Study (APOSS) for the above SNPs. Lumbar spine BMD was measured at baseline and at 6–7 year follow-up. P2RX7 genotyping was performed by homogeneous mass extension. We found association of c.946A (p.Arg307Gln) with lower LS-BMD at baseline (P=0.004, β=−0.12) and follow-up (P=0.002, β=−0.13). Further analysis showed that a combined group of subjects who had LOF SNPs (n=48) had nearly ninefold greater annualised percent change in LS-BMD than subjects who were wild type at the six SNP positions (n=84; rate of loss=−0.94%/year and −0.11%/year, respectively, P=0.0005, unpaired t-test). This is the first report that describes association of the c.946A (p.Arg307Gln) LOF SNP with low LS-BMD, and that other LOF SNPs, which result in reduced or no function of the P2X7 receptor, may contribute to accelerated bone loss. Certain polymorphic variants of P2RX7 may identify women at greater risk of developing osteoporosis.

Rho-kinase: important new therapeutic target in cardiovascular diseases

Rho-kinase (ROCKs) belongs to the family of serine/threonine kinases and is an important downstream effector of the small GTP-binding protein RhoA. There are two isoforms of Rho-kinase, ROCK1 and ROCK2, and they have different functions with ROCK1 for circulating inflammatory cells and ROCK2 for vascular smooth muscle cells. It has been demonstrated that the RhoA/Rho-kinase pathway plays an important role in various fundamental cellular functions, including contraction, motility, proliferation, and apoptosis, leading to the development of cardiovascular disease. The important role of Rho-kinase in vivo has been demonstrated in the pathogenesis of vasospasm, arteriosclerosis, ischemia-reperfusion injury, hypertension, pulmonary hypertension, stroke, and heart failure. Furthermore, the beneficial effects of fasudil, a selective Rho-kinase inhibitor, have been demonstrated for the treatment of several cardiovascular diseases in humans. Thus the Rho-kinase pathway is an important new therapeutic target in cardiovascular medicine.

Parathyroid hormone regulates osteoblast differentiation in a Wnt/β-catenin-dependent manner

Intermittent parathyroid hormone (PTH) administration shows an anabolic effect on bone. However, the mechanisms are not fully studied. Recent studies suggest that Wnt signaling is involved in PTH-induced bone formation. The current study was to examine if Wnt/β-catenin pathway is required during PTH-induced osteoblast differentiation. Osteoblastic MC3T3-E1 cells were treated with human PTH (1-34) (hPTH [1-34]) and expression levels of osteoblast differentiation markers were detected by real-time PCR. RNA levels of β-catenin, Runx2, Osteocalcin, Alkaline phosphatase, and Bone sialoprotein were significantly up-regulated after treatment with 10(-8) M of hPTH (1-34) for 6 h. Alkaline phosphatase activity and protein expression of β-catenin were also increased after 6 days of intermittent treatment with hPTH (1-34) in MC3T3-E1 cells. hPTH (1-34) significantly enhanced Topflash Luciferase activity after 6 h of treatment. More important, PTH-induced Alkaline phosphatase activity was significantly inhibited by knocking down β-catenin expression in cells using siRNA. Real-time RT-PCR results further showed down regulation of Runx2, Osteocalcin, Alkaline phosphatase, Bone sialoprotein gene expression in β-catenin siRNA transfected cells with/without PTH treatment. These results clearly indicate that PTH stimulates Wnt/β-catenin pathway in MC3T3-E1 cells and osteoblast differentiation markers expression was up-regulated by activation of Wnt/β-catenin signaling. Our study demonstrated that PTH-induced osteoblast differentiation mainly through activation of Wnt/β-catenin pathway in osteoblastic MC3T3-E1 cells.

Osteoclastogenic activity and RANKL expression are inhibited in osteoblastic cells expressing constitutively active Gα(12) or constitutively active RhoA

Gα(12)-RhoA signaling is a parathyroid hormone (PTH)-stimulated pathway that mediates effects in bone and may influence genetic susceptibility to osteoporosis. To further elucidate effects of the pathway in osteoblasts, UMR-106 osteoblastic cells were stably transfected with constitutively active (ca) Gα(12) or caRhoA or dominant negative (dn) RhoA and co-cultured with RAW 264.7 cells to determine effects on hormone-stimulated osteoclastogenesis. Whereas PTH and calcitriol-stimulated osteoclastogenesis in co-cultures with UMR-106 cells expressing pcDNA or dominant negative RhoA, the osteoclastogenic effects of PTH and calcitriol were significantly attenuated when the UMR-106 cells expressed either caRhoA or caGα(12). These inhibitory effects were partially reversed by the Rho kinase inhibitor Y27632. None of the constructs affected osteoclastogenesis in untreated co-cultures, and the constructs did not inhibit the osteoclastogenic responses to receptor activator of NFκB ligand (RANKL). To investigate the mechanism of the inhibitory effects of caGα(12) and caRhoA, expression of RANKL, osteoprotegerin (OPG), osteopontin (OPN), and intercellular adhesion molecule-1 (ICAM) in response to PTH or calcitriol was examined in the UMR-106 cells. In the cells expressing pcDNA or dnRhoA, PTH and calcitriol increased RANKL mRNA and decreased OPG mRNA, whereas these effects were absent in the cells expressing caGα(12) or caRhoA. Basal expression of RANKL and OPG was unaffected by the constructs. The results suggest that Gα(12)-RhoA signaling can inhibit hormone-stimulated osteoclastogenesis by effects on expression of RANKL and OPG. Since PTH can stimulate the Gα(12)-RhoA pathway, the current findings could represent a homeostatic mechanism for regulating osteoclastogenic action.

Antagonist minigenes identify genes regulated by parathyroid hormone through G protein-selective and G protein co-regulated mechanisms in osteoblastic cells

Parathyroid hormone (PTH) is the major hormone regulating bone remodeling. Binding of PTH to the PTH1 receptor (PTH1R), a heterotrimeric G protein coupled receptor (GPCR), can potentially trigger multiple signal transduction pathways mediated through several different G proteins. In this study, we employed G protein antagonist minigenes inhibiting Gα(s), Gα(q) or Gα₁₂ to selectively dissect out which of these G proteins were responsible for effects of PTH(1-34) in targeted signaling and osteogenesis arrays consisting of 159 genes. Among the 32 genes significantly regulated by 24h PTH treatment in UMR-106 osteoblastic cells, 9 genes were exclusively regulated through G(s), 6 genes were solely mediated through G(q), and 3 genes were only controlled through G₁₂. Such findings support the concept that there is some absolute specificity in downstream responses initiated at the G protein level following binding of PTH to the PTH1R. On the other hand, 6 PTH-regulated genes were regulated by both G(s) and G(q), 3 genes were regulated by both G(s) and G₁₂, and 3 genes were controlled by G(s), G(q) and G₁₂. These findings indicate potential overlapping or sequential interactions among different G protein-mediated pathways. In addition, two PTH-regulated genes were not regulated through any of the G proteins examined, suggesting that additional signaling mechanisms may be involved. Selectivity was largely maintained over a 2-48-hour time period. The minigene effects were mimicked by downstream inhibitors. The dissection of the differential effects of multiple G protein pathways on gene regulation provides a more complete understanding of PTH signaling in osteoblastic cells.

Rho-kinase inhibition: a novel therapeutic target for the treatment of cardiovascular diseases

The Rho/rho-kinase (ROCK) pathway has an important role in the pathogenesis of several cardiovascular diseases. The activation of ROCK is involved in the regulation of vascular tone, endothelial dysfunction, inflammation and remodeling. The inhibition of ROCK has a beneficial effect in a variety of cardiovascular disorders. Evidence from animal models and from clinical use of ROCK inhibitors, such as Y-27632, fasudil and statins (i.e. pleiotropic effects), supports the hypothesis that ROCK is a potential therapeutic target. This review provides a current understanding of the role of ROCK pathway in the regulation of vascular function and the use of ROCK inhibitors in the treatment of cardiovascular disorders.

Regulation of interleukin-6 expression in osteoblasts by oxidized phospholipids

Epidemiological evidence suggests that cardiovascular disease is associated with osteoporosis, independent of age. Bone resorptive surface is increased in mice on a high-fat diet, and osteoclastic differentiation of bone marrow preosteoclasts is promoted by oxidized phospholipids. Because osteoclastic differentiation requires cytokines produced by osteoblasts, we hypothesized that the stimulatory mechanism of oxidized phospholipids is via induction of osteoclast-regulating cytokines in osteoblasts. To investigate the effects of oxidized phospholipids on expression of such cytokines, murine calvarial preosteoblasts, MC3T3-E1, were treated with oxidized 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphocholine (ox-PAPC), an active component of oxidized lipoproteins. Results showed that ox-PAPC increased expression of interleukin-6 (IL-6) and tumor necrosis factor-alpha. IL-6 expression was also elevated in calvarial tissues from hyperlipidemic but not in wild-type mice. Ox-PAPC also induced IL-6 protein levels in both MC3T3-E1 and primary calvarial cells. Promoter-reporter assay analysis showed that ox-PAPC, but not PAPC, induced murine IL-6 promoter activity. Effects of ox-PAPC on IL-6 expression and the promoter activity were attenuated by H89, a PKA inhibitor. Analysis of deletion and mutant IL-6 promoter constructs suggested that CAAT/enhancer binding protein (C/EBP) partly mediates the ox-PAPC effects. Taken together, the data suggest that oxidized phospholipids induce IL-6 expression in osteoblasts in part via C/EBP.

Rho GTPase signaling and PTH 3-34, but not PTH 1-34, maintain the actin cytoskeleton and antagonize bisphosphonate effects in mouse osteoblastic MC3T3-E1 cells

Cytoskeletal elements are critical for cell morphology and signal transduction, and are involved in many cellular processes including motility, intracellular transport, and differentiation. Small GTP-binding proteins (G proteins) of the Ras family, such as RhoA, influence various elements of the cytoskeleton. RhoA stabilizes the actin cytoskeleton and promotes formation of focal adhesions. We found previously that RhoA is expressed in osteoblastic cells and is translocated to the plasma membrane and activated by PTH 1-34 as well as by Nleu(8,18) Tyr(34) PTH 3-34 amide, a PTH analog that does not increase cAMP. We therefore investigated effects of manipulating RhoA on the actin cytoskeleton of osteoblastic MC3T3-E1 cells. Three inhibitors were used: 1) GGTI-2166, a geranylgeranyl transferase I inhibitor that prevents the isoprenylation and membrane translocation of RhoA, 2) Y-27632, a Rho kinase inhibitor, and 3) alendronate, a nitrogen (N)-containing bisphosphonate that reduces intracellular geranylgeranylpyrophosphate through inhibiting farnesyl pyrophosphate synthase. To increase RhoA activity, we used the geranylgeranyl group donor geranylgeraniol (GGOH), and a constitutively active RhoA. The F-actin cytoskeleton and focal adhesions (FA) were visualized with rhodamine-phalloidin and fluorescent anti-vinculin antibodies, respectively. Cells were imaged with confocal microscopy. Actin stress fiber density, edge actin bundle density, focal adhesion density, cellular area and circularity (a morphological descriptor relating area and perimeter) were quantified by a program developed with Matlab software. GGTI-2166, Y-27632, and alendronate reduced actin stress fibers, FA density, and FA size, but had no effect on edge actin bundle density, cellular area, or circularity. GGOH completely antagonized the effects of alendronate, but did not significantly affect responses to GGTI-2166 or Y-27632. Constitutively active RhoA antagonized the effects of alendronate and GGTI-2166, but not those of Y-27632. The effects of alendronate were also antagonized by Nleu(8,18) Tyr(34) PTH 3-34 amide, but not by PTH 1-34. The results indicate that RhoA is involved in the maintenance of stress fibers and focal adhesions in osteoblastic cells, that PTH can affect this pathway independently of cAMP, and that a N-containing bisphosphonate can affect the actin cytoskeleton and focal adhesions through actions on geranylgeranyl groups and potentially through RhoA. In view of the importance of the actin cytoskeleton, the findings constitute evidence that N-containing bisphosphonates, when they attain certain concentrations, have effects on osteoblasts that could influence bone remodeling.

The small GTPase RhoA is crucial for MC3T3-E1 osteoblastic cell survival

Prolongation of cell survival through prevention of apoptosis is considered to be a significant factor leading to anabolic responses in bone. The current studies were carried out to determine the role of the small GTPase, RhoA, in osteoblast apoptosis, since RhoA has been found to be critical for cell survival in other tissues. We investigated the effects of inhibitors and activators of RhoA signaling on osteoblast apoptosis. In addition, we assessed the relationship of this pathway to parathyroid hormone (PTH) effects on apoptotic signaling and cell survival. RhoA is activated by geranylgeranylation, which promotes its membrane anchoring. In serum-starved MC3T3-E1 osteoblastic cells, inhibition of geranylgeranylation with geranylgeranyl transferase I inhibitors increased activity of caspase-3, a component step in the apoptosis cascade, and increased cell death. Dominant negative RhoA and Y27632, an inhibitor of the RhoA effector Rho kinase, also increased caspase-3 activity. A geranylgeranyl group donor, geranylgeraniol, antagonized the effect of the geranylgeranyl transferase I inhibitor GGTI-2166, but could not overcome the effect of the Rho kinase inhibitor. PTH 1-34, a potent anti-apoptotic agent, completely antagonized the stimulatory effects of GGTI-2166, dominant negative RhoA, and Y27632, on caspase-3 activity. The results suggest that RhoA signaling is essential for osteoblastic cell survival but that the survival effects of PTH 1-34 are independent of this pathway.

Rho kinase activation and gene expression related to vascular remodeling in normotensive rats with high angiotensin I converting enzyme levels

The RhoA/Rho kinase (ROCK) pathway is a new mechanism of remodeling and vasoconstriction. Few data are available regarding ROCK activation when angiotensin I-converting enzyme is high and blood pressure is normal. We hypothesized that ROCK is activated in the vascular wall in normotensive rats with genetically high angiotensin I-converting enzyme levels, and it causes increased vascular expression of genes promoting vascular remodeling and also oxidative stress. Aortic ROCK activation, mRNA and protein levels (of monocyte chemoattractant protein-1, transforming growth factor [TGF]-beta(1), and plasminogen activator inhibitor-1 [PAI-1]), NADPH oxidase activity, and O(2)(*-) production were measured in normotensive rats with genetically high (Brown Norway [BN]) and low (Lewis) angiotensin-I-converting enzyme levels and in BN rats treated with the ROCK antagonist fasudil (100 mg/kg per day) for 7 days. ROCK activation was 12-fold higher in BN versus Lewis rats (P<0.05) and was reduced with fasudil by 100% (P<0.05). Aortic TGF-beta1, PAI-1, and monocyte chemoattractant protein-1 mRNA levels were higher in BN versus Lewis rats by 300%, 180%, and 1000%, respectively (P<0.05). Aortic TGF-beta1, PAI-1, and monocyte chemoattractant protein-1 protein levels were higher in BN versus Lewis rats (P<0,05). Fasudil reduced TGF-beta1 and PAI-1 mRNA and TGF-beta1, PAI-1, and monocyte chemoattractant protein-1 protein aortic levels to those observed in Lewis rats. Aortic reduced nicotinamide-adenine dinucleotide phosphate oxidase activity and (*)O(2)(-) production were increased by 88% and 300%, respectively, in BN rats (P<0.05) and normalized by fasudil. In conclusion, ROCK is significantly activated in the aortic wall in normotensive rats with genetically high angiotensin-I-converting enzyme and angiotensin II, and it causes activation of genes that promote vascular remodeling and also increases vascular oxidative stress.

Small GTPase Ras and Rho expression in rat osteoblasts during spaceflight

Rat osteoblasts were cultured for 4 and 5 days aboard a space shuttle and solubilized after a 24-h treatment with 1alpha,25 dihydroxyvitamin D(3). The quantitative RT-PCR determined the mRNA levels of signaling molecules upstream and downstream Ras. The small GTPase is activated by guanine nucleotide exchange protein (GEF) and deactivated by GTPase-activating protein (GAP). When external stimuli are transduced into intracellular signals, various pathways are recruited: focal adhesion kinase (FAK) is associated with integrin-beta, and directs tyrosine phosphorylation of downstream substrates, including phospholipase C-gamma (PLC-gamma) and son of sevenless (SOS, a Ras GEF). The mRNA levels of FAK and PLC-gamma1 and -gamma2 in the flight cultures were increased 150% and 250% of the ground controls. The SOS mRNA levels in the flight cultures were increased 520% and 320% of the ground controls. Signals via G protein-coupled receptors are transmitted through PLC-beta and Ras GRF (another Ras GEF). Activated Ras then stimulates Raf, mitogen-activated protein kinase (MAPK) cascades. The mRNA levels of Raf, extracellular signal-regulated protein kinase of MAPK family (ERK-1 and -2), and PLC-beta were increased during spaceflight. Rho GAP expression in the flight cultures was increased twofold of the ground controls. Since Rho GAP deactivates Rho, microgravity may suppress Rho signals, regulating actin filament rearrangement. Microgravity signals may involve two pathways (G protein-coupled receptor-mediated pathway and tyrosine phosphorylation-mediated pathway) that activate Ras, Raf, and MAPK cascades in rat osteoblasts.

Progress of the Study of Rho-kinase and Future Perspective of the Inhibitor

Rho-kinase has been identified as one of the effectors of the small GTP-binding protein Rho. Accumulating evidence has demonstrated that the Rho/Rho-kinase pathway plays an important role in various cellular functions, not only in vascular smooth muscle cell (VSMC) contraction but also in VSMC proliferation, cell migration, and gene expression. Two isoforms of Rho-kinase encoded by two different genes have been identified: ROCK1 and ROCK2. These isoforms are ubiquitously expressed, but with preferential expression of ROCK2 in the brain and skeletal muscle. The expression of Rho-kinase itself is mediated by the protein kinase C/NF-kappaB pathway with an inhibitory and stimulatory modulation by estrogen and nicotine, respectively. At the cellular level, Rho-kinase mediates VSMC contraction, stimulates VSMC proliferation and migration, and enhances inflammatory cell motility. Rho-kinase also upregulates various molecules that accelerate inflammation/oxidative stress, thrombus formation, and fibrosis, while it downregulates endothelial nitric oxide synthase and inhibits insulin signaling. Rho-kinase activity regulates major morphogenetic events during embryonic development through cell migration, differentiation, and axis formation. In animal and clinical studies, Rho-kinase has been shown to be substantially involved in the pathogenesis of vasospasm, arteriosclerosis, hypertension, pulmonary hypertension, and ischemia/reperfusion injury. Fasudil, a selective Rho-kinase inhibitor developed in Japan, is effective for the treatment of a wide range of cardiovascular diseases, with reasonable safety. Thus Rho-kinase is an important therapeutic target in cardiovascular medicine. This review summarizes the recent progress in the study of Rho-kinase and addresses future perspectives of Rho-kinase inhibitors.

Parathyroid hormone stimulates expression of the Notch ligand Jagged1 in osteoblastic cells

We previously demonstrated that activation of the Parathyroid Hormone Receptor (PTH1R) in osteoblastic cells increases the Notch ligand Jagged1 and expands hematopoietic stem cells (HSC) through Notch signaling. However, regulation of Jagged1 by PTH in osteoblasts is poorly understood. The present study demonstrates that PTH treatment increases Jagged1 levels in a subpopulation of osteoblastic cells in vivo and in UMR106 osteoblastic cells in vitro. Since PTH(1-34) activates both Adenylate Cyclase/Protein Kinase A (AC/PKA) and Protein Kinase C (PKC) downstream of the PTH1R in osteoblastic cells, we independently determined the effect of either pathway on Jagged1. Activation of AC with Forskolin or PKA with PTH(1-31) or cell-permeable cAMP analogues increased osteoblastic Jagged1. This PTH-dependent Jagged1 increase was blocked by H89 and PKI, specific PKA inhibitors. In contrast, PKC activation with phorbol ester (PMA) or PTH(13-34) did not stimulate Jagged1 expression, and PTH-dependent Jagged1 stimulation was not blocked by Gö6976, a conventional PKC inhibitor. Therefore, PTH treatment stimulates osteoblastic Jagged1 mainly through the AC/PKA signaling pathway downstream of the PTH1R. Since Jagged1/Notch signaling has been implicated not only in stromal-HSC interactions but also in osteoblastic differentiation, Jagged1 may play a critical role in mediating the PTH-dependent expansion of HSC, as well as the anabolic effect of PTH in bone.

Effects of calcitriol on type 5b tartrate-resistant acid phosphatase and interleukin-6 in secondary hyperparathyroidism

BACKGROUND/AIMS

Secondary hyperparathyroidism (SHP) is characterized by high bone turnover and elevated serum bone remodeling markers. Elevation of serum interleukin-6 (IL-6) levels is also characteristic of end-stage renal disease. This study investigates the effects of intravenous calcitriol on serum bone resorptive markers, namely, type 5b tartrate-resistant acid phosphatase (TRACP5b) and IL-6 in patients with SHP.

METHODS

Intravenous calcitriol therapy was given for 16 weeks to 24 patients on maintenance hemodialysis with plasma intact parathyroid hormone (iPTH) levels >300 pg/ml. Blood was drawn at baseline and every 4 weeks for 16 weeks for determination of the levels of biochemical parameters, iPTH, IL-6 and bone remodeling markers, including bone-specific alkaline phosphatase (bAP) and TRACP5b.

RESULTS

Only 21 patients responded to the calcitriol therapy, with significant decrements in serum iPTH after 4 weeks of therapy and thereafter. After 16 weeks of calcitriol therapy, 21 patients had significant decrements in serum iPTH (707.9 +/- 317.8 vs. 205.0 +/- 63.1 pg/ml, p < 0.01). Prior to treatment, a significant correlation was found between increased levels of serum iPTH and IL-6 levels (r = 0.45, p < 0.05). After treatment, there was also a significant and parallel lowering of levels of serum iPTH, IL-6 (8.52 +/- 3.59 vs. 7.24 +/- 2.81 pg/ml, p < 0.01), bAP (54.68 +/- 36.17 vs. 24.55 +/- 13.84 U/l, p < 0.01) and TRACP5b (3.41 +/- 1.89 vs. 1.80 +/- 0.55 U/l, p < 0.01). Our results additionally showed significant positive correlationsbetween baseline levels of serum IL-6 and those of iPTH, bAP and TRACP5b. After 16 weeks of calcitriol treatment, the correlation between IL-6 and iPTH levels lost significance but levels of serum IL-6, bAP and TRACP5b remained significantly correlated.

CONCLUSIONS

Elevated levels of serum IL-6 and bone remodeling markers, namely, bAP and TRACP5b which are common features of SHP, are effectively suppressed by calcitriol therapy. This indicates that hyperparathyroidism not only accelerates bone remodeling but may also aggravate inflammation in patients on maintenance hemodialysis.

Differential Role of Rho-Kinase in Pathological and Physiological Cardiac Hypertrophy in Rats

The present study was undertaken to investigate the effect of fasudil, a specific Rho-kinase inhibitor, in pathological cardiac hypertrophy induced by partial abdominal aortic constriction (PAAC) for 4 weeks in comparison with physiological cardiac hypertrophy caused by chronic swimming training (CST) for 8 weeks in rats. Fasudil (15 and 30 mg/kg day(-1) p.o.) treatment was started 3 days before PAAC and CST, and was continued for 4 weeks in PAAC and 8 weeks in the CST experimental model. Left ventricular (LV) function and LV hypertrophy were assessed by measuring LVDP, +dp/dt(max), -dp/dt(max), ratio of LV weight to body weight (LVW/BW), LV wall thickness (LVWT), LV collagen content, protein content and RNA concentration. Further, venous pressure (VP) and mean arterial blood pressure (MABP) were recorded. Moreover, DNA gel electrophoresis was employed to assess myocardial cell death. PAAC but not CST produced LV dysfunction by decreasing LVDP, +dp/dt(max), -dp/dt(max) and increasing LV collagen content. Further, PAAC and CST were noted to produce LV hypertrophy by increasing LVW/BW, LVWT, LV protein content and LV RNA concentration. Moreover, in contrast to CST, PAAC has significantly increased VP, MABP and LV necrotic cell death. Fasudil, a Rho-kinase inhibitor, markedly attenuated PAAC-induced LV dysfunction, LV hypertrophy, increase in VP, MABP and LV necrotic cell death. However, it did not modulate the CST-induced LV hypertrophy. These results have implicated Rho-kinase in PAAC-induced LV dysfunction and pathological cardiac hypertrophy. However, Rho-kinase may not be involved in CST-induced physiological cardiac hypertrophy.

Rho-kinase is an important therapeutic target in cardiovascular medicine

Rho-kinase has been identified as one of the effectors of the small GTP-binding protein Rho. Accumulating evidence has demonstrated that Rho/Rho-kinase pathway plays an important role in various cellular functions, not only in vascular smooth muscle cell (VSMC) contraction but also in actin cytoskeleton organization, cell adhesion and motility, cytokinesis, and gene expressions, all of which may be involved in the pathogenesis of cardiovascular disease. At molecular level, Rho-kinase upregulates various molecules that accelerate inflammation/oxidative stress, thrombus formation, and fibrosis, whereas it downregulates endothelial nitric oxide synthase. The expression of Rho-kinase itself is mediated by protein kinase C/NF-kappaB pathway with an inhibitory and stimulatory modulation by estrogen and nicotine, respectively. At cellular level, Rho-kinase mediates VSMC hypercontraction, stimulates VSMC proliferation and migration, and enhances inflammatory cell motility. In animal studies, Rho-kinase has been shown to be substantially involved in the pathogenesis of vasospasm, arteriosclerosis, ischemia/reperfusion injury, hypertension, pulmonary hypertension, stroke and heart failure, and to enhance central sympathetic nerve activity. Finally, in clinical studies, fasudil, a Rho-kinase inhibitor, is effective for the treatment of a wide range of cardiovascular disease, including cerebral and coronary vasospasm, angina, hypertension, pulmonary hypertension, and heart failure, with a reasonable safety. Thus, Rho-kinase is an important therapeutic target in cardiovascular medicine.

G alpha12/G alpha13 subunits of heterotrimeric G proteins mediate parathyroid hormone activation of phospholipase D in UMR-106 osteoblastic cells

PTH, a major regulator of bone remodeling and a therapeutically effective bone anabolic agent, stimulates several signaling pathways in osteoblastic cells. Our recent studies have revealed that PTH activates phospholipase D (PLD) -mediated phospholipid hydrolysis through a RhoA-dependent mechanism in osteoblastic cells, raising the question of the upstream link to the PTH receptor. In the current study, we investigated the role of heterotrimeric G proteins in mediating PTH-stimulated PLD activity in UMR-106 osteoblastic cells. Transfection with antagonist minigenes coding for small peptide antagonists to G alpha 12 and G alpha13 subunits of heterotrimeric G proteins prevented PTH-stimulated activation of PLD, whereas an antagonist minigene to G alphas failed to produce this effect. Effects of pharmacological inhibitors (protein kinase inhibitor, Clostridium botulinum exoenzyme C3) were consistent with a role of Rho small G proteins, but not of cAMP, in the effect of PTH on PLD. Expression of constitutively active G alpha12 and G alpha13 activated PLD, an effect that was inhibited by dominant-negative RhoA. The results identify G alpha12 and G alpha13 as upstream transducers of PTH effects on PLD, mediated through RhoA in osteoblastic cells.