Tumor necrosis factor-α accelerates the calcification of human aortic valve interstitial cells obtained from patients with calcific aortic valve stenosis via the BMP2-Dlx5 pathway

Calcific aortic valve stenosis (CAS) is the most frequent heart valve disease in the elderly, accompanied by valve calcification. Tumor necrosis factor-α (TNF-α), a pleiotropic cytokine secreted mainly from macrophages, has been detected in human calcified valves. However, the role of TNF-α in valve calcification remains unclear. To clarify whether TNF-α accelerates the calcification of aortic valves, we investigated the effect of TNF-α on human aortic valve interstitial cells (HAVICs) obtained from patients with CAS (CAS group) and with aortic regurgitation or aortic dissection having a noncalcified aortic valve (control group). HAVICs (2 × 10(4)) were cultured in a 12-well dish in Dulbecco's modified Eagle's medium with 10% fetal bovine serum. The medium containing TNF-α (30 ng/ml) was replenished every 3 days after the cells reached confluence. TNF-α significantly accelerated the calcification and alkaline phosphatase (ALP) activity of HAVICs from CAS but not the control group after 12 days of culture. Furthermore, gene expression of calcigenic markers, ALP, bone morphogenetic protein 2 (BMP2), and distal-less homeobox 5 (Dlx5) were significantly increased after 6 days of TNF-α treatment in the CAS group but not the control group. Dorsomorphin, an inhibitor of mothers against decapentaplegic homologs (Smads) 1/5/8 phosphorylation, significantly inhibited the enhancement of TNF-α-induced calcification, ALP activity, Smad phosphorylation, and Dlx5 gene expression of HAVICs from the CAS group. These results suggest that HAVICs from the CAS group have greater sensitivity to TNF-α, which accelerates the calcification of aortic valves via the BMP2-Dlx5 pathway.

Contribution of bone morphogenetic protein-2 to aortic valve calcification in aged rat

Although aging is well established as an important risk factor for aortic stenosis, the mechanism of age-related aortic valve calcification is yet unknown. Here, we investigated this mechanism in tissue and cellular levels using middle-aged rats. Aortic valve specimens were obtained by dissecting from 9-week-old (young) and 30-week-old (aged) male Wistar rats. In the aged rats, the main risk factors for aortic stenosis in plasma were still in the normal range; however, their number of calcified specimens was significantly increased in comparison with the young rats. Aortic valve interstitial cells (AVICs) obtained from explants of aortic valve specimens were cultured for 14 days after reaching confluence. Spontaneous calcification, the expressions of calcigenic genes, that is, BMP-2, alkaline phosphatase (ALP), and osterix (osteogenic transcription factor) and ALP enzyme activity in AVICs from aged rats were enhanced in comparison with those from young rats. However, neither typical calcification inducing reagents (dexamethasone, β-glycerophosphate, and high concentration of phosphate) nor tumor necrosis factor-α (an inflammatory cytokine) accelerated the spontaneous calcification of AVICs from aged rats. These results suggest that aortic valve calcification progresses with age partly through an activation of the BMP-2 pathway.

A functional RNAi screen for Runx2-regulated genes associated with ectopic bone formation in human spinal ligaments

Ossification of the posterior longitudinal ligament of the spine (OPLL) is characterized by ectopic ossification in the spinal ligaments, which enlarges with time and compresses the spinal cord, resulting in serious neurological symptoms. We previously reported that Runx2 expression was enhanced in spinal ligament cells from OPLL patients (OPLL cells). To clarify genes regulated by Runx2, Runx2 expression was first enhanced by culturing primary OPLL cells in osteogenic medium (OS induction) and then inhibited by siRNAs targeted to Runx2. DNA microarray demonstrated that in addition to chondrogenic factors such as connective tissue growth factor and cartilage oligomeric matrix protein, angiopoietin-1 was also significantly increased by OS induction and decreased by siRNAs for Runx2 in OPLL cells, suggesting that these genes are regulated by Runx2. However, these changes were not observed in non-OPLL control cells (from cervical spondylotic myelopathy patients). Furthermore, Runx2 was not decreased by siRNAs for angiopoietin-1. OS induction and RNAi inhibition of angiopoietin-1 expression was also observed in osteoblasts. Both siRNAs for Runx2 and angiopoietin-1 completely inhibited aggrecan-1 expression. These results suggest that angiopoietin-1 is downstream of Runx2 in both OPLL primary cells and osteoblasts. Angiopoietin-1 may play an important role in ectopic ossification.

Possible role of extracellular nucleotides in ectopic ossification of human spinal ligaments

To reveal the involvement of extracellular nucleotides in the ossification process in ossification of the posterior longitudinal ligament of the spine (OPLL), the mRNA expression profiles of P2 purinoceptors, mechanical stress-induced ATP release, and ATP-stimulated expression of osteogenic genes were analyzed in ligament cells derived from the spinal ligament of OPLL patients (OPLL cells) and non-OPLL cells derived from the spinal ligaments of cervical spondylotic myelopathy patients as a control. The extracellular ATP concentrations of OPLL cells in static culture were significantly higher than those of non-OPLL cells, and this difference was diminished in the presence of ARL67156, an ecto-nuclease inhibitor. Cyclic stretch markedly increased the extracellular ATP concentrations of both cell types to almost the same level. P2Y1 purinoceptor subtypes were intensively expressed in OPLL cells, but only weakly expressed in non-OPLL cells. Not only ATP addition but also cyclic stretch raised the mRNA levels of alkaline phosphatase and osteopontin in OPLL cells, which were blocked by MRS2179, a selective P2Y1 antagonist. These increases in the expression of osteogenic genes were not observed in non-OPLL cells. These results suggest an important role of P2Y1 and extracellular ATP in the progression of OPLL stimulated by mechanical stress.

Inhibitory effects of glucocorticoids on urocortin-mediated increases in interleukin-6 gene expression in rat aortic smooth muscle cells

Urocortin (Ucn) 1, Ucn2, and Ucn3 have potent effects on appetite and the cardiovascular system. Endogenous Ucns in combination with CRF receptor type 2beta may have a physiological role in the cardiovascular system. We previously demonstrated that both Ucn1 and Ucn2 increased IL-6 output levels in A7r5 aortic smooth muscle cells. In the present study, we extended observations on stress or hormone-induced changes in IL-6 gene expression in the cardiovascular system, and determined the effects of glucocorticoids on Ucn-mediated increases in IL-6 mRNA levels, protein levels, and gene transcription activity in A7r5 cells. Ucn1, Ucn2, and Ucn3 all increased IL-6 mRNA levels via CRF receptor type 2. Dexamethasone blocked the ability of Ucn1 to increase IL-6 mRNA and protein levels, while it failed to attenuate the Ucns-mediated changes in cyclic AMP (cAMP)-response element binding protein or extracellular signal-related kinases phosphorylation. Dexamethasone also suppressed Ucn1- or cAMP-stimulated IL-6 gene transcription via a glucocorticoid receptor. Together, these findings demonstrate that glucocorticoids suppress IL-6 gene transcription via Ucn-induced cAMP-dependent pathways in A7r5 cells.

Cardiac mitochondrial cGMP stimulates cytochrome c release

Although the existence of cardiac mitochondrial cGMP has been reported previously [Kimura and Murad (1974) J. Biol. Chem. 249, 6910-6916], the physiological and pathophysiological properties of cGMP in cardiac mitochondria have remained unknown. The aim of the present study was to clarify whether cardiac mitochondrial cGMP regulates the apoptosis of cardiomyocytes. In the presence of GTP, the NO donors SNAP (S-nitroso-N-acetyl-DL-penicillamine; 1 mmol/l) and SNP (sodium nitroprusside; 1 mmol/l) each markedly increased the cGMP level in a highly purified mitochondrial protein fraction prepared from left ventricular myocytes of male Wistar rats, and these increases were inhibited by 1 micromol/l ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one), an inhibitor of NO-sensitive guanylate cyclase. In purified mitochondria, both SNAP (1 mmol/l) and the membrane-permeant cGMP analogue 8-Br-cGMP (8-bromo-cGMP; 1 mmol/l), but not cGMP (1 mmol/l), increased cytochrome c release from succinate-energized mitochondria without inducing mitochondrial swelling and depolarization of the mitochondrial membrane as factors of activation of MPT (mitochondrial permeability transition). The cytochrome c release mediated by SNAP was inhibited in the presence of 1 micromol/l ODQ. On the other hand, 1 mmol/l SNAP induced apoptosis in primary cultured adult rat cardiomyocytes in a time-dependent manner, and this induction was significantly inhibited in the presence of ODQ. Furthermore, apoptosis induced in primary cultured cardiomyocytes by hypoxia/re-oxygenation was also inhibited by ODQ. These results suggest that the acceleration of cGMP production in cardiac mitochondria stimulates cytochrome c release from mitochondria in an MPT-independent manner, resulting in apoptosis.

Assessment of the Effects of L- and N-Type Ca2+ Channel Blocking Drugs Using Canine Blood-Perfused Papillary Muscle Preparations

It is important to accurately and conveniently assess the effects of L- and N-type Ca(2+) channel blocking drugs, which are commonly used for treatment of hypertension, but no method is available to simultaneously assess the effects of them in the same preparation. We have therefore designed an ex vivo method to measure the changes in contractile response of anterior papillary muscle of right ventricle and myocardial interstitial norepinephrine (NE) level using canine blood-perfused papillary muscle preparations. Papillary muscle-developed tension (PMDT) induced by an electronic stimulator was measured with force transducer. Myocardial interstitial NE effluent was collected by microdialysis fiber, which was implanted at the base of the papillary muscle, and measured with high performance liquid chromatography. Cilnidipine, a typical L- and N-type Ca(2+) channel blocker, was used to prove the efficiency of this method. First, to assess the effects of drugs on L-type Ca(2+) channel, the changes in basal PMDT were measured. Cilnidipine and nicardipine, a selective L-type Ca(2+) channel blocker, but not omega-conotoxin GVIA (omega-CTX), a selective N-type Ca(2+) channel blocking peptide, decreased basal PMDT dose-dependently. Second, to assess the effects of drugs on N-type Ca(2+) channel, the changes in PMDT and myocardial interstitial NE level by intracardiac sympathetic ganglion stimulation were measured. Cilnidipine and omega-CTX, but not nicardipine, dose-dependently reduced sympathomimetic increases in PMDT and myocardial interstitial NE level. These results indicate that our method is efficient to assess the effects of various L- and N-type Ca(2+) channel blocking drugs in the same papillary muscle preparation.

Tumour necrosis factor alpha-stimulated gene-6 inhibits osteoblastic differentiation of human mesenchymal stem cells induced by osteogenic differentiation medium and BMP-2

To better understand the molecular pathogenesis of OPLL (ossification of the posterior longitudinal ligament) of the spine, an ectopic bone formation disease, we performed cDNA microarray analysis on cultured ligament cells from OPLL patients. We found that TSG-6 (tumour necrosis factor alpha-stimulated gene-6) is down-regulated during osteoblastic differentiation. Adenovirus vector-mediated overexpression of TSG-6 inhibited osteoblastic differentiation of human mesenchymal stem cells induced by BMP (bone morphogenetic protein)-2 or OS (osteogenic differentiation medium). TSG-6 suppressed phosphorylation and nuclear accumulation of Smad 1/5 induced by BMP-2, probably by inhibiting binding of the ligand to the receptor, since interaction between TSG-6 and BMP-2 was observed in vitro. TSG-6 has two functional domains, a Link domain (a hyaluronan binding domain) and a CUB domain implicated in protein interaction. The inhibitory effect on osteoblastic differentiation was completely lost with exogenously added Link domain-truncated TSG-6, while partial inhibition was retained by the CUB domain-truncated protein. In addition, the inhibitory action of TSG-6 and the in vitro interaction of TSG-6 with BMP-2 were abolished by the addition of hyaluronan. Thus, TSG-6, identified as a down-regulated gene during osteoblastic differentiation, suppresses osteoblastic differentiation induced by both BMP-2 and OS and is a plausible target for therapeutic intervention in OPLL.

Nifedipine enhances cGMP production through the activation of soluble guanylyl cyclase in rat ventricular papillary muscle

It is known that nifedipine, an L-type calcium channel blocker, increases cGMP production, which partially contributes to the relaxation of vascular smooth muscle. The aim of our investigation was to clarify whether or not nifedipine regulates cGMP production, which has a physiological role in cardiac muscle. To measure contractile responses and tissue cGMP levels, left ventricular papillary muscles prepared from male Wistar rats (350-400 g) were mounted in the isolated organ chamber under isometric conditions and electrically paced by means of platinum punctate electrodes (1 Hz, 1 ms duration). In papillary muscle preparation, the negative inotropic effect induced by nifedipine (30 to 300 nM) was significantly inhibited in the presence of ODQ(1H-[1,2,4]oxidazolo[4,3-a]quinoxaline1-one; 10 microM), a soluble guanylyl cyclase inhibitor. Furthermore, nifedipine (100 nM) strongly increased the tissue cGMP level, which was significantly decreased in the presence of ODQ. On the other hand,N(G)-monomethyl-(L)-arginine (100 microM), a nitric oxide synthase inhibitor, did not inhibit either the negative inotropic effect or cGMP production induced by nifedipine. These results indicate that in rat left ventricular papillary muscle, nifedipine augments its negative inotropic effect at least partly through direct activation of cardiac soluble guanylyl cyclase but not nitric oxide synthase.

Current Topics in Pharmacological Research on Bone Metabolism: Molecular Basis of Ectopic Bone Formation Induced by Mechanical Stress

Ectopic bone formation (EBF) is frequently found in various tissues and affects the prognosis of diseases accompanied by EBF. Although the mechanism of EBF remains unclear, several local factors that influence the progression of EBF have been proposed. We have been focusing on the role of mechanical stress as a local factor in EBF in spinal ligament tissues, that is, ossification of the posterior longitudinal ligament (OPLL), which causes serious neurological deficiencies. Transcriptome analyses revealed that the expressions of several marker genes related to bone remodeling were enhanced after exposure of ligament cells derived from OPLL patients (OPLL cells) to cyclic stretching as a type of mechanical stress. However, no significant alterations in gene expressions were detected after cyclic stretching of ligament cells derived from non-OPLL patients. OPLL cells exposed to cyclic stretching released several autocrine/paracrine factors that are known to mediate bone remodeling. These results suggest that OPLL cells have been transformed into cells that are highly sensitive to mechanical stress, which may induce the progression of OPLL. These observations provide information regarding the role of mechanical stress in the process of EBF.

Changes in pH Increase Perfusion Pressure of Coronary Arteries in the Rat

Stricture of coronary arteries is closely related to ischemic heart disease. The purpose of this study was to examine whether changes in pH caused contraction of rat coronary arteries, as determined using Langendorff perfused hearts. Changing the pH of the perfusate increased perfusion pressure as an indication of the contractile state of coronary arteries. Alkaline pH-induced increase of perfusion pressure in Wistar Kyoto rats (WKY) was almost identical to that of spontaneously hypertensive rats (SHR), whereas acidic pH-induced increase in SHR was much greater than that in WKY. Acidic pH-induced increase in perfusion pressure was inhibited by verapamil, cromakalim, and adenosine. Feeding WKY with N(G)-nitro-L-arginine resulted in hypertension followed by enhanced acidic pH-induced increase in perfusion pressure. These results suggest that acidic-pH induced contraction of rat coronary arteries is caused by Ca(2+) influx through voltage-dependent Ca(2+) channels and the contraction is enhanced by hypertension.

Gene expression and functional activity of sodium/calcium exchanger enhanced in vascular smooth muscle cells of spontaneously hypertensive rats

Effects of hypertension on the function of the Na+/Ca2+ exchanger (NCX) were investigated by analyzing vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats. Angiotensin II-induced 45Ca2+ efflux from VSMCs mediated by NCX was enhanced by up to 3-fold in SHR compared with WKY, whereas ionomycin-induced Ca efflux mediated by NCX was not different between SHR and WKY. The decline rate from the peak value of intracellular 45Ca2+ concentration ([Ca2+]i) mobilized by angiotensin II was decelerated by removal of extracellular sodium (Na+o) in SHR but not in WKY. Gene expressions of NCX subtype 1 and angiotensin II receptor type1A assessed by quantitative RT-PCR were increased by 1.3- and 1.5-fold, respectively in SHR compared with WKY. NCX protein was also increased 1.6-fold in SHR compared with WKY. MEK inhibitor, PD98059, partly blocked the Nao-dependent acceleration of the [Ca2+]i recovery rate and tyrosine kinase inhibitor, genistein, diminished it in SHR. Genistein decreased angiotensin II-induced Nao- dependent 45Ca2+ efflux. However, angiotensin II did not enhance the tyrosine phosphorylation of NCX. These results suggest that acceleration of Ca2+ efflux from VSMCs of SHR was at least partly due to the enhancement of functional activity of NCX via increased gene expression and tyrosine phosphorylation in connection with hypertension.

Vasodilative effects of urocortin II via protein kinase A and a mitogen-activated protein kinase in rat thoracic aorta

Four corticotropin-releasing factor (CRF)-related peptides have been found in mammals and are known as CRF, urocortin, urocortin II, and urocortin III (also known as stresscopin). The three urocortins have considerably higher affinities for CRF receptor type 2 (CRF R2) than CRF, and urocortin II and urocortin III are highly selective for CRF R2. In the present study, the authors examined the hypothesis that urocortin II or urocortin III, in addition to urocortin, produces vasodilation as a candidate for natural ligands of CRF R2beta in rat thoracic aorta. Involvement of protein kinases on urocortin-induced vasodilation was also explored. The vasodilative effects of urocortin II and urocortin III were more potent than that of CRF, but less potent than that of urocortin. Urocortin II-induced vasodilation was significantly attenuated by a CRF R2-selective antagonist, antisauvagine-30. Both SQ22536, an adenylate cyclase inhibitor, and Rp-8-Br-cAMPS, a protein kinase A (PKA) inhibitor, were found to attenuate the urocortin II-induced vasodilation. SB203580, a p38 mitogen-activated protein (MAP) kinase inhibitor, also inhibited the effects of urocortin and urocortin II on vasodilation. Thus, urocortins contribute to vasodilation via p38 MAP kinase as well as PKA pathways.

Role of Corticotropin-Releasing Factor Receptor Type 2β in Urocortin-Induced Vasodilation of Rat Aortas

Urocortin has a high affinity for the corticotropin-releasing factor receptor type 2beta (CRF-R2beta). This study was conducted to reveal the role of CRF-R2beta in blood vessels. CRF-R2beta expressions were detected both in smooth muscle and endothelium from Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) aortas, and there was no significant difference between them. Urocortin reduced phenylephrine-induced contraction of aorta with endothelium dose-dependently in both rats. However, deendothelialization significantly but not completely (about 50%) reduced the vasodilation. The reduction of vasodilatory action of urocortin by deendothelialization was age-dependent in SHR. An adenylyl cyclase inhibitor, SQ22536, significantly inhibited urocortin-induced relaxation in denuded WKY and SHR aortas, while in preparations with endothelium, neither SQ22536 nor L-NMMA reduced the relaxation. However, simultaneous addition of both drugs significantly reduced the relaxation. In contrast to young rats (7-week-old), in aged rats (19-week-old), L-NMMA successfully reduced urocortin-induced relaxation of aorta with endothelium. These results suggest that urocortin relaxes aorta at least partly via two signal pathways, that is, an increase in intracellular cAMP by binding to CRF-R2beta expressed in smooth muscle cells and NO production from endothelium evoked by binding to the receptors expressed in endothelium and that aging increases the role of the latter system.

[Role of PGI2 in ectopic bone formation of spinal ligaments]

Ossification of the posterior longitudinal ligament (OPLL) is characterized by ectopic bone formation in the spinal ligaments. It has been suggested some role of mechanical stress in the progression of OPLL. Differential display RT-PCR was carried out to identify the genes participating in OPLL. A cDNA fragment corresponding to PGI2 synthase was highly expressed in OPLL cells compared to non-OPLL cells. To examine the effect of mechanical stress on the PGI2 synthase expression, cells were subjected to cyclic stretch and PGI2 synthase expression was assessed by quantitative RT-PCR. Cyclic stretch induced a time-dependent increase in PGI2 synthase in OPLL cells but not in non-OPLL cells. The increase in PGI2 synthase was diminished by SQ22536, a potent adenylate cyclase inhibitor. Cyclic stretch also induced PGI2 production. Beraprost and dibutyryl cAMP increased the mRNA expression of alkaline phosphatase (ALP) as a marker for osteogenic differentiation in OPLL cells, whereas no change was observed in non-OPLL cells. Beraprost- and stretch-induced increases in ALP expressions were inhibited by SQ22536. These data suggest that PGI2 synthase activated by mechanical stress plays a key role in the progression of OPLL, at least in part through the osteogenic differentiation in spinal ligament cells via the PGI2/cAMP system.

Genomewide linkage and linkage disequilibrium analyses identify COL6A1, on chromosome 21, as the locus for ossification of the posterior longitudinal ligament of the spine

Ossification of the posterior longitudinal ligament (OPLL) of the spine is a subset of "bone-forming" diseases, characterized by ectopic ossification in the spinal ligaments. OPLL is a common disorder among elderly populations in eastern Asia and is the leading cause of spinal myelopathy in Japan. We performed a genomewide linkage study with 142 affected sib pairs, to identify genetic loci related to OPLL. In multipoint linkage analysis using GENEHUNTER-PLUS, evidence of linkage to OPLL was detected on chromosomes 1p, 6p, 11q, 14q, 16q, and 21q. The best evidence of linkage was detected near D21S1903 on chromosome 21q22.3 (maximum Zlr=3.97); therefore, the linkage region was extensively investigated for linkage disequilibrium with single-nucleotide polymorphisms (SNPs) covering 20 Mb. One hundred fifty positional candidate genes lie in the region, and 600 gene-based SNPs were genotyped. There were positive allelic associations with seven genes (P<.01) in 280 patients and 210 controls, and four of the seven genes were clustered within a region of 750 kb, approximately 1.2 Mb telomeric to D21S1903. Extensive linkage disequilibrium and association studies of the four genes indicated that SNPs in the collagen 6A1 gene (COL6A1) were strongly associated with OPLL (P=.000003 for the SNP in intron 32 [-29]). Haplotype analysis with three SNPs in COL6A1 gave a single-point P value of.0000007. Identification of the locus of susceptibility to OPLL by genomewide linkage and linkage disequilibrium studies permits us to investigate the pathogenesis of the disease, which may lead to the development of novel therapeutic tools.

Endothelium-dependent vasodilatory effect of vitisin C, a novel plant oligostilbene from Vitis plants (Vitaceae), in rabbit aorta

We investigated the pharmacological properties of vitisin C, a novel plant oligostilbene from Vitis plants. Vitisin C (1-10 microM) dose-dependently inhibited the contractile responses of endothelium-intact rabbit thoracic aorta induced by phenylephrine (1 microM). These inhibitory effects were abolished in the presence of N (G)-nitro-L-arginine methyl ester (L-NAME; 300 microM), a potent inhibitor of nitric oxide synthase, but not atropine (1 microM), a non-selective muscarinic cholinoceptor antagonist. In endothelium-denuded rabbit aorta, vitisin C was ineffective in attenuating phenylephrine-induced contraction. Moreover, vitisin C (10 microM) increased cGMP production in endothelium-intact, but not endothelium-denuded, aorta, and this increase was abolished in the presence of L-NAME (300 microM). To assess Ca(2+) movement across the endothelial cell membrane induced by vitisin C, we further investigated (45)Ca(2+) influx into cultured rabbit aortic endothelial cells in the presence of vitisin C (3 microM), carbachol (1 microM) or A23187 (10 nM). Vitisin C and carbachol significantly enhanced (45)Ca(2+) influx, which was inhibited by nifedipine (10 microM), a blocker of L-type Ca(2+) channels. In the presence of SK&F96365, a blocker of receptor-operated Ca(2+) channels, (45)Ca(2+) influx induced by carbachol was significantly inhibited, whereas that induced by vitisin C was not affected. On the other hand, A23187 enhanced (45)Ca(2+) influx in the presence and absence of nifedipine and SK&F96365. These results suggest that vitisin C evokes endothelium-dependent vasorelaxation through enhancing nitric oxide release, which is facilitated by Ca(2+) influx into endothelial cells via nifedipine-sensitive Ca(2+) channels.

Role of prostaglandin I2 in the gene expression induced by mechanical stress in spinal ligament cells derived from patients with ossification of the posterior longitudinal ligament

Ossification of the posterior longitudinal ligament of the spine (OPLL) is characterized by ectopic bone formation in the spinal ligaments, and mechanical stress has been suggested to play an important role in the progression of OPLL. To identify the genes that participate in OPLL, the differential display reverse transcription-polymerase chain reaction (RT-PCR) method was used. A 283-base pair cDNA fragment corresponding to prostaglandin I2 (PGI2) synthase was highly expressed in OPLL cells compared with non-OPLL cells. To examine the effect of mechanical stress on the expression of PGI2 synthase, cells were subjected to uniaxial cyclic stretch (0.5 Hz, 20% stretch), and PGI2 synthase mRNA expression was assessed by quantitative RT-PCR. Cyclic stretch induced an increase in PGI2 synthase in OPLL cells in a time-dependent manner, whereas no change was observed in non-OPLL cells. Cyclic stretch for 9 h also induced a 2.86x increase in PGI2 production. Beraprost (a stable PGI2 analog) and dibutyryl cAMP (a membrane-permeable cAMP analog) increased the mRNA expression of alkaline phosphatase (ALP) as a marker for osteogenic differentiation up to 240 and 200%, respectively, in OPLL cells, whereas no change was observed in non-OPLL cells. The increases in ALP mRNA induced by beraprost and cyclic stretch were both inhibited by SQ22536, a potent adenylate cyclase inhibitor. These data suggest that the increase in PGI2 synthase induced by mechanical stress plays a key role in the progression of OPLL, at least in part through the induction of osteogenic differentiation in spinal ligament cells via the PGI2/cAMP system.

Stimulated tyrosine phosphorylation of phosphatidylinositol 3-kinase causes acidic pH-induced contraction in spontaneously hypertensive rat aorta

Acidic pH induced a contraction (APIC) in isolated aortas from spontaneously hypertensive (SHR) and Wistar Kyoto rats, but failed to produce any response in age-matched Wistar rat aorta. This study was conducted to test the hypothesis that tyrosine phosphorylation of proteins is a molecular mechanism underlying the APIC. Tyrosine kinase inhibitors, genistein and tyrphostin 23 inhibited the APIC in a concentration-dependent manner. APIC was inhibited by phosphatidylinositol 3-kinase (PI3-kinase) inhibitors, LY-294002 [2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one hydrochloride] and wortmannin. Consistent with the results from tension measurement experiments, Western blot analysis showed that acidic pH induced an appreciable increment of tyrosine phosphorylation of 85-kDa protein (p85) in SHR aorta, which was completely inhibited by tyrphostin 23, whereas in Wistar rat aorta, the protein tyrosine phosphorylation was not observed. Further investigations using immunoprecipitation followed by Western blotting confirmed an increase in the tyrosine phosphorylation of p85. Analysis by SDS-polyacrylamide gel electrophoresis followed by silver staining of the gel revealed that amounts of multiple proteins with molecular sizes of 120, 130, 210, and 225 kDa were increased at acidic pH, which were immunoprecipitated with anti-phosphotyrosine antibody. Western blotting using a specific anti-PI3-kinase antibody identified the p85 as the regulatory subunit of PI3-kinase, whereas 120-, 130-, and 225-kDa proteins were identified by mass spectrometry as pro-alpha2 (I) collagen, collagen alpha1 (I) chain, and fibernectin I, respectively. As assayed by Western blotting using anti-myosin light chain (MLC) antibody, acidic pH induced a stimulation of MLC phosphorylation, and the stimulated MLC phosphorylation was abolished by tyrphostin 23 and LY-294002. These results suggest that acidic pH induces an increase in tyrosine phosphorylation of PI3-kinase, resulting in the MLC phosphorylation-dependent contraction of SHR aorta.

Antisense-inhibition of plasma membrane Ca2+ pump induces apoptosis in vascular smooth muscle cells

The effect of antisense oligodeoxynucleotides (ODNs) of plasma membrane Ca(2+)-pumping ATPase (PMCA) on rat aortic vascular smooth muscle cells (VSMCs) in primary culture was examined. More than 80% of the PMCA expressed in cultured VSMCs was the PMCA-1B subtype. Exposed to antisense ODNs against PMCA-1, not only the expression of the PMCA protein but also mRNA of PMCA-1B was diminished in a concentration-dependent manner. Extracellular Na(+)-independent (45)Ca(2+) efflux catalyzed via PMCA was inhibited with antisense ODNs. Both the resting and ionomycin- or ATP-stimulated levels of intracellular Ca(2+) were increased by antisense ODNs. Furthermore, prolonged treatment with antisense ODNs caused apoptosis in VSMCs. The occurrence of apoptosis was inhibited by FK506, a potent immunosuppressant. These results demonstrate that the PMCA was specifically inhibited by antisense ODNs and suggest that PMCA plays an important role in regulation of intracellular Ca(2+) concentrations, especially at the resting condition to prevent an occurrence of apoptosis that may be induced through the activation of calcineurin.

Possible roles of CTGF/Hcs24 in the initiation and development of ossification of the posterior longitudinal ligament

STUDY DESIGN

A biochemical and histochemical study investigating the role of CTGF/Hcs24 in the ossification of the posterior longitudinal ligament (OPLL) was conducted.

OBJECTIVE

To clarify the involvement of CTGF/Hcs24 in ectopic bone formation in OPLL through endochondral ossification using human tissue.

SUMMARY OF BACKGROUND DATA

Previous studies have shown that various cytokines are involved in the occurrence or development of ectopic bone formation in OPLL. Recently, the authors cloned an mRNA predominantly expressed in chondrocytes by differential display PCR and found that its gene, hcs24, is identical to that of connective tissue growth factor. It has been shown that CTGF/Hcs24 plays a major role in endochondral ossification.

METHODS

Ossified ligament tissues were taken from seven male OPLL patients during surgery. Immunohistochemical staining was performed using an antibody specific for CTGF/Hcs24. Spinal ligament cells were isolated from five OPLL patients as well as five non-OPLL patients. The cells were incubated with recombinant human CTGF/Hcs24 or TGFbeta. The expression of ALP was analyzed by RT-PCR. For the effects of TGFbeta, the expression of CTGF/Hcs24 mRNA was analyzed.

RESULTS

Immunohistochemical staining showed that chondrocytes in the transitional region from nonossified to ossified ligament were stained with an antibody against CTGF/Hcs24. It was found that CTGF/Hcs24 enhanced the expression ALP mRNA in OPLL cells, whereas the expression remained unchanged in non-OPLL cells. The expression of CTGF/Hcs24 mRNA in OPLL and non-OPLL cell lines was increased by TGFbeta, and there was no significant difference between the two groups. However, TGFbeta and CTGF/Hcs24 enhanced the expression of ALP mRNA only in OPLL cells.

CONCLUSIONS

According to the study results, CTGF/Hcs24 may not only be an important factor in the development of endochondral ossification in OPLL, but may also be responsible for initiating osteogenesis in spinal ligament cells.