Absence of association of asporin polymorphisms and osteoarthritis susceptibility in US Caucasians

OBJECTIVE

An association between osteoarthritis (OA) and functional polymorphisms in the aspartic acid (d) repeat of the asporin (ASPN) gene was reported in Japanese and Han Chinese populations. The aim of this study was to assess the association of variants in the ASPN gene with the presence of radiographic hand and/or knee OA in a US Caucasian population.

METHODS

Ten single nucleotide polymorphisms (SNPs) within the ASPN gene were genotyped in 775 affected siblings with radiographically confirmed hand and/or knee OA, and the allelic, genotypic and haplotypic association results were examined.

RESULTS

One variant (SNP RS7033979) showed nominal evidence of association with both hand OA (P=0.042) and knee OA (P=0.032). Four additional SNPs showed nominal evidence of association with knee OA only. These associations were only observed with genotypic tests; the corresponding allelic and haplotype tests did not corroborate the single-point association results.

CONCLUSION

These data suggest that polymorphisms within ASPN are not a major influence in susceptibility to hand or knee OA in US Caucasians.

Expression and function of TbetaRII-B, a variant of the type II TGF-beta receptor, in human chondrocytes

OBJECTIVE

Transforming growth factor-beta (TGF-beta) has profound effects on chondrocyte proliferation and matrix production, and dysregulation of TGF-beta action has been implicated in osteoarthritis. The mechanisms by which the diverse actions of TGF-beta are regulated in chondrocytes are unclear. Although it is well documented that TGF-beta signaling is transduced by types I and II receptors, other TGF-beta receptors may play critical roles by regulating signaling receptor activity. Our objective was to examine the expression of TbetaRII-B, a splice variant of the type II TGF-beta receptor, and to analyze its role in regulating TGF-beta signaling in human chondrocytes.

METHODS

TbetaRII-B expression was examined in human cartilage tissue specimens, human chondrocyte cell lines C28/I2 and tsT/AC62, and human primary chondrocytes by Western blot and reverse-transcriptase-polymerase chain reaction. Ligand binding and heteromerization of TbetaRII-B with other TGF-beta receptors on the cell surface were analyzed by affinity labeling, immunoprecipitation, and two-dimensional SDS-PAGE. Regulation of TGF-beta responses by TbetaRII-B was determined by examining Smad2 phosphorylation, Smad3-specific signaling, transcriptional activity, and type II collagen levels.

RESULTS

TbetaRII-B is expressed in normal and osteoarthritic human cartilage. Furthermore, it is a dynamic component of the TGF-beta receptor system in human chondrocytes, forming heteromeric complexes with the types I and II TGF-beta receptors, betaglycan and endoglin. Importantly, overexpression of TbetaRII-B leads to enhanced TGF-beta signaling and responses in chondrocytes.

CONCLUSIONS

These results suggest that TbetaRII-B may play a key role in the regulation of TGF-beta action in human chondrocytes.

In situ-formed asymmetric membrane capsule for osmotic release of poorly water-soluble drug

A non-disintegrating, in situ-formed, asymmetric membrane, polymeric capsular system, offering improved osmotic effect, was used to deliver poorly water-soluble drug in a controlled manner. The poorly water-soluble drug ketoprofen was selected as a model drug to demonstrate how controlled release characteristics can be manipulated by design of in situ-formed polymeric capsule with an asymmetric membrane and core formulations. In situ-formed, asymmetric membrane capsule was made by dry method via precipitation of asymmetric membrane on the walls of hard gelatin capsule. Resulting asymmetric membrane composed of a dense outer region with fewer pores and a lighter inner porous region. The present study evaluates the influence of variables based on two-factor composite design, namely, ethylcellulose and osmogen (sodium chloride), apart from studying effect of varying osmotic pressures of dissolution medium and level of pore-former concentration (glycerol) on drug release. Statistical significance was tested at P < 0.05. Results showed the best formulation (F-5) to closely corresponded to extra design checkpoint formulation by a similarity (f2) value of 95.41 and capsules made with 15% w/v EC, 50 mg sodium chloride, 8% w/v glycerol and 30 mg citric acid (F-11), to achieve therapeutic concentration within first hour of dissolution not observed with any other formulations used in the study. Drug release followed Fickinan diffusion and was independent of pH but dependent on the osmotic pressure of the dissolution medium.

Acquired Robertsonian translocations in two leukemia patients

Robertsonian translocations were observed in two leukemia patients. The first case was a patient with chronic lymphocytic leukemia, who was found to have a rare Robertsonian translocation der(14;15)(q10;q10). The second case, a patient with acute myeloid leukemia, had multiple Robertsonian translocations: der(15)t(13;15)(q11.1;p11.1), der(14;22)(q10;q10), and dic(21;22)(p11.1;p11.1). Acquired multiple Robertsonian translocations have not been reported previously in leukemia.

Systemic steroid pretreatment improves cerebral protection after circulatory arrest

BACKGROUND

This study evaluates whether systemic steroid pretreatment enhances neuroprotection during deep hypothermic circulatory arrest (DHCA) compared with steroid in cardiopulmonary bypass (CPB) prime.

METHODS

Four-week-old piglets randomly placed into two groups (n = 5 per group) were given methylprednisolone (30 mg/kg) into the pump prime (group PP), or pretreated intravenously 4 hours before CPB (group PT). All animals underwent 100 minutes of DHCA (15 degrees C), were weaned off CPB, and were sacrificed 6 hours later. Postoperative changes in body weight, bioimpedance, and colloid oncotic pressure (COP) were measured. Cerebral trypan blue content, immunohistochemical evaluation of transforming growth factor-beta1 (TGF-beta1) expression, and caspase-3 activity were performed.

RESULTS

Percentage weight gain (group PP 25.0% +/- 10.4% versus group PT 12.5% +/- 4.0%; p = 0.036), and percentage decrease in bioimpedance (PP 37.2% +/- 14.5% versus PT 15.6% +/- 7.9%; p = 0.019) were significantly lower, whereas postoperative COP was significantly higher in group PT versus group PP (PT 15.3 +/- 1.8 mm Hg versus PP 11.6 +/- 0.8 mm Hg; p = 0.003). Cerebral trypan blue (ng/g dry tissue) was significantly lower in group PT (PT 5.6 x 10(-3) +/- 1.1 x 10(-3) versus PP 9.1 x 10(-3) +/- 5.7 x 10(-4); p = 0.001). Increased TGF-beta1 expression and decreased caspase-3 activity were shown in group PT.

CONCLUSIONS

Systemic steroid pretreatment significantly reduced total body edema and cerebral vascular leak and was associated with better immunohistochemical indices of neuroprotection after DHCA.

Characterization of a 150 kDa accessory receptor for TGF-beta 1 on keratinocytes: direct evidence for a GPI anchor and ligand binding of the released form

Transforming growth factor-beta (TGF-beta) is a key modulator of epidermal development and homeostasis, and has been shown to potently regulate keratinocyte migration and function during wound repair. There are three cloned TGF-beta receptors termed type I, type II, and type III that are found on most cell types. The types I and II are the signaling receptors, while the type III is believed to facilitate TGF-beta binding to the types I and II receptors. Recently, we reported that in addition to these receptors, human keratinocytes express a 150 kDa TGF-beta 1 binding protein (r150) which forms a heteromeric complex with the TGF-beta signaling receptors. This accessory receptor was described as glycosyl phosphatidylinositol-specific anchored based on its sensitivity to phosphatidylinositol phospholipase C (PIPLC). In the present study, we demonstrate that the GPI-anchor is contained in r150 itself and not on a tightly associated protein and that it binds TGF-beta 1 with an affinity similar to those of the types I and II TGF-beta signaling receptors. Furthermore, the PIPLC released (soluble) form of this protein is capable of binding TGF-beta 1 independently from the signaling receptors. In addition, we provide evidence that r150 is released from the cell surface by an endogenous phospholipase C. Our observation that r150 interacts with the TGF-beta signaling receptors, together with the finding that the soluble r150 binds TGF-beta 1 suggest that r150 in either its membrane anchored or soluble form may potentiate or antagonize TGF-beta signaling. Elucidating the mechanism by which r150 functions as an accessory molecule in TGF-beta signaling may be critical to understanding the molecular mechanisms underlying the regulation of TGF-beta action in keratinocytes.

Fetal and adult human skin fibroblasts display intrinsic differences in contractile capacity

One of the differences between fetal and adult skin healing is the unique ability of fetal wounds to heal without contracture and scar formation. Studies have shown that the ratio between the three isoforms of TGFbeta is different in adult and fetal wounds. Thus, we analyzed the capacity of adult and fetal human skin fibroblasts to contract collagen gels after stimulation with TGFbeta isoforms. In control medium, fetal fibroblasts had a contractile capacity similar to that of adult fibroblasts. However, the growth capacity of fetal fibroblasts was completely inhibited, in contrast to adult fibroblasts. When cells were treated with TGFbeta, fetal fibroblasts showed an inhibition of their contractile capacity whereas adult fibroblasts further contracted gels. The contractile response was similar for all isoforms of TGFbeta although TGFbeta3 always had the strongest effect. We considered that the regulation of cell contractile capacity by TGFbeta may be dependent on receptor expression for this cytokine, on myofibroblast differentiation of the cells, or in cell links with matrix. Since TGFbeta receptor analysis did not show differences in receptor affinity, we studied the expression of alpha-smooth muscle (SM) actin, a fibroblast contractile marker and of three integrins, the cell surface receptors specific of the attachment of the fibroblasts with collagen matrix. We observed that the expression of alpha-SM actin and alpha3 and beta1 integrin subunits was increased when TGFbeta was added to the medium of adult fibroblasts whereas the levels of the alpha1 and alpha2 subunits were unchanged. In contrast, fetal fibroblasts treated with TGFbeta showed a decrease of alpha1, alpha2, and beta1 integrin expression but no change in alpha3 integrin and in alpha-SM actin expression. These results indicate that intrinsic differences between fetal and adult fibroblasts might explain their opposite responses to TGFbeta stimuli. The variations in their alpha-SM actin and integrin expression patterns represent potentially important mechanisms used by fetal fibroblasts to regulate their response to cytokines, and likely contribute to the resultant differences in the quality of wound repair.

Protein-tyrosine kinase Pyk2 mediates endothelin-induced p38 MAPK activation in glomerular mesangial cells

Endothelin-1 (ET-1), a member of a family of 21 amino acid peptides possessing vasoconstrictor properties, is known to stimulate mesangial cell proliferation. In this study, ET-1 (100 nm) induced a rapid activation of p21(ras) in human glomerular mesangial cells (HMC). Inhibition of Src family tyrosine kinase activation with [4-Amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine] or chelation of intracellular free calcium with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester significantly decreased ET-1dependent p21(ras) activation and suggested the involvement of the cytoplasmic proline-rich tyrosine kinase Pyk2. We have observed that Pyk2 was expressed in HMC and was tyrosine-phosphorylated within 5 min of ET-1 treatment. ET-1-induced activation of Pyk2 was further confirmed using phospho-specific anti-Pyk2 antibodies. Surprisingly, Src kinase activity was required upstream of ET-1-induced autophosphorylation of Pyk2. To determine whether Pyk2 autophosphorylation mediated ET-1-dependent p21(ras) activation, adenovirus-mediated transfer was employed to express a dominant-negative form of Pyk2 (CRNK). CRNK expression inhibited ET-1-induced endogenous Pyk2 autophosphorylation, but did not abolish ET-1-mediated increases in GTP-bound p21(ras) levels. ET-1-induced activation of the p38 MAPK (but not ERK) pathway was inhibited in HMC and in rat glomerular mesangial cells expressing the dominant-negative form of Pyk2. These findings suggest that the engagement of Pyk2 is important for ET-1-mediated p38 MAPK activation and hence the biological effect of this peptide in mesangial cells.

Localization of specific binding sites for 125I-TGF-beta1 to fenestrated endothelium in bone and anastomosing capillary networks in enamel organ suggests a role for TGF-beta1 in angiogenesis

Previous studies have shown endothelial cells to be a major target for endocrine TGF-beta in several soft tissues in the normal growing rat. The potent effect of TGF-beta1 on bone formation prompted us to analyze in detail the localization of specific binding sites for endocrine TGF-beta in hard tissues. At 2.5 minutes after injection of 125I-TGF-beta1, specific binding, as demonstrated by quantitative radioautography, was localized to fenestrated endothelium participating in angiogenesis in the vascular invasion region of the growth plate in bone as well as to anatomizing capillary networks in the maturation zone of the enamel organ. At 15 minutes after injection, the bound ligand was internalized into endocytic vesicles of endothelial cells. In bone, quantitation revealed significant differences in receptor density between endothelia undergoing proliferation vs those in a state of elongation and anastomosis with neighboring endothelial cells. In the rat incisor, specific binding of 125I-TGF-beta1 to endothelium correlated with increased formation of anastomotic capillary networks. These studies identify differential specific binding sites of 125I-TGF-beta1 in angiogenically active endothelium, providing an important link between TGF-beta1, the endothelium, and hard tissue development.

Endoglin expression on human microvascular endothelial cells association with betaglycan and formation of higher order complexes with TGF-beta signalling receptors

Transforming growth factor-beta (TGF-beta) plays an important role in angiogenesis and vascular function. Endoglin, a transmembrane TGF-beta binding protein, is highly expressed on vascular endothelial cells and is the target gene for the hereditary haemorrhagic telangiectasia type I (HHT1), a dominantly inherited vascular disorder. The specific function of endoglin responsible for HHT1 is believed to involve alterations in TGF-beta responses. The initial interactions on the cell surface between endoglin and TGF-beta receptors may be an important mechanism by which endoglin modulates TGF-beta signalling, and thereby responses. Here it is shown that on human microvascular endothelial cells, endoglin is co-expressed and is associated with betaglycan, a TGF-beta accessory receptor with which endoglin shares limited amino acid homology. This complex formation may occur in either a ligand-dependent or a ligand-independent manner. In addition, the occurrence of three higher order complexes containing endoglin, type II and/or type I TGF-beta receptors, on these cells is demonstrated. Our findings suggest that endoglin may modify TGF-beta signalling by interacting with both betaglycan and the TGF-beta signalling receptors at physiological receptor concentrations and ratios.

Ectodomain cleavage and shedding of the type III transforming growth factor-beta receptor in lung membranes effect of temperature, ligand binding and membrane solubilization

Previous studies from our laboratory [Philip, A. & O'Connor-McCourt, M. D. (1991) J. Biol. Chem. 266, 22290--22296] have shown that the lung exhibited the highest uptake of circulating [125I]-transforming growth factor-beta1 (TGF-beta1) on a per gram basis. This observation, together with the lack of information on TGF-beta receptor expression in the lung, prompted us to attempt to characterize TGF-beta receptors in this tissue. In the present report we show that the type III TGF-beta receptor is the most abundant TGF-beta binding protein in rat lung membranes and that it exhibits a 10-fold higher affinity for TGF-beta2 than for TGF-beta1. We observed that the majority of the type III receptor population in lung membranes is cleaved at a site in the central portion of the ectodomain, the resulting two fragments (95 kDa and 58 kDa) being held together by disulfide bonds. Furthermore, we demonstrate that a soluble form of the ectodomain of the type III receptor is shed from rat lung membranes in an efficient manner, with protease cleavage occurring at a site close to the transmembrane domain. This shedding is controllable by temperature, thus providing a system to study the mechanism of ectodomain release. Using this system, we show that the shedding is inhibited by prior ligand binding and by membrane solubilization. The identification of a membrane preparation which exhibits controllable and quantitative release of the type III receptor ectodomain provides a unique cell-free system for further studies of the mechanism of shedding of the type III TGF-beta receptor ectodomain.

TGF-beta receptor expression on human keratinocytes: a 150 kDa GPI-anchored TGF-beta1 binding protein forms a heteromeric complex with type I and type II receptors

Keratinocytes play a critical role in re-epithelialization during wound healing, and alterations in keratinocyte proliferation and function are associated with the development of various skin diseases. Although it is well documented that TGF-beta has profound effects on keratinocyte growth and function, there is a paucity of information on the types, isoform specificity and complex formation of TGF-beta receptors on keratinocytes. Here, we report that in addition to the types I, II, and III TGF-beta receptors, early passage adult and neonatal human keratinocytes display a cell surface glycosylphosphatidylinositol (GPI)-anchored 150 kDa TGF-beta1 binding protein. The identities of the four proteins were confirmed on the basis of their affinity for TGF-beta isoforms, immunoprecipitation with specific anti-receptor antibodies, sensitivity to phosphatidylinositol specific phospholipase C and dithiothreitol, and 2-dimensional electrophoresis. Interestingly, the antitype I TGF-beta receptor antibody immunoprecipitated not only the type I receptor, but also the type II receptor and the 150 kDa component, suggesting that the 150 kDa component form heteromeric complexes with the signalling receptors. In addition, two-dimensional (nonreducing/reducing) electrophoresis confirmed the occurrence of a heterotrimeric complex consisting of the 150 kDa TGF-beta1 binding protein, the type II receptor, and the type I receptor. This technique also demonstrated the occurrence of types I and II heterodimers and type I homodimers of TGF-beta receptors on keratinocytes, supporting the heterotetrameric model of TGF-beta signalling proposed using mutant cells and cells transfected to overexpress these receptors. The keratinocytes responded to TGF-beta by markedly downregulating all four TGF-beta binding proteins and by potently inhibiting DNA synthesis. The demonstration that the 150 kDa GPI-anchored TGF-beta1 binding protein forms a heteromeric complex with the TGF-beta signalling receptors suggests that this GPI-anchored protein may modify TGF-beta signalling in human keratinocytes.

Transforming growth factor-beta receptor expression on human skin fibroblasts: dimeric complex formation of type I and type II receptors and identification of glycosyl phosphatidylinositol-anchored transforming growth factor-beta binding proteins

Fibroblasts play a critical role in wound repair and in the development of fibrotic diseases, and transforming growth factor-beta (TGF-beta) has been shown to profoundly modulate fibroblast function. However, there is limited information on the TGF-beta receptor types, isoform specificity, and complex formation in skin fibroblasts. Here, we report that normal adult human skin fibroblasts display two isoform-specific, cell surface glycosyl phosphatidylinositol (GPI)-anchored, TGF-beta binding proteins in addition to the type I, II, and III TGF-beta receptors. The identities of these proteins are confirmed on the basis of their affinity for TGF-beta isoforms, immunoprecipitation with specific antireceptor antibodies, and other biochemical analyses. Immunoprecipitation results also indicated oligomeric complex formation between type I and II and between type II and III TGF-beta receptors. Furthermore, by using affinity labeling and two-dimensional electrophoresis, we demonstrate the occurrence of type I and II heterodimers and type I homodimers of TGF-beta receptors on these cells. Because the type I receptor does not bind TGF-beta in the absence of type II receptor, these results indicate that one molecule of TGF-beta induces the formation of a heterooligomeric complex containing more than one molecule each of type I and II TGF-beta receptors on these cells. These cells respond to TGF-beta by markedly down-regulating all five binding proteins and by potently augmenting DNA synthesis. These results allow the expansion of the proposed heteromeric TGF-beta receptor signaling paradigm using mutant cells that are unresponsive to TGF-beta and cell lines that have been transfected to overexpress these receptors, to include normal TGF-beta-responsive cells. In addition, the definition of TGF-beta receptor profiles in human skin fibroblasts provides important information for studying their alterations in these cells in various skin diseases.

Angiogenesis and growth factor expression in a model of transmyocardial revascularization

BACKGROUND

The mechanism by which transmyocardial revascularization (TMR) exerts a beneficial effect remains unknown. We hypothesize that the myocardial punctures of TMR cause a myocardial injury, leading to an angiogenic response mediated by a number of growth factors.

METHODS

Fifty-three rats underwent ligation of the left coronary artery. Group I (n = 25) served as controls, whereas group II (n = 28) underwent concomitant TMR by the creation of six transmural channels with a 25-gauge needle in the ischemic zone. Surviving animals in both groups were sacrificed at intervals of 1, 2, 4, and 8 weeks (n = 5 in each subgroup). Immunohistochemistry in the infarct areas was performed for factor VIII to assess vascular density. Immunohistochemistry using specific antibodies was also performed for transforming growth factor-beta, basic-fibroblast growth factor, and vasoendothelial growth factor. Growth factor expression was quantitated by comparing areas of staining (in mm2) with computerized morphometric analysis.

RESULTS

Mortality was similar in both groups (5/25 versus 8/28; not significant). Group II had significantly greater vascular density than group I (5.65 versus 4.06 vessels/high-power field; p < 0.001), with a peak at 1 week postoperatively (9.12 versus 5.56 vessels/high-power field; p < 0.0001) in both groups. Overall, levels of both transforming growth factor-beta and basic-fibroblast growth factor were significantly higher in the TMR group compared with the control group (0.207 versus 0.141 mm2/mm2, p < 0.05; and 0.125 versus 0.099 mm2/ mm2, p < 0.05).

CONCLUSIONS

This model of TMR is associated with a significant angiogenic response, which appears to be mediated by the release of certain angiogenic growth factors such as transforming growth factor-beta and basic-fibroblast growth factor. With the long-term patency of laser-created myocardial channels in clinical TMR increasingly in doubt, its mechanism of myocardial revascularization may be similar to that observed in our model.