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Biomedical subjects

S L Cheng

Publications and source records attributed to S L Cheng.

At least 19 recordsLinked to original sources
PubMed2004

Randomization of heavily damaged regions in annealed low energy Ge(+)-implanted (001)Si.

Apparent growth of amorphous layers during low temperature annealing was observed in low energy Ge(+)-implanted (001)Si by high-resolution transmission electron microscopy. The occurrence of abnormal growth is due to the randomization of heavily damaged regions beneath the original amorphous/crystalline interfaces. The randomization process is attributed to the strain, incurred by the presence of a high density of large Ge atoms in the heavily damaged Si substrate, relaxation to lower the free energy of the systems. The randomization upon annealing may be fruitfully applied to minimize the transient enhanced diffusion in shallow junction formation.

Journal Article↗
PubMed2004

Genetic polymorphism of epoxide hydrolase and glutathione S-transferase in COPD.

Genetic susceptibility to the development of chronic obstructive pulmonary disease (COPD) might depend on variation in the activities of enzymes that detoxify cigarette smoke products, such as microsomal epoxide hydrolase (mEPHX) and glutathione S-transferase (GST). It was investigated whether polymorphisms in these genes had any association with susceptibility to COPD and COPD severity. The genotypes of 184 patients with COPD and 212 control subjects were determined by polymerase chain reaction followed by restriction fragment length polymorphism analysis of the mEPHX, GSTM1, GSTT1 and GSTP1 genes. All subjects were smokers or exsmokers. The proportion of GSTM1-null genotypes was significantly higher in patients with COPD than in control subjects (61.4 versus 42.5%). No differences were observed in the frequency of polymorphic genotypes for mEPHX, GSTT1 and GSTP1. During combined analysis of genetic polymorphisms for mEPHX, GSTM1 and GSTP1, it was found that there are strong indicators for susceptibility to COPD (genotype combination with at least one mutant mEPHX exon-3 allele (histidine 113), GSTM1 null and homozygous for the GSTPI isoleucine 105 allele). The frequencies of homozygous mutant alleles of mEPHX exon 3 and the GSTMI-null genotype were significantly higher in patients with severe COPD (forced expiratory volume in one second of <35% of the predicted value). It is proposed that the combination of genetic variants including at least one mutant microsomal epoxide hydrolase exon-3 allele and glutathione S-transferase M1-null and homozygous isoleucine 105 glutathione S-transferase P1 genotypes are significant indicators of susceptibility to chronic obstructive pulmonary disease in the Taiwanese population. In addition, the homozygous variant of microsomal epoxide hydrolase exon 3 and the glutathione S-transferase M1-null genotype are independent risk factors for developing severe chronic obstructive pulmonary disease.

Case-Control Studies↗
PubMed2002

Transmission electron microscopy investigation of the formation of C54-TiSi(2) phase on stressed (001)Si.

The effects of stress on the formation of C54-TiSi2 phase in Ti/(001)Si samples have been investigated by high-resolution transmission electron microscopy in conjunction with auto-correlation function (ACF) analysis. The C54-TiSi2 phase transformation temperature in tensily stressed samples was found to be lowered by about 100 degrees C than that in compressively stressed samples. The thickness of amorphous interlayers (a-interlayers) between Ti metal thin films and Si substrates was found to be thicker and thinner in the tensily and compressively stressed Si samples, respectively. Furthermore, the thicker a-interlayer was found to consist of a higher density of crystallites from the ACF analysis. With a higher density of crystallites in the a-interlayer, the grain size of C49-TiSi2 was reduced since more nucleation sites are available for the formation of C49-TiSi2. The small grain size of C49-TiSi2 in turn enhances the formation of C54-TiSi2. As a result, the phase transformation of C49- to C54-TiSi2 is enhanced by the tensile stress present in silicon substrates.

Journal Article↗
PubMed2002

Structural evolution in amorphous silicon and germanium thin films.

The structural evolution in amorphous silicon and germanium thin films has been investigated by high-resolution transmission electron microscopy (HRTEM) in conjunction with autocorrelation function (ACF) analysis. The results established that the structure of as-deposited semiconductor films is of a high density of nanocrystallites embedded in the amorphous matrix. In addition, from ACF analysis, the structure of a-Ge is more ordered than that of a-Si. The density of embedded nanocrystallites in amorphous films was found to diminish with annealing temperature first, then to increase. The conclusions also corroborate well with the results of diminished medium-range order in annealed amorphous films determined previously by a variable coherence microscopy method.

Alloys↗
PubMed2001

Sustained activation of the extracellular signal-regulated kinase pathway is required for extracellular calcium stimulation of human osteoblast proliferation.

Elevated levels of [Ca(2+)](o) in bone milieu as a result of the resorptive action of osteoclasts are implicated in promoting proliferation and migration of osteoblasts during bone remodeling. However, mitogenic effects of [Ca(2+)](o) have only been shown in some, but not all, clonal osteoblast-like cells, and the molecular mechanisms underlying [Ca(2+)](o)-induced mitogenic signaling are largely unknown. In this study we demonstrated for the first time that [Ca(2+)](o) stimulated proliferation of primary human osteoblasts and selectively activated extracellular signal-regulated kinases (ERKs). Neither p38 mitogen-activated protein (MAP) kinase nor stress-activated protein kinase was activated by [Ca(2+)](o). Treatment of human osteoblasts with a MAP kinase kinase inhibitor, PD98059, impaired both basal and [Ca(2+)](o)-stimulated phosphorylation of ERKs and also reduced both basal and [Ca(2+)](o)-stimulated proliferation. [Ca(2+)](o) treatment resulted in two distinctive phases of ERK activation: an acute phase and a sustained phase. An inhibition time course revealed that it was the sustained phase, not the acute phase, that was critical for [Ca(2+)](o)-stimulated osteoblast proliferation. Our results demonstrate that mitogenic responsiveness to [Ca(2+)](o) is present in primary human osteoblasts and is mediated via prolonged activation of the MAP kinase kinase/ERK signal pathway.

3T3 Cells↗
PubMed2001

Efficacy of inhaled human insulin in type 1 diabetes mellitus: a randomised proof-of-concept study.

BACKGROUND: Effective glycaemic control in type 1 diabetes mellitus usually requires two or more insulin injections daily. Inhaled intrapulmonary delivery of insulin offers a potential new way to deliver meal-related insulin, eliminating the need for preprandial injections. METHODS: 73 patients with type 1 diabetes mellitus were studied in an open-label, proof-of-concept, parallel-group randomised trial. Patients in the experimental group received preprandial inhaled insulin plus a bedtime subcutaneous ultralente insulin injection. Patients in the control group received their usual insulin regimen of two to three injections per day. Participants monitored their blood glucose four times daily, and adjusted insulin doses weekly to achieve preprandial glucose targets of 5.6-8.9 mmol/L. The primary outcome measure was change in glycosylated haemoglobin (HbA1c) after 12 weeks. Secondary outcomes were fasting and postprandial glucose response to a mixed meal; hypoglycaemia frequency and severity; pulmonary function; and patients' satisfaction. FINDINGS: Changes in HbA1c were indistinguishable between groups (difference 0.2% [95% CI -0.2 to 0.5]). Changes in fasting and postprandial glucose concentrations, and occurrence and severity of hypoglycaemia were also similar between groups. Inhaled insulin was well tolerated and had no effect on pulmonary function (ie, spirometry, lung volumes, diffusion capacity, and oxygen saturation). INTERPRETATION: This proof-of-concept study shows that preprandial insulin can be given by inhalation in individuals with insulin-deficient type 1 diabetes as a less invasive alternative to conventional preprandial insulin injections.

Administration, Inhalation↗
PubMed2001

Erk is essential for growth, differentiation, integrin expression, and cell function in human osteoblastic cells.

Extracellular signal-regulated kinases (Erks), members of the mitogen-activated protein kinase superfamily, play an important role in cell proliferation and differentiation. In this study we employed a dominant negative approach to determine the role of Erks in the regulation of human osteoblastic cell function. Human osteoblastic cells were transduced with a pseudotyped retrovirus encoding either a mutated Erk1 protein with a dominant negative action against both Erk1 and Erk2 (Erk1DN cells) or the LacZ protein (LacZ cells) as a control. Both basal and growth factor-stimulated MAPK activity and cell proliferation were inhibited in Erk1DN cells. Expression of Erk1DN protein suppressed both osteoblast differentiation and matrix mineralization by decreasing alkaline phosphatase activity and the deposition of bone matrix proteins. Cell adhesion to collagen, osteopontin, and vitronectin was decreased in Erk1DN cells as compared with LacZ cells. Cell spreading and migration on these matrices were also inhibited. In Erk1DN cells, expression of alphabeta(1), alpha(v)beta(3), and alpha(v)beta(5) integrins on the surface was decreased. Metabolic labeling indicated that the synthesis of these integrins was inhibited in Erk1DN cells. These data suggest that Erks are not only essential for the growth and differentiation of osteoblasts but also are important for osteoblast adhesion, spreading, migration, and integrin expression.

Alkaline Phosphatase↗
PubMed2001

Isoflavone transformation during soybean koji preparation and subsequent miso fermentation supplemented with ethanol and NaCl.

Soybeans were soaked with water for 4 h, steam-cooked, inoculated with the conidia of Aspergillus oryzae, and incubated for 3 days for koji preparation. The koji was then mixed with water-soaked and steam-cooked soybeans (1:2, w/w), ground into paste, and supplemented with 15% ethanol and 12.5% NaCl or 3% ethanol and 6% NaCl for miso fermentation at 30 degrees C. Daidzin, genistin, daidzein, and genistein contents were extracted from the lyophilized and pulverized soybean powder or from the miso homogenate by a developed one-tube procedure and analyzed with an HPLC. After water soaking, daidzein and genistein contents increased markedly, whereas daidzin and genistin contents decreased. Further increases of daidzein and genistein contents and decreases of daidzin and genistin contents were observed after koji mold growth. During fermentation, fungal and lactic acid bacterial (LAB) growth in the miso products was inhibited, whereas soluble protein contents increased much more rapidly in the low-salt miso products supplemented with 3% ethanol and 6% NaCl than the other products. When the 4- and 8-week-fermented miso products were cooked with tofu for sensory evaluation, flavor ratings of the low-salt products were higher than that of a popular commercial product. In both products, the most daidzins and genistins were hydrolyzed after 4 weeks of fermentation. The hydrolytic enzymes contributing to isoflavone transformation originated from soybeans after water soaking and from koji with mold growth. It was of merit that the low-salt fermented products were fairly acceptable in flavor rating and rich in daidzein and genistein contents after 4 weeks of fermentation.

Aspergillus oryzae↗
PubMed2001

The outcome of failed free flaps in head and neck and extremity reconstruction: what is next in the reconstructive ladder?

The indications for free flaps have been more or less clarified; however, the course of reconstruction after the failure of a free flap remains undetermined. Is it better to insist on one's initial choice, or should surgeons downgrade their reconstructive goals? To establish a preliminary guideline, this study was designed to retrospectively analyze the outcome of failed free-tissue transfers performed in the authors hospital. Over the past 8 years (1990 through 1997), 3361 head and neck and extremity reconstructions were performed by free-tissue transfers, excluding toe transplantations. Among these reconstructions, 1235 flaps (36.7 percent) were transferred to the head and neck region, and 2126 flaps (63.3 percent) to the extremities. A total of 101 failures (3.0 percent total plus the partial failure rate) were encountered. Forty-two failures occurred in the head and neck region, and 59 in the extremities. Evaluation of the cases revealed that one of three following approaches to handling the failure was taken: (1) a second free-tissue transfer; (2) a regional flap transfer; or (3) conservative management with debridement, wound care, and subsequent closure by secondary intention, whether by local flaps or skin grafting. In the head and neck region, 17 second free flaps (40 percent) and 15 regional flaps (36 percent) were transferred to salvage the reconstruction, whereas conservative management was undertaken in the remaining 10 cases (24 percent). In the extremities, 37 failures were treated conservatively (63 percent) in addition to 17 second free flaps (29 percent) and three regional flaps (5 percent) used to salvage the failed reconstruction. Two cases underwent amputation (3 percent). The average time elapsed between the failure and second free-tissue transfer was 12 days (range, 2 to 60 days) in the head and neck region and 18 days (range, 2 to 56 days) in the extremities. In a total of 34 second free-tissue transfers at both localizations, there were only three failures (9 percent). However, in the head and neck region, seven of the regional flaps transferred (47 percent) and four cases that were conservatively treated (40 percent) either failed or developed complications that lengthened the reconstruction period because of additional procedures. Six other free-tissue transfers had to be performed to manage these complicated cases. Conservative management was quite successful in the extremities; most patients' wounds healed, although more than one skin-graft procedure was required in 10 patients (27 percent). In conclusion, a second free-tissue transfer is, in general, a relatively more reliable and more effective procedure for the treatment of flap failure in the head and neck region, as well as failed vascularized bone flaps in the reconstruction of the extremities. Conservative treatment may be a simple and valid alternative to second (free) flaps for soft-tissue coverage in extremities with partial and even total losses.

Extremities↗
PubMed2001

Traction avulsion amputation of the major upper limb: a proposed new classification, guidelines for acute management, and strategies for secondary reconstruction.

Major replantation of a traction avulsion amputation is undertaken with the goal of not only the reestablishment of circulation, but also functional outcome. This type of amputation is characterized by different levels of soft-tissue divisions involving crushing, traction, and avulsion injuries to various structures. Between 1985 and 1998, 27 cases were referred for secondary reconstruction following amputation of the upper extremity involving both arm and forearm. Replantation was performed by at least 12 qualified plastic surgeons using different approaches and management, resulting in different outcomes. Initial replantation management significantly affects the later reconstruction. For comparing studies and prognostic implications, the authors propose a new classification according to the level of injury to muscles and innervated nerves: type I, amputation at or close to the musculotendinous aponeurosis with muscles remaining essentially intact; type II, amputation within the muscle bellies but with the proximal muscles still innervated; type III, amputation involving the motor nerve or neuromuscular junction, thereby causing total loss of muscle function; and type IV, amputation through the joint; i.e., disarticulation of the elbow or shoulder joint. Some patients required further reconstruction for functional restoration after replantation, but some did not. Through this retrospective study based on the proposed classification system, prospective guidelines for the management of different types of traction avulsion amputation are provided, including the value of replantation, length of bone shortening, primary or delayed muscle or nerve repair, necessity of fasciotomy, timing for using free tissue transfer for wound coverage, and the role of functioning free muscle transplantation for late reconstruction. The final functional outcome can also be anticipated prospectively through this classification system.

Adolescent↗
PubMed2001

Transient kinetic and dynamic interactions between verapamil and dofetilide, a class III antiarrhythmic.

Potential kinetic and dynamic interactions between the new class III antiarrhythmic dofetilide (D) and the calcium channel blocker verapamil (V) were determined in 12 young healthy male volunteers. A fixed sequence of V80 mg tid, placebo, D 0.5 mg bid, and D + V was given as matching active and placebo capsules. In steady-state conditions during combination treatment, a modest increase in mean (+/- SD) peak plasma concentration of dofetilide from 2.40 +/- 0.42 to 3.43 +/- 0.71 ng x ml(-1) (43% increase, p < 0.1) was noted. During the combination period, for the first 4 hours, mean AUC values for D increased from 7.4 +/- 1.0 (D alone) to 9.2 +/- 1.4 ng x h x ml(-1) (26% increase, p <0.1). No other significant pharmacokinetic interaction was seen. These transient changes were concurrent with trends for a dynamic interaction. The maximal mean increase in QT, over steady-state baseline values was 20 msec for D alone versus 26 msec during combination therapy. This relatively small interactive effect occurred only while peak plasma drug concentrations were developing at 1 to 3 hours after dosing and is probably caused by the known effect of verapamil to increase hepatic and portal bloodflow. In view of this interaction and the relationship between dofetilide plasma concentration and torsade, verapamil is contraindicated in patients receiving dofetilide.

Adult↗
PubMed2001

Bone mineralization and osteoblast differentiation are negatively modulated by integrin alpha(v)beta3.

Numerous bone matrix proteins can interact with alpha(v)-containing integrins including alpha(v)beta3. To elucidate the net effects of the interaction between these proteins and alpha(v)beta3 on osteoblast function, we developed a murine osteoblastic cell line that overexpressed human alpha(v)beta3. Human alpha(v)beta3-integrin was expressed on cell membrane, in which its presence did not alter the surface level of endogenous mouse alpha(v)beta3. The expressed human alpha(v)beta3 was functional because cell adhesion to osteopontin was increased and this increment was abolished by antibody against human alpha(v)beta3. The proliferation rate of cells overexpressing alpha(v)beta3 (alpha(v)beta3-cells) was increased whereas matrix mineralization was decreased. To elucidate the mechanisms leading to inhibition of matrix mineralization, the expression of proteins important for mineralization was analyzed. Alkaline phosphatase activity and the expression of osteocalcin, type I collagen, and bone sialoprotein (BSP) were decreased whereas osteopontin was stimulated in alpha(v)beta3-cells. The regulation of osteopontin, osteocalcin, and BSP expression was mediated via transcriptional mechanism because their promoter activities were altered. Examination of molecules involved in integrin signaling indicated that activator protein-1 (AP-1) and extracellular signal-regulated kinase (Erk) activities were enhanced whereas c-jun N-terminal kinase (JNK) activity was decreased in alpha(v)beta3-cells. The activity of p38 and the levels of focal adhesion kinase (FAK) and vinculin were not altered. Moreover, the adhesions of alpha(v)beta3-cells to type I collagen and fibronectin were inhibited, which was attributed to decreased beta1-integrin levels on cell surface. In conclusion, overexpressing alpha(v)beta3-integrin in osteoblasts stimulated cell proliferation but retarded differentiation, which were derived via altered integrin-matrix interactions, signal transduction, and matrix protein expression.

Alkaline Phosphatase↗
PubMed2001

In vitro and in vivo induction of bone formation using a recombinant adenoviral vector carrying the human BMP-2 gene.

It has been well established that bone morphogenetic protein-2 (BMP-2) can induce bone formation both in vivo and in vitro, although high concentrations (up to milligrams) of BMP-2 have been required to achieve this effect in vivo. Further, clinical applications are usually limited to a single dose at the time of implantation. In an attempt to prolong the transforming effect of BMP-2 we used a recombinant adenoviral vector carrying the human BMP-2 gene (Adv-BMP2) to transduce marrow-derived mesenchymal stem cells (MSC) of skeletally mature male New Zealand white rabbits. The pluripotential MSC were incubated with Adv-BMP2 overnight followed by culture in growth medium for 1 week. Assays on tissue cultures demonstrated that these Adv-BMP2 transduced MSC produced BMP-2 protein, differentiated into an osteoprogenitor line, and induced bone formation in vitro. These MSC had increased alkaline phosphatase activity, increased expression of type I collagen, osteopontin, and osteocalcin mRNA, and induced matrix mineralization compared with both non-transduced cells and cells transduced with a control adenoviral construct. To analyze the osteogenic potential in vivo, Adv-BMP2-transduced MSC were autologously implanted into the intertransverse process space between L5 and L6 of the donor rabbits. The production of new bone was demonstrated by radiographic examination 4 weeks later in areas implanted with cells transduced with Adv-BMP2, whereas no bone was evident at sites implanted with cells transduced with the control adenoviral construct. Histological examination further confirmed the presence of new bone formation. These accumulated data indicate that it is possible to successfully transduce mesenchymal stem cells with a recombinant adenoviral vector carrying the gene for BMP-2 such that these cells will produce BMP-2, differentiate into an osteoprogenitor line, and induce bone formation both in vitro and in vivo. Moreover, incubation of the Adv-BMP2-transduced cells for an additional 7 days in culture before transplantation enhances the success rate in bone formation (three out of three) as compared with our previous report (one out of five, Calcif Tissue Int 63:357-360, 1998).

Adenoviridae↗
PubMed2000

Transforming growth factor-beta up-regulates the beta 5 integrin subunit expression via Sp1 and Smad signaling.

Integrin-mediated cell-matrix interactions play important roles in regulating cell function. Since transforming growth factor-beta (TGF-beta) modulates many osteoblast activities, we hypothesized that the growth factor acts in part by modulating integrin expression. TGF-beta increased cell adhesion to vitronectin and up-regulated the surface level of alpha(v)beta(5) via increasing beta(5) protein synthesis by a transcriptional mechanism. Promoter activity analysis demonstrated that a TGF-beta-responsive element resides between nucleotides -63 and -44. Electrophoretic mobility shift assay and immunoprecipitation/Western studies indicated that the nuclear complex formed using the -66/-42 oligonucleotide contained both Sp1/Sp3 and Smad proteins. Since nuclear Sp1/Sp3 levels were not altered, whereas Smad levels were increased by TGF-beta, we investigated the roles of Smad proteins in the up-regulation of beta(5) gene activation. Co-transfection of cells with beta(5) promoter reporter construct and expression vectors for Smad3, Smad4, and Sp1 increased the stimulatory effect of TGF-beta. Furthermore, expression of dominant negative Smad3 or Smad4 in cells decreased or abolished the stimulation of beta(5) promoter activity by TGF-beta. Smad4 mutant also inhibited the up-regulation of surface beta(5) level by TGF-beta. Thus, TGF-beta increases expression of the integrin beta(5) gene by mechanisms involving Sp1/Sp3 and Smad transcription factors.

Animals↗
PubMed2000

Relative abundance of different cadherins defines differentiation of mesenchymal precursors into osteogenic, myogenic, or adipogenic pathways.

Cadherins, a family of cell-cell adhesion molecules, provide recognition signals that are important for cell sorting and aggregation during tissue development. This study was performed to determine whether distinct cadherin repertoires define tissue-specific lineages during differentiation of immature C3H10T1/2 and C2C12 mesenchymal cells. Both cell lines expressed mRNA for N-cadherin (N-cad), cadherin-11 (C11), and R-cadherin (R-cad). After induction of osteogenesis by recombinant human BMP-2 (rhBMP-2) treatment, steady state N-cad mRNA slightly increased in C3H10T1/2 cells. Likewise, the abundance of C11 mRNA increased in both cell lines, although the changes were more remarkable in C2C12 cells. By contrast, R-cad expression was almost shut off by rhBMP-2. The immature but committed osteoblastic MC3T3-E1 cells exhibited only minor changes in N-cad and C11 mRNA abundance after rhBMP-2 treatment. Whereas adipogenic differentiation was associated with a net decrease of N-cad and C11 expression in C3H10T1/2 cells, induction of myogenesis in C2C12 cells resulted in up-regulation of N-cad, while R-cad mRNA became undetectable in either case. Similarly, the adipocytic 3T3-L1 cells expressed very low levels of all cadherins when fully differentiated. Therefore, the repertoire of cadherins present in undifferentiated mesenchymal cells undergoes distinct changes during transition to mature cell phenotypes. Although neither N-cad nor C11 represent strict tissue-specific markers, the relative abundance of these mesenchymal cadherins defines lineage-specific signatures, perhaps providing recognition signals for aggregation and differentiation of committed precursors.

3T3 Cells↗
PubMed2000

Sp1/Sp3 and PU.1 differentially regulate beta(5) integrin gene expression in macrophages and osteoblasts.

Murine osteoclast precursors and osteoblasts express the integrin alpha(v)beta(5), the appearance of which on the cell surface is controlled by the beta(5), and not the alpha(v), subunit. Here, we show that a 173-base pair proximal region of the beta(5) promoter mediates beta(5) basal transcription in macrophage (osteoclast precursor)-like and osteoblast-like cells. DNase I footprinting reveal four regions (FP1-FP4) within the 173-base pair region, protected by macrophage nuclear extracts. In contrast, osteoblast nuclear extracts protect only FP1, FP2, and FP3. FP1, FP2, and FP3 bind Sp1 and Sp3 from both macrophage and osteoblast nuclear extracts. FP4 does not bind osteoblast proteins but binds PU.1 from macrophages. Transfection studies show that FP1 and FP2 Sp1/Sp3 sites act as enhancers in both MC3T3-E1 (osteoblast-like) and J774 (macrophage-like) cell lines, whereas the FP3 Sp1/Sp3 site serves as a silencer. Mutation of the FP2 Sp1/Sp3 site totally abolishes promoter activity in J774 cells, with only partial reduction in MC3T3-E1 cells. Finally, we demonstrate that PU.1 acts as a beta(5) silencer in J774 cells but plays no role in MC3T3-E1 cells. Thus, three Sp1/Sp3 sites regulate beta(5) gene expression in macrophages and osteoblast-like cells, with each element exhibiting cell-type and/or activation-suppression specificity.

Animals↗
PubMed2000

Regulation of alphaVbeta3 and alphaVbeta5 integrins by dexamethasone in normal human osteoblastic cells.

Long-term administration of pharmacological doses of glucocorticoids inhibits bone formation and results in osteoporosis. Since integrin-mediated cell-matrix interactions are essential for osteoblast function, we hypothesized that the detrimental effect of glucocorticoids on bone derived, at least in part, from decreased integrin-matrix interactions. Because alphavbeta3 and alphavbeta5 integrins can interact with several bone matrix proteins, we analyzed the effects of dexamethasone (Dex) on the expression of these integrins in normal human osteoblastic cells. We found adhesion of these cells to osteopontin and vitronectin to be dependent on alphavbeta3 and alphavbeta5, respectively; this ligand specificity was not altered by Dex. The effects of Dex on the adhesion of human osteoblastic cells to osteopontin and vitronectin were biphasic with an increase after 2 days, followed by a decrease after 8 days of treatment. Consistently, surface alphavbeta3 and alphavbeta5 integrins, which were increased after 2 days of Dex treatment, were decreased after 8 days. Similarly, total cellular alphav, beta3, and beta5 proteins, which were increased by Dex early in the culture, were diminished after 8 days. Metabolic labeling studies indicated that Dex exhibited biphasic regulation on the biosynthesis of alphavbeta5, with stimulation observed during the second day of treatment, followed by inhibition during the 8th day of exposure. By contrast, the biosynthesis of alphavbeta3 was inhibited by Dex on day 1 and remained inhibited on day 8. Analysis of the mRNA indicated that alphav and beta5 levels were increased by Dex during early exposure (1-3 days), followed by inhibition after prolonged exposure (>/=7 days). By contrast, Dex decreased beta3 mRNA level at all the time points analyzed. Consistently, Dex decreased beta3 promoter activity after 1 day and persisted over 8-day period. By contrast, Dex stimulated beta5 promoter activity after 1 or 2 days but had no effect after 8 days. To further evaluate mechanism(s) leading to the decreased integrin expression after prolonged Dex treatment, mRNA stability was analyzed. Dex was found to accelerate the degradation of alphav, beta3 and beta5 mRNA after an 8-day treatment. Thus, the regulation of alphavbeta3 was dependent on transcription and posttranscriptional events whereas the expression of alphavbeta5 was dependent mainly on posttranscriptional events after prolonged Dex treatment. In conclusion, Dex exhibited time-dependent regulation on the expression of alphavbeta3 and alphavbeta5 integrins in normal human osteoblastic cells. Short-term exposure to Dex increased the levels of alphavbeta3 and alphavbeta5 on the surface and cell adhesion to osteopontin and vitronectin whereas long-term exposure to Dex decreased the expression of both integrins and inhibited the cell adhesion to matrix proteins.

Antigens, CD↗