Biomedical subjects

Jeong-Hwa Baek

Publications and source records attributed to Jeong-Hwa Baek.

10 recordsLinked to original sources

PubMed2006

Nano-fibrous scaffolding promotes osteoblast differentiation and biomineralization.

Nano-fibrous poly(L-lactic acid) (PLLA) scaffolds with interconnected pores were developed under the hypothesis that nano-fibrous scaffolding would mimic a morphological function of collagen fibrils to create a more favorable microenvironment for cells versus solid-walled scaffolds. In this study, an in vitro system was used to examine biological properties of the nano-fibrous scaffolds compared with those of solid-walled scaffolds for their potential use in bone tissue engineering. Biomineralization was enhanced substantially on the nano-fibrous scaffolds compared to solid-walled scaffolds, and this was confirmed by von Kossa staining, measurement of calcium contents, and transmission electron microscopy. In support of this finding, osteoblasts cultured on the nano-fibrous scaffolds exhibited higher alkaline phosphatase activity and an earlier and enhanced expression of the osteoblast phenotype versus solid-walled scaffolds. Most notable were the increases in runx2 protein and in bone sialoprotein mRNA in cells cultured on nano-fibrous scaffolds versus solid-walled scaffolds. At the day 1 of culture, alpha2 and beta1 integrins as well as alphav and beta3 integrins were highly expressed on the surface of cells seeded on nano-fibrous scaffolds, and linked to this were higher levels of phospho-Paxillin and phospho-FAK in cell lysates. In contrast, cells seeded on solid-walled scaffolds expressed significantly lower levels of these integrins, phospho-Paxillin, and phospho-FAK. To further examine the role of nano-fibrous architecture, we inhibited the formation of collagen fibrils by adding 3,4-dehydroproline to cultures and then assayed cells for expression of alpha2 integrin. Cells seeded on nano-fibrous scaffolds sustained expression of alpha2 integrin in the presence of dehydroproline, while suppression of alpha2 integrin was evident in cells seeded on solid-walled scaffolds. These results provide initial evidence that synthetic nano fibers may exhibit certain properties that are comparable to natural collagen fibers, and thus, the nano-fibrous architecture may serve as a superior scaffolding versus solid-walled architecture for promoting osteoblast differentiation and biomineralization.

Animals↗

PubMed2006

TGF-beta2 stimulates cranial suture closure through activation of the Erk-MAPK pathway.

Cranial sutures are important growth sites of the skull. During suture closure, the dura mater is one of the most important sources of various positive and negative regulatory signals. Previous results indicate that TGF-beta2 from dura mater strongly accelerates suture closure, however, its exact regulatory mechanism is still unclear. In this study, we confirmed that removal of dura mater in calvarial organ culture strongly accelerates sagittal suture closure and that this effect is further enhanced by TGF-beta2 treatment. TGF-beta2 stimulated cell proliferation in the MC3T3-E1 cell line. Similarly, it stimulated the proliferation of cells in the sutural space in calvarial organ culture. Furthermore, TGF-beta2-mediated enhanced cell proliferation and suture closure were almost completely inhibited by an Erk-MAPK blocker, PD98059. These results indicate that TGF-beta2-induced activation of Erk-MAPK is an important signaling component that stimulates cell proliferation to enrich osteoprogenitor cells, thereby promoting their differentiation into osteoblasts to achieve a rapid calvarial bone expansion.

Animals↗

PubMed2006

Tetraspanin CD9 regulates osteoclastogenesis via regulation of p44/42 MAPK activity.

Tetraspanin CD9 has been shown to regulate cell-cell fusion in sperm-egg fusion and myotube formation. However, the role of CD9 in osteoclast, another multinucleated cell type, is not still clear. Therefore, we investigated the role of CD9 in osteoclast differentiation. CD9 was expressed in osteoclast lineage cells and its expression level increased during the progression of RANKL-induced osteoclastogenesis. KMC8, a neutralizing antibody specific to CD9, significantly suppressed RANKL-induced multinucleated osteoclast formation and the mRNA expression of osteoclast differentiation marker genes. To define CD9-regulated osteoclastogenic signaling pathway, MAPK pathways were examined. KMC8 induced long-term phosphorylation of p44/42 MAPK, but not of p38 MAPK. Constitutive activation of p44/42 MAPK by overexpressing constitutive-active mutant of MEK1 almost completely blocked osteoclast differentiation. Taken together, these results suggest that CD9 expressed on osteoclast lineage cells might positively regulate osteoclastogenesis via the regulation of p44/42 MAPK activity.

Animals↗

PubMed2006

Regulation of histone acetyltransferase activity of p300 and PCAF by proto-oncogene protein DEK.

The proto-oncogene protein DEK has been implicated in the t(6;9) chromosomal translocation associated with a subtype of acute myelogenous leukemia (AML), which results in the formation of a DEK-CAN fusion protein. Histone acetylation is an important post-translational modification which is involved in transcriptional regulation. In this study, we report that the acidic domain containing protein DEK interacts with histones and exerts a potent inhibitory effect on both p300 and PCAF-mediated histone acetyltransferase activity and transcription. Using chromatin immunoprecipitation assays, we have demonstrated that the recruitment of DEK to the appropriate promoter induces the histone H3 and H4 hypoacetylation of chromatin. Collectively, our data illustrate the important regulatory role played by protein DEK in transcriptional regulation, and suggest that transcription-regulating acidic domain regions may play a role in leukemogenesis.

Acetylation↗

PubMed2006

Bone-related gene profiles in developing calvaria.

Generating a comprehensive understanding of osteogenesis-related gene profiles is very important in the development of new treatments for osteopenic conditions. Developing calvaria undergoes a typical intramembranous bone-forming process. To identify genes associated with osteoblast differentiation, we isolated total RNAs from parietal bones, that represent active osteoblasts, and sutural mesenchyme, that represents osteoprogenitor cells, and comprehensively analyzed their gene expression profiles using an oligo-based Affymetrix microarray chip containing 22,690 probes. About 2100 genes with "Present" calls had more than 2-fold higher expression in bone compared to sutures while 73 of these genes had more than 8-fold expression. Some of these genes are already known to be bone-related biomarkers: VitD receptor, bone sialoprotein, osteocalcin, osteopontin, MMP13, etc. Eight genes were selected and subjected to confirmation by quantitative real-time RT-PCR analyses. All the genes tested showed higher expression in bones, ranging from 5- to 140-fold. Several of these genes are ESTs while others are already known but their functions in osteogenesis were not previously known. Most genes of the BMP and FGF families probed in the Genechip analysis were more highly expressed in bone tissues compared to suture. All differentially-expressed Runx and Dlx family genes also showed higher expression in bone. These results imply that our data is valid and can be used as a good standard for the mining of osteogenesis-related genes.

Animals↗

PubMed2006

Dexamethasone inhibits the formation of multinucleated osteoclasts via down-regulation of beta3 integrin expression.

Although glucocorticoids are known to affect osteoclast differentiation and function, there have been conflicting reports about the effect of glucocorticoids on osteoclast formation, leading to the assumption that microenvironment and cell type influence their action. We explored the effect of the synthetic glucocorticoid analog dexamethasone on the formation of osteoclasts. Dexamethasone inhibited the formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated osteoclasts without affecting the formation of TRAP-positive mononuclear cells in a coculture of mouse osteoblasts and bone marrow cells. Dexamethasone did not inhibit mRNA expression levels of the receptor activator of nuclear factor-kappaB ligand and osteoprotegerin, the essential regulators of osteoclastogenesis. Dexamethasone down-regulated the expression of beta3 integrin mRNA and protein but did not alter expression of other osteoclast differentiation marker genes. Both dexamethasone and echistatin, a beta3 integrin function blocker, inhibited TRAP-positive multinucleated osteoclast formation but not TRAP-positive mononuclear cell formation. These results suggest that dexamethasone inhibits the formation of multinucleated osteoclasts, at least in part, through the down-regulation of beta3 integrin, which plays an important role in the formation of multinucleated osteoclasts.

Animals↗

PubMed2003

Determination of specific interactions between glucose ligand carrying polymer and glucose transporter type-1 (GLUT-1) using different cell types.

In order to develop a biomimetic polymer for cell recognition, poly [3-O-(4'-vinylbenzyl)-D-glucose] (PVG) and different types of glucose transport (GLUT)-carrying cells, namely, HepG2 cells (GLUT-1), 3T3-L1 fibroblast cells (GLUT-1 and GLUT-4), and MIN6 cells (GLUT-2), were tested for specific interaction. To clarify the nature of interaction between PVG and the different cell types, rhodamine-B isothiocyanate (RITC)-labeled polymers were used to prove and visualize the interactions. In this study, we found that labeled polymer strongly binds to HepG2 cells. The fluorescence intensity of PVG with in the presence of HepG2 cells was found to be stronger than that of 3T3-L1 fibroblast cells (0.11 +/- 0.05) and MIN6 cells, which carry GLUT-2 (0.028 +/- 0.01); a confocal laser microscopic study confirmed this interaction. To confirm the specificity of the interaction mediated by GLUT, the cells were pretreated with phloretin, an inhibitor of GLUT-1, before adding RITC-labeled PVG polymer to the cell culture medium. This treatment suppressed the interaction of PVG with HepG2 cells and partially suppressed its interaction with 3T3-L1 fibroblast cells.

Animals↗

PubMed2003

High extracellular Ca2+ alone stimulates osteoclast formation but inhibits in the presence of other osteoclastogenic factors.

High ambient Ca2+ at bone resorption sites have been implicated to play an important role in the regulation of bone remodeling. The present study was performed to clarify the mode of high extracellular Ca2+ (Ca2+(e))-induced modulation of osteoclastogenesis and the expression of receptor activator of nuclear factor-kappaB ligand (RANKL) and osteoprotegerin (OPG), thereby to define its role in osteoclast formation. Mouse bone marrow cells were cocultured with osteoblastic cells in the absence or presence of osteoclastogenic factors such as 1,25-dihydroxyvitaminD3 (1,25-(OH)2vitD3)and macrophage colony-stimulating factor/soluble RANKL. Ca2+ concentration in media (1.8 mM) was adjusted to 3, 5, 7 or 10 mM. Osteoclast formation was confirmed by the appearance of tartrate-resistant acid phosphatase (TRAP)-positive multinuclear cells and the expression of osteoclast phenotypic markers (calcitonin receptor, vitronectin receptor, cathepsin K, matrix metalloproteinase-9, carbonic anhydrase 2). High Ca2+(e) alone significantly stimulated osteoclast formation in a dose-dependent manner. However, in the presence of highly osteoclastogenic factors, high Ca2+(e) significantly inhibited osteoclastogenesis. High Ca2+(e) alone continuously up-regulated RANKL expression while only transiently increased OPG expression. However, in the presence of 1,25-(OH)(2)vitD(3), high Ca2+(e) did not change the 1,25-(OH)2vitD3-induced RANKL expression while increased OPG expression. Taken together, these findings suggest that high Ca2+(e) alone increase osteoclastogenesis but inhibit in the presence of other osteoclastogenic factors. In addition, high CaCa2+(e)-induced osteoclastogenesis may be mediated by osteoblasts via up-regulation of RANKL expression. Meanwhile up-regulated OPG might participate in the inhibitory effect of high Ca2+(e) on 1,25-(OH)2vitD3-induced osteoclastogenesis.

Animals↗

PubMed2003

p44/42 MAPK activation is necessary for receptor activator of nuclear factor-kappaB ligand induction by high extracellular calcium.

Although extracellular calcium (Ca(2+)(o)) has been suggested to modulate bone remodeling, the exact mechanism is unclear. This study was performed to explore the signaling pathways of high Ca(2+)(o) that are responsible for controlling the expression of receptor activator of NF-kappaB ligand (RANKL) in mouse osteoblastic cells. As previously reported, high Ca(2+)(o) increased RANKL expression. However, the G protein-coupled Ca(2+)(o)-sensing receptor (CaSR) was not detected in the primary cultured mouse osteoblastic cell. The inhibition of the pertussis-sensitive G protein, phospholipase C, protein kinase C, intracellular calcium mobilization, p38 MAPK, or phosphoinositide 3-kinase did not block RANKL induction caused by high Ca(2+)(o). In contrast, the inhibition of p44/42 MAPK pathway reduced the RANKL expression induced by high Ca(2+)(o). Moreover, high Ca(2+)(o) activated p44/42 MAPK and MEK1/2. These results suggest that RANKL induction by high Ca(2+)(o) might not be mediated by CaSR and its putative downstream signaling pathways, but the pathway employing p44/42 MAPK is involved in the high Ca(2+)(o)-induced RANKL expression in mouse osteoblastic cells.

Animals↗

PubMed2003

Common genes responsible for differentiation and senescence of human mucosal and epidermal keratinocytes.

Serial subcultures of normal human oral keratinocytes (NHOKs) and normal human epidermal keratinocytes (NHEKs) to the postmitotic stage result in terminal differentiation and replicative senescence. In order to investigate the common mode of differentiation and/or senescence between mucosal and epidermal keratinocytes, gene expression profiling on both NHOKs and NHEKs was performed by a cDNA microarray analysis. Primary NHOKs and NHEKs were serially subcultured, and the expression level of 3,063 genes was compared between the exponentially growing and senescent cultures. The senescent NHOKs and NHEKs highly expressed 55 and 37 genes, respectively. Among these genes, 16 genes were common in both NHOKs and NHEKs while the other genes were upregulated either in the NHOKs or in the NHEKs. Furthermore, the expression levels of the common genes did not change in the human diploid fibroblasts during the subcultures. These results suggest that subculture-induced differentiation and/or replicative senescence in NHOKs and NHEKs has similar characteristics, but that the pathways leading to these processes are distinct and keratinocyte specific.

Blotting, Northern↗