Spreading Shape and Area Regulate the Osteogenesis of Mesenchymal Stem Cells

BACKGROUND: Mesenchymal stem cells (MSCs) have strong self-renewal ability and multiple differentiation potential. Some studies confirmed that spreading shape and area of single MSCs influence cell differentiation, but few studies focused on the effect of the circularity of cell shape on the osteogenic differentiation of MSCs with a confined area during osteogenic process.METHODS: In the present study, MSCs were seeded on a micropatterned island with a spreading area lower than that of a freely spreading area. The patterns had circularities of 1.0 or 0.4, respectively, and areas of 314, 628, or 1256 µm² . After the cells were grown on a micropatterned surface for 1 or 3 days, cell apoptosis and F-actin were stained and analyzed. In addition, the expression of β-catenin and three osteogenic differentiation markers were immunofluorescently stained and analyzed, respectively.RESULTS: Of these MSCs, the ones with star-like shapes and large areas promoted the expression of osteogenic differentiation markers and the survival of cells. The expression of F-actin and its cytosolic distribution or orientation also correlated with the spreading shape and area. When actin polymerization was inhibited by cytochalasin D, the shape-regulated differentiation and apoptosis of MSCs with the confined spreading area were abolished.CONCLUSION: This study demonstrated that a spreading shape of low circularity and a larger spreading area are beneficial to the survival and osteogenic differentiation of individual MSCs, which may be regulated through the cytosolic expression and distribution of F-actin.

Yap1 plays a protective role in suppressing free fatty acid-induced apoptosis and promoting beta-cell survival

Mammalian pancreatic β-cells play a pivotal role in development and glucose homeostasis through the production and secretion of insulin. Functional failure or decrease in β-cell number leads to type 2 diabetes (T2D). Despite the physiological importance of β-cells, the viability of β-cells is often challenged mainly due to its poor ability to adapt to their changing microenvironment. One of the factors that negatively affect β-cell viability is high concentration of free fatty acids (FFAs) such as palmitate. In this work, we demonstrated that Yes-associated protein (Yap1) is activated when β-cells are treated with palmitate. Our loss- and gain-of-function analyses using rodent insulinoma cell lines revealed that Yap1 suppresses palmitate-induced apoptosis in β-cells without regulating their proliferation. We also found that upon palmitate treatment, re-arrangement of F-actin mediates Yap1 activation. Palmitate treatment increases expression of one of the Yap1 target genes, connective tissue growth factor (CTGF). Our gain-of-function analysis with CTGF suggests CTGF may be the downstream factor of Yap1 in the protective mechanism against FFA-induced apoptosis.

Staurosporine Induces ROS-Mediated Process Formation in Human Gingival Fibroblasts and Rat Cortical Astrocytes

In the present study, we investigated the effect of staurosporine on the formation of cellular processes in human gingival fibroblasts and rat astrocytes. Staurosporine caused a rapid induction of process formation in human gingival fibroblasts and rat astrocytes in a concentration dependent manner. The process formation of human gingival fibroblasts and rat astrocytes was prevented by the pretreatment with N-acetylcysteine, suggesting that staurosporine-induced ROS production was responsible for the process formation. Colchicine, a microtubule depolymerizing agent, inhibited the staurosporine-induced process formation, whereas cytochalasin D, an actin filament breakdown agent, failed to suppress the formation of cellular processes. This result indicated that polymerization of microtubule, and not actin filament, was responsible for the formation of cellular processes induced by staurosporine. In support of this hypothesis, Western blot analysis was conducted using anti-tubulin antibody, and the results showed that the amount of polymerized microtubule was increased by the treatment with staurosporine while that of depolymerized beta-tubulin in soluble fraction was decreased. These results indicate that staurosporine induces ROS-mediated, microtubule-dependent formation of cellular processes in human gingival fibroblasts and rat astrocytes.

The relationship between c-fos gene and filamentous actin cytoskeleton in MG-63 osteoblasts under cyclic tensile stress / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the relationship between c-fos gene and filamentous actin (F-actin) in MG-63 osteoblasts under cyclic tensile stress.</p><p><b>METHODS</b>MG-63 osteoblasts were subjected to cyclic tensile stress (0.5 Hz, 2 000 microstrain) for 3, 6, and 12 h. The changes of c-fos gene were investigated by fluorescent quantitation polymerase chain reaction. Then the best loading time group was screened as the experimental group compared with 0 h group. The changes of F-actin and c-fos were investigated with or without cytochalasin D treatment.</p><p><b>RESULTS</b>Cyclic tensile stress induced high expression of c-fos mRNA, and peaked at 3 h. After loading, F-actin had a structure reorganization, but had no change in expression. After cytochalasin D treatment, the formation of stress fibers and the fluorescence intensity of F-actin cytoskeleton significantly reduced, meanwhile the c-fos mRNA expression was inhibited.</p><p><b>CONCLUSION</b>After loading, there is only structure reorganization for F-actin, and the expression has not any change. That means the remodeling F-actin is the existing one. F-actin reorganization is an important part in c-fos gene expression induced by stress.</p>

Cytochalasin D, a tropical fungal metabolite, inhibits CT26 tumor growth and angiogenesis

OBJECTIVE@#To investigate whether cytochalasin D can induce antitumor activities in a tumor model.@*METHODS@#Murine CT26 colorectal carcinoma cells were cultured in vitro and cytochalasin D was used as a cytotoxic agent to detect its capabilities of inhibiting CT26 cell proliferation and inducing cell apoptosis by MTT and a TUNEL-based apoptosis assay. Murine CT26 tumor model was established to observe the tumor growth and survival time. Tumor tissues were used to detect the microvessel density by immunohistochemistry. In addition, alginate encapsulated tumor cell assay was used to quantify the tumor angiogenesis in vivo.@*RESULTS@#Cytochalasin D inhibited CT26 tumor cell proliferation in time and dose dependent manner and induced significant CT26 cell apoptosis, which almost reached the level induced by the positive control nuclease. The optimum effective dose of cytochalasin D for in vivo therapy was about 50 mg/kg. Cytochalasin D in vivo treatment significantly inhibited tumor growth and prolonged the survival times in CT26 tumor-bearing mice. The results of immunohistochemistry analysis and alginate encapsulation assay indicated that the cytochalasin D could effectively inhibited tumor angiogenesis.@*CONCLUSIONS@#Cytochalasin D inhibits CT26 tumor growth potentially through inhibition of cell proliferation, induction of cell apoptosis and suppression of tumor angiogenesis.

Aggregatibacter actinomycetemcomitans Strongly Stimulates Endothelial Cells to Produce Monocyte Chemoattractant Protein-1 and Interleukin-8

Aggregatibacter actinomycetemcomitans is the most important etiologic agent of aggressive periodontitis and can interact with endothelial cells. Monocyte chemoattractant protein-1 (MCP-1) and interleukin-8 (IL-8) are chemokines, playing important roles in periodontal pathogenesis. In our current study, the effects of A. actinomycetemcomitans on the production of MCP-1 and IL-8 by human umbilical vein endothelial cells (HUVEC) were investigated. A. actinomycetemcomitans strongly induced the gene expression and protein release of both MCP-1 and IL-8 in a dose- and time-dependent manner. Dead A. actinomycetemcomitans cells were as effective as live bacteria in this induction. Treatment of HUVEC with cytochalasin D, an inhibitor of endocytosis, did not affect the mRNA up-regulation of MCP-1 and IL-8 by A. actinomycetemcomitans. However, genistein, an inhibitor of protein tyrosine kinases, substantially inhibited the MCP-1 and IL-8 production by A. actinomycetemcomitans, whereas pharmacological inhibition of each of three members of mitogen-activated protein (MAP) kinase family had little effect. Furthermore, gel shift assays showed that A. actinomycetemcomitans induces a biphasic activation (early at 1-2 h and late at 8-16 h) of nuclear factor-kappaB (NF-kappaB) and an early brief activation (0.5-2 h) of activator protein-1 (AP-1). Activation of canonical NF-kappaB pathway (IkappaB kinase activation and IkappaB-alpha degradation) was also demonstrated in these experiments. Although lipopolysaccharide from A. actinomycetemcomitans also induced NF-kappaB activation, this activation profile over time differed from that of live A. actinomycetemcomitans. These results suggest that the expression of MCP-1 and IL-8 is potently increased by A. actinomycetemcomitans in endothelial cells, and that the viability of A. actinomycetemcomitans and bacterial internalization are not required for this effect, whereas the activation of protein tyrosine kinase(s), NF-kappaB, and AP-1 appears to play important roles. The secretion of high levels of MCP-1 and IL-8 resulting from interactions of A. actinomycetemcomitans with endothelial cells may thus contribute to the pathogenesis of aggressive periodontitis.

Staurosporine and cytochalasin D induce chondrogenesis by regulation of actin dynamics in different way

Actin cytoskeleton has been known to control and/or be associated with chondrogenesis. Staurosporine and cytochalasin D modulate actin cytoskeleton and affect chondrogenesis. However, the underlying mechanisms for actin dynamics regulation by these agents are not known well. In the present study, we investigate the effect of staurosporine and cytochalasin D on the actin dynamics as well as possible regulatory mechanisms of actin cytoskeleton modulation. Staurosporine and cytochalasin D have different effects on actin stress fibers in that staurosporine dissolved actin stress fibers while cytochalasin D disrupted them in both stress forming cells and stress fiber-formed cells. Increase in the G-/F-actin ratio either by dissolution or disruption of actin stress fiber is critical for the chondrogenic differentiation. Cytochalasin D reduced the phosphorylation of cofilin, whereas staurosporine showed little effect on cofilin phosphorylation. Either staurosporine or cytochalasin D had little effect on the phosphorylation of myosin light chain. These results suggest that staurosporine and cytochalasin D employ different mechanisms for the regulation of actin dynamics and provide evidence that removal of actin stress fibers is crucial for the chondrogenic differentiation.

The Role of Intracellular Receptor NODs for Cytokine Production by Macrophages Infected with Mycobacterium leprae

The nucleotide-oligomerization domain (NOD) proteins are members of the NOD-like receptor (NLR) family, which are intracellular and cytoplasmic receptors. We analyzed the role of NODs for cytokine production by macrophages infected with intracellular pathogen M. leprae, the causative agent of leprosy. Production of pro-inflammatory cytokines such as IL-1beta and TNF-alpha was inhibited in the presence of cytochalasin D, an agent blocking phagocytosis, suggesting that intracellular signaling was, partially, required for macrophage activation to M. leprae infection. Next, we investigated the role of NOD1 and NOD2 proteins on NF-kappaB activation and cytokine expression. Treatment with M. leprae significantly increased NF-kappaB activation and expression of TNF-alpha and IL-1beta in NOD1- and NOD2-transfected cells. Interestingly, their activation and expression were inhibited by cytochalasin D, suggesting that stimulation of NOD proteins may be associated with the enhancement of cytokine production in host to M. leprae.

Mechanisms Underlying Enterococcus faecalis-Induced Tumor Necrosis Factor-alpha Production in Macrophages

Enterococcus faecalis, a gram-positive bacterium, has been implicated in endodontic infections, particularly in chronic apical periodontitis. Proinflammatory cytokines, including tumor necrosis factor-alpha (TNF-alpha), are involved in the pathogenesis of these apical lesions. E. faecalis has been reported to stimulate macrophages to produce TNF-alpha. The present study investigated the mechanisms involved in TNF-alpha production by a murine macrophage cell line, RAW 264.7 in response to exposure to E. faecalis. Both live and heat-killed E. faecalis induced high levels of gene expression and protein release of TNF-alpha. Treatment of RAW 264.7 cells with cytochalasin D, an inhibitor of endocytosis, prevented the mRNA up-regulation of TNF-alpha by E. faecalis. In addition, antioxidant treatment reduced TNF-alpha production to baseline levels. Inhibition of extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein (MAP) kinase also significantly attenuated E. faecalis-induced TNF-alpha expression by RAW 264.7 cells. Furthermore, activation of NF-kappaB and AP-1 in RAW 264.7 cells was also stimulated by E. faecalis. These results suggest that the phagocytic uptake of bacteria is necessary for the induction of TNF-alpha in E. faecalis-stimulated macrophages, and that the underlying intracellular signaling pathways involve reactive oxygen species, ERK, p38 MAP kinase, NF-kappaB, and AP-1.

Mechanisms Underlying Enterococcus faecalis-Induced Tumor Necrosis Factor-alpha Production in Macrophages

Enterococcus faecalis, a gram-positive bacterium, has been implicated in endodontic infections, particularly in chronic apical periodontitis. Proinflammatory cytokines, including tumor necrosis factor-alpha (TNF-alpha), are involved in the pathogenesis of these apical lesions. E. faecalis has been reported to stimulate macrophages to produce TNF-alpha. The present study investigated the mechanisms involved in TNF-alpha production by a murine macrophage cell line, RAW 264.7 in response to exposure to E. faecalis. Both live and heat-killed E. faecalis induced high levels of gene expression and protein release of TNF-alpha. Treatment of RAW 264.7 cells with cytochalasin D, an inhibitor of endocytosis, prevented the mRNA up-regulation of TNF-alpha by E. faecalis. In addition, antioxidant treatment reduced TNF-alpha production to baseline levels. Inhibition of extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein (MAP) kinase also significantly attenuated E. faecalis-induced TNF-alpha expression by RAW 264.7 cells. Furthermore, activation of NF-kappaB and AP-1 in RAW 264.7 cells was also stimulated by E. faecalis. These results suggest that the phagocytic uptake of bacteria is necessary for the induction of TNF-alpha in E. faecalis-stimulated macrophages, and that the underlying intracellular signaling pathways involve reactive oxygen species, ERK, p38 MAP kinase, NF-kappaB, and AP-1.

Effect of cytoskeleton integrity on the expression of c-fos in osteoblasts induced by fluid shear stress / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the effect of cytoskeleton integrity on the expression of c-fos gene in osteoblasts induced by fluid shear stress.</p><p><b>METHODS</b>BALB/c mouse primary osteoblasts were divided into four groups (according to fluid shear stress loaded or not and cytochalasin D used or not). The Tagman probe real-time PCR and immunofluorescence were performed to detect the expression levels of c-fos mRNA, c-fos protein and cytoskeleton, respectively. The data were analysed using two-way ANOVA.</p><p><b>RESULTS</b>In control group and cytochalasin D group, fluid shear stress could significantly increase the expression levels of c-fos mRNA (0.1637 +/- 0.0303 and 0.0104 +/- 0.0070, respectively) and protein (177.14 +/- 9.37 and 150.95 +/- 6.17, respectively) in osteoblasts, compared with the unloaded osteoblasts of the control group and the cytochalasin D group (0.0057 +/- 0.0021 and 0.0032 +/- 0.0014, respectively for c-fos mRNA, and 117.96 +/- 4.11 and 119.77 +/- 5.19, respectively for protein, P < 0.05). Induced by the fluid shear stress, the expression levels of c-fos mRNA and protein in cytochalasin D group were lower than control group, and the difference had statistical significance (P < 0.05).</p><p><b>CONCLUSIONS</b>The cytoskeleton integrity in osteoblasts was essential to the expression of c-fos gene induced by fluid shear stress.</p>

CD98 activation increases surface expression and clusteringof beta 1 integrins in MCF-7 cells through FAK/Src- and cytoskeleton-independent mechanisms

CD98, a disulfide-linked 125-kDa heterodimeric type II transmembrane glycoprotein, regulates beta 1 integrin- mediated cell adhesion. However, the molecular mechanisms underlying CD98-mediated activation of beta 1 integrin are presently unclear. In this study, the effects of CD98 signaling on the expression and clustering of beta 1 integrin were investigated. Activation of CD98 augmented surface expression of beta 1 integrin on MCF-7 cells. Cross-linking CD98 induced clustering of beta 1 integrins. Inhibition of phosphorylation of focal adhesion kimase (FAK) by PP2, an inhibitor of Src family kinase, reduced cell-extracellular matrix adhesion, but not surface expression and clustering of beta1 integrin on MCF-7 cells. This result was confirmed by over-expression of dominant negative forms of FAK. In addition, phalloidin or cytochalasin D inhibited CD98-mediated induction of cell-ECM adhesion, but not surface expression and clustering of b1 integrins. The inhibitory effects of PP2, cytochalasin D or phalloidin on CD98-stimulated cell adhesion were diminished by pretreatment of cells with Mn2+, which is shown to induce conformational change of integrins. These results provide the first evidence that CD98 activation increases not only beta1 integrin affinity but also its surface expression and clustering and the latter is independent of FAK/Src and cytoskeleton.

CD98 Activation Increases the Invasion of Human Breast Carcinoma MCF-7 Cells / 체질인류학회지

CD98, a disulfide-linked 125-kDa heterodimeric type II transmembrane glycoprotein, regulates the func-tions of beta1 integrin, suggesting that it may play a role in tumor cell invasion. In this study, the effects of CD98 signaling on the adhesion and invasion of tumor cells were investigated. The expression of CD98 on MCF-7 human breast carcinoma cells was confirmed by immunohistochemistry. The effects of CD98 activation on the adhesion to extracellular matrix (ECM) and invasion of MCF-7 cells were determined by adhesion assay and cell invasion assay. Dominant negative forms of focal adhesion kinase (FAK) were transiently transfected into MCF-7 cells using liposome reagents. CD98 stimulation increased the adhesion of MCF-7 cells to fibronectin, laminin and collagen IV. Activation of CD98 augmented the invasion rate of MCF-7 cells through ECM. EDTA or a function-blocking anti-beta1 integrin mAb suppressed the effect of CD98 on invasiveness. Inhibition of phosphorylation of FAK by PP2, an inhibitor of Src family kinase, reduced CD98-induced invasion of MCF-7 cells. This result was confirmed by over-expression of dominant negative forms of FAK. In addition, cytochalasin D or phalloidin inhibited CD98-mediated induction of tumor cell invasion. Inhibitory effects of PP2, cytochalasin D or phalloidin on CD98-stimulated invasion of MCF-7 cells were diminished by pretreatment of cells with Mn++, which is shown to induce conformational change of beta1 intgerin. These results provide the first evidence that CD98 activation increases tumor cell invasion by activating beta1 integrin affinity, and that FAK phosphorylation and subsequent cytoskeletal reorganization may be essential for CD98-mediated regulation of cell motility.

Efeitos de inibidores da biossíntese do ergosterol, de proteínas quinases e do citoesqueleto em Trypanosoma cruzi / Effect of sterol biosynthesis inhibitors, of kinases proteins and the cytoskeleton in Trypanosoma cruzi

Trypanosoma cruzi é o agente etiológico da doença de Chagas. Novos compostos vêm sendo desenvolvidos tendo como alvo a biossíntese e função de esteróis, já que T. cruzi requer esteróis endógenos específicos para o crescimento e sobrevivência. Inibidores da biossíntese do ergosterol (SBIs) são drogas comumente usadas contra doenças fúngicas... Ambas as drogas inibiram a multiplicação dos parasitos, com IC50/72 h de 24,3 and 4,5 mM, respectivamente. O segundo grupo de drogas estudadas neste trabalho foram WSP 413, WSP 414, WSP 415, WSP 488, WSP 501 e WSP 561, inibidores específicos da D24(25)-esterol metiltransferase. Todas as drogas inibiram a multiplicação dos parasitos a concentrações muito baixas, com valores de IC50/72 h de 0,53, 0,59, 0,53, 0,48, 0,44 e 0,48 mM, respectivamente. Os dois inibidores da SQS e WSP 488, WSP 501 e WSP 561 induziram mudanças morfológicas drásticas nos parasitos incluindo (a) destacamento de um dos folhetos da membrana, formando bolhas, (b) destacamento da membrana do corpo celular e do flagelo dos microtúbulos subpeliculares e axonemais, respectivamente, (c) aumento da bolsa flagelar, (d) aparecimento de um vacúolo localizado próximo à bolsa flagelar, que parece corresponder ao vacúolo contrátil, (e) inchaço da mitocôndria, com o aparecimento de estruturas concêntricas formadas pelas invaginações da membrana mitocondrial interna, (f) alterações no núcleo de algumas células, onde a cromatina aparece em grumos, como descrito para células apoptóticas, e (g) bloqueio do processo de divisão celular... WSP 414 e BPQ-OH foram testados em células infectadas com amastigotas intracelulares de T. cruzi. WSP 414 a 1 mM praticamente eliminou a infecção das células, e os parasitos sobreviventes não se diferenciaram em tripomastigotas. BPQ-OH teve pouco efeito sobre a infecção. Ambas as drogas causaram alterações morfológicas nos parasitos sem afetar a célula hospedeira. O terceiro grupo de drogas testadas neste trabalho foram inibidores de proteínas quinases. Staurosporina, genisteína e wortmanina inibiram o crescimento dos parasitos... O quarto e último grupo de drogas testadas foram os inibidores de polimerização e despolimerização de actina e microtúbulos. Foram testadas três drogas: jasplakinolida, citocalasina D e nocodazol. Todas as três drogas inibiram o crescimento dos parasitos e a divisão celular, mas tiveram poucos efeitos sobre a ultraestrutura dos parasitos.

Adesäo e invasäo de Paracoccidioides brasiliensis em cultura de células vero / Adherence and invasion of Paraccidioides brasiliensis (isolate 18) to Vero cells

A capacidade de aderir e invadir tecidos do hospedeiro tem sido imputada como importante mecanismo de patogenicidade. Neste trabalho foi estudado o processo de adesäo e invasäo de P. brasiliensis amostra 18, fase L, as culturas celulares da linhagem Vero, usando várias técnicas de microscopia. P. brasiliensis aderiu às células Vero após 30 minutos e formas intracitoplasmáticas apareceram após 5 horas de infecçäo. As células Vero apresentaram modificaçöes na presença do fungo, comportando-se como célula fagocítica, formando protusöes e projeçöes citoplasmáticas em dedo de luva, na tentativa de interiorizar o fungo. O fungo aderido às células exibiu padräo de reconhecimento semelhante ao de culturas com os soros anti-"cell-free" e anti-gp 43. Ambos os antígenos distribuíram-se regularmente na parede fúngica, de maneira específica, e a gp 43 foi mais evidente na conexäo entre as células mäe e filha e também nas proximidades da interaçäo fungo-célula. Células de P. brasiliensis näo foram observadas intracelularmente após tratamento com citocalasina D, sugerindo que um dos mecanismos que o fungo utiliza durante o processo de invasäo e via microfilamentos de actina. Por meio deste trabalho, informaçöes relevantes sobre os processos de adesäo e p emvolvimento do citoesqueleto durante a invasäo puderam ser demonstradas, podendo auxiliar no entendimento da patogênese de P. brasiliensis.

Possibility of involvement of Porphyromonas gingivalis in coronary heart disease

Porphyromonas gingivalis has been implicated in periodontal diseases. Accumulating evidence suggests that cardiovascular disease is the most prevalent medical problem in patients with periodontal diseases. In order to check the possibility that P. gingivalis is involved in coronary heart disease, the present study was performed to observe P. gingivalis adherence and invasion of human coronary artery endothelial cells (HCAEC) and production of cytokines and growth factors by HCAEC upon P. gingivalis infection. 3H-labeled P. gingivalis 381 was incubated with HCAEC for 90 min. The radioactivity of the washed HCAEC was a measure of the absorbed (adhering and invading) P. gingivalis. The absorption radioactivity of the HCAEC infected by P. gingivalis was determined to be 59.58% of the input bacterial cells. In contrast, the absorption radioactivity of the cells infected by S. gordonii Challis which was employed as a control was negligible (0.59%). DPG3, a P. gingivalis mutant defective of fimbriae, appeared to be impaired to some extent in capability of adherence/invasion as compared to that of the parental strain 381, showing 43.04% of the absorption radioactivity. The absorption radioactivity of the HCAEC infected by P. gingivalis 381 in the presence of excessive fimbriae at the concentrations of 50 mug and 100 mug/ml was 57.27 and 45.44%, respectively. Invasion of HCAEC by P. gingivalis 381 was observed by an antibiotic (metronidazole) protection assay and transmission electron microscopy (TEM). In the antibiotic protection assay, invasion by the bacterium was measured to be 0.73, 1.09, and 1.51% of the input bacterial cells after incubation for 30, 60, and 90 min, respectively. Invasion by DPG3 was shown to be 0.16% after 90-min incubation. In comparison of invasion efficiency at 90 min of the incubation, the invasion efficiency of DPG3 was 0.37% while that of its parental strain 381 was 2.54%. The immunoblot analysis revealed fimbriae of P. gingivalis did not interact with the surface of HCAEC. These results suggest that fimbriae are not the major contribution to the adherence of P. gingivalis to HCAEC but may be important in the invasion of HCAEC by the bacterium. The presence of cytochalasin D (1 mug/ml) and staurosporine (1 muM) reduced the invasion of HCAEC by P. gingivalis 381 by 78.86 and 53.76%, respectively, indicating that cytoskeletal rearrangement and protein kinase of HCAEC are essential for the invasion. Infection of P. gingivalis induced HCAEC to increase the production of TNF-alpha by 60.6%. At 90 min of the incubation, the HCAEC infected with P. gingivalis cells was apparently atypical in the shape, showing loss of the nuclear membrane and subcellular organelles. The overall results suggest that P. gingivalis may cause coronary heart disease by adhering to and invading endothelial cells, and subsequently damaging the cells.

Morphological Changes of Cultured Rat Hepatocytes Induced by Phalloidin and Cytochalasin D / 대한해부학회지

The microfilaments of hepatocyte are distributed throughout the vicinity of cell membranes, especially numerous around the region of bile canaliculus, and provide the maintenance of cell shape, cellular wall tension, canalicular motility, the secretion for bile, etc. To evaluate the relationship between the microfilament and alteration of cell shape, we examined the morphological changes of cultured rat hepatocytes, following treatments with phalloidin or cytochalasin D with fluorescent and electron microscopes. 1. In the fluorescent micrographs, actin microfilament was distributed near the plasma membrane and bile canaliculus. 2. Both drugs, phalloidin or cytochalasin D, produce the cytoplasmic protrusions from the surface. Their shapes were pedunculated with narrow neck or bulged with broad base, respectively. 3. In the phalloidin treated group, cytoplasmic protrusion was seperated from the internal cytoplasm by microfila-ments networks at the narrow base. In contrast, in the cytochalasin D treated group, cytoplasm was bulged with broad base and kept in direct continuity with the canalicular ectoplasm. 4. Pericanalicular ectoplasm of phalloidin treated group was widened and accumulated with microfilaments. But, bile canaliculus of cytochalasin D treated group was markedly dilated and devoid of microvilli, and the ectoplasm was almost disappeared. Considering above results, dysfunction of microfilaments leads to the structural changes and inhibition of bile secretion of hepatocytes.

Ultrastructural Changes of the Cultured Hepatocytes in Microfilamentous Dysfunction induced by Drugs / 대한해부학회지

To examine the role of actin microfilaments which are located at beneath the plasma membrane, we observed the ultrastructural changes of rat hepatocyte induced by alteration of the microfilamentous integrity. The isolated hepatocytes from Sprague-Dawley were cultured in the L-15 medium containing phalloidin (agent that cause polymerization of actin) or cytochalasin D (agent that cause depolymerization of actin) for 30 min, 1 hour, 2 hours, 4 hours, 10 hours and 20 hours, respectively. The results observed with scanning and transmission electron microscope were as follows. 1. Following the alteration of actin microfilaments, bile canaliculi were dilated and devoid of microvilli. In phalloidin treated group, the thickening of microfilamentous ectoplasm was more marked than that of cytochalasin D treated group. Whereas, the dilation of bile canaliculi was more marked in cytochalasin D group. 2. Both drugs, phalloidin or cytochalasin D, produced the alteration of cell shape to form cytoplasmic protrusions at the cell surface. In the phalloidin treated group, protrusions were pedunculated, and the microfilament networks were accumulated at the narrow neck region. 3. In cytochalasin D treated group, no microfilament barrier was seen at the broad base of protrusion which exhibit direct continuity with the internal cytoplasm. 4. Single hepatocyte tend to recover their structural integrity as those in vivo. The new bile canaliculus was sealed off at the intercellular space by tight junctions, and intercellular contacts were established by the junctional complexes. The results demonstrated that excessive accumulation or depletion of microfilaments induced by phalloidin or cytochalasin D altered the cell shape different, respectively. The microfilaments of ectoplasm play an important role in the maintenance of the structural integrity of cultured hepatocytes.

Role of the microtubular system in platelet aggregation

1. Four structural systems are involved in the process of platelet activation that leads to aggregation: 1) the membrane system, i.e., the cytoplasmic membrane, the dense tubular structure and the open canalicular structure; 2) alpha and dense granules; 3) the peripheral microtubular coils; 4) the microfibrillar meshwork of actin-myosin bundles. 2. We added four compounds which modify cell ultrastructure to normal platelet-rich plasma to analyze the behavior of the structural systems of platelet activation: vinblastine (100 micrograms/ml) and cimetidine (100 micrograms/ml) that act on the membrane system, ticlopidine (200 micrograms/ml) and colchicine (100 micrograms/ml) that affect primarily the microtubular structure, cytochalasin B (30 micrograms/ml) and phorbol myristate acetate (100 ng/ml) that act upon the granular system, and cytochalasin D (30 micrograms/ml) and concanavalin A (50 micrograms/ml) that influence the microfibrillar structure. Platelet aggregation was stimulated by epinephrine or thrombin. 3. Cimetidine and ticlopidine prevented aggregation. However, neither substance affected the microtubular structure. Colchicine and cytochalasin B only partially impaired aggregation, because pieces of microtubules remained in the presence of these substances. The other substances did not present anti-aggregant activity and did not preserve the microtubules. 4. We infer that the disappearance of the microtubules is necessary to produce aggregation. When they remain intact no aggregation is produced, even though the other structural systems are activated.

The Effects of Cytoskeletons on the Cultured Human Melanocytes

BACKGROUND: Cytoskeletons, the complex set of protein fibers found in the cytoplasm, have important roles in the movement of cells and subcellular structures and the generation of shapes. Melanocytes have numerous dendritic processes which are in direct contact with many keratinocytes and transfer the melanosomes into the neighboring keratinocytes. Little information is available on the structure and function of cytoskeletons, and the effects of ultraviolet light on the cytoskeletons of the melanocytes. OBJECTIVE: The purpose of this study was to investigate the general cytoskeletal system of cultured melanocytes and to find out the effects of the cytoskeletal antagonists and UVB on the cytoskeletal system of the cultured melanocytes. METHODS: Melanocytes were cultured from adult foreskin and then exposed to various cytoskeletal antagonists and UVB radiation. The changes of the cultured melanocytes were evaluated by using phase contrast microscopy, immunofluorescence staining methods and electron microscopic examinations. RESULTS: Colchicine produced shortening of dendrites, stellate cellular contour and granular fluorescence of the tubulin. Cytochalasin D produced round cellular contour and granular fluorescence of the actin. Acrylamide produced disorganization of cytoplasmic constituents, but no specific fluorescent change was observed. Colchicine also had inhibitory effects on the vimentin. Cellular responses induced by these agents were reversible. UVB caused morphological changes of the melanocytes, but their effects on the organization of the cytoskeletal system could not be detected in this method. CONCLUSION: Microtubules are related to the dendritic movement of the melanocytes. Vimentin may be involved in the transfer of cellular organelles, probably including the melanosomes. Cytoskeletal antagonists produce their characteristic morphological changes to cultured melanocytes.