In situ embedding of cell monolayers cultured on plastic surfaces for electron microscopy

Embedding cell monolayers to investigate nanoparticle-plasmalemma interactions at transmission electron microscopy

Transmission electron microscopy is the technique of choice to visualize the spatial relationships between nanoconstructs and cells and especially to monitor the uptake process of nanomaterials. It is therefore crucial that the cell surface be preserved in its integrity, to obtain reliable ultrastructural evidence: the plasmalemma represents the biological barrier the nanomaterials have to cross, and the mode of membrane-nanoconstruct interaction is responsible for the intracellular fate of the nanomaterials. In this paper, we describe a simple and inexpensive method to process cell monolayers for ultrastructural morphology and immunocytochemistry, ensuring consistent preservation of the cell surface and of the occurring interactions with nanoparticles of different chemical composition.

Crucial factor causing collapse and aggregation of cultured cells in epon resin

Ultrastructural artifacts regarding collapse and aggregation of cultured cells have been problematic, especially when investigated apoptotic cells. The infiltration process during sample preparation is considered to be the most crucial factor for this problem. This study was conducted using two culture systems: a suspension culture system of human T-lymphocyte Jurkat cells and rabbit mature dendritic cells and a monolayer culture system of human lung macrophages, human breast cancer cells (A-546 cells) and cat bone-invasive gingival cancer cells (sccf3 cells). Fixation was conducted prior to removing or detaching the cells from the culture dishes. Initial infiltration with a 1 : 3 volume ratio of epon resin : propylene oxide was found to be the most crucial step among these cultured cells. The improved epon-resin infiltration method could eliminate the artifacts. Thus, differentiation between artifactual images and true images is highly possible.

SATB2 participates in regulation of menadione-induced apoptotic insults to osteoblasts

Special AT-rich sequence binding protein 2 (SATB2), a nuclear matrix attachment region-binding protein, can regulate embryonic development, cell differentiation, and cell survival. Previous studies showed that SATB2 is involved in osteoblast differentiation and skeletal development. In this study, we evaluated the role of SATB2 in oxidative stress-induced apoptotic insults to human osteoblast-like MG63 cells and mouse MC3T3-E1 cells. Exposure of MG63 cells to menadione increased intracellular reactive oxygen species levels in a concentration- and time-dependent manner. Simultaneously, menadione-induced oxidative stress triggered cell shrinkage and decreased cell viability. In addition, treatment of MG63 cells with menadione time-dependently decreased the mitochondrial membrane potential but enhanced caspase-3 activity. As a result, menadione-induced DNA fragmentation and cell apoptosis. As to the mechanism, exposure of MG63 cells to menadione amplified SATB2 messenger (m)RNA and protein expression in a time-dependent manner. Knockdown of translation of SATB2 mRNA using RNA interference led to chromatin disruption and nuclear damage. When MG63 cells and MC3T3-E1 cells were treated with SATB2 small interfering RNA, menadione-induced cell apoptosis was increased. We conclude that menadione causes oxidative stress in human osteoblasts and induces cellular apoptosis via a mitochondrion-caspase protease pathway. In addition, SATB2 may play a crucial role in protecting against oxidative stress-induced osteoblast apoptosis.

Tumour-associated E-cadherin mutations alter cellular morphology, decrease cellular adhesion and increase cellular motility

A major function of the cell-to-cell adhesion molecule E-cadherin is the maintenance of cell adhesion and tissue integrity. E-cadherin deficiency in tumours leads to changes in cell morphology and motility, so that E-cadherin is considered to be a suppressor of invasion. In this study we investigated the functional consequences of three tumour-associated gene mutations that affect the extracellular portion of E-cadherin: in-frame deletions of exons 8 or 9 and a point mutation in exon 8, as they were found in human gastric carcinomas. Human MDA-MB-435S breast carcinoma cells and mouse L fibroblasts were stably transfected with the wild-type and mutant cDNAs, and the resulting changes in localization of E-cadherin, cell morphology, strength of calcium-dependent aggregation as well as cell motility and actin cytoskeleton organization were studied. We found that cells transfected with wild-type E-cadherin showed an epitheloid morphology, while all cell lines expressing mutant E-cadherin exhibited more irregular cell shapes. Cells expressing E-cadherin mutated in exon 8 showed the most scattered appearance, whereas cells with deletion of exon 9 had an intermediate state. Mutant E-cadherins were localized to the lateral regions of cell-to-cell contact sites. Additionally, both exon 8-mutated E-cadherins showed apical and perinuclear localization, and actin filaments were drastically reduced. MDA-MB-435S cells with initial calcium-dependent cell aggregation exhibited decreased aggregation and, remarkably, increased cell motility, when mutant E-cadherin was expressed. Therefore, we conclude that these E-cadherin mutations may not simply affect cell adhesion but may act in a trans-dominant-active manner, i.e. lead to increased cell motility. Our study suggests that E-cadherin mutations affecting exons 8 or 9 are the cause of multiple morphological and functional disorders and could induce the scattered morphology and the invasive behaviour of diffuse type-gastric carcinomas.

Cooperative effect of TNFalpha, bFGF, and VEGF on the formation of tubular structures of human microvascular endothelial cells in a fibrin matrix. Role of urokinase activity

In angiogenesis associated with tissue repair and disease, fibrin and inflammatory mediators are often involved. We have used three-dimensional fibrin matrices to investigate the humoral requirements of human microvascular endothelial cells (hMVEC) to form capillary-like tubular structures. bFGF and VEGF165 were unable to induce tubular structures by themselves. Simultaneous addition of one or both of these factors with TNFalpha induced outgrowth of tubules, the effect being the strongest when bFGF, VEGF165, and TNFalpha were added simultaneously. Exogenously added u-PA, but not its nonproteolytic amino-terminal fragment, could replace TNFalpha, suggesting that TNFalpha-induced u-PA synthesis was involved. Soluble u-PA receptor (u-PAR) or antibodies that inhibited u-PA activity prevented the formation of tubular structures by 59-99%. epsilon-ACA and trasylol which inhibit the formation and activity of plasmin reduced the extent of tube formation by 71-95%. TNFalpha or u-PA did not induce tubular structures without additional growth factors. bFGF and VEGF165 enhanced of the u-PAR by 72 and 46%, but TNFalpha itself also increased u-PAR in hMVEC by 30%. Induction of mitogenesis was not the major contribution of bFGF and VEGF165 because the cell number did not change significantly in the presence of TNFalpha, and tyrphostin A47, which inhibited mitosis completely, reduced the formation of tubular structures only by 28-36%. These data show that induction of cell-bound u-PA activity by the cytokine TNFalpha is required in addition to the angiogenic factors VEGF165 and/or bFGF to induce in vitro formation of capillary-like structures by hMVEC in fibrin matrices. These data may provide insight in the mechanism of angiogenesis as occurs in pathological conditions.