Biomedical subjects

Gabor Csucs

Publications and source records attributed to Gabor Csucs.

9 recordsLinked to original sources

PubMed2006

Surface engineering approaches to micropattern surfaces for cell-based assays.

The ability to produce patterns of single or multiple cells through precise surface engineering of cell culture substrates has promoted the development of cellular bioassays that provide entirely new insights into the factors that control cell adhesion to material surfaces, cell proliferation, differentiation and molecular signaling pathways. The ability to control shape and spreading of attached cells and cell-cell contacts through the form and dimension of the cell-adhesive patches with high precision is important. Commitment of stem cells to different specific lineages depends strongly on cell shape, implying that controlled microenvironments through engineered surfaces may not only be a valuable approach towards fundamental cell-biological studies, but also of great importance for the design of cell culture substrates for tissue engineering. Furthermore, cell patterning is an important tool for organizing cells on transducers for cell-based sensing and cell-based drug discovery concepts. From a material engineering standpoint, patterning approaches have greatly profited by combining microfabrication technologies, such as photolithography, with biochemical functionalization to present to the cells biological cues in spatially controlled regions where the background is rendered non-adhesive ("non-fouling") by suitable chemical modification. The focus of this review is on the surface engineering aspects of biologically motivated micropatterning of two-dimensional (flat) surfaces with the aim to provide an introductory overview and critical assessment of the many techniques described in the literature. In particular, the importance of non-fouling surface chemistries, the combination of hard and soft lithography with molecular assembly techniques as well as a number of less well known, but useful patterning approaches, including direct cell writing, are discussed.

Adsorption↗

PubMed2006

Tocopherol cyclase (VTE1) localization and vitamin E accumulation in chloroplast plastoglobule lipoprotein particles.

Chloroplasts contain lipoprotein particles termed plastoglobules. Plastoglobules are generally believed to have little function beyond lipid storage. Here we report on the identification of plastoglobule proteins using mass spectrometry methods in Arabidopsis thaliana. We demonstrate specific plastoglobule association of members of the plastid lipid-associated proteins/fibrillin family as well as known metabolic enzymes, including the tocopherol cyclase (VTE1), a key enzyme of tocopherol (vitamin E) synthesis. Moreover, comparative analysis of chloroplast membrane fractions shows that plastoglobules are a site of vitamin E accumulation in chloroplasts. Thus, in addition to their lipid storage function, we propose that plastoglobules are metabolically active, taking part in tocopherol synthesis and likely other pathways.

Arabidopsis↗

PubMed2006

Focal adhesion size controls tension-dependent recruitment of alpha-smooth muscle actin to stress fibers.

Expression of alpha-smooth muscle actin (alpha-SMA) renders fibroblasts highly contractile and hallmarks myofibroblast differentiation. We identify alpha-SMA as a mechanosensitive protein that is recruited to stress fibers under high tension. Generation of this threshold tension requires the anchoring of stress fibers at sites of 8-30-microm-long "supermature" focal adhesions (suFAs), which exert a stress approximately fourfold higher (approximately 12 nN/microm2) on micropatterned deformable substrates than 2-6-microm-long classical FAs. Inhibition of suFA formation by growing myofibroblasts on substrates with a compliance of < or = 11 kPa and on rigid micropatterns of 6-microm-long classical FA islets confines alpha-SMA to the cytosol. Reincorporation of alpha-SMA into stress fibers is established by stretching 6-microm-long classical FAs to 8.1-microm-long suFA islets on extendable membranes; the same stretch producing 5.4-microm-long classical FAs from initially 4-microm-long islets is without effect. We propose that the different molecular composition and higher phosphorylation of FAs on supermature islets, compared with FAs on classical islets, accounts for higher stress resistance.

Actins↗

PubMed2005

Pattern stability under cell culture conditions--a comparative study of patterning methods based on PLL-g-PEG background passivation.

Despite the rapidly increasing number of publications on the fabrication and use of micro-patterns for cell studies, comparatively little is know about the long-term stability of such patterns under cell culture conditions. Here, we report on the long-term stability of cellular patterns created by three different patterning techniques: selective molecular assembly patterning, micro-contact printing and molecular assembly patterning by lift-off. We demonstrate that although all three techniques were combined with the same background passivation chemistry based on assembly of a PEG-graft copolymer, there are considerable differences in the long-term stability between the three different pattern types under cell culture conditions. Our results suggest that these differences are not cell-dependent but are due to different (substrate-dependent) interactions between the patterned substrate, the passivating molecule and the serum containing cellular medium.

3T3 Cells↗

PubMed2004

Exon skipping of cathepsin B: mitochondrial targeting of a lysosomal peptidase provokes cell death.

The alternatively spliced messenger RNA of the human cysteine peptidase cathepsin B missing exons 2 and 3 encodes a truncated form of the enzyme lacking the signal peptide and part of the inhibitory propeptide. This deletion results in a new N-terminal leader sequence characteristic of proteins predestined for transport into mitochondria. We determined enzyme targeting to intracellular organelles by transfecting HeLa cells with constructs containing segments of variable length of the N terminus of truncated cathepsin B fused to green fluorescent protein. Co-localization of the constructs with mitochondria and the endoplasmic reticulum was probed with specific markers. None of the chimeric products were found in the endoplasmic reticulum, showing that truncated cathepsin B is misrouted from its regular biosynthetic pathway and forced to enter the mitochondria instead of lysosomes as its final destination. The first 20 amino acids of the new N terminus were necessary and sufficient for mitochondrial targeting, but only cells expressing the complete truncated cathepsin B sequence died by nuclear fragmentation. This new and unexpected behavior draws attention to an additional extralysosomal role for a cysteine peptidase with several recognized important pathophysiological functions. Mitochondrial targeting of cathepsin B may have significant consequences on cell life in pathological or physiological situations characterized by excessive transcription of the cathepsin B message lacking exons 2 and 3, as observed for instance in osteoarthritic cartilage.

Alternative Splicing↗

PubMed2003

The alternative use of exons 2 and 3 in cathepsin B mRNA controls enzyme trafficking and triggers nuclear fragmentation in human cells.

Pathological overexpression and trafficking of the cysteine peptidase cathepsin B depend in part on the composition of its mRNA. To investigate the roles of the alternatively spliced exons 2 and 3 in the 5'-untranslated region of cathepsin B mRNA we produced constructs of cathepsin B fused to green fluorescent protein. Expression and trafficking of the fluorescent chimeric products was followed in living human immortalized chondrocytes and HeLa cells. Although synthesized at different rates, proteins encoded by the full transcript and by that missing exon 2 followed a classic route, with the endosomal-lysosomal compartment as the final target. The point-mutated variant missing the glycosylation site for lysosomal targeting followed the secretory pathway. A truncated form of cathepsin B lacking the signal peptide and part of the propeptide, and encoded by the construct missing exons 2 and 3, was neither found in the Golgi apparatus nor in vesicles, but rather in the cytoplasm as patches associated with membranous and short fibrillar elements. This particular form of truncated cathepsin B produced nuclear damage and shrinking of the trans Golgi network and of the acidic compartment. The C-terminal, six-amino acid-long propeptide of cathepsin B did not exhibit a discernible role in protein trafficking.

Alternative Splicing↗

PubMed2003

Microcontact printing of novel co-polymers in combination with proteins for cell-biological applications.

Microcontact printing (microcP) is a cost effective and simple method to create chemically micropatterned surfaces for cell biological applications. We have combined the technique with the spontaneous molecular assembly of a polycationic PEG-grafted copolymer, poly-L-lysine-g-poly(ethylene glycol) (PLL-g-PEG). PLL-g-PEG with omega-functionalized PEG chains was print-transferred onto tissue culture polystyrene (TCPS) or glass substrates, resulting in patterns with a lateral resolution down to 1 microm. Subsequently, dipping in an aqueous solution of non-functionalized PLL-g-PEG was used to backfill the non-printed regions of the surface, rendering them highly protein and thus cell resistant. In a second approach, proteins were stamped and a PLL-g-PEG backfill was applied for passivation of the bare surface regions. Printing of peptide(RGD)-functionalized PLL-g-PEG or proteins combined with a subsequent PLL-g-PEG backfill can be applied to a wide variety of substrate materials with negatively charged surfaces such as TCPS, glass and many metal oxides. We have tested the printed surfaces with human foreskin fibroblasts for cell adhesion and long-term performance and with fish epidermal keratocytes for cell motility and short-time behaviour. Both cell types reacted selectively to the surface micropatterns. Fibroblasts adhered to the printed (adhesive) regions only, where they remained attached up to at least 1 week and were even able to proliferate. Keratocyte spreading and motility were also directed by the geometry of the underlying patterns. The results prove that microcP in conjunction with the use of PLL-g-PEG and its derivatives provides a simple and robust alternative to previously reported micropatterning methods for future cell biological and biotechnological applications.

Animals↗

PubMed2003

Exploring the role of 5' alternative splicing and of the 3'-untranslated region of cathepsin B mRNA.

The cysteine peptidase cathepsin B is responsible for connective tissue breakdown in several diseases. The pathological expression of cathepsin B may depend on the structure of its mRNA. We investigated the translational efficiency of the cathepsin B mRNA untranslated regions (UTRs) using fusion constructs to green fluorescent protein (GFP) and luciferase. Transfection of fusion constructs with GFP and luciferase containing the full-length 5'-UTR, the variant lacking exon 2, and that lacking exons 2 and 3 into mammalian cells, resulted in modulation of the biosynthetic rate of cathepsin B in a cell-specific manner. Constructs missing these exons were biosynthetically more efficient than the full-length counterpart. Luciferase was cloned upstream of the 3'-UTR, downstream of the 5'-UTR, or sandwiched between the 5'- and the 3'-UTR. The UTRs of cathepsin B downregulated luciferase biosynthesis moderately when present individually, with the 3'-UTR being more efficient than the 5'-UTR, and downregulated it even more when present simultaneously. A truncated cathepsin B-GFP chimeric product derived from the 5'-UTR missing exons 2 and 3 induced cell death. The increased biosynthetic rate and abnormal trafficking of cathepsin B observed in pathologies such as cancer and osteoarthritis may depend on alternative splicing of pre-mRNA.

3' Untranslated Regions↗

PubMed2002

Single muscle fiber contraction is dictated by inter-sarcomere dynamics.

This paper presents first results from a study where we developed a generic framework for analysing inter-sarcomere dynamics. Our objective is to find an accurate description of a muscle as a linear motor composed of parallel and series coupled subunits. The quality of theoretical models can be tested through their ability to predict experimental observations. With the current method we have found rigorous mathematical explanations for mechanisms such as sarcomere popping, extra tension and homogenization. These phenomena have been observed for many years in single fibers experiments, yet have never been completely understood in terms of a mechanical model. Now they can be explained on a theoretical basis. Interestingly, rather simplistic descriptions of each of the various molecular components in the sarcomere (actin-myosin cross-bridges, titin and contributions from passive elastic components) are sufficient to predict these behaviors. The complexity of a real muscle fiber is addressed through rigorous coupling of the single component models in a system of differential equations. We examine the properties of the differential equations, based on a down-stripped model, which permits the derivation of analytical solutions. They suggest that the contraction characteristics of inter-connected sarcomeres are essentially dictated by the initial distribution of the sarcomeres on the force-length curve and their starting velocities. The complete model is applied to show the complexity of inter-sarcomere dynamics of activated fibers in stretch-release experiments with either external force or length control. Seemingly contradictory and unexpected observations from single fiber experiments, which have hitherto been discussed with the argument of uncontrollable biological variability, turn out to be a consistent set of possible fiber responses. They result from a convolution of multiple relatively simple rules each of them defining a certain characteristics of the single sarcomere.

Animals↗