Modulation of Fibroblast Morphology and Adhesion during Collagen Matrix Remodeling

When fibroblasts are placed within a three-dimensional collagen matrix, cell locomotion results in translocation of the flexible collagen fibrils of the matrix, a remodeling process that has been implicated in matrix morphogenesis during development and wound repair. In the current experiments, we studied formation and maturation of cell–matrix interactions under conditions in which we could distinguish local from global matrix remodeling. Local remodeling was measured by the movement of collagen-embedded beads towards the cells. Global remodeling was measured by matrix contraction. Our observations show that no direct relationship occurs between protrusion and retraction of cell extensions and collagen matrix remodeling. As fibroblasts globally remodel the collagen matrix, however, their overall morphology changes from dendritic to stellate/bipolar, and cell–matrix interactions mature from punctate to focal adhesion organization. The less well organized sites of cell–matrix interaction are sufficient for translocating collagen fibrils, and focal adhesions only form after a high degree of global remodeling occurs in the presence of growth factors. Rho kinase activity is required for maturation of fibroblast morphology and formation of focal adhesions but not for translocation of collagen fibrils

Dendritic Fibroblasts in Three-dimensional Collagen Matrices

Cell motility determines form and function of multicellular organisms. Most studies on fibroblast motility have been carried out using cells on the surfaces of culture dishes. In situ, however, the environment for fibroblasts is the three-dimensional extracellular matrix. In the current research, we studied the morphology and motility of human fibroblasts embedded in floating collagen matrices at a cell density below that required for global matrix remodeling (i.e., contraction). Under these conditions, cells were observed to project and retract a dendritic network of extensions. These extensions contained microtubule cores with actin concentrated at the tips resembling growth cones. Platelet-derived growth factor promoted formation of the network; lysophosphatidic acid stimulated its retraction in a Rho and Rho kinase-dependent manner. The dendritic network also supported metabolic coupling between cells. We suggest that the dendritic network provides a mechanism by which fibroblasts explore and become interconnected to each other in three-dimensional space

Excitation, Fragmentation and Control of Large Finite Systems: C60\mathrm{C_{60}} in Moderately Strong Laser Fields

Recent progress in the understanding of the primary excitation mechanisms of the C$_{60}$ fullerene in intense laser pulses is reported. By analyzing mass spectra as a function of pulse duration, laser intensity and time delay between pump- and probe pulse insight into fundamental photoinduced processes such as ionization and fragmentation is obtained. Using ultrashort sub-10fs pulses excitation times are addressed which lie well below the characteristic time scales for electron–electron and electron–phonon coupling. The measured saturation intensities of multiply charged parent ions indicate that for higher charge states the well known C$_{60}$ giant plasmon resonance is involved in creating ions and a significant amount of large fragments through a non-adiabatic multi-electron dynamics. To enhance the formation of large fragments femtosecond laser pulses tailored with closed-loop, optimal control feedback were used. A characteristic pulse sequence excites oscillations in C$_{60}$ with large amplitude by coherent heating of nuclear motion. Again, the experimental findings can be understood by a laser-induced multi-electron excitation via the electronically excited resonance followed by efficient coupling to the radial symmetric breathing vibration of C$_{60}$