Orientation dependent molecular friction on organic layer compound crystals

High resolution friction force maps of the benzylammonium terminated crystalline surface of a layer compound are presented. The lateral force map acquired with an atomic force microscope, reveals a significant contrast between different molecular orientations yielding molecular rows which differ from their neighboring ones. The single crystals are formed by stacks of copper oxalate sheets sandwiched between stereoregular organic cations, resulting in highly organized surface structures. Single molecular defects are observed at small loads. The experimental results are compared with numerical calculations which indicate a transition from an unperturbed state at small loads to a distorted state at higher loads. (C) 2011 American Institute of Physics.

Differential requirement for ROCK in dendritic cell migration within lymphatic capillaries in steady-state and inflammation

Dendritic cell (DC) migration via lymphatic vessels to draining lymph nodes (dLNs) is crucial for the initiation of adaptive immunity. We imaged this process by intravital microscopy (IVM) in the ear skin of transgenic mice bearing red-fluorescent vasculature and yellow-fluorescent DCs. DCs within lymphatic capillaries were rarely transported by flow, but actively migrated within lymphatics and were significantly faster than in the interstitium. Pharmacologic blockade of the Rho-associated protein kinase (ROCK), which mediates nuclear contraction and de-adhesion from integrin ligands, significantly reduced DC migration from skin to dLNs in steady-state. IVM revealed that ROCK blockade strongly reduced the velocity of interstitial DC migration, but only marginally affected intralymphatic DC migration. By contrast, during tissue inflammation, ROCK blockade profoundly decreased both interstitial and intralymphatic DC migration. Inhibition of intralymphatic migration was paralleled by a strong up-regulation of ICAM-1 in lymphatic endothelium, suggesting that during inflammation ROCK mediates de-adhesion of DC-expressed integrins from lymphatic-expressed ICAM-1. Flow chamber assays confirmed an involvement of lymphatic-expressed ICAM-1 and DC-expressed ROCK in DC crawling on lymphatic endothelium. Overall, our findings further define the role of ROCK in DC migration to dLNs and reveal a differential requirement for ROCK in intralymphatic DC crawling during steady-state and inflammation.

Role of RhoA/ROCK-dependent actin contractility in the induction of tenascin-C by cyclic tensile strain

In chick embryo fibroblasts, the mRNA for extracellular matrix protein tenascin-C is induced 2-fold by cyclic strain (10%, 0.3 Hz, 6 h). This response is attenuated by inhibiting Rho-dependent kinase (ROCK). The RhoA/ROCK signaling pathway is primarily involved in actin dynamics. Here, we demonstrate its crucial importance in regulating tenascin-C expression. Cyclic strain stimulated RhoA activation and induced fibroblast contraction. Chemical activators of RhoA synergistically enhanced the effects of cyclic strain on cell contractility. Interestingly, tenascin-C mRNA levels perfectly matched the extent of RhoA/ROCK-mediated actin contraction. First, RhoA activation by thrombin, lysophosphatidic acid, or colchicine induced tenascin-C mRNA to a similar extent as strain. Second, RhoA activating drugs in combination with cyclic strain caused a super-induction (4- to 5-fold) of tenascin-C mRNA, which was again suppressed by ROCK inhibition. Third, disruption of the actin cytoskeleton with latrunculin A abolished induction of tenascin-C mRNA by chemical RhoA activators in combination with cyclic strain. Lastly, we found that myosin II activity is required for tenascin-C induction by cyclic strain. We conclude that RhoA/ROCK-controlled actin contractility has a mechanosensory function in fibroblasts that correlates directly with tenascin-C gene expression. Previous RhoA/ROCK activation, either by chemical or mechanical signals, might render fibroblasts more sensitive to external tensile stress, e.g., during wound healing.

Different migration of vascular smooth muscle cells from human coronary artery bypass vessels. Role of Rho/ROCK pathway

BACKGROUND: We examined whether vascular smooth muscle (VSMC) or endothelial cell (EC) migration from internal mammary artery (MA) differed from VSMC or EC migration from saphenous vein (SV). METHODS AND RESULTS: Migration to PDGF-BB (1-10 ng/ml) was lower in VSMC from MA than SV; however, attachment, movement without chemokine, and chemokinesis were identical. Unlike VSMC, migration of EC was similar in response to several mediators. Expression of PDGF receptor-beta was lower in VSMC from MA than SV, while alpha-receptor expression was higher. PDGF-BB-induced RhoA activity was lower in MA than SV, while basal activity was identical. Rosuvastatin and hydroxyfasudil impaired PDGF-BB-induced migration of VSMC from MA and SV. Mevalonate and geranylgeranylpyrophosphate rescued inhibition by rosuvastatin. PDGF-BB induced less stress fiber formation in VSMC from MA than SV. A dominant negative RhoA mutant inhibited stress fiber formation to PDGF-BB, while a constitutively active mutant resulted in maximal stress fiber formation in MA and SV. Rosuvastatin and hydroxyfasudil impaired PDGF-BB-induced stress fiber formation in MA and SV. CONCLUSIONS: VSMC migration to PDGF-BB is lower in MA than SV, which is at least in part related to lower activity of the Rho/ROCK pathway.

Induction of tenascin-C by cyclic tensile strain versus growth factors: distinct contributions by Rho/ROCK and MAPK signaling pathways

Expression of the extracellular matrix (ECM) protein tenascin-C is induced in fibroblasts by growth factors as well as by tensile strain. Mechanical stress can act on gene regulation directly, or indirectly via the paracrine release of soluble factors by the stimulated cells. To distinguish between these possibilities for tenascin-C, we asked whether cyclic tensile strain and soluble factors, respectively, induced its mRNA via related or separate mechanisms. When cyclic strain was applied to chick embryo fibroblasts cultured on silicone membranes, tenascin-C mRNA and protein levels were increased twofold within 6 h compared to the resting control. Medium conditioned by strained cells did not stimulate tenascin-C mRNA in resting cells. Tenascin-C mRNA in resting cells was increased by serum; however, cyclic strain still caused an additional induction. Likewise, the effect of TGF-beta1 or PDGF-BB was additive to that of cyclic strain, whereas IL-4 or H2O2 (a reactive oxygen species, ROS) did not change tenascin-C mRNA levels. Antagonists for distinct mitogen-activated protein kinases (MAPK) inhibited tenascin-C induction by TGF-beta1 and PDGF-BB, but not by cyclic strain. Conversely, a specific inhibitor of Rho-dependent kinase strongly attenuated the response of tenascin-C mRNA to cyclic strain, but had limited effect on induction by growth factors. The data suggest that regulation of tenascin-C in fibroblasts by cyclic strain occurs independently from soluble mediators and MAPK pathways; however, it requires Rho/ROCK signaling.