not only a complex biochemical environment but also a diverse biomechanical environment. How cells respond to variations in mechanical forces is critical in homeostasis and many diseases. The mechanisms by which mechanical forces lead to eventual biochemical and molecular responses remain undefined, and unraveling this mystery will undoubtedly provide new insight into strengthening bone, growing cartilage, improving cardiac contractility, and constructing tissues for artificial organs. In this article we review the physical bases underlying the mechanotransduction process, techniques used to apply controlled mechanical stresses on living cells and tissues to probe mechanotransduction, and some of the important lessons that we are learning from mechanical stimulation of cells with precisely controlled forces.cytoskeleton; micromanipulation; cell signaling ALL LIVING ORGANISMS face mechanical forces, from the fluid forces around a bacterium to the high forces in a human knee during stair climbing. The process of converting physical forces into biochemical signals and integrating these signals into the cellular responses is referred to as mechanotransduction. Although this review cannot cover all that has been discovered about mechanotransduction, we discuss the molecule-and cell-level structures that may participate in mechanotransduction, provide an overview of prominent techniques currently used for exerting mechanical stresses on cells, and conclude with an overview of the tissue-level response to mechanical signaling. FORCE TRANSDUCTION PATHWAYS AND SIGNALINGForce transmission pathways at the cellular and subcellular scales. Understanding the molecular basis for mechanotransduction requires knowledge of the magnitude and distribution of forces throughout the cell at the molecular scale. At present, we have sufficient information to measure molecular scale forces in only a very few cases. We can, however, analyze the mechanisms by which force is transmitted throughout the cell and use that as a basis for speculation about the molecular mechanisms of mechanotransduction. A variety of different methods have been used to mechanically stimulate a cell, and the cellular response is multifaceted and diverse. Similarly, there are likely to be a variety of sensing mechanisms and locations within the cell where forces can be transduced from a mechanical to a biochemical signal. Despite this apparent complexity, it is probable that cells stimulated in different ways are activated by similar mechanisms at the molecular level. To identify these commonalities, it is useful to consider how externally applied forces are transmitted into and throughout the cell, as well as the magnitudes and distribution of force corresponding to these different methods of stimulation.Both continuum and microstructural approaches have been used to determine force distributions. In the case of a continuum model, the details of the microstructure are ignored, and the forces transmitted via the individual microstructural elements are described in...

Routine immunohistochemical analysis of a conventional endomyocardial-biopsy sample appears to be a highly sensitive and specific diagnostic test for ARVC.

Background-Increased biomechanical stresses in the fibrous cap of atherosclerotic plaques contribute to plaque rupture and, consequently, to thrombosis and myocardial infarction. Thin fibrous caps and large lipid pools are important determinants of increased plaque stresses. Although coronary calcification is associated with worse cardiovascular prognosis, the relationship between atheroma calcification and stresses is incompletely described. Methods and Results-To test the hypothesis that calcification impacts biomechanical stresses in human atherosclerotic lesions, we studied 20 human coronary lesions with techniques that have previously been shown to predict plaque rupture locations accurately. Ten ruptured and 10 stable lesions derived from post mortem coronary arteries were studied using large-strain finite element analysis. Maximum stress was not correlated with percentage of calcification, but it was positively correlated with the percentage of lipid (Pϭ0.024). When calcification was eliminated and replaced with fibrous plaque, stress changed insignificantly; the median increase in stress for all specimens was 0.1% (range, 0% to 8%; Pϭ0.85). In contrast, stress decreased by a median of 26% (range, 1% to 78%; Pϭ0.02) when lipid was replaced with fibrous plaque. Conclusions-Calcification does not increase fibrous cap stress in typical ruptured or stable human coronary atherosclerotic lesions. In contrast to lipid pools, which dramatically increase stresses, calcification does not seem to decrease the mechanical stability of the coronary atheroma.