Increasing complexity: Mechanical guidance and feedback loops as a basis for self-organization in morphogenesis

When Stiffness Matters: Mechanosensing in Heart Development and Disease

During embryonic morphogenesis, the heart undergoes a complex series of cellular phenotypic maturations (e.g., transition of myocytes from proliferative to quiescent or maturation of the contractile apparatus), and this involves stiffening of the extracellular matrix (ECM) acting in concert with morphogenetic signals. The maladaptive remodeling of the myocardium, one of the processes involved in determination of heart failure, also involves mechanical cues, with a progressive stiffening of the tissue that produces cellular mechanical damage, inflammation, and ultimately myocardial fibrosis. The assessment of the biomechanical dependence of the molecular machinery (in myocardial and non-myocardial cells) is therefore essential to contextualize the maturation of the cardiac tissue at early stages and understand its pathologic evolution in aging. Because systems to perform multiscale modeling of cellular and tissue mechanics have been developed, it appears particularly novel to design integrated mechano-molecular models of heart development and disease to be tested in ex vivo reconstituted cells/tissue-mimicking conditions. In the present contribution, we will discuss the latest implication of mechanosensing in heart development and pathology, describe the most recent models of cell/tissue mechanics, and delineate novel strategies to target the consequences of heart failure with personalized approaches based on tissue engineering and induced pluripotent stem cell (iPSC) technologies.

Cell-Based Mechanosensation, Epigenetics, and Non-Coding RNAs in Progression of Cardiac Fibrosis

The heart is par excellence the 'in-motion' organ in the human body. Compelling evidence shows that, besides generating forces to ensure continuous blood supply (e.g., myocardial contractility) or withstanding passive forces generated by flow (e.g., shear stress on endocardium, myocardial wall strain, and compression strain at the level of cardiac valves), cells resident in the heart respond to mechanical cues with the activation of mechanically dependent molecular pathways. Cardiac stromal cells, most commonly named cardiac fibroblasts, are central in the pathologic evolution of the cardiovascular system. In their normal function, these cells translate mechanical cues into signals that are necessary to renew the tissues, e.g., by continuously rebuilding the extracellular matrix being subjected to mechanical stress. In the presence of tissue insults (e.g., ischemia), inflammatory cues, or modifiable/unmodifiable risk conditions, these mechanical signals may be 'misinterpreted' by cardiac fibroblasts, giving rise to pathology programming. In fact, these cells are subject to changing their phenotype from that of matrix renewing to that of matrix scarring cells-the so-called myo-fibroblasts-involved in cardiac fibrosis. The links between alterations in the abilities of cardiac fibroblasts to 'sense' mechanical cues and molecular pathology programming are still under investigation. On the other hand, various evidence suggests that cell mechanics may control stromal cells phenotype by modifying the epigenetic landscape, and this involves specific non-coding RNAs. In the present contribution, we will provide examples in support of this more integrated vision of cardiac fibrotic progression based on the decryption of mechanical cues in the context of epigenetic and non-coding RNA biology.