Mechanical Forces Reshape Differentiation Cues That Guide Cardiomyogenesis

Abstract

Soluble morphogen gradients have long been studied in the context of heart specification and patterning. However, recent data have begun to challenge the notion that long-standing in vivo observations are driven solely by these gradients alone. Evidence from multiple biological models, from stem cells to ex vivo biophysical assays, now supports a role for mechanical forces in not only modulating cell behavior but also inducing it de novo in a process termed mechanotransduction. Structural proteins that connect the cell to its niche, for example, integrins and cadherins, and that couple to other growth factor receptors, either directly or indirectly, seem to mediate these changes, although specific mechanistic details are still being elucidated. In this review, we summarize how the wingless (Wnt), transforming growth factor-β, and bone morphogenetic protein signaling pathways affect cardiomyogenesis and then highlight the interplay between each pathway and mechanical forces. In addition, we will outline the role of integrins and cadherins during cardiac development. For each, we will describe how the interplay could change multiple processes during cardiomyogenesis, including the specification of undifferentiated cells, the establishment of heart patterns to accomplish tube and chamber formation, or the maturation of myocytes in the fully formed heart.

Keywords: cadherins; heart; integrins; stem cells; transforming growth factor.

Figure 1. Cardiomyogenesis during stages of development

Overview of the stages of cardiomyogenesis from the first appearance of cardiac precursor cells in the pregastrulation epiblast through the emergence of the 4-chambered heart. The embryonic (E) days noted at each stage reflect mouse development. Both biochemical and biophysical influences on cardiomyogenesis are summarized at each developmental stage. BMP, bone morphogenetic protein; ECM, extracellular matrix; EV, early ventricle; IFT, inflow tract; LA, left aorta; LV, left ventricle; OFT, outflow tract; PLA, primitive left aorta; PRA, primitive right aorta; RA, right aorta; RV, right ventricle; and TGFβ, transforming growth factor-β.

Figure 2. Influence of mechanical forces during gastrulation and early mesoderm formation

Schematic illustration depicting the role of mechanical forces in initiation of tissue invagination during gastrulation (left) and establishment of chemical gradients during mesoderm development (right). Mechanical force induces expression of twist and snail genes that mediate folded gastrulation (Fog) secretion and receptor binding to activate myosin II–dependent cell constriction. This generates tension at the cell surface that drives invagination at the onset of gastrulation. Asymmetrical gradients of sonic hedgehog (SHH) and retinoic acid (RA) are created as nodal cilia rotate to generate nodal flow to drive SHH/RA-containing vesicles to the left region of the primitive streak node.

Figure 3. Force-induced modulation of Wnt signaling during cardiomyogenesis

A, Schematic representation of Wnt signaling cascade and cadherin-based mechanical interactions between adjacent cells. Wnt ligand signaling through its Frizzled receptor inhibits the proteolytic degradation of β-catenin by its destruction complex, enabling cytoplasmic accumulation. Increased cytoplasmic β-catenin drives nuclear translocation and initiates expression of Wnt-related genes to modulate cardiomyogenesis. Cadherins interact with the Wnt pathway by binding β-catenin to block its cytoplasmic accumulation and subsequent nuclear translocation. B, Illustration of epithelial–mesenchymal transition (EMT) driving myocyte specification and migration. The loss of E-cadherin–based mechanical connections between cells enables cell migration and increases intracellular β-catenin pools to drive expression of EMT-related genes. APC indicates adenomatous polyposis coli; GSK3β, glycogen synthase kinase 3 β; LEF, lymphoid enhancer–binding factor; and TCF, transcription factor.

Figure 4. Role of mechanical forces in regulation of transforming growth factor-β(TGFβ) superfamily signaling

Biophysical forces regulate TGFβ superfamily signaling at multiple points in the pathway. A, Both passive and active mechanical cues alter gene expression of bone morphogenetic protein (BMP) ligands and mothers against decapentaplegic homolog (SMAD) effector proteins. B, Membrane tension generated by mechanical interactions with the extracellular matrix (ECM) drives TGFβ receptor endocytosis. C, TGFβ ligands are sequestered by the ECM through interactions with latency-associated protein (LAP) and latent TGFβ-binding protein (LTBP). Cell contraction initiates ligand release by unfolding mechanosensitive LAP to interfere with LAP–TGFβ binding.

Figure 5. Interplay of chemical and mechanical signals that underlie cardiac specification and development

Schematic representation of integrin-mediated signaling specifically detailing how chemical signals (left), for example, integrin ligation, drive focal adhesion formation, and downstream events leading to transcriptional changes. Mechanical signals (right) are mediated by actomyosin contractions. Both influence transcriptional changes via common mechanisms diagrammed at the bottom of the illustration, including chromatin remodeling and changes in nuclear pore complex diffusion among others. Dash and solid lines indicate the direction of biophysical and biochemical interactions, respectively. AKT indicates protein kinase B; ECM, extracellular matrix; FAK, focal adhesion kinase; GSK, glycogen synthase kinase; ILK, integrin-linked kinase; and PI3K, phosphoinositide 3-kinase.