Chronic changes in stress and strain on the heart are associated with the activation of gene programs that drive pathological growth and remodeling. Long-term upregulation of these genes can lead to cardiac hypertrophy and disease, yet how a change in mechanical force is transduced to a change in gene expression is poorly understood. Recent studies in non-muscle cells have found that strain transmission to the nucleus via the Linkers of the Nucleo- and Cytoskeleton (LINC) complex may be critical for force-dependent gene expression. The LINC complex forms protein-protein interactions that connect the cytoskeleton to the inner nuclear membrane and associated chromatin, forming a potential route for force-dependent gene regulation. Interestingly, mutations in many cytoskeletal, nucleoskeletal and LINC complex proteins have been linked to dilated cardiomyopathy (DCM). The experiments outlined in this proposal will define which components of the LINC complex and cytoskeleton transmit strain to the nucleus in adult cardiomyocytes (CMs), and whether those components are involved in strain-dependent gene expression. Based on my preliminary data, I hypothesize that the muscle- specific intermediate filament (IF) desmin and cardiac microtubules (MTs) are critical for strain transmission and regulate strain-dependent gene expression in adult CMs. The first goal of this proposal is to determine which LINC and cytoskeletal components transmit stress and strain to CM nuclei. I predict desmin and MTs will be critical for this process based on my preliminary evidence that depolymerization of the MT network reduces strain transmitted to nuclei. To determine which other components are important for strain transmission to the nucleus, I will assess the degree of nuclear deformation upon stretch/contraction in control myocytes and upon manipulations that disrupt desmin, actin, and components of the LINC complex. The second goal of this proposal is to determine whether the LINC complex and cytoskeleton contribute to strain- mediated gene expression. I hypothesize that desmin and MTs regulate strain-dependent gene expression via the LINC complex. I will test this hypothesis by cyclically stretching populations of isolated CMs and measuring alternations in gene expression using RNAseq both in control and in conditions where the cytoskeleton and LINC complex are disrupted. To complement this cellular approach, I will determine whether these components also regulate strain-dependent gene expression in an intact heart. These experiments will be the first to identify which components of the CM LINC complex and cytoskeleton regulate strain transmission to the nucleus and strain-induced gene expression. If successful, the results of this work will provide key insight into the mechanism by which chronic changes in stress and strain on the heart induce changes in gene expression.
For decades, it has been known that excess mechanical force on the heart, such as occurs during high blood pressure, can cause upregulation of genetic programs that drive heart disease and failure, yet the mechanism by which a heart cell senses a change in force and transduces that to a genetic response is unclear. Here we will test if and how mechanical forces are transmitted through the heart cell cytoskeleton to the nucleus. I will first test which components of the cytoskeleton transmit strain to the nucleus, and will then asses how perturbation of that strain transmission alters mechanotransduction and mechanically-induced gene expression, both in isolated cells and in a whole-heart model.
