Effects of stretch and shortening on gene expression in intact myocardium.

Multiple cues have been suggested as the mechanical stimulus for the heart's hypertrophic response. Our work has previously suggested that the amount of cyclic shortening in cardiomyocytes controls myocyte shape and the amount of stretch controls myocyte size. To identify gene expression changes that occur in response to these mechanical perturbations, we used microarray analysis of papillary muscles cultured for 12 h at physiological or reduced levels of cyclic shortening and physiological or reduced mean stretch. Overall, genes related to extracellular matrix (ECM) were surprisingly prominent in our analysis. Connective tissue growth factor was among a small group of genes regulated by the amount of cyclic shortening regardless of the level of mean stretch, and many more ECM genes were regulated by shortening with reduced amounts of stretch. When we compared our results to gene expression data from an in vivo model of pressure overload (PO), which also decreases myocyte shortening, we found the genes that were commonly regulated in PO and our decreased shortening groups were most significantly enriched for ontology terms related to the ECM, followed by genes associated with mechanosensing and the cytoskeleton. The list of genes regulated in PO and our decreased shortening groups also includes genes known to change early in hypertrophy, such as myosin heavy chain 7, brain natriuretic peptide, and myosin binding protein C. We conclude that in intact myocardium, the amount of cyclic shortening may be an important regulator not only of myocyte genes classically associated with hypertrophy but also of ECM genes.

Whole-genome metabolic network reconstruction and constraint-based modeling.

With the advent of modern high-throughput genomics, there is a significant need for genome-scale analysis techniques that can assist in complex systems analysis. Metabolic genome-scale network reconstructions (GENREs) paired with constraint-based modeling are an efficient method to integrate genomics, transcriptomics, and proteomics to conduct organism-specific analysis. This text explains key steps in the GENRE construction process and several methods of constraint-based modeling that can help elucidate basic life processes and development of disease treatment, bioenergy solutions, and industrial bioproduction applications.

Isometric contraction induces rapid myocyte remodeling in cultured rat right ventricular papillary muscles.

The hypothesis that elevated systolic stress induces myocyte thickening has been difficult to test directly. We tested this hypothesis in working rat right ventricular papillary muscles using a recently developed technique for long-term muscle culture. Muscles were cultured for 36 h either isometrically at different levels of systolic stress or at physiological amounts and rates of shortening. Isometric contraction induced rapid increases in myocyte diameter regardless of the level of systolic stress, whereas control myocyte dimensions were maintained if physiological amounts and rates of systolic shortening were imposed. Myocyte thickening was accompanied by a significant decrease in cell length and number of sarcomeres in series along the long axis of the myocyte, suggesting that thickening may have occurred in part by rearrangement of existing sarcomeres. We conclude that the pattern of systolic shortening and/or diastolic lengthening regulates myocyte shape in working rat right ventricular papillary muscles, whereas systolic stress plays little or no role.

Tissue engineering of skeletal muscle.

Loss of skeletal muscle profoundly affects the health and well-being of patients, and there currently is no way to replace lost muscle. We believe that a key step in the development of a prosthesis for reconstruction of dysfunctional muscular tissue is the ability to reconstitute the in vivo-like 3-dimensional (3D) organization of skeletal muscle in vitro with isolated satellite cells. In our present proof of principle studies, we have successfully constructed a multilayered culture of skeletal muscle cells, derived from neonatal satellite cells, that are distributed in a 3D pattern of organization that mimics many of the features of intact tissue. These multilayered cultures are composed of elongated multinucleated myotubes that are MyoD positive. Histological studies indicate that the multiple layers of myotubes can be distinguished. Expression of muscle-specific markers such as myosin heavy chain, dystrophin, integrin alpha-7, alpha-enolase, and beta-enolase was detected using real-time reverse transcriptase polymerase chain reaction at levels near adult values. Physiological measurements of the engineered skeletal muscle showed that they tetanize and display physiologic force length behavior, although developed force per cross-sectional area was below that of native rat skeletal muscle.