Myocardial infarct extension, a process involving the enlargement of infarct and border zone, leads to progressive degeneration of left ventricular (LV) function and eventually gives rise to heart failure. Despite carrying a high risk, the causation of infarct extension is still a subject of much speculation. In this study, patient-specific LV models were developed to investigate the correlation between infarct extension and impaired regional mechanics. Subsequently, sensitivity analysis was performed to examine the causal factors responsible for the impaired regional mechanics observed in regions surrounding the infarct and border zone. From our simulations, fibre strain, fibre stress and fibre stress-strain loop (FSSL) were the key biomechanical variables affected in these regions. Among these variables, only FSSL was correlated with infarct extension, as reflected in its work density dissipation (WDD) index value, with high WDD indices recorded at regions with infarct extension. Impaired FSSL is caused by inadequate contraction force generation during the isovolumic contraction and ejection phases. Our further analysis revealed that the inadequacy in contraction force generation is not necessarily due to impaired myocardial intrinsic contractility, but at least in part, due to inadequate muscle fibre stretch at end-diastole, which depresses the ability of myocardium to generate adequate contraction force in the subsequent systole (according to the Frank-Starling law). Moreover, an excessively stiff infarct may cause its neighbouring myocardium to be understretched at end-diastole, subsequently depressing the systolic contractile force of the neighbouring myocardium, which was found to be correlated with infarct extension.
Current xeno-free and chemically defined methods for the differentiation of hPSCs (human pluripotent stem cells) into cardiomyocytes are not efficient and are sometimes not reproducible. Therefore, it is necessary to develop reliable and efficient methods for the differentiation of hPSCs into cardiomyocytes for future use in cardiovascular research related to drug discovery, cardiotoxicity screening, and disease modeling. We evaluated two representative differentiation methods that were reported previously, and we further developed original, more efficient methods for the differentiation of hPSCs into cardiomyocytes under xeno-free, chemically defined conditions. The developed protocol successively differentiated hPSCs into cardiomyocytes, approximately 90-97% of which expressed the cardiac marker cTnT, with beating speeds and sarcomere lengths that were similar to those of a healthy adult human heart. The optimal cell culture biomaterials for the cardiac differentiation of hPSCs were also evaluated using extracellular matrix-mimetic material-coated dishes. Synthemax II-coated and Laminin-521-coated dishes were found to be the most effective and efficient biomaterials for the cardiac differentiation of hPSCs according to the observation of hPSC-derived cardiomyocytes with high survival ratios, high beating colony numbers, a similar beating frequency to that of a healthy adult human heart, high purity levels (high cTnT expression) and longer sarcomere lengths similar to those of a healthy adult human heart.
Abstract: Meat tenderness is the most important criterion in food quality because it strongly influences the consumer's satisfaction. Tenderness generally depends on connective tissue and sarcomere length of muscle. One of the effective methods for meat tenderizing is protease treatment. In this study, Manihot esculenta root was chosen as a protease source due to its skin blistering effect, suggesting the presence of strong proteolytic activity. The extraction of the crude protease was optimized by using response surface methodology (RSM) with four independent variables, which were pH (X1), CaCl2 (X2), Triton X-100 (X3) and 2-mercaptoethanol (X4). Based on the RSM model, all the independent variables were significant and the optimum extraction conditions were pH 9, 3.24 mM CaCl2, 4.12% Triton X-100 and 6.32 mM 2-mercaptoethanol. Tukey's test results showed that the difference between the expected and experimental protease activity value was 0.05%. A reduction of meat firmness was observed when samples treated with enzyme were compared with a control by using a texture analyser. Electrophoretic patterns also showed extensive proteolysis and a reduction of intensity and number of the protein bands in the treated sample. SEM clearly revealed the degradation of muscle fibres and connective tissue of meat treated with crude protease.