Dietary Branched Chain Amino Acids Modify Post-Infarct Cardiac Remodeling and Function in the Murine Heart.

Introduction: Branch-chain amino acids (BCAA) are markedly elevated in the heart following myocardial infarction (MI) in both humans and animal models. Nevertheless, it remains unclear whether dietary BCAA levels influence post-MI remodeling. We hypothesize that lowering dietary BCAA levels prevents adverse cardiac remodeling after MI. Methods and Results: To assess whether altering dietary BCAA levels would impact circulating BCAA concentrations, mice were fed a low (1/3×), normal (1×), or high (2×) BCAA diet over a 7-day period. We found that mice fed the low BCAA diet had >2-fold lower circulating BCAA concentrations when compared with normal and high BCAA diet feeding strategies; notably, the high BCAA diet did not further increase BCAA levels over the normal chow diet. To investigate the impact of dietary BCAAs on cardiac remodeling and function after MI, male and female mice were fed either the low or high BCAA diet for 2 wk prior to MI and for 4 wk after MI. Although body weights or heart masses were not different in female mice fed the custom diets, male mice fed the high BCAA diet had significantly higher body and heart masses than those on the low BCAA diet. Echocardiographic assessments revealed that the low BCAA diet preserved stroke volume and cardiac output for the duration of the study, while the high BCAA diet led to progressive decreases in cardiac function. Although no discernible differences in cardiac fibrosis, scar collagen topography, or cardiomyocyte cross-sectional area were found between the dietary groups, male mice fed the high BCAA diet showed longer cardiomyocytes and higher capillary density compared with the low BCAA group. Conclusions: Provision of a diet low in BCAAs to mice mitigates eccentric cardiomyocyte remodeling and loss of cardiac function after MI, with dietary effects more prominent in males.

Beating heart cells: Using cultured cardiomyocytes to study cellular structure and contractility in laboratory exercises.

Heart muscle cells, or cardiomyocytes, exhibit intrinsic contractility in vitro. We found that commercially-available mammalian cardiomyocytes serve as an excellent model system for studying the cytoskeleton and cellular contractility, fundamental topics in undergraduate cell and molecular biology courses. Embryonic rat cardiomyocytes were plated on cell culture dishes or glass coverslips and visualized using an inverted phase-contrast microscope. The cardiomyocytes began contracting within 1-2 days after plating and continued to contract for many weeks, allowing their use in multiple laboratory sessions. Following background reading and instruction, students fixed and triple-stained the cardiomyocytes to examine the relative distributions of actin filaments and microtubules and the position of nuclei. Analysis and image capture with fluorescence microscopy provided striking examples of highly organized cytoskeletal elements. Students then designed experiments in which cardiomyocyte intrinsic contractility was explored. Changes in contraction rates were examined after treatment with signaling molecules, such as epinephrine. The addition of epinephrine to the culture medium, within a usable concentration window, increased the rate of contraction. These adaptable exercises provide undergraduate cell and molecular biology students with the exciting opportunity to study cardiomyocytes using standard cell culture and microscopy techniques.