Although changes in gene expression represent a fundamental feature of cardiac disease, transcript levels often poorly correlate with respective protein levels, suggesting post-transcriptional gene expression control may be disease-regulated in the heart. We developed a new experimental method to identify which transcripts are actively translated in cardiac myocytes in the diseased mouse heart, in vivo. We combined ribosome profiling with a ribosome-tagging approach that enabled us to isolate and sequence transcripts that are engaged in protein synthesis specifically from mouse cardiac myocytes in vivo; defined as the cardiac myocyte translatome. Using this cell-type–specific Ribo-seq approach, we defined the translational response of cardiac myocytes during hypertrophic stress (pressure overload). This work demonstrates the magnitude of the cellular stress response at the translational level and lays the foundation for discovery of novel molecular mechanisms across all areas of cardiovascular pathophysiology.
Our studies of protein secretion began when we turned our attention to the effects of cellular stress and protein misfolding on cellular secretion of critical paracrine proteins, and discovered a unique mechanism of secretion of MANF, a novel ER stress response protein. This study led the way to our research into a more global view of proteins secreted from cardiac myocytes, wherein we examined the cardiac myocyte secretome in response to protein folding stresses.
We previously discovered a novel molecular pathway known as the endoplasmic reticulum (ER) stress response, to be activated when cells or tissues are subjected to ischemia, the loss of oxygen and nutrients. Furthermore, we found that the activation of the ER stress response is necessary to protect cells from death during and after ischemia. In the first study to examine any ER-localized E3 ubiquitin-protein ligase in the heart, we found that cardiac pathology activates the previously unappreciated process of ER-associated protein degradation (ERAD), which moderates pathological cardiac myocyte remodeling. One of the highest impact findings of our work so far is that protein quality control in the ER of cardiac myocytes is a critical component of heart function.