Bernstein Lab for Cardiovascular Research

Our research program focuses on regulation of cardiovascular function in both normal physiologic states as well as in disease states such as cardiomyopathy. Our major focus at this time is on hypertrophic cardiomyopathy (HCM) and how mutations in sarcomeric proteins such as α-myosin lead to alterations in cellular physiology and morphology. Over the past two decades we have gained substantial insight into the genes that are responsible for HCM, however, despite this knowledge, there are still many unanswered questions on how these mutations translate into the clinical phenotypes we see in patients.

Unanswered questions regarding HCM include: (1) why is there such clinic variability in patient phenotype, even within a single family with the same mutation? (2) why is there often a decades-long delay in the development of clinical disease, when the mutations are present at birth? (3) why are some mutations (pediatric-onset mutations) more severe and likely to cause disease in younger patients, even in newborns? (4) how is it that some mutations lead to a decrease in force at the myosin molecule level but increase force generation at the whole cell level? And (5) if the myocytes are hypercontractile, why does hypertrophy develop at all? What do you need more cardiac mass if the function is already super-normal?

We are utilizing a range of novel platforms to answer these questions: the optical trap assay to provide direct mechanistic insight into how force regulates assembly of sarcomeric structure; Cryo-electron tomography (Cryo-ET) proving a near-molecular scale picture of sarcomere structure in both normal hearts and in HCM; human induced pluripotent stem cell cardiomyocytes (h-iPSC-CMs) which have been CRISPR gene-edited to express HCM mutations; genetically altered murine models of HCM; and a genetically encoded force sensor (vinculin-FRET-TS) in the protein vinculin, which allows us to measure force directly inside cells for the first time.

We are specifically interested in how altered force, sensed inside the cell at the Z-disc (the intracellular structure that anchors actin filaments at the center of each sarcomere) are translated into altered cell structure (hypertrophy). This concept is known as mechanotransduction, and our preliminary data show that it is likely to be mediated by cell signaling cascades such as calcineurin, MLP, and PKC.  Using our FRET-tension sensor we can study for the first time how intracellular forces are altered in HCM and in dilated cardiomyopathy (DCM, where contractility is decreased) and the downstream signaling cascades that are altered, resulting in hypertrophy.

We have also shown marked metabolic derangements, including mitochondrial injury, in patients with HCM, much earlier in their disease than previously expected. Our biobank of septal myectomy tissue from HCM patients allows us to study, using a multi-omic approach, multiple facets of this disease, including metabolism, fibrosis, inflammation and arrhythmogenesis.

Finally, a key pathologic feature of HCM is myofiber disarray, where the myofibers are arranged in disorder rather than in parallel structures. We have shown that this disarray extends far beyond the myofibrillar level, finding that individual myosin filaments are also disarrayed in patients with HCM. This level of disarray is an early hallmark of disease and may be present years of even decades before clinical signs (hypertrophy on echocardiogram) are present. Further proof of this finding could have major implications for consideration of early treatment in genotype +/phenotype – patients.