H E L M S L A B
Hypertrophic Cardiomyopathy
Hypertrophic cardiomyopathy (HCM) is caused by genetic variants that lead to abnormal thickening of the heart muscle. Over time, HCM can lead to arrhythmias and/or heart failure. We primarily study HCM due to variants in the gene MYBPC3, which are collectively the most genetic cause of HCM. We have found that truncating variants in MYBPC3 lead to loss of function, dysregulating contractile function in cardiomyocytes (using iPSC-CM methods, see below). We have created a range of tools to study MYBPC3 HCM, including gene-edited iPSC-CM models, reporter iPSC-CMs, and novel mouse models. We also derive iPSC-CMs from patients who have generously donated cells for research. Additionally, we are using functional genomics approaches to determine the transcriptional regulation of MYBPC3 (see below). We also participate in the largest international registry of hypertrophic cardiomyopathy (SHaRe, https://www.theshareregistry.org/).
Previous studies include:
Helms AS, Thompson AD, Glazier AA, Hafeez N, Kabani S, Rodriguez J, Yob JM, Woolcock H, Mazzarotto F, Lakdawala NK, Wittekind SG, Pereira AC, Jacoby DL, Colan SD, Ashley EA, Saberi S, Ware JS, Ingles J, Semsarian C, Michels M, Olivotto I, Ho CY, Day SM, SHaRe investigators. Spatial and Functional Distribution of MYBPC3 Pathogenic Variants and Clinical Outcomes in Patients with Hypertrophic Cardiomyopathy. Circ Cardiovasc Genet. 2020 Oct;13(5):396-405. PMCID: PMC7676622.
Helms AS, Tang VT, O'Leary TS, Friedline S, Wauchope M, Arora A, Wasserman AH, Smith ED, Lee LM, Wen XW, Shavit JA, Liu AP, Previs MJ, Day SM: Effects of MYBPC3 loss-of-function mutations preceding hypertrophic cardiomyopathy. JCI Insight. 2020 Jan 30;5(2). PMCID PMC31877118.
Helms AS, Alvarado FJ, Yob J, Tang VT, Pagani F, Russell MW, Valdivia HH, Day SM: Genotype-Dependent and -Independent Calcium Signaling Dysregulation in Human Hypertrophic Cardiomyopathy. Circulation. 2016 Nov 29;134(22):1738-1748. PMCID: PMC5127749.
Ho CY, Day SM, Ashley, EA, Michels M, Pereira A, Jacoby D, Cirino AL, Fox JC, Lakdawala NK, Ware JS, Caleshu CA, Helms AS, Colan SD, Girolami F, Cecchi F, Seidman CE, Sajeev G, Signorovitch J, Green EM, Olivotto I. Genotype and Lifetime Burden of Disease in Hypertrophic Cardiomyopathy: Insights from the Sarcomeric Human Cardiomyopathy Registry (SHaRe). Circulation. 2018 Aug; 138(14). PMCID: PMC6170149.
IPSC-CM models of MYBPC3 hypertrophic cardiomyopathy were generated through CRISPR-Cas9 gene editing. Impact of variants on myofibrillar structure was analyzed in micropatterned cardiomyocytes to induce a 7:1 aspect ratio that results in aligned myofibrils. Contractile function was analyzed using traction force microscopy. See more at https://insight.jci.org/articles/view/133782.
Arrhythmogenic Cardiomyopathy
Arrhythmogenic cardiomyopathy (HCM) is most frequently caused by genetic variants that lead to abnormal cell-cell connections in the heart. In particular, we focus on the gene desmoplakin, DSP. Desmoplakin cardiomyopathy is a unique form of cardiomyopathy that causes development of injury and scar in the heart muscle prior to the development of contractile dysfunction - however, the mechanisms have not been clearly proven and no targeted treatments currently exist. To determine these mechanisms and develop treatments, we have generated gene edited iPSC-CM models using CRISPR-Cas9, and we have also been privileged to derive iPSC-CMs from patient donated cells. We have developed specific assays to detect dysfunction in these models that take advantage of the cardiac muscle bundle approach we developed (see below). We have also developed a novel mouse model for DSP cardiomyopathy.
Previous studies include:
Smith ED, Lakdawala NK, Papoutsidakis N, Aubert G, Mazzanti A, McCanta AC, Agarwal PP, Arscott P, Dellefave-Castillo LM, Vorovich EE, Nutakki K, Wilsbacher LD, Priori SG, Jacoby DL, McNally EM, Helms AS§. Desmoplakin Cardiomyopathy, a Fibrotic and Inflammatory Form of Cardiomyopathy Distinct from Typical Dilated or Arrhythmogenic Right Ventricular Cardiomyopathy. Circulation. 2020, 141(23):1872-1884. PMID: 32372669.
Desmoplakin cardiomyopathy hearts demonstrate fibrosis in the subepicardial muscle layer of the left ventricle prior to development of contractile dysfunction (red arrows indicate areas of scar/fibrosis in a heart with DSP cardiomyopathy). See more at https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.119.044934.
IPSC-Cardiomyocytes
Biomechanical models and maturation
Cardiomyocytes differentiated from human induced pluripotent stem cells (iPSC-CMs) have enabled direct study of live human heart muscle cells - a major advance for the field since live human heart muscle cells are otherwise not readily obtained. However, iPSC-CMs are naturally immature and their function is difficult to assess without specific approaches to organize their growth and development. We have tackled this problem using both single cell and cardiac muscle bundle approaches that induce cell/tissue organization and hence make structure/function quantification highly tractable. We are also using functional genomics approaches (see below), including CRISPR-activation based screens, to identify regulators of developmental maturation of iPSC-CMs. Our lab is part of the NSF-funded engineering research center, CELL-MET (https://www.bu.edu/cell-met/). The goals of this ERC include development of cardiac patch technology and improving the robustness of muscle bundle platforms. Participation in CELL-MET allows regular interaction with a diverse group of scientists with expertise spanning biomedical engineering, iPSC-CM based technologies, and cardiovascular biology (https://www.bu.edu/cell-met/about-us/5256-2/). At the University of Michigan, we collaborate closely with the Baker (https://www.baker.bme.umich.edu/), Heemskerk (https://idseheemskerk.com/), and Nordsletten (https://heart.engin.umich.edu/) labs.
Previous studies include:
Tsan YC, DePalma SJ, Zhao YT, Capilnasiu A, Wu YW, Elder B, Panse I, Ufford K, Matera DL, Friedline S, O'Leary TS, Wubshet N, Ho KKY, Previs MJ, Nordsletten D, Isom LL, Baker BM, Liu AP, Helms AS§. Physiologic biomechanics enhance reproducible contractile development in a stem cell derived cardiac muscle platform. Nature Communications. 2021, 12(1):6167. PMCID: PMC8546060.
Ufford K, Friedline S, Tong Z, Tang VT, Dobbs AS, Tsan YC, Bielas SL, Liu AP, Helms AS§. Myofibrillar Structural Variability Underlies Contractile Function in Stem Cell-Derived Cardiomyocytes. Stem Cell Reports. 2021;16(3):470-477. PMCID: PMC7940249.
DePalma SJ, Davidson CD, Stis AE, Helms AS, Baker BM. Microenvironmental determinants of organized iPSC-cardiomyocyte tissues on synthetic fibrous matrices. Biomater Sci. 2021, 9(1):93-107. PMCID: PMC7971708.
DePalma SJ, Jillberto J, Stis AE, Huang DD, Lo J, Davidson CD, Chowdhury A, Jewett ME, Kobeissi H, Chen CS, Lejeune E, Helms AS, Nordsletten DA, Baker BM. Matrix architecture and mechanics regulate myofibril organization, costamere assembly, and contractility of engineered myocardial microtissues. BioRxiv. 2023, Oct 23. PMID: 37961415.
Code for myofilament and contractile quantification using our cardiac muscle bundle approach is shared on GitHub:
https://github.com/Cardiomyocyte-Imaging-Analysis/
Cardiac muscle bundle platform enables highly organized development of iPSC-CMs with aligned myofibrils and a uniaxial contractile direction that is highly tractable for automated contractile quantification. See more at https://www.nature.com/articles/s41467-021-26496-1.
Single cell micropatterned iPSC-CMs on polyacrylamide gels enable real-time tracking of contractile function and live-cell imaging of myofibrillar structure. See more at https://doi.org/10.1016/j.stemcr.2021.01.007.
Functional Genomics
We further take advantage of the scale possible with human iPSC-CMs to develop functional genomics approaches. We have performed CRISPR-activation based screens to identify regulators of cardiac maturation using reporter cells through our work with NSF-RECODE and NSF-CELL-MET projects. In a new project, we are systematically mapping the role of noncoding variants in affecting gene expression for major causes of cardiomyopathy. In the process, we are parsing the transcription factor grammar responsible for regulating expression of key cardiomyopathy associated genes. We collaborate with the Kitzman lab (https://medicine.umich.edu/dept/human-genetics/jacob-kitzman-phd) on these projects.
