Zachary T. Weber

BACKGROUND: Cardiomyopathies frequently arise from rare, highly penetrant coding variants with variable clinical expressivity. Genome-wide association studies (GWAS) suggest significant polygenic contributions to cardiovascular diseases, including cardiomyopathy. Most GWAS loci map to poorly conserved noncoding regions, requiring human genome context for experimental validation. METHODS: We created engineered heart tissues (EHTs) from human induced pluripotent stem cell-derived cardiomyocytes and primary cardiac fibroblasts. We assayed single-cell gene expression and chromatin accessibility to generate comprehensive genome-wide regulatory maps. Open chromatin regions were integrated with chromatin contact information and used to fine-map cardiomyopathy GWAS single-nucleotide polymorphisms. Single-nucleotide polymorphisms and their associated open chromatin regions were assessed using reporter assays, genome editing, and expression profiling. RESULTS: EHT Single-cell RNA-seq recapitulated major cardiac cell types, with advanced cardiomyocyte maturation compared with monolayer human induced pluripotent stem cell cardiomyocytes. More than 400 000 open chromatin regions were resolved to cell types and assayed for transcription factor motifs. Functional fine-mapping of GWAS loci prioritized 5817 variants, and reporter assays validated allele-specific enhancer activity. We identified an intergenic chr3p25.1 locus harboring significant GWAS signals from both dilated cardiomyopathy and left ventricular ejection fraction. Several of these variants lie in open chromatin regions participating in long-range chromatin interactions with SLC6A6 and GRIP2 . Haplotype-resolved and synthetic reporter assays confirmed enhancer activity and narrowed candidate single-nucleotide polymorphisms. CRISPR-deletion of this region reduced expression of both SLC6A6 and GRIP2 , indicating the enhancer regulates the expression of multiple genes. EHTs with the enhancer deletion displayed markedly reduced contractile function, confirming that this enhancer region contributes to myocardial function. CONCLUSIONS: EHTs are an experimentally tractable platform for testing the function of noncoding variants as modifiers of cardiomyopathy. Variants fine-mapped from cardiomyopathies using EHT regulatory maps have functional consequences and provide a set of prioritized sites to advance the study of polygenic heart failure.

In response to hypoxic stress at high altitudes, variation at the EPAS1 locus has experienced strong selection in Tibetans. Functional dissection of the selection signals at this locus identified ENH5, an enhancer within the adaptive haplotype that has a blunted response to hypoxic stress in Tibetans. ENH5 was shown to be pleiotropic in several tissues related to hypoxia response, suggesting that a possible mechanism behind the strong selection signatures could be adaptive pleiotropy. Tibetans not only experience hypoxic conditions, but also cold temperatures due to the altitude and climate of the Tibetan Plateau. However, it is unclear whether cold temperatures affect ENH5 activity possibly contributing to the selective pressure at this locus. Here, we further characterized the role of ENH5 in subcutaneous white adipose tissue, an important tissue type that regulates body temperature in response to cold temperatures by releasing stored fat as heat through a process called thermogenesis. In this work, we investigated the role of ENH5 in adipocytes using ENH5 knockout mice (ENH5 KO), which phenocopy the reduced activity of the Tibetan allele. We show that ENH5 KO mice at normoxia and room temperature do not have significant differences in organismal phenotypes related to adiposity and metabolism compared to WT mice on a high fat diet. However, we detected effects of ENH5 conditional on thermogenic stimulation and hypoxia exposure, independently, in adipocytes cultured in vitro . Under either of these conditions, ENH5 KO has stronger differential expression of key genes involved in thermogenesis activity and adipocyte differentiation compared to WT. This differential response to thermogenic stimulation expands on the pleiotropic effects of the Tibetan ENH5 allele(s), in addition to those previously shown in well-established hypoxia-responsive tissues. Our results raise the possibility that pleiotropic effects of ENH5 may implicate unforeseen mechanisms, such as cellular energetics and thermogenesis, possibly contributing to the phenotypic adaptation to high altitude in Tibetans.

Background Inherited cardiomyopathies frequently arise from rare, highly penetrant coding variants with variable clinical expressivity. Recent biobank-scale genome-wide association studies (GWAS) suggest significant polygenic contributions to cardiovascular diseases, including cardiomyopathy. Most GWAS loci map to noncoding regions, which are poorly conserved across species, requiring a human genome context for experimental validation. Methods We created engineered heart tissues (EHTs) from human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes and primary cardiac fibroblasts. We assayed single-cell gene expression and chromatin accessibility to generate comprehensive genome-wide regulatory maps. Open chromatin regions (OCRs) were integrated with chromatin contact information and used to functionally fine-map single nucleotide polymorphisms (SNPs) in cardiomyopathy GWAS. SNPs and their associated regulatory regions were assessed using reporter assays, genome editing, and expression profiling. Results Single-cell RNA-seq of EHTs confirmed populations recapitulating major cell types found in hearts, with advanced cardiomyocyte maturation compared to monolayer hiPSC-cardiomyocytes. More than 400,000 OCRs were resolved to cell type and assayed for canonical transcription factor footprints. Functional fine-mapping of GWAS loci prioritized 5817 variants, and reporter assays on select variants validated allele-specific enhancer activity. We identified a locus harboring significant GWAS signals from both dilated cardiomyopathy and left ventricle ejection fraction in an intergenic region at chr3p25.1. Several of these variants lie in OCRs participating in long range chromatin interactions with SLC6A6 and GRIP2. Haplotype-resolved and synthetic reporter assays confirmed enhancer activity and narrowed candidate SNPs. CRISPR-deletion of this region reduced expression of both SLC6A6 and GRIP2, indicating the enhancer regulates the expression of more than one gene. Conclusions EHTs derived from hiPSCs are an experimentally tractable platform for testing the function of noncoding variants as modifiers of cardiomyopathy. Variants fine-mapped from cardiomyopathies using EHT regulatory maps have functional consequences and provide a set of prioritized sites to advance the study of polygenic heart failure liability.

Obesity-associated morbidity is exacerbated by abdominal obesity, which can be measured as the waist-to-hip ratio adjusted for the body mass index (WHRadjBMI). Here we identify genes associated with obesity and WHRadjBMI and characterize allele-sensitive enhancers that are predicted to regulate WHRadjBMI genes in women. We found that several waist-to-hip ratio-associated variants map within primate-specific Alu retrotransposons harboring a DNA motif associated with adipocyte differentiation. This suggests that a genetic component of adipose distribution in humans may involve co-option of retrotransposons as adipose enhancers. We evaluated the role of the strongest female WHRadjBMI-associated gene, SNX10, in adipose biology. We determined that it is required for human adipocyte differentiation and function and participates in diet-induced adipose expansion in female mice, but not males. Our data identify genes and regulatory mechanisms that underlie female-specific adipose distribution and mediate metabolic dysfunction in women.

Cell-free DNA (cfDNA) has the potential to inform tumor subtype classification and help guide clinical precision oncology. Here we develop Griffin, a framework for profiling nucleosome protection and accessibility from cfDNA to study the phenotype of tumors using as low as 0.1x coverage whole genome sequencing data. Griffin employs a GC correction procedure tailored to variable cfDNA fragment sizes, which generates a better representation of chromatin accessibility and improves the accuracy of cancer detection and tumor subtype classification. We demonstrate estrogen receptor subtyping from cfDNA in metastatic breast cancer. We predict estrogen receptor subtype in 139 patients with at least 5% detectable circulating tumor DNA with an area under the receive operator characteristic curve (AUC) of 0.89 and validate performance in independent cohorts (AUC = 0.96). In summary, Griffin is a framework for accurate tumor subtyping and can be generalizable to other cancer types for precision oncology applications.

PURPOSE: In metastatic triple-negative breast cancer (mTNBC), consistent biomarkers of immune checkpoint inhibitor (ICI) therapy benefit remain elusive. We evaluated the immune, genomic, and transcriptomic landscape of mTNBC in patients treated with ICIs. METHODS: We identified 29 patients with mTNBC treated with pembrolizumab or atezolizumab, either alone (n = 9) or in combination with chemotherapy (n = 14) or targeted therapy (n = 6), who had tumor tissue and/or blood available before ICI therapy for whole-exome sequencing. RNA sequencing and CIBERSORTx-inferred immune population analyses were performed (n = 20). Immune cell populations and programmed death-ligand 1 expression were assessed using multiplexed immunofluorescence (n = 18). Clonal trajectories were evaluated via serial tumor/circulating tumor DNA whole-exome sequencing (n = 4). Association of biomarkers with progression-free survival and overall survival (OS) was assessed. RESULTS: Progression-free survival and OS were longer in patients with high programmed death-ligand 1 expression and tumor mutational burden. Patients with longer survival also had a higher relative inferred fraction of CD8+ T cells, activated CD4+ memory T cells, M1 macrophages, and follicular helper T cells and enrichment of inflammatory gene expression pathways. A mutational signature of defective repair of DNA damage by homologous recombination was enriched in patients with both shorter OS and primary resistance. Exploratory analysis of clonal evolution among four patients treated with programmed cell death protein 1 blockade and a tyrosine kinase inhibitor suggested that clonal stability post-treatment was associated with short time to progression. CONCLUSION: This study identified potential biomarkers of response to ICIs among patients with mTNBC: high tumor mutational burden; presence of CD8+, CD4 memory T cells, follicular helper T cells, and M1 macrophages; and inflammatory gene expression pathways. Pretreatment deficiencies in the homologous recombination DNA damage repair pathway and the absence of or minimal clonal evolution post-treatment may be associated with worse outcomes.

Cell-free DNA (cfDNA) has the potential to inform tumor subtype classification and help guide clinical precision oncology. Here we developed Griffin, a new method for profiling nucleosome protection and accessibility from cfDNA to study the phenotype of tumors using as low as 0.1x coverage whole genome sequencing (WGS) data. Griffin employs a novel GC correction procedure tailored to variable cfDNA fragment sizes, which improves the prediction of chromatin accessibility. Griffin achieved excellent performance for detecting tumor cfDNA in early-stage cancer patients (AUC=0.96). Next, we applied Griffin for the first demonstration of estrogen receptor (ER) subtyping in metastatic breast cancer from cfDNA. We analyzed 254 samples from 139 patients and predicted ER subtype with high performance (AUC=0.89), leading to insights about tumor heterogeneity. In summary, Griffin is a framework for accurate clinical subtyping and can be generalizable to other cancer types for precision oncology applications.

Our pilot study tests whether university counseling centers (UCC) can apply the concept of cluster analysis, and geospatial analysis to identify clusters of “hot spots”. Participants: Study partici...

Certain regions on the surfaces of developing pollen grains exhibit very limited deposition of pollen wall exine. These regions give rise to pollen apertures, which are highly diverse in their patterns and specific for individual species. Arabidopsis thaliana pollen develops three equidistant longitudinal apertures. The precision of aperture formation suggests that, to create them, pollen employs robust mechanisms that generate distinct cellular domains. To identify players involved in this mechanism, we screened natural Arabidopsis accessions and discovered one accession, Martuba, whose apertures form abnormally due to the disruption of the protein kinase D6PKL3. During pollen development, D6PKL3 accumulates at the three plasma membrane domains underlying future aperture sites. Both D6PKL3 localization and aperture formation require kinase activity. Proper D6PKL3 localization is also dependent on a polybasic motif for phosphoinositide interactions, and we identified two phosphoinositides that are specifically enriched at the future aperture sites. The other known aperture factor, INAPERTURATE POLLEN1, fails to aggregate at the aperture sites in d6pkl3 mutants, changes its localization when D6PKL3 is mislocalized, and, in turn, affects D6PKL3 localization. The discovery of aperture factors provides important insights into the mechanisms cells utilize to generate distinct membrane domains, develop cell polarity, and pattern their surfaces.