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Pathological cardiac hypertrophy is associated with increased morbidity and mortality. Understanding the mechanisms whereby pathological cardiac growth can be reversed could be of therapeutic value. Here, we show that pathways leading to regression of pathological cardiac hypertrophy are strongly dependent on the hypertrophic trigger and are significantly modified by sex. Two pathological stimuli causing hypertrophy via distinct pathways were administered to male and female mice: angiotensin II (ANG II) or isoproterenol (Iso). Stimuli were removed after 7 days of treatment, and left ventricles (LVs) were studied at 1, 4, and 7 days. ANG II-treated females did not show regression after stimulus removal. Iso-treated males showed rapid LV hypertrophy regression. Somewhat surprisingly, RNAseq analysis at

Supplementary Tables 1-2, Figures 1-5 from Cancer Causes Cardiac Atrophy and Autophagy in a Sexually Dimorphic Manner

Approximately one-third of cancer deaths are caused by cachexia, a severe form of skeletal muscle and adipose tissue wasting that affects men more than women. The heart also undergoes atrophy in cancer patients, but the mechanisms and the basis for apparent sex differences are unclear. In a mouse colon-adenocarcinoma model, cancer causes a loss of cardiac mass due to a decrease in cardiac myocyte size that is associated with reduced levels of all sarcomeric proteins. Unlike skeletal muscle cachexia, atrophic hearts do not upregulate the ubiquitin-proteasome system or its activity but increase autophagy. Thus, cancer causes cardiac atrophy by a mechanism distinct from that in skeletal muscle. Male tumor-bearing mice have a more severe phenotype than females, including greater cardiac mass loss and mortality, a more robust pro-inflammatory response to the tumor, and greater cardiac autophagy. In females, estrogen protects against cancer-induced cardiac atrophy and body weight loss by signaling through its receptor. Sex differences in cardiac atrophy need to be considered during the treatment of patients suffering from chemotherapy-induced cardiomyopathy to prevent exacerbation of cardiac dysfunction. Cancer Res; 71(5); 1710–20. ©2010 AACR.

Variants in >12 genes encoding sarcomeric proteins can cause various cardiomyopathies. The two most common are hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM). Current therapeutics do not target the root causes of these diseases, but attempt to prevent disease progression and/or to manage symptoms. Accordingly, novel approaches are being developed to treat the cardiac muscle dysfunction directly. Challenges to developing therapeutics for these diseases include the diverse mechanisms of pathogenesis, some of which are still being debated and defined. Four small molecules that modulate the myosin motor protein in the cardiac sarcomere have shown great promise in the settings of HCM and DCM, regardless of the underlying genetic pathogenesis, and similar approaches are being developed to target other components of the sarcomere. In the setting of HCM, mavacamten and aficamten bind to the myosin motor and decrease the ATPase activity of myosin. In the setting of DCM, omecamtiv mecarbil and danicamtiv increase myosin activity in cardiac muscle (but omecamtiv mecarbil decreases myosin activity in vitro). In this Review, we discuss the therapeutic strategies to alter sarcomere contractile activity and summarize the data indicating that targeting one protein in the sarcomere can be effective in treating patients with genetic variants in other sarcomeric proteins, as well as in patients with non-sarcomere-based disease.

Background: Aortic valve stenosis is a sexually dimorphic disease, with women often presenting with sustained fibrosis and men with more extensive calcification. However, the intracellular molecular mechanisms that drive these clinically important sex differences remain underexplored. Methods: Hydrogel biomaterials were designed to recapitulate key aspects of the valve tissue microenvironment and to serve as a culture platform for sex-specific valvular interstitial cells (VICs; precursors to profibrotic myofibroblasts). The hydrogel culture system was used to interrogate intracellular pathways involved in sex-dependent VIC-to-myofibroblast activation and deactivation. RNA sequencing was used to define pathways involved in driving sex-dependent activation. Interventions with small molecule inhibitors and siRNA transfections were performed to provide mechanistic insight into sex-specific cellular responses to microenvironmental cues, including matrix stiffness and exogenously delivered biochemical factors. Results: In both healthy porcine and human aortic valves, female leaflets had higher baseline activation of the myofibroblast marker α-smooth muscle actin compared with male leaflets. When isolated and cultured, female porcine and human VICs had higher levels of basal α-smooth muscle actin stress fibers that further increased in response to the hydrogel matrix stiffness, both of which were higher than in male VICs. A transcriptomic analysis of male and female porcine VICs revealed Rho-associated protein kinase signaling as a potential driver of this sex-dependent myofibroblast activation. Furthermore, we found that genes that escape X-chromosome inactivation such as BMX and STS (encoding for Bmx nonreceptor tyrosine kinase and steroid sulfatase, respectively) partially regulate the elevated female myofibroblast activation through Rho-associated protein kinase signaling. This finding was confirmed by treating male and female VICs with endothelin-1 and plasminogen activator inhibitor-1, factors that are secreted by endothelial cells and known to drive myofibroblast activation through Rho-associated protein kinase signaling. Conclusions: Together, in vivo and in vitro results confirm sex dependencies in myofibroblast activation pathways and implicate genes that escape X-chromosome inactivation in regulating sex differences in myofibroblast activation and subsequent aortic valve stenosis progression. Our results underscore the importance of considering sex as a biological variable to understand the molecular mechanisms of aortic valve stenosis and to help guide sex-based precision therapies.

Myocardial fibrosis is a key pathologic feature of hypertrophic cardiomyopathy (HCM). However, the fibrotic pathways activated by HCM-causing sarcomere protein gene mutations are poorly defined. Because lysophosphatidic acid is a mediator of fibrosis in multiple organs and diseases, we tested the role of the lysophosphatidic acid pathway in HCM. Lysphosphatidic acid receptor 1 (LPAR1), a cell surface receptor, is required for lysophosphatidic acid mediation of fibrosis. We bred HCM mice carrying a pathogenic myosin heavy-chain variant (403 +/− ) with Lpar1 -ablated mice to create mice carrying both genetic changes (403 +/− LPAR1 −/− ) and assessed development of cardiac hypertrophy and fibrosis. Compared with 403 +/− LPAR1 WT , 403 +/− LPAR1 −/− mice developed significantly less hypertrophy and fibrosis. Single-nucleus RNA sequencing of left ventricular tissue demonstrated that Lpar1 was predominantly expressed by lymphatic endothelial cells (LECs) and cardiac fibroblasts. Lpar1 ablation reduced the population of LECs, confirmed by immunofluorescence staining of the LEC markers Lyve1 and Ccl21a and, by in situ hybridization, for Reln and Ccl21a . Lpar1 ablation also altered the distribution of fibroblast cell states. FB1 and FB2 fibroblasts decreased while FB0 and FB3 fibroblasts increased. Our findings indicate that Lpar1 is expressed predominantly by LECs and fibroblasts in the heart and is required for development of hypertrophy and fibrosis in an HCM mouse model. LPAR1 antagonism, including agents in clinical trials for other fibrotic diseases, may be beneficial for HCM.

Nearly all cardiovascular diseases show sexual dimorphisms in prevalence, presentation, and outcomes. Until recently, most clinical trials were carried out in males, and many animal studies either failed to identify the sex of the animals or combined data obtained from males and females. Cellular sex in the heart is relatively understudied and many studies fail to report the sex of the cells used for in vitro experiments. Moreover, in the small number of studies in which sex is reported, most of those studies use male cells. The observation that cells from males and females are inherently different is becoming increasingly clear - either due to acquired differences from hormones and other factors or due to intrinsic differences in genotype (XX or XY). Because of the likely contribution of cellular sex differences in cardiac health and disease, here, we explore differences in mammalian male and female cells in the heart, including the less-studied non-myocyte cell populations. We discuss how the heart's microenvironment impacts male and female cellular phenotypes and vice versa, including how secretory profiles are dependent on cellular sex, and how hormones contribute to sexually dimorphic phenotypes and cellular functions. Intracellular mechanisms that contribute to sex differences, including gene expression and epigenetic remodeling, are also described. Recent single-cell sequencing studies have revealed unexpected sex differences in the composition of cell types in the heart which we discuss. Finally, future recommendations for considering cellular sex differences in the design of bioengineered in vitro disease models of the heart are provided.

Left ventricular hypertrophy is a leading risk factor for cardiovascular morbidity and mortality. Although reverse ventricular remodelling was long thought to be irreversible, evidence from the past three decades indicates that this process is possible with many existing heart disease therapies. The regression of pathological hypertrophy is associated with improved cardiac function, quality of life and long-term health outcomes. However, less than 50% of patients respond favourably to most therapies, and the reversibility of remodelling is influenced by many factors, including age, sex, BMI and disease aetiology. Cardiac hypertrophy also occurs in physiological settings, including pregnancy and exercise, although in these cases, hypertrophy is associated with normal or improved ventricular function and is completely reversible postpartum or with cessation of training. Studies over the past decade have identified the molecular features of hypertrophy regression in health and disease settings, which include modulation of protein synthesis, microRNAs, metabolism and protein degradation pathways. In this Review, we summarize the evidence for hypertrophy regression in patients with current first-line pharmacological and surgical interventions. We further discuss the molecular features of reverse remodelling identified in cell and animal models, highlighting remaining knowledge gaps and the essential questions for future investigation towards the goal of designing specific therapies to promote regression of pathological hypertrophy.

The design of compounds that can discriminate between closely related target proteins remains a central challenge in drug discovery. Specific therapeutics targeting the highly conserved myosin motor family are urgently needed as mutations in at least 6 of its members cause numerous diseases. Allosteric modulators, like the myosin-II inhibitor blebbistatin, are a promising means to achieve specificity. However, it remains unclear why blebbistatin inhibits myosin-II motors with different potencies given that it binds at a highly conserved pocket that is always closed in blebbistatin-free experimental structures. We hypothesized that the probability of pocket opening is an important determinant of the potency of compounds like blebbistatin. To test this hypothesis, we used Markov state models (MSMs) built from over 2 milliseconds of aggregate molecular dynamics simulations with explicit solvent. We find that blebbistatin’s binding pocket readily opens in simulations of blebbistatin-sensitive myosin isoforms. Comparing these conformational ensembles reveals that the probability of pocket opening correctly identifies which isoforms are most sensitive to blebbistatin inhibition and that docking against MSMs quantitatively predicts blebbistatin binding affinities (R2=0.82). To test our ability to make blind predictions, we predicted blebbistatin’s binding affinity for an isoform (Myh7b) whose blebbistatin sensitivity was unknown. Encouragingly, we find good agreement between the predicted and measured IC50 (0.67 µM vs. 0.36 µM). Therefore, we expect this framework to be useful for the development of novel specific drugs across numerous protein targets.SignificanceDrug development requires the discovery of compounds which specifically target one member of a protein family without triggering side effects that arise from interactions with other related proteins. Myosins are a family of motor proteins that are drug targets for heart diseases, cancer, and parasitic infections. Here, we investigate why the compound blebbistatin specifically inhibits some myosins more potently than others, even though its binding site is closed in all known experimental structures. We find that the blebbistatin binding pocket opens in molecular dynamics simulations of certain myosin motors, and that the probability of opening predicts how potently blebbistatin inhibits a particular motor. Our work suggests that differences in cryptic pocket formation can be exploited to develop specific therapeutics.

Background The coronavirus disease 2019 pandemic spread to >200 countries in Methods Given high residence hall student density, the University of Colorado Boulder established a mandatory weekly screening test program. We analyzed longitudinal data from 6408 students and identified 116 likely transmission events in which a second roommate tested positive within 14 days of the index roommate. Results Although the infection rate was lower in single-occupancy rooms (10%) than in multiple-occupancy rooms (19%), interroommate transmission occurred only about 20% of the time. Cases were usually asymptomatic at the time of detection. Notably, individuals who likely transmitted had an average viral load approximately 6.5-fold higher than individuals who did not (mean quantification cycle [Cq], 26.2 vs 28.9). Although students with diagnosed SARS-CoV-2 infection moved to isolation rooms, there was no difference in time to isolation between cases with or without interroommate transmission. Conclusions This analysis argues that interroommate transmission occurs infrequently in residence halls and provides strong correlative evidence that viral load is proportional to transmission probability.

Non-traditional animal models present an opportunity to discover novel biology that has evolved to allow such animals to survive in extreme environments. One striking example is the Burmese python (Python molurus bivittatus), which exhibits extreme physiological adaptation in various metabolic organs after consuming a large meal following long periods of fasting. The response to such a large meal in pythons involves a dramatic surge in metabolic rate, lipid overload in plasma, and massive but reversible organ growth through the course of digestion. Multiple studies have reported the physiological responses in post-prandial pythons, while the specific molecular control of these processes is less well-studied. Investigating the mechanisms that coordinate organ growth and adaptive responses offers the opportunity to gain novel insight that may be able to treat various pathologies in humans. Here, we summarize past research on the post-prandial physiological changes in the Burmese python with a focus on the gastrointestinal tract, heart, and liver. Specifically, we address our recent molecular discoveries in the post-prandial python liver which demonstrate transient adaptations that may reveal new therapeutic targets. Lastly, we explore new biology of the aquaporin 7 gene that is potently upregulated in mammalian cardiac myocytes by circulating factors in post-prandial python plasma.

Numerous diseases, including those of the heart, are characterized by increased stiffness due to excessive deposition of extracellular matrix proteins. Cardiomyocytes continuously adapt their morphology and function to the mechanical changes of their microenvironment. Because traditional cell culture is conducted on substrates that are many orders of magnitude stiffer than any environment encountered by a cardiomyocyte in health or disease, alternate culture systems are necessary to model these processes in vitro. Here, we employ photo-clickable thiol-ene poly(ethylene glycol) (PEG) hydrogels for three-dimensional cell culture of adult mouse cardiomyocytes. PEG hydrogels serve as versatile biocompatible scaffolds, whose stiffness can be precisely tuned to mimic physiological and pathological microenvironments. Compared to traditional culture, adult cardiomyocytes encapsulated in PEG hydrogels exhibited longer survival and preserved sarcomeric and T-tubular architecture. Culture in PEG hydrogels of varying stiffnesses regulated the subcellular localization of the mechanosensitive transcription factor, YAP, in adult cardiomyocytes, indicating PEG hydrogels offer a versatile platform to study the role of mechanical cues in cardiomyocyte biology.

Myosin heavy chain 7b (MYH7b) is an evolutionarily ancient member of the sarcomeric myosin family, which typically supports striated muscle function. However, in mammals, alternative splicing prevents MYH7b protein production in cardiac and most skeletal muscles and limits expression to a subset of specialized muscles and certain nonmuscle environments. In contrast, MYH7b protein is abundant in python cardiac and skeletal muscles. Although the MYH7b expression pattern diverges in mammals versus reptiles, MYH7b shares high sequence identity across species. So, it remains unclear how mammalian MYH7b function may differ from that of other sarcomeric myosins and whether human and python MYH7b motor functions diverge as their expression patterns suggest. Thus, we generated recombinant human and python MYH7b protein and measured their motor properties to investigate any species-specific differences in activity. Our results reveal that despite having similar working strokes, the MYH7b isoforms have slower actin-activated ATPase cycles and actin sliding velocities than human cardiac β-MyHC. Furthermore, python MYH7b is tuned to have slower motor activity than human MYH7b because of slower kinetics of the chemomechanical cycle. We found that the MYH7b isoforms adopt a higher proportion of myosin heads in the ultraslow, super-relaxed state compared with human cardiac β-MyHC. These findings are supported by molecular dynamics simulations that predict MYH7b preferentially occupies myosin active site conformations similar to those observed in the structurally inactive state. Together, these results suggest that MYH7b is specialized for slow and energy-conserving motor activity and that differential tuning of MYH7b orthologs contributes to species-specific biological roles.

As an opportunistic predator, the Burmese python (Python molurus bivittatus) consumes large and infrequent meals, fasting for up to a year. Upon consuming a large meal, the Burmese python exhibits extreme metabolic responses. To define the pathways that regulate these postprandial metabolic responses, we performed a comprehensive profile of plasma metabolites throughout the digestive process. Following ingestion of a meal equivalent to 25% of its body mass, plasma lipoproteins and metabolites, such as chylomicra and bile acids, reach levels observed only in mammalian models of extreme dyslipidemia. Here, we provide evidence for an adaptive response to postprandial nutrient overload by the python liver, a critical site of metabolic homeostasis. The python liver undergoes a substantial increase in mass through proliferative processes, exhibits hepatic steatosis, hyperlipidemia-induced insulin resistance indicated by PEPCK activation and pAKT deactivation, and de novo fatty acid synthesis via FASN activation. This postprandial state is completely reversible. We posit that Burmese pythons evade the permanent hepatic damage associated with these metabolic states in mammals using evolved protective measures to inactivate these pathways. These include a transient activation of hepatic nuclear receptors induced by fatty acids and bile acids, including PPAR and FXR, respectively. The stress-induced p38 MAPK pathway is also transiently activated during the early stages of digestion. Taken together, these data identify a reversible metabolic response to hyperlipidemia by the python liver, only achieved in mammals by pharmacologic intervention. The factors involved in these processes may be relevant to or leveraged for remediating human hepatic pathology.

Background Although the roles of alpha‐myosin heavy chain (α‐MyHC) and beta‐myosin heavy chain (β‐MyHC) proteins in cardiac contractility have long been appreciated, the biological contribution of another closely related sarcomeric myosin family member, MYH7b (myosin heavy chain 7b), has become a matter of debate. In mammals, MYH7b mRNA is transcribed but undergoes non‐productive alternative splicing that prevents protein expression in a tissue‐specific manner, including in the heart. However, several studies have recently linked MYH7b variants to different cardiomyopathies or have reported MYH7b protein expression in mammalian hearts. Methods and Results By analyzing mammalian cardiac transcriptome and proteome data, we show that the vast majority of MYH7b RNA is subject to exon skipping and cannot be translated into a functional myosin molecule. Notably, we discovered a lag in the removal of introns flanking the alternatively spliced exon, which could retain the non‐coding RNA in the nucleus. This process could play a significant role in controlling MYH7b expression as well as the activity of other cardiac genes. Consistent with the negligible level of full‐length protein coding mRNA, no MYH7b protein expression was detected in adult mouse, rat, and human hearts by Western blot analysis. Furthermore, proteome surveys including quantitative mass spectrometry analyses revealed only traces of cardiac MYH7b protein and even then, only in a subset of individual samples. Conclusions The comprehensive analysis presented here suggests that previous studies showing cardiac MYH7b protein expression were likely attributable to antibody cross‐reactivity. More importantly, our data predict that the MYH7b disease‐associated variants may operate through the alternately spliced RNA itself.

The speed of muscle contraction is related to body size; muscles in larger species contract at slower rates. Since contraction speed is a property of the myosin isoform expressed in a muscle, we investigated how sequence changes in a range of muscle myosin II isoforms enable this slower rate of muscle contraction. We considered 798 sequences from 13 mammalian myosin II isoforms to identify any adaptation to increasing body mass. We identified a correlation between body mass and sequence divergence for the motor domain of the 4 major adult myosin II isoforms (β/Type I, IIa, IIb, and IIx), suggesting that these isoforms have adapted to increasing body mass. In contrast, the non-muscle and developmental isoforms show no correlation of sequence divergence with body mass. Analysis of the motor domain sequence of β-myosin (predominant myosin in Type I/slow and cardiac muscle) from 67 mammals from 2 distinct clades identifies 16 sites, out of 800, associated with body mass (padj < 0.05) but not with the clade (padj > 0.05). Both clades change the same small set of amino acids, in the same order from small to large mammals, suggesting a limited number of ways in which contraction velocity can be successfully manipulated. To test this relationship, the 9 sites that differ between human and rat were mutated in the human β-myosin to match the rat sequence. Biochemical analysis revealed that the rat–human β-myosin chimera functioned like the native rat myosin with a 2-fold increase in both motility and in the rate of ADP release from the actin–myosin crossbridge (the step that limits contraction velocity). Thus, these sequence changes indicate adaptation of β-myosin as species mass increased to enable a reduced contraction velocity and heart rate., Heart and skeletal muscles of larger mammals contract more slowly than smaller ones. This study identifies amino acid changes in myosin isoforms that correlate with species size; mutating the residues in human β-myosin to match the rat sequence at these positions increased its in vitro velocity to that of the rat protein.

Background Biological sex is an important modifier of cardiovascular disease and women generally have better outcomes compared with men. However, the contribution of cardiac fibroblasts (CFs) to this sexual dimorphism is relatively unexplored. Methods and Results Isoproterenol (ISO) was administered to rats as a model for chronic β‐adrenergic receptor (β‐AR)‐mediated cardiovascular disease. ISO‐treated males had higher mortality than females and also developed fibrosis whereas females did not. Gonadectomy did not abrogate this sex difference. To determine the cellular contribution to this phenotype, CFs were studied. CFs from both sexes had increased proliferation in vivo in response to ISO, but CFs from female hearts proliferated more than male cells. In addition, male CFs were significantly more activated to myofibroblasts by ISO. To investigate potential regulatory mechanisms for the sexually dimorphic fibrotic response, β‐AR mRNA and PKA (protein kinase A) activity were measured. In response to ISO treatment, male CFs increased expression of β1‐ and β2‐ARs, whereas expression of both receptors decreased in female CFs. Moreover, ISO‐treated male CFs had higher PKA activity relative to vehicle controls, whereas ISO did not activate PKA in female CFs. Conclusions Chronic in vivo β‐AR stimulation causes fibrosis in male but not female rat hearts. Male CFs are more activated than female CFs, consistent with elevated fibrosis in male rat hearts and may be caused by higher β‐AR expression and PKA activation in male CFs. Taken together, our data suggest that CFs play a substantial role in mediating sex differences observed after cardiac injury.

Significance We analyzed data from saliva-based COVID-19 screening deployed on the University of Colorado Boulder campus. Our dataset is unique in that all SARS-CoV-2−positive individuals reported no symptoms at the time of saliva collection, and therefore were infected but asymptomatic or presymptomatic. We found that 1) the distribution of viral loads observed in our asymptomatic college population was indistinguishable from what has been reported in hospitalized populations; 2) regardless of symptomatic status, approximately 50% of individuals who test positive for SARS-CoV-2 seem to be in noninfectious phases of the infection; and 3) just 2% of infected individuals carry 90% of the virions circulating within communities, serving as viral “supercarriers” and likely also superspreaders., We analyze data from the fall 2020 pandemic response efforts at the University of Colorado Boulder, where more than 72,500 saliva samples were tested for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) using qRT-PCR. All samples were collected from individuals who reported no symptoms associated with COVID-19 on the day of collection. From these, 1,405 positive cases were identified. The distribution of viral loads within these asymptomatic individuals was indistinguishable from what has been previously observed in symptomatic individuals. Regardless of symptomatic status, ∼50% of individuals who test positive for SARS-CoV-2 seem to be in noninfectious phases of the disease, based on having low viral loads in a range from which live virus has rarely been isolated. We find that, at any given time, just 2% of individuals carry 90% of the virions circulating within communities, serving as viral “supercarriers” and possibly also superspreaders.

Aortic valve stenosis (AVS) is a progressive fibrotic disease that is caused by thickening and stiffening of valve leaflets. At the cellular level, quiescent valve interstitial cells (qVICs) activate to myofibroblasts (aVICs) that persist within the valve tissue. Given the persistence of myofibroblasts in AVS, epigenetic mechanisms have been implicated. Here, we studied changes that occur in VICs during myofibroblast activation by using a hydrogel matrix to recapitulate different stiffnesses in the valve leaflet during fibrosis. We first compared the chromatin landscape of qVICs cultured on soft hydrogels and aVICs cultured on stiff hydrogels, representing the native and diseased phenotypes respectively. Using assay for transposase-accessible chromatin sequencing (ATAC-Seq), we found that open chromatin regions in aVICs were enriched for transcription factor binding motifs associated with mechanosensing pathways compared to qVICs. Next, we used RNA-Seq to show that the open chromatin regions in aVICs correlated with pro-fibrotic gene expression, as aVICs expressed higher levels of contractile fiber genes, including myofibroblast markers such as alpha smooth muscle actin (αSMA), compared to qVICs. In contrast, chromatin remodeling genes were downregulated in aVICs compared to qVICs, indicating qVICs may be protected from myofibroblast activation through epigenetic mechanisms. Small molecule inhibition of one of these remodelers, CREB Binding Protein (CREBBP), prevented qVICs from activating to aVICs. Notably, CREBBP is more abundant in valves from healthy patients compared to fibrotic valves. Our findings reveal the role of mechanical regulation in chromatin remodeling during VIC activation and quiescence and highlight one potential therapeutic target for treating AVS.

In 2019-2020, the COVID-19 pandemic spread to over 200 countries in less than six months. To understand the basis of this aggressive spread, it is essential to determine the transmission rate and define the factors that increase the risk of transmission. One complication is the large fraction of asymptomatic cases, particularly in young populations: these individuals have viral loads indistinguishable from symptomatic people and do transmit the SARS-CoV-2 virus, but they often go undetected. As university students living in residence halls commonly share a small living space with roommates, some schools established regular, high density testing programs to mitigate on-campus spread. In this study, we analyzed longitudinal testing data of residence hall students at the University of Colorado Boulder. We observed that students in single rooms were infected at a lower rate than students in multiple occupancy rooms. However, this was not due to high rates of transmission between roommates, which only occurred approximately 20% of the time. Since these cases were usually asymptomatic at the time of diagnosis, this provides further evidence for asymptomatic transmission. Notably, individuals who likely transmitted to their roommates had an average viral load ∼6.5 times higher than individuals who did not. Although students were moved to separate isolation rooms after diagnosis, there was no difference in time to isolation between these cases with or without transmission. This analysis argues that inter-roommate transmission occurs in a minority of cases in university residence halls and provides strong correlative evidence that viral load can be proportional to the probability of transmission.

Background Cardiac fibroblasts (CFs) have the ability to sense stiffness changes and respond to biochemical cues to modulate their states as either quiescent or activated myofibroblasts. Given the potential for secretion of bioactive molecules to modulate the cardiac microenvironment, we sought to determine how the CF secretome changes with matrix stiffness and biochemical cues and how this affects cardiac myocytes via paracrine signaling. Methods and Results Myofibroblast activation was modulated in vitro by combining stiffness cues with TGFβ1 (transforming growth factor β 1) treatment using engineered poly (ethylene glycol) hydrogels, and in vivo with isoproterenol treatment. Stiffness, TGFβ1, and isoproterenol treatment increased AKT (protein kinase B) phosphorylation, indicating that this pathway may be central to myofibroblast activation regardless of the treatment. Although activation of AKT was shared, different activating cues had distinct effects on downstream cytokine secretion, indicating that not all activated myofibroblasts share the same secretome. To test the effect of cytokines present in the CF secretome on paracrine signaling, neonatal rat ventricular cardiomyocytes were treated with CF conditioned media. Conditioned media from myofibroblasts cultured on stiff substrates and activated by TGFβ1 caused hypertrophy, and one of the cytokines in that media was insulin growth factor 1, which is a known mediator of cardiac myocyte hypertrophy. Conclusions Culturing CFs on stiff substrates, treating with TGFβ1, and in vivo treatment with isoproterenol all caused myofibroblast activation. Each cue had distinct effects on the secretome or genes encoding the secretome, but only the secretome of activated myofibroblasts on stiff substrates treated with TGFβ1 caused myocyte hypertrophy, most likely through insulin growth factor 1.

Pythons are infrequent feeders that can ingest meals equal to their own body mass. The extreme metabolic response required to digest such large meals is associated with a dramatic increase in the mass of most organs, including the heart. Recently, we have been able to assess functional effects of feeding using isolated python cardiomyocytes and myofibrils, advancing our understanding of extreme cardiac adaptation in python ( Python regius ). Twenty-four hours after feeding, python cardiomyocytes showed prolonged Ca 2+ transients, increased maximal tension and Ca 2+ sensitivity of myofibrils as compared to fasted pythons. Post-prandial positive inotropy was accompanied by enhanced metabolic output via increased mitochondrial ATP production rate and by AMP-dependent kinase (AMPK) activation and phosphofructokinase-2 reduction, suggesting a key role for fatty acid, but not glucose, metabolism after feeding. In addition, 24h post-fed hearts had significantly reduced tissue stiffness and myofibril passive tension. Finally, chromatin condensation was reduced about 30% after feeding in python cardiomyocytes and confirmed by increased histone acetylation, indicating a predominant role for epigenetics in post-prandial adaptation. These results suggest that feeding promotes positive cardiac inotropy in python via a number of coordinated mechanisms to enhance energy production, increase myofibril and tissue compliance, and increase chromatin accessibility. As heart failure is commonly characterized by depressed contractility, compromised energetics, and increased tissue stiffness, assessing post-prandial adaptation in python hearts provides us with powerful insights that could inform the development of therapeutics for human heart diseases.

Here, we develop a simple molecular test for SARS-CoV-2 in saliva based on reverse transcription loop-mediated isothermal amplification (RT-LAMP). The test has two steps: 1) heat saliva with a stabilization solution, and 2) detect virus by incubating with a primer/enzyme mix. After incubation, saliva samples containing the SARS-CoV-2 genome turn bright yellow. Because this test is pH dependent, it can react falsely to some naturally acidic saliva samples. We report unique saliva stabilization protocols that rendered 295 healthy saliva samples compatible with the test, producing zero false positives. We also evaluated the test on 278 saliva samples from individuals who were infected with SARS-CoV-2 but had no symptoms at the time of saliva collection, and from 54 matched pairs of saliva and anterior nasal samples from infected individuals. The Saliva TwoStep test described herein identified infections with 94% sensitivity and >99% specificity in individuals with sub-clinical (asymptomatic or pre-symptomatic) infections.

During pregnancy, the heart undergoes significant and numerous changes, including hypertrophy, that are usually described as physiological and reversible. Two aspects of the cardiac response to pregnancy are relatively understudied: advanced maternal age and multiple pregnancies (multiparity). Repeated breeder (RB) mice that have undergone five to seven consecutive pregnancies were euthanized 21 days after the weaning of their last pups and compared with age-matched primiparous, one-time pregnant (O1P) mice. The ages of the older mouse groups were similar (12 ± 1 mo). Pregnancy at a later age resulted in reduced fertility (40%); resorption was 29%, maternal mortality was 10%, and mortality of the pups was 17%. Contractile function as indicated by percent fractional shortening was significantly decreased in O1P and RB groups compared with the old nonpregnant control (ONP) group. There was no pathological induction of the fetal program of gene expression, with the exception of β-myosin heavy chain mRNA, which was induced in O1P compared with ONP mice ( P < 0.05) but not in RB mice. MicroRNA-208a was significantly increased in O1P compared with ONP mice ( P < 0.05) but significantly decreased in RB compared with ONP mice ( P < 0.05). mRNA of genes regulating angiogenesis (i.e., vascular endothelial growth factor-A) were significantly downregulated, whereas proinflammatory genes [i.e., interleukin-6, chemokine (C-C motif) ligand 2, and Cd36] were significantly upregulated in O1P ( P < 0.05) but not in RB mice. Overall, our results suggest that rather than multiparity, pregnancy in advanced age is a much more stressful event in both pregnant dams and fetuses, as evidenced by increased mortality, lower fertility, downregulation of angiogenesis, upregulation of inflammation, and cardiac dysfunction. NEW & NOTEWORTHY Pregnancy in older mice significantly decreases cardiac function, although repeated breeder mice demonstrated increased wall hypertrophy and dilated chamber size compared with one-time pregnant mice. Interestingly, many of the molecular changes were altered in one-time pregnant mice but not in repeated breeder mice, which may contribute to adverse pregnancy outcomes in a first pregnancy at a later age.

Background: Hypertrophic cardiomyopathy (HCM) is characterized by myocyte hypertrophy and fibrosis. Studies in two mouse models (R92W-TnT/R403Q-MyHC) at early HCM stage revealed upregulation of endothelin (ET1) signaling in both mutants, but TGFβ signaling only in TnT mutants. Dysregulation of miR-29 expression has been implicated in cardiac fibrosis. But it is unknown whether expression of miR-29a/b/c and profibrotic genes is commonly regulated in mouse and human HCM. Methods: In order to understand mechanisms underlying fibrosis in HCM, and examine similarities/differences in expression of miR-29a/b/c and several profibrotic genes in mouse and human HCM, we performed parallel studies in rat cardiac myocyte/fibroblast cultures, examined gene expression in two mouse models of (non-obstructive) HCM (R92W-TnT, R403Q-MyHC)/controls at early (5 weeks) and established (24 weeks) disease stage, and analyzed publicly available mRNA/miRNA expression data from obstructive-HCM patients undergoing septal myectomy/controls (unused donor hearts). Results: Myocyte cultures: ET1 increased superoxide/H2O2, stimulated TGFβ expression/secretion, and suppressed miR-29a expression in myocytes. The effect of ET1 on miR-29 and TGFβ expression/secretion was antagonized by N-acetyl-cysteine, a reactive oxygen species scavenger. Fibroblast cultures: ET1 had no effect on pro-fibrotic gene expression in fibroblasts. TGFβ1/TGFβ2 suppressed miR-29a and increased collagen expression, which was abolished by miR-29a overexpression. Mouse and human HCM: Expression of miR-29a/b/c was lower, and TGFB1/collagen gene expression was higher in TnT mutant-LV at 5 and 24 weeks; no difference was observed in expression of these genes in MyHC mutant-LV and in human myectomy tissue. TGFB2 expression was higher in LV of both mutant mice and human myectomy tissue. ACE2, a negative regulator of the renin-angiotensin-aldosterone system, was the most upregulated transcript in human myectomy tissue. Pathway analysis predicted upregulation of the anti-hypertrophic/anti-fibrotic liver X receptor/retinoid X receptor (LXR/RXR) pathway only in human myectomy tissue. Conclusions: Our in vitro studies suggest that activation of ET1 signaling in cardiac myocytes increases reactive oxygen species and stimulates TGFβ secretion, which downregulates miR-29a and increases collagen in fibroblasts, thus contributing to fibrosis. Our gene expression studies in mouse and human HCM reveal allele-specific differences in miR-29 family/profibrotic gene expression in mouse HCM, and activation of anti-hypertrophic/anti-fibrotic genes and pathways in human HCM.

Exercise elicits coordinated multi-organ responses including skeletal muscle, vasculature, heart, and lung. In the short term, the output of the heart increases to meet the demand of strenuous exercise. Long-term exercise instigates remodeling of the heart including growth and adaptive molecular and cellular re-programming. Signaling pathways such as the insulin-like growth factor 1/PI3K/Akt pathway mediate many of these responses. Exercise-induced, or physiologic, cardiac growth contrasts with growth elicited by pathological stimuli such as hypertension. Comparing the molecular and cellular underpinnings of physiologic and pathologic cardiac growth has unveiled phenotype-specific signaling pathways and transcriptional regulatory programs. Studies suggest that exercise pathways likely antagonize pathological pathways, and exercise training is often recommended for patients with chronic stable heart failure or following myocardial infarction. Herein, we summarize the current understanding of the structural and functional cardiac responses to exercise as well as signaling pathways and downstream effector molecules responsible for these adaptations.

Adults who were affected by intrauterine growth restriction (IUGR) suffer from reductions in muscle mass and insulin resistance, suggesting muscle growth may be restricted by molecular events that occur during fetal development. To explore the basis of restricted fetal muscle growth, we used a sheep model of progressive placental insufficiency-induced IUGR to assess myoblast proliferation within intact skeletal musclein vivoand isolated myoblasts stimulated with insulinin vitro. Gastrocnemius and soleus muscle weights were reduced by 25% in IUGR fetuses compared to those in controls (CON). The ratio of PAX7+ nuclei (a marker of myoblasts) to total nuclei was maintained in IUGR muscle compared to CON, but the fraction of PAX7+ myoblasts that also expressed Ki-67 (a marker of cellular proliferation) was reduced by 23%. Despite reduced proliferationin vivo, fetal myoblasts isolated from IUGR biceps femoris and cultured in enriched mediain vitroresponded robustly to insulin in a dose- and time-dependent manner to increase proliferation. Similarly, insulin stimulation of IUGR myoblasts upregulated key cell cycle genes and DNA replication. There were no differences in the expression of myogenic regulatory transcription factors that drive commitment to muscle differentiation between CON and IUGR groups. These results demonstrate that the molecular machinery necessary for transcriptional control of proliferation remains intact in IUGR fetal myoblasts, indicating thatin vivofactors such as reduced insulin and IGF1, hypoxia and/or elevated counter-regulatory hormones may be inhibiting muscle growth in IUGR fetuses.

The transcatheter aortic valve replacement (TAVR) procedure has emerged as a minimally invasive treatment for patients with aortic valve stenosis (AVS). However, alterations in serum factor composition and biological activity after TAVR remain unknown. Here, we quantified the systemic inflammatory effects of the TAVR procedure and hypothesized that alterations in serum factor composition would modulate valve and cardiac fibrosis. Serum samples were obtained from patients with AVS immediately before their TAVR procedure (pre-TAVR) and about 1 month afterward (post-TAVR). Aptamer-based proteomic profiling revealed alterations in post-TAVR serum composition, and ontological analysis identified inflammatory macrophage factors implicated in myofibroblast activation and deactivation. Hydrogel biomaterials used as valve matrix mimics demonstrated that post-TAVR serum reduced myofibroblast activation of valvular interstitial cells relative to pre-TAVR serum from the same patient. Transcriptomics and curated network analysis revealed a shift in myofibroblast phenotype from pre-TAVR to post-TAVR and identified p38 MAPK signaling as one pathway involved in pre-TAVR–mediated myofibroblast activation. Post-TAVR serum deactivated valve and cardiac myofibroblasts initially exposed to pre-TAVR serum to a quiescent fibroblast phenotype. Our in vitro deactivation data correlated with patient disease severity measured via echocardiography and multimorbidity scores, and correlations were dependent on hydrogel stiffness. Sex differences in cellular responses to male and female sera were also observed and may corroborate clinical observations regarding sex-specific TAVR outcomes. Together, alterations in serum composition after TAVR may lead to an antifibrotic fibroblast phenotype, which suggests earlier interventions may be beneficial for patients with advanced AVS to prevent further disease progression., One-sentence summary: Transcatheter aortic valve replacement alters a patient’s serum proteome, reversing valvular interstitial cell and cardiac myofibroblast activation., Editor’s Summary: Responding to replacement Aortic valve stenosis (narrowing of the aortic valve) contributes to inadequate blood flow, fibrosis, hypertrophy, and, ultimately, heart failure. Transcatheter aortic valve replacement (TAVR) improves blood flow, but little is known about cardiac remodeling after the procedure. Aguado and colleagues performed proteomics on serum samples collected from patients before and after TAVR and studied the effects of serum on valve and cardiac cells using hydrogel culture platforms. A role for p38 MAPK signaling in activating cells was identified using pre-TAVR serum, whereas post-TAVR serum returned cells to a quiescent state. Along with preliminary insights into sex-specific differences, the authors’ research supports a role for TAVR-induced alteration of circulating inflammatory cytokines in regulating valve cell phenotype.

Background In mammals, muscle contraction is controlled by a family of 10 sarcomeric myosin motors. The expression of one of its members, MYH 7b, is regulated by alternative splicing, and while the protein is restricted to specialized muscles such as extraocular muscles or muscle spindles, RNA that cannot encode protein is expressed in most skeletal muscles and in the heart. Remarkably, birds and snakes express MYH 7b protein in both heart and skeletal muscles. This observation suggests that in the mammalian heart, the motor activity of MYH 7b may only be needed during development since its expression is prevented in adult tissue, possibly because it could promote disease by unbalancing myocardial contractility. Methods and Results We have analyzed MYH 7b null mice to determine the potential role of MYH 7b during cardiac development and also generated transgenic mice with cardiac myocyte expression of MYH 7b protein to measure its impact on cardiomyocyte function and contractility. We found that MYH 7b null mice are born at expected Mendelian ratios and do not have a baseline cardiac phenotype as adults. In contrast, transgenic cardiac MYH 7b protein expression induced early cardiac dilation in males with significantly increased left ventricular mass in both sexes. Cardiac dilation is progressive, leading to early cardiac dysfunction in males, but later dysfunction in females. Conclusions The data presented show that the expression of MYH 7b protein in the mammalian heart has been inhibited during the evolution of mammals most likely to prevent the development of a severe cardiomyopathy that is sexually dimorphic.

Striated muscle myosins are encoded by a large gene family in all mammals, including humans. These isoforms define several of the key characteristics of the different striated muscle fiber types, including maximum shortening velocity. We have previously used recombinant isoforms of the motor domains of seven different human myosin isoforms to define the actin·myosin cross-bridge cycle in solution. Here, we present data on an eighth isoform, the perinatal, which has not previously been characterized. The perinatal is distinct from the embryonic isoform, appearing to have features in common with the adult fast-muscle isoforms, including weak affinity of ADP for actin·myosin and fast ADP release. We go on to use a recently developed modeling approach, MUSICO, to explore how well the experimentally defined cross-bridge cycles for each isoform in solution can predict the characteristics of muscle fiber contraction, including duty ratio, shortening velocity, ATP economy, and load dependence of these parameters. The work shows that the parameters of the cross-bridge cycle predict many of the major characteristics of each muscle fiber type and raises the question of what sequence changes are responsible for these characteristics.

Striated muscles express an array of sarcomeric myosin motors that are tuned to accomplish specific tasks. Each myosin isoform found in muscle fibers confers unique contractile properties to the fiber in order to meet the demands of the muscle. The sarcomeric myosin heavy chain (MYH) genes expressed in the major cardiac and skeletal muscles have been studied for decades. However, three ancient myosins, MYH7b, MYH15, and MYH16, remained uncharacterized due to their unique expression patterns in common mammalian model organisms and due to their relatively recent discovery in these genomes. This article reviews the literature surrounding these three ancient sarcomeric myosins and the specialized muscles in which they are expressed. Further study of these ancient myosins and how they contribute to the functions of the specialized muscles may provide novel insight into the history of striated muscle evolution.

The embryonic myosin isoform is expressed during fetal development and rapidly down-regulated after birth. Freeman-Sheldon syndrome (FSS) is a disease associated with missense mutations in the motor domain of this myosin. It is the most severe form of distal arthrogryposis, leading to overcontraction of the hands, feet, and orofacial muscles and other joints of the body. Availability of human embryonic muscle tissue has been a limiting factor in investigating the properties of this isoform and its mutations. Using a recombinant expression system, we have studied homogeneous samples of human motors for the WT and three of the most common FSS mutants: R672H, R672C, and T178I. Our data suggest that the WT embryonic myosin motor is similar in contractile speed to the slow type I/β cardiac based on the rate constant for ADP release and ADP affinity for actin-myosin. All three FSS mutations show dramatic changes in kinetic properties, most notably the slowing of the apparent ATP hydrolysis step (reduced 5-9-fold), leading to a longer lived detached state and a slowed Vmax of the ATPase (2-35-fold), indicating a slower cycling time. These mutations therefore seriously disrupt myosin function.

Powering down yields a healthier heart In hypertrophic cardiomyopathy (HCM), the heart muscle enlarges and becomes progressively less efficient at pumping blood. HCM can be caused by mutations in components of the sarcomere (the heart's contractile unit), most notably myosin. Hypercontractility is among the earliest heart disturbances seen in mice carrying these myosin mutations, implying that the mutations inflict their damage by increasing myosin's power production. Green et al. identified a small molecule that binds to myosin and inhibits its activity (see the Perspective by Warshaw). When orally administered to young mice, the molecule prevented the development of several hallmark features of HCM without adversely affecting skeletal muscle. Science , this issue p. 617 ; see also p. 556

Introduction: Biological sex is an important modifier of cardiovascular disease (CVD). However, women and female animals have traditionally been excluded from clinical trials and most preclinical research studies, resulting in therapeutics that are not as effective, or with different side effects, in women relative to men. Methods and Results: We show here that expression of α- and β-adrenergic receptors, cardiac stiffness, myofibroblast proliferation, and expression of fibrotic markers are sexually dimorphic at baseline. To determine whether pathogenesis was different between the sexes, the β-adrenergic agonist, isoproterenol (ISO), was administered to rats. In response to 7-days of ISO treatment, female animals were more likely to survive than their male counterparts (percent survival: 44% in males versus 77% in females). Both sexes developed significant cardiac hypertrophy, activation of cardiac fetal genes (ANF and β-MHC) compared to vehicle controls. Cardiac myocytes from ISO treated animals took less time to reach peak shortening and displayed increased departure velocity; however, only male ISO treated cells exhibited reduced relaxation times and increased return velocities. Importantly, ISO treated animals developed significant fibrosis prompting us to analyze isolated cardiac fibroblasts at baseline and in response to ISO. We observed significantly increased expression of α-SMA and Col1a, two indicators of myofibroblast activation, only in fibroblasts isolated from ISO treated males. Both ISO treated male and female fibroblasts showed significant increases in periostin and decreases in TCF21, indicative of increases in myofibroblasts and decreases in quiescent fibroblasts, respectively. In addition, both sexes revealed increased fibroblast proliferation in vivo , as measured by EdU incorporation, in response to ISO. Conclusions: Chronic in vivo β-adrenergic receptor stimulation revealed dramatic sex differences in mortality, cardiac hypertrophy, myocyte contractility, and cardiac fetal gene expression. Increases in myofibroblast differentiation and fibroblast proliferation should lead to a robust fibrotic response in both male and female ISO treated animals.

Aims To define the molecular mechanisms of cardiotoxicity induced by Sunitinib and to identify the role of biological sex in modulating toxicity. Methods and results Exposure of isolated cardiomyocytes to plasma-relevant concentrations of Sunitinib and other tyrosine kinase inhibitors produces a broad spectrum of abnormalities and cell death via apoptosis downstream of sexually dimorphic kinase inhibition. Phosphorylation of protein kinase C and phospholipase γ abrogates these effects for most tyrosine kinase inhibitors tested. Female sex and estradiol cause increased cardiotoxicity, which is mediated by reduced expression of a drug efflux transporter and a metabolic enzyme. Female but not male mice exposed to a 28-day course of oral Sunitinib exhibit similar abnormalities as well as functional deficits and their hearts exhibit differential expression of genes responsible for transport and metabolism of Sunitinib. Conclusion We identify the specific pathways affected by tyrosine kinase inhibitors in mammalian cardiomyocytes, interactions with biological sex, and a role for oestrogen in modulating drug efflux and metabolism. These findings represent a critical step toward reducing the incidence of cardiotoxicity with tyrosine kinase inhibitor chemotherapeutics.

Use of soy supplements to inhibit cancer cell growth is increasing among patients due to the perception that phytoestrogens in soy inhibit carcinogenesis via induction of apoptosis. Genistein, the most prevalent phytoestrogen in soy, is a potent endocrine disruptor and tyrosine kinase inhibitor (TKI) that causes apoptosis in many cells types. Chemotherapeutic TKIs limit cancer cell growth via the same mechanisms. However, TKIs such as Sunitinib cause cardiotoxicity in a significant number of patients. Molecular interactions between Sunitinib and dietary TKIs like genistein have not been examined in cardiomyocytes. Significant lethality occurred in mice treated with Sunitinib and fed a phytoestrogen-supplemented diet. Isolated cardiomyocytes co-treated with genistein and Sunitinib exhibited additive inhibition of signaling molecules important for normal cardiac function and increased apoptosis compared with Sunitinib alone. Thus, dietary soy supplementation should be avoided during administration of Sunitinib due to exacerbated cardiotoxicity, despite evidence for positive effects in cancer.