Robert W. Mills

Bioengineering Human Myocardium on Native Extracellular Matrix

RATIONALE More than 25 million individuals have heart failure worldwide, with ≈4000 patients currently awaiting heart transplantation in the United States. Donor organ shortage and allograft rejection remain major limitations with only ≈2500 hearts transplanted each year. As a theoretical alternative to allotransplantation, patient-derived bioartificial myocardium could provide functional support and ultimately impact the treatment of heart failure. OBJECTIVE The objective of this study is to translate previous work to human scale and clinically relevant cells for the bioengineering of functional myocardial tissue based on the combination of human cardiac matrix and human induced pluripotent stem cell-derived cardiomyocytes. METHODS AND RESULTS To provide a clinically relevant tissue scaffold, we translated perfusion-decellularization to human scale and obtained biocompatible human acellular cardiac scaffolds with preserved extracellular matrix composition, architecture, and perfusable coronary vasculature. We then repopulated this native human cardiac matrix with cardiomyocytes derived from nontransgenic human induced pluripotent stem cells and generated tissues of increasing 3-dimensional complexity. We maintained such cardiac tissue constructs in culture for 120 days to demonstrate definitive sarcomeric structure, cell and matrix deformation, contractile force, and electrical conduction. To show that functional myocardial tissue of human scale can be built on this platform, we then partially recellularized human whole-heart scaffolds with human induced pluripotent stem cell-derived cardiomyocytes. Under biomimetic culture, the seeded constructs developed force-generating human myocardial tissue and showed electrical conductivity, left ventricular pressure development, and metabolic function. CONCLUSIONS Native cardiac extracellular matrix scaffolds maintain matrix components and structure to support the seeding and engraftment of human induced pluripotent stem cell-derived cardiomyocytes and enable the bioengineering of functional human myocardial-like tissue of multiple complexities.

Novel Chemical Suppressors of Long QT Syndrome Identified by an in vivo Functional Screen

Background— Genetic long QT (LQT) syndrome is a life-threatening disorder caused by mutations that result in prolongation of cardiac repolarization. Recent work has demonstrated that a zebrafish model of LQT syndrome faithfully recapitulates several features of human disease, including prolongation of ventricular action potential duration, spontaneous early afterdepolarizations, and 2:1 atrioventricular block in early stages of development. Because of their transparency, small size, and absorption of small molecules from their environment, zebrafish are amenable to high-throughput chemical screens. We describe a small-molecule screen using the zebrafish KCNH2 mutant breakdance to identify compounds that can rescue the LQT type 2 phenotype. Methods and Results— Zebrafish breakdance embryos were exposed to test compounds at 48 hours of development and scored for rescue of 2:1 atrioventricular block at 72 hours in a 96-well format. Only compounds that suppressed the LQT phenotype in 3 of 3 fish were considered hits. Screen compounds were obtained from commercially available small-molecule libraries (Prestwick and Chembridge). Initial hits were confirmed with dose-response testing and time-course studies. Optical mapping with the voltage-sensitive dye di-4 ANEPPS was performed to measure compound effects on cardiac action potential durations. Screening of 1200 small molecules resulted in the identification of flurandrenolide and 2-methoxy-N-(4-methylphenyl) benzamide (2-MMB) as compounds that reproducibly suppressed the LQT phenotype. Optical mapping confirmed that treatment with each compound caused shortening of ventricular action potential durations. Structure activity studies and steroid receptor knockdown suggest that flurandrenolide functions via the glucocorticoid signaling pathway. Conclusions— Using a zebrafish model of LQT type 2 syndrome in a high-throughput chemical screen, we have identified 2 compounds, flurandrenolide and the novel compound 2-MMB, as small molecules that rescue the zebrafish LQT type 2 syndrome by shortening the ventricular action potential duration. We provide evidence that flurandrenolide functions via the glucocorticoid receptor–mediated pathway. These 2 molecules and future discoveries from this screen should yield novel tools for the study of cardiac electrophysiology and may lead to novel therapeutics for human LQT patients.

Rapid Cellular Phenotyping of Human Pluripotent Stem Cell-Derived Cardiomyocytes using a Genetically Encoded Fluorescent Voltage Sensor

Summary In addition to their promise in regenerative medicine, pluripotent stem cells have proved to be faithful models of many human diseases. In particular, patient-specific stem cell-derived cardiomyocytes recapitulate key features of several life-threatening cardiac arrhythmia syndromes. For both modeling and regenerative approaches, phenotyping of stem cell-derived tissues is critical. Cellular phenotyping has largely relied upon expression of lineage markers rather than physiologic attributes. This is especially true for cardiomyocytes, in part because electrophysiological recordings are labor intensive. Likewise, most optical voltage indicators suffer from phototoxicity, which damages cells and degrades signal quality. Here we present the use of a genetically encoded fluorescent voltage indicator, ArcLight, which we demonstrate can faithfully report transmembrane potentials in human stem cell-derived cardiomyocytes. We demonstrate the application of this fluorescent sensor in high-throughput, serial phenotyping of differentiating cardiomyocyte populations and in screening for drug-induced cardiotoxicity.

Photochemical activation of TRPA1 channels in neurons and animals

Optogenetics is a powerful research tool because it enables high-resolution optical control of neuronal activity. However, current optogenetic approaches are limited to transgenic systems expressing microbial opsins and other exogenous photoreceptors. Here, we identify optovin, a small molecule that enables repeated photoactivation of motor behaviors in wild type animals. Surprisingly, optovins behavioral effects are not visually mediated. Rather, photodetection is performed by sensory neurons expressing the cation channel TRPA1. TRPA1 is both necessary and sufficient for the optovin response. Optovin activates human TRPA1 via structure-dependent photochemical reactions with redox-sensitive cysteine residues. In animals with severed spinal cords, optovin treatment enables control of motor activity in the paralyzed extremities by localized illumination. These studies identify a light-based strategy for controlling endogenous TRPA1 receptors in vivo, with potential clinical and research applications in non-transgenic animals, including humans.

Overexpression of KCNN3 results in sudden cardiac death

BACKGROUND A recent genome-wide association study identified a susceptibility locus for atrial fibrillation at the KCNN3 gene. Since the KCNN3 gene encodes for a small conductance calcium-activated potassium channel, we hypothesized that overexpression of the SK3 channel increases susceptibility to cardiac arrhythmias. METHODS AND RESULTS We characterized the cardiac electrophysiological phenotype of a mouse line with overexpression of the SK3 channel. We generated homozygote (SK3(T/T)) and heterozygote (SK3(+/T)) mice with overexpression of the channel and compared them with wild-type (WT) controls. We observed a high incidence of sudden death among SK3(T/T) mice (7 of 19 SK3(T/T) mice). Ambulatory monitoring demonstrated that sudden death was due to heart block and bradyarrhythmias. SK3(T/T) mice displayed normal body weight, temperature, and cardiac function on echocardiography; however, histological analysis demonstrated that these mice have abnormal atrioventricular node morphology. Optical mapping demonstrated that SK3(T/T) mice have slower ventricular conduction compared with WT controls (SK3(T/T) vs. WT; 0.45 ± 0.04 vs. 0.60 ± 0.09 mm/ms, P = 0.001). Programmed stimulation in 1-month-old SK3(T/T) mice demonstrated inducible atrial arrhythmias (50% of SK3(T/T) vs. 0% of WT mice) and also a shorter atrioventricular nodal refractory period (SK3(T/T) vs. WT; 43 ± 6 vs. 52 ± 9 ms, P = 0.02). Three-month-old SK3(T/T) mice on the other hand displayed a trend towards a more prolonged atrioventricular nodal refractory period (SK3(T/T) vs. WT; 61 ± 1 vs. 52 ± 6 ms, P = 0.06). CONCLUSION Overexpression of the SK3 channel causes an increased risk of sudden death associated with bradyarrhythmias and heart block, possibly due to atrioventricular nodal dysfunction.

The HIV Care Continuum: Changes over Time in Retention in Care and Viral Suppression

Background The HIV care continuum (diagnosis, linkage to care, retention in care, receipt of antiretroviral therapy (ART), viral suppression) has been used to identify opportunities for improving the delivery of HIV care. Continuum steps are typically calculated in a conditional manner, with the number of persons completing the prior step serving as the base population for the next step. This approach may underestimate the prevalence of viral suppression by excluding patients who are suppressed but do not meet standard definitions of retention in care. Understanding how retention in care and viral suppression interact and change over time may improve our ability to intervene on these steps in the continuum. Methods We followed 17,140 patients at 11 U.S. HIV clinics between 2010-2012. For each calendar year, patients were classified into one of five categories: (1) retained/suppressed, (2) retained/not-suppressed, (3) not-retained/suppressed, (4) not-retained/not-suppressed, and (5) lost to follow-up (for calendar years 2011 and 2012 only). Retained individuals were those completing ≥2 HIV medical visits separated by ≥90 days in the year. Persons not retained completed ≥1 HIV medical visit during the year, but did not meet the retention definition. Persons lost to follow-up had no HIV medical visits in the year. HIV viral suppression was defined as HIV-1 RNA ≤200 copies/mL at the last measure in the year. Multinomial logistic regression was used to determine the probability of patients’ transitioning between retention/suppression categories from 2010 to 2011 and 2010 to 2012, adjusting for age, sex, race/ethnicity, HIV risk factor, insurance status, CD4 count, and use of ART. Results Overall, 65.8% of patients were retained/suppressed, 17.4% retained/not-suppressed, 10.0% not-retained/suppressed, and 6.8% not-retained/not-suppressed in 2010. 59.5% of patients maintained the same status in 2011 (kappa=0.458) and 53.3% maintained the same status in 2012 (kappa=0.437). Conclusions Not counting patients not-retained/suppressed as virally suppressed, as is commonly done in the HIV care continuum, underestimated the proportion suppressed by 13%. Applying the care continuum in a longitudinal manner will enhance its utility.

Healthcare Coverage for HIV Provider Visits Before and After Implementation of the Affordable Care Act

BACKGROUND Before implementation of the Patient Protection and Affordable Care Act (ACA) in 2014, 100 000 persons living with human immunodeficiency virus (HIV) (PLWH) lacked healthcare coverage and relied on a safety net of Ryan White HIV/AIDS Program support, local charities, or uncompensated care (RWHAP/Uncomp) to cover visits to HIV providers. We compared HIV provider coverage before (2011-2013) versus after (first half of 2014) ACA implementation among a total of 28 374 PLWH followed up in 4 sites in Medicaid expansion states (California, Oregon, and Maryland), 4 in a state (New York) that expanded Medicaid in 2001, and 2 in nonexpansion states (Texas and Florida). METHODS Multivariate multinomial logistic models were used to assess changes in RWHAP/Uncomp, Medicaid, and private insurance coverage, using Medicare as a referent. RESULTS In expansion state sites, RWHAP/Uncomp coverage decreased (unadjusted, 28% before and 13% after ACA; adjusted relative risk ratio [ARRR], 0.44; 95% confidence interval [CI], .40-.48). Medicaid coverage increased (23% and 38%; ARRR, 1.82; 95% CI, 1.70-1.94), and private coverage was unchanged (21% and 19%; 0.96; .89-1.03). In New York sites, both RWHAP/Uncomp (20% and 19%) and Medicaid (50% and 50%) coverage were unchanged, while private coverage decreased (13% and 12%; ARRR, 0.86; 95% CI, .80-.92). In nonexpansion state sites, RWHAP/Uncomp (57% and 52%) and Medicaid (18% and 18%) coverage were unchanged, while private coverage increased (4% and 7%; ARRR, 1.79; 95% CI, 1.62-1.99). CONCLUSIONS In expansion state sites, half of PLWH relying on RWHAP/Uncomp coverage shifted to Medicaid, while in New York and nonexpansion state sites, reliance on RWHAP/Uncomp remained constant. In the first half of 2014, the ACA did not eliminate the need for RWHAP safety net provider visit coverage.

Novel Mutation in FLNC (Filamin C) Causes Familial Restrictive CardiomyopathyCLINICAL PERSPECTIVE

Background— Restrictive cardiomyopathy (RCM) is a rare cardiomyopathy characterized by impaired diastolic ventricular function resulting in a poor clinical prognosis. Rarely, heritable forms of RCM have been reported, and mutations underlying RCM have been identified in genes that govern the contractile function of the cardiomyocytes. Methods and Results— We evaluated 8 family members across 4 generations by history, physical examination, electrocardiography, and echocardiography. Affected individuals presented with a pleitropic syndrome of progressive RCM, atrioventricular septal defects, and a high prevalence of atrial fibrillation. Exome sequencing of 5 affected members identified a single novel missense variant in a highly conserved residue of FLNC (filamin C; p.V2297M). FLNC encodes filamin C—a protein that acts as both a scaffold for the assembly and organization of the central contractile unit of striated muscle and also as a mechanosensitive signaling molecule during cell migration and shear stress. Immunohistochemical analysis of FLNC localization in cardiac tissue from an affected family member revealed a diminished localization at the z disk, whereas traditional localization at the intercalated disk was preserved. Stem cell-derived cardiomyocytes mutated to carry the effect allele had diminished contractile activity when compared with controls. Conclusion— We have identified a novel variant in FLNC as pathogenic variant for familial RCM—a finding that further expands on the genetic basis of this rare and morbid cardiomyopathy.

HIV and Hepatitis C Virus Screening Practices in a Geographically Diverse Sample of American Community Health Centers.

Because of the advent of highly effective treatments, routine screening for HIV and hepatitis C virus (HCV) has been recommended for many Americans. This study explored the perceived barriers surrounding routine HIV and HCV screening in a diverse sample of community health centers (CHCs). The Community Health Applied Research Network (CHARN) is a collaboration of CHCs, with a shared clinical database. In July, 2013, 195 CHARN providers working in 12 CHCs completed a survey of their attitudes and beliefs about HIV and HCV testing. Summary statistics were generated to describe the prevalence of HIV and HCV and associated demographics by CHCs. HIV and HCV prevalence ranged from 0.1% to 5.7% for HIV and from 0.1% to 3.7% for HCV in the different CHCs. About 15% of the providers cared for at least 50 individuals with HIV and the same was true for HCV. Two-thirds saw less than 10 patients with HIV and less than half saw less than 10 patients with HCV. Less than two-thirds followed USPHS guidelines to screen all patients for HIV between the ages of 13 and 64, and only 44.4% followed the guidance to screen all baby boomers for HCV. Providers with less HIV experience tended to be more concerned about routine screening practices. More experienced providers were more likely to perceive lack of time being an impediment to routine screening. Many US CHC providers do not routinely screen their patients for HIV and HCV. Although additional education about the rationale for routine screening may be indicated, incentives to compensate providers for the additional time they anticipate spending in counseling may also facilitate increased screening rates.

TRPM4-linked isolated cardiac conduction defects: bad trafficking causes electrical gridlock.

Cardiac conduction system disease (CCD) is a common medical problem, with about 3 million people worldwide with pacemakers and 600 000 implanted each year.1 Despite its prevalence, there is little known about the molecular pathogenesis of CCD in the general population. Therefore, investigators have turned to cases of familial conduction system disease to gain insights. Article see p 374 This approach has led to the discovery of several genes involved in syndromic CCD (reviewed by Wolf and Berul).2 Mutations in the transcription factor NKX2.5 cause atrial septal defects and progressive atrioventricular block (AVB). Defects in another transcription factor, Tbx5, cause Holt-Oram syndrome, characterized by atrial septal defects, progressive AVB, and radial limb deformities. Muscular dystrophies can be associated with AVB as well. Emery-Dreifuss muscular dystrophy, whether caused by defects in Emerin or Lamin A/C, is associated with AVB, and myotonic dystrophy, caused by expansion of a trinucleotide repeat downstream of the DMPK gene, is also associated with progressive AVB. Atrioventricular block is a frequent finding in patients with PRKAG2 mutations who also have accessory atrioventricular connections and glycogen storage cardiomyopathy. Finally, AVB can be seen as part of the Andersen-Tawil syndrome of prolonged QT interval, potassium-sensitive periodic paralysis, ventricular arrhythmias, and dysmorphic features. What about isolated atrioventricular conduction disease? Until recently, the only gene implicated in human-isolated progressive CCD was the cardiac voltage-gated sodium channel, SCN5a.3 Thus, there is great interest in the causative gene recently identified in a large South African family with autosomal dominant progressive familial heart block, type I.4 …