Arrhythmias and ion channelopathies causing sudden cardiac death in Hispanic/Latino and Indigenous populations.

The limited literature and increasing interest in studies on cardiac electrophysiology, explicitly focusing on cardiac ion channelopathies and sudden cardiac death in diverse populations, has prompted a comprehensive examination of existing research. Our review specifically targets Hispanic/Latino and Indigenous populations, which are often underrepresented in healthcare studies. This review encompasses investigations into genetic variants, epidemiology, etiologies, and clinical risk factors associated with arrhythmias in these demographic groups. The review explores the Hispanic paradox, a phenomenon linking healthcare outcomes to socioeconomic factors within Hispanic communities in the United States. Furthermore, it discusses studies exemplifying this observation in the context of arrhythmias and ion channelopathies in Hispanic populations. Current research also sheds light on disparities in overall healthcare quality in Indigenous populations. The available yet limited literature underscores the pressing need for more extensive and comprehensive research on cardiac ion channelopathies in Hispanic/Latino and Indigenous populations. Specifically, additional studies are essential to fully characterize pathogenic genetic variants, identify population-specific risk factors, and address health disparities to enhance the detection, prevention, and management of arrhythmias and sudden cardiac death in these demographic groups.

Contribution of cytokine-mediated prolongation of QTc interval to the multi-hit theory of Torsade de Pointes.

BACKGROUND: Torsade de pointes is a potentially lethal polymorphic ventricular tachyarrhythmia that can occur in the setting of long QT syndrome (LQTS). LQTS is multi-hit in nature and multiple factors combine their effects leading to increased arrhythmic risk. While hypokalemia and multiple medications are accounted for in LQTS, the arrhythmogenic role of systemic inflammation is increasingly recognized but often overlooked. We tested the hypothesis that the inflammatory cytokine interleukin(IL)-6 will significantly increase the incidence of arrhythmia when combined with other pro-arrhythmic conditions (hypokalemia and the psychotropic medication, quetiapine). METHODS: Guinea pigs were injected intraperitoneally with IL-6/soluble IL-6 receptor and QT changes were measured in vivo. Subsequently, hearts were cannulated via Langendorff perfusion for ex vivo optical mapping measurements of action potential duration (APD90) and arrhythmia inducibility. Computer simulations (MATLAB) were performed to investigate IKr inhibition at varying IL-6 and quetiapine concentrations. RESULTS: IL-6 prolonged QTc in vivo guinea pigs from 306.74 ± 7.19 ms to 332.60 ± 8.75 ms (n = 8, p = .0021). Optical mapping on isolated hearts demonstrated APD prolongation in IL-6- vs saline groups (3Hz APD90:179.67 ± 2.47 ms vs 153.5 ± 7.86 ms, p = .0357). When hypokalemia was introduced, the APD90 increased to 195.8 ± 5.02 ms[IL-6] and 174.57 ± 10.7 ms[saline] (p = .2797), and when quetiapine was added to hypokalemia to 207.67 ± 3.03 ms[IL-6] and 191.37 ± 9.49 ms[saline] (p = .2449). After the addition of hypokalemia ± quetiapine, arrhythmia was induced in 75% of IL-6-treated hearts (n = 8), while in none of the control hearts (n = 6). Computer simulations demonstrated spontaneous depolarizations at ∼83% aggregate IKr inhibition. CONCLUSIONS: Our experimental observations strongly suggest that controlling inflammation, specifically IL-6, could be a viable and important route for reducing QT prolongation and arrhythmia incidence in the clinical setting.

Recent Progress and Challenges in the Development of Antisense Therapies for Myotonic Dystrophy Type 1.

Myotonic dystrophy type 1 (DM1) is a dominant genetic disease in which the expansion of long CTG trinucleotides in the 3' UTR of the myotonic dystrophy protein kinase (DMPK) gene results in toxic RNA gain-of-function and gene mis-splicing affecting mainly the muscles, the heart, and the brain. The CUG-expanded transcripts are a suitable target for the development of antisense oligonucleotide (ASO) therapies. Various chemical modifications of the sugar-phosphate backbone have been reported to significantly enhance the affinity of ASOs for RNA and their resistance to nucleases, making it possible to reverse DM1-like symptoms following systemic administration in different transgenic mouse models. However, specific tissue delivery remains to be improved to achieve significant clinical outcomes in humans. Several strategies, including ASO conjugation to cell-penetrating peptides, fatty acids, or monoclonal antibodies, have recently been shown to improve potency in muscle and cardiac tissues in mice. Moreover, intrathecal administration of ASOs may be an advantageous complementary administration route to bypass the blood-brain barrier and correct defects of the central nervous system in DM1. This review describes the evolution of the chemical design of antisense oligonucleotides targeting CUG-expanded mRNAs and how recent advances in the field may be game-changing by forwarding laboratory findings into clinical research and treatments for DM1 and other microsatellite diseases.

Increased sarcoplasmic/endoplasmic reticulum calcium ATPase 2a activity underlies the mechanism of the positive inotropic effect of ivabradine.

NEW FINDINGS: What is the central question of this study? The therapeutic effect of ivabradine on patients with chronic heart failure and chronic stable angina pectoris is mediated through a reduction in heart rate: what are the haemodynamic characteristics and the mechanism of the inotropic effect? What is the main finding and its importance? Ivabradine has a positive inotropic effect and lowers the heart rate both in vivo and in vitro. These effects are likely mediated by ivabradine's significant increase of the fast component rate constant mediated by sarcoplasmic/endoplasmic reticulum calcium ATPase 2a and decrease of the slow component rate constant that is mediated by the Na+ /Ca2+ exchanger and sarcolemmal Ca2+ -ATPase during the Ca2+ transient decay phase. ABSTRACT: Ivabradine's therapeutic effect is mediated by a reduction of the heart rate; however, its haemodynamic characteristics and the mechanism of its inotropic effect are poorly understood. We aimed to investigate the positive inotropic effect of ivabradine and its underlying mechanism. The results demonstrated that ivabradine increased the positive inotropy of the rat heart in vivo by increasing the stroke work, cardiac output, stroke volume, end-diastolic volume, end-systolic pressure, ejection fraction, ±dP/dtmax , left ventricular end-systolic elastance and systolic blood pressure without altering the diastolic blood pressure and arterial elastance. This inotropic effect was observed in both non-paced and paced rat isolated heart. Ivabradine increased the Ca2+ transient amplitude and the reuptake rates of sarcoplasmic/endoplasmic reticulum calcium ATPase 2a (SERCA2a), lowered the diastolic Ca2+ level and suppressed the combined extrusion rate of the Na+ /Ca2+ exchanger and the sarcolemmal Ca2+ -ATPase. In addition, ivabradine widened the action potential duration, hyperpolarized the resting membrane potential, increased sarcoplasmic reticulum Ca2+ content and reduced Ca2+ leak. Overall, ivabradine had a positive inotropic effect brought about by enhanced SERCA2a activity, which might be mediated by increased phospholamban phosphorylation. The positive inotropic effect along with the lowered heart rate underlies ivabradine's therapeutic effect in heart failure.

Role of spatial dispersion of repolarization in reentry around a functional core versus reentry around a fixed anatomical core.

INTRODUCTION: Successful initiation of spiral wave reentry in the neonatal rat ventricular myocyte (NRVM) monolayer implicitly assumes the presence of spatial dispersion of repolarization (DR), which is difficult to quantify. We recently introduced a NRVM monolayer that utilizes anthopleurin-A to impart a prolonged plateau to the NRVM action potential. This was associated with a significant degree of spatial DR that lends itself to accurate quantification. METHODS AND RESULTS: We utilized the monolayer and fluorescence optical mapping of intracellular calcium transients (FCai ) to systematically study and compare the contribution of spatial dispersion of the duration of FCai (as a surrogate of DR) to induction of spiral wave reentry around a functional core versus reentry around a fixed anatomical obstacle. We show that functional reentry could be initiated by a premature stimulus acting on a substrate of spatial DR resulting in a functional line of propagation block. Subsequent wave fronts circulated around a central core of functional obstacle created by sustained depolarization from the circulating wave front. Both initiation and termination of spiral wave reentry around an anatomical obstacle consistently required participation of a region of functional propagation block. This region was similarly based on spatial DR. Spontaneous termination of spiral wave reentry also resulted from block in the functional component of the circuit obstacle, usually preceded by beat-to-beat slowing of propagation. CONCLUSIONS: The study demonstrates the critical contribution of DR to spiral wave reentry around a purely functional core as well as reentry around a fixed anatomical core.

Acquired long QT syndrome and torsade de pointes.

Since its initial description by Jervell and Lange-Nielsen in 1957, the congenital long QT syndrome (LQTS) has been the most investigated cardiac ion channelopathy. Although congenital LQTS continues to remain the domain of cardiologists, cardiac electrophysiologists, and specialized centers, the by far more frequent acquired drug-induced LQTS is the domain of all physicians and other members of the health care team who are required to make therapeutic decisions. This report will review the electrophysiological mechanisms of LQTS and torsade de pointes, electrocardiographic characteristics of acquired LQTS, its clinical presentation, management, and future directions in the field.

Regulation of Cardiac Voltage-Gated Sodium Channel by Kinases: Roles of Protein Kinases A and C.

In the heart, voltage-gated sodium (Nav) channel (Nav1.5) is defined by its pore-forming α-subunit and its auxiliary ß-subunits, both of which are important for its critical contribution to the initiation and maintenance of the cardiac action potential (AP) that underlie normal heart rhythm. The physiological relevance of Nav1.5 is further marked by the fact that inherited or congenital mutations in Nav1.5 channel gene SCN5A lead to altered functional expression (including expression, trafficking, and current density), and are generally manifested in the form of distinct cardiac arrhythmic events, epilepsy, neuropathic pain, migraine, and neuromuscular disorders. However, despite significant advances in defining the pathophysiology of Nav1.5, the molecular mechanisms that underlie its regulation and contribution to cardiac disorders are poorly understood. It is rapidly becoming evident that the functional expression (localization, trafficking and gating) of Nav1.5 may be under modulation by post-translational modifications that are associated with phosphorylation. We review here the molecular basis of cardiac Na channel regulation by kinases (PKA and PKC) and the resulting functional consequences. Specifically, we discuss: (1) recent literature on the structural, molecular, and functional properties of cardiac Nav1.5 channels; (2) how these properties may be altered by phosphorylation in disease states underlain by congenital mutations in Nav1.5 channel and/or subunits such as long QT and Brugada syndromes. Our expectation is that understanding the roles of these distinct and complex phosphorylation processes on the functional expression of Nav1.5 is likely to provide crucial mechanistic insights into Na channel associated arrhythmogenic events and will facilitate the development of novel therapeutic strategies.

Novel function of α1D L-type calcium channel in the atria.

Ca entry through atrial L-type Calcium channels (α1C and α1D) play an important role in muscular contraction, regulation of gene expression, and release of hormones including atrial natriuretic peptide (ANP), and brain natriuretic peptide (BNP). α1D Ca channel is exclusively expressed in atria, and has been shown to play a key role in the pathogenesis of atrial fibrillation. Recent data have shown that the small conductance calcium-activated potassium channel, SK4 is also atrial specific and also contributes prominently to the secretion of ANP and BNP. However, its functional role in the heart is still poorly understood. Here we used α1D gene heterozygous (α1D+/-) mice and HL-1 cells to determine the functional contribution of SK4 channels to α1D-dependent regulation of ANP and BNP secretion in response to endothelin (ET), and/or mechanical stretch. Immunoprecipitation with α1D specific antibody and western blotting with SK4 specific antibody on the immuno-precipitated protein complex showed a band at 50 KDa confirming the presence of SK4 in the complex and provided evidence of interaction between SK4 and α1D channels. Using RT-PCR, we observed a 2.9 fold decrease in expression of Cacna1d (gene encoding α1D) mRNA in atria from α1D+/-mice. The decrease in α1D mRNA corresponded with a 4.2 fold decrease in Kcnn4 (gene encoding SK4) mRNA from α1D+/- mice. These changes were paralleled with a 77% decrease in BNP serum levels from α1D+/- mice. When α1D was knocked down in HL-1cardiomyocytes using CRISPR/Cas9 technology, a 97% decrease in secreted BNP was observed even in cells subjected to stretch and endothelin. In conclusion, our data are first to show that α1D Ca and SK4 channels are coupled in the atria, and that deletion of α1D leads to decreased SK4 mRNA and BNP secretion providing evidence for a novel role of α1D in atrial endocrine function. Elucidating the regulatory factors that underlie the secretory function of atria will identify novel therapeutic targets for treatment and prevention of cardiac arrhythmias such as atrial fibrillation.

Induced pluripotent stem-cell-derived cardiomyocytes: cardiac applications, opportunities, and challenges.

Chronic diseases are the primary cause of mortality worldwide, accounting for 67% of deaths. One of the major challenges in developing new treatments is the lack of understanding of the exact underlying biological and molecular mechanisms. Chronic cardiovascular diseases are the single most common cause of death worldwide, and sudden deaths due to cardiac arrhythmias account for approximately 50% of all such cases. Traditional genetic screening for genes involved in cardiac disorders is labourious and frequently fails to detect the mutation that explains or causes the disorder. However, when mutations are identified, human induced pluripotent stem cells (hiPSCs) derived from affected patients make it possible to address fundamental research questions directly relevant to human health. As such, hiPSC technology has recently been used to model human diseases and patient-specific hiPSC-derived cardiomyocytes (hiPSC-CMs) thus offer a unique opportunity to investigate potential disease-causing genetic variants in their natural environment. The purpose of this review is to present the current state of knowledge regarding hiPSC-CMs, including their potential, limitations, and challenges and to discuss future prospects.

Congenital Long QT syndrome and torsade de pointes.

Since its initial description by Jervell and Lange-Nielsen in 1957, the congenital long QT syndrome (LQTS) has been the most investigated cardiac ion channelopathy. A prolonged QT interval in the surface electrocardiogram is the sine qua non of the LQTS and is a surrogate measure of the ventricular action potential duration (APD). Congenital as well as acquired alterations in certain cardiac ion channels can affect their currents in such a way as to increase the APD and hence the QT interval. The inhomogeneous lengthening of the APD across the ventricular wall results in dispersion of APD. This together with the tendency of prolonged APD to be associated with oscillations at the plateau level, termed early afterdepolarizations (EADs), provides the substrate of ventricular tachyarrhythmia associated with LQTS, usually referred to as torsade de pointes (TdP) VT. This review will discuss the genetic, molecular, and phenotype characteristics of congenital LQTS as well as current management strategies and future directions in the field.

Development and Evaluation of Two Abbreviated Questionnaires for Mentoring and Research Self-Efficacy.

OBJECTIVES: To reduce respondent burden for future evaluations of the National Heart, Lung, and Blood Institute-supported Programs to Increase Diversity Among Individuals Engaged in Health-Related Research (PRIDE), a mentored-research education program, we sought to shorten the 33-item Ragins and McFarlin Mentor Role Instrument (RMMRI), measuring mentor-role appraisals, and the 69-item Clinical Research Appraisal Inventory (CRAI), measuring research self-efficacy. METHODS: Three nationally recruited, junior-faculty cohorts attended two, annual 2-3 week Summer Institutes (SI-1/SI-2: 2011/2012, 2012/2013, 2013/2014) at one of six PRIDE sites. Mentees completed the RMMRI two months after mentor assignment and the CRAI at baseline (pre-SI-1) and 6-month (mid-year) and 12-month (post-SI-2) follow-up. Publications data obtained from Scopus in October 2015 were verified with mentees' curriculum vitae. The RMMRI and CRAI were shortened using an iterative process of principal-components analysis. The shortened measures were examined in association with each other (multiple linear regression) and with increase in publications (repeated-measures analysis of covariance). RESULTS: PRIDE enrolled 152 mentees (70% women; 60% Black, 35% Hispanic/Latino). Cronbach's alphas for the new 9-item RMMRI, 19-item CRAI, and four CRAI-19 subscales were excellent. Controlling for baseline self-efficacy and cohort, RMMRI-9 scores were independently, positively associated with post-SI-2 scores on the CRAI-19 and three subscales (writing, study design/data analysis, and collaboration/grant preparation). Controlling for cohort, higher RMMRI-9 and post-SI-2 CRAI-19 scores were each associated with greater increase in publications. CONCLUSIONS: The RMMRI-9 and CRAI-19 retained the excellent psychometric properties of the longer measures. Findings support use of the shortened measures in future evaluations of PRIDE.

Mentored Training to Increase Diversity among Faculty in the Biomedical Sciences: The NHLBI Summer Institute Programs to Increase Diversity (SIPID) and the Programs to Increase Diversity among Individuals Engaged in Health-related Research (PRIDE).

OBJECTIVE: To report baseline characteristics of junior-level faculty participants in the Summer Institute Programs to Increase Diversity (SIPID) and the Programs to Increase Diversity among individuals engaged in Health-Related Research (PRIDE), which aim to facilitate participants' career development as independent investigators in heart, lung, blood, and sleep research. DESIGN AND SETTING: Junior faculty from groups underrepresented in the biomedical-research workforce attended two, 2-3 week, annual summer research-education programs at one of six sites. Programs provided didactic and/or laboratory courses, workshops to develop research, writing and career-development skills, as well as a mentoring component, with regular contact maintained via phone, email and webinar conferences. Between summer institutes, trainees participated in a short mid-year meeting and an annual scientific meeting. Participants were surveyed during and after SIPID/PRIDE to evaluate program components. PARTICIPANTS: Junior faculty from underrepresented populations across the United States and Puerto Rico participated in one of three SIPID (2007-2010) or six PRIDE programs (2011-2014). RESULTS: Of 204 SIPID/PRIDE participants, 68% were female; 67% African American and 27% Hispanic/Latino; at enrollment, 75% were assistant professors and 15% instructors, with most (96%) on non-tenure track. Fifty-eight percent had research doctorates (PhD, ScD) and 42% had medical (MD, DO) degrees. Mentees' feedback about the program indicated skills development (eg, manuscript and grant writing), access to networking, and mentoring were the most beneficial elements of SIPID and PRIDE programs. Grant awards shifted from primarily mentored research mechanisms to primarily independent investigator awards after training. CONCLUSIONS: Mentees reported their career development benefited from SIPID and PRIDE participation.

Induction of autoimmune response to the extracellular loop of the HERG channel pore induces QTc prolongation in guinea-pigs.

KEY POINTS: Channelopathies of autoimmune origin are novel and are associated with corrected QT (QTc) prolongation and complex ventricular arrhythmias. We have recently demonstrated that anti-SSA/Ro antibodies from patients with autoimmune diseases and with QTc prolongation on the ECG target the human ether-à-go-go-related gene (HERG) K+ channel by inhibiting the corresponding current, IKr , at the pore region. Immunization of guinea-pigs with a peptide (E-pore peptide) corresponding to the extracellular loop region connecting the S5 and S6 segments of the HERG channel induces high titres of antibodies that inhibit IKr , lengthen the action potential and cause QTc prolongation on the surface ECG. In addition, anti-SSA/Ro-positive sera from patients with connective tissue diseases showed high reactivity to the E-pore peptide. The translational impact is the development of a peptide-based approach for the diagnosis and treatment of autoimmune-associated long QT syndrome. ABSTRACT: We recently demonstrated that anti-SSA/52 kDa Ro antibodies (Abs) from patients with autoimmune diseases and corrected QT (QTc) prolongation directly target and inhibit the human ether-à-go-go-related gene (HERG) K+ channel at the extracellular pore (E-pore) region, where homology with SSA/52 kDa Ro antigen was demonstrated. We tested the hypothesis that immunization of guinea-pigs with a peptide corresponding to the E-pore region (E-pore peptide) will generate pathogenic inhibitory Abs and cause QTc prolongation. Guinea-pigs were immunized with a 31-amino-acid peptide corresponding to the E-pore region of HERG. On days 10-62 after immunization, ECGs were recorded and blood was sampled for the detection of E-pore peptide Abs. Serum samples from patients with autoimmune diseases were evaluated for reactivity to E-pore peptide by enzyme-linked immunosorbent assay (ELISA), and histology was performed on hearts using Masson's Trichrome. Inhibition of the HERG channel was assessed by electrophysiology and by computational modelling of the human ventricular action potential. The ELISA results revealed the presence of high titres of E-pore peptide Abs and significant QTc prolongation after immunization. High reactivity to E-pore peptide was found using anti-SSA/Ro Ab-positive sera from patients with QTc prolongation. Histological data showed no evidence of fibrosis in immunized hearts. Simulations of simultaneous inhibition of repolarizing currents by anti-SSA/Ro Ab-positive sera showed the predominance of the HERG channel in controlling action potential duration and the QT interval. These results are the first to demonstrate that inhibitory Abs to the HERG E-pore region induce QTc prolongation in immunized guinea-pigs by targeting the HERG channel independently from fibrosis. The reactivity of anti-SSA/Ro Ab-positive sera from patients with connective tissue diseases with the E-pore peptide opens novel pharmacotherapeutic avenues in the diagnosis and management of autoimmune-associated QTc prolongation.

Pathogenesis of the Novel Autoimmune-Associated Long-QT Syndrome.

BACKGROUND: Emerging clinical evidence demonstrates high prevalence of QTc prolongation and complex ventricular arrhythmias in patients with anti-Ro antibody (anti-Ro Ab)-positive autoimmune diseases. We tested the hypothesis that anti-Ro Abs target the HERG (human ether-a-go-go-related gene) K(+) channel, which conducts the rapidly activating delayed K(+) current, IKr, thereby causing delayed repolarization seen as QT interval prolongation on the ECG. METHODS AND RESULTS: Anti-Ro Ab-positive sera, purified IgG, and affinity-purified anti-52kDa Ro Abs from patients with autoimmune diseases and QTc prolongation were tested on IKr using HEK293 cells expressing HERG channel and native cardiac myocytes. Electrophysiological and biochemical data demonstrate that anti-Ro Abs inhibit IKr to prolong action potential duration by directly binding to the HERG channel protein. The 52-kDa Ro antigen-immunized guinea pigs showed QTc prolongation on ECG after developing high titers of anti-Ro Abs, which inhibited native IKr and cross-reacted with guinea pig ERG channel. CONCLUSIONS: The data establish that anti-Ro Abs from patients with autoimmune diseases inhibit IKr by cross-reacting with the HERG channel likely at the pore region where homology between anti-52-kDa Ro antigen and HERG channel is present. The animal model of autoimmune-associated QTc prolongation is the first to provide strong evidence for a pathogenic role of anti-Ro Abs in the development of QTc prolongation. It is proposed that adult patients with anti-Ro Abs may benefit from routine ECG screening and that those with QTc prolongation should receive counseling about drugs that may increase the risk for life-threatening arrhythmias.

High-fat diet-dependent modulation of the delayed rectifier K(+) current in adult guinea pig atrial myocytes.

Obesity is associated with hyperlipidemia, electrical remodeling of the heart, and increased risk of supraventricular arrhythmias in both male and female patients. The delayed rectifier K(+) current (IK), is an important regulator of atrial repolarization. There is a paucity of studies on the functional role of IK in response to obesity. Here, we assessed the obesity-mediated functional modulation of IK in low-fat diet (LFD), and high-fat diet (HFD) fed adult guinea pigs. Guinea pigs were randomly divided into control and obese groups fed, ad libitum, with a LFD (10 kcal% fat) or a HFD (45 kcal% fat) respectively. Action potential duration (APD), and IK were studied in atrial myocytes and IKr and IKs in HEK293 cells using whole-cell patch clamp electrophysiology. HFD guinea pigs displayed a significant increase in body weight, total cholesterol and total triglycerides within 50 days. Atrial APD at 30% (APD30) and 90% (APD90) repolarization were shorter, while atrial IK density was significantly increased in HFD guinea pigs. Exposure to palmitic acid (PA) increased heterologously expressed IKr and IKs densities, while oleic acid (OA), severely reduced IKr and had no effect on IKs. The data are first to show that in obese guinea pigs abbreviated APD is due to increased IK density likely through elevations of PA. Our findings may have crucial implications for targeted treatment options for obesity-related arrhythmias.

A Perspective on Promoting Diversity in the Biomedical Research Workforce: The National Heart, Lung, and Blood Institute's PRIDE Program.

Aspiring junior investigators from groups underrepresented in the biomedical sciences face various challenges as they pursue research independence. However, the biomedical research enterprise needs their participation to effectively address critical research issues such as health disparities and health inequities. In this article, we share a research education and mentoring initiative that seeks to address this challenge: Programs to Increase Diversity among Individuals Engaged in Health Related Research (PRIDE), funded by the National Heart, Lung, and Blood Institute (NHLBI). This longitudinal research-education and mentoring program occurs through summer institute programs located at US-based academic institutions. Recruited participants are exposed to didactic and lab-based research-skill enhancement experiences, with year-round mentoring over the course of two years. Mentor-mentee matching is based on shared research interests to promote congruence and to enhance skill acquisition. Program descriptions and sample narratives of participants' perceptions of PRIDE's impact on their career progress are showcased. Additionally, we highlight the overall program design and structure of four of seven funded summer institutes that focus on cardiovascular disease, related conditions, and health disparities. Mentees' testimonials about the value of the PRIDE mentoring approach in facilitating career development are also noted. Meeting the clinical and research needs of an increasingly diverse US population is an issue of national concern. The PRIDE initiative, which focuses on increasing research preparedness and professional development of groups underrepresented in the biomedical research workforce, with an emphasis on mentoring as the critical approach, provides a robust model that is impacting the careers of future investigators.

All members in the sphingomyelin synthase gene family have ceramide phosphoethanolamine synthase activity.

Sphingomyelin synthase-related protein (SMSr) synthesizes the sphingomyelin analog ceramide phosphoethanolamine (CPE) in cells. Previous cell studies indicated that SMSr is involved in ceramide homeostasis and is crucial for cell function. To further examine SMSr function in vivo, we generated Smsr KO mice that were fertile and had no obvious phenotypic alterations. Quantitative MS analyses of plasma, liver, and macrophages from the KO mice revealed only marginal changes in CPE and ceramide as well as other sphingolipid levels. Because SMS2 also has CPE synthase activity, we prepared Smsr/Sms2 double KO mice. We found that CPE levels were not significantly changed in macrophages, suggesting that CPE levels are not exclusively dependent on SMSr and SMS2 activities. We then measured CPE levels in Sms1 KO mice and found that Sms1 deficiency also reduced plasma CPE levels. Importantly, we found that expression of Sms1 or Sms2 in SF9 insect cells significantly increased not only SM but also CPE formation, indicating that SMS1 also has CPE synthase activity. Moreover, we measured CPE synthase Km and Vmax for SMS1, SMS2, and SMSr using different NBD ceramides. Our study reveals that all mouse SMS family members (SMSr, SMS1, and SMS2) have CPE synthase activity. However, neither CPE nor SMSr appears to be a critical regulator of ceramide levels in vivo.