Caveolin-3 and Caveolae regulate ventricular repolarization.

RATIONALE: Flask-shaped invaginations of the cardiomyocyte sarcolemma called caveolae require the structural protein caveolin-3 (Cav-3) and host a variety of ion channels, transporters, and signaling molecules. Reduced Cav-3 expression has been reported in models of heart failure, and variants in CAV3 have been associated with the inherited long-QT arrhythmia syndrome. Yet, it remains unclear whether alterations in Cav-3 levels alone are sufficient to drive aberrant repolarization and increased arrhythmia risk. OBJECTIVE: To determine the impact of cardiac-specific Cav-3 ablation on the electrophysiological properties of the adult mouse heart. METHODS AND RESULTS: Cardiac-specific, inducible Cav3 homozygous knockout (Cav-3KO) mice demonstrated a marked reduction in Cav-3 expression by Western blot and loss of caveolae by electron microscopy. However, there was no change in macroscopic cardiac structure or contractile function. The QTc interval was increased in Cav-3KO mice, and there was an increased propensity for ventricular arrhythmias. Ventricular myocytes isolated from Cav-3KO mice exhibited a prolonged action potential duration (APD) that was due to reductions in outward potassium currents (Ito, Iss) and changes in inward currents including slowed inactivation of ICa,L and increased INa,L. Mathematical modeling demonstrated that the changes in the studied ionic currents were adequate to explain the prolongation of the mouse ventricular action potential. Results from human iPSC-derived cardiomyocytes showed that shRNA knockdown of Cav-3 similarly prolonged APD. CONCLUSION: We demonstrate that Cav-3 and caveolae regulate cardiac repolarization and arrhythmia risk via the integrated modulation of multiple ionic currents.

Caveolin-3 Overexpression Attenuates Cardiac Hypertrophy via Inhibition of T-type Ca2+ Current Modulated by Protein Kinase Cα in Cardiomyocytes.

Pathological cardiac hypertrophy is characterized by subcellular remodeling of the ventricular myocyte with a reduction in the scaffolding protein caveolin-3 (Cav-3), altered Ca(2+) cycling, increased protein kinase C expression, and hyperactivation of calcineurin/nuclear factor of activated T cell (NFAT) signaling. However, the precise role of Cav-3 in the regulation of local Ca(2+) signaling in pathological cardiac hypertrophy is unclear. We used cardiac-specific Cav-3-overexpressing mice and in vivo and in vitro cardiac hypertrophy models to determine the essential requirement for Cav-3 expression in protection against pharmacologically and pressure overload-induced cardiac hypertrophy. Transverse aortic constriction and angiotensin-II (Ang-II) infusion in wild type (WT) mice resulted in cardiac hypertrophy characterized by significant reduction in fractional shortening, ejection fraction, and a reduced expression of Cav-3. In addition, association of PKCα and angiotensin-II receptor, type 1, with Cav-3 was disrupted in the hypertrophic ventricular myocytes. Whole cell patch clamp analysis demonstrated increased expression of T-type Ca(2+) current (ICa, T) in hypertrophic ventricular myocytes. In contrast, the Cav-3-overexpressing mice demonstrated protection from transverse aortic constriction or Ang-II-induced pathological hypertrophy with inhibition of ICa, T and intact Cav-3-associated macromolecular signaling complexes. siRNA-mediated knockdown of Cav-3 in the neonatal cardiomyocytes resulted in enhanced Ang-II stimulation of ICa, T mediated by PKCα, which caused nuclear translocation of NFAT. Overexpression of Cav-3 in neonatal myocytes prevented a PKCα-mediated increase in ICa, T and nuclear translocation of NFAT. In conclusion, we show that stable Cav-3 expression is essential for protecting the signaling mechanisms in pharmacologically and pressure overload-induced cardiac hypertrophy.

Impacts and challenges of United States medical students during the COVID-19 pandemic.

The delivery of medical student education has changed rapidly during the coronavirus disease 2019 (COVID-19) pandemic. Students in their pre-clinical years have transitioned to online courses and examinations. Students in their clinical years are not permitted on clinical rotations, and face uncertainties in career exploration and the residency application process. Medical students in all stages of training are volunteering and helping their communities. The future presence of COVID-19 throughout the United States is unknown, and medical students are eager to return to their training. This paper outlines current challenges in medical student education and the various responses that have been adopted. We also discuss possible future directions for students through involvement in telemedicine, outpatient clinic visits, and non-respiratory inpatient care tasks as adequate personal protective equipment, COVID-19 testing, and resources become more widely available.

Pediatric Dilated Cardiomyopathy-Associated LRRC10 (Leucine-Rich Repeat-Containing 10) Variant Reveals LRRC10 as an Auxiliary Subunit of Cardiac L-Type Ca2+ Channels.

BACKGROUND: Genetic causes of dilated cardiomyopathy (DCM) are incompletely understood. LRRC10 (leucine-rich repeat-containing 10) is a cardiac-specific protein of unknown function. Heterozygous mutations in LRRC10 have been suggested to cause DCM, and deletion of Lrrc10 in mice results in DCM. METHODS AND RESULTS: Whole-exome sequencing was carried out on a patient who presented at 6 weeks of age with DCM and her unaffected parents, filtering for rare, deleterious, recessive, and de novo variants. Whole-exome sequencing followed by trio-based filtering identified a homozygous recessive variant in LRRC10, I195T. Coexpression of I195T LRRC10 with the L-type Ca2+ channel (Cav1.2, ß2CN2, and α2δ subunits) in HEK293 cells resulted in a significant ≈0.5-fold decrease in ICa,L at 0 mV, in contrast to the ≈1.4-fold increase in ICa,L by coexpression of LRRC10 (n=9-12, P<0.05). Coexpression of LRRC10 or I195T LRRC10 did not alter the surface membrane expression of Cav1.2. LRRC10 coexpression with Cav1.2 in the absence of auxiliary ß2CN2 and α2δ subunits revealed coassociation of Cav1.2 and LRRC10 and a hyperpolarizing shift in the voltage dependence of activation (n=6-9, P<0.05). Ventricular myocytes from Lrrc10-/- mice had significantly smaller ICa,L, and coimmunoprecipitation experiments confirmed association between LRRC10 and the Cav1.2 subunit in mouse hearts. CONCLUSIONS: Examination of a patient with DCM revealed homozygosity for a previously unreported LRRC10 variant: I195T. Wild-type and I195T LRRC10 function as cardiac-specific subunits of L-type Ca2+ channels and exert dramatically different effects on channel gating, providing a potential link to DCM.