Lee, Hon-chi

Introduction: Although the prevalence of atrial fibrillation (AF) is higher in men than in women, the onset of AF appears to diminish the survival advantage in women. The pathophysiologic factors underlying survival outcome in AF are not well understood. Methods: A cohort of 3480 Olmsted County, Minnesota residents (mean age 72.8±14 years, 51.8% female) with incident AF who underwent transthoracic echocardiography within 30 days of AF diagnosis [median (IQR) 1, 1-6 days] were retrospectively studied. We examined the association of clinical parameters and survival according to gender. Kaplan-Meier and Cox proportional hazards models were used to compare overall survival in males and females. Results: Females were older and slimmer than males and more frequently had hypertension, prior stroke, and had higher CHA 2 DS 2 vasc score, pulse pressure and effective arterial elastance. Women also had smaller LV end diastolic dimension with higher LV ejection fraction, LA volume index, E/e prime ratio, and PASP (43.6±13.8 vs 39.1±13.3; <.001). During a mean follow-up of 7.4±6.2 years (median 6.6 years), 2569 patients died. Women had a lower 5-year survival compared to men. The probability of 1- and 5-year survival rates for women vs men were 80.2% vs 84.1% at 1 year and 54.4% vs 63.7% at 5 years (log-rank P <.001). In multivariable Cox regression analysis, after accounting for potential confounders, the independent predictors of mortality were age (HR 1.07 [95% CI 1.06-1.08]), PASP (per 5 unit increment) (HR 1.11 [95% CI 1.09-1.12]), effective arterial elastance (HR 1.06 [95% CI 1.01-1.12]), previous heart failure (HR 1.34 [95% CI 1.20-1.49]), diabetes (HR 1.33 [95% CI 1.20-1.48]), prior stroke (HR 1.26 [95% CI 1.13-1.41]), smoking (HR 1.13 [95% CI 1.06-1.20]), chronic lung disease (HR 1.32 [95% CI 1.20-1.45]), peripheral arterial disease (HR, 1.32 [95% CI 1.18-1.48]), and chronic kidney disease (HR, 1.52 [95% CI 1.38-1.69]). Conclusions: In a community-based cohort of patients with incident AF, markers of arterial stiffness and diastolic dysfunction were more prevalent in women compared to men and were strongly predictive of mortality. Our findings suggest that vascular stiffness may underlie the increased risk of mortality observed in women after a new diagnosis of AF.

Introduction: Doxorubicin (DOX) is widely used for chemotherapy, but cardiotoxicity and cardiomyopathy are major adverse effects. The canonical transient receptor potential 6 gene ( TRPC6) is a putative risk gene for cardiomyopathy. Recently, a TRPC6 N338S mutation was found in a patient with DOX-induced heart failure. However, the TRPC6 N338S mutant has not been characterized, and how it affects cardiac function is unknown. Hypothesis: We hypothesized that TRPC6 N338S is a gain-of-function mutation producing intracellular Ca 2+ overload in cardiomyocytes. Methods: Using patch clamp recording, molecular biological and molecular docking analyses, we assessed the function of TRPC6 N338S heterologously expressed in HL-1 cardiac cells. Results: TRPC6 N338S significantly increased the current densities of TRPC6 (defined as 1 μM BI-749327 sensitive components, a highly selective TRPC6 inhibitor) in HL-1 cells at baseline and after exposure to 50 μM 1-oleoyl 2-acetyl-sn-glycerol (OAG, an activator of TRPC6), compared to cells expressing TRPC6 WT. Moreover, a 24-h pretreatment with 0.5 μM DOX further potentiated the OAG effects on TRPC6 WT currents with a significantly greater response in the N338S currents. Ca 2+ imaging also showed enhanced intracellular Ca 2+ levels in cells expressing the N338S mutant with OAG and DOX treatment. Biological studies found that the cytoplasmic and surface expression of TRPC6 WT and N338S mutant were identical in HL-1 cells, but those of TRPC6 N338S were markedly upregulated after treatment with 0.5 μM DOX, compared to TRPC6 WT. Molecular docking and dynamics simulation analysis unraveled that OAG binds to a pocket constituted by the pore-helix, S5 and S6 domains of TRPC6 through polar interactions. OAG binds to the same site in TRPC6 N338S with shortened interfacial distances due to additional polar and hydrogen bonding between OAG and the N338S mutant. Conclusions: TRPC6 N338S mutation strengthens the interaction with OAG, stabilizes the OAG-TRPC6 N338S complex, and enhances the OAG effects. Treatment with DOX significantly increases the expression and function of TRPC6 N338S in HL-1 cells. Hence, the TRPC6 N338S is a gain-of-function mutation and may contribute to cardiotoxicity in patients with anthracycline treatment.

Aldosterone is a critical driver for cardiovascular disease (CVD). We recently discovered that MANP, a novel atrial natriuretic peptide (ANP) analog, possessed more potent aldosterone inhibitory action than ANP. MANP is currently entering clinical trials for hypertension and thus understanding its aldosterone suppressing mechanism is important. The mechanism of aldosterone inhibition by natriuretic peptides (NPs) remains to be clearly defined. Conflicting results were reported on the roles of particulate guanylyl cyclase A receptor (pGC-A) and NP clearance receptor (NPRC) in aldosterone inhibition. Furthermore, the functions of protein kinase G (PKG) and phosphodiesterases (PDE) on aldosterone regulation are not clear. Herein, we investigated the molecular mechanism of aldosterone regulation in the human adrenocortical cell line H295R and in mice. We firstly showed that pGC-A mediates aldosterone inhibition. In contrast, with NPRC agonist and antagonist, we showed that NPRC did not inhibit aldosterone. Next, we confirmed that MANP inhibits aldosterone via PDE2, not PKG, with specific agonists, antagonists, siRNA silencing, and fluorescence resonance energy transfer (FRET) experiments. Specifically, MANP suppressed ANGII mediated activation of aldosterone (fold change) MANP+ANGII 3.2±0.1* vs. ANGII 3.8±0.1 (*p<0.05) with IBMX, a PDEs inhibitor and the PDE2 antagonist Bay 60-7550 reversed MANP-mediated aldosterone suppression (IBMX+MANP+ANGII 3.9±0.2 and Bay+MANP+ANGII 4.1±0.1). With PKG agonists and inhibitors, aldosterone levels were not changed. In PDE2 activity FRET studies, aldosterone control was 3.7±0.4 and with MANP 0.9±0.2* supporting PDE2 activation by MANP. Further, the inhibitory effect of PDE2 is mediated by a reduction of intracellular Ca2+ concentration (~22%). We then showed that MANP directly reduced aldosterone synthase CYP11B2 expression in vitro. Lastly, in PDE2 knockout mice (embryonic lethal), embryonic adrenal CYP11B2 expression is markedly increased (wild type: 1±0.2, KO: 2.8±0.5*). Our findings innovatively elucidate the pGC-A/cGMP/PDE2 pathway in aldosterone inhibition by MANP in vitro and in vivo. Additionally, our data also support the development of MANP as a novel ANP analog drug for CVD.