Citations

BACKGROUND: It is unknown whether cardiac resynchronization therapy (CRT) improves systemic metabolomic profile by enhancing left ventricular function. The observational cohort study aimed to investigate the effect of CRT on left ventricular ejection fraction (LVEF) and circulating plasma metabolites in patients who had heart failure with reduced LVEF. METHODS: We prospectively screened patients with ischemic cardiomyopathy and nonischemic cardiomyopathy who received CRT with a defibrillator for LVEF ≤35% according to current guidelines. Clinical assessment included echocardiography and device interrogation. Blood samples for metabolomic analysis were collected before CRT and at 6-month follow-up. Plasma was subjected to gas chromatography-mass spectrometry and 1 H nuclear magnetic resonance-based metabolomic analysis. RESULTS: Totally 92 patients were enrolled, with a mean age of 67.3±11.3 years (37.0% female). LVEF was significantly improved from 28.9±7.6% at baseline to 36.0±11.3% at 6 months ( P <0.001) and to 40.1±12.6% at 12 months ( P <0.001). After CRT, 42 metabolite features were significantly decreased compared with the baseline. The ketone bodies, including 3-hydroxybutyrate ( P <0.001) and acetone ( P =0.01), were reduced. A branched-chain amino acid, isoleucine, was also decreased after CRT ( P =0.01). These metabolomic changes were mainly observed in the nonischemic cardiomyopathy group, while the metabolomic profile in the ischemic cardiomyopathy group was characterized by enhanced amino acid oxidation and elevated levels of lactate and pyruvate. The improvement in LVEF positively correlated with the ratio of changes in ketone bodies and isoleucine. CONCLUSIONS: CRT may modulate the systemic plasma metabolomic profile, which correlated with improvement in left ventricular function in patients with severe heart failure with reduced ejection fraction.

BACKGROUND: TRPC6 (transient receptor potential canonical 6) channels, encoded by the TRPC6 gene, are widely expressed in cardiomyocytes and play a critical role in maintaining intracellular Ca 2 + homeostasis. Variants in TRPC6 are associated with chemotherapy-related cardiomyopathy. Specifically, the TRPC6 A404V polymorphism, with a minor (404 V) allele frequency of 12% in the general population, has been identified in patients undergoing anthracycline therapy. However, the underlying mechanisms remain largely unexplored. METHODS: Using patch-clamp recordings, Ca 2 + imaging, computational analysis, and molecular biology techniques, we assessed the effects of doxorubicin and its metabolite, doxorubicinol, on regulating TRPC6 alanine (A) at position 404 replaced by valine (V; A404V) channel expression and function in a heterologous expression system and native cardiac cells. RESULTS: Both additive and recessive models demonstrated a significant association between the TRPC6 A404V variant and doxorubicin-related cardiomyopathy. The TRPC6 A404V channel exhibited higher membrane expression levels compared with the wild type (WT) control. Patch-clamp recordings showed that both TRPC6 WT and A404V channels remained mostly inactive at baseline. Application of 50 μmol/L 1-oleoyl acetyl-sn-glycerol (OAG), a TRPC6 activator, significantly increased the inward- and outward-current densities of WT and A404V channels. Furthermore, a 24-hour treatment with 0.5 μmol/L doxorubicin enhanced TRPC6 mRNA expression and potentiated the OAG effects on both WT and A404V channels, with a more pronounced response in A404V channels. Treatment with 0.5 μmol/L doxorubicinol had no effect on OAG-induced current densities in either WT or A404V channels. Doxorubicin effects on intracellular Ca 2 + levels were confirmed by Ca 2 + imaging in native cardiac cells. Computational modeling revealed that the A404V mutation induces a conformational change in the OAG-binding pocket, enhancing its interaction with OAG in the A404V protein compared with the WT control. CONCLUSIONS: The TRPC6 A404V is a gain-of-function variant that exhibits enhanced activity in the presence of doxorubicin. Therefore, the TRPC6 A404V variant represents a risk factor for anthracycline-induced cardiotoxicity in patients with cancer.

ABSTRACT Gain-of-function mutations in the transient receptor potential 6 (TRPC6) channel have recently been recognized as risk factors for both doxorubicin (DOX)-induced cardiomyopathy. Functional evaluation of TRPC6 missense variants is therefore important for cancer patients undergoing anthracycline treatment. However, traditional electrophysiological methods are labor-intensive and time-consuming. In this study, we compared the functional responses of TRPC6 missense variants to 1-oleoyl-2-acetyl-sn-glycerol (OAG), a TRPC6 agonist, using molecular docking and patch clamp recording techniques. For the wild-type (WT) TRPC6 structure (PDB ID: 6UZ8), OAG exhibited a binding energy of -4.49 kcal/mol and a dissociation constant (Kd) of 0.511 mM. Twenty TRPC6 missense variants were identified from cancer patients in the Mayo Clinic database. Of these, fifteen variants had resolvable structures, nine of which displayed increased Kd values and six decreased Kd values compared to WT in molecular docking analysis. Patch clamp recordings revealed that TRPC6 WT and mutant channels were inactive at baseline but were activated upon 50 μM OAG stimulation, except two loss-of-function variants. Moreover, a 24-h treatment with 0.5 μM DOX significantly enhanced OAG-induced channel activation. All three variants identified in patients with heart failure demonstrated gain-of-function properties in both electrophysiological measurements and in-silico predictions. Importantly, the results obtained from molecular docking and patch clamp recordings were strongly correlated, showing an 82% concordance, higher than the predictions from AlphaMissense. These findings indicate that our computational analysis provides a rapid and reliable method for predicting the functional impact of TRPC6 missense variants, which may aid clinical decision-making in cancer patients receiving chemotherapy.

Background: We have previously reported that Sorbs2 (sorbin and SH3 domain 2) knockout mice have significant cardiac structural and electrical remodeling, including atrial enlargement and fibrosis. The mechanisms of such changes were unknown. Hypothesis: We hypothesized that loss of Sorbs2 in cardiac fibroblasts promotes profibrotic signaling pathways and alters the balance between matrix metalloproteinases (MMPs), and their inhibitors (TIMPs) resulting in excessive collagen deposition in the atria. Methods: We used Sorbs2 global knockout ( Sorbs2 KO) mice and age-matched wild-type (WT) controls at 4 to 5 months of age. Left atrial fibrosis was quantitated by Masson's trichrome staining in serial sections. Scratch wound healing assays and transwell migration assays were performed in isolated Sorbs2 KO and WT atrial fibroblasts. Protein expression was determined by Western blots. Interleukin-6 (IL-6) production in cultured fibroblast supernatants was measured by ELISA. Results: Sorbs2 KO mice showed significant increase in atrial diameter (16.6 ± 1.5 mm vs 12.0 ± 1.1 mm in WT; n=3, p < 0.05) and atrial fibrosis (fraction of fibrotic areas: 18.6± 2.9 % vs. 7.6 ± 0.9 % in WT; p < 0.01). Collagen 1 and collagen 3 protein levels in Sorbs2 KO mouse atria were 1.8-fold and 1.7-fold higher than those of WT respectively. Sorbs2 KO atrial fibroblasts showed impaired function with significantly reduced migration and slower scratch-wound closure (migration area after 24h: 18.5 ± 3.8 % vs 70.1 ± 6.7 % in WT; n=6, p < 0.01).Moreover, transforming growth factor β1 (TGF-β1), α-smooth muscle actin, and periostin expression levels were significantly reduced in isolated fibroblasts and atrial myocardia from Sorbs2 KO mice, suggesting that fibrosis is not caused by TGF-b1-dependent mechanisms or from myofibroblast transformation. Analysis of ECM proteins showed significant downregulation of MMP1 and MMP3 but upregulation of TIMP1, while TIMP3 was unchanged. Consistent with a pro-inflammatory phenotype, Sorbs2 KO atrial fibroblasts secreted higher IL-6 levels at baseline (3303± 463 pg/mL vs. 2075 ± 731 pg/mL in WT; n=6, p < 0.01) and with LPS stimulation (7791 ± 604 pg/mL vs. 5588 ± 763 pg/mL in WT; n=6, p < 0.01). Conclusion: Sorbs2 deficiency is associated with abnormal atrial fibroblast function showing impaired migration and scratch wound healing, as well as increased IL-6 production and imbalanced MMP/TIMP. These changes result in collagen accumulation and enhanced fibrosis.

Background: Voltage-gated Nav1.5 channel, encoded by SCN5A , is essential for initiation and propagation of action potentials (AP) in atria. Nav1.5 channelopathy is strongly associated with arrhythmogenesis, including atrial fibrillation. Sorbin and SH3 domain-containing protein 2 (Sorbs2), encoded by SORBS2 , is an important cytoskeletal protein for maintaining atrial structural and electrical integrity. However, the specific mechanisms through which Sorbs2 modulates Nav1.5 function in atria is unknown. Hypothesis: Sorbs2 modulates atrial Nav1.5 expression and function through direct protein-protein interaction. Methods: We created the cardiac-specific Sorbs2 knockout ( c-Sorbs2 KO) mice. We determined the mechanisms by which Sorbs2 regulates Nav1.5 channel expression and function by performing electrophysiological experiments using atrial cells and tissues from control and c-Sorbs2 KO mice, in conjunction with molecular biological studies and in silico analysis. Results: c-Sorbs2 KO mice at 8-10 months showed marked left atrial (LA) enlargement, and ECG showed significantly prolonged P-R durations. Compared to wild-type controls, intracellular recordings in LA tissues isolated from c-Sorbs2 KO mice showed reduced AP amplitude, decreased upstroke velocity, prolonged AP duration at 90% repolarization and effective refractory period, spontaneous atrial tachycardias and triggered activity. Patch-clamp recordings in freshly isolated atrial cardiomyocytes showed a significantly reduced peak sodium current density in c-Sorbs2 KO mice (-12.0 ± 1.6 pA/pF at -45 mV, n = 10), compared to controls (-21.3 ± 4.0 pA/pF at -45 mV, n = 12, p < 0.05). Also, the steady-state activation and inactivation curves of Nav1.5 channel were rightward shifted in c-Sorbs2 KO atrial cardiomyocytes. Molecular docking analysis showed that the Sorbs2 SH3 domain interacts directly with the voltage-sensing domain of Nav1.5. Co-immunoprecipitation assays confirmed the physical interactions between Nav1.5 and the C-terminal SH3 domain of Sorbs2. Furthermore, results from membrane biotinylation study demonstrated that deletion of the SH3 domains of Sorbs2 significantly reduced Nav1.5 surface expression in HEK293 cells. Sorbs2 interacts directly with Nav1.5 through its SH3 domain, playing a key role in regulating Nav1.5 channel gating kinetics and surface expression in atrial cardiomyocytes. Loss of Sorbs2 results in Nav1.5 channelopathy and contributes to atrial electrical remodeling.

Background: Cardiac myosin-binding protein C (cMyBP-C, encoded by MYBPC3 ) and Sorbin and SH3 domain-containing protein 2 (Sorbs2, encoded by SORBS2 ) are critical sarcomeric components that maintain cardiac structure and function. MYBPC3 and SORBS2 are linked to hypertrophic and dilated cardiomyopathies. But the relationship between Sorbs2 and cMyBP-C regulation, and their roles in the pathogenesis of atrial fibrotic cardiomyopathy (AFCM), remains unclear. Hypothesis: Sorbs2 acts as a cytoskeletal and RNA-binding protein that regulates cMyBP-C expression in atrial myocardium. Methods: We created the cardiac-specific Sorbs2 knockout ( c-Sorbs2 KO mice. We used next-generation RNA sequencing, molecular biology techniques, and in silico analysis to study how Sorbs2 regulates cMyBP-C expression in the atria of c-Sorbs2 KO mice. Results: Compared to age-matched wild-type (WT) mice at 8-9 months of age, the c-Sorbs2 KO male exhibited significant left atrial (LA) enlargement (diameter: 2.41±0.11 mm vs 1.82 ± 0.05 mm in WT; n = 8; p < 0.001) and severe atrial fibrosis (fibrotic area: 12.29±1.73 vs 2.83 ± 0.41% in WT; p < 0.001), accompanied by marked reductions in both mRNA and protein levels of cMyBP-C in LA. In vitro knock-down of Sorbs2 by 60% via shRNA led to an 86.3% decrease in cMyBP-C protein levels, while a 3-fold Sorbs2 overexpression via adenoviral transduction resulted in a 1.4-fold increase in cMyBP-C protein levels in HL-1 cells . cMyBP-C mRNAs were identified in the ribonucleoprotein complexes immunoprecipitated with anti-Sorbs2 antibodies from cardiomyocyte lysates. Loss of Sorbs2 significantly reduced the half-life of cMyBP-C mRNA (from 2.1 hrs in WT to 1.2 hrs in KO). Co-immunoprecipitation with truncated Sorbs2 constructs showed that the C-terminal SH3 domains of Sorbs2, but not the N-terminal SoHo domain, interacted with cMyBP-C protein. Molecular docking and modeling showed hydrophobic interactions and hydrogen bonds between residues H906 and G907 in the SH3 domain of Sorbs2 and residue A954, P955 and T957 in the SH3-binding motif (949-MA P GA P VT-957) of cMyBP-C with a weighted score of -1036 using ClusPro online service. Conclusions: Sorbs2 regulates cMyBP-C expression through direct interaction with both cMyBP-C mRNA and protein. Loss of Sorbs2 results in reduced cMyBP-C expression, atrial fibrosis, and chamber enlargement, revealing a novel Sorbs2/cMyBP-C axis underlying AFCM pathogenesis.

Background: Gain-of-function mutations in the canonical transient receptor potential 6 (TRPC6) channel contribute to heart failure (HF) and focal segmental glomerulosclerosis in humans. Our GWAS results indicated that the TRPC6 A404V variant, having a minor allele frequency of 12% in the population, is associated with doxorubicin-induced cardiotoxicity. However, the underlying ionic mechanisms of this variant have not been fully examined. Methods: Combining patch clamp recording, site-directed mutagenesis, and in-silico analysis, we evaluated the TRPC6 A404V variant function. Results: Whole-cell TRPC6 currents were elicited in HEK293 cells using a voltage ramp protocol from -100 mV to +100 mV with a holding potential of -60 mV, 48 hours after transfection with TRPC6 WT or A404V cDNAs. The inward-current densities at -100 mV and the outward-current densities at +100 mV for TRPC6 WT and A404V variant were similar at baseline. However, after exposure to 50 μM 1-oleoyl acetyl-sn-glycerol (OAG, a TRPC6 activator), these current densities were significantly increased by 2.6-fold and 4.5-fold respectively in the WT (n=20 cells), and by 8.4-fold and 8.9-fold respectively in the A404V variant (n=12 cells, p<0.05 vs. WT). The OAG effects were abolished by superfusion with 1 μM BI-749327 (a specific TRPC6 inhibitor). Moreover, a 24-hour treatment with 0.5 μM doxorubicin (DOX) further amplified the effects of OAG, increasing the total inward- and outward-current densities by 7.2-fold and 9.5-fold respectively in TRPC6 WT (n=11 cells), and by 13.9-fold and 14.7-fold respectively in the A404V variant (n=13 cells, p<0.05 vs. WT). In comparison, the OAG effects on TRPC6 WT and A404V channels were not potentiated by treatment with 0.5 μM doxorubicinol (DOXol, a metabolite of DOX) for 24 h (n=10-12 cells, p=N.S.). Molecular docking studies showed that OAG had a lower binding energy (-5.60 kcal/mol) and a smaller apparent equilibrium constant (Kd) of 0.079 mM with the A404V variant, compared to those of -4.49 kcal/mol and 0.511 mM respectively with TTRPC6 WT. Conclusion: TRPC6 A404V is a gain-of-function variant with a higher binding affinity to OAG. Treatment with DOX but not DOXol greatly enhances TRPC6 WT and A404V channel activation by OAG. Thus, cancer patients carrying the TRPC6 A404V variant may be more vulnerable to develop HF upon treatment with anthracycline.

Introduction Current evidence suggests that abnormal ventriculo-vascular coupling may contribute to the development of atrial fibrillation (AF) by increasing ventricular filling pressures and consequently, left atrial pressure. Recent investigations have also suggested that inflammation might have a role in the pathophysiology of AF. We hypothesize that autoimmune vasculitis plays a significant role in the pathogenetic mechanism of AF. Methods In this longitudinal cohort study, residents of Olmsted County, MN with first- time diagnosed AF during 1980-2000 and a reference age- and sex-matched control group from the same underlying population and time period were identified and followed until death, or 2000. The relationship between autoimmune vasculitis and first documented AF was analyzed. Results Of a total of 8766 patients (mean age 61.1+14.9 years; 56% women), 691 (7.9%) were diagnosed with autoimmune vasculitis during the 20 year period. The prevalence of autoimmune vasculitis in the AF group was 9.9% and 5.9% in the control group; p <0.001, respectively. After adjusting for CAD and LV dysfunction, the odds of autoimmune vasculitis in AF was 1.7 times higher than in controls (OR 1.69, 95%; CI 1.42 - 2.01, p < 0.0001). AF patients with autoimmune vasculitis had a worse survival compared to controls; p=.0114 (log-rank test). Conclusion Autoimmune vasculitis strongly increases the risk of atrial fibrillation and portends shorter survival in the AF population. These observations may represent one mechanism linking increased arterial stiffness and inflammation in the pathogenesis and prognosis of AF as an age-related disorder.

BACKGROUND: Shear stress-induced dilation (SSD) is an important vascular endothelial function that is impaired in diseases such as diabetes mellitus. Caveolin-1 is the major structural protein required for the formation of endothelial caveolae, where signaling molecules and pathways are assembled. In this study, we hypothesized that SSD of mouse small coronary arteries (MCA) is caveolae-dependent. METHODS: MCA (80-130 μm) freshly isolated from WT and Cav-1 knockout (KO) mice were mounted in a vessel chamber, pressurized at 80 mmHg, pre-contracted to 60-80% baseline diameter with endothelin-1, and subjected to physiological levels of shear stress at 25 dyn/cm 2 using a microinjection pump coupled to a pressure servo controller. SSD was measured by videomicroscopy and expressed as % of maximum diameter measured in the absence of Ca 2+ . Donor (intact WT or KO) and detector (WT with no endothelium) vessels were mounted in separate chambers connected by a micropipette. Diabetes mellitus was produced by streptozotocin (STZ) injection. RESULTS: SSD of MCA is significantly diminished in KO mice. 25 dyn/cm 2 produced 92.9±1.2% SSD in WT but only 42.0±0.7% in KO (n=10 for both, *p<0.05). Removal of endothelium reduced SSD to 22.3±3.3% in WT and to 14.9±1.3% in KO (n=8 for both, * vs. intact vessels but not WT vs. KO). Inhibition of eNOS (L-NAME), PGIS (Indocin), and CYP monooxygenase (SKF525A) reduced endothelial-dependent SSD by 44%, 34%, and 21% respectively in WT (all * vs control) but had no effect in KO, suggesting deficiency in shear stress-induced generation of vasodilators in KO. This is confirmed by the significant reduction in SSD in detector vessels with KO serving as donors (*42.0±0.7%, n=6 vs. 64.3±6.4% n=4, WT donor). With diabetes, MCA from WT and KO lost the ability for SSD (WT 25.9±2.4%, n=6 and KO 24.4±2.3%, n=5), which was similar to the effects of endothelium denudation. CONCLUSION: Integrity of caveolae is critical for endothelium-dependent SSD in MCA. KO endothelium is deficient in shear stress-mediated generation of vasodilators including NO, PGI 2 , and EET. Diabetic MCA have impaired endothelial function with loss of SSD. Caveolae plays a critical role in endothelial signal transduction from shear stress to vasodilator production and release.

Background: We have found that the vascular large conductance Ca 2+ -activated K + channels (BK) are targeted to caveolae. The goal of this study is to determine the role of caveolae in BK regulation by angiotensin II (AII) in normal and diabetic rats. Results: In coronary arterial smooth muscle cells (CASMC) from control rats, AII (2 μ M) inhibited BK by 40.5% from 227±26 pA/pF to 135±14 pA/pF (HP −60 mV, TP 150 mV, n=7, p<0.05). However, AII had no effects on BK in CASMC transfected with caveolin-1 siRNA (vs 50% inhibition in cells transfected with control siRNA) or in cells from Cav1−/− mice, suggesting the AII effects are caveolae-dependent. Density gradient analysis of rat vessel homogenates showed that caveolin-1, BK, Gq, cSrc, and NOX-1 all reside in the caveolae-rich fraction, where AT 1 R was absent unless the animal was pre-treated with AII, suggesting receptor translocation upon agonist activation. However, CASMC from streptozotocin-induced diabetic rats showed significant reduction in BK (61.5±10.6 pA/pF) with no response to AII (61.2±15.7 pA/pF, n=8). Vascular BK, caveolin-1, AT 1 R, cSrc, and NOX-1 expression in caveolae were all upregulated by 1.6- to 3.1-fold in diabetes. Density gradient analysis of diabetic vessels showed the presence of AT 1 R in the caveolae-rich fraction without AII pretreatment, suggesting that the AT 1 R signaling pathway might be constitutively active in diabetes. This was accompanied by a 2-fold increase in BK tyrosine phosphorylation and BK tyrosine nitration. The AII effects on BK function in diabetic CASMC were abolished by pretreatment (1 hr) with PKC inhibitor or by LavA (cSrc inhibitor) and can be mimicked by incubation (2 hr) of control CASMC with peroxynitrite. Conclusion: AT 1 R-BK-enzyme complex in the caveolae microdomain is critical in vascular BK regulation. Enhanced AII-signaling facilitates BK post-translational modification, resulting in BK dysfunction in diabetes.