Tetrahydrobiopterin improves diastolic dysfunction by reversing changes in myofilament properties

Abstract

Despite the increasing prevalence of heart failure with preserved left ventricular function, there are no specific treatments, partially because the mechanism of impaired relaxation is incompletely understood. Evidence indicates that cardiac relaxation may depend on nitric oxide (NO), generated by NO synthase (NOS) requiring the co-factor tetrahydrobiopterin (BH4). Recently, we reported that hypertension-induced diastolic dysfunction was accompanied by cardiac BH4 depletion, NOS uncoupling, a depression in myofilament cross-bridge kinetics, and S-glutathionylation of myosin binding protein C (MyBP-C). We hypothesized that the mechanism by which BH4 ameliorates diastolic dysfunction is by preventing glutathionylation of MyBP-C and thus reversing changes of myofilament properties that occur during diastolic dysfunction. We used the deoxycorticosterone acetate (DOCA)-salt mouse model, which demonstrates mild hypertension, myocardial oxidative stress, and diastolic dysfunction. Mice were divided into two groups that received control diet and two groups that received BH4 supplement for 7 days after developing diastolic dysfunction at post-operative day 11. Mice were assessed by echocardiography. Left ventricular papillary detergent-extracted fiber bundles were isolated for simultaneous determination of force and ATPase activity. Sarcomeric protein glutathionylation was assessed by immunoblotting. DOCA-salt mice exhibited diastolic dysfunction that was reversed after BH4 treatment. Diastolic sarcomere length (DOCA-salt 1.70±0.01 vs. DOCA-salt+BH4 1.77±0.01 μm, P<0.001) and relengthening (relaxation constant, τ, DOCA-salt 0.28±0.02 vs. DOCA-salt+BH4 0.08±0.01, P<0.001) were also restored to control by BH4 treatment. pCa50 for tension increased in DOCA-salt compared to sham but reverted to sham levels after BH4 treatment. Maximum ATPase rate and tension cost (ΔATPase/ΔTension) decreased in DOCA-salt compared to sham, but increased after BH4 treatment. Cardiac MyBP-C glutathionylation increased in DOCA-salt compared to sham, but decreased with BH4 treatment. MyBP-C glutathionylation correlated with the presence of diastolic dysfunction. Our results suggest that by depressing S-glutathionylation of MyBP-C, BH4 ameliorates diastolic dysfunction by reversing a decrease in cross-bridge turnover kinetics. These data provide evidence for modulation of cardiac relaxation by post-translational modification of myofilament proteins.

Mitochondrial Ca 2+ Influx Contributes to Arrhythmic Risk in Nonischemic Cardiomyopathy

“…Consistent with previous reports in other models of cardiomyopathy, these DOCA‐treated nonischemic HF mice showed reduced ejection fraction and reduced systolic cytoplasmic Ca 2+ transients 14, 15, 42, 43, 44. Similar to other myopathic models, these nonischemic HF mice showed electrical remodeling with prolonged QTc intervals and APDs 1.…”

Histone deacetylase activity governs diastolic dysfunction through a nongenomic mechanism

“…Although we observed a modest increase in TnI phosphorylation in hearts of DSS rats fed HS and treated with ITF2357, calcium sensitivity was unchanged in HS-fed and HS-fed ITF2357-treated DSS rats, indicating a divergent mechanism of thin filament regulation upon HDAC inhibition. Increased myofibril calcium sensitivity due to glutathionylation of MyBP-C has also been previously linked to diastolic dysfunction (35). However, the lack of a change in calcium sensitivity upon ITF2357 treatment suggests that the ability of the HDAC inhibitor to improve relaxation of the heart is independent of effects on glutathionylation of MyBP-C.…”

A change of heart: oxidative stress in governing muscle function?

“…In addition to these effects, NO signalling also has anti-fibrotic, anti-hypertrophic, and anti-adrenergic actions that oppose adverse cardiac remodelling and thus serve as potential therapeutic strategies for HFpEF. Furthermore, BH4 and eNO synthase activators could be useful in reducing diastolic dysfunction, since the DOCA-salt mouse model is associated with BH4 depletion and uncoupled NO synthase activity, and BH4 administration consistently reduced DOCA-salt-associated MyBP-C glutathionylation and diastolic dysfunction (Lovelock et al 2012;Jeong et al 2013;Patel et al 2013). A successful therapeutic strategy for HFpEF must focus on selecting more consistent patient populations to control for the impact of comorbidities.…”

“…These mice exhibited high oxidative stress associated with myocytes and diastolic abnormalities, but no changes in cellular Ca 2+ -fluxes were seen (Lovelock et al 2012). Depression of S-glutathionylation in cMyBP-C ameliorates diastolic dysfunction as it reverts in the slow cross-bridge turnover kinetics (Jeong et al 2013), indicative of a strong correlation between S-glutathionylation and diastolic dysfunction. The S-glutathionylation of cMyBP-C has been implicated in increased myofilament Ca 2+ -sensitivity, thus suggesting the involvement of S-glutathionylation of cMyBP-C in the maintenance of longitudinal rigidity and cross-bridge kinetics .…”

“…, and Cys 655 of the C3, C4, and C5 domains of MyBP-C in a desoxycorticosterone acetate (DOCA)-salt hypertensive mouse model (Lovelock et al 2012;Jeong et al 2013;Patel et al 2013). These mice exhibited high oxidative stress associated with myocytes and diastolic abnormalities, but no changes in cellular Ca 2+ -fluxes were seen (Lovelock et al 2012).…”