Reciprocal regulation between M3 muscarinic acetylcholine receptor and protein kinase C-epsilon in ventricular myocytes during myocardial ischemia in rats

Choline Attenuates Cardiac Fibrosis by Inhibiting p38MAPK Signaling Possibly by Acting on M3 Muscarinic Acetylcholine Receptor

Choline has been reported to produce a variety of cellular functions including cardioprotection via activating M₃ muscarinic acetylcholine receptor (M₃R) under various insults. However, whether choline offers similar beneficial effects via the same mechanism in cardiac fibrosis remained unexplored. The present study aimed to investigate the effects of choline on cardiac fibrosis and the underlying signaling mechanisms, particularly the possible involvement of M₃R. Transverse aortic constriction (TAC) mouse model was established to simulate the cardiac fibrosis. Transforming growth factor (TGF)-β1 treatment was employed to induce proliferation of cardiac fibroblasts in vitro. Choline chloride and M₃R antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) were used to unravel the potential role of M₃R. Cardiac function was assessed by echocardiography and interstitial fibrosis was quantified by Masson staining. Protein levels of collagens I and III were determined by Western blot analysis. The role of M₃R in the proliferation cardiac fibroblasts was validated by silencing M₃R with specific small interference RNA (siRNA). Furthermore, the mitogen-activated protein kinase (MAPK) signaling pathway including p38MAPK and ERK1/2 as well as the TGF-β1/Smad pathway were analyzed. M₃R protein was found abundantly in cardiac fibroblasts. M₃R protein level, as identified by Western blotting, was higher in mice with excessive cardiac fibrosis and in TGF-β1-induced cardiac fibrosis as well. Choline significantly inhibited interstitial fibrosis, and this beneficial action was reversed by 4-DAMP. Production of collagens I and III was reduced after choline treatment but restored by 4-DAMP. Expression silence of endogenous M₃R using siRNA increased the level of collagen I. Furthermore, the TGF-β1/Smad2/3 and the p38MAPK pathways were both suppressed by choline. In summary, choline produced an anti-fibrotic effect both in vivo and in vitro by regulating the TGF-β1/Smad2/3 and p38MAPK pathways. These findings unraveled a novel pharmacological property of choline linked to M₃R, suggesting that choline regulates cardiac fibrosis and the associated heart diseases possibly by acting on M₃R.

Age-related peculiarities of inotropic response of rat myocardium to selective block of M1-cholinoreceptors

In vitro effect of M1-cholinoreceptor blockade on the cardiac inotropic function was examined in rats aging 1, 3, 6, 8, and 20 weeks. In 1- and 3-week old rat pups, the sympathetic control of the heart has not developed, the age of 7-8 weeks being pubertal. Adult 20-week rats were used as the controls. In rats of all age groups, preliminary blockade of M1-cholinoreceptors did not prevent the inhibitory effect of carbacholine on contractility of the atrial and ventricular myocardium. The inhibitory effect of pirenzepine on the contractile force of ventricular myocardium was revealed in 6-week rats.

Choline protects against cardiac hypertrophy induced by increased after-load

BACKGROUND

Although inadequate intake of essential nutrient choline has been known to significantly increase cardiovascular risk, whether additional supplement of choline offering a protection against cardiac hypertrophy remain unstudied.

METHODS

The effects of choline supplements on pathological cardiac hypertrophic growth induced by transverse aorta constriction (TAC) for three weeks and cardiomyocyte hypertrophy in cultured cells induced by isoproterenol (ISO) 10 μM for 48 h stimulation were investigated. Western blot analysis and real-time PCR were used to determine the expression of ANP, BNP, β-MHC, miR-133a and Calcineurin.

RESULTS

Administration of 14 mg/kg choline to mice undergone TAC effectively attenuated the cardiac hypertrophic responses, as indicated by the reduced heart weight, left ventricular weight, ventricular thickness, and reduced expression of biomarker genes of cardiac hypertrophy. This anti-hypertrophic efficacy was reproduced in a cellular model of cardiomyocyte hypertrophy induced by isoproterenol in cultured neonatal cardiomyocytes. Our results further showed that choline rescued the aberrant downregulation of the muscle-specific microRNA miR-133a expression, a recently identified anti-hypertrophic factor, and restored the elevated calcineurin protein level, the key signaling molecule for the development of cardiac hypertrophy. These effects of choline were abolished by the M3 mAChR-specific antagonist 4-DAMP.

CONCLUSION

Our study unraveled for the first time the cardioprotection of choline against cardiac hypertrophy, with correction of expression of miR-133a and calcineurin as a possible mechanism. Our findings suggest that choline supplement may be considered for adjunct anti-hypertrophy therapy.