P6276Impact of the cardiac specific deletion of AMPKalpha2 on the contractile and metabolic phenotype of the heart in male and female mice

Introduction

Mitochondrial dysfunction plays a major role in the Heart Failure (HF) pathophysiology.The AMP activated protein kinase (AMPK) is activated by a high AMP-ADP/ATP ratio and regulates a number of metabolic pathways. Many studies have highlighted a protective role of AMPK in HF, but its relevance to cardiac tissue, its metabolic part and its sex specificity are not well established.

Purpose

Then, the aim of this study is to determine the role of AMPK in the healthy and failing heart in male and female mice.

Methods

We developed and validated a mouse strain with an adult-inducible cardiac-specific deletion of AMPKα2, the major cardiac isoform, using the Cre-Lox system (40mg/kg tamoxifen injection on two consecutive days at adult age). At four months after the deletion, cardiac contractility, morphology and metabolism were studied in control and KO mice from both sexes.

Results

We observed only in male KO mice a decrease of left ventricular ejection fraction (−10%), an increase of the total fibrosis (+64%) and defects in mitochondrial structures. Male KO mice also showed a reduced (−28%) mitochondrial respiration via complex I associated with a different cardiolipin species distribution.

Conclusion

Our results reveal in adult healthy hearts, a sex-specificity in the effects of AMPKα2 deletion, leading to impaired contractile function related to metabolic and non-metabolic alterations only in male mice.

P3483Diet governs metabolic and electrical properties of the atrial myocardium in mice

Background

Obesity is associated with an increased risk of atrial fibrillation. This epidemiologic observation may not only be due to shared co-morbidities but also from direct impacts of metabolic disorders on myocardium Here, we examined the impact of high fat diet (HFD) induced obesity on atrial properties in mice.

Methods

Eight weeks old C57Bl/6J mice were subjected to 2 or 4 months of HFD (60% fat) or normal diet (ND, 4% fat). Rapid burst atrial pacing were delivered using a trans-esophageal probe to induced AF in anesthetized animals. Action potential (AP) were recorded in left atrial trabeculae using glass microelectrode technique. Potassium currents were recorded in isolated atrial myocytes using the whole cell or perforated patch clamp configurations. Metabolomic and lipidomic analysis were performed on whole left atria. Mitochondrial respiration was studied in situ in saponin-permeabilized atrial muscle fibres using a Clarke electrode and oxygen consumption was measured after successive addition of ADP (2 mM), malate (4 mM), palmitoyl-CoA and carnitine (pCoA-Ca) (100 μM and 2 mM), pyruvate (1 mM), glutamate (10 mM), succinate (15 mM), amytal (1 mM) and tetramethyl-paraphenylenediamine (TMPD)/ascorbate (0.5/0.5 mM).

Results

HFD mice showed a higher atrial vulnerability to AF as indicated by longer AF episodes compared to ND mice. APs were shorter in HFD versus ND mice (AP duration measured at 90% of repolarization: 47.9±2.4 msec in HFD vs 58.2±1.4 msec in ND, P<0.001 after 2 months of HFD) and more sensitive to the K ATP channel blocker, glibenclamide. In perforated but not whole cell, patch clamped atrial myocytes, the K-ATP component of the potassium current was enhanced in HFD mice (at +70 mV: 0.41±0.12 pA/pF in HFD vs 0.13±0.08 pA/pF in ND, P<0.05). Metabolomic analysis indicated an increased consumption of free fatty acid by the beta-oxidation and an accumulation of long chain fatty acid. Although the mitochondrial respiration measurements showed a trend towards a lower complex IV-driven respiration in HFD mice, no significant difference between ND and HFD was noted regarding complex I and complex II-driven respiration. However, the ability of fatty acids (pCoA-Car) to support mitochondrial respiration was higher in HFD

Conclusions

High fat diet induces a shift from carbon hydrate to a beta oxidation of the atrial myocardium metabolism together with an enhanced use of fatty acids by mitochondria. These metabolic changes could result in an enhanced activity of K-ATP channels and AP shortening that might contribute to AF vulnerability in this clinical setting.

Acknowledgement/Funding

ANR-10-IAHU-05

Right ventricular mitochondrial respiratory function in a piglet model of chronic pulmonary hypertension

OBJECTIVE

We aimed to assess the mitochondrial respiratory capacities in the right ventricle in the setting of ventricular remodeling induced by pressure overload.

METHODS

Chronic thromboembolic pulmonary hypertension was induced in 8 piglets over a 12-week period (chronic thromboembolic pulmonary hypertension model). Right ventricular remodeling, right ventricular function, and mitochondrial respiratory function were assessed at 3, 6, and 12 weeks after induction of pulmonary hypertension and were compared with sham animals (n = 5). Right ventricular cardiomyocytes and mitochondrial structure were studied in transmission electronic microscopy after 12 weeks.

RESULTS

As of 3 weeks, chronic pressure overload induced right ventricular dilatation, right ventricular hypertrophy, and right ventricular dysfunction. Maladaptive remodeling in the chronic thromboembolic pulmonary hypertension model was confirmed by the decrease of right ventricular pulmonary artery coupling and right fractional area change. Mitochondrial functional assays in permeabilized right ventricular myocardial fibers revealed that oxidative phosphorylation capacities (complex I, complex II, and IV of the mitochondrial respiratory chain) were degraded. Furthermore, no change in substrate preference of mitochondria was found in the overloaded right ventricle. There was a good correlation between maximal mitochondrial oxygen consumption rate and right ventricular pulmonary artery coupling (Pearson coefficient r = 0.83). Transmission electronic microscopy analysis showed that the composition of cardiomyocytes was no different between the chronic thromboembolic pulmonary hypertension group and the sham group. However, mitochondrial structure anomalies were significantly increased in the chronic thromboembolic pulmonary hypertension group.

CONCLUSIONS

Mitochondrial respiratory function impairment is involved early in the development of right ventricular dysfunction in a piglet model of chronic thromboembolic pulmonary hypertension. Underlying mechanisms remain to be elucidated.

Altered skeletal muscle mitochondrial biogenesis but improved endurance capacity in trained OPA1-deficient mice

The role of OPA1, a GTPase dynamin protein mainly involved in the fusion of inner mitochondrial membranes, has been studied in many cell types, but only a few studies have been conducted on adult differentiated tissues such as cardiac or skeletal muscle cells. Yet OPA1 is highly expressed in these cells, and could play different roles, especially in response to an environmental stress like exercise. Endurance exercise increases energy demand in skeletal muscle and repeated activity induces mitochondrial biogenesis and activation of fusion-fission cycles for the synthesis of new mitochondria. But currently no study has clearly shown a link between mitochondrial dynamics and biogenesis. Using a mouse model of haploinsufficiency for the Opa1 gene (Opa1(+/-)), we therefore studied the impact of OPA1 deficiency on the adaptation ability of fast skeletal muscles to endurance exercise training. Our results show that, surprisingly, Opa1(+/-) mice were able to perform the same physical activity as control mice. However, the adaptation strategies of both strains after training differed: while in control mice mitochondrial biogenesis was increased as expected, in Opa1(+/-) mice this process was blunted. Instead, training in Opa1(+/-) mice led to an increase in endurance capacity, and a specific adaptive response involving a metabolic remodelling towards enhanced fatty acid utilization. In conclusion, OPA1 appears necessary for the normal adaptive response and mitochondrial biogenesis of skeletal muscle to training. This work opens new perspectives on the role of mitochondrial dynamics in skeletal muscle cells and during adaptation to stress.