Heart failure with preserved ejection fraction (HFpEF) is associated with exercise intolerance due to alterations in the skeletal muscle (SKM). Leucine supplementation is known to alter the anabolic/catabolic balance and to improve mitochondrial function. Thus, we investigated the effect of leucine supplementation in both a primary and a secondary prevention approach on SKM function and factors modulating muscle function in an established HFpEF rat model. Female ZSF1 obese rats were randomized to an untreated, a primary prevention, and a secondary prevention group. For primary prevention, leucine supplementation was started before the onset of HFpEF (8 weeks of age) and for secondary prevention, leucine supplementation was started after the onset of HFpEF (20 weeks of age). SKM function was assessed at an age of 32 weeks, and SKM tissue was collected for the assessment of mitochondrial function and histological and molecular analyses. Leucine supplementation prevented the development of SKM dysfunction whereas it could not reverse it. In the primary prevention group, mitochondrial function improved and higher expressions of mitofilin, Mfn-2, Fis1, and miCK were evident in SKM. The expression of UCP3 was reduced whereas the mitochondrial content and markers for catabolism (MuRF1, MAFBx), muscle cross-sectional area, and SKM mass did not change. Our data show that leucine supplementation prevented the development of skeletal muscle dysfunction in a rat model of HFpEF, which may be mediated by improving mitochondrial function through modulating energy transfer.

Background: Heart failure with preserved ejection fraction (HFpEF) is associated with exercise intolerance, accompanied by alterations in the peripheral skeletal muscle (SKM). We have recently shown that titin, a giant sarcomere protein, is hyperphosphorylated in HFpEF. MuRF1 is a muscle‐specific ubiquitin E3‐ligase that interacts with titin. Blocking this interaction via small molecules (MyoMed205) can improve muscle function and mitochondrial activity in HFpEF. This study aimed to investigate the impact of MyoMed205 on titin phosphorylation and its association with changes in muscle structure and function.Methods: Obese ZSF1 rats with established HFpEF received rat chow with (n = 15) or without (n = 15) MyoMed205 and were compared with lean littermates (n = 15), serving as controls. After 12 weeks, in vitro SKM force, atrophy and titin—as well as contractile protein expression—were evaluated (soleus and extensor digitorum longus [EDL]). Statistical analysis was performed via multiple unpaired t‐test or one‐way ANOVA.Results: In HFpEF, titin hyperphosphorylation by 13% in the EDL (p = 0.09) and 14% (p = 0.03) in the soleus muscle was evident. This hyperphosphorylation was driven in part by an increase in S11878 phosphorylation (EDL: +68%, p = 0.004; Sol: +23.8%, p = 0.03), which was linked to myofiber atrophy (r = −0.68, p = 0.006) and a decline in maximal specific muscle force (r = −0.54, p = 0.008). In the EDL, significant changes in protein expression related to atrophy (MuRF1 [+24.9%, p = 0.02], GDF8 [+20.6%, p = 0.09]) and calcium handling (slow troponin C [−46%, p = 0.02], fast troponin I [+35.8%, p = 0.02]) were found in HFpEF. All of the above‐mentioned effects in HFpEF were almost completely abolished by MyoMed205 treatment, and significantly elevated titin expression was visible (+19.7%, p_con = 0.04, p_HFpEF = 0.01).Conclusions: Titin hyperphosphorylation may negatively impact skeletal muscle integrity and function in HFpEF. MyoMed205 reduced titin hyperphosphorylation and was associated with preserved skeletal muscle function and mass. Further studies are necessary to confirm the direct role of titin hyperphosphorylation on muscle function and to evaluate the therapeutic potential of MyoMed205 in HFpEF.

Mitochondrial dysfunction contributes to impaired myocardial energetics and performance in heart failure with preserved ejection fraction (HFpEF). Elamipretide (Ela) enhances mitochondrial bioenergetics in preclinical models, yet its relevance in HFpEF remains unclear. This study examined the effects of Ela on cardiac mitochondrial function, structure, and cardiovascular performance in a rodent HFpEF model. Female obese ZSF1 rats received vehicle or Ela for 12 weeks, with age-matched lean rats as controls. Cardiac function and hemodynamics were assessed by echocardiography and pressure–volume analysis. Mitochondrial respiration was measured in permeabilized fibers and ultrastructure evaluated by transmission electron microscopy. Molecular and histological analyses included cardiolipin lipidomics and mRNA/protein profiling of hypertrophic, fibrotic, and inflammatory markers. Ela modestly improved complex I and II respiration, whereas mitochondrial ultrastructure, cardiolipin composition, and tafazzin expression were unchanged. Diastolic dysfunction persisted, reflected by unchanged E/é, ventricular stiffness factor β, and titin phosphorylation. Compared to untreated HFpEF, systolic performance showed a mild decline, with small reductions in LV ejection fraction and end-systolic elastance. Accordingly, cardiac remodeling, including hypertrophy, fibrosis, and inflammatory activation, remained unaltered. Vascular stiffness slightly increased, while carotid reactivity and morphology were preserved. In conclusion, despite enhanced mitochondrial respiration following Ela treatment, no functional or structural benefits were observed in experimental HFpEF, suggesting limited therapeutic efficacy once HFpEF is established.

Heart failure with preserved ejection fraction (HFpEF) is characterized by biomechanically dysfunctional cardiomyocytes. Underlying cellular changes include perturbed myocardial titin expression and titin hypophosphorylation leading to titin filament stiffening. Beside these well-studied alterations at the cardiomyocyte level, exercise intolerance is another hallmark of HFpEF caused by molecular alterations in skeletal muscle (SKM). Currently, there is a lack of data regarding titin modulation in the SKM of HFpEF. Therefore, the aim of the present study was to analyze molecular alterations in limb SKM (tibialis anterior (TA)) and in the diaphragm (Dia), as a more central SKM, with a focus on titin, titin phosphorylation, and contraction-regulating proteins. This study was performed with muscle tissue, obtained from 32-week old female ZSF-1 rats, an established a HFpEF rat model. Our results showed a hyperphosphorylation of titin in limb SKM, based on enhanced phosphorylation at the PEVK region, which is known to lead to titin filament stiffening. This hyperphosphorylation could be reversed by high-intensity interval training (HIIT). Additionally, a negative correlation occurring between the phosphorylation state of titin and the muscle force in the limb SKM was evident. For the Dia, no alterations in the phosphorylation state of titin could be detected. Supported by data of previous studies, this suggests an exercise effect of the Dia in HFpEF. Regarding the expression of contraction regulating proteins, significant differences between Dia and limb SKM could be detected, supporting muscle atrophy and dysfunction in limb SKM, but not in the Dia. Altogether, these data suggest a correlation between titin stiffening and the appearance of exercise intolerance in HFpEF, as well as a differential regulation between different SKM groups.

Heart failure with preserved ejection fraction (HFpEF) shows diverse disease patterns, with various combinations of comorbidities and symptoms. A common hallmark is exercise intolerance, caused by alterations in the peripheral skeletal muscle (SKM) including a recently indicated titin hyperphosphorylation. Our aim is to compare a metabolic syndrome- (ZSF-1 rats) and a hypertension-driven (Dahl salt-sensitive (DSS) rats) HFpEF rat-model in relation to SKM function and titin phosphorylation. Obese ZSF-1 and high-salt fed DSS rats (HFpEF) were compared to lean ZSF-1 and low-salt fed rats (con). HFpEF was confirmed by echocardiography and invasive haemodynamic measurements. SKM atrophy, in vitro force measurements, titin- and contractile protein expression were evaluated. Obese ZSF-1 HFpEF rats showed muscle atrophy, reduced muscle force and increased titin phosphorylation compared to controls, which was not detected in hypertensive DSS rats. Fiber type specific troponins, myostatin and four and a half LIM domain 1 were differently regulated between the two models. Altogether, our results show that both animal models of HFpEF exhibit different SKM phenotypes, probably based on the divergent disease etiologies, which may help to define the most suitable animal model for HFpEF to test potential treatment regimens.

BACKGROUND: Exercise intolerance, promoted by skeletal muscle- and mitochondrial dysfunction, has been identified as a therapeutic target in heart failure with preserved ejection fraction (HFpEF). In the context of mitochondrial dysfunction, altered cardiolipin integrity has been reported in the myocardium of HFpEF, suggesting Elamipretide, a cardiolipin stabilizing agent, as potential therapeutic approach. The present study investigated cardiolipin dysregulation in the skeletal muscle of HFpEF rats and analyzed the effect of Elamipretide treatment. METHODS: Female zucker fatty spontaneously hypertensive heart failure F1 hybrid lean (n=10, control) and obese rats (n=24, HFpEF) were included. At 20 weeks of age, HFpEF rats were randomized into 2 groups receiving NaCl (n=12) or Elamipretide (n=12) for 12 weeks. Skeletal muscle tissue was collected for whole-muscle force, single-fiber mechanics, mitochondrial respiration, histology and molecular analyses. RESULTS: HFpEF rats exhibited reduced cardiolipin levels (−6.8%, P =0.007) and maturation (shown via tafazzin expression), contractile dysfunction, titin hyperphosphorylation, fiber atrophy and increased oxidative stress markers. Elamipretide improved whole muscle (soleus: +8.2%, P =0.041, extensor digitorum longus: +10.9%, P =0.016) and single-fiber (soleus: +173.2%, P <0.001, extensor digitorum longus: +66.0%, P =ns) contractile function and titin phosphorylation (soleus: −35.4%, P <0.001, extensor digitorum longus: −40.2%, P <0.001), while preventing atrophy development (soleus: +49%, P =0.001, extensor digitorum longus: +54.8%, P <0.001). Improved mitochondrial function, presumably through cardiolipin-mediated improvements in oxidative phosphorylation, could be associated with muscle force and cardiolipin integrity. CONCLUSIONS: Our data highlight cardiolipin stabilization as a key modulator of mitochondrial and contractile function in HFpEF, identifying Elamipretide as a promising therapeutic approach for skeletal muscle dysfunction.