Caloric Restriction Rejuvenates Skeletal Muscle Growth in Heart Failure With Preserved Ejection Fraction

Visual Abstract

HFpEF is characterized by a distinct, but poorly understood, skeletal muscle pathology, which could offer an alternative therapeutic target.In a rat model, we identified impaired myonuclear accretion as a mechanism for low myofiber growth in HFpEF following resistance exercise.Acute caloric restriction rescued skeletal muscle pathology in HFpEF, whereas cardiac therapies had no effect.Mechanisms regulating myonuclear accretion were dysregulated in patients with HFpEF.Overall, these findings may have widespread implications in Skeletal muscle health has widespread clinical consequences in heart failure, impacting functional, 3 metabolic, 5 and mental health 6 status.
Although poor skeletal muscle health in HFpEF is closely associated with symptoms, quality of life, and mortality, 7 the underlying mechanisms remain poorly defined.Morphological changes include reduced capillarity, 8 increased fat infiltration, 9 a fiber-type transition (Type I to Type II), 8 and mitochondrial abnormalities that increase reliance on fatigue-related anaerobic metabolism. 10,11In particular, reduced skeletal muscle mass (pathological atrophy) is a serious clinical complication in HFpEF, causing frailty and poor prognosis. 12cause HFpEF is incurable, preserving skeletal muscle health is critical for patients to maintain an acceptable quality of life. 3One way to achieve this is by increasing muscle mass or myofiber growth (physiological hypertrophy), which is determined by 2 nonexclusive mechanisms: 1) elevated protein synthesis via Akt-mTOR signaling; and/or 2) addition of new myonuclei via muscle stem cell (MuSC) recruitment. 13It currently remains unclear why patients with HFpEF have decreased muscle mass, but studies in both patients and animal models have focused on mechanisms related to myofiber atrophy [14][15][16][17][18] rather than myofiber growth.
At present, there are few treatments for the skeletal muscle pathology in HFpEF.Whereas many pharmacological treatments targeting the cardiovascular system have been clinically neutral, 2 it remains unclear whether they provide secondary benefits to skeletal muscle health.Apart from exercise training, 19

Mechanisms of Skeletal Muscle Pathology in HFpEF
pathology in HFpEF and improve quality of life, 5,20 CR improves lifespan as well as homeostasis in multiple cells and tissues, 21 including myofibers 22 and MuSCs, 23 however the mechanistic effects of CR on skeletal muscle health in HFpEF remain untested.
Overall, the inability to stimulate skeletal muscle growth in HFpEF has severe clinical consequences. 125][26][27][28][29][30] Our integrative, multiorgan approach identified decreased overload-induced myofiber growth that was rejuve- recent studies now indicate that around 45% are male. 31Based upon this, and on evidence that muscle mass and growth can be influenced by female sex hormones (eg, estrogen) that are generally very low in elderly females such as those with HFpEF, 32 this study selected to use male rats to reduce confounding variables.5][26][27][28][29][30] We 16,25,33 and others 18 identified skeletal muscle atrophy as a major pathological feature in obese ZSF1 rats that develop HFpEF.
After confirming the clinical HFpEF phenotype of this model in comparison to age-matched lean control rats (Supplemental Figure 1), we tested whether improving cardiac function could rescue skeletal muscle pathology in HFpEF.
Clinically approved sacubitril/valsartan (Sac/Val) is a neprilysin inhibitor and angiotensin II Type I (AT 1 ) receptor blocker that improves cardiac function and remodeling in HFpEF animal models and showed potential benefits in patients. 34,35To date, no study has comprehensively addressed the effects of this drug on myofiber pathology in HFpEF. 29Therefore, we evaluated the effects of Sac/Val on the cardiac and skeletal muscle phenotype of obese male ZSF1 HFpEF rats (Figure 1A).Ten weeks of treatment with Sac/Val improved cardiac structure and function in rats with HFpEF, which included reduced ventricular hypertrophy (Figure 1B), improved diastolic function as seen by the normalization of the diastolic mitral inflow E wave to A wave ratio (E/A) using echocardiography (Figure 1C).1O).This approach found fiber atrophy in HFpEF compared with control rats independent of Sac/Val treatment (Figure 1P), which was independent of isoform shifts (Figure 1Q) and associated with overt global and local capillary rarefaction Espino-Gonzalez et al   13 Here, we subjected control and HFpEF male rats to mechanical overload via synergist ablation by surgically removing the tibialis anterior from the right leg, and then evaluated the overload-induced EDL growth after 14 days (Figure 2A).EDL-specific overload provides a more physiologically relevant response compared with optional plantaris overload. 40 decreased muscle blood flow and capillarity, 8,33 which are important for overload-induced myofiber growth. 41We tested whether overload-induced myofiber growth is associated with changes in muscle capillarity in both healthy and HFpEF rats.We evaluated the muscle capillary network in EDL cryosections and then modelled these data to simulate muscle oxygen transport kinetics during resting and maximal metabolic rates. 42After overload, global capillary-to-fiber ratio increased in both control and  Espino-Gonzalez et al  4f).Furthermore, our in silico simulations identified that overload did not cause significant changes to muscle PO 2 at rest (Supplemental Figures 4g and 4h) or at maximal metabolic rates in both groups (Figures 2I and 2J).

Mechanisms of Skeletal Muscle Pathology in HFpEF
Muscle blood flow is physiologically dynamic, and this can affect muscle mass and function. 43,44To assess this, we used a unique in situ bilateral limb and normalities that closely correlate with symptom severity. 10,11Disturbed mitochondrial homeostasis directly impacts myofiber size, 45 but this relationship has not been explored in HFpEF.Protein synthesis is a highly energetic process, meaning impairments in mitochondrial ATP production could lower cellular energetic state to limit protein synthesis and blunt myofiber hypertrophy. 46We determined whether changes in overload-induced hypertrophy are accompanied by alterations in mitochondrial function.In situ mitochondrial high-resolution respirometry experiments in permeabilized EDL fibers showed that, after overload, complex I-dependent respiration increased in control rats relative to the nonoverload leg but was unchanged in HFpEF rats (Figure 2M).We next examined citrate synthase activity in each group as a marker of mitochondrial content but found no effect (Supplemental Figure 5a), identifying mitochondrial function rather than content increased after mechanical overload in control rats, but not HFpEF.This suggestion was further strengthened when we determined the mitochondrial coupling efficiency in the EDL, which increased by 51% in control rats after overload, but no effect was seen in HFpEF (Figure 2N).These data support that mitochondrial functional properties could limit load-induced myofiber growth in HFpEF.
To further explore a molecular mechanism regulating myofiber size related to mitochondrial efficiency and function, 45   For example, CR in young and old age improves skeletal muscle homeostasis, 22,23 whereas lifelong CR increases load-induced myofiber growth in aged rats via restored Akt-mTORC1 signaling. 48Based on evidence from clinical 5 and rodent 5 experiments, we reasoned combining mechanical overload with CR in HFpEF could rejuvenate myofiber growth.
To test this hypothesis, we subjected male HFpEF rats to acute CR over 4 weeks 49 starting with a stepwise reduction in calories by 10% and 25% in weeks 1 and 2, followed by 40% in the final 2 weeks in combination with mechanical overload to stimulate EDL myofiber growth (Figure 3A).Body mass was not changed, but hyperglycemia was reduced, whereas histological analysis of cardiac cryosections to assess structural remodeling showed that ventricular hypertrophy tended to be lower in HFpEF rats after CR (Supplemental Figure 6).Consistent with our initial experiments (Figure 2), analysis of EDL cryosections (Figure 3B) confirmed myofiber growth following overload was absent in HFpEF (Figures 3B and 3C).
Remarkably, however, treatment with CR restored the hypertrophic response in HFpEF toward control rats, with a 35% increase in myofiber size observed (Figure 3C).In particular, myofiber growth in control rats and HFpEFþCR treatment was generally prevalent across all fiber types in response to overload,  13 To assess protein synthesis, we injected rats before sacrifice with puromycin, a structural analog of tyrosyl-tRNA that incorporates into nascent polypeptides. 50We then assessed global rates of protein synthesis by Western blotting using specific antibody against puromycin in EDL homogenates.We found no change in puromycin expression between groups when assessing relative changes between nonoverload vs overload muscle (Figure 3I, Supplemental Figure 9a).Decreased Akt-mTORC1 signaling is linked to reduced mechanical overload-induced myofiber hypertrophy in aging rats but restored by lifelong CR. 48We therefore probed phosphorylation of downstream mTORC1 targets S6 and 4E-BP1, but again found no difference between control, HFpEF, and HFpEFþCR rats in the nonoverload or overload conditions (Figure 3I, Supplemental Espino-Gonzalez et al

Mechanisms of Skeletal Muscle Pathology in HFpEF
between groups despite a trend for the response to be lower after overload in HFpEF (Figure 3J).Because changes in anabolic signaling can be transient, occurring over minutes to hours, 51 we subjected the soleus muscle from healthy, HFpEF, and HFpEFþCR rats to repeated isometric contractions in vitro.After the protocol, we immediately froze tissue for Western blot analysis in order to measure acute expression of anabolic signaling proteins.However, we found no major differences between groups in terms of phosphorylated and total S6, 4E-BP1, and AMPK protein expression (Figure 3K, Supplemental Figures 9l to 9t).
Myofiber size is determined, not only by the rates of protein synthesis, but also by the relative rate of protein degradation. 52We therefore explored whether low myofiber growth in HFpEF was due to elevated catabolic signaling and increased atrogene expression.Activation of the energetic stress sensor AMPK is an upstream trigger that increases fiber atrophy in a FOXO-dependent manner, 52 and has been linked to impaired load-induced myofiber growth. 53 found no differences between groups in phosphorylated AMPK following mechanical load challenge (Figure 3I, Supplemental Figures 9h to 9j).In line with this, no change was found in the expression of key ubiquitin proteasome-dependent atrogenes MuRF1 and MAFBx (Figures 3L and 3M), in the myostatin-TGFb signaling pathway (Figure 3N) or autophagy-dependent p62 (Figure 3I, Supplemental Figure 9k), with all tending to be lower across groups after mechanical overload.Taken together, these data do not support inhibition of protein synthesis via Akt-mTORC1 signaling as a primary mechanism for decreased load-induced myofiber growth in HFpEF.4D).AMPK is known to decrease mTORC1 activation and overload-induced myofiber hypertrophy, 53 but, based upon our earlier observation of limited changes to protein synthesis and AMPK expression (Figure 3I), we focused our attention on the other pathways identified.

LOW MYONUCLEAR ACCRETION AS
Our pathway analysis suggested decreased overload-induced myofiber growth in HFpEF could be associated with changes in MuSC homeostasis, given that Hedgehog (Hh) signaling is critical for myogenesis 54 and linked to overload-induced myofiber growth, 55 and apelin is a peptide myokine linked to sarcopenia that regulates MuSC function. 56We validated these targets and other relevant myogenic genes using quantitative polymerase chain reaction.
For Hh signaling, we probed the expression of its receptor, patched (Ptch), and transcription factor, Gli2.
Whereas Ptch was not different between groups, expression of Gli2 was lower in HFpEF compared to controls rats (Figures 4E and 4F).We also measured both apelin and its receptor but found no differences between groups (Figures 4G and 4H).Myofiber growth depends on the activation, proliferation, differentiation, and fusion of MuSCs. 57Therefore, we measured gene expression of myogenic transcription factors with HFpEF (Figure 4M).This indicates potential disruptions in MuSC-dependent myonuclear fusion could be present in HFpEF. 58e addition of new myonuclei via MuSCs is required for effective overload-induced myofiber growth. 40,58,59We therefore hypothesized addition of new myonuclei could be a limiting mechanism for load-induced myofiber growth in HFpEF, but can be overcome after acute CR given the known benefits on MuSC homeostasis. 23To test this and provide an index of myonuclear accretion, we quantified nuclei number per myofiber in EDL from overload and nonoverload cryosections in control, HFpEF, and HFpEFþCR rats (Figure 4N).Whereas myonuclear accretion showed a robust increase after overload in healthy control rats by 90%, this effect was blunted in HFpEF and rescued in HFpEF rats treated with CR (Figure 4O).1). 14,15,18We measured basal myogenic expression in the vastus lateralis of patients with HFpEF compared with age-matched control subjects, and performed comparative measures in the EDL of our rat model using immunoblotting (Supplemental Table 2) and qPCR (Supplemental Table 3).Notably, rats with HFpEF showed lower basal expression in the key myogenic transcription factors Pax7 and MyoD by w50%, as well as the fusogen protein myomaker, when compared with control subjects (Figure 5A).We further measured established regulators of MuSC homeostasis including apelin 56 and piezo1, 61 but found only Hh signaling and IGF1 were significantly reduced in HFpEF vs control subjects (Figure 5A).
Based on these findings, in our human samples, we focused on measuring basal expression of the myogenic transcription factors Pax7 and MyoD.
Relative to healthy control subjects, we found protein HFpEF n ¼ 4, HFpEFþCR n ¼ 3).REACTOME pathway analysis showed clear differences in down-regulated pathways (especially the proportion of terms related to cell cycle regulation relative to the total number) between (P) CON (n ¼ 4) vs (Q) HFpEF (n ¼ 4), but not CON vs (R) HFpEFþCR (n ¼ 4).The adjusted P value was corrected using the Benjamini and Hochberg method.Differences were assessed by 2-way analysis of variance followed by Bonferroni post hoc test.Data are presented as mean AE SD, and the level of significance was accepted as *P < 0.05; **P < 0.01; and ***P < 0.001 for all analyses.Abbreviations as in Figure 1.
Espino-Gonzalez et al Mechanisms of Skeletal Muscle Pathology in HFpEF expression of Pax7 was lower by w50% in patients with HFpEF, whereas myogenin was higher by 2-fold (Figure 5B).These data support that patients with HFpEF may have disturbances in basal MuSC homeostasis that could limit myofiber growth when subjected to physical loads.

DISCUSSION
HFpEF is no longer considered a simple syndrome of cardiac dysfunction, but rather a systemic disease that includes several extracardiac pathologies including skeletal muscle dysfunction. 2,4The skeletal   Espino-Gonzalez et al Mechanisms of Skeletal Muscle Pathology in HFpEF muscle pathology is associated with worse symptoms and quality of life in HFpEF, 3 however, we still have a poor understanding of the mechanisms and treatments.In this study, using a clinically relevant rat model characterized by cardiac dysfunction and exercise intolerance with multiple comorbidities including obesity, hypertension, and diabetes, [24][25][26][27][28][29][30] we demonstrated a fundamental limitation for myofibers to hypertrophy in HFpEF when subjected to a resistance exercise intervention.We identified low myonuclear accretion as a mechanism for the decreased overload-induced myofiber growth in HFpEF, which was underpinned by changes in the transcriptional phenotype of myogenic homeostasis.
These effects were reflected in skeletal muscle of patients with HFpEF.We established that skeletal muscle homeostasis could be rescued by acute dietary CR, which increased myonuclear accretion in line with myofiber growth.Furthermore, we highlighted that upstream limitations in muscle blood flow and capillarity are unlikely to impair overload-induced myofiber growth in HFpEF, although a role for mitochondrial dysfunction cannot be excluded.We also confirmed that treating HFpEF with pharmacological drugs to increase cardiac function did not rescue the skeletal muscle pathology.
HFpEF is associated with a multiple skeletal muscle abnormalities, including loss of muscle mass and strength, which are closely related to poor quality of life. 3,7One common approach is to use cardiactargeted pharmacological therapeutics to increase cardiac function, with the expectation this will improve skeletal muscle perfusion and, subsequently, skeletal muscle pathology in heart failure.
However consistent with past evidence, 62,63 our findings suggest that cardiocentric medications have limited impact on skeletal muscle remodeling in HFpEF.These data are consistent with the majority of trials using pharmacological treatments in patients with HFpEF, which have shown neutral effects in terms of quality of life and clinical outcomes, 2 excluding recent breakthrough using SGLT2 inhibitors. 64Together, this indicates that medications by the balance between myofiber anabolic and catabolic signaling. 52In studies on rats and humans with HFpEF, a general trend for increased catabolic signaling via ubiquitin proteasome-dependent activity has been reported. 14,15,18To date, however, the regulation of myofiber growth in HFpEF and associated anabolic signaling remained poorly defined.
Strikingly, we identified that load-induced myofiber growth was severely attenuated in HFpEF compared with healthy control subjects.However, acute CR restored myofiber growth in HFpEF following mechanical loading.Myofiber growth is regulated via elevated protein synthesis and/or addition of new myonuclei via MuSCs. 13Evidence regarding skeletal muscle anabolic signaling/protein synthesis in HFpEF is absent, although in heart failure with reduced ejection fraction, some, but limited, data indicate protein synthesis is lower. 65Our findings do not support a role for impaired protein synthesis as a mechanism for decreased load-induced myofiber growth in HFpEF.This is in contrast to studies in aging and other conditions, which demonstrated that myofiber growth during mechanical load is reduced and limited by protein synthesis in an mTORC1-dependent manner, 66,67 yet overcome by lifelong CR. 48erload-induced myofiber growth can also be limited by myonuclear accretion. 68The addition of new myonuclei is governed by MuSCs, which reside in the basal membrane and are required to activate, proliferate, differentiate, and fuse into the myofiber in order to aid effective growth (with a proportion also returning to quiescence to maintain the MuSC pool). 57Evidence strongly supports that MuSCdependent myonuclei accretion, including effective fusion via myomaker, is required for myofiber growth during increased physical loads. 40,58,59Our finding Effective myofiber growth also requires the integration of important upstream mechanisms, which include normal vascular and mitochondrial function.
These mechanisms are impaired in both patients and animal models of HFpEF, 8,10,11,33 16,18,[24][25][26][27][28][29][30] The present study included mostly female patients, and therefore, our findings may not fully translate to males with HFpEF, although current evidence indicates no apparent sex-specific skeletal muscle differences. 10,73It should be appreciated that our findings in patients came from a leg muscle (vastus lateralis) that may not translate to other muscles in the body.However, because muscle alterations in heart failure patients from the lower limb have been closely correlated to changes in the upper limb, 74 it is likely our findings are important for other muscle groups.Further research will be required to confirm this suggestion.An inherent limitation for interpreting bulk skeletal muscle analysis is that fiber-type-specific changes cannot be discerned, which may have masked myofiber-specific changes in molecular signaling being detected. 75We also assessed a single time point after mechanical overload, therefore, further complexity in protein synthesis and/or myonuclear accretion may be present over a temporal range.However, we did assess the acute response immediately following muscle contraction and found no evidence to contradict our conclusions.
This study focused on the acute effects of CR.A limitation of this study was that cardiac function was

FUNDING SUPPORT AND AUTHOR DISCLOSURES
pathology, which is emerging as an alternative therapeutic target.Using a rat model, we first demonstrated that clinical drugs improving cardiac function did not rescue skeletal muscle pathology.Surprisingly, using a local exercise intervention, we next identified a previously unknown mechanistic deficit in HFpEF that showed failure to increase muscle growth.We then discovered that acute dietary caloric restriction restored muscle growth in HFpEF in combination with exercise intervention, which mechanistically could be explained via increasing myonuclear accretion and restoring myogenic homeostasis.Given we found similar mechanisms dysregulated in muscle tissue from patients with HFpEF, our findings indicate combining dietary restriction with exercise could be an optimal approach to rescue skeletal muscle pathology in HFpEF that should be further investigated.ISSN 2452-302X https://doi.org/10.1016/j.jacbts.2023.09.014SUMMARY Heart failure with preserved ejection fraction (HFpEF) is a major clinical problem, with limited treatments.
HFpEF, indicating combined dietary with exercise interventions as a beneficial approach to overcome skeletal muscle pathology.(J Am Coll Cardiol Basic Trans Science 2024;9:223-240) © 2024 The Authors.Published by Elsevier on behalf of the American College of Cardiology Foundation.This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).H eart failure is an incurable disease for mil- lions of people worldwide, one-half of whom die within 5 years of diagnosis, and rates continue to rise. 1 Heart failure characterized by preserved ejection fraction (HFpEF) is rapidly becoming more frequent than classic heart failure with reduced ejection fraction and represents one of the biggest challenges in modern cardiology. 1,2HFpEF is a complex, systemic syndrome characterized by both cardiac and extracardiac pathologies. 3,4Extracardiac organ dysfunction in HFpEF is central to disease progression, with skeletal muscle considered a key emerging therapeutic target. 3Whereas many established cardiocentric pharmacological treatments do not improve quality of life or clinical outcomes in HFpEF, 2 treating the skeletal muscle pathology could provide an alternative strategy. 3 dietary interventions such as caloric restriction (CR) may offer an effective nonpharmacological approach to attenuate muscle A B B R E V I A T I O N S A N D A C R O N Y M S CR = caloric restriction EDL = extensor digitorum longus HFpEF = heart failure with preserved ejection fraction MuSC = muscle stem cell Sac/Val = sacubitril/valsartan From the a School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom; b Department of Anatomy & Embryology, Faculty of Health, Medicine and Life Sciences, Maastricht University, Maastricht, the Netherlands; c Department of Pathology, School of Medicine, University of Mississippi Medical Center, Jackson, Mississippi, USA; d Leeds Institute of Cardiovascular and Metabolic Medicine, Faculty of Medicine, University of Leeds, Leeds, United Kingdom; e Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway; f Department of Pharmacology and Toxicology, School of Medicine, University of Mississippi Medical Center, Jackson, Mississippi, USA; and the g Heart Center Dresden, TU-Dresden, Dresden, Germany.The authors attest they are in compliance with human studies committees and animal welfare regulations of the authors' institutions and Food and Drug Administration guidelines, including patient consent where appropriate.For more information, visit the Author Center.Manuscript received July 7, 2023; revised manuscript received September 22, 2023, accepted September 25, 2023.
nated following acute CR as a fundamental feature and potential treatment of skeletal muscle pathology in HFpEF.The mechanism for absent myofiber growth in HFpEF was linked to low myonuclear accretion associated with disturbances in MuSC homeostasis.We further provide evidence that these mechanisms are present in the skeletal muscle of patients with HFpEF.Taken together, our experiments suggest that acute dietary restriction is capable of rejuvenating skeletal muscle health in HFpEF.METHODS All protocols and experimental details are outlined in full detail within the Supplemental Appendix.All experiments in animals and humans were ethically approved, and all human participants provided written informed consent.Although past studies indicate that the majority of patients with HFpEF are female, 1

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FIGURE 1
FIGURE 1 Sac/Val Improves Cardiac Function in HFpEF, But Does Not Attenuate Skeletal Muscle Pathology

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FIGURE 2
FIGURE 2 Skeletal Muscle Growth Following Mechanical Overload Is Absent in HFpEF Figures 4i to 4l).Whereas control and HFpEF ratsshowed no difference in absolute resting leg blood flow after overload (Figure2K), the functional hyperemia (ie, increase in blood flow relative to muscle mass) in response to stimulated contractions was lower in control rats by 44% but unchanged in HFpEF rats after overload (Figure2L).Collectively, these data show that muscle capillarity and blood flow respond adequately to the overload stimuli in HFpEF, and indicate other mechanisms are likely responsible for low myofiber growth.IMPAIRED MITOCHONDRIAL ADAPTATION ACCOMPANIES DECREASED MYOFIBER GROWTH IN HFpEF.HFpEF is characterized by skeletal muscle mitochondrial ab-

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Figure 5k to 5l).Taken together, these data suggest that decreased load-induced myofiber growth in HFpEF may be limited, at least in part, by mitochondrial dysfunction.CALORIC RESTRICTION REJUVENATES LOAD-INDUCED MYOFIBER GROWTH IN HFpEF.Although our data highlight a novel mechanistic deficit in HFpEF related to anabolic resistance, the fundamental mechanisms that impairs myofiber growth and an intervention that rescues myofiber growth in HFpEF are not established.Preliminary evidence from patients indicates that CR could improve skeletal muscle health, especially when combined with exercise training. 5,20

FiguresFIGURE
Figures 9b to 9g).We also measured gene expression of IGF1, given it is a key upstream regulator of Akt-mTORC1 signaling, but this was not different

FIGURE 5
FIGURE 5 Basal Myogenic Expression Is Dysregulated in Rats and Patients With HFpEF .

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A C C : B A S I C T O T R A N S L A T I O N A L SCIENCE VOL. 9, NO. 2, 2024 typically used to improve cardiac function and clinical outcomes in patients with HFpEF do not treat the skeletal muscle pathology.As such, identifying alternative nonpharmacological therapies for HFpEF skeletal muscle pathology remains an urgent priority.One of the few effective treatments for HFpEF is exercise training, which improves physical function and quality of life.19In addition, a landmark clinical trial showed that 20 weeks of CR in obese patients with HFpEF improved cardiac function, exercise capacity, glucose metabolism, and body mass, and subsequently, increased quality of life. 5Importantly, the application of CR in combination with exercise training showed additive benefits in these patients, including on skeletal muscle function.5,20This guided us to explore whether CR alongside mechanical overload (ie, as a resistance exercise intervention) could stimulate therapeutic improvements in muscle mass and function.Low muscle mass is determined that CR increased myonuclear accretion along with myofiber growth supports a novel concept that MuSCdependent myonuclear accretion is an important mechanism regulating skeletal muscle hypertrophy in HFpEF.Based on past evidence in other conditions,23 the mechanism(s) limiting myonuclear accretion and how this is overcome following acute CR in HFpEF is likely explained by changes in the MuSC environment, potentially due to deficits in cell cycle Espino-Gonzalez et alJ A C C : B A S I C T O T R A N S L A T I O N A L S C I E N C E V O L .9 , N O . 2 , 2 0 2 4Mechanisms of Skeletal Muscle Pathology in HFpEFF E B R U A R Y 2 0 2 4 : 2 2 3 -2 4 0regulation (eg, via perturbing quiescence/activation)60  and/or myogenic progression/fusion (via MyoD, myomaker).58This would align with past studies in aging showing MuSC dysfunction, senescence, and impaired cell cycle regulation are linked to sarcopenia,69 whereas use of CR can reverse these effects.23MuSC function in HFpEF remains unknown, although a recent study in patients following aerobic exercise training showed relatively minor changes.70This supports our hypothesis that patients with HFpEF have impaired MuSC homeostasis, which decreases skeletal muscle remodeling in response to adequate cues.Our findings of dysregulated basal myogenic expression in both HFpEF patients and rats further supports this hypothesis.Future studies are warranted to expand our knowledge of the role of MuSCs and their influence on the skeletal muscle pathology in HFpEF.

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A C C : B A S I C T O T R A N S L A T I O N A L SCIENCE VOL. 9, NO. 2, 2024 Espino-Gonzalez et al F E B R U A R Y 2 0 2 4 : 2 2 3 -2 4 0 Mechanisms of Skeletal Muscle Pathology in HFpEF not directly assessed after caloric restriction, although we did measure structural changes via histology.Given past studies in heart failure have documented caloric restriction increases cardiac function, 5,76,77 and our current study confirmed beneficial effects on cardiac remodeling, together this indicates both function and structure were probably improved after caloric restriction in HFpEF.Our experiments were performed in male rats, and we cannot exclude sexual dimorphism in the effects of CR on the muscle phenotype in HFpEF.Moreover, the long-term effects of CR in HFpEF remain uncertain.Some heart failure patients are susceptible to sarcopenia and frailty, 12 whereas obese patients in general show better survival than normal or underweight patients, 78 meaning the clinical effects of CR on muscle loss must be carefully considered. 5,20We also acknowledge that to fully support clinical translation, a randomized exercise trial is required where patients with HFpEF and healthy control subjects perform strength training, and myonuclear accretion and myofiber growth are assessed, however, this was beyond the scope of the current study.CONCLUSIONS This study has identified a novel mechanism to explain the skeletal muscle pathology in HFpEF and revealed an effective treatment centered on nonpharmacological approaches of combined diet and strength exercise.ACKNOWLEDGMENT The authors thank Prof Michelle Peckham, University of Leeds, for providing critical comments.
PERSPECTIVES COMPETENCY IN MEDICAL KNOWLEDGE: Key symptoms in HFpEF such as exercise intolerance cannot be solely explained by cardiac dysfunction, meaning other treatment targets should be considered.HFpEF is known to induce a skeletal muscle pathology, which is closely linked to worse symptoms.What mechanisms cause and how to treat skeletal muscle pathology in HFpEF remain poorly known.This paper comprehensively addresses what mechanisms are involved in the skeletal muscle pathology in HFpEF and highlights therapeutic targets and relevant treatments in the form of nonpharmacological approaches related to exercise and diet that could be important for optimizing future treatment in the clinic.TRANSLATIONAL OUTLOOK: We have identified potential novel mechanisms and treatments of skeletal muscle pathology in HFpEF using animal models, and show data these are conserved in patients.Given clinical evidence indicates that caloric restriction alone reduces symptoms in patients with HFpEF, tailored combination therapy that optimizes both exercise regimes and pharmacological treatments warrant further exploration as this will likely provide the greatest benefits to quality of life.Espino-Gonzalez et al J A C C : B A S I C T O T R A N S L A T I O N A L S C I E N C E V O L .9 , N O . 2 , 2 0 2 4 Mechanisms of Skeletal Muscle Pathology in HFpEF F E B R U A R Y 2 0 2 4 : 2 2 3 -2 4 0 Dr Espino-Gonzalez is a recipient of a doctoral fellowship from the Mexican National Council of Science and Technology (CONACYT).Dr Altara's work was supported by a grant from the K.G.Jebsen Center for Heart Failure Research.Dr Cheng is supported by BHF Mautner Career Development Fellowship.Dr Justo da Silva was supported by the South-Eastern Norway Regional Health Authority (HSØ-RHF, Project No. 25674).Dr Booz has received support from the Pharmacology Clinical Research Core of the University of Mississippi Medical Center School of Medicine.Dr Bowen has received funding from the Medical Research Council (UK) (MR/S025472/1) and Heart Research UK (TRP16/19).All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.ADDRESS FOR CORRESPONDENCE: Dr T. Scott Bowen, School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, United Kingdom.E-mail: t.s.bowen@leeds.ac.uk.
2. Gevaert AB, Kataria R, Zannad F, et al.Heart failure with preserved ejection fraction: recent concepts in diagnosis, mechanisms and management.Heart.2022;108:1342-1350.3. Pandey A, Shah SJ, Butler J, et al.Exercise intolerance in older adults with heart failure 4. Sharma K, Kass DA.Heart failure with preserved ejection fraction: mechanisms, clinical features, and therapies.Circ Res.2014;115:79-96.5. Kitzman DW, Brubaker P, Morgan T, et al.Effect of caloric restriction or aerobic exercise training on peak oxygen consumption and quality of life in obese older patients with heart failure with preserved ejection fraction: a randomized clinical trial.JAMA.2016;315:36-46.6. Warraich HJ, Kitzman DW, Whellan DJ, et al.Physical function, frailty, cognition, depression, and quality of life in hospitalized adults >/¼60 years with acute decompensated heart failure with preserved versus reduced ejection fraction.Circ Heart Fail.2018;11:e005254.