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Gallagher H, Hendrickse PW, Pereira MG, Bowen TS. Skeletal muscle atrophy, regeneration, and dysfunction in heart failure: Impact of exercise training. JOURNAL OF SPORT AND HEALTH SCIENCE 2023; 12:557-567. [PMID: 37040849 PMCID: PMC10466197 DOI: 10.1016/j.jshs.2023.04.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2022] [Revised: 11/30/2022] [Accepted: 02/20/2023] [Indexed: 05/31/2023]
Abstract
This review highlights some established and some more contemporary mechanisms responsible for heart failure (HF)-induced skeletal muscle wasting and weakness. We first describe the effects of HF on the relationship between protein synthesis and degradation rates, which determine muscle mass, the involvement of the satellite cells for continual muscle regeneration, and changes in myofiber calcium homeostasis linked to contractile dysfunction. We then highlight key mechanistic effects of both aerobic and resistance exercise training on skeletal muscle in HF and outline its application as a beneficial treatment. Overall, HF causes multiple impairments related to autophagy, anabolic-catabolic signaling, satellite cell proliferation, and calcium homeostasis, which together promote fiber atrophy, contractile dysfunction, and impaired regeneration. Although both wasting and weakness are partly rescued by aerobic and resistance exercise training in HF, the effects of satellite cell dynamics remain poorly explored.
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Affiliation(s)
- Harrison Gallagher
- School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, UK
| | - Paul W Hendrickse
- School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, UK
| | - Marcelo G Pereira
- School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, UK
| | - T Scott Bowen
- School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, UK.
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Kumar RA, Hahn D, Kelley RC, Muscato DR, Shamoun A, Curbelo-Bermudez N, Butler WG, Yegorova S, Ryan TE, Ferreira LF. Skeletal muscle Nox4 knockout prevents and Nox2 knockout blunts loss of maximal diaphragm force in mice with heart failure with reduced ejection fraction. Free Radic Biol Med 2023; 194:23-32. [PMID: 36436728 PMCID: PMC10191720 DOI: 10.1016/j.freeradbiomed.2022.11.025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/18/2022] [Revised: 11/14/2022] [Accepted: 11/14/2022] [Indexed: 11/27/2022]
Abstract
Patients with heart failure with reduced ejection fraction (HFrEF) experience diaphragm weakness that contributes to the primary disease symptoms of fatigue, dyspnea, and exercise intolerance. Weakness in the diaphragm is related to excessive production of reactive oxygen species (ROS), but the exact source of ROS remains unknown. NAD(P)H Oxidases (Nox), particularly the Nox2 and 4 isoforms, are important sources of ROS within skeletal muscle that contribute to optimal cell function. There are reports of increased Nox activity in the diaphragm of patients and animal models of HFrEF, implicating these complexes as possible sources of diaphragm dysfunction in HFrEF. To investigate the role of these proteins on diaphragm weakness in HFrEF, we generated inducible skeletal muscle specific knockouts of Nox2 or Nox4 using the Cre-Lox system and assessed diaphragm function in a mouse model of HFrEF induced by myocardial infarction. Diaphragm maximal specific force measured in vitro was depressed by ∼20% with HFrEF. Skeletal muscle knockout of Nox4 provided full protection against the loss of maximal force (p < 0.01), while the knockout of Nox2 provided partial protection (7% depression, p < 0.01). Knockout of Nox2 from skeletal myofibers improved survival from 50 to 80% following myocardial infarction (p = 0.026). Our findings show an important role for skeletal muscle NAD(P)H Oxidases contributing to loss of diaphragm maximal force in HFrEF, along with systemic pathophysiological responses following myocardial infarction.
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Affiliation(s)
- Ravi A Kumar
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, USA; King's College London British Heart Foundation Centre of Excellence, School of Cardiovascular Medicine & Sciences, London, United Kingdom
| | - Dongwoo Hahn
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, USA; Department of Integrative Biology and Physiology, University of Minnesota, Minneapolis, MN, USA
| | - Rachel C Kelley
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, USA; Endocrine Society, Washington, D.C, USA
| | - Derek R Muscato
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, USA
| | - Alex Shamoun
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, USA
| | - Nuria Curbelo-Bermudez
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, USA
| | - W Greyson Butler
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, USA
| | - Svetlana Yegorova
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, USA
| | - Terence E Ryan
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, USA
| | - Leonardo F Ferreira
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, USA.
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Yegorova S, Yegorov O, Ferreira LF. RNA-sequencing reveals transcriptional signature of pathological remodeling in the diaphragm of rats after myocardial infarction. Gene 2020; 770:145356. [PMID: 33333219 DOI: 10.1016/j.gene.2020.145356] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2020] [Revised: 11/11/2020] [Accepted: 12/01/2020] [Indexed: 12/21/2022]
Abstract
The diaphragm is the main inspiratory muscle, and the chronic phase post-myocardial infarction (MI) is characterized by diaphragm morphological, contractile, and metabolic abnormalities. However, the mechanisms of diaphragm weakness are not fully understood. In the current study, we aimed to identify the transcriptome changes associated with diaphragm abnormalities in the chronic stage MI. We ligated the left coronary artery to cause MI in rats and performed RNA-sequencing (RNA-Seq) in diaphragm samples 16 weeks post-surgery. The sham group underwent thoracotomy and pericardiotomy but no artery ligation. We identified 112 differentially expressed genes (DEGs) out of a total of 9664 genes. Myocardial infarction upregulated and downregulated 42 and 70 genes, respectively. Analysis of DEGs in the framework of skeletal muscle-specific biological networks suggest remodeling in the neuromuscular junction, extracellular matrix, sarcomere, cytoskeleton, and changes in metabolism and iron homeostasis. Overall, the data are consistent with pathological remodeling of the diaphragm and reveal potential biological targets to prevent diaphragm weakness in the chronic stage MI.
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Affiliation(s)
- Svetlana Yegorova
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL 32611, USA.
| | - Oleg Yegorov
- Department of Neurosurgery, University of Florida, Gainesville, FL 32611, USA.
| | - Leonardo F Ferreira
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL 32611, USA.
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Diaphragm weakness and proteomics (global and redox) modifications in heart failure with reduced ejection fraction in rats. J Mol Cell Cardiol 2020; 139:238-249. [PMID: 32035137 DOI: 10.1016/j.yjmcc.2020.02.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/18/2019] [Revised: 01/02/2020] [Accepted: 02/03/2020] [Indexed: 12/16/2022]
Abstract
Inspiratory dysfunction occurs in patients with heart failure with reduced ejection fraction (HFrEF) in a manner that depends on disease severity and by mechanisms that are not fully understood. In the current study, we tested whether HFrEF effects on diaphragm (inspiratory muscle) depend on disease severity and examined putative mechanisms for diaphragm abnormalities via global and redox proteomics. We allocated male rats into Sham, moderate (mHFrEF), or severe HFrEF (sHFrEF) induced by myocardial infarction and examined the diaphragm muscle. Both mHFrEF and sHFrEF caused atrophy in type IIa and IIb/x fibers. Maximal and twitch specific forces (N/cm2) were decreased by 19 ± 10% and 28 ± 13%, respectively, in sHFrEF (p < .05), but not in mHFrEF. Global proteomics revealed upregulation of sarcomeric proteins and downregulation of ribosomal and glucose metabolism proteins in sHFrEF. Redox proteomics showed that sHFrEF increased reversibly oxidized cysteine in cytoskeletal and thin filament proteins and methionine in skeletal muscle α-actin (range 0.5 to 3.3-fold; p < .05). In conclusion, fiber atrophy plus contractile dysfunction caused diaphragm weakness in HFrEF. Decreased ribosomal proteins and heighted reversible oxidation of protein thiols are candidate mechanisms for atrophy or anabolic resistance as well as loss of specific force in sHFrEF.
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Diaphragm abnormalities in heart failure and aging: mechanisms and integration of cardiovascular and respiratory pathophysiology. Heart Fail Rev 2018; 22:191-207. [PMID: 27000754 DOI: 10.1007/s10741-016-9549-4] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Inspiratory function is essential for alveolar ventilation and expulsive behaviors that promote airway clearance (e.g., coughing and sneezing). Current evidence demonstrates that inspiratory dysfunction occurs during healthy aging and is accentuated by chronic heart failure (CHF). This inspiratory dysfunction contributes to key aspects of CHF and aging cardiovascular and pulmonary pathophysiology including: (1) impaired airway clearance and predisposition to pneumonia; (2) inability to sustain ventilation during physical activity; (3) shallow breathing pattern that limits alveolar ventilation and gas exchange; and (4) sympathetic activation that causes cardiac arrhythmias and tissue vasoconstriction. The diaphragm is the primary inspiratory muscle; hence, its neuromuscular integrity is a main determinant of the adequacy of inspiratory function. Mechanistic work within animal and cellular models has revealed specific factors that may be responsible for diaphragm neuromuscular abnormalities in CHF and aging. These include phrenic nerve and neuromuscular junction alterations as well as intrinsic myocyte abnormalities, such as changes in the quantity and quality of contractile proteins, accelerated fiber atrophy, and shifts in fiber type distribution. CHF, aging, or CHF in the presence of aging disturbs the dynamics of circulating factors (e.g., cytokines and angiotensin II) and cell signaling involving sphingolipids, reactive oxygen species, and proteolytic pathways, thus leading to the previously listed abnormalities. Exercise-based rehabilitation combined with pharmacological therapies targeting the pathways reviewed herein hold promise to treat diaphragm abnormalities and inspiratory muscle dysfunction in CHF and aging.
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Ahn B, Coblentz PD, Beharry AW, Patel N, Judge AR, Moylan JS, Hoopes CW, Bonnell MR, Ferreira LF. Diaphragm Abnormalities in Patients with End-Stage Heart Failure: NADPH Oxidase Upregulation and Protein Oxidation. Front Physiol 2017; 7:686. [PMID: 28119629 PMCID: PMC5220111 DOI: 10.3389/fphys.2016.00686] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2016] [Accepted: 12/23/2016] [Indexed: 01/10/2023] Open
Abstract
Patients with heart failure (HF) have diaphragm abnormalities that contribute to disease morbidity and mortality. Studies in animals suggest that reactive oxygen species (ROS) cause diaphragm abnormalities in HF. However, the effects of HF on ROS sources, antioxidant enzymes, and protein oxidation in the diaphragm of humans is unknown. NAD(P)H oxidase, especially the Nox2 isoform, is an important source of ROS in the diaphragm. Our main hypothesis was that diaphragm from patients with HF have heightened Nox2 expression and p47phox phosphorylation (marker of enzyme activation) that is associated with elevated protein oxidation. We collected diaphragm biopsies from patients with HF and brain-dead organ donors (controls). Diaphragm mRNA levels of Nox2 subunits were increased 2.5–4.6-fold over controls (p < 0.05). Patients also had increased protein levels of Nox2 subunits (p47phox, p22phox, and p67phox) and total p47phox phosphorylation, while phospho-to-total p47phox levels were unchanged. The antioxidant enzyme catalase was increased in patients, whereas glutathione peroxidase and superoxide dismutases were unchanged. Among markers of protein oxidation, carbonyls were increased by ~40% (p < 0.05) and 4-hydroxynonenal and 3-nitrotyrosines were unchanged in patients with HF. Overall, our findings suggest that Nox2 is an important source of ROS in the diaphragm of patients with HF and increases in levels of antioxidant enzymes are not sufficient to maintain normal redox homeostasis. The net outcome is elevated diaphragm protein oxidation that has been shown to cause weakness in animals.
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Affiliation(s)
- Bumsoo Ahn
- Department of Applied Physiology and Kinesiology, University of Florida Gainesville, FL, USA
| | - Philip D Coblentz
- Department of Applied Physiology and Kinesiology, University of Florida Gainesville, FL, USA
| | - Adam W Beharry
- Department of Physical Therapy, University of Florida Gainesville, FL, USA
| | - Nikhil Patel
- Department of Applied Physiology and Kinesiology, University of Florida Gainesville, FL, USA
| | - Andrew R Judge
- Department of Physical Therapy, University of Florida Gainesville, FL, USA
| | | | - Charles W Hoopes
- Division of Cardiothoracic Surgery, University of Alabama at Birmingham Birmingham, AL, USA
| | - Mark R Bonnell
- Division of Cardiothoracic Surgery, University of Toledo Medical Center Toledo, OH, USA
| | - Leonardo F Ferreira
- Department of Applied Physiology and Kinesiology, University of Florida Gainesville, FL, USA
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Laitano O, Ahn B, Patel N, Coblentz PD, Smuder AJ, Yoo JK, Christou DD, Adhihetty PJ, Ferreira LF. Pharmacological targeting of mitochondrial reactive oxygen species counteracts diaphragm weakness in chronic heart failure. J Appl Physiol (1985) 2016; 120:733-42. [PMID: 26846552 DOI: 10.1152/japplphysiol.00822.2015] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2015] [Accepted: 01/28/2016] [Indexed: 12/15/2022] Open
Abstract
Diaphragm muscle weakness in chronic heart failure (CHF) is caused by elevated oxidants and exacerbates breathing abnormalities, exercise intolerance, and dyspnea. However, the specific source of oxidants that cause diaphragm weakness is unknown. We examined whether mitochondrial reactive oxygen species (ROS) cause diaphragm weakness in CHF by testing the hypothesis that CHF animals treated with a mitochondria-targeted antioxidant have normal diaphragm function. Rats underwent CHF or sham surgery. Eight weeks after surgeries, we administered a mitochondrial-targeted antioxidant (MitoTEMPO; 1 mg·kg(-1)·day(-1)) or sterile saline (Vehicle). Left ventricular dysfunction (echocardiography) pre- and posttreatment and morphological abnormalities were consistent with the presence of CHF. CHF elicited a threefold (P < 0.05) increase in diaphragm mitochondrial H2O2 emission, decreased diaphragm glutathione content by 23%, and also depressed twitch and maximal tetanic force by ∼20% in Vehicle-treated animals compared with Sham (P < 0.05 for all comparisons). Diaphragm mitochondrial H2O2 emission, glutathione content, and twitch and maximal tetanic force were normal in CHF animals receiving MitoTEMPO. Neither CHF nor MitoTEMPO altered the diaphragm protein levels of antioxidant enzymes: superoxide dismutases (CuZn-SOD or MnSOD), glutathione peroxidase, and catalase. In both Vehicle and MitoTEMPO groups, CHF elicited a ∼30% increase in cytochrome c oxidase activity, whereas there were no changes in citrate synthase activity. Our data suggest that elevated mitochondrial H2O2 emission causes diaphragm weakness in CHF. Moreover, changes in protein levels of antioxidant enzymes or mitochondrial content do not seem to mediate the increase in mitochondria H2O2 emission in CHF and protective effects of MitoTEMPO.
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Affiliation(s)
- Orlando Laitano
- Department of Applied Physiology and Kinesiology, College of Health and Human Performance, University of Florida, Gainesville, Florida
| | - Bumsoo Ahn
- Department of Applied Physiology and Kinesiology, College of Health and Human Performance, University of Florida, Gainesville, Florida
| | - Nikhil Patel
- Department of Applied Physiology and Kinesiology, College of Health and Human Performance, University of Florida, Gainesville, Florida
| | - Philip D Coblentz
- Department of Applied Physiology and Kinesiology, College of Health and Human Performance, University of Florida, Gainesville, Florida
| | - Ashley J Smuder
- Department of Applied Physiology and Kinesiology, College of Health and Human Performance, University of Florida, Gainesville, Florida
| | - Jeung-Ki Yoo
- Department of Applied Physiology and Kinesiology, College of Health and Human Performance, University of Florida, Gainesville, Florida
| | - Demetra D Christou
- Department of Applied Physiology and Kinesiology, College of Health and Human Performance, University of Florida, Gainesville, Florida
| | - Peter J Adhihetty
- Department of Applied Physiology and Kinesiology, College of Health and Human Performance, University of Florida, Gainesville, Florida
| | - Leonardo F Ferreira
- Department of Applied Physiology and Kinesiology, College of Health and Human Performance, University of Florida, Gainesville, Florida
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Kennel PJ, Mancini DM, Schulze PC. Skeletal Muscle Changes in Chronic Cardiac Disease and Failure. Compr Physiol 2015; 5:1947-69. [PMID: 26426472 DOI: 10.1002/cphy.c110003] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Peak exercise performance in healthy man is limited not only by pulmonary or skeletal muscle function but also by cardiac function. Thus, abnormalities in cardiac function will have a major impact on exercise performance. Many cardiac diseases affect exercise performance and indeed for some cardiac conditions such as atherosclerotic heart disease, exercise testing is frequently used not only to measure functional capacity but also to make a diagnosis of heart disease, evaluate the efficacy of treatment, and predict prognosis. Early in the course of cardiac diseases, exercise performance will be minimally affected but with disease progression impairment in exercise capacity will become apparent. Ejection fraction, that is, the percent of blood volume ejected with each cardiac cycle is often used as a measure of cardiac performance but frequently there is a dissociation between the ejection fraction and exercise capacity in patients with heart disease. How abnormalities in cardiac function impacts the muscles, vasculature, and lungs to impact exercise performance will here be reviewed. The focus of this work will be on patients with systolic heart failure as the incidence and prevalence of heart failure is reaching epidemic proportions and heart failure is the end result of many other chronic cardiac diseases. The prognostic role of exercise and benefits of exercise training will also be discussed.
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Affiliation(s)
- Peter J Kennel
- Center for Advanced Cardiac Care, Division of Cardiology, New York-Presbyterian Hospital and Columbia University Medical Center, New York, USA
| | - Donna M Mancini
- Center for Advanced Cardiac Care, Division of Cardiology, New York-Presbyterian Hospital and Columbia University Medical Center, New York, USA
| | - P Christian Schulze
- Center for Advanced Cardiac Care, Division of Cardiology, New York-Presbyterian Hospital and Columbia University Medical Center, New York, USA
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Heart failure decreases passive tension generation of rat diaphragm fibers. Int J Cardiol 2009; 141:275-83. [PMID: 19150150 DOI: 10.1016/j.ijcard.2008.12.042] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/30/2008] [Accepted: 12/04/2008] [Indexed: 11/21/2022]
Abstract
BACKGROUND Diaphragm dysfunction is well-known to limit quality of life and prognosis of patients with heart failure (HF), but its underlying mechanisms are not well understood. In an animal model for HF we recently showed that impaired diaphragm contractility arises at the single fiber level and is associated with sarcomeric injuries. For optimal muscle function and sarcomeric stability passive elastic structures, like titin, are indispensable. The current study aimed to investigate if impaired passive elasticity contributes to diaphragm dysfunction in rats with heart failure. METHODS Skinned muscle fibers were isolated from the diaphragm and soleus of rats with chronic HF, induced by left coronary artery ligation and of sham-operated rats. Passive tension-length relationships were determined by applying segmental extension tests. Immunofluorescence was performed on muscle cryosections using antibodies (T12) against a titin epitope near the Z-line. Titin content was determined by SDS-agarose-gel electrophoresis. Titin's mobility on gel was studied to detect changes in titin size. RESULTS Passive tension generation upon stretch was significantly reduced (>35%) in HF diaphragm fibers compared to sham. Immunostaining intensities against titin were reduced in diaphragm cryosections of HF rats compared to sham. Soleus fibers from HF and sham rats did not display differences, neither in passive tension nor in immunostaining. No differences in titin's size were detected in HF and sham diaphragm. Titin content, however, was significantly reduced ( approximately 25%) in HF diaphragm. DISCUSSION We conclude that in the diaphragm of HF rats, passive elasticity is impaired, mainly resulting from titin loss.
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van Hees HWH, van der Heijden HFM, Ottenheijm CAC, Heunks LMA, Pigmans CJC, Verheugt FWA, Brouwer RMHJ, Dekhuijzen PNR. Diaphragm single-fiber weakness and loss of myosin in congestive heart failure rats. Am J Physiol Heart Circ Physiol 2007; 293:H819-28. [PMID: 17449557 DOI: 10.1152/ajpheart.00085.2007] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Diaphragm weakness commonly occurs in patients with congestive heart failure (CHF) and is an independent predictor of mortality. However, the pathophysiology of diaphragm weakness is poorly understood. We hypothesized that CHF induces diaphragm weakness at the single-fiber level by decreasing myosin content. In addition, we hypothesized that myofibrillar Ca(2+) sensitivity is decreased and cross-bridge kinetics are slower in CHF diaphragm fibers. Finally, we hypothesized that loss of myosin in CHF diaphragm weakness is associated with increased proteolytic activities of caspase-3 and the proteasome. In skinned diaphragm single fibers of rats with CHF, induced by left coronary artery ligation, maximum force generation was reduced by approximately 35% (P < 0.01) compared with sham-operated animals for slow, 2a, and 2x fibers. In these CHF diaphragm fibers, myosin heavy chain content per half-sarcomere was concomitantly decreased (P < 0.01). Ca(2+) sensitivity of force generation and the rate constant of tension redevelopment were significantly reduced in CHF diaphragm fibers compared with sham-operated animals for all fiber types. The cleavage activity of the proteolytic enzyme caspase-3 and the proteasome were approximately 30% (P < 0.05) and approximately 60% (P < 0.05) higher, respectively, in diaphragm homogenates from CHF rats than from sham-operated rats. The present study demonstrates diaphragm weakness at the single-fiber level in a myocardial infarct model of CHF. The reduced maximal force generation can be explained by a loss of myosin content in all fiber types and is associated with activation of caspase-3 and the proteasome. Furthermore, CHF decreases myofibrillar Ca(2+) sensitivity and slows cross-bridge cycling kinetics in diaphragm fibers.
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Affiliation(s)
- Hieronymus W H van Hees
- Department of Pulmonary Diseases - 454, University Medical Centre Nijmegen, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
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