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Bruns DR, McNair BD, Peelor FF, Borowik AK, Pranay A, Yusifov A, Miller BF. Skeletal and cardiac muscle have different protein turnover responses in a model of right heart failure. GeroScience 2023; 45:2545-2557. [PMID: 37118350 PMCID: PMC10651599 DOI: 10.1007/s11357-023-00777-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2023] [Accepted: 03/20/2023] [Indexed: 04/30/2023] Open
Abstract
Right heart failure (RHF) is a common and deadly disease in aged populations. Extra-cardiac outcomes of RHF such as skeletal muscle atrophy contribute to morbidity and mortality. Despite the significance of maintaining right ventricular (RV) and muscle function, the mechanisms of RHF and muscle atrophy are unclear. Metformin (MET) improves cardiac and muscle function through the regulation of metabolism and the cellular stress response. However, whether MET is a viable therapeutic for RHF and muscle atrophy is not yet known. We used deuterium oxide labeling to measure individual protein turnover in the RV as well as subcellular skeletal muscle proteostasis in aged male mice subjected to 4 weeks of hypobaric hypoxia (HH)-induced RHF. Mice exposed to HH had elevated RV mass and impaired RV systolic function, neither of which was prevented by MET. HH resulted in a higher content of glycolytic, cardiac, and antioxidant proteins in the RV, most of which were inhibited by MET. The synthesis of these key RV proteins was generally unchanged by MET, suggesting MET accelerated protein breakdown. HH resulted in a loss of skeletal muscle mass due to inhibited protein synthesis alongside myofibrillar protein breakdown. MET did not impact HH-induced muscle protein turnover and did not prevent muscle wasting. Together, we show tissue-dependent responses to HH-induced RHF where the RV undergoes hypertrophic remodeling with higher expression of metabolic and stress response proteins. Skeletal muscle undergoes loss of protein mass and atrophy, primarily due to myofibrillar protein breakdown. MET did not prevent HH-induced RV dysfunction or muscle wasting, suggesting that the identification of other therapies to attenuate RHF and concomitant muscle atrophy is warranted.
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Affiliation(s)
- Danielle R Bruns
- Division of Kinesiology & Health, University of Wyoming, 1000 E. University Ave, Dept. 3196, Laramie, WY, 82071, USA.
- Wyoming WWAMI Medical Education, Laramie, WY, USA.
| | - Benjamin D McNair
- Division of Kinesiology & Health, University of Wyoming, 1000 E. University Ave, Dept. 3196, Laramie, WY, 82071, USA
| | - Frederick F Peelor
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA
| | - Agnieszka K Borowik
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA
| | - Atul Pranay
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA
| | - Aykhan Yusifov
- Division of Kinesiology & Health, University of Wyoming, 1000 E. University Ave, Dept. 3196, Laramie, WY, 82071, USA
| | - Benjamin F Miller
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA
- Oklahoma City VA Medical Center, Oklahoma City, OK, USA
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McNair BD, Polson SM, Shorthill SK, Yusifov A, Walker LA, Weiser-Evans MCM, Kovacs EJ, Bruns DR. Metformin protects against pulmonary hypertension-induced right ventricular dysfunction in an age- and sex-specific manner independent of cardiac AMPK. Am J Physiol Heart Circ Physiol 2023. [PMID: 37389952 PMCID: PMC10393374 DOI: 10.1152/ajpheart.00124.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/01/2023] [Accepted: 06/16/2023] [Indexed: 07/02/2023]
Abstract
Right ventricular (RV) function is the strongest predictor of survival in age-related heart failure as well as other clinical contexts in which aging populations suffer significant morbidity and mortality. However, despite the significance of maintaining RV function with age and disease, mechanisms of RV failure remain poorly understood and no RV-directed therapies exist. The anti-diabetic drug and AMP-activated protein kinase (AMPK) activator metformin protects against left ventricular dysfunction, suggesting cardioprotective properties may translate to the RV. Here, we aimed to understand the impact of advanced age on pulmonary hypertension induced right ventricular dysfunction. We further aimed to test whether metformin is cardioprotective in the RV and if the protection afforded by metformin requires cardiac AMPK. We used a murine model of PH by exposing adult (4-6 months) and aged (18 months) male and female mice to hypobaric hypoxia (HH) for 4 weeks. Cardiopulmonary remodeling was exacerbated in aged mice compared to adult as evidenced by elevated RV weight and impaired RV systolic function. Metformin attenuated HH induced RV dysfunction but only in adult male mice. Metformin still protected the adult male RV even in the absence of cardiac AMPK. Together, we suggest that aging exacerbates PH-induced RV remodeling and that metformin may represent a therapeutic option for this disease in a sex and age-dependent, but in an AMPK independent manner. Ongoing efforts are aimed at elucidating the molecular basis for RV remodeling as well as delineating the mechanisms of cardioprotection provided by metformin in the absence of cardiac AMPK.
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Affiliation(s)
- Benjamin D McNair
- Division of Kinesiology and Health, University of Wyoming, Laramie, WY, United States
| | - Sydney M Polson
- Division of Kinesiology and Health, University of Wyoming, Laramie, WY, United States
| | - Samantha K Shorthill
- Division of Kinesiology and Health, University of Wyoming, Laramie, WY, United States
| | - Aykhan Yusifov
- Division of Kinesiology and Health, University of Wyoming, Laramie, WY, United States
| | - Lori A Walker
- Division of Cardiology, Department of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Mary C M Weiser-Evans
- Division of Renal Diseases and Hypertension, Department of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
- Consortium for Fibrosis Research and Translation, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Elizabeth J Kovacs
- Department of Surgery, Division of GI, Trauma and Endocrine Surgery, and Burn Research Program, University of Colorado Denver, Aurora, CO, United States
- GI and Liver Innate Immune Program, University of Colorado Denver, Aurora, CO, United States
| | - Danielle R Bruns
- Division of Kinesiology and Health, University of Wyoming, Laramie, WY, United States
- Wyoming WWAMI Medical Education, Department of Rehabilitation Medicine, University of Washington, Seattle, WA, United States
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McNair BD, Shorthill SK, Bruns DR. More than just a small left ventricle: the right ventricular fibroblast and ECM in health and disease. Am J Physiol Heart Circ Physiol 2023. [PMID: 37389951 PMCID: PMC10396282 DOI: 10.1152/ajpheart.00213.2023] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/14/2023] [Accepted: 06/22/2023] [Indexed: 07/02/2023]
Abstract
Fibroblasts intricately organize and regulate the extracellular matrix (ECM) in cardiac health and disease. Excess deposition of ECM proteins causes fibrosis, resulting in disrupted signaling conduction and contributing to the development of arrhythmias and impaired cardiac function. Fibrosis is causally involved in cardiac failure in the left ventricle (LV). Fibrosis likely occurs in right ventricle (RV) failure yet mechanisms remain unclear. Indeed, RV fibrosis is poorly understood with mechanisms often extrapolated from the LV to the RV. However, emerging data suggests that the LV and RV are distinct cardiac chambers and differ in regulation of the ECM and response to fibrotic stimuli. In the present review, we will discuss differences in ECM regulation in the healthy RV and LV. We will discuss the importance of fibrosis in the development of RV disease in pressure overload, inflammation, and aging. During this discussion, we will highlight mechanisms of fibrosis with respect to the synthesis of ECM proteins while acknowledging the importance of considering collagen breakdown. We will also discuss current knowledge of anti-fibrotic therapies in the RV and the need for additional research to help delineate the shared and distinct mechanisms of RV and LV fibrosis.
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Affiliation(s)
- Benjamin D McNair
- Division of Kinesiology & Health, University of Wyoming, Laramie, WY, United States
| | - Samantha K Shorthill
- Division of Kinesiology & Health, University of Wyoming, Laramie, WY, United States
| | - Danielle R Bruns
- Division of Kinesiology & Health, University of Wyoming, Laramie, WY, United States
- Wyoming WWAMI Medical Education, Department of Rehabilitation Medicine, University of Washington, Seattle, WA, United States
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Fullerton ZS, McNair BD, Marcello NA, Schmitt EE, Bruns DR. Exposure to High Altitude Promotes Loss of Muscle Mass That Is Not Rescued by Metformin. High Alt Med Biol 2022; 23:215-222. [PMID: 35653735 PMCID: PMC9526469 DOI: 10.1089/ham.2022.0015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Accepted: 04/22/2022] [Indexed: 11/12/2022] Open
Abstract
Fullerton, Zackery S., Benjamin D. McNair, Nicholas A. Marcello, Emily E. Schmitt, and Danielle R. Bruns. Exposure to high altitude promotes loss of muscle mass that is not rescued by metformin. High Alt Med Biol. 23:215-222, 2022. Background: Exposure to high altitude (HA) causes muscle atrophy. Few therapeutic interventions attenuate muscle atrophy; however, the diabetic drug, metformin (Met), has been suggested as a potential therapeutic to preserve muscle mass with aging and obesity-related atrophy. The purpose of the present study was to test the hypothesis that HA would induce muscle atrophy that could be attenuated by Met. Methods: C57Bl6 male and female mice were exposed to simulated HA (∼5,200 m) for 4 weeks, while control (Con) mice remained at resident altitude (∼2,180 m). Met was administered in drinking water at 200 mg/(kg·day). We assessed muscle mass, myocyte cell size, muscle and body composition, and expression of molecular mediators of atrophy. Results: Mice exposed to HA were leaner and had a smaller hind limb complex (HLC) mass than Con mice. Loss of HLC mass and myocyte size were not attenuated by Met. Molecular markers for muscle atrophy were activated at HA in a sex-dependent manner. While the atrophic regulator, atrogin, was unchanged at HA or with Met, myostatin expression was upregulated at HA. In female mice, Met further stimulated myostatin expression. Conclusions: Although HA exposure resulted in loss of muscle mass, particularly in male mice, Met did not attenuate muscle atrophy. Identification of other interventions to preserve muscle mass during ascent to HA is warranted.
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Affiliation(s)
- Zackery S. Fullerton
- Division of Kinesiology and Health, University of Wyoming, Laramie, Wyoming, USA
| | - Benjamin D. McNair
- Division of Kinesiology and Health, University of Wyoming, Laramie, Wyoming, USA
| | - Nicholas A. Marcello
- Division of Kinesiology and Health, University of Wyoming, Laramie, Wyoming, USA
| | - Emily E. Schmitt
- Division of Kinesiology and Health, University of Wyoming, Laramie, Wyoming, USA
- Wyoming WWAMI Medical Education, Laramie, Wyoming, USA
| | - Danielle R. Bruns
- Division of Kinesiology and Health, University of Wyoming, Laramie, Wyoming, USA
- Wyoming WWAMI Medical Education, Laramie, Wyoming, USA
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Abstract
Aging induces physiological and molecular changes in the heart that increase the risk for heart disease. Several of these changes are targetable by exercise. We hypothesize that the mechanisms by which exercise improves cardiac function in the aged heart differ from those in the young exercised heart.
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Affiliation(s)
| | - Benjamin D McNair
- Division of Kinesiology & Health, University of Wyoming, Laramie, WY
| | - Sydney M Polson
- Division of Kinesiology & Health, University of Wyoming, Laramie, WY
| | - Ross F Cook
- Division of Kinesiology & Health, University of Wyoming, Laramie, WY
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McNair BD, Schlatter JA, Cook RF, Yusifova M, Bruns DR. Inhibition of mTOR by rapamycin does not improve hypoxic pulmonary hypertension-induced right heart failure in old mice. Exp Gerontol 2021; 151:111395. [PMID: 33971279 DOI: 10.1016/j.exger.2021.111395] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Revised: 05/03/2021] [Accepted: 05/04/2021] [Indexed: 02/07/2023]
Abstract
Inhibition of the mammalian target of rapamycin (mTOR) by rapamycin attenuates heart failure (HF) and age-associated changes in left ventricular (LV) function. Rapamycin has also been suggested as a therapy for pulmonary hypertension (PH) and concomitant right heart failure (PH-RHF) based on reports of elevated mTOR signaling in young models with PH. However, rapamycin has yet to be tested in the setting of aging, PH, and right heart disease despite the fact that RV function predicts survival in both age-related HF as well as several pulmonary disease states including PH. Thus we tested the hypothesis that rapamycin treatment would attenuate hypoxic PH-RHF in old mice using a mouse model of hypobaric hypoxia (HH)-induced PH and right ventricular (RV) remodeling. Exposure to HH resulted in significant loss of body weight which was exacerbated by rapamycin. HH elevated lung and RV weight, RV wall thickness as well as RV systolic dysfunction as evidenced by RV stroke volume and cardiac output. While rapamycin rescued pulmonary artery acceleration time in males, it generally did not improve other indexes cardiopulmonary remodeling or function. As expected, HH induced expression of hypoxia-regulated genes in the RV and the lungs; however, this transcriptional activation was attenuated by rapamycin, representing a potential mechanism by which rapamycin is detrimental in the aged RV in the setting of chronic hypoxia. Together, we demonstrate that rapamycin is not a viable therapeutic in hypoxic PH in old mice, likely due to exacerbated loss of body weight in this setting. We suggest that future efforts should take into consideration the differences between the RV and LV and the interaction between mTOR and hypoxia in the setting of age-related disease.
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Affiliation(s)
- Benjamin D McNair
- Division of Kinesiology & Health, University of Wyoming, Laramie, WY, United States of America
| | - Jacob A Schlatter
- Division of Kinesiology & Health, University of Wyoming, Laramie, WY, United States of America
| | - Ross F Cook
- Division of Kinesiology & Health, University of Wyoming, Laramie, WY, United States of America
| | - Musharraf Yusifova
- Division of Kinesiology & Health, University of Wyoming, Laramie, WY, United States of America
| | - Danielle R Bruns
- Division of Kinesiology & Health, University of Wyoming, Laramie, WY, United States of America.
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Yusifov A, Chhatre VE, Zumo JM, Cook RF, McNair BD, Schmitt EE, Woulfe KC, Bruns DR. Cardiac response to adrenergic stress differs by sex and across the lifespan. GeroScience 2021; 43:1799-1813. [PMID: 33651247 DOI: 10.1007/s11357-021-00345-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Accepted: 02/21/2021] [Indexed: 02/07/2023] Open
Abstract
The aging heart is well-characterized by a diminished responsiveness to adrenergic activation. However, the precise mechanisms by which age and sex impact adrenergic-mediated cardiac function remain poorly described. In the current investigation, we compared the cardiac response to adrenergic stress to gain mechanistic understanding of how the response to an adrenergic challenge differs by sex and age. Juvenile (4 weeks), adult (4-6 months), and aged (18-20 months) male and female mice were treated with the β-agonist isoproterenol (ISO) for 1 week. ISO-induced morphometric changes were age- and sex-dependent as juvenile and adult mice of both sexes had higher left ventricle weights while aged mice did not increase cardiac mass. Adults increased myocyte cell size and deposited fibrotic matrix in response to ISO, while juvenile and aged animals did not show evidence of hypertrophy or fibrosis. Juvenile females and adults underwent expected changes in systolic function with higher heart rate, ejection fraction, and fractional shortening. However, cardiac function in aged animals was not altered in response to ISO. Transcriptomic analysis identified significant differences in gene expression by age and sex, with few overlapping genes and pathways between groups. Fibrotic and adrenergic signaling pathways were upregulated in adult hearts. Juvenile hearts upregulated genes in the adrenergic pathway with few changes in fibrosis, while aged mice robustly upregulated fibrotic gene expression without changes in adrenergic genes. We suggest that the response to adrenergic stress significantly differs across the lifespan and by sex. Mechanistic definition of these age-related pathways by sex is critical for future research aimed at treating age-related cardiac adrenergic desensitization.
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Affiliation(s)
- Aykhan Yusifov
- Division of Kinesiology and Health, University of Wyoming, Laramie, WY, USA
| | | | - Jacob M Zumo
- School of Medicine, WWAMI Medical Education, University of Washington, Seattle, WA, USA
| | - Ross F Cook
- Division of Kinesiology and Health, University of Wyoming, Laramie, WY, USA
| | - Benjamin D McNair
- Division of Kinesiology and Health, University of Wyoming, Laramie, WY, USA
| | - Emily E Schmitt
- Division of Kinesiology and Health, University of Wyoming, Laramie, WY, USA.,School of Medicine, WWAMI Medical Education, University of Washington, Seattle, WA, USA
| | - Kathleen C Woulfe
- Divisions of Cardiology and Geriatric Medicine, University of Colorado-Denver, Aurora, CO, USA
| | - Danielle R Bruns
- Division of Kinesiology and Health, University of Wyoming, Laramie, WY, USA. .,School of Medicine, WWAMI Medical Education, University of Washington, Seattle, WA, USA.
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McNair BD, Marcello NA, Smith DT, Schmitt EE, Bruns DR. Changes in Muscle Mass and Composition by Exercise and Hypoxia as Assessed by DEXA in Mice. ACTA ACUST UNITED AC 2020; 56:medicina56090446. [PMID: 32899136 PMCID: PMC7558449 DOI: 10.3390/medicina56090446] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2020] [Revised: 08/31/2020] [Accepted: 09/02/2020] [Indexed: 11/16/2022]
Abstract
Background and Objective: Skeletal muscle is critical for overall health and predicts quality of life in several chronic diseases, thus quantification of muscle mass and composition is necessary to understand how interventions promote changes in muscle quality. The purpose of this investigation was to quantify changes in muscle mass and composition in two distinct pre-clinical models of changes in muscle quality using a clinical dual X-ray absorptiometry (DEXA), validated for use in mice. Materials and Methods: Adult C57Bl6 male mice were given running wheels (RUN; muscle hypertrophy) or placed in hypobaric hypoxia (HH; muscle atrophy) for four weeks. Animals received weekly DEXA and terminal collection of muscle hind limb complex (HLC) and quadriceps weights and signaling for molecular regulators of muscle mass and composition. Results: HH decreased total HLC muscle mass with no changes in muscle composition. RUN induced loss of fat mass in both the quadriceps and HLC. Molecular mediators of atrophy were upregulated in HH while stimulators of muscle growth were higher in RUN. These changes in muscle mass and composition were quantified by a clinical DEXA, which we described and validated for use in pre-clinical models. Conclusions: RUN improves muscle composition while HH promotes muscle atrophy, though changes in composition in hypoxia remain unclear. Use of the widely available clinical DEXA for use in mice enhances translational research capacity to understand the mechanisms by which atrophy and hypertrophy promote skeletal muscle and overall health.
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