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Mun Y, Kim W, Shin D. Melanocortin 1 Receptor (MC1R): Pharmacological and Therapeutic Aspects. Int J Mol Sci 2023; 24:12152. [PMID: 37569558 PMCID: PMC10418475 DOI: 10.3390/ijms241512152] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2023] [Revised: 06/22/2023] [Accepted: 07/27/2023] [Indexed: 08/13/2023] Open
Abstract
Melanocortins play crucial roles in regulating the stress response, inflammation, and skin pigmentation. In this review, we focus on the melanocortin 1 receptor (MC1R), a G protein-coupled receptor primarily known for regulating skin pigmentation and exhibiting anti-inflammatory effects. First, we provide an overview of the structure, signaling pathways, and related diseases of MC1R. Next, we discuss the potential therapeutic use of synthetic peptides and small molecule modulators of MC1R, highlighting the development of various drugs that enhance stability through amino acid sequence modifications and small molecule drugs to overcome limitations associated with peptide characteristics. Notably, MC1R-targeted drugs have applications beyond skin pigmentation-related diseases, which predominantly affect MC1R in melanocytes. These drugs can also be useful in treating inflammatory diseases with MC1R expression present in various cells. Our review underscores the potential of MC1R-targeted drugs to treat a wide range of diseases and encourages further research in this area.
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Affiliation(s)
- Yoonwoo Mun
- College of Pharmacy, Gachon University, 191 Hambakmoe-ro, Yeonsu-gu, Incheon 21936, Republic of Korea; (Y.M.); (W.K.)
| | - Woohyun Kim
- College of Pharmacy, Gachon University, 191 Hambakmoe-ro, Yeonsu-gu, Incheon 21936, Republic of Korea; (Y.M.); (W.K.)
| | - Dongyun Shin
- College of Pharmacy, Gachon University, 191 Hambakmoe-ro, Yeonsu-gu, Incheon 21936, Republic of Korea; (Y.M.); (W.K.)
- Gachon Pharmaceutical Research Institute, Gachon University, 191 Hambakmoe-ro, Yeonsu-gu, Incheon 21936, Republic of Korea
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Protective Effects of the Chalcone-Based Derivative AN07 on Inflammation-Associated Myotube Atrophy Induced by Lipopolysaccharide. Int J Mol Sci 2022; 23:ijms232112929. [PMID: 36361718 PMCID: PMC9655064 DOI: 10.3390/ijms232112929] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2022] [Revised: 10/24/2022] [Accepted: 10/24/2022] [Indexed: 12/02/2022] Open
Abstract
Inflammation is a major cause of skeletal muscle atrophy in various diseases. 2-Hydroxy-4′-methoxychalcone (AN07) is a chalcone-based peroxisome-proliferator-activated receptor gamma (PPARγ) agonist with various effects, such as antiatherosclerosis, anti-inflammation, antioxidative stress, and neuroprotection. In this study, we examined the effects of AN07 on protein homeostasis pathway and mitochondrial function in inflammation-associated myotube atrophy induced by lipopolysaccharides (LPS). We found that AN07 significantly attenuated NF-κB activation, inflammatory factors (TNF-α, IL-1β, COX-2, and PGE2), Nox4 expression, and reactive oxygen species levels in LPS-treated C2C12 myotubes. Moreover, AN07 increased SOD2 expression and improved mitochondrial function, including mitochondrial membrane potential and mitochondrial oxygen consumption rate. We also demonstrated that AN07 attenuated LPS-induced reduction of myotube diameter, MyHC expression, and IGF-1/IGF-1R/p-Akt-mediated protein synthesis signaling. Additionally, AN07 downregulated LPS-induced autophagy–lysosomal protein degradation molecules (LC3-II/LC3-I and degraded p62) and ubiquitin–proteasome protein degradation molecules (n-FoxO1a/MuRF1/atrogin-1). However, the regulatory effects of AN07 on protein synthesis and degradation signaling were inhibited by the IGF-1R inhibitor AG1024 and the PI3K inhibitor wortmannin. In addition, the PPARγ antagonist GW9662 attenuated the effects of AN07 against LPS-induced inflammation, oxidation, and protein catabolism. In conclusion, our findings suggest that AN07 possesses protective effects on inflammation-induced myotube atrophy and mitochondrial dysfunction.
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Chen Y, Banie L, Breyer BN, Tan Y, Wang Z, Zhou F, Wang G, Lin G, Liu J, Qi LS, Lue TF. Enhanced Myogenesis by Silencing Myostatin with Nonviral Delivery of dCas9 Ribonucleoprotein Complex. CRISPR J 2022; 5:598-608. [PMID: 35758824 DOI: 10.1089/crispr.2022.0009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Stress urinary incontinence (SUI) and pelvic floor disorder (PFD) are common conditions with limited treatment options in women worldwide. Regenerative therapy to restore urethral striated and pelvic floor muscles represents a valuable therapeutic approach. We aim to determine the CRISPR interference-mediated gene silencing effect of the nonviral delivery of nuclease-deactivated dCas9 ribonucleoprotein (RNP) complex on muscle regeneration at the cellular and molecular level. We designed four myostatin (MSTN)-targeting sgRNAs and transfected them into rat myoblast L6 cells together with the dCas9 protein. Myogenesis assay and immunofluorescence staining were performed to evaluate muscle differentiation, while CCK8 assay, cell cycle assay, and 5-ethynyl-2'-deoxyuridine staining were used to measure muscle proliferation. Reverse transcription-polymerase chain reaction and Western blotting were also performed to examine cellular signaling. Myogenic factors (including myosin heavy chain, MSTN, myocardin, and serum response factor) increased significantly after day 5 during myogenesis. MSTN was efficiently silenced after transfecting the dCas9 RNP complex, which significantly promoted more myotube formation and a higher fusion index for L6 cells. In cellular signaling, MSTN repression enhanced the expression of MyoG and MyoD, phosphorylation of Smad2, and the activity of Wnt1/GSK-3β/β-catenin pathway. Moreover, MSTN repression accelerated L6 cell growth with a higher cell proliferation index as well as a higher expression of cyclin D1 and cyclin E. Nonviral delivery of the dCas9 RNP complex significantly promoted myoblast differentiation and proliferation, providing a promising approach to improve muscle regeneration for SUI and PFD. Further characterization and validation of this approach in vivo are needed.
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Affiliation(s)
- Yinwei Chen
- Knuppe Molecular Urology Laboratory, Department of Urology, School of Medicine, University of California, San Francisco, San Francisco, California, USA.,Reproductive Medicine Center, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Lia Banie
- Knuppe Molecular Urology Laboratory, Department of Urology, School of Medicine, University of California, San Francisco, San Francisco, California, USA
| | - Benjamin N Breyer
- Knuppe Molecular Urology Laboratory, Department of Urology, School of Medicine, University of California, San Francisco, San Francisco, California, USA
| | - Yan Tan
- Knuppe Molecular Urology Laboratory, Department of Urology, School of Medicine, University of California, San Francisco, San Francisco, California, USA
| | - Zhao Wang
- Knuppe Molecular Urology Laboratory, Department of Urology, School of Medicine, University of California, San Francisco, San Francisco, California, USA
| | - Feng Zhou
- Knuppe Molecular Urology Laboratory, Department of Urology, School of Medicine, University of California, San Francisco, San Francisco, California, USA
| | - Guifang Wang
- Knuppe Molecular Urology Laboratory, Department of Urology, School of Medicine, University of California, San Francisco, San Francisco, California, USA
| | - Guiting Lin
- Knuppe Molecular Urology Laboratory, Department of Urology, School of Medicine, University of California, San Francisco, San Francisco, California, USA
| | - Jihong Liu
- Department of Urology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Lei S Qi
- Department of Bioengineering, Stanford University, Stanford, California, USA.,ChEM-H, Stanford University, Stanford, California, USA
| | - Tom F Lue
- Knuppe Molecular Urology Laboratory, Department of Urology, School of Medicine, University of California, San Francisco, San Francisco, California, USA
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Role of Glucocorticoid Signaling and HDAC4 Activation in Diaphragm and Gastrocnemius Proteolytic Activity in Septic Rats. Int J Mol Sci 2022; 23:ijms23073641. [PMID: 35408999 PMCID: PMC8998191 DOI: 10.3390/ijms23073641] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Revised: 03/23/2022] [Accepted: 03/24/2022] [Indexed: 02/04/2023] Open
Abstract
Sepsis increases glucocorticoid and decreases IGF-1, leading to skeletal muscle wasting and cachexia. Muscle atrophy mainly takes place in locomotor muscles rather than in respiratory ones. Our study aimed to elucidate the mechanism responsible for this difference in muscle proteolysis, focusing on local inflammation and IGF-1 as well as on their glucocorticoid response and HDAC4-myogenin activation. Sepsis was induced in adult male rats by lipopolysaccharide (LPS) injection (10 mg/kg), and 24 h afterwards, rats were euthanized. LPS increased TNFα and IL-10 expression in both muscles studied, the diaphragm and gastrocnemius, whereas IL-6 and SOCS3 mRNA increased only in diaphragm. In comparison with gastrocnemius, diaphragm showed a lower increase in proteolytic marker expression (atrogin-1 and LC3b) and in LC3b protein lipidation after LPS administration. LPS increased the expression of glucocorticoid induced factors, KLF15 and REDD1, and decreased that of IGF-1 in gastrocnemius but not in the diaphragm. In addition, an increase in HDAC4 and myogenin expression was induced by LPS in gastrocnemius, but not in the diaphragm. In conclusion, the lower activation of both glucocorticoid signaling and HDAC4-myogenin pathways by sepsis can be one of the causes of lower sepsis-induced proteolysis in the diaphragm compared to gastrocnemius.
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Martín AI, Priego T, Moreno-Ruperez Á, González-Hedström D, Granado M, López-Calderón A. IGF-1 and IGFBP-3 in Inflammatory Cachexia. Int J Mol Sci 2021; 22:ijms22179469. [PMID: 34502376 PMCID: PMC8430490 DOI: 10.3390/ijms22179469] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2021] [Revised: 08/05/2021] [Accepted: 08/28/2021] [Indexed: 02/04/2023] Open
Abstract
Inflammation induces a wide response of the neuroendocrine system, which leads to modifications in all the endocrine axes. The hypothalamic–growth hormone (GH)–insulin-like growth factor-1 (IGF-1) axis is deeply affected by inflammation, its response being characterized by GH resistance and a decrease in circulating levels of IGF-1. The endocrine and metabolic responses to inflammation allow the organism to survive. However, in chronic inflammatory conditions, the inhibition of the hypothalamic–GH–IGF-1 axis contributes to the catabolic process, with skeletal muscle atrophy and cachexia. Here, we review the changes in pituitary GH secretion, IGF-1, and IGF-1 binding protein-3 (IGFBP-3), as well as the mechanism that mediated those responses. The contribution of GH and IGF-1 to muscle wasting during inflammation has also been analyzed.
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Affiliation(s)
- Ana Isabel Martín
- Department of Physiology, Faculty of Medicine, Complutense University of Madrid, 28040 Madrid, Spain; (A.I.M.); (Á.M.-R.)
| | - Teresa Priego
- Department of Physiology, Faculty of Nursing, Physiotherapy and Podiatry, Complutense University of Madrid, 28040 Madrid, Spain;
| | - Álvaro Moreno-Ruperez
- Department of Physiology, Faculty of Medicine, Complutense University of Madrid, 28040 Madrid, Spain; (A.I.M.); (Á.M.-R.)
| | - Daniel González-Hedström
- Department of Physiology, Faculty of Medicine, Autonomous University of Madrid, 28049 Madrid, Spain; (D.G.-H.); (M.G.)
- Pharmactive Biotech Products S.L. Parque Científico de Madrid, Avenida del Doctor Severo Ochoa, 37 Local 4J, 28108 Alcobendas, Spain
| | - Miriam Granado
- Department of Physiology, Faculty of Medicine, Autonomous University of Madrid, 28049 Madrid, Spain; (D.G.-H.); (M.G.)
- CIBER Fisiopatología de la Obesidad y Nutrición, Instituto de Salud Carlos III, 28029 Madrid, Spain
| | - Asunción López-Calderón
- Department of Physiology, Faculty of Medicine, Complutense University of Madrid, 28040 Madrid, Spain; (A.I.M.); (Á.M.-R.)
- Correspondence: ; Tel.: +34-913-941-491
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Dinparastisaleh R, Mirsaeidi M. Antifibrotic and Anti-Inflammatory Actions of α-Melanocytic Hormone: New Roles for an Old Player. Pharmaceuticals (Basel) 2021; 14:ph14010045. [PMID: 33430064 PMCID: PMC7827684 DOI: 10.3390/ph14010045] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2020] [Revised: 01/04/2021] [Accepted: 01/06/2021] [Indexed: 12/16/2022] Open
Abstract
The melanocortin system encompasses melanocortin peptides, five receptors, and two endogenous antagonists. Besides pigmentary effects generated by α-Melanocytic Hormone (α-MSH), new physiologic roles in sexual activity, exocrine secretion, energy homeostasis, as well as immunomodulatory actions, exerted by melanocortins, have been described recently. Among the most common and burdensome consequences of chronic inflammation is the development of fibrosis. Depending on the regenerative capacity of the affected tissue and the quality of the inflammatory response, the outcome is not always perfect, with the development of some fibrosis. Despite the heterogeneous etiology and clinical presentations, fibrosis in many pathological states follows the same path of activation or migration of fibroblasts, and the differentiation of fibroblasts to myofibroblasts, which produce collagen and α-SMA in fibrosing tissue. The melanocortin agonists might have favorable effects on the trajectories leading from tissue injury to inflammation, from inflammation to fibrosis, and from fibrosis to organ dysfunction. In this review we briefly summarized the data on structure, receptor signaling, and anti-inflammatory and anti-fibrotic properties of α-MSH and proposed that α-MSH analogues might be promising future therapeutic candidates for inflammatory and fibrotic diseases, regarding their favorable safety profile.
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Affiliation(s)
- Roshan Dinparastisaleh
- Division of Pulmonary and Critical Care Medicine, Johns Hopkins University, Baltimore, MD 21218, USA;
| | - Mehdi Mirsaeidi
- Division of Pulmonary and Critical Care, University of Miami, Miami, FL 33146, USA
- Correspondence: ; Tel.: +1-305-243-1377
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Supinski GS, Wang L, Schroder EA, Callahan LAP. MitoTEMPOL, a mitochondrial targeted antioxidant, prevents sepsis-induced diaphragm dysfunction. Am J Physiol Lung Cell Mol Physiol 2020; 319:L228-L238. [PMID: 32460519 DOI: 10.1152/ajplung.00473.2019] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Clinical studies indicate that sepsis-induced diaphragm dysfunction is a major contributor to respiratory failure in mechanically ventilated patients. Currently there is no drug to treat this form of diaphragm weakness. Sepsis-induced muscle dysfunction is thought to be triggered by excessive mitochondrial free radical generation; we therefore hypothesized that therapies that target mitochondrial free radical production may prevent sepsis-induced diaphragm weakness. The present study determined whether MitoTEMPOL, a mitochondrially targeted free radical scavenger, could reduce sepsis-induced diaphragm dysfunction. Using an animal model of sepsis, we compared four groups of mice: 1) sham-operated controls, 2) animals with sepsis induced by cecal ligation puncture (CLP), 3) sham controls given MitoTEMPOL (10 mg·kg-1·day-1 ip), and 4) CLP animals given MitoTEMPOL. At 48 h after surgery, we measured diaphragm force generation, mitochondrial function, proteolytic enzyme activities, and myosin heavy chain (MHC) content. We also examined the effects of delayed administration of MitoTEMPOL (by 6 h) on CLP-induced diaphragm weakness. The effects of MitoTEMPOL on cytokine-mediated alterations on muscle cell superoxide generation and cell size in vitro were also assessed. Sepsis markedly reduced diaphragm force generation. Both immediate and delayed MitoTEMPOL administration prevented sepsis-induced diaphragm weakness. MitoTEMPOL reversed sepsis-mediated reductions in mitochondrial function, activation of proteolytic pathways, and decreases in MHC content. Cytokines increased muscle cell superoxide generation and decreased cell size, effects that were ablated by MitoTEMPOL. MitoTEMPOL and other compounds that target mitochondrial free radical generation may be useful therapies for sepsis-induced diaphragm weakness.
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Affiliation(s)
- Gerald S Supinski
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Internal Medicine, University of Kentucky, Lexington, Kentucky
| | - Lin Wang
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Internal Medicine, University of Kentucky, Lexington, Kentucky
| | - Elizabeth A Schroder
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Internal Medicine, University of Kentucky, Lexington, Kentucky
| | - Leigh Ann P Callahan
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Internal Medicine, University of Kentucky, Lexington, Kentucky
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Martín AI, Gómez-SanMiguel AB, Priego T, López-Calderón A. Formoterol treatment prevents the effects of endotoxin on muscle TNF/NF-kB, Akt/mTOR, and proteolytic pathways in a rat model. Role of IGF-I and miRNA 29b. Am J Physiol Endocrinol Metab 2018; 315:E705-E714. [PMID: 29969314 DOI: 10.1152/ajpendo.00043.2018] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Inflammatory diseases are associated with muscle wasting as a result of an increase in proteolysis. The purpose of this study was to elucidate whether administration of a β2 adrenergic agonist, formoterol, was able to prevent the acute effects of sepsis induced by liposaccharide (LPS) injection on rat gastrocnemius muscle and to evaluate the possible roles of corticosterone, IGF-I, miR-23a, and miR-29b. For this purpose, male Wistar rats were injected with LPS and/or formoterol. Formoterol treatment decreased LPS-induced increase in serum corticosterone, TNFα upregulation, and NF-κB(p65) and Forkhead box protein O1 activation in the gastrocnemius. Atrogin-1, muscle RING-finger protein-1, microtubule-associated protein-1 light chain 3b (LC3b), and the lipidation of LC3b-I to LC3b-II were increased by LPS, and formoterol blocked these effects. Serum IGF-I and its mRNA levels in the gastrocnemius were decreased, whereas mecano growth factor and IGF binding protein 3 mRNA levels were increased in the rats injected with LPS but not in the rats that received LPS and formoterol. Similarly, LPS decreased Akt and mammalian target of rapamycin phosphorylation, and formoterol blocked these decreases. Finally, miR-29b expression in the gastrocnemius was upregulated by endotoxin injection, whereas miR-23a was not significantly different. Formoterol treatment did not significantly modify LPS-induced increase in muscle miR-29b. Furthermore, in control rats formoterol increased the expression of this miRNA. We conclude that formoterol decreases endotoxin-induced inflammation and proteolysis in rat skeletal muscle. Those responses can be a direct effect of β2 adrenergic receptor stimulation or/and of blocking the effects of LPS on corticosterone and IGF-I. Muscle miR-23a and -29b do not seem to play an important role in those responses.
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Affiliation(s)
- Ana Isabel Martín
- Department of Physiology, Faculty of Medicine, Complutense University , Madrid , Spain
| | | | - Teresa Priego
- Department of Physiology, Faculty of Medicine, Complutense University , Madrid , Spain
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Liu G, Li M, Saeed M, Xu Y, Ren Q, Sun C. αMSH inhibits adipose inflammation via reducing FoxOs transcription and blocking Akt/JNK pathway in mice. Oncotarget 2018; 8:47642-47654. [PMID: 28514752 PMCID: PMC5564594 DOI: 10.18632/oncotarget.17465] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2017] [Accepted: 04/07/2017] [Indexed: 12/21/2022] Open
Abstract
Alpha melanocyte stimulating hormone (αMSH) abates inflammation in multiple tissues, while Forkhead box proteins O (FoxOs) stimulate inflammatory cascade. However, the relationship between αMSH and FoxOs in adipose inflammation remains unclear. In this study, we used LPS-induced inflammation model, attempted to interpret the function of αMSH in inflammation and the interactions with FoxOs. Results indicated that upon inflammatory situation, the secretion of αMSH and the expression of its receptor MC5R were greatly decreased, but FoxOs expressions were elevated. After the treatment with αMSH, LPS-induced adipose inflammation together with FoxOs expressions was significantly reduced. Conversely, when Foxo1, Foxo3a or Foxo4 overexpressed in αMSH treated inflammatory mouse model, all the anti-inflammatory impacts of αMSH were found disappeared. We further studied the mechanisms by which αMSH exerts its anti-inflammatory impacts and how FoxOs reverse αMSH's function. Foxo4 was found as a negative regulator for MC5R transcription in αMSH inhibited inflammation. Moreover, a negative role was found of αMSH in regulating both Akt and JNK signal pathways by observing the enhanced the anti-inflammatory impacts of pathway-specific inhibitors with αMSH treatment. Our findings demonstrate αMSH plays a key role in the prevention of adipose inflammation and inflammatory diseases by down-regulating Akt/JNK signal pathway and negatively interacting with FoxOs, which brings up αMSH as a novel candidate factor in the adipose anti-inflammation process in obesity.
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Affiliation(s)
- Guannv Liu
- College of Animal Science and Technology, Northwest A&F University, Yangling, Shaanxi, 712100, China
| | - Meihang Li
- College of Animal Science and Technology, Northwest A&F University, Yangling, Shaanxi, 712100, China
| | - Muhammad Saeed
- College of Animal Science and Technology, Northwest A&F University, Yangling, Shaanxi, 712100, China
| | - Yatao Xu
- College of Animal Science and Technology, Northwest A&F University, Yangling, Shaanxi, 712100, China
| | - Qian Ren
- College of Animal Science and Technology, Northwest A&F University, Yangling, Shaanxi, 712100, China
| | - Chao Sun
- College of Animal Science and Technology, Northwest A&F University, Yangling, Shaanxi, 712100, China
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The Role of IGF-1 Signaling in Skeletal Muscle Atrophy. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2018; 1088:109-137. [PMID: 30390250 DOI: 10.1007/978-981-13-1435-3_6] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Insulin-like growth factor 1 (IGF-1) is a key anabolic growth factor stimulating phosphatidylinositol 3-kinase (PI3K)/Akt signaling which is well known for regulating muscle hypertrophy. However, the role of IGF-1 in muscle atrophy is less clear. This review provides an overview of the mechanisms via which IGF-1 signaling is implicated in several conditions of muscle atrophy and via which mechanisms protein turnover is altered. IGF-1/PI3K/Akt signaling stimulates the rate of protein synthesis via p70S6Kinase and p90 ribosomal S6 kinase and negatively regulates protein degradation, predominantly by its inhibiting effect on proteasomal and lysosomal protein degradation. Caspase-dependent protein degradation is also attenuated by IGF/PI3K/Akt signaling, whereas evidence for an effect on calpain-dependent protein degradation is inconclusive. IGF-1/PI3K/Akt signaling reduces during denervation-, unloading-, and joint immobilization-induced muscle atrophy, whereas IGF-1/PI3K/Akt signaling seems unaltered during aging-associated muscle atrophy. During denervation and aging, IGF-1 overexpression or injection counteracts denervation- and aging-associated muscle atrophy, despite enhanced anabolic resistance with regard to IGF-1 signaling with aging. It remains unclear whether pharmacological stimulation of IGF-1/PI3K/Akt signaling attenuates immobilization- or unloading-induced muscle atrophy. Exploration of the possibilities to interfere with IGF-1/PI3K/Akt signaling reveals that microRNAs targeting IGF-1 signaling components are promising targets to counterbalance muscle atrophy. Overall, the findings summarized in this review show that in disuse conditions, but not with aging, IGF-1/PI3K/Akt signaling is attenuated and that in some conditions stimulation of this pathway may alleviate skeletal muscle atrophy.
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