Invited Review: Autocrine/paracrine IGF-I and skeletal muscle adaptation

2002 ◽  
Vol 93 (3) ◽  
pp. 1159-1167 ◽  
Author(s):  
Gregory R. Adams
Keyword(s):  
Skeletal Muscle ◽  
Growth Factor ◽  
Signaling Pathways ◽  
Intracellular Signaling ◽  
Muscle Hypertrophy ◽  
Muscle Adaptation ◽  
Factor I ◽  
Important Mediator ◽  
Signaling Mechanisms ◽  
Igf I

This brief review presents the basic premises suggesting that insulin-like growth factor I (IGF-I), functioning in an autocrine/paracrine mode, is an important mediator of skeletal muscle adaptation. Key intracellular signaling mechanisms associated with ligation of the primary IGF-I receptor are highlighted to illustrate the mechanisms by which IGF-I may promote muscle hypertrophy. In addition, a number of recent findings are presented that highlight the potential for interactions between IGF-I-related signaling pathways and intracellular signaling mechanisms activated by cytokines or hormonal systems.

Viral expression of insulin-like growth factor-I isoforms promotes different responses in skeletal muscle

2006 ◽  
Vol 100 (6) ◽  
pp. 1778-1784 ◽  
Author(s):  
Elisabeth R. Barton
Keyword(s):  
Skeletal Muscle ◽  
Growth Factor ◽  
Muscle Mass ◽  
Muscle Hypertrophy ◽  
Muscle Development ◽  
Muscle Size ◽  
Insulin Like Growth Factor ◽  
Factor I ◽  
Igf I ◽  
Growth Factor I

Insulin-like growth factor I (IGF-I) is a critical protein for skeletal muscle development and regeneration. Its ability to promote skeletal muscle hypertrophy has been demonstrated by several methods. Alternative splicing of the Igf-1 gene does not affect the mature IGF-I protein but does produce different E peptide extensions, which have been reported to modify the potency of IGF-I. Viral-mediated delivery of murine IGF-IA and IGF-IB into skeletal muscle of 2-wk-old and 6-mo-old mice was utilized to compare the effects of the isoforms on muscle mass. In young mice, tissue content of IGF-I protein was significantly higher in rAAV-treated muscles than control muscles at 1, 2, and 4 mo postinjection. Viral injection of IGF-IB produced two- to sevenfold more IGF-I than rAAVIGF-IA. Hypertrophy was observed 2 and 4 mo postinjection, where both rAAVIGF-IA and rAAVIGF-IB were equally effective in increasing muscle mass. These results suggest that there is a threshold of IGF-I production necessary to promote muscle hypertrophy in young growing animals regardless of isoform. In 6-mo-old animals, only rAAVIGF-IA produced significant increases in muscle size, even though increased IGF-I content was observed after injection of both isoforms. Therefore, the ability for IGF-IB to promote muscle hypertrophy is only effective in growing animals, suggesting that the bioavailability of this isoform or its receptor affinity diminishes with age.

Insulin and insulin-like growth factor I signaling pathways in rainbow trout (Oncorhynchus mykiss) during adipogenesis and their implication in glucose uptake

2010 ◽  
Vol 299 (1) ◽  
pp. R33-R41 ◽  
Author(s):  
L. Bouraoui ◽  
E. Capilla ◽  
J. Gutiérrez ◽  
I. Navarro
Keyword(s):  
Rainbow Trout ◽  
Growth Factor ◽  
Oncorhynchus Mykiss ◽  
Glucose Uptake ◽  
Signaling Pathways ◽  
Mapk Phosphorylation ◽  
Factor I ◽  
Rainbow Trout Oncorhynchus Mykiss ◽  
Igf I ◽  
Stimulation Of

Primary cultures of rainbow trout ( Oncorhynchus mykiss ) adipocytes were used to examine the main signaling pathways of insulin and insulin-like growth factor I (IGF-I) during adipogenesis. We first determined the presence of IGF-I receptors (IGF-IR) and insulin receptors (IR) in trout preadipocytes ( day 5) and adipocytes ( day 14). IGF-IRs were more abundant and appeared to be in higher levels in differentiated cells than in preadipocytes, whereas IRs were detected in lower but constant levels throughout the culture. The cells were immunoreactive against ERK1/2 MAPK, and AKT/PI3K, components of the two main signal transduction pathways for insulin and IGF-I receptors. Stimulation of MAPK phosphorylation by IGF-I was higher in preadipocytes than in adipocytes, while no effects were observed in MAPK phosphorylation after incubation of cells with insulin. AKT phosphorylation increased in the presence of both insulin and IGF-I, with higher levels of stimulation in adipocytes than in preadipocytes. Activation of both pathways was blocked by the use of specific inhibitors of MAPK (PD98059) and AKT (wortmannin). We describe here, for the first time, the effects of IGF-I and insulin on 2-deoxyglucose uptake in primary culture of trout adipocytes. IGF-I was more potent in stimulating glucose uptake than insulin, and PD98059 and wortmannin inhibited the stimulation of glucose uptake by this growth factor, suggesting that IGF-I plays an important metabolic role in trout adipocytes. Our results suggest that differential activation of the MAPK and AKT pathways are involved in the IGF-I- and insulin-induced effects of trout adipocytes during the various stages of adipogenesis.

scholarly journals Protective Effect of Pyropia yezoensis Peptide on Dexamethasone-Induced Myotube Atrophy in C2C12 Myotubes

Marine Drugs ◽  
2019 ◽  
Vol 17 (5) ◽  
pp. 284 ◽  
Author(s):  
Min-Kyeong Lee ◽  
Jeong-Wook Choi ◽  
Youn Hee Choi ◽  
Taek-Jeong Nam
Keyword(s):  
Skeletal Muscle ◽  
Growth Factor ◽  
Signaling Pathway ◽  
Muscle Atrophy ◽  
Skeletal Muscle Atrophy ◽  
C2c12 Myotubes ◽  
Protective Effects ◽  
Factor I ◽  
Igf I ◽  
Foxo Signaling Pathway

Dexamethasone (DEX), a synthetic glucocorticoid, causes skeletal muscle atrophy. This study examined the protective effects of Pyropia yezoensis peptide (PYP15) against DEX-induced myotube atrophy and its association with insulin-like growth factor-I (IGF-I) and the Akt/mammalian target of rapamycin (mTOR)-forkhead box O (FoxO) signaling pathway. To elucidate the molecular mechanisms underlying the effects of PYP15 on DEX-induced myotube atrophy, C2C12 myotubes were treated for 24 h with 100 μM DEX in the presence or absence of 500 ng/mL PYP15. Cell viability assays revealed no PYP15 toxicity in C2C12 myotubes. PYP15 activated the insulin-like growth factor-I receptor (IGF-IR) and Akt-mTORC1 signaling pathway in DEX-induced myotube atrophy. In addition, PYP15 markedly downregulated the nuclear translocation of transcription factors FoxO1 and FoxO3a, and inhibited 20S proteasome activity. Furthermore, PYP15 inhibited the autophagy-lysosomal pathway in DEX-stimulated myotube atrophy. Our findings suggest that PYP15 treatment protected against myotube atrophy by regulating IGF-I and the Akt-mTORC1-FoxO signaling pathway in skeletal muscle. Therefore, PYP15 treatment appears to exert protective effects against skeletal muscle atrophy.

Effects of prior exercise on the action of insulin-like growth factor I in skeletal muscle

1992 ◽  
Vol 263 (2) ◽  
pp. E340-E344 ◽  
Author(s):  
E. J. Henriksen ◽  
L. L. Louters ◽  
C. S. Stump ◽  
C. M. Tipton
Keyword(s):  
Skeletal Muscle ◽  
Amino Acid ◽  
Growth Factor ◽  
Glucose Transport ◽  
Amino Acid Transport ◽  
Acid Transport ◽  
Factor I ◽  
System A ◽  
Prior Exercise ◽  
Igf I

Prior exercise increases insulin sensitivity for glucose and system A neutral amino acid transport activities in skeletal muscle. Insulin-like growth factor I (IGF-I) also activates these transport processes in resting muscle. It is not known, however, whether prior exercise increases IGF-I action in muscle. Therefore we determined the effect of a single exhausting bout of swim exercise on IGF-I-stimulated glucose transport activity [assessed by 2-deoxy-D-glucose (2-DG) uptake] and system A activity [assessed by alpha-(methylamino)isobutyric acid (MeAIB) uptake] in the isolated rat epitrochlearis muscle. When measured 3.5 h after exercise, the responses to a submaximal concentration (0.2 nM), but not a maximal concentration (13.3 nM), of insulin for activation of 2-DG uptake and MeAIB uptake were enhanced. In contrast, prior exercise increased markedly both the submaximal (5 nM) and maximal (20 nM) responses to IGF-I for activation of 2-DG uptake, whereas only the submaximal response to IGF-I (3 nM) for MeAIB uptake was enhanced after exercise. We conclude that 1) prior exercise significantly enhances the response to a submaximal concentration of IGF-I for activation of the glucose transport and system A neutral amino acid transport systems in skeletal muscle and 2) the enhanced maximal response for IGF-I action after exercise is restricted to the signaling pathway for activation of the glucose transport system.

scholarly journals Akt-Dependent and -Independent Survival Signaling Pathways Utilized by Insulin-Like Growth Factor I

1998 ◽  
Vol 18 (11) ◽  
pp. 6711-6718 ◽  
Author(s):  
George Kulik ◽  
Michael J. Weber
Keyword(s):  
Growth Factor ◽  
Signaling Pathways ◽  
Signaling Pathway ◽  
Alternative Pathway ◽  
Pi3 Kinase ◽  
Dominant Negative ◽  
Factor I ◽  
Igf I ◽  
Survival Signaling ◽  
Growth Factor I

ABSTRACT Protein kinase B (PKB)/Akt is implicated in survival signaling in a wide variety of cells including fibroblasts and epithelial and neuronal cells. We and others have described a linear survival signaling cascade used by insulinlike growth factor I (IGF-I) that consists of the IGF-I receptor, phosphoinositide 3-kinase (PI3 kinase), Akt, and Bad. Activation of this pathway can be sufficient to protect cells from apoptosis. However, previous work had not determined whether this pathway is invariably necessary for protection from apoptosis or whether there are alternative survival signaling pathways. In this communication, we report the existence of two survival signaling pathways, one dependent on PI3 kinase and Akt and the other independent of these enzymes. We found that survival signaling initiated by IGF-I treatment of Rat-1 cells could be blocked by overexpression of a dominant negative kinase-deficient Akt (K179A) as well as by wortmannin. This demonstrates a survival signaling pathway dependent on PI3 kinase and Akt. However, when IGF-I receptors were overexpressed in a Rat-1 background (RIG cells), an alternative pathway became apparent, in which survival mediated by IGF-I was no longer sensitive to wortmannin or to overexpression of dominant negative Akt, even though Akt activation and Bad phosphorylation were still wortmannin sensitive. Experiments with inhibitors of RNA synthesis showed that transcriptional activation is dispensable for this alternative PI3 kinase/Akt-independent survival signaling. These findings demonstrate the existence of a new survival signaling pathway independent of PI3 kinase, Akt, and new transcription and which is evident in fibroblasts overexpressing the IGF-I receptor.

scholarly journals Insulin-like growth factor I stimulates degradation of an mRNA transcript encoding the 14 kDa ubiquitin-conjugating enzyme

1996 ◽  
Vol 319 (2) ◽  
pp. 455-461 ◽  
Author(s):  
Simon S WING ◽  
Nathalie BEDARD
Keyword(s):  
Skeletal Muscle ◽  
Growth Factor ◽  
Binding Proteins ◽  
Mrna Levels ◽  
Insulin Like Growth Factor ◽  
Mrna Transcript ◽  
Factor I ◽  
Igf I ◽  
Ubiquitin Conjugating Enzyme ◽  
Growth Factor I

Upon fasting, the ubiquitin-dependent proteolytic system is activated in skeletal muscle in parallel with the increases in rates of proteolysis. Levels of mRNA encoding the 14 kDa ubiquitin-conjugating enzyme (E214k), which can catalyse the first irreversible reaction in this pathway, rise and fall in parallel with the rates of proteolysis [Wing and Banville (1994) Am. J. Physiol. 267, E39-E48], indicating that the conjugation of ubiquitin to proteins is a regulated step. To characterize the mechanisms of this regulation, we have examined the effects of insulin, insulin-like growth factor I (IGF-I) and des(1–3) insulin-like growth factor I (DES-IGF-I), which does not bind IGF-binding proteins, on E214k mRNA levels in L6 myotubes. Insulin suppressed levels of E214k mRNA with an IC50 of 4×10-9 M, but had no effects on mRNAs encoding polyubiquitin and proteasome subunits C2 and C8, which, like E214k, also increase in skeletal muscle upon fasting. Reduction of E214k mRNA levels was more sensitive to IGF-I with an IC50 of approx. 5×10-10 M. During the incubation of these cells for 12 h there was significant secretion of IGF-I-binding proteins into the medium. DES-IGF-I, which has markedly reduced affinity for these binding proteins, was found to potently reduce E214k mRNA levels with an IC50 of 3×10-11 M. DES-IGF-I did not alter rates of transcription of the E214k gene, but enhanced the rate of degradation of the 1.2 kb mRNA transcript. The half-life of the 1.2 kb transcript was approximately one-third that of the 1.8 kb transcript and can explain the more marked regulation of this transcript observed previously. This indicates that the additional 3´ non-coding sequence in the 1.8 kb transcript confers stability. These observations suggest that IGF-I is an important regulator of E214k expression and demonstrate, for the first time, stimulation of degradation of a specific mRNA transcript by this hormone, while overall RNA accumulates.

scholarly journals Skeletal Unloading Induces Resistance to Insulin-Like Growth Factor-I (IGF-I) by Inhibiting Activation of the IGF-I Signaling Pathways

2003 ◽  
Vol 19 (3) ◽  
pp. 436-446 ◽  
Author(s):  
Takeshi Sakata ◽  
Yongmei Wang ◽  
Bernard P Halloran ◽  
Hashem Z Elalieh ◽  
Jay Cao ◽  
...  
Keyword(s):  
Growth Factor ◽  
Signaling Pathways ◽  
Insulin Like Growth Factor ◽  
Skeletal Unloading ◽  
Factor I ◽  
Igf I ◽  
Resistance To Insulin ◽  
Growth Factor I
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