Administration of adiponectin receptor agonist AdipoRon relieves cancer cachexia by mitigating inflammation in tumour-bearing mice

BACKGROUND

Cancer cachexia is a life-threatening, inflammation-driven wasting syndrome that remains untreatable. Adiponectin, the most abundant adipokine, plays an important role in several metabolic processes as well as in inflammation modulation. Our aim was to test whether administration of AdipoRon (AR), a synthetic agonist of the adiponectin receptors, prevents the development of cancer cachexia and its related muscle atrophy.

METHODS

The effect of AR on cancer cachexia was investigated in two distinct murine models of colorectal cancer. First, 7-week-old CD2F1 male mice were subcutaneously injected with colon-26 carcinoma cells (C26) or vehicle (CT). Six days after injection, mice were treated for 5 days with AdipoRon (50 mg/kg/day; C26 + AR) or the corresponding vehicle (CT and C26). Additionally, a genetic model, the ApcMin/+ mouse, that develops spontaneously numerous intestinal polyps, was used. Eight-week-old male ApcMin/+ mice were treated with AdipoRon (50 mg/kg/day; Apc + AR) or the corresponding vehicle (Apc) over a period of 12 weeks, with C57BL/6J wild-type mice used as controls. In both models, several parameters were assessed in vivo: body weight, grip strength and serum parameters, as well as ex vivo: molecular changes in muscle, fat and liver.

RESULTS

The protective effect of AR on cachexia development was observed in both cachectic C26 and ApcMin/+ mice. In these mice, AR administration led to a significant alleviation of body weight loss and muscle wasting, together with rescued muscle strength (P < 0.05 for all). In both models, AR had a strong anti-inflammatory effect, reflected by lower systemic interleukin-6 levels (-55% vs. C26, P < 0.001 and -80% vs. Apc mice, P < 0.05), reduced muscular inflammation as indicated by lower levels of Socs3, phospho-STAT3 and Serpina3n, an acute phase reactant (P < 0.05 for all). In addition, AR blunted circulating levels of corticosterone (-46% vs. C26 mice, P < 0.001 and -60% vs. Apc mice, P < 0.05), the predominant murine glucocorticoid known to induce muscle atrophy. Accordingly, key glucocorticoid-responsive factors implicated in atrophy programmes were-or tended to be-significantly blunted in skeletal muscle by AR. Finally, AR protected against lipid metabolism alterations observed in ApcMin/+ mice, as it mitigated the increase in circulating triglyceride levels (-38%, P < 0.05) by attenuating hepatic triglyceride synthesis and fatty acid uptake by the liver.

CONCLUSIONS

Altogether, these results show that AdipoRon rescued the cachectic phenotype by alleviating body weight loss and muscle atrophy, along with restraining inflammation and hypercorticism in preclinical murine models. Therefore, AdipoRon could represent an innovative therapeutic strategy to counteract cancer cachexia.

Identification of myokines susceptible to improve glucose homeostasis after bariatric surgery

IMPORTANCE AND OBJECTIVE

The identification of myokines susceptible to improve glucose homeostasis following bariatric surgery could lead to new therapeutic approaches for type 2 diabetes.

METHODS

Changes in the homeostasis model assessment (HOMA) test were assessed in patients before and 3 months after bariatric surgery. Changes in myokines expression and circulating levels were assessed using real-time quantitative polymerase chain reaction (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA). Myokines known to regulate glucose homeostasis were identified using literature (targeted study) and putative myokines using RNA-sequencing (untargeted study). A linear regression analysis adjusted for age and sex was used to search for associations between changes in the HOMA test and changes in myokines.

RESULTS

In the targeted study, brain-derived neurotrophic factor (BDNF) expression was upregulated (+30%, P = .006) while BDNF circulating levels were decreased (-12%, P = .001). Upregulated BDNF expression was associated with decreased HOMA of insulin resistance (HOMA-IR) (adjusted estimate [95% confidence interval {CI}]: -0.51 [-0.88 to -0.13], P = .010). Decreased BDNF serum levels were associated with decreased HOMA of beta-cell function (HOMA-B) (adjusted estimate [95% CI] = 0.002 [0.00002-0.0031], P = .046). In the untargeted study, upregulated putative myokines included XYLT1 (+64%, P < .001), LGR5 (+57, P< .001), and SPINK5 (+46%, P < .001). Upregulated LGR5 was associated with decreased HOMA-IR (adjusted estimate [95% CI] = -0.50 [-0.86 to -0.13], P = .009). Upregulated XYLT1 and SPINK5 were associated with increased HOMA of insulin sensitivity (HOMA-S) (respectively, adjusted estimate [95% CI] = 109.1 [28.5-189.8], P = .009 and 16.5 [0.87-32.19], P = .039).

CONCLUSIONS

Improved glucose homeostasis following bariatric surgery is associated with changes in myokines expression and circulating levels. In particular, upregulation of BDNF, XYLT1, SPINK5, and LGR5 is associated with improved insulin sensitivity. These results suggest that these myokines could contribute to improved glucose homeostasis following bariatric surgery.

STUDY REGISTRATION

NCT03341793 on ClinicalTrials.gov (https://clinicaltrials.gov/).

EDA2R-NIK signalling promotes muscle atrophy linked to cancer cachexia

Skeletal muscle atrophy is a hallmark of the cachexia syndrome that is associated with poor survival and reduced quality of life in patients with cancer¹. Muscle atrophy involves excessive protein catabolism and loss of muscle mass and strength². An effective therapy against muscle wasting is currently lacking because mechanisms driving the atrophy process remain incompletely understood. Our gene expression analysis in muscle tissues indicated upregulation of ectodysplasin A2 receptor (EDA2R) in tumour-bearing mice and patients with cachectic cancer. Here we show that activation of EDA2R signalling promotes skeletal muscle atrophy. Stimulation of primary myotubes with the EDA2R ligand EDA-A2 triggered pronounced cellular atrophy by induction of the expression of muscle atrophy-related genes Atrogin1 and MuRF1. EDA-A2-driven myotube atrophy involved activation of the non-canonical NFĸB pathway and was dependent on NFκB-inducing kinase (NIK) activity. Whereas EDA-A2 overexpression promoted muscle wasting in mice, deletion of either EDA2R or muscle NIK protected tumour-bearing mice from loss of muscle mass and function. Tumour-induced oncostatin M (OSM) upregulated muscle EDA2R expression, and muscle-specific oncostatin M receptor (OSMR)-knockout mice were resistant to tumour-induced muscle wasting. Our results demonstrate that EDA2R-NIK signalling mediates cancer-associated muscle atrophy in an OSM-OSMR-dependent manner. Thus, therapeutic targeting of these pathways may be beneficial in prevention of muscle loss.

Activin A Causes Muscle Atrophy through MEF2C-Dependent Impaired Myogenesis

Activin A (ActA) is considered to play a major role in cancer-induced cachexia (CC). Indeed, circulating ActA levels are elevated and predict survival in patients with CC. However, the mechanisms by which ActA mediates CC development and in particular skeletal muscle (SM) atrophy in humans are not yet fully understood. In this work, we aimed to investigate the effects of ActA on human SM and in mouse models of CC. We used a model of human muscle cells in culture to explore how ActA acts towards human SM. In this model, recombinant ActA induced myotube atrophy associated with the decline of MyHC-β/slow, the main myosin isoform in human muscle cells studied. Moreover, ActA inhibited the expression and activity of MEF2C, the transcription factor regulating MYH7, the gene which codes for MyHC-β/slow. This decrease in MEF2C was involved in the decline of MyHC-β/slow expression, since inhibition of MEF2C by a siRNA leads to the decrease in MyHC-β/slow expression. The relevance of this ActA/MEF2C pathway in vivo was supported by the parallel decline of MEF2C expression and SM mass, which are both blunted by ActA inhibition, in animal models of CC. In this work, we showed that ActA is a potent negative regulator of SM mass by inhibiting MyHC-β/slow synthesis through downregulation of MEF2C. This observation highlights a novel interaction between ActA signaling and MEF2C transcriptional activity which contributes to SM atrophy in CC models.

p21-Activated Kinase 1 Is Permissive for the Skeletal Muscle Hypertrophy Induced by Myostatin Inhibition

Skeletal muscle, the most abundant tissue in the body, plays vital roles in locomotion and metabolism. Understanding the cellular processes that govern regulation of muscle mass and function represents an essential step in the development of therapeutic strategies for muscular disorders. Myostatin, a member of the TGF-β family, has been identified as a negative regulator of muscle development. Indeed, its inhibition induces an extensive skeletal muscle hypertrophy requiring the activation of Smad 1/5/8 and the Insulin/IGF-I signaling pathway, but whether other molecular mechanisms are involved in this process remains to be determined. Using transcriptomic data from various Myostatin inhibition models, we identified Pak1 as a potential mediator of Myostatin action on skeletal muscle mass. Our results show that muscle PAK1 levels are systematically increased in response to Myostatin inhibition, parallel to skeletal muscle mass, regardless of the Myostatin inhibition model. Using Pak1 knockout mice, we investigated the role of Pak1 in the skeletal muscle hypertrophy induced by different approaches of Myostatin inhibition. Our findings show that Pak1 deletion does not impede the skeletal muscle hypertrophy magnitude in response to Myostatin inhibition. Therefore, Pak1 is permissive for the skeletal muscle mass increase caused by Myostatin inhibition.

Increased Serpina3n release into circulation during glucocorticoid-mediated muscle atrophy

BACKGROUND

Glucocorticoids (GC) play a major role in muscle atrophy. As skeletal muscle is a secretory organ, characterization of the muscle secretome elicited by muscle atrophy should allow to better understand the cellular mechanisms and to identify circulating biomarkers of this condition. Our project aimed to identify the changes in the muscle secretome associated with GC-induced muscle atrophy and susceptible to translate into circulation.

METHODS

We have identified the GC-induced changes in the secretome of C₂ C₁₂ muscle cells by proteomic analysis, and then, we have determined how these changes translate into the circulation of mice or human subjects exposed to high concentrations of GC.

RESULTS

This approach led us to identify Serpina3n as one of the most markedly secreted protein in response to GC. Our original in vitro results were confirmed in vivo by an increased expression of Serpina3n in skeletal muscle (3.9-fold; P < 0.01) and in the serum (two-fold; P < 0.01) of mice treated with GC. We also observed increased levels of the human orthologue Serpina3 in the serum of Cushing's syndrome patients compared with healthy controls matched for age and sex (n = 9/group, 2.5-fold; P < 0.01). An increase of Serpina3n was also demonstrated in muscle atrophy models mediated by GC such as cancer cachexia (four-fold; P < 0.01), sepsis (12.5-fold; P < 0.001), or diabetes (two-fold; P < 0.01). In contrast, levels of Serpina3n both in skeletal muscle and in the circulation were reduced in several models of muscle hypertrophy induced by myostatin inhibition (P < 0.01). Furthermore, a cluster of data suggests that the regulation of muscle Serpina3n involves mTOR, an essential determinant of the muscle cell size.

CONCLUSIONS

Taken together, these data suggest that Serpina3n may represent a circulating biomarker of muscle atrophy associated to GC and, broadly, a reflection of dynamic changes in muscle mass.

Circulating Activin A predicts survival in cancer patients

BACKGROUND

Several experimental evidences pinpoint the possible role of Activin A (ActA) as a driver of cancer cachexia. Supporting this hypothesis, we showed recently that human cancer cachexia is associated with high ActA levels. Moreover, ActA levels were correlated with body weight loss and skeletal muscle density, two prognostic factors in cancer patients. Our goal was therefore to investigate the value of ActA to predict survival in cancer patients.

METHODS

Patients with colorectal or lung cancer were prospectively enrolled at the time of diagnosis or relapse between January 2012 and March 2014. At baseline, patients had clinical, nutritional, and functional assessment. Body composition and skeletal muscle density were measured by CT scan, and plasma ActA concentrations were determined. Overall survival (OS) was analysed since inclusion to 24 months later.

RESULTS

Survival data were available for 149 patients out of 152. Patients with high ActA (≥408 pg/mL) had lower OS than those with low levels, regardless the type of cancer (OS in colorectal cancer, 50% vs. 79%, P < 0.05; and in lung cancer, 27% vs. 67%, P = 0.001). The multivariable analysis confirmed the prognostic value of ActA independently of tumour stage or inflammatory markers, particularly in lung cancer. Low muscularity was also an independent prognostic factor.

CONCLUSIONS

Our study demonstrates that high ActA level is an independent prognosis factor of survival in cancer patients. More than a basic marker of the severity of the neoplastic disease or of the inflammatory process, ActA seems to influence survival by contributing to the development of cachexia and loss of skeletal muscle mass.

Comparative Proteomic and Transcriptomic Analysis of Follistatin-Induced Skeletal Muscle Hypertrophy

Skeletal muscle, the most abundant body tissue, plays vital roles in locomotion and metabolism. Myostatin is a negative regulator of skeletal muscle mass. In addition to increasing muscle mass, Myostatin inhibition impacts muscle contractility and energy metabolism. To decipher the mechanisms of action of the Myostatin inhibitors, we used proteomic and transcriptomic approaches to investigate the changes induced in skeletal muscles of transgenic mice overexpressing Follistatin, a physiological Myostatin inhibitor. Our proteomic workflow included a fractionation step to identify weakly expressed proteins and a comparison of fast versus slow muscles. Functional annotation of altered proteins supports the phenotypic changes induced by Myostatin inhibition, including modifications in energy metabolism, fiber type, insulin and calcium signaling, as well as membrane repair and regeneration. Less than 10% of the differentially expressed proteins were found to be also regulated at the mRNA level but the Biological Process annotation, and the KEGG pathways analysis of transcriptomic results shows a great concordance with the proteomic data. Thus this study describes the most extensive omics analysis of muscle overexpressing Follistatin, providing molecular-level insights to explain the observed muscle phenotypic changes.

Role of IGF-I in follistatin-induced skeletal muscle hypertrophy

Follistatin, a physiological inhibitor of myostatin, induces a dramatic increase in skeletal muscle mass, requiring the type 1 IGF-I receptor/Akt/mTOR pathway. The aim of the present study was to investigate the role of IGF-I and insulin, two ligands of the IGF-I receptor, in the follistatin hypertrophic action on skeletal muscle. In a first step, we showed that follistatin increases muscle mass while being associated with a downregulation of muscle IGF-I expression. In addition, follistatin retained its full hypertrophic effect toward muscle in hypophysectomized animals despite very low concentrations of circulating and muscle IGF-I. Furthermore, follistatin did not increase muscle sensitivity to IGF-I in stimulating phosphorylation of Akt but, surprisingly, decreased it once hypertrophy was present. Taken together, these observations indicate that increased muscle IGF-I production or sensitivity does not contribute to the muscle hypertrophy caused by follistatin. Unlike low IGF-I, low insulin, as obtained by streptozotocin injection, attenuated the hypertrophic action of follistatin on skeletal muscle. Moreover, the full anabolic response to follistatin was restored in this condition by insulin but also by IGF-I infusion. Therefore, follistatin-induced muscle hypertrophy requires the activation of the insulin/IGF-I pathway by either insulin or IGF-I. When insulin or IGF-I alone is missing, follistatin retains its full anabolic effect, but when both are deficient, as in streptozotocin-treated animals, follistatin fails to stimulate muscle growth.

Role of Activin A and myostatin in human cancer cachexia

CONTEXT

Cachexia is a multifactorial syndrome, characterized by the loss of skeletal muscle mass and not fully reversible by nutritional support. Recent animal observations suggest that production of Activin A (ActA) and Myostatin (Mstn) by some tumors might contribute to cancer cachexia.

OBJECTIVE

Our goal was to investigate the role of ActA and Mstn in the development of the human cancer cachexia.

DESIGN/SETTING

The ACTICA study is a cross-sectional study, which prospectively enrolled patients from a tertiary-care center between January 2012 and March 2014. Subjects/Outcome Measures: One hundred fifty two patients with colorectal or lung cancer had clinical, nutritional and functional assessment. Body composition was measured by CT-scan, anthropometry, and bioimpedance. Plasma concentrations of ActA, Mstn, and Follistatin were determined.

RESULTS

Cachexia was associated with reduced lean and fat mass (p < .01 and p < .001), reduced physical function, lower quality of life, and increased symptoms (QLQC30; p < .001). Anorexia (SNAQ score < 14) was more common in cachectic patients (CC) than in noncachectic patients (CNC) (p < .001). ActA concentrations in CC patients were higher than in CNC patients (+40%; p < .001) and were correlated positively with weight loss (R = 0.323; p < .001) and negatively with the SNAQ score (R = -0.225; p < .01). In contrast, Mstn concentrations were decreased in CC patients compared to CNC patients (-35%; p < .001).

CONCLUSIONS

These results demonstrate an association between circulating concentrations of ActA and the presence of the anorexia/cachexia syndrome in cancer patients. Given the known muscle atrophic effects of ActA, our study suggests that increased circulating concentrations of ActA may contribute to the development of cachexia in cancer patients.

Role of IGF-I and the TNFα/NF-κB pathway in the induction of muscle atrogenes by acute inflammation

Several catabolic states (sepsis, cancer, etc.) associated with acute inflammation are characterized by a loss of skeletal muscle due to accelerated proteolysis. The main proteolytic systems involved are the autophagy and the ubiquitin-proteasome (UPS) pathways. Among the signaling pathways that could mediate proteolysis induced by acute inflammation, the transcription factor NF-κB, induced by TNFα, and the transcription factor forkhead box O (FOXO), induced by glucocorticoids (GC) and inhibited by IGF-I, are likely to play a key role. The aim of this study was to identify the nature of the molecular mediators responsible for the induction of these muscle proteolytic systems in response to acute inflammation caused by LPS injection. LPS injection robustly stimulated the expression of several components of the autophagy and the UPS pathways in the skeletal muscle. This induction was associated with a rapid increase of circulating levels of TNFα together with a muscular activation of NF-κB followed by a decrease in circulating and muscle levels of IGF-I. Neither restoration of circulating IGF-I nor restoration of muscle IGF-I levels prevented the activation of autophagy and UPS genes by LPS. The inhibition of TNFα production and muscle NF-κB activation, respectively by using pentoxifilline and a repressor of NF-κB, did not prevent the activation of autophagy and UPS genes by LPS. Finally, inhibition of GC action with RU-486 blunted completely the activation of these atrogenes by LPS. In conclusion, we show that increased GC production plays a more crucial role than decreased IGF-I and increased TNFα/NF-κB pathway for the induction of the proteolytic systems caused by acute inflammation.

Urotensin II and urocortin trigger the expression of myostatin, a negative regulator of cardiac growth, in cardiomyocytes

Urotensin II (UII) and urocortin (UCN) are potent contributors to the physiopathology of heart failure. Our study investigated the effects of UII and UCN on the expression of myostatin (Mstn) in primary culture of adult cardiomyocytes. Adult rat cardiomyocytes were stimulated for 48 h with UII and UCN. Cell size and protein content were determined. Mstn gene expression was determined by real time quantitative polymerase chain reaction. Treatment with UII and UCN stimulates hypertrophy of adult cardiomyocytes. This effect was associated with a twofold increase of Mstn gene expression. We have established for the first time that the two hypertrophic peptides UII and UCN stimulate the expression of Mstn.

The type 1 insulin-like growth factor receptor (IGF-IR) pathway is mandatory for the follistatin-induced skeletal muscle hypertrophy

Myostatin inhibition by follistatin (FS) offers a new approach for muscle mass enhancement. The aim of the present study was to characterize the mediators responsible for the FS hypertrophic action on skeletal muscle in male mice. Because IGF-I and IGF-II, two crucial skeletal muscle growth factors, are induced by myostatin inhibition, we assessed their role in FS action. First, we tested whether type 1 IGF receptor (IGF-IR) is required for FS-induced hypertrophy. By using mice expressing a dominant-negative IGF-IR in skeletal muscle, we showed that IGF-IR inhibition blunted by 63% fiber hypertrophy caused by FS. Second, we showed that FS caused the same degree of fiber hypertrophy in wild-type and IGF-II knockout mice. We then tested the role of the signaling molecules stimulated by IGF-IR, in particular the Akt/mammalian target of rapamycin (mTOR)/70-kDa ribosomal protein S6 kinase (S6K) pathway. We investigated whether Akt phosphorylation is required for the FS action. By cotransfecting a dominant-negative form of Akt together with FS, we showed that Akt inhibition reduced by 65% fiber hypertrophy caused by FS. Second, we evaluated the role of mTOR in FS action. Fiber hypertrophy induced by FS was reduced by 36% in rapamycin-treated mice. Finally, because the activity of S6K is increased by FS, we tested its role in FS action. FS caused the same degree of fiber hypertrophy in wild-type and S6K1/2 knockout mice. In conclusion, the IGF-IR/Akt/mTOR pathway plays a critical role in FS-induced muscle hypertrophy. In contrast, induction of IGF-II expression and S6K activity by FS are not required for the hypertrophic action of FS.

Urotensin II induction of adult cardiomyocytes hypertrophy involves the Akt/GSK-3beta signaling pathway

Urotensin II (UII) a potent vasoactive peptide is upregulated in the failing heart and promotes cardiomyocytes hypertrophy, in particular through mitogen-activated protein kinases. However, the regulation by UII of GSK-3beta, a recognized pivotal signaling element of cardiac hypertrophy has not yet been documented. We therefore investigated in adult cardiomyocytes, if UII phosphorylates GSK-3beta and Akt, one of its upstream regulators and stabilizes beta-catenin, a GSK-3beta dependent nuclear transcriptional co-activator. Primary cultures of adult rat cardiomyocytes were stimulated for 48h with UII. Cell size and protein/DNA contents were determined. Phosphorylated and total forms of Akt, GSK-3beta and the total amount of beta-catenin were quantified by western blot. The responses of cardiomyocytes to UII were also evaluated after pretreatment with the chemical phosphatidyl-inositol-3-kinase inhibitor, LY294002, and urantide, a competitive UII receptor antagonist. UII increased cell size and the protein/DNA ratio, consistent with a hypertrophic response. UII also increased phosphorylation of Akt and its downstream target GSK-3beta. beta-Catenin protein levels were increased. All of these effects of UII were prevented by LY294002, and urantide. The UII-induced adult cardiomyocytes hypertrophy involves the Akt/GSK-3beta signaling pathways and is accompanied by the stabilization of the beta-catenin. All these effects are abolished by competitive inhibition of the UII receptor, consistent with new therapeutic perspectives for heart failure treatment.

Follistatin induces muscle hypertrophy through satellite cell proliferation and inhibition of both myostatin and activin

Follistatin (FS) inhibits several members of the TGF-beta superfamily, including myostatin (Mstn), a negative regulator of muscle growth. Mstn inhibition by FS represents a potential therapeutic approach of muscle atrophy. The aim of our study was to investigate the mechanisms of the FS-induced muscle hypertrophy. To test the role of satellite cells in the FS effect, we used irradiation to destroy their proliferative capacity. FS overexpression increased the muscle weight by about 37% in control animals, but the increase reached only 20% in irradiated muscle, supporting the role of cell proliferation in the FS-induced hypertrophy. Surprisingly, the muscle hypertrophy caused by FS reached the same magnitude in Mstn-KO as in WT mice, suggesting that Mstn might not be the only ligand of FS involved in the regulation of muscle mass. To assess the role of activin (Act), another FS ligand, in the FS-induced hypertrophy, we electroporated FSI-I, a FS mutant that does not bind Act with high affinity. Whereas FS electroporation increased muscle weight by 32%, the muscle weight gain induced by FSI-I reached only 14%. Furthermore, in Mstn-KO mice, FSI-I overexpression failed to induce hypertrophy, in contrast to FS. Therefore, these results suggest that Act inhibition may contribute to FS-induced hypertrophy. Finally, the role of Act as a regulator of muscle mass was supported by the observation that ActA overexpression induced muscle weight loss (-15%). In conclusion, our results show that satellite cell proliferation and both Mstn and Act inhibition are involved in the FS-induced muscle hypertrophy.

Role of Akt/GSK-3beta/beta-catenin transduction pathway in the muscle anti-atrophy action of insulin-like growth factor-I in glucocorticoid-treated rats

Decrease of muscle IGF-I plays a critical role in muscle atrophy caused by glucocorticoids (GCs) because IGF-I gene electrotransfer prevents muscle atrophy caused by GCs. The goal of the present study was to identify the intracellular mediators responsible for the IGF-I anti-atrophic action in GC-induced muscle atrophy. We first assessed the IGF-I transduction pathway alterations caused by GC administration and their reversibility by local IGF-I overexpression performed by electrotransfer. Muscle atrophy induced by dexamethasone (dexa) administration occurred with a decrease in Akt (-53%; P<0.01) phosphorylation together with a decrease in beta-catenin protein levels (-40%; P<0.001). Prevention of atrophy by IGF-I was associated with restoration of Akt phosphorylation and beta-catenin levels. We then investigated whether muscle overexpression of these intracellular mediators could mimic the IGF-I anti-atrophic effects. Overexpression of a constitutively active form of Akt induced a marked fiber hypertrophy in dexa-treated animals (+175% of cross-sectional area; P<0.001) and prevented dexa-induced atrophy. This hypertrophy was associated with an increase in phosphorylated GSK-3beta (+17%; P<0.05) and in beta-catenin content (+35%; P<0.05). Furthermore, overexpression of a dominant-negative GSK-3beta or a stable form of beta-catenin increased fiber cross-sectional area by, respectively, 23% (P<0.001) and 29% (P<0.001) in dexa-treated rats, preventing completely the atrophic effect of GC. In conclusion, this work indicates that Akt, GSK-3beta, and beta-catenin probably contribute together to the IGF-I anti-atrophic effect in GC-induced muscle atrophy.

IGF-I does not prevent myotube atrophy caused by proinflammatory cytokines despite activation of Akt/Foxo and GSK-3beta pathways and inhibition of atrogin-1 mRNA

Myofibrillar protein loss occurring in catabolic situations is considered to be mediated by the release of proinflammatory cytokines and associated with a decrease in circulating and muscle levels of insulin-like growth factor I (IGF-I). In this paper, we investigated whether the C(2)C(12) myotube atrophy caused in vitro by TNF-alpha/IFN-gamma cytokines might be reversed by exogenous IGF-I. Our results showed that, despite the presence of TNF-alpha/IFN-gamma, IGF-I retained its full ability to induce the phosphorylation of Akt, Foxo3a, and GSK-3beta (respectively, 16-fold, 9-fold, and 2-fold) together with a decrease in atrogin-1 mRNA (-39%, P < 0.001). Although this ubiquitin ligase has been reported to accelerate the degradation of MyoD, a myogenic transcription factor driving the transcription of myosin heavy chain (MHC), IGF-I failed to blunt the reduction of MyoD and MHC caused by TNF-alpha/IFN-gamma. Moreover, IGF-I only very slightly attenuated the myotube atrophy induced by TNF-alpha/IFN-gamma (TNF-alpha/IFN-gamma 15.48 mum alone vs. TNF-alpha/IFN-gamma/IGF-I 16.97 mum, P < 0.001). In conclusion, our data show that IGF-I does not reverse the myotube atrophy induced by TNF-alpha/IFN-gamma despite the phosphorylation of Foxo and GSK-3beta and the downregulation of atrogin-1 mRNA. Our study suggests therefore that factors other than IGF-I decrease are responsible for the muscle atrophy caused by proinflammatory cytokines.

Myostatin gene deletion prevents glucocorticoid-induced muscle atrophy

Glucocorticoids mediate muscle atrophy in many catabolic states. Myostatin expression, a negative regulator of muscle growth, is increased by glucocorticoids and myostatin overexpression is associated with lower muscle mass. This suggests that myostatin is required for the catabolic effects of glucocorticoids. We therefore investigated whether myostatin gene disruption could prevent muscle atrophy caused by glucocorticoids. Male myostatin knockout (KO) and wild-type mice were subjected to dexamethasone treatment (1 mg/kg.d for 10 d or 5 mg/kg.d for 4 d). In wild-type mice, daily administration of low-dose dexamethasone for 10 d resulted in muscle atrophy (tibialis anterior: -15%; gastrocnemius: -13%; P < 0.01) due to 15% decrease in the muscle fiber cross-sectional area (1621 +/- 31 vs. 1918 +/- 64 microm(2), P < 0.01). In KO mice, there was no reduction of muscle mass nor fiber cross-sectional area after dexamethasone treatment. Muscle atrophy after 4 d of high-dose dexamethasone was associated with increased mRNA of enzymes involved in proteolytic pathways (atrogin-1, muscle ring finger 1, and cathepsin L) and increased chymotrypsin-like proteasomal activity. In contrast, the mRNA of these enzymes and the proteasomal activity were not significantly affected by dexamethasone in KO mice. Muscle IGF-I mRNA was paradoxically decreased in KO mice (-35%, P < 0.05); this was associated with a potentially compensatory increase of IGF-II expression in both saline and dexamethasone-treated KO mice (2-fold, P < 0.01). In conclusion, our results show that myostatin deletion prevents muscle atrophy in glucocorticoid-treated mice, by blunting the glucocorticoid-induced enhanced proteolysis, and suggest an important role of myostatin in muscle atrophy caused by glucocorticoids.

Insulin-like growth factor-I gene transfer by electroporation prevents skeletal muscle atrophy in glucocorticoid-treated rats

Catabolic states caused by injury are characterized by a loss of skeletal muscle. The anabolic action of IGF-I on muscle and the reduction of its muscle content in response to injury suggest that restoration of muscle IGF-I content might prevent skeletal muscle loss caused by injury. We investigated whether local overexpression of IGF-I protein by gene transfer could prevent skeletal muscle atrophy induced by glucocorticoids, a crucial mediator of muscle atrophy in catabolic states. Localized overexpression of IGF-I in tibialis anterior (TA) muscle was performed by injection of IGF-I cDNA followed by electroporation 3 d before starting dexamethasone injections (0.1 mg/kg.d sc). A control plasmid was electroporated in the contralateral TA muscle. Dexamethasone induced atrophy of the TA muscle as illustrated by reduction in muscle mass (403 +/- 11 vs. 461 +/- 19 mg, P < 0.05) and fiber cross-sectional area (1759 +/- 131 vs. 2517 +/- 93 mum(2), P < 0.05). This muscle atrophy was paralleled by a decrease in the IGF-I muscle content (7.2 +/- 0.9 vs. 15.7 +/- 1.4 ng/g of muscle, P < 0.001). As the result of IGF-I gene transfer, the IGF-I muscle content increased 2-fold (15.8 +/- 1.2 vs. 7.2 +/- 0.9 ng/g of muscle, P < 0.001). In addition, the muscle mass (437 +/- 8 vs. 403 +/- 11 mg, P < 0.01) and the fiber cross-sectional area (2269 +/- 129 vs. 1759 +/- 131 mum(2), P < 0.05) were increased in the TA muscle electroporated with IGF-I DNA, compared with the contralateral muscle electroporated with a control plasmid. Our results show therefore that IGF-I gene transfer by electroporation prevents muscle atrophy in glucocorticoid-treated rats. Our observation supports the important role of decreased muscle IGF-I in the muscle atrophy caused by glucocorticoids.

Role of the insulin-like growth factor I decline in the induction of atrogin-1/MAFbx during fasting and diabetes

In catabolic conditions, atrogin-1/MAFbx, a muscle-specific ubiquitin-ligase required for muscle atrophy, is increased, and concentrations of IGF-I, a growth factor known to have antiproteolytic action, are reduced. To define the relationship between the decline in IGF-I and the induction of atrogin-1/MAFbx, we studied the effect of IGF-I replacement on atrogin-1/MAFbx mRNA in rats fasted for 51 h and in rats made diabetic with streptozotocin (STZ). Fasting produced a 5.8-fold increase in atrogin-1/MAFbx (P < 0.001). This was attenuated to a 2.5-fold increase by injections of IGF-I (P < 0.05 vs. fasting). Animals with STZ-induced diabetes experienced a 15.1-fold increase in atrogin-1/MAFbx (P < 0.001). Normalization of their circulating IGF-I concentrations by IGF-I infusion blunted the induction of atrogin-1/MAFbx to 6.3-fold (P < 0.05 vs. STZ diabetes without IGF-I). To further delineate the regulation of atrogin-1/MAFbx by IGF-I, we studied a model of cultured muscle cells. We observed that IGF-I produced a time- and dose-dependent reduction of atrogin-1/MAFbx mRNA, with a 50% effective dose of 5 nm IGF-I, a physiological concentration. The degradation rate of atrogin-1/MAFbx mRNA was not affected by IGF-I, suggesting that the reduction of atrogin-1/MAFbx mRNA by IGF-I is a transcriptional effect. Exposure of muscle cells in culture to dexamethasone increased atrogin-1/MAFbx mRNA with a 50% effective dose of 10 nm, a pharmacological concentration. In the presence of dexamethasone, IGF-I at physiological concentrations retained its full inhibitory effect on atrogin-1/MAFbx mRNA. We conclude that IGF-I inhibits atrogin-1/MAFbx expression and speculate that this effect might contribute to the antiproteolytic action of IGF-I in muscle.

Early activation of cardiac and renal endothelin systems in experimental heart failure

We investigated the time course of the expression of cardiac and renal endothelin systems in tachycardia-induced heart failure in dogs. Eleven beagles underwent rapid pacing at a progressively increased rate over a period of 5 wk, with a weekly clinical examination, echocardiography, measurement of circulating and urinary endothelin-1 (ET-1), and myocardial and renal tissue biopsies. Real-time quantitative PCR was used for determinations of tissue prepro-ET-1 (ppET-1), ET-1-converting enzyme (ECE-1), and ETA and ETB receptor mRNA. Cardiac and renal tissue ET-1 contents were evaluated by immunostaining and measured by radioimmunoassay at autopsy. Rapid pacing caused a progressive increase in end-systolic and end-diastolic ventricular volumes (P < 0.05) from week 2 together with a decrease in ejection fraction and in mean velocity of circumferential shortening (P < 0.05) from week 1. These changes were tightly correlated to myocardial ppET-1 and renal ETA receptor mRNA and less so to myocardial ECE-1 mRNA, and they occurred before any increase in plasma and urinary ET-1 (P < 0.05 from week 4) and clinical signs of heart failure. Renal ppET-1 did not change. Both cardiac and renal ET-1 peptide contents were increased at autopsy. We conclude that tachycardia-induced heart failure in dogs is characterized by an early activation of the cardiac and renal tissue endothelin systems, which occurs before any changes in circulating and urinary ET-1 and is closely related to altered ventricular function.

In vitro effects of oestradiol on galanin gene expression in rat anterior pituitary cells

While the pituitary galanin gene is highly responsive to oestrogen stimulation in vivo, in vitro effects of oestrogens on pituitary galanin gene expression have been less studied. We therefore examined the short-term effects of 17beta-oestradiol on galanin synthesis by dispersed rat anterior pituitary cell cultures and investigated the mechanisms by which oestrogens may modulate galanin gene expression. 17beta-oestradiol increased galanin mRNA expression in a dose-dependent manner, with a maximal increase observed at a concentration of 10-7 M. The 17beta-oestradiol (10-7 M)-induced increase in galanin mRNA expression varied from 3- to 20-fold (average 12-fold) depending upon the experiments and was also time-dependent, reaching significance after 6 h. A 1-h exposure of anterior pituitary cells to 17beta-oestradiol was sufficient to induce markedly galanin mRNA expression after 24 h (by 16-fold) and 48 h (by 25-fold). Tamoxifen administered simultaneously with or following 17beta-oestradiol treatment completely abolished the oestrogen-induced increase of galanin mRNA levels. Cycloheximide (10 microg/ml), a protein synthesis inhibitor, also blocked 17beta-oestradiol-induced galanin gene expression. Using transcription blockade by actinomycin D, we observed similar decreases of pituitary galanin mRNA concentrations, in the presence and absence of 17beta-oestradiol, implying no oestrogen effect on mRNA stability. We conclude that oestrogens stimulate rat pituitary galanin gene expression, mainly through a transcriptional mechanism, and that this effect requires persistent binding of the hormone to its nuclear receptor and newly synthesized protein intermediates.

Monoclonal antibodies to growth hormone (GH) prolong liver GH binding and GH-induced IGF-I/IGFBP-3 synthesis

This time-course study further explored the mechanisms whereby monoclonal antibodies (MAbs) may enhance growth hormone (GH) effects. Hypophysectomized rats were killed 0, 1, 3, 6, 12, 24, and 48 h after a single injection of bovine (b) GH alone or complexed with an anti-bGH MAb. Serum insulin-like growth factor I (IGF-I) concentrations were increased more and for a longer period after MAb-GH complexes (peak at 24 h: 295 +/- 24 ng/ml) than after bGH alone (peak at 12 h: 219 +/- 37 ng/ml; P < 0.01), whereas liver IGF-I mRNA was similar at 12 h in both groups but remained higher at 24 h (by 65%, P < 0.001) and 48 h (by 64%, P < 0.001) in the presence of the MAb. Induction of serum insulin-like growth factor-binding protein (IGFBP)-3 and liver IGFBP-3 mRNA by bGH also was markedly amplified by the MAb (3.6- and 2-fold at 24 h, respectively; P < 0.01). GH receptors (GHR) remained occupied for a longer period after MAb-GH injection (36 +/- 16 and 35 +/- 8% at 6 and 12 h, respectively) compared with bGH alone (0 +/- 28 and -15 +/- 11%), whereas total liver GH-binding sites and GHR mRNA levels were not affected by the MAb. We conclude that MAbs against GH amplify and prolong the serum IGF-I response to GH, which may result from both a prolongation of liver IGF-I synthesis and an enhanced induction of IGFBP-3. These two effects may in turn be the consequences of sustained GH binding to its liver receptors in the presence of MAb.

After portal branch ligation in rat, nuclear factor kappaB, interleukin-6, signal transducers and activators of transcription 3, c-fos, c-myc, and c-jun are similarly induced in the ligated and nonligated lobes

Several studies have emphasized the involvement of transcription factors, cytokines, and proto-oncogenes in initiating the regenerative process after partial hepatectomy. To assess whether these events do specifically occur in a cellular system undergoing regeneration, we studied the induction of nuclear factor kappaB (NFkappaB), interleukin-6 (IL-6), signal transducers and activators of transcription 3 (Stat3), c-fos, c-myc, c-jun, after portal branch ligation (PBL), which produces atrophy of the deprived lobes (70% of the liver parenchyma), whereas the perfused lobes undergo compensatory regeneration. Nuclear extracts and total RNA were prepared from control livers as well as from atrophying and regenerating lobes at 0.5, 1, 2, 5, and 8 after PBL. NFkappaB and Stat3 induction were studied by electrophoretic mobility shift assays and Western blotting. IL-6 and proto-oncogenes expressions were assessed by reverse transcription polymerase chain reaction and Northern blotting, respectively. Assays were also performed after a sham operation. NFkappaB and Stat3 protein expression and DNA binding were rapidly and similarly induced in nuclear extracts from the atrophying and regenerating lobes. IL-6 was elevated in both lobes from 1 to 8 hours after PBL as well as c-fos, c-myc, and c-jun during the first 2 hours. IL-6 and Stat3 but not NFkappaB were also elevated after a sham operation. These findings suggest that the cellular and molecular changes occurring early in a regenerating liver are nonspecific, possibly stress-induced, cellular responses. They do not indicate the future evolution towards atrophy or regeneration.

Continuous administration of growth hormone does not prevent the decrease of IGF-I gene expression in zinc-deprived rats despite normalization of liver GH binding

To determine the role of reduced liver GH binding (GHR) in the decreased IGF-I observed in zinc-deficient (ZD) animals, we investigated the effects of GHR restoration on growth, insulin-like growth factor I (IGF-I) and its binding proteins (IGFBPs) in ZD rats. Rats were fed for 4 weeks a zinc-deficient diet (ZD Zn, 0 ppm) or a Zinc-normal diet (pair-fed or PF; Zn, 75 ppm). ZD rats received continuous s.c. infusion of bovine growth hormone (bGH) (100 microg/d) for the 4 weeks or for the last week of the study. Compared with pair-fed rats, zinc deficiency produced attenuated weight gain (-43%, P < 0.001), lower serum IGF-I and liver IGF-I mRNA (-52%, P < 0.001 and -44%, P < 0.05), lower serum IGFBPs (IGFBP-3 -66%, IGFBP-4 -48%, 34-29 kDa IGFBP cluster -53%, P < 0.05), lower liver GHR and its mRNA (-20 and -34%, P < 0.05) and lower serum growth hormone binding protein (GHBP) and its mRNA (-56 and -48%, P < 0.05; all comparisons vs PF rats). Exogenous bGH given continuously normalized the liver GHR, serum GHBP and their liver mRNAs, as well as circulating IGFBPs. Despite restoration of GHR and GHBP to normal, growth, serum IGF-I and its liver mRNA were not stimulated by GH infusion in ZD rats, indicating that IGF-I synthesis requires the presence of zinc in addition to GH, and that the lack of growth-promoting action of GH in zinc-deprived rats results from a defect beyond GH binding to its liver receptors.

Failure of exogenous IGF-I to restore normal growth in rats submitted to dietary zinc deprivation

Dietary zinc deficiency in rats causes growth retardation associated with decreased circulating IGF-I concentrations. To investigate the potential role of low IGF-I in this condition, we attempted to reverse the growth failure by administration of exogenous IGF-I. Rats were fed for 4 weeks a zinc-deficient diet (ZD, Zn 0 ppm) or were pair-fed a zinc-normal diet (PF, Zn 75 ppm). We compared the anabolic action of recombinant human (rh) IGF-I infused at the dose of 120 microg/day for the last experimental week in ZD, PF and freely fed control (CTRL) rats. Zinc deficiency caused growth stunting (weight gain 47% of PF; P<0.001), decreased circulating IGF-I (52% of PF; P<0.01) and liver IGF-I mRNA (67% of PF; P<0.01). Serum insulin-like growth factor-binding protein-3 (IGFBP-3) assessed by ligand blot was also reduced in ZD rats (65% of PF; P<0. 01). While exogenous IGF-I increased body weight in CTRL (+12 g; P<0. 01) and PF (+7 g; not significant) animals, growth was not stimulated in ZD rats (-1.5 g) in comparison with the corresponding untreated groups. However, circulating IGF-I and IGFBP-3 levels were restored by IGF-I infusion to levels similar to those in untreated CTRL rats. In conclusion, restoration of normal circulating levels of IGF-I and IGFBP-3 by rhIGF-I infusion fails to reverse the growth retardation induced by zinc deficiency. These results suggest that growth retardation related to zinc deficiency is not only caused by low serum IGF-I concentrations, but also by inhibition of the anabolic actions of IGF-I.

Insulin inhibits glucocorticoid-induced stimulation of liver 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase gene transcription

6-Phosphofructo-2-kinase (PFK-2)/fructose-2,6-bisphosphatase (FBPase-2) catalyzes the synthesis and degradation of fructose 2,6-bisphosphate, a potent stimulator of glycolysis. Transcription of the mRNA encoding rat liver PFK-2/FBPase-2 is stimulated by insulin and by glucocorticoids in rat hepatoma cells. We show here that insulin can also prevent and reverse this glucocorticoid effect. The inhibitory effect of insulin is independent of extracellular glucose and does not require ongoing protein synthesis. We conclude that insulin exerts opposite effects on PFK-2/FBPase-2 gene transcription depending on the hormonal context.