Systemic IGF-I administration attenuates the inhibitory effect of chronic arthritis on gastrocnemius mass and decreases atrogin-1 and IGFBP-3

Role of Glucocorticoid Signaling and HDAC4 Activation in Diaphragm and Gastrocnemius Proteolytic Activity in Septic Rats

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.

Unresolved intramuscular inflammation, not diminished skeletal muscle regenerative capacity, is at the root of rheumatoid cachexia: insights from a rat CIA model

Rheumatoid arthritis targets numerous organs in patients, including the skeletal muscle, resulting in rheumatoid cachexia. In the muscle niche, satellite cells, macrophages, and myofibroblasts may be affected and the factors they release altered. This study aimed to assess these cell types, cytokines, and growth factors and their relationships to muscle fiber size and number in a rodent collagen-induced arthritis (CIA) model, in order to identify new therapeutic targets. Fiber cross-sectional area (CSA) was 57% lower in CIA than controls (p < 0.0001), thus smaller but more fibers visible per field of view. Immunostaining indicated the increased presence of satellite cells, macrophages, myofibroblasts, and myonuclei per field of view in CIA (p < 0.01), but this finding was not maintained when taking fiber number into consideration. Western blots of gastrocnemius samples indicated that tumor necrosis factor-α was significantly elevated (p < 0.01) while interleukin-10 (IL-10) was decreased (p < 0.05) in CIA. This effect was maintained (and heightened for IL-10) when expressed per fiber number. Myogenic regulatory factors (MyoD and myogenin), transforming growth factor-β and inhibitor of differentiation were significantly elevated in CIA muscle and levels correlated significantly with CSA. Several of these factors remained elevated, but bone morphogenetic protein-7 decreased when considering fiber number per area. In conclusion, CIA-muscle demonstrated a good regenerative response. Myoblast numbers per fiber were not elevated, suggesting their activity results from the persistent inflammatory signaling which also significantly hampered maintenance of muscle fiber size. A clearer picture of signaling events at cellular level in arthritis muscle may be derived from expressing data per fiber.

IGF-1 and IGFBP-3 in Inflammatory Cachexia

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.

Rheumatoid cachexia: the underappreciated role of myoblast, macrophage and fibroblast interplay in the skeletal muscle niche

Although rheumatoid arthritis affects 1% of the global population, the role of rheumatoid cachexia, which occurs in up to a third of patients, is relatively neglected as research focus, despite its significant contribution to decreased quality of life in patients. A better understanding of the cellular and molecular processes involved in rheumatoid cachexia, as well as its potential treatment, is dependent on elucidation of the intricate interactions of the cells involved, such as myoblasts, fibroblasts and macrophages. Persistent RA-associated inflammation results in a relative depletion of the capacity for regeneration and repair in the satellite cell niche. The repair that does proceed is suboptimal due to dysregulated communication from the other cellular role players in this multi-cellular environment. This includes the incomplete switch in macrophage phenotype resulting in a lingering pro-inflammatory state within the tissues, as well as fibroblast-associated dysregulation of the dynamic control of the extracellular matrix. Additional to this endogenous dysregulation, some treatment strategies for RA may exacerbate muscle wasting and no multi-cell investigation has been done in this context. This review summarizes the most recent literature characterising clinical RA cachexia and links these features to the roles of and complex communication between multiple cellular contributors in the muscle niche, highlighting the importance of a targeted approach to therapeutic intervention.

Mechanisms of IGF-1-Mediated Regulation of Skeletal Muscle Hypertrophy and Atrophy

Insulin-like growth factor-1 (IGF-1) is a key growth factor that regulates both anabolic and catabolic pathways in skeletal muscle. IGF-1 increases skeletal muscle protein synthesis via PI3K/Akt/mTOR and PI3K/Akt/GSK3β pathways. PI3K/Akt can also inhibit FoxOs and suppress transcription of E3 ubiquitin ligases that regulate ubiquitin proteasome system (UPS)-mediated protein degradation. Autophagy is likely inhibited by IGF-1 via mTOR and FoxO signaling, although the contribution of autophagy regulation in IGF-1-mediated inhibition of skeletal muscle atrophy remains to be determined. Evidence has suggested that IGF-1/Akt can inhibit muscle atrophy-inducing cytokine and myostatin signaling via inhibition of the NF-κΒ and Smad pathways, respectively. Several miRNAs have been found to regulate IGF-1 signaling in skeletal muscle, and these miRs are likely regulated in different pathological conditions and contribute to the development of muscle atrophy. IGF-1 also potentiates skeletal muscle regeneration via activation of skeletal muscle stem (satellite) cells, which may contribute to muscle hypertrophy and/or inhibit atrophy. Importantly, IGF-1 levels and IGF-1R downstream signaling are suppressed in many chronic disease conditions and likely result in muscle atrophy via the combined effects of altered protein synthesis, UPS activity, autophagy, and muscle regeneration.

Redox Status and Muscle Pathology in Rheumatoid Arthritis: Insights from Various Rat Hindlimb Muscles

Due to atrophy, muscle weakness is a common occurrence in rheumatoid arthritis (RA). The majority of human studies are conducted on the vastus lateralis muscle—a muscle with mixed fiber type—but little comparative data between multiple muscles in either rodent or human models are available. The current study therefore assessed both muscle ultrastructure and selected redox indicators across various muscles in a model of collagen-induced rheumatoid arthritis in female Sprague-Dawley rats. Only three muscles, the gastrocnemius, extensor digitorum longus (EDL), and soleus, had lower muscle mass (38%, 27%, and 25% loss of muscle mass, respectively; all at least P < 0.01), while the vastus lateralis muscle mass was increased by 35% (P < 0.01) in RA animals when compared to non-RA controls. However, all four muscles exhibited signs of deterioration indicative of rheumatoid cachexia. Cross-sectional area was similarly reduced in gastrocnemius, EDL, and soleus (60%, 58%, and 64%, respectively; all P < 0.001), but vastus lateralis (22% smaller, P < 0.05) was less affected, while collagen deposition was significantly increased in muscles. This pathology was associated with significant increases in tissue levels of reactive oxygen species (ROS) in all muscles except the vastus lateralis, while only the gastrocnemius had significantly increased levels of lipid peroxidation (TBARS) and antioxidant activity (FRAP). Current data illustrates the differential responses of different skeletal muscles of the hindlimb to a chronic inflammatory challenge both in terms of redox changes and resistance to cachexia.

Collagen-induced arthritis as an animal model of rheumatoid cachexia

BACKGROUND

Rheumatoid arthritis is characterized by chronic polyarticular synovitis and presents systemic changes that impact quality of life, such as impaired muscle function, seen in up to 66% of the patients. This can progress to severely debilitating state known as rheumatoid cachexia-without loss of fat mass and body weight-for which there is little consensus in terms of diagnosis or treatment. This study aims to evaluate whether the collagen-induced arthritis (CIA) animal model also develops clinical and functional features characteristic of rheumatoid cachexia.

METHODS

Male DBA1/J mice were randomly divided into 2 groups: healthy animals (CO, n = 11) and CIA animals (n = 13). The clinical score and edema size, animal weight and food intake, free exploratory locomotion, grip strength, and endurance exercise performance were tested 0, 18, 35, 45, 55, and 65 days after disease induction. After euthanasia, several organs, visceral and brown fat, and muscles were dissected and weighed. Muscles were used to assess myofiber diameter. Ankle joint was used to assess arthritis severity by histological score. Statistical analysis were performed using one-way and two-way analyses of variance followed by Tukey's and Bonferroni's test or t-test of Pearson and statistical difference were assumed for a P value under 0.05.

RESULTS

The CIA had significantly higher arthritis scores and larger hind paw edema volumes than CO. The CIA had decreased endurance exercise performance total time (fatigue; 23, 22, 24, and 21% at 35, 45, 55, and 65 days, respectively), grip strength (27, 55, 63, 60, and 66% at 25, 35, 45, 55, and 65 days, respectively), free locomotion (43, 57, 59, and 66% at 35, 45, 55, and 65 days, respectively), and tibialis anterior and gastrocnemius muscle weight (25 and 24%, respectively) compared with CO. Sarcoplasmic ratios were also reduced in CIA (TA: 23 and GA: 22% less sarcoplasmic ratio), confirming the atrophy of skeletal muscle mass in these animals than in CO. Myofiber diameter was also reduced 45% in TA and 41% in GA in CIA when compared with the CO. Visceral and brown fat were lighter in CIA (54 and 39%, respectively) than CO group.

CONCLUSIONS

The CIA model is a valid experimental model for rheumatoid cachexia given that the clinical changes observed were similar to those described in patients with rheumatoid arthritis.

High-Methionine Diet Attenuates Severity of Arthritis and Modulates IGF-I Related Gene Expressions in an Adjuvant Arthritis Rats Model

Rheumatoid arthritis, a synthesized form of adjuvant arthritis exhibited throughout many animal species, inhibits liver function and circulation of IGF-I and contributes to the degradation of skeletal muscle mass. One of the primary goals of the present study is determining whether a high-Methionine (high-Met) diet is capable of reducing the adverse effects of arthritis, namely, loss of body mass. Following adjuvant injection, forty arthritic rats were randomly assigned to either a control group with a basal diet or a high-Met group with the same basal diet + 0.5% Methionine. After 14 days all rats were terminated. The high-Met group exhibited an increase in body weight and food intake in comparison with the control group (P < 0.05). High-Met diet debilitated arthritis-induced surges in the gastrocnemius in both atrogin-1 and the MuRF1 expressions; however, it was observed to have little to no effect on atrogin-1 and MuRF1 gene expression in soleus. At the same time, high-Met diet rats experienced a rise in IGF-I, with lowering of IGFBP-3 gene expression in the gastrocnemius and the soleus. These data suggest that arthritis severity can be partly attenuated by high-Met diet.

Formoterol decreases muscle wasting as well as inflammation in the rat model of rheumatoid arthritis

Adjuvant-induced arthritis is an experimental model of rheumatoid arthritis that is associated with body weight loss and muscle wasting. β2-adrenergic receptor agonists are powerful anabolic agents that trigger skeletal muscle hypertrophy and have been proposed as a promising treatment for muscle wasting in human patients. The aim of this work was to determine whether formoterol, a selective β2-adrenoreceptor agonist, is able to ameliorate muscle wasting in arthritic rats. Arthritis was induced in male Wistar rats by intradermal injection of Freund's adjuvant. Control and arthritic rats were injected daily with 50 μg/kg sc formoterol or saline for 12 days. Body weight change, food intake, and arthritis index were analyzed. After euthanasia, in the gastrocnemius mRNA was analyzed by PCR, and proteins were analyzed by Western blotting. Arthritis decreased gastrocnemius weight, cross-sectional area, and myofiber size, whereas formoterol increased those variables in both arthritic and control rats. Formoterol decreased the external signs of arthritis as well as NF-κB(p65) activation, TNFα, and COX-2 levels in the gastrocnemius of arthritic and control rats. Those effects of formoterol were associated with a decreased expression of myostatin, atrogin-1, and MuRF1 and in LC3b lipidation. Arthritis increased the expression of MyoD, myogenin, IGF-I, and IGFBP-3 and -5 in the gastrocnemius. In control and in arthritic rats, treatment with formoterol increased Akt phosphorylation and myogenin levels, whereas it decreased IGFBP-3 expression in the gastrocnemius. These data suggest that formoterol has an anti-inflammatory effect and decreases muscle wasting in arthritic rats through increasing Akt activity and myogenin and decreasing myostatin, the p-NF-κB(p65)/TNF pathway, and IGFBP-3.

The melanocortin receptor type 3 agonist d-Trp(8)-γMSH decreases inflammation and muscle wasting in arthritic rats

BACKGROUND

Chronic inflammatory diseases induce cachexia that increases mortality and morbidity of the illness. Adjuvant-induced arthritis is an experimental model of rheumatoid arthritis that is associated with body weight loss and muscle wasting. Alpha-melanocyte stimulating hormone has an anti-inflammatory effect in arthritic rats and decreases muscle wasting. The aim of this work was to elucidate whether the anti-cachectic action of alpha-melanocyte stimulating hormone is mediated by the melanocortin receptor type 3 pathway.

METHODS

Arthritis was induced in male Wistar rats by intradermal injection of Freund's adjuvant, and 6 days afterwards, arthritic rats were injected with the selective melanocortin receptor type 3 agonist d-Trp(8)-gammaMSH ( d-Trp(8)-γMSH) 500 µg/kg subcutaneously. or saline twice a day, for 10 days.

RESULTS

d-Trp(8)-γMSH decreased the external signs of inflammation and body weight loss, but it was not able to modify the anorexigenic effect of arthritis or the increase in hypothalamic cyclooxygenase-2 (COX-2) expression. In contrast, d-Trp(8)-γMSH prevented arthritis-induced increase in hypothalamic IL-1β and serum corticosterone levels and the decrease in serum IGF-I levels. d-Trp(8)-γMSH treatment also prevented arthritis-induced NF-kB(p65) phosphorylation and tumour necrosis factor-α mRNA increase in the gastrocnemius. d-Trp(8)-γMSH administration to arthritic rats increased gastrocnemius mass, its cross-sectional area, and mean fast fibre area. Those effects of d-Trp(8)-γMSH were associated with a decreased expression of atrogin-1 and muscle ring-finger protein-1 in the gastrocnemius. In rats treated with saline, arthritis increased the expression of autophagy marker genes LC3b, Bnip-3, and Gabarap1 as well as the conversion of LC3b I to LC3b II by lipidation in the gastrocnemius. d-Trp(8)-γMSH decreased gastrocnemius LC3b, Bnip-3, and Gabarap1 mRNA expression and prevented the increase in LC3b II in arthritic rats.

CONCLUSION

These data suggest that d-Trp(8)-γMSH administration prevents the effect of arthritis on corticosterone and insulin-like growth factor-I serum levels and decreases muscle wasting, by down-regulating atrogenes and autophagy through modifying the NF-kB(p65)/tumour necrosis factor-α signalling transduction pathway.

Preserved skeletal muscle protein anabolic response to acute exercise and protein intake in well-treated rheumatoid arthritis patients

Introduction

Rheumatoid arthritis (RA) is often associated with diminished muscle mass, reflecting an imbalance between protein synthesis and protein breakdown. To investigate the anabolic potential of both exercise and nutritional protein intake we investigated the muscle protein synthesis rate and anabolic signaling response in patients with RA compared to healthy controls.

Methods

Thirteen RA patients (age range 34–84 years; diagnosed for 1–32 years, median 8 years) were individually matched with 13 healthy controls for gender, age, BMI and activity level (CON). Plasma levels of C-reactive protein (CRP), interleukin (IL)-6 and tumor necrosis factor (TNF)-α were measured using enzyme-linked immunosorbent assay (ELISA) in resting blood samples obtained on two separate days. Skeletal muscle myofibrillar and connective tissue protein fractional synthesis rate (FSR) was measured by incorporation of the amino acid ¹³C₆-phenylalanine tracer in the overnight fasted state for 3 hours (BASAL) and 3 hours after intake of whey protein (0.5 g/kg lean body mass) alone (PROT, 3 hrs) and in combination with knee-extensor exercise (EX) with one leg (8 × 10 reps at 70 % of 1RM; PROT + EX, 3 hrs). Expression of genes related to inflammatory signaling, myogenesis and muscle growth/atrophy were analyzed by real-time reverse transcriptase-polymerase chain reaction (RT-PCR).

Results

CRP was significantly higher in the RA patients (2.25 (0.50) mg/l) than in controls (1.07 (0.25) mg/l; p = 0.038) and so was TNF-α (RA 1.18 (0.30) pg/ml vs. CON 0.64 (0.07) pg/ml; p = 0.008). Muscle myofibrillar protein synthesis in both RA patients and CON increased in response to PROT and PROT + EX, and even more with PROT + EX (p < 0.001), with no difference between groups (p > 0.05). The gene expression response was largely similar in RA vs. CON, however, expression of the genes coding for TNF-α, myogenin and HGF1 were more responsive to exercise in RA patients than in CON.

Conclusions

The study demonstrates that muscle protein synthesis rate and muscle gene expression can be stimulated by protein intake alone and in combination with physical exercise in patients with well-treated RA to a similar extent as in healthy individuals. This indicates that moderately inflamed RA patients have maintained their muscle anabolic responsiveness to physical activity and protein intake.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0758-3) contains supplementary material, which is available to authorized users.

Chronic exposure to cigarette smoke causes extrapulmonary abnormalities in rats

Pathophysiological features of chronic obstructive pulmonary disease (COPD) include systemic abnormalities, such as weight loss and skeletal muscle wasting. Although cigarette smoke (CS) is a major risk factor in COPD, the systemic effects of CS exposure remain to be elucidated. In this study, rats were exposed to CS or smoke-free air for 12 weeks. CS-exposed rats developed emphysema and had significantly lower body weight and food intake than control rats. The plasma ghrelin levels significantly increased with an upregulation of gastric ghrelin mRNA expression induced by CS exposure. Further, we observed low plasma insulin-like growth factor-1 levels and high tumor necrosis factor-α levels. A significant reduction of skeletal muscle strength and an increase in the mRNA expression of catabolic factors was observed in CS-exposed rats. These results indicated that chronic CS exposure induced not only pulmonary emphysema but also systemic abnormalities related to muscle catabolism associated with inflammatory responses.

Muscle wasting in collagen-induced arthritis and disuse atrophy

The mechanisms of muscle wasting and decreased mobility have a major functional effect in rheumatoid arthritis, but they have been poorly studied. The objective of our study is to describe muscular involvement and the pathways in an experimental model of arthritis compared to the pathways in disuse atrophy. Female Wistar rats were separated into three groups: control (CO), collagen-induced arthritis (CIA), and immobilized (IM). Spontaneous locomotion and weight were evaluated weekly. The gastrocnemius muscle was evaluated by histology and immunoblotting to measure the expression of myostatin (a negative regulator), LC3 (autophagy), MuRF-1 (proteasome-mediated proteolysis), MyoD, and myogenin (satellite-cell activation). The significance level was set at P < 0.05, and histological analysis of joints confirmed the severity of the arthropathy. There was a significant difference in spontaneous locomotion in the CIA group. Animal body weight, gastrocnemius muscle weight, and relative muscle weight decreased 20%, 30%, and 20%, respectively, in the CIA rats. Inflammatory infiltration and swelling were present in the gastrocnemius muscles of the CIA rats. The mean cross-sectional area was reduced by 30% in the CIA group and by 60% in the IM group. The expressions of myostatin and LC3 between the groups were similar. There was increased expression of MuRF-1 in the IM (1.9-fold) and CIA (3.1-fold) groups and of myogenin in the muscles of the CIA animals (1.7-fold), while MyoD expression was decreased in the IM (20%) rats. This study demonstrated that the development of experimental arthritis is associated with decreased mobility, body weight, and muscle loss. Both IM and CIA animal models presented muscle atrophy, but while proteolysis and the regeneration pathways were activated in the CIA model, there was no activation of regeneration in the IM model. We can assume that muscle atrophy in experimental arthritis is associated with the disease itself and not simply with decreased mobility.

The therapeutic potential of IGF-I in skeletal muscle repair

Skeletal muscle loss due to aging, motor-neuron degeneration, cancer, heart failure, and ischemia is a serious condition for which currently there is no effective treatment. Insulin-like growth factor 1 (IGF-I) plays an important role in muscle maintenance and repair. Preclinical studies have shown that IGF-I is involved in increasing muscle mass and strength, reducing degeneration, inhibiting the prolonged and excessive inflammatory process due to toxin injury, and increasing the proliferation potential of satellite cells. However, clinical trials have not been successful due to ineffective delivery methods. Choosing the appropriate isoforms or peptides and developing targeted delivery techniques can resolve this issue. Here we discuss the latest development in the field with special emphasis on novel therapeutic approaches.

Lopinavir/Ritonavir Impairs Physical Strength in Association with Reduced Igf1 Expression in Skeletal Muscle of Older Mice

Background

Late-middle age HIV patients are prone to fatigue despite effective viral control by antiretroviral therapies. Rodent models to recapitulate this phenotype are still not available.

Hypothesis

Drug treatment may compromise muscle strength and physical performance more in older individuals with pre-existing metabolic disorders than normal young ones.

Methods

Kaletra was given to overweight male mice at late-middle age and normal young adults; both on a rodent diet containing 30% fat calorie. Body composition and grip strength were measured at baseline and after drug treatment. Rota-rod running, insulin and glucose tolerance were measured at the end of the experiment. Drug effect on metabolic activity and spontaneous movements were assessed using the metabolic cage system. Representative muscle and fat tissue were analyzed for protein and mRNA expression. Selected findings were tested using murine C2C12 myotubes.

Results

Kaletra reduced grip strength in both young and older mice but impaired rotarod performance only in the old. Spontaneous movements were also reduced in Kaletra-treated old mice. Kaletra reduced IGF-1 expression in all muscle groups tested for the old and in cultured myotubes but to a less extent in the muscle of young animals. Reduced IGF-1 expression correlated with increased expression of muscle-specific atrogene MAFbx and MuRF1. Kaletra also increased abdominal fat mass markedly in the old animals and to a less extend in the young.

Conclusion

Long-term Kaletra intake aggravated abdominal obesity and impaired muscle strength. This effect was worse in older animals than in normal young adults.

Fenofibrate administration to arthritic rats increases adiponectin and leptin and prevents oxidative muscle wasting

Chronic inflammation induces skeletal muscle wasting and cachexia. In arthritic rats, fenofibrate, a peroxisome proliferator-activated receptor α (PPARα (PPARA)) agonist, reduces wasting of gastrocnemius, a predominantly glycolytic muscle, by decreasing atrogenes and myostatin. Considering that fenofibrate increases fatty acid oxidation, the aim of this study was to elucidate whether fenofibrate is able to prevent the effect of arthritis on serum adipokines and on soleus, a type I muscle in which oxidative metabolism is the dominant source of energy. Arthritis was induced by injection of Freund's adjuvant. Four days after the injection, control and arthritic rats were gavaged daily with fenofibrate (300 mg/kg bw) or vehicle over 12 days. Arthritis decreased serum leptin, adiponectin, and insulin (P<0.01) but not resistin levels. In arthritic rats, fenofibrate administration increased serum concentrations of leptin and adiponectin. Arthritis decreased soleus weight, cross-sectional area, fiber size, and its Ppar α mRNA expression. In arthritic rats, fenofibrate increased soleus weight, fiber size, and Ppar α expression and prevented the increase in Murf1 mRNA. Fenofibrate decreased myostatin, whereas it increased MyoD (Myod1) and myogenin expressions in the soleus of control and arthritic rats. These data suggest that in oxidative muscle, fenofibrate treatment is able to prevent arthritis-induced muscle wasting by decreasing Murf1 and myostatin expression and also by increasing the myogenic regulatory factors, MyoD and myogenin. Taking into account the beneficial action of adiponectin on muscle wasting and the correlation between adiponectin and soleus mass, part of the anticachectic action of fenofibrate may be mediated through stimulation of adiponectin secretion.

Short-term growth hormone or IGF-I administration improves the IGF-IGFBP system in arthritic rats

OBJECTIVE

Adjuvant-induced arthritis is an experimental model of rheumatoid arthritis that inhibits the GH-IGF-I axis and decreases body weight gain and muscle mass. Although chronic GH or IGF-I treatment increases body weight gain in arthritic rats, muscle resistance to GH and IGF-I is a very common complication in inflammatory diseases. In this study we examine the effect of short-term administration of rhGH and rhIGF-I on liver and muscle IGF-I, IGFBP-3 and -5 as well as on the ubiquitin-ligases MuRF1 and atrogin-1 in the muscle of arthritic rats.

DESIGN

Arthritis was induced in adult male Wistar rats by an intradermal injection of 4 mg of Freund's adjuvant. Fifteen days after adjuvant injection, 300 μg/kg of rhGH or 200 μg/kg of rhIGF or saline was administrated 18 and 3h before decapitation. A pair-fed group injected with saline was included in order to discard a possible effect of decreased food intake. Gene expression of IGF-I, GHR, IGFBP-3, IGFBP-5, atrogin-1 and MuRF1 were quantified using RT-PCR. In serum, IGF-I was measured by radioimmunoassay (RIA) and IGFBP-3 by ligand blot.

RESULTS

Arthritis decreased serum IGF-I and IGF mRNA in liver (P<0.05), but not in skeletal muscle. In arthritic rats, rhGH increased serum IGF-I and liver IGF-I mRNA similar to the levels of pair-fed rats. Arthritis increased atrogin-1, MuRF1, IGFBP-3 and IGFBP-5 mRNA in muscle (P<0.01). IGFBP-3 mRNA was downregulated by rhIGF-I, but not by rhGH, administration in control and arthritic rats (P<0.05). Administration of rhGH and rhIGF-I increased IGFBP-5 in the gastrocnemius of arthritic rats.

CONCLUSIONS

Short-term rhGH and rhIGF-I administration was found to increase muscle IGFBP-5 mRNA, whereas only rhIGF-I administration decreased muscle IGFBP-3 mRNA in control and arthritic rats. These data suggest that arthritis does not induce GH or IGF-I resistance in skeletal muscle.

Molecular mechanisms of cachexia in chronic disease

Cachexia is a metabolic syndrome that manifests with excessive weight loss and disproportionate muscle wasting. It is related to many different chronic diseases, such as cancer, infections, liver disease, inflammatory bowel disease, cardiac disease, chronic obstructive pulmonary disease, chronic renal failure and rheumatoid arthritis. Cachexia is linked with poor outcome for the patients. In this article, we explore the role of the hypothalamus, liver, muscle tissue and adipose tissue in the pathogenesis of this syndrome, particularly concentrating on the role of cytokines, hormones and cell energy-controlling pathways (such as AMPK, PI3K/Akt and mTOR). We also look at possible future directions for therapeutic strategies.

Comparison of the effects of the n-3 polyunsaturated fatty acid eicosapentaenoic and fenofibrate on the inhibitory effect of arthritis on IGF1

Adjuvant-induced arthritis is a chronic inflammatory illness that induces muscle wasting and decreases circulating IGF1. Eicosapentaenoic acid (EPA) and fenofibrate, a peroxisome proliferator-activated receptors α agonist, have anti-inflammatory actions and ameliorate muscle wasting in arthritic rats. The aim of this work was to elucidate whether EPA and fenofibrate administration are able to prevent the effect of arthritis on the IGF1-IGFBP system. On day 4 after adjuvant injection control, arthritic rats were gavaged with EPA (1 g/kg) or fenofibrate (300 mg/kg) until day 15 when all rats were killed. Arthritis decreased body weight gain, serum IGF1, and liver Igf1 mRNA, whereas it increased gastrocnemius Igfbp3 mRNA. EPA, but not fenofibrate, administration prevented arthritis-induced decrease in serum IGF1 and liver Igf1 mRNA. In the rats treated with EPA arthritis increased Igfbp5 mRNA in the gastrocnemius. Fenofibrate treatment decreased IGF1 and Igf1 mRNA in the liver and gastrocnemius. In arthritic rats, fenofibrate increased body weight gain and decreased gastrocnemius Igfbp3 and Igfbp5 mRNA. These data suggest that the mechanisms through which EPA and fenofibrate act on the IGF1 system and ameliorate muscle wasting in arthritic rats are different. EPA administration increased circulating levels of IGF1, whereas fenofibrate decreased the Igfbp3 and Igfbp5 in the gastrocnemius muscle.

Fenofibrate, a PPAR{alpha} agonist, decreases atrogenes and myostatin expression and improves arthritis-induced skeletal muscle atrophy

Arthritis is a chronic inflammatory illness that induces cachexia, which has a direct impact on morbidity and mortality. Fenofibrate, a selective PPARα activator prescribed to treat human dyslipidemia, has been reported to decrease inflammation in rheumatoid arthritis patients. The aim of this study was to elucidate whether fenofibrate is able to ameliorate skeletal muscle wasting in adjuvant-induced arthritis, an experimental model of rheumatoid arthritis. On day 4 after adjuvant injection, control and arthritic rats were treated with 300 mg/kg fenofibrate until day 15, when all rats were euthanized. Fenofibrate decreased external signs of arthritis and liver TNFα and blocked arthritis-induced decreased in PPARα expression in the gastrocnemius muscle. Arthritis decreased gastrocnemius weight, which results from a decrease in cross-section area and myofiber size, whereas fenofibrate administration to arthritic rats attenuated the decrease in both gastrocnemius weight and fast myofiber size. Fenofibrate treatment prevented arthritis-induced increase in atrogin-1 and MuRF1 expression in the gastrocnemius. Neither arthritis nor fenofibrate administration modify Akt-FoxO3 signaling. Myostatin expression was not modified by arthritis, but fenofibrate decreased myostatin expression in the gastrocnemius of arthritic rats. Arthritis increased muscle expression of MyoD, PCNA, and myogenin in the rats treated with vehicle but not in those treated with fenofibrate. The results indicate that, in experimental arthritis, fenofibrate decreases skeletal muscle atrophy through inhibition of the ubiquitin-proteasome system and myostatin.