IFN-γ does not mimic the catabolic effects of TNF-α

Main Pathogenic Mechanisms and Recent Advances in COPD Peripheral Skeletal Muscle Wasting

Chronic obstructive pulmonary disease (COPD) is a worldwide prevalent respiratory disease mainly caused by tobacco smoke exposure. COPD is now considered as a systemic disease with several comorbidities. Among them, skeletal muscle dysfunction affects around 20% of COPD patients and is associated with higher morbidity and mortality. Although the histological alterations are well characterized, including myofiber atrophy, a decreased proportion of slow-twitch myofibers, and a decreased capillarization and oxidative phosphorylation capacity, the molecular basis for muscle atrophy is complex and remains partly unknown. Major difficulties lie in patient heterogeneity, accessing patients' samples, and complex multifactorial process including extrinsic mechanisms, such as tobacco smoke or disuse, and intrinsic mechanisms, such as oxidative stress, hypoxia, or systemic inflammation. Muscle wasting is also a highly dynamic process whose investigation is hampered by the differential protein regulation according to the stage of atrophy. In this review, we report and discuss recent data regarding the molecular alterations in COPD leading to impaired muscle mass, including inflammation, hypoxia and hypercapnia, mitochondrial dysfunction, diverse metabolic changes such as oxidative and nitrosative stress and genetic and epigenetic modifications, all leading to an impaired anabolic/catabolic balance in the myocyte. We recapitulate data concerning skeletal muscle dysfunction obtained in the different rodent models of COPD. Finally, we propose several pathways that should be investigated in COPD skeletal muscle dysfunction in the future.

Cancer cachexia as a multiorgan failure: Reconstruction of the crime scene

Cachexia is a devastating syndrome associated with the end-stage of several diseases, including cancer, and characterized by body weight loss and severe muscle and adipose tissue wasting. Although different cancer types are affected to diverse extents by cachexia, about 80% of all cancer patients experience this comorbidity, which highly reduces quality of life and response to therapy, and worsens prognosis, accounting for more than 25% of all cancer deaths. Cachexia represents an urgent medical need because, despite several molecular mechanisms have been identified, no effective therapy is currently available for this devastating syndrome. Most studies focus on skeletal muscle, which is indeed the main affected and clinically relevant organ, but cancer cachexia is characterized by a multiorgan failure. In this review, we focus on the current knowledge on the multiple tissues affected by cachexia and on the biomarkers with the attempt to define a chronological pathway, which might be useful for the early identification of patients who will undergo cachexia. Indeed, it is likely that the inefficiency of current therapies might be attributed, at least in part, to their administration in patients at the late stages of cachexia.

Macrophage migration inhibitory factor contributes to immunopathogenesis during Plasmodium yoelii 17XL infection

Macrophage migration inhibitory factor (MIF) is a cytokine recognized regulator of the inflammatory immune response associated with several immune cells that produce inflammatory cytokines such as IL-1β, IL-6, IL-12, IL-18, and TNF-α. This study aimed to understand the effect of MIF on the immune response and pathogenesis during Plasmodium infection. Wild-type (Wt) and MIF knockout (Mif ^-/-) mice were intravenously infected with 1×10³ Plasmodium yoelii (Py) 17XL-parasitized red blood cells. Our data showed that Py17XL-infected Wt mice died 11 days postinfection, while Mif ^-/- mice showed reduced parasitemia and an increase in their survival at day 11 up to 58%, importantly they succumb up to day 21 postinfection. The increased survival rate in Mif ^-/- mice was associated with less severe cachexia and anemia as a result of a mixed Th1/Th2 cytokine profile, high levels of IL-12, IL-17/IL-4, and IL-10 in serum; and high levels of IL-4 and IL-10, and low levels of IFN-γ in spleen cells compared to Py17XL infected Wt mice. Moreover, macrophages (Mφs) from Mif ^-/- mice exhibited higher concentrations of IL-10 and IL-12 and reduced levels of TNF-α and nitric oxide (NO) compared to Py17XL-infected Wt mice. These results demonstrate that MIF has an important role in regulating the immune response associated with host pathogenesis and lethality, which is relevant to consider in preventing/reducing complications in Plasmodium infections.

Cervical Cancer HeLa Cell Autocrine Apoptosis Induced by Coimmobilized IFN-γ plus TNF-α Biomaterials

Using external methods to induce the death of cancer cells is recognized as one of the main strategies for cancer treatment. Research indicated that TNF-α is frequently used in tumor biotherapy while IFN-γ can directly inhibit tumor cell proliferation. In our study, TNF-α and IFN-γ were coimmobilized on polystyrene material (PSt) or Fe₃O₄-oleic acid nanoparticles (NPs). Then the structural change of these two proteins can be observed. Meanwhile, the expressions of both TNF-α and IFN-α increased significantly, as determined by gene microarray analysis; however, in the presence of TNF-α plus IFN-α inhibitors, TNF-α and IFN-α did not increase in HeLa cells induced by coimmobilized IFN-γ plus TNF-α. Our results indicate that such change can stimilate HeLa cells to secrete more TNF-α and IFN-α, by which the apoptosis of HeLa cells could be further induced. This study is the first report of autocrine-induced apoptosis of HeLa cells. In addition, we performed ELISA, RT-PCR, flow cytometry, and Western blot analyses, as well as a series of analytical tests at the animal level. our data also indicate that the PSt-coimmobilized IFN-γ plus TNF-α has apparent effects for cancer treatment in vivo, which is of great significance for translation into clinical medicine.

The Roles of CD137 Signaling in Atherosclerosis

The tumor necrosis factor receptor superfamily (TNFRSF), which includes CD40, LIGHT, and OX40, plays important roles in the initiation and progression of cardiovascular diseases, involving atherosclerosis. CD137, a member of TNFRSF, is a well-known activation-induced T cell co-stimulatory molecule and has been reported to be expressed in human atherosclerotic plaque lesions, and plays pivotal roles in mediating disease processes. In this review, we focus on and summarize recent advances in mouse studies on the involvement of CD137 signaling in the pathogenesis and plaque stability of atherosclerosis, thereby highlighting a valuable therapeutic target in atherosclerosis.

Transcriptional regulation of important cellular processes in skeletal myogenesis through interferon-γ

The purpose of the present study was to investigate the effect of interferon (IFN)-γ on the transcriptomic profile of differentiating mouse C2C12 myogenic cells. Global gene expression was evaluated using whole mouse genome oligonucleotide microarrays, and the results were validated through real-time PCR. IFN-γ (1 ng/mL) increased myoblast proliferation but decreased cell respiration and myosin heavy chain content and slightly decreased the fusion index in differentiating C2C12 cell cultures. The genes upregulated through IFN-γ were involved in cell cycle; regulation of cell proliferation; programmed cell death; chemotaxis; and cytokine, growth factor, and peptidase activity, whereas the genes downregulated through IFN-γ primarily contributed to the regulation of transcription, cell-cell signaling, nitrogen compound biosynthesis, ser/thr protein kinase signaling, and regulation of the Wnt pathway. In conclusion, IFN-γ affects the expression of numerous genes associated with the regulation of several processes in myogenesis. The effects of IFN-γ on cellular transcription include (1) alteration of cytokine/growth factor expression, promoting cell proliferation and migration but inhibiting differentiation, (2) impairment of pro-myogenic transcription, (3) disruption of cell adhesion and sarcolemma/cytoskeleton organization, and (4) increased peptidase activity leading to enhanced proteolysis and apoptosis.

Decorin mimic regulates platelet-derived growth factor and interferon-γ stimulation of vascular smooth muscle cells

Following balloon injury, smooth muscle cells (SMCs) serve as targets for many of the pro-inflammatory and pro-fibrotic factors, including platelet-derived growth factor (PDGF) and interferon-γ (IFN-γ) released from activated inflammatory cells and platelets. Previously, our lab designed a mimic of the proteoglycan decorin, termed DS-SILY20, that suppressed vascular SMC proliferation, migration, and protein synthesis in vitro, and injured vessels treated with DS-SILY20 demonstrated reduced hyperplasia in vivo. Here we characterize the effects of DS-SILY20 on modulating PDGF and IFN-γ stimulation in both proliferative and quiescent human SMCs to further evaluate the potential impact of DS-SILY20-SMC interaction on restenosis. Nanomolar dissociation constants were observed between DS-SILY20 and both PDGF and IFN-γ. PDGF significantly increased migration, proliferation, and protein and cytokine expression, as well as increased ERK-1/2 and p38 MAPK phosphorylation in both quiescent and proliferative cultures. However, DS-SILY20 inhibited these increases, presumably through sequestration of the PDGF. Consistent with the complex responses seen with IFN-γ in SMC physiology in the literature, the response of SMC cultures to IFN-γ was variable and complex. However, where increased activity was seen with IFN-γ, DS-SILY20 attenuated this activity. Overall, the results suggest that DS-SILY20 would be an ideal alternative to traditional therapeutics used and may be an effective therapy for the prevention of intimal hyperplasia after balloon angioplasty.

Characterization and regulation of mechanical loading-induced compensatory muscle hypertrophy

In mammalian systems, skeletal muscle exists in a dynamic state that monitors and regulates the physiological investment in muscle size to meet the current level of functional demand. This review attempts to consolidate current knowledge concerning development of the compensatory hypertrophy that occurs in response to a sustained increase in the mechanical loading of skeletal muscle. Topics covered include: defining and measuring compensatory hypertrophy, experimental models, loading stimulus parameters, acute responses to increased loading, hyperplasia, myofiber-type adaptations, the involvement of satellite cells, mRNA translational control, mechanotransduction, and endocrinology. The authors conclude with their impressions of current knowledge gaps in the field that are ripe for future study.

Protective effect of melatonin on TNF-α-induced muscle atrophy in L6 myotubes

Muscle atrophy, characterized by decreased cell number and size, is a serious concern for patients afflicted with inflammatory diseases. Mounting evidence indicates that tumor necrosis factor alpha (TNF-α) plays a critical role in muscle atrophy in a number of clinical settings. We hypothesize that reactive oxygen species (ROS) mediate TNF-α-induced muscle cell death and hypotrophy. Recently, melatonin has attracted attention because of its free-radical scavenging and antioxidant properties. The aim of the current study was to evaluate the possible protective role of melatonin in TNF-α-induced muscle cell death and hypotrophy in rat L6 myotubes. To examine this possible role, L6 myotubes were exposed to various concentrations of recombinant TNF-α for 24 hr. We found that TNF-α at a concentration of 100 ng/mL induced ROS generation and decreased cell viability. Further analysis revealed that apoptosis, but not autophagy, may be important for TNF-α-induced cell death. Melatonin significantly attenuated TNF-α-induced ROS generation and apoptosis. In addition, decreased muscle fiber diameter and increased muscle cell proteolysis by TNF-α was highly attenuated by treatment with melatonin. The effects of melatonin were mediated neither through its plasmalemmal receptors nor by modulating the nuclear factor kappa B pathway activated by TNF-α. Taken together, these results suggest that TNF-α may mediate ROS-induced muscle cell death and hypotrophy and that melatonin may be a useful tool for protecting against muscle atrophy stemming from inflammatory diseases.

Low Vitamin D Impairs Strength Recovery After Anterior Cruciate Ligament Surgery

The purpose of this study was to identify strength gains after an anterior cruciate ligament injury and surgery and during inflammatory challenge in participants with disparate vitamin D levels. Plasma samples were obtained from those who had not previously experienced an anterior cruciate ligament injury and from injured patients 2 weeks before and 3 months after anterior cruciate ligament surgery. Plasma 25-hydroxyvitamin D and cytokine concentrations were measured in each blood sample. Single-leg peak isometric forces were measured 2 weeks presurgery and 3 months postsurgery. Compared with noninjured participants, inflammatory cytokines were elevated prior to and following anterior cruciate ligament reconstruction. During this inflammatory challenge, the peak isometric force increases after surgery were significantly lower in those with plasma 25-hydroxyvitamin D concentrations <30 ng/mL compared with those with concentrations ≥30 ng/mL. The authors conclude that low vitamin D appears to hinder strength recovery after anterior cruciate ligament surgery and during inflammatory insult.

Gamma interferon modulates myogenesis through the major histocompatibility complex class II transactivator, CIITA

Gamma interferon (IFN-γ) is an inflammatory cytokine that has complex effects on myogenesis. Here, we show that the IFN-γ-induced inhibition of myogenesis is mediated by the major histocompatibility complex (MHC) class II transactivator, CIITA, which binds to myogenin and inhibits its activity. In IFN-γ-treated myoblasts, the inhibition of muscle-specific genes includes the expression of myogenin itself, while in myotubes, myogenin expression is unaffected. Thus, CIITA appears to act by both repressing the expression and inhibiting the activity of myogenin at different stages of myogenesis. Stimulation by IFN-γ in skeletal muscle cells induces CIITA expression as well as MHC class II gene expression. The IFN-γ-mediated repression is reversible, with myogenesis proceeding normally upon removal of IFN-γ. Through overexpression studies, we confirm that the expression of CIITA, independent of IFN-γ, is sufficient to inhibit myogenesis. Through knockdown studies, we also demonstrate that CIITA is necessary for the IFN-γ-mediated inhibition of myogenesis. Finally, we show that CIITA, which lacks DNA binding activity, is recruited to muscle-specific promoters coincident with reductions in RNA polymerase II recruitment. Thus, this work reveals how IFN-γ modulates myogenesis and demonstrates a key role for CIITA in this process.

Validation of a single biopsy approach and bolus protein feeding to determine myofibrillar protein synthesis in stable isotope tracer studies in humans

Background

Minimizing the number of muscle biopsies has important methodological implications and minimizes subject discomfort during a stable isotope amino acid infusion. We aimed to determine the reliability of obtaining a single muscle biopsy for the calculation of muscle protein fractional synthetic rate (FSR) as well as the amount of incorporation time necessary to obtain that biopsy after initiating a stable isotope infusion (Study 1). The calculation of muscle protein FSR requires tracer steady-state during the stable isotope infusion. Therefore, a second aim was to examine if steady-state conditions are compromised in the precursor pools (plasma free or muscle intracellular [IC]) after ingestion of a tracer enriched protein drink and after resistance exercise (Study 2).

Methods

Sixteen men (23 ± 3 years; BMI = 23.8 ± 2.2 kg/m², means ± SD) were randomized to perform Study 1 or Study 2 (n = 8, per study). Subjects received a primed, constant infusion of L-[ring-¹³C₆]phenylalanine coupled with muscle biopsies of the vastus lateralis to measure rates of myofibrillar protein synthesis (MPS). Subjects in Study 2 were fed 25 g of whey protein immediately after an acute bout of unilateral resistance exercise.

Results

There was no difference (P = 0.3) in rates of MPS determined using the steady-state precursor-product equation and determination of tracer incorporation between sequential biopsies 150 min apart or using plasma protein as the baseline enrichment, provided the infusion length was sufficient (230 ± 0.3 min). We also found that adding a modest amount of tracer (4% enriched), calculated based on the measured phenylalanine content of the protein (3.5%) in the drink, did not compromise steady-state conditions (slope of the enrichment curve not different from zero) in the plasma free or, more importantly, the IC pool (both P > 0.05).

Conclusions

These data demonstrate that the single biopsy approach yields comparable rates of muscle protein synthesis, provided a longer incorporation time is utilized, to that seen with a traditional two biopsy approach. In addition, we demonstrate that enriching protein-containing drinks with tracer does not disturb isotopic steady-state and thus both are reliable techniques to determine rates of MPS in humans.

Inflammation: good or bad for ADHD?

Attention deficit hyperactivity disorder (ADHD) is characterised by the typical behavioural core symptoms of inattentiveness, hyperactivity and impulsiveness. ADHD is a usually chronic health conditions, mostly diagnosed in childhood, creating a significant challenge for youth, their families and professionals who treat it. This disorder requires long-term treatments, including psychotherapeutic and pharmacological interventions, which in some cases may lead to adverse effects. Understanding the mechanism by which ADHD risk factors affect the biochemical processes in the human brain and consequentially the behaviour will help to identify novel targets for the development of therapeutics with less adverse results and better efficacy including higher responder rates. Although inflammatory responses in the brain have been recognised for years as critical in neurodegeneration and behaviour in a number of neurological and psychiatric disorders, their role for the development, treatment and prevention of ADHD has been so far largely overlooked, although historically, ADHD symptoms were initially observed in patients who survived an ONJ infection, i.e. inflammation. In this review, we discuss the interrelationship between different ADHD risk factors and inflammation with respect to the triggered molecular mechanisms and the contribution they are likely to have to this disorder. This paper provides a rationale for future studies on ADHD with an intent to inspiring the development of new agents for a more efficient management of this disorder.

The RNA editor gene ADAR1 is induced in myoblasts by inflammatory ligands and buffers stress response

Muscle atrophy remains a significant concern in multiple inflammatory conditions, including injury, sepsis, cachexia, and HIV-associated wasting. Herein, we show that inflammatory stressors, including TNF-alpha, IFN-gamma, or lipopolysaccharide, potently induced the novel expression of the RNA editor ADAR1, an observation not previously described in muscle cells. We also observed that cytokine stimulation suppressed muscle-associated microRNAs, an observation also not previously demonstrated. To map potential effects of ADAR1 induction in the muscle program, we conducted knockdown and overexpression studies in the mouse C2C12 muscle precursor cell (MPC) line and in primary human MPCs. We show that knockdown of stress-induced ADAR1 increased inflammation-mediated declines in the muscle differentiation markers Myogenin and myosin heavy chain, and knockdown reduced levels of active phosphorylated Akt (phospho-Akt), but had no effect on microRNA transcript levels, suggesting a role for ADAR1 in buffering inflammatory stress effects on myogenic transcription and protein synthesis pathways. In addition, overexpression of recombinant ADAR1 suppressed active phosphorylated double-stranded RNA (dsRNA)-dependent protein kinase (phospho-PKR), consistent with a role for ADAR1 in limiting inflammation-driven catabolic atrophy pathways. Collectively, these data identify a novel regulatory role for ADAR1 activation under inflammatory stress to both promote muscle protein synthesis pathways and limit atrophy pathways.

Insulin-like growth factor I signaling in skeletal muscle and the potential for cytokine interactions

Recent research has demonstrated that intracellular signaling components associated with several proinflammatory cytokines have the potential to interact with signaling pathways that regulate anabolic processes in skeletal muscle. This presentation and the ensuing brief review are intended to present a selection of the potential interactions between these two critical processes.

Treatment with TNF-alpha and IFN-gamma alters the activation of SER/THR protein kinases and the metabolic response to IGF-I in mouse c2c12 myogenic cells

The aim of this study was to compare the effects of TNF-alpha, IL-1beta and IFN-gamma on the activation of protein kinase B (PKB), p70(S6k), mitogen-activated protein kinase (MAPK) and p90( rsk ), and on IGF-I-stimulated glucose uptake and protein synthesis in mouse C2C12 myotubes. 100 nmol/l IGF-I stimulated glucose uptake in C2C12 myotubes by 198.1% and 10 ng/ml TNF-alpha abolished this effect. Glucose uptake in cells differentiated in the presence of 10 ng/ml IFN-gamma increased by 167.2% but did not undergo significant further modification upon the addition of IGF-I. IGF-I increased the rate of protein synthesis by 249.8%. Neither TNF-alpha nor IFN-gamma influenced basal protein synthesis, but both cytokines prevented the IGF-I effect. 10 ng/ml IL-1beta did not modify either the basal or IGF-I-dependent glucose uptake and protein synthesis. With the exception of TNF-alpha causing an 18% decrease in the level of PKB protein, the cellular levels of PKB, p70(S6k), p42(MAPK), p44(MAPK) and p90( rsk ) were not affected by the cytokines. IGF-I caused the phosphorylation of PKB (an approximate 8-fold increase above the basal value after 40 min of IGF-I treatment), p42(MAPK) (a 2.81-fold increase after 50 min), and the activation of p70(S6k) and p90( rsk ), manifesting as gel mobility retardation. In cells differentiated in the presence of TNF-alpha or IFN-gamma, this IGF-I-mediated PKB and p70(S6k) phosphorylation was significantly diminished, and the increase in p42(MAPK) and p90( rsk ) phosphorylation was prevented. The basal p42(MAPK) phosphorylation in C2C12 cells treated with IFN-gamma was high and comparable with the activation of this kinase by IGF-I. Pretreatment of myogenic cells with IL-1beta did not modify the IGF-I-stimulated phosphorylation of PKB, p70(S6k), p42(MAPK) and p90( rsk ).

IN CONCLUSION

i) TNF-alpha and IFN-gamma, but not IL-1beta, if present in the extracellular environment during C2C12 myoblast differentiation, prevent the stimulatory action of IGF-I on protein synthesis. ii) TNF-alpha- and IFN-gamma-induced IGF-I resistance of protein synthesis could be associated with the decreased phosphorylation of PKB and p70(S6k). iii) The activation of glucose uptake in C2C12 myogenic cells treated with IFN-gamma is PKB independent. iv) The similar effects of TNF-alpha and IFN-gamma on the signalling and action of IGF-I on protein synthesis in myogenic cells could suggest the involvement of both of these cytokines in protein loss in skeletal muscle.

Interleukin-1 stimulates catabolism in C2C12 myotubes

Interleukin-1 (IL-1) is an inflammatory cytokine that has been linked to muscle catabolism, a process regulated by muscle-specific E3 proteins of the ubiquitin-proteasome pathway. To address cellular mechanism, we tested the hypothesis that IL-1 induces myofibrillar protein loss by acting directly on muscle to increase expression of two critical E3 proteins, atrogin1/muscle atrophy F-box (MAFbx) and muscle RING-finger 1 (MuRF1). Experiments were conducted using mature C2C12 myotubes to eliminate systemic cytokine effects and avoid paracrine signaling by nonmuscle cell types. Time-course protocols were used to define the sequence of cellular responses. We found that atrogin1/MAFbx mRNA and MuRF1 mRNA are elevated 60-120 min after myotube exposure to either IL-1alpha or IL-1beta. These responses are preceded by signaling events that promote E3 expression. Both IL-1 isoforms stimulate phosphorylation of p38 mitogen-activated protein kinase and stimulate nuclear factor-kappaB (NF-kappaB) signaling; I-kappaB levels fall and NF-kappaB DNA binding activity increases. Other regulators of E3 expression are unaffected by IL-1 [cytosolic oxidant activity, Forkhead-O (Foxo) activity] or respond paradoxically (AKT). Chronic exposure of C2C12 myotubes over 48 h resulted in reduced myotube width and loss of sarcomeric actin. We conclude that IL-1alpha and IL-1beta act via an oxidant- and AKT/Foxo-independent mechanism to activate p38 MAPK, stimulate NF-kappaB signaling, increase expression of atrogin1/MAFbx and MuRF1, and reduce myofibrillar protein in differentiated myotubes.

Myostatin reduces Akt/TORC1/p70S6K signaling, inhibiting myoblast differentiation and myotube size

Myostatin is a negative regulator of skeletal muscle size, previously shown to inhibit muscle cell differentiation. Myostatin requires both Smad2 and Smad3 downstream of the activin receptor II (ActRII)/activin receptor-like kinase (ALK) receptor complex. Other transforming growth factor-beta (TGF-beta)-like molecules can also block differentiation, including TGF-beta(1), growth differentiation factor 11 (GDF-11), activins, bone morphogenetic protein 2 (BMP-2) and BMP-7. Myostatin inhibits activation of the Akt/mammalian target of rapamycin (mTOR)/p70S6 protein synthesis pathway, which mediates both differentiation in myoblasts and hypertrophy in myotubes. Blockade of the Akt/mTOR pathway, using small interfering RNA to regulatory-associated protein of mTOR (RAPTOR), a component of TOR signaling complex 1 (TORC1), increases myostatin-induced phosphorylation of Smad2, establishing a myostatin signaling-amplification role for blockade of Akt. Blockade of RAPTOR also facilitates myostatin's inhibition of muscle differentiation. Inhibition of TORC2, via rapamycin-insensitive companion of mTOR (RICTOR), is sufficient to inhibit differentiation on its own. Furthermore, myostatin decreases the diameter of postdifferentiated myotubes. However, rather than causing upregulation of the E3 ubiquitin ligases muscle RING-finger 1 (MuRF1) and muscle atrophy F-box (MAFbx), previously shown to mediate skeletal muscle atrophy, myostatin decreases expression of these atrophy markers in differentiated myotubes, as well as other genes normally upregulated during differentiation. These findings demonstrate that myostatin signaling acts by blocking genes induced during differentiation, even in a myotube, as opposed to activating the distinct "atrophy program." In vivo, inhibition of myostatin increases muscle creatine kinase activity, coincident with an increase in muscle size, demonstrating that this in vitro differentiation measure is also upregulated in vivo.

TNF induction of atrogin-1/MAFbx mRNA depends on Foxo4 expression but not AKT-Foxo1/3 signaling

Murine models of starvation-induced muscle atrophy demonstrate that reduced protein kinase B (AKT) function upregulates the atrophy-related gene atrogin-1/MAFbx (atrogin). The mechanism involves release of inhibition of Forkhead transcription factors, namely Foxo1 and Foxo3. Elevated atrogin mRNA also corresponds with elevated TNF in inflammatory catabolic states, including cancer and chronic heart failure. Exogenous tumor necrosis factor (TNF) increases atrogin mRNA in vivo and in vitro. We used TNF-treated C2C12 myotubes to test the hypothesis that AKT-Foxo1/3 signaling mediates TNF regulation of atrogin mRNA. Here we confirm that exposure to TNF increases atrogin mRNA (+125%). We also confirm that canonical AKT-mediated regulation of atrogin is active in C2C12 myotubes. Inhibition of phosphoinositol-3 kinase (PI3K)/AKT signaling with wortmannin reduces AKT phosphorylation (-87%) and increases atrogin mRNA (+340%). Activation with insulin-like growth factor (IGF) increases AKT phosphorylation (+126%) and reduces atrogin mRNA (-15%). Although AKT regulation is intact, our data suggest it does not mediate TNF effects on atrogin. TNF increases AKT phosphorylation (+50%) and stimulation of AKT with IGF does not prevent TNF induction of atrogin mRNA. Nor does TNF appear to signal through Foxo1/3 proteins. TNF has no effect on Foxo1/3 mRNA or Foxo1/3 nuclear localization. Instead, TNF increases nuclear Foxo4 protein (+55%). Small interfering RNA oligos targeted to two distinct regions of Foxo4 mRNA reduce the TNF-induced increase in atrogin mRNA (-34% and -32%). We conclude that TNF increases atrogin mRNA independent of AKT via Foxo4. These results suggest a mechanism by which inflammatory catabolic states may persist in the presence of adequate growth factors and nutrition.