Regulation of the intracellular localization of Foxo3a by stress-activated protein kinase signaling pathways in skeletal muscle cells

[Pathophysiology of skeletal muscle during sepsis]

While sepsis mortality is reducing in developed countries due to advances in intensive care medicine, morbidity is increasing due to aging and obesity. ICU-acquired weakness (ICU-AW) is a respiratory and limb muscle weakness experienced by many sepsis survivors and is present in 50-75% of sepsis patients. ICU-AW can persist for several years, making reintegration of sepsis survivors difficult and leading to a secondary decrease in long-term survival. Exposure of septic patients to multiple muscle-damaging factors during ICU admission, including hyperglycemia, immobility, mechanical ventilation, administration of muscle relaxants, and administration of steroidal anti-inflammatory drugs, may compound the hyper cytokine, hyper nitric oxide, and hyper oxidative conditions, leading to the development of ICU-AW. However, the pathogenesis of ICU-AW remains unclear, and the pathophysiology of ICU-AW awaits further elucidation to develop therapeutic strategies. Recent ICU-AW studies have also revealed that skeletal muscle itself is a key organ in the inflammatory response and metabolic abnormalities in sepsis. In this article, we review the pathophysiology of skeletal muscle in sepsis and international trends in the development of therapeutic agents based on our research results.

Hesperidin Ameliorates Sarcopenia through the Regulation of Inflammaging and the AKT/mTOR/FoxO3a Signaling Pathway in 22-26-Month-Old Mice

Faced with a globally aging society, the maintenance of health and quality of life in older people is very important. The age-related loss of muscle mass and strength, known as sarcopenia, severely reduces quality of life and increases the risks of various diseases. In this study, we investigated the inhibitory effect of hesperidin (HES) on inflammaging, with the intention of evaluating its potential use as a treatment for sarcopenia. We studied 22-26-month-old mice, corresponding to humans aged ≥70 years, with aging-related sarcopenia, and young mice aged 3-6 months. The daily administration of HES for 8 weeks resulted in greater muscle mass and strength and increased the fiber size of the old mice. HES also restored the immune homeostasis that had been disrupted by aging, such as the imbalance in M1/M2 macrophage ratio. In addition, we found that HES ameliorated the sarcopenia by regulating AKT/mammalian target of rapamycin/forkhead box 3a signaling through an increase in insulin-like growth factor (IGF)-1 expression in the old mice. Therefore, HES represents a promising candidate inhibitor of sarcopenia in older people, and its effects are achieved through the maintenance of immune homeostasis.

Mesenchymal stem cells alleviate dexamethasone-induced muscle atrophy in mice and the involvement of ERK1/2 signalling pathway

BACKGROUND

High dosage of dexamethasone (Dex) is an effective treatment for multiple diseases; however, it is often associated with severe side effects including muscle atrophy, resulting in higher risk of falls and poorer life quality of patients. Cell therapy with mesenchymal stem cells (MSCs) holds promise for regenerative medicine. In this study, we aimed to investigate the therapeutic efficacy of systemic administration of adipose-derived mesenchymal stem cells (ADSCs) in mitigating the loss of muscle mass and strength in mouse model of DEX-induced muscle atrophy.

METHODS

3-month-old female C57BL/6 mice were treated with Dex (20 mg/kg body weight, i.p.) for 10 days to induce muscle atrophy, then subjected to intravenous injection of a single dose of ADSCs ([Formula: see text] cells/kg body weight) or vehicle control. The mice were killed 7 days after ADSCs treatment. Body compositions were measured by animal DXA, gastrocnemius muscle was isolated for ex vivo muscle functional test, histological assessment and Western blot, while tibialis anterior muscles were isolated for RNA-sequencing and qPCR. For in vitro study, C2C12 myoblast cells were cultured under myogenic differentiation medium for 5 days following 100 [Formula: see text]M Dex treatment with or without ADSC-conditioned medium for another 4 days. Samples were collected for qPCR analysis and Western blot analysis. Myotube morphology was measured by myosin heavy chain immunofluorescence staining.

RESULTS

ADSC treatment significantly increased body lean mass (10-20%), muscle wet weight (15-30%) and cross-sectional area (CSA) (~ 33%) in DEX-induced muscle atrophy mice model and down-regulated muscle atrophy-associated genes expression (45-65%). Hindlimb grip strength (~ 37%) and forelimb ex vivo muscle contraction property were significantly improved (~ 57%) in the treatment group. Significant increase in type I fibres (~ 77%) was found after ADSC injection. RNA-sequencing results suggested that ERK1/2 signalling pathway might be playing important role underlying the beneficial effect of ADSC treatment, which was confirmed by ERK1/2 inhibitor both in vitro and in vivo.

CONCLUSIONS

ADSCs restore the pathogenesis of Dex-induced muscle atrophy with an increased number of type I fibres, stronger muscle strength, faster recovery rate and more anti-fatigue ability via ERK1/2 signalling pathway. The inhibition of muscle atrophy-associated genes by ADSCs offered this treatment as an intervention option for muscle-associated diseases. Taken together, our findings suggested that adipose-derived mesenchymal stem cell therapy could be a new treatment option for patient with Dex-induced muscle atrophy.

Mitochondrial transplantation as a possible therapeutic option for sarcopenia

With advancing age, the skeletal muscle phenotype is characterized by a progressive loss of mass, strength, and quality. This phenomenon, known as sarcopenia, has a negative impact on quality of life and increases the risk of morbidity and mortality in older adults. Accumulating evidence suggests that damaged and dysfunctional mitochondria play a critical role in the pathogenesis of sarcopenia. Lifestyle modifications, such as physical activity, exercise, and nutrition, as well as medical interventions with therapeutic agents, are effective in the management of sarcopenia and offer solutions to maintain and improve skeletal muscle health. Although a great deal of effort has been devoted to the identification of the best treatment option, these strategies are not sufficient to overcome sarcopenia. Recently, it has been reported that mitochondrial transplantation may be a possible therapeutic approach for the treatment of mitochondria-related pathological conditions such as ischemia, liver toxicity, kidney injury, cancer, and non-alcoholic fatty liver disease. Given the role of mitochondria in the function and metabolism of skeletal muscle, mitochondrial transplantation may be a possible option for the treatment of sarcopenia. In this review, we summarize the definition and characteristics of sarcopenia and molecular mechanisms associated with mitochondria that are known to contribute to sarcopenia. We also discuss mitochondrial transplantation as a possible option. Despite the progress made in the field of mitochondrial transplantation, further studies are needed to elucidate the role of mitochondrial transplantation in sarcopenia. KEY MESSAGES: Sarcopenia is the progressive loss of skeletal muscle mass, strength, and quality. Although the specific mechanisms that lead to sarcopenia are not fully understood, mitochondria have been identified as a key factor in the development of sarcopenia. Damaged and dysfunctional mitochondria initiate various cellular mediators and signaling pathways, which largely contribute to the age-related loss of skeletal muscle mass and strength. Mitochondrial transplantation has been reported to be a possible option for the treatment/prevention of several diseases. Mitochondrial transplantation may be a possible therapeutic option for improving skeletal muscle health and treating sarcopenia. Mitochondrial transplantation as a possible treatment option for sarcopenia.

Mealworm Ethanol Extract Enhances Myogenic Differentiation and Alleviates Dexamethasone-Induced Muscle Atrophy in C2C12 Cells

Aging, and other disease-related muscle disorders are serious health problems. Dexamethasone (DEX), a synthetic glucocorticoid, can trigger skeletal muscle atrophy. This study examined the effects of mealworm (Tenebrio molitor larva) ethanol extract (TME) on C2C12 myoblast differentiation and DEX-induced myotube atrophy. TME induced myotube formation compared to the differentiation medium (DM) group. TME also significantly increased the mRNA expression of muscle creatine kinase (CKm) and myogenic regulatory factors (MRFs), such as myogenin (MyoG), myogenic factor (Myf)5, and MRF4 (Myf6). TME dramatically increased the muscle-specific protein, MyoG, compared to the control, whereas the expression of myogenic differentiation 1 (MyoD) remained unchanged. It also activated the mammalian target of rapamycin (mTOR) signaling pathway. In the DEX-induced muscle atrophy C2C12 model, TME reduced the gene expression of atrogin-1, muscle RING finger protein-1 (MuRF-1), and myostatin, which are involved in protein degradation in skeletal muscles. Furthermore, TME elevated the phosphorylation of forkhead box O3 (FoxO3α) and protein kinase B (Akt). These findings suggest that TME can enhance myotube hypertrophy by regulating the mTOR signaling pathway, and can rescue DEX-induced muscle atrophy by alleviating atrophic muscle markers mediated by Akt activation. Thus, TME can be a potential therapeutic agent for treating muscle weakness and atrophy.

Exercise Training Attenuates Ovariectomy-Induced Alterations in Skeletal Muscle Remodeling, Apoptotic Signaling, and Atrophy Signaling in Rat Skeletal Muscle

PURPOSE

The effects of aerobic exercise training on soleus muscle morphology, mitochondria-mediated apoptotic signaling, and atrophy/hypertrophy signaling in ovariectomized rat skeletal muscle were investigated.

METHODS

Female Sprague-Dawley rats were divided into control (CON), ovariectomy (OVX), and ovariectomy plus exercise (OVX+EX) groups. After ovarian excision, exercise training was performed using a rat treadmill at 20 m/min, 50 min/day, 5 days/week for 12 weeks. Protein levels of mitochondria-mediated apoptotic signaling and atrophy/hypertrophy signaling in the skeletal muscle (soleus) were examined through western immunoblot analysis.

RESULTS

The number of myocytes and myocyte cross-sectional area (CSA) were increased and the extramyocyte space was decreased in the OVX group compared to those in the CON group. However, aerobic exercise training significantly increased myocyte CSA and decreased extramyocyte space in the OVX+EX group compared to those in the OVX group. The protein levels of proapoptotic signaling and muscle atrophy signaling were significantly increased, whereas the protein levels of muscle hypertrophy signaling were significantly decreased in the OVX group compared to that in the CON group. Aerobic exercise training significantly decreased the protein levels of proapoptotic signaling and increased the protein level of antiapoptotic protein in the OVX+EX group compared to that in the OVX group. Aerobic exercise training significantly increased the protein levels of hypertrophy signaling and decreased protein levels of atrophy signaling in the OVX+EX group compared to those in the OVX group.

CONCLUSION

Treadmill exercise improved estrogen deficiency-induced impairment in skeletal muscle remodeling, mitochondria-mediated apoptotic signaling, and atrophy/hypertrophy signaling in skeletal muscle.

Role of Pannexin 1 ATP-Permeable Channels in the Regulation of Signaling Pathways during Skeletal Muscle Unloading

Skeletal muscle unloading results in atrophy. We hypothesized that pannexin 1 ATP-permeable channel (PANX1) is involved in the response of muscle to unloading. We tested this hypothesis by blocking PANX1, which regulates efflux of ATP from the cytoplasm. Rats were divided into six groups (eight rats each): non-treated control for 1 and 3 days of the experiments (1C and 3C, respectively), 1 and 3 days of hindlimb suspension (HS) with placebo (1H and 3H, respectively), and 1 and 3 days of HS with PANX1 inhibitor probenecid (PRB; 1HP and 3HP, respectively). When compared with 3C group there was a significant increase in ATP in soleus muscle of 3H and 3HP groups (32 and 51%, respectively, p < 0.05). When compared with 3H group, 3HP group had: (1) lower mRNA expression of E3 ligases MuRF1 and MAFbx (by 50 and 38% respectively, p < 0.05) and MYOG (by 34%, p < 0.05); (2) higher phosphorylation of p70S6k and p90RSK (by 51 and 35% respectively, p < 0.05); (3) lower levels of phosphorylated eEF2 (by 157%, p < 0.05); (4) higher level of phosphorylated GSK3β (by 189%, p < 0.05). In conclusion, PANX1 ATP-permeable channels are involved in the regulation of muscle atrophic processes by modulating expression of E3 ligases, and protein translation and elongation processes during unloading.

Molecular Dynamics Simulations of Human FOXO3 Reveal Intrinsically Disordered Regions Spread Spatially by Intramolecular Electrostatic Repulsion

The human transcription factor FOXO3 (a member of the 'forkhead' family of transcription factors) controls a variety of cellular functions that make it a highly relevant target for intervention in anti-cancer and anti-aging therapies. FOXO3 is a mostly intrinsically disordered protein (IDP). Absence of knowledge of its structural properties outside the DNA-binding domain constitutes a considerable obstacle to a better understanding of structure/function relationships. Here, I present extensive molecular dynamics (MD) simulation data based on implicit solvation models of the entire FOXO3/DNA complex, and accelerated MD simulations under explicit solvent conditions of a central region of particular structural interest (FOXO3^120-530). A new graphical tool for studying and visualizing the structural diversity of IDPs, the Local Compaction Plot (LCP), is introduced. The simulations confirm the highly disordered nature of FOXO3 and distinguish various degrees of folding propensity. Unexpectedly, two 'linker' regions immediately adjacent to the DNA-binding domain are present in a highly extended conformation. This extended conformation is not due to their amino acid composition, but rather is caused by electrostatic repulsion of the domains connected by the linkers. FOXO3 is thus an IDP present in an unusually extended conformation to facilitate interaction with molecular interaction partners.

Exosomal microRNAs in cancer-related sarcopenia: Tumor-derived exosomal microRNAs in muscle atrophy

Cancer-associated sarcopenia is a complex metabolic syndrome marked by muscle mass wasting. Muscle wasting is a serious complication that is a primary contributor to cancer-related mortality. The underlying molecular mechanisms of cancer-associated sarcopenia have not been completely described to date. In general, evidence shows that the main pathophysiological alterations in sarcopenia are associated with the degradation of cellular components, an exceptional inflammatory secretome and mitochondrial dysfunction. Importantly, we highlight the prospect that several miRNAs carried by tumor-derived exosomes that have shown the ability to promote inflammatory secretion, activate catabolism, and even participate in the regulation of cellular degradation pathways can be delivered to and exert effects on muscle cells. In this review, we aim to describe the current knowledge about the functions of exosomal miRNAs in the induction of cancer-associated muscle wasting and propose potential treatment strategies.

Inhibition of mitochondrial and cytosolic calpain attenuates atrophy in myotubes co-cultured with colon carcinoma cells

Cancer cachexia is a life-threatening syndrome characterized by muscle atrophy. Cancer cachectic muscle atrophy (CCMA) is associated with mitochondrial injury. Mitochondrial calpains have been reported to induce mitochondrial injury in mouse cardiomyocytes and pulmonary smooth muscle. In the present study, the presence of calpain in the mitochondria of skeletal muscle and its potential role in CCMA were investigated. Transwell plates were used to develop a myotube-carcinoma cell co-culture model to simulate the cancer cachexia environment in vitro. The calpain inhibitors, calpastatin (CAST) and calpeptin (CAPT), were used to inhibit calpain activity in myotubes during co-culture. Calpain-1, calpain-2 and CAST were found to be present in mouse myotube mitochondria. Co-culture activated calpain in both cytoplasm and mitochondria, which caused myotube atrophy. CAST and CAPT treatment prevented calpain activation in both cytoplasm and mitochondria, which inhibited myotube atrophy during co-culture. Additionally, CAST and CAPT treatment increased mitochondrial complex I activity, decreased mitochondrial permeability transition pore opening and improved mitochondrial membrane potential in myotubes during co-culture. In addition, CAST and CAPT treatment increased AKT/mTOR activity, inhibited FoxO3a activity and decreased atrogin-1 content in myotubes during co-culture. The present findings provide new insights to understand the mechanism of CCMA and further help the development of focused approaches to treat CCMA by manipulating the mitochondrial and cytosolic calpain activity.

Acylated and unacylated ghrelin relieve cancer cachexia in mice through multiple mechanisms

Cancer cachexia is a wasting syndrome resulting from decreased protein synthesis and increased protein degradation. Calpain-dependent cleavage of myofilament is the initial step of myofilament degradation and plays a critical role in muscle atrophy. Ghrelin is a multifunctional hormone known to improve protein synthesis and inhibit protein degradation. However, its mechanism of action is not fully understood. Here we investigated whether acylated ghrelin (AG) and unacylated ghrelin (UnAG) could protect against cancer cachexia in mice bearing CT26 colorectal adenocarcinoma. We found for the first time that both AG and UnAG could inhibit calpain activity in skeletal muscle of cancer cachectic mice. AG and UnAG also improved tumor-free body weight, grip strength, muscle mass, epididymal fat mass, and nutritional state in tumor-bearing (TB) mice. Moreover, AG and UnAG reduced serum tumor necrosis factor-± concentration, increased Akt activity, and downregulated atrogin-1 expression in TB mice. Our results may contribute to the development of an AG/UnAG-based therapy for cancer cachexia.

In vitro activation of ovarian cortex and autologous transplantation: A novel approach to primary ovarian insufficiency and diminished ovarian reserve

BACKGROUND

Primary ovarian insufficiency (POI) and diminished ovarian reserve are two conditions that affect women’s fertility. Oocyte donation remains an option for these patients; however, the development of certain novel technologies, such as in vitro activation of ovarian cortex (IVA), enables the possibility of activating the pool of resting primordial follicles, increasing the chance of pregnancy.

OBJECTIVE AND RATIONALE

Here, we review the main pathways (PI3K and Hippo signaling) that govern the activation of primordial follicles and its application through the development of culture systems that support ovarian cortex for autologous transplantation. We also review the available data from case reports regarding outcomes of pregnancy and live birth rates with IVA.

SEARCH METHODS

A PubMed search was conducted using the PubMed-NCBI database to identify literature pertinent to the pathways involved in the activation of primordial follicles and the outcomes of IVA techniques from 2013 to the present.

OUTCOMES

Women with POI have around a 5% chance of spontaneous pregnancy. Recently, novel techniques involving the activation of primordial follicles through molecular pathways have been developed, thus increasing the odds of these patients. More recently, the introduction of a drug-free IVA technique has shown to increase the number of antral follicles with successful oocyte maturation after gonadotropin treatment, reaching pregnancy rates over 30%, either through spontaneous conception or by the implementation of assisted reproductive technology.

LIMITATIONS

The evidence of this review is based on a few small series, so data should be interpreted with caution, and only randomized controlled trials could estimate the real magnitude and success of the procedure.

REASONS FOR CAUTION

IVA technique remains an experimental strategy, with limited available data and the requirement of invasive procedures. Moreover, possible carcinogenic effects not yet determined after transplantation require special caution.

WIDER IMPLICATIONS

In view of the results achieved, IVA could provide a promising option for the preservation of fertility in some cancer patients and prepuberal girls where the only alternative is tissue cryopreservation.

STUDY FUNDING/COMPETING INTERESTS

The authors received no specific funding for this work and declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Differences in the Role of HDACs 4 and 5 in the Modulation of Processes Regulating MAFbx and MuRF1 Expression during Muscle Unloading

Unloading leads to skeletal muscle atrophy via the upregulation of MuRF-1 and MAFbx E3-ligases expression. Reportedly, histone deacetylases (HDACs) 4 and 5 may regulate the expression of MuRF1 and MAFbx. To examine the HDAC-dependent mechanisms involved in the control of E3-ubiquitin ligases expression at the early stages of muscle unloading we used HDACs 4 and 5 inhibitor LMK-235 and HDAC 4 inhibitor Tasqinimod (Tq). Male Wistar rats were divided into four groups (eight rats per group): nontreated control (C), three days of unloading/hindlimb suspension (HS) and three days HS with HDACs inhibitor LMK-235 (HSLMK) or Tq (HSTq). Treatment with LMK-235 diminished unloading-induced of MAFbx, myogenin (MYOG), ubiquitin and calpain-1 mRNA expression (p < 0.05). Tq administration had no effect on the expression of E3-ligases. The mRNA expression of MuRF1 and MAFbx was significantly increased in both HS and HSTq groups (1.5 and 4.0 folds, respectively; p < 0.05) when compared with the C group. It is concluded that during three days of muscle unloading: (1) the HDACs 4 and 5 participate in the regulation of MAFbx expression as well as the expression of MYOG, ubiquitin and calpain-1; (2) the inhibition of HDAC 4 has no effect on MAFbx expression. Therefore, HDAC 5 is perhaps more important for the regulation of MAFbx expression than HDAC 4.

P38α-MAPK Signaling Inhibition Attenuates Soleus Atrophy during Early Stages of Muscle Unloading

To test the hypothesis that p38α-MAPK plays a critical role in the regulation of E3 ligase expression and skeletal muscle atrophy during unloading, we used VX-745, a selective p38α inhibitor. Three groups of rats were used: non-treated control (C), 3 days of unloading/hindlimb suspension (HS), and 3 days HS with VX-745 inhibitor (HSVX; 10 mg/kg/day). Total weight of soleus muscle in HS group was reduced compared to C (72.3 ± 2.5 vs 83.0 ± 3 mg, respectively), whereas muscle weight in the HSVX group was maintained (84.2 ± 5 mg). The expression of muscle RING-finger protein-1 (MuRF1) mRNA was significantly increased in the HS group (165%), but not in the HSVX group (127%), when compared with the C group. The expression of muscle-specific E3 ubiquitin ligases muscle atrophy F-box (MAFbx) mRNA was increased in both HS and HSVX groups (294% and 271%, respectively) when compared with C group. The expression of ubiquitin mRNA was significantly higher in the HS (423%) than in the C and HSVX (200%) groups. VX-745 treatment blocked unloading-induced upregulation of calpain-1 mRNA expression (HS: 120%; HSVX: 107%). These results indicate that p38α-MAPK signaling regulates MuRF1 but not MAFbx E3 ligase expression and inhibits skeletal muscle atrophy during early stages of unloading.

Selective and ATP-competitive kinesin KIF18A inhibitor suppresses the replication of influenza A virus

The influenza virus is one of the major public health threats. However, the development of efficient vaccines and therapeutic drugs to combat this virus is greatly limited by its frequent genetic mutations. Because of this, targeting the host factors required for influenza virus replication may be a more effective strategy for inhibiting a broader spectrum of variants. Here, we demonstrated that inhibition of a motor protein kinesin family member 18A (KIF18A) suppresses the replication of the influenza A virus (IAV). The expression of KIF18A in host cells was increased following IAV infection. Intriguingly, treatment with the selective and ATP‐competitive mitotic kinesin KIF18A inhibitor BTB‐1 substantially decreased the expression of viral RNAs and proteins, and the production of infectious viral particles, while overexpression of KIF18A enhanced the replication of IAV. Importantly, BTB‐1 treatment attenuated the activation of AKT, p38 MAPK, SAPK and Ran‐binding protein 3 (RanBP3), which led to the prevention of the nuclear export of viral ribonucleoprotein complexes. Notably, administration of BTB‐1 greatly improved the viability of IAV‐infected mice. Collectively, our results unveiled a beneficial role of KIF18A in IAV replication, and thus, KIF18A could be a potential therapeutic target for the control of IAV infection.

Forkhead transcription factor FOXO3a mediates interferon-γ-induced MHC II transcription in macrophages

Macrophages are professional antigen-presenting cells relying on the expression of class II major histocompatibility complex (MHC II) genes. Interferon-γ (IFN-γ) activates MHC II transcription via the assembly of an enhanceosome centred on class II trans-activator (CIITA). In the present study, we investigated the role of the forkhead transcription factor FOXO3a in IFN- γ-induced MHC II transcription in macrophages. Knockdown of FOXO3a, but not FOXO1 or FOXO4, diminished IFN-γ-induced MHC II expression in RAW cells. On the contrary, over-expression of FOXO3a, but neither FOXO1 nor FOXO4, enhanced CIITA-mediated trans-activation of the MHC II promoter. IFN-γ treatment promoted the recruitment of FOXO3a to the MHC II promoter. Co-immunoprecipitation and RE-ChIP assays showed that FOXO3a was a component of the MHC II enhanceosome forming interactions with CIITA, RFX5, RFXB and RFXAP. FOXO3a contributed to MHC II transcription by altering histone modifications surrounding the MHC II promoter. Of interest, FOXO3a was recruited to the type IV CIITA promoter and directly activated CIITA transcription by interacting with signal transducer of activation and transcription 1 in response to IFN-γ stimulation. In conclusion, our data unveil a novel role for FOXO3a in the regulation of MHC II transcription in macrophages.

Circular RNA circ-FoxO3 Inhibits Myoblast Cells Differentiation

CircRNA is a type of closed circular non-coding RNA formed by reverse splicing and plays an important role in regulating the growth and development of plants and animals. To investigate the function of circ-FoxO3 in mouse myoblast cells' (C2C12) differentiation and proliferation, we used RT-qPCR to detect the expression level of circ-FoxO3 in mouse myoblast cells at different densities and different differentiation stages, and the specific interference fragment was used to inhibit the expression level of circ-FoxO3 in myoblast cells to observe its effect on myoblast cells proliferation and differentiation. We found that the expression level of circ-FoxO3 in myoblast cells increased with the prolongation of myoblast cells differentiation time, and its expression level decreased with the proliferation of myoblast cells. At the same time, we found that the differentiation ability of the cells was significantly increased (p < 0.05), but the cell proliferation was unchanged (p > 0.05) after inhibiting the expression of circ-FoxO3 in myoblast cells. Combining the results of bioinformatics analysis and the dual luciferase reporter experiment, we found that circ-FoxO3 is a sponge of miR-138-5p, which regulates muscle differentiation. Our study shows that circ-FoxO3 can inhibit the differentiation of C2C12 myoblast cells and lay a scientific foundation for further study of skeletal muscle development at circRNA levels.

RAGE in the pathophysiology of skeletal muscle

Emerging evidence suggests that the signalling of the Receptor for Advanced Glycation End products (RAGE) is critical for skeletal muscle physiology controlling both the activity of muscle precursors during skeletal muscle development and the correct time of muscle regeneration after acute injury. On the other hand, the aberrant re-expression/activity of RAGE in adult skeletal muscle is a hallmark of muscle wasting that occurs in response to ageing, genetic disorders, inflammatory conditions, cancer, and metabolic alterations. In this review, we discuss the mechanisms of action and the ligands of RAGE involved in myoblast differentiation, muscle regeneration, and muscle pathological conditions. We highlight potential therapeutic strategies for targeting RAGE to improve skeletal muscle function.

Restoration of skeletal muscle homeostasis by hydrogen sulfide during hyperhomocysteinemia-mediated oxidative/ER stress condition 1

Elevated homocysteine (Hcy), i.e., hyperhomocysteinemia (HHcy), causes skeletal muscle myopathy. Among many cellular and metabolic alterations caused by HHcy, oxidative and endoplasmic reticulum (ER) stress are considered the major ones; however, the precise molecular mechanism(s) in this process is unclear. Nevertheless, there is no treatment option available to treat HHcy-mediated muscle injury. Hydrogen sulfide (H₂S) is increasingly recognized as a potent anti-oxidant, anti-apoptotic/necrotic/pyroptotic, and anti-inflammatory compound and also has been shown to improve angiogenesis during ischemic injury. Patients with CBS mutation produce less H₂S, making them vulnerable to Hcy-mediated cellular damage. Many studies have reported bidirectional regulation of ER stress in apoptosis through JNK activation and concomitant attenuation of cell proliferation and protein synthesis via PI3K/AKT axis. Whether H₂S mitigates these detrimental effects of HHcy on muscle remains unexplored. In this review, we discuss molecular mechanisms of HHcy-mediated oxidative/ER stress responses, apoptosis, angiogenesis, and atrophic changes in skeletal muscle and how H₂S can restore skeletal muscle homeostasis during HHcy condition. This review also highlights the molecular mechanisms on how H₂S could be developed as a clinically relevant therapeutic option for chronic conditions that are aggravated by HHcy.

Increasing autophagy does not affect neurogenic muscle atrophy

Physiological autophagy plays a crucial role in the regulation of muscle mass and metabolism, while the excessive induction or the inhibition of the autophagic flux contributes to the progression of several diseases. Autophagy can be activated by different stimuli, including cancer, exercise, caloric restriction and denervation. The latter leads to muscle atrophy through the activation of catabolic pathways, i.e. the ubiquitin-proteasome system and autophagy. However, the kinetics of autophagy activation and the upstream molecular pathways in denervated skeletal muscle have not been reported yet. In this study, we characterized the kinetics of autophagic induction, quickly triggered by denervation, and report the Akt/mTOR axis activation. Besides, with the aim to assess the relative contribution of autophagy in neurogenic muscle atrophy, we triggered autophagy with different stimuli along with denervation, and observed that four week-long autophagic induction, by either intermitted fasting or rapamycin treatment, did not significantly affect muscle mass loss. We conclude that: i) autophagy does not play a major role in inducing muscle loss following denervation; ii) nonetheless, autophagy may have a regulatory role in denervation induced muscle atrophy, since it is significantly upregulated as early as eight hours after denervation; iii) Akt/mTOR axis, AMPK and FoxO3a are activated consistently with the progression of muscle atrophy, further highlighting the complexity of the signaling response to the atrophying stimulus deriving from denervation.

Hydrogen sulfide alleviates hyperhomocysteinemia-mediated skeletal muscle atrophy via mitigation of oxidative and endoplasmic reticulum stress injury

Although hyperhomocysteinemia (HHcy) occurs because of the deficiency in cystathionine-β-synthase (CBS) causing skeletal muscle dysfunction, it is still unclear whether this effect is mediated through oxidative stress, endoplasmic reticulum (ER) stress, or both. Nevertheless, there is no treatment option available to improve HHcy-mediated muscle injury. Hydrogen sulfide (H₂S) is an antioxidant compound, and patients with CBS mutation do not produce H₂S. In this study, we hypothesized that H₂S mitigates HHcy-induced redox imbalance/ER stress during skeletal muscle atrophy via JNK phosphorylation. We used CBS^+/- mice to study HHcy-mediated muscle atrophy, and treated them with sodium hydrogen sulfide (NaHS; an H₂S donor). Proteins and mRNAs were examined by Western blots and quantitative PCR. Proinflammatory cytokines were also measured. Muscle mass and strength were studied via fatigue susceptibility test. Our data revealed that HHcy was detrimental to skeletal mass, particularly gastrocnemius and quadriceps muscle weight. We noticed that oxidative stress was reversed by NaHS in homocysteine (Hcy)-treated C2C12 cells. Interestingly, ER stress markers (GRP78, ATF6, pIRE1α, and pJNK) were elevated in vivo and in vitro, and NaHS mitigated these effects. Additionally, we observed that JNK phosphorylation was upregulated in C2C12 after Hcy treatment, but NaHS could not reduce this effect. Furthermore, inflammatory cytokines IL-6 and TNF-α were higher in plasma from CBS as compared with wild-type mice. FOXO1-mediated Atrogin-1 and MuRF-1 upregulation were attenuated by NaHS. Functional studies revealed that NaHS administration improved muscle fatigability in CBS^+/- mice. In conclusion, our work provides evidence that NaHS is beneficial in mitigating HHcy-mediated skeletal injury incited by oxidative/ER stress responses.

Critical role of FOXO3a in carcinogenesis

FOXO3a is a member of the FOXO subfamily of forkhead transcription factors that mediate a variety of cellular processes including apoptosis, proliferation, cell cycle progression, DNA damage and tumorigenesis. It also responds to several cellular stresses such as UV irradiation and oxidative stress. The function of FOXO3a is regulated by a complex network of processes, including post-transcriptional suppression by microRNAs (miRNAs), post-translational modifications (PTMs) and protein–protein interactions. FOXO3a is widely implicated in a variety of diseases, particularly in malignancy of breast, liver, colon, prostate, bladder, and nasopharyngeal cancers. Emerging evidences indicate that FOXO3a acts as a tumor suppressor in cancer. FOXO3a is frequently inactivated in cancer cell lines by mutation of the FOXO3a gene or cytoplasmic sequestration of FOXO3a protein. And its inactivation is associated with the initiation and progression of cancer. In experimental studies, overexpression of FOXO3a inhibits the proliferation, tumorigenic potential, and invasiveness of cancer cells, while silencing of FOXO3a results in marked attenuation in protection against tumorigenesis. The role of FOXO3a in both normal physiology as well as in cancer development have presented a great challenge to formulating an effective therapeutic strategy for cancer. In this review, we summarize the recent findings and overview of the current understanding of the influence of FOXO3a in cancer development and progression.

In-vitro regulation of primordial follicle activation: challenges for fertility preservation strategies

Ovarian tissue is increasingly being collected from cancer patients and cryopreserved for fertility preservation. While the only available option to restore fertility is autologous transplantation, this treatment is not appropriate for all patients due to the risk of reintroducing cancer cells and causing disease recurrence. Harnessing the full reproductive potential of this tissue to restore fertility requires the development of culture systems that support oocyte development from the primordial follicle stage. While this has been achieved in the mouse, the goal of obtaining oocytes of sufficient quality to support embryo development has not been reached in higher mammals despite decades of effort. In vivo, primordial follicles gradually exit the resting pool, whereas when primordial follicles are placed into culture, global activation of these follicles occurs. Therefore, the addition of a factor(s) that can regulate primordial follicle activation in vitro may be beneficial to the development of culture systems for ovarian tissue from cancer patients. Several factors have been observed to inhibit follicle activation, including anti-Müllerian hormone, stromal-derived factor 1 and members of the c-Jun-N-terminal kinase pathway. This review summarizes the findings from studies of these factors and discusses their potential integration into ovarian tissue culture strategies for fertility preservation.

Quantitation of IRF3 Nuclear Translocation in Heterogeneous Cellular Populations from Cervical Tissue Using Imaging Flow Cytometry

Imaging flow cytometry (IFC) has become a powerful tool for studying the activation of transcriptional factors in heterogeneous cell populations in high-content imaging mode. With considerable interest to the clinical development of IFC, the question becomes how we can accelerate its application to solid tissues. We developed the first IFC-based procedure to quantify the nuclear translocation of interferon regulatory factor (IRF) 3, an important measure of induction of type I interferon antiviral response, in primary human immune cells including in solid tissues. After tissue digestion and protocol optimization by spectral flow cytometry, cell suspension is stained for intracellular IRF3 and acquired by IFC. Image analysis is performed using an optimized nuclear mask and similarity score parameter to correlate the location of IRF3 staining and a nuclear dye. The technique measures IRF3 activation at a single cell level and can detect small changes in the percent of activated cells providing objective quantitative data for statistical analysis.

A Peroxidase Peroxiredoxin 1-Specific Redox Regulation of the Novel FOXO3 microRNA Target let-7

Precision in redox signaling is attained through posttranslational protein modifications such as oxidation of protein thiols. The peroxidase peroxiredoxin 1 (PRDX1) regulates signal transduction through changes in thiol oxidation of its cysteines. We demonstrate here that PRDX1 is a binding partner for the tumor suppressive transcription factor FOXO3 that directly regulates the FOXO3 stress response. Heightened oxidative stress evokes formation of disulfide-bound heterotrimers linking dimeric PRDX1 to monomeric FOXO3. Absence of PRDX1 enhances FOXO3 nuclear localization and transcription that are dependent on the presence of Cys31 or Cys150 within FOXO3. Notably, FOXO3-T32 phosphorylation is constitutively enhanced in these mutants, but nuclear translocation of mutant FOXO3 is restored with PI3K inhibition. Here we show that on H₂O₂ exposure, transcription of tumor suppressive miRNAs let-7b and let-7c is regulated by FOXO3 or PRDX1 expression levels and that let-7c is a novel target for FOXO3. Conjointly, inhibition of let-7 microRNAs increases let-7-phenotypes in PRDX1-deficient breast cancer cells. Altogether, these data ascertain the existence of an H₂O₂-sensitive PRDX1-FOXO3 signaling axis that fine tunes FOXO3 activity toward the transcription of gene targets in response to oxidative stress. Antioxid. Redox Signal. 28, 62-77.

Pharmacological treatment with inhibitors of nuclear export enhances the antitumor activity of docetaxel in human prostate cancer

Background and aims

Docetaxel (DTX) modestly increases patient survival of metastatic castration-resistant prostate cancer (mCRPC) due to insurgence of pharmacological resistance. Deregulation of Chromosome Region Maintenance (CRM-1)/ exportin-1 (XPO-1)-mediated nuclear export may play a crucial role in this phenomenon.

Material and methods

Here, we evaluated the effects of two Selective Inhibitor of Nuclear Export (SINE) compounds, selinexor (KPT-330) and KPT-251, in association with DTX by using 22rv1, PC3 and DU145 cell lines with their. DTX resistant derivatives.

Results and conclusions

We show that DTX resistance may involve overexpression of β-III tubulin (TUBB3) and P-glycoprotein as well as increased cytoplasmic accumulation of Foxo3a. Increased levels of XPO-1 were also observed in DTX resistant cells suggesting that SINE compounds may modulate DTX effectiveness in sensitive cells as well as restore the sensitivity to DTX in resistant ones. Pretreatment with SINE compounds, indeed, sensitized to DTX through increased tumor shrinkage and apoptosis by preventing DTX-induced cell cycle arrest. Basally SINE compounds induce FOXO3a activation and nuclear accumulation increasing the expression of FOXO-responsive genes including p21, p27 and Bim causing cell cycle arrest. SINE compounds-catenin and survivin supporting apoptosis. βdown-regulated Cyclin D1, c-myc, Nuclear sequestration of p-Foxo3a was able to reduce ABCB1 and TUBB3 H2AX levels, prolonged γ expression. Selinexor treatment increased DTX-mediated double strand breaks (DSB), and reduced the levels of DNA repairing proteins including DNA PKc and Topo2A. Our results provide supportive evidence for the therapeutic use of SINE compounds in combination with DTX suggesting their clinical use in mCRPC patients.

Skeletal muscle autophagy and mitophagy in endurance-trained runners before and after a high-fat meal

Objective

We tested the hypothesis that skeletal muscle of endurance-trained male runners would exhibit elevated autophagy and mitophagy markers, which would be associated with greater metabolic flexibility following a high-fat meal (HFM).

Methods

Muscle biopsies were collected to determine differences in autophagy and mitophagy protein markers and metabolic flexibility under fasting conditions and 4 h following a HFM between endurance-trained male runners (n = 10) and sedentary, non-obese controls (n = 9).

Results

Maximal oxygen consumption (ml·kg·min⁻¹) was approximately 50% higher (p < 0.05) in endurance-trained runners compared with sedentary controls (65.8 ± 2.3 and 43.1 ± 3.4, respectively). Autophagy markers were similar between groups. Mitophagy and mitochondrial dynamics protein markers were significantly higher in skeletal muscle of endurance-trained runners compared with sedentary controls in the fasted state, although unaffected by the HFM. Skeletal muscle metabolic flexibility was similar between groups when fasted (p > 0.05), but increased in response to the HFM in endurance-trained athletes only (p < 0.005). Key mitophagy markers, phospho-Pink1^Thr257 and phospho-Parkin^S65 (r = 0.64, p < 0.005), and phospo-Parkin^Ser65 and phospho-Drp1^Ser616 (r = 0.70, p < 0.05) were correlated only within the endurance-trained group. Autophagy and mitophagy markers were not correlated with metabolic flexibility.

Conclusion

In summary, mitophagy may be enhanced in endurance-trained runners based on elevated markers of mitophagy and mitochondrial dynamics. The HFM did not alter autophagy or mitophagy in either group. The absence of a relationship between mitophagy markers and metabolic flexibility suggests that mitophagy is not a key determinant of metabolic flexibility in a healthy population, but further investigation is warranted.

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Basal autophagy is similar in skeletal muscle of endurance-trained and sedentary males.

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Trained and sedentary skeletal muscle autophagy is unaltered following high-fat meal.

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Mitophagy activity is greater in endurance-trained than sedentary skeletal muscle.

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Greater mitophagy is related to increased metabolic flexibility after high-fat meal.

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Trained and sedentary skeletal muscle mitophagy is unaltered following high-fat meal.

Acylated and unacylated ghrelin inhibit atrophy in myotubes co-cultured with colon carcinoma cells

Cancer cachexia is a result of increased protein degradation and decreased protein synthesis. The multifunctional circulating hormone ghrelin promotes synthesis and inhibits degradation of muscle protein, but its mechanism of action is not fully understood. Here, we investigated whether co-culturing C2C12 myotubes with CT26 colon carcinoma cells induces myotube atrophy, and whether acylated ghrelin (AG) and unacylated ghrelin (UnAG) had anti-atrophic effects. We found that co-culture induced myotube atrophy and increased tumor necrosis factor-alpha (TNF-α) and myostatin concentrations in the culture medium. Moreover, co-culture down-regulated myogenin and MyoD expression, inhibited the Akt signaling, up-regulated ubiquitin E3 ligase expression, and activated the calpain system and autophagy in myotubes. Both AG and UnAG inhibited these changes. Our study describes a novel in vitro model that can be employed to investigate cancer cachexia, and our findings suggest a possible use for AG and UnAG in treating cancer cachexia.

Testosterone modulates FoxO3a and p53-related genes to protect C2C12 skeletal muscle cells against apoptosis

The loss of muscle mass and strength with aging, sarcopenia, is a prevalent condition among the elderly, associated with skeletal muscle dysfunction and enhanced muscle cell apoptosis. We have previously demonstrated that testosterone protects against H₂O₂-induced apoptosis in C2C12 muscle cells, at different levels: morphological, biochemical and molecular. Since we have observed that testosterone reduces p-p53 and maintains the inactive state of FoxO3a transcription factor, induced by H₂O₂, we analyzed if the hormone was exerting its antiapoptotic effect at transcriptional level, by modulating pro and antiapoptotic genes associated to them. We detected the upregulation of the proapoptotic genes Puma, PERP and Bim, and MDM2 in response to H₂O₂ at different periods of the apoptotic process, and the downregulation of the antiapoptotic gene Bcl-2, whereas testosterone was able to modulate and counteract H₂O₂ effects. Furthermore, ERK and JNK kinases have been demonstrated to be linked to FoxO3a phosphorylation and thus its subcellular distribution. This work show some transcription level components, upstream of the classical apoptotic pathway, that are activated during oxidative stress and that are points where testosterone exerts its protective action against apoptosis, exposing some of the puzzle pieces of the intricate network that aged skeletal muscle apoptosis represents.

Effect of irradiation on Akt signaling in atrophying skeletal muscle

Muscle irradiation (IRR) exposure can accompany unloading during spaceflight or cancer treatment, and this has been shown to be sufficient by itself to induce skeletal muscle signaling associated with a remodeling response. Although protein kinase B/Akt has an established role in the regulation of muscle growth and metabolism, there is a limited understanding of how Akt signaling in unloaded skeletal muscle is affected by IRR. Therefore, we examined the combined effects of acute IRR and short-term unloading on muscle Akt signaling. Female C57BL/6 mice were subjected to load bearing or hindlimb suspension (HS) for 5 days (n = 6/group). A single, unilateral hindlimb IRR dose (0.5 Gy X-ray) was administered on day 3 Gastrocnemius muscle protein expression was examined. HS resulted in decreased Akt^T308 phosphorylation, whereas HS+IRR resulted in increased Akt^T308 phosphorylation above baseline. HS resulted in reduced Akt^S473 phosphorylation, which was rescued by HS+IRR. Interestingly, IRR alone resulted in increased phosphorylation of Akt^S473, but not that of Akt^T308 HS resulted in decreased mTORC1 signaling, and this suppression was not altered by IRR. Both IRR and HS resulted in increased MuRF-1 expression, whereas atrogin-1 expression was not affected by either condition. These results demonstrate that either IRR alone or when combined with HS can differentially affect Akt phosphorylation, but IRR did not disrupt suppressed mTORC1 signaling by HS. Collectively, these findings highlight that a single IRR dose is sufficient to disrupt the regulation of Akt signaling in atrophying skeletal muscle.

NOTCH1 Inhibits Activation of ATM by Impairing the Formation of an ATM-FOXO3a-KAT5/Tip60 Complex

The DNA damage response (DDR) signal transduction pathway is responsible for sensing DNA damage and further relaying this signal into the cell. ATM is an apical DDR kinase that orchestrates the activation and the recruitment of downstream DDR factors to induce cell-cycle arrest and repair. We have previously shown that NOTCH1 inhibits ATM activation upon DNA damage, but the underlying mechanism remains unclear. Here, we show that NOTCH1 does not impair ATM recruitment to DNA double-strand breaks (DSBs). Rather, NOTCH1 prevents binding of FOXO3a and KAT5/Tip60 to ATM through a mechanism in which NOTCH1 competes with FOXO3a for ATM binding. Lack of FOXO3a binding to ATM leads to the loss of KAT5/Tip60 association with ATM. Moreover, expression of NOTCH1 or depletion of ATM impairs the formation of the FOXO3a-KAT5/Tip60 protein complex. Finally, we show that pharmacological induction of FOXO3a nuclear localization sensitizes NOTCH1-driven cancers to DNA-damage-induced cell death.

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NOTCH1 does not inhibit recruitment of ATM to DSBs

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NOTCH1 competes with FOXO3a for binding to the FATC domain of ATM

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FOXO3a is necessary for KAT5/Tip60 binding to ATM

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Induction of FOXO3a nuclear localization sensitizes TALL-1 cancer cells to DNA damage

Alpha-ketoglutarate promotes skeletal muscle hypertrophy and protein synthesis through Akt/mTOR signaling pathways

Skeletal muscle weight loss is accompanied by small fiber size and low protein content. Alpha-ketoglutarate (AKG) participates in protein and nitrogen metabolism. The effect of AKG on skeletal muscle hypertrophy has not yet been tested, and its underlying mechanism is yet to be determined. In this study, we demonstrated that AKG (2%) increased the gastrocnemius muscle weight and fiber diameter in mice. Our in vitro study also confirmed that AKG dose increased protein synthesis in C2C12 myotubes, which could be effectively blocked by the antagonists of Akt and mTOR. The effects of AKG on skeletal muscle protein synthesis were independent of glutamate, its metabolite. We tested the expression of GPR91 and GPR99. The result demonstrated that C2C12 cells expressed GPR91, which could be upregulated by AKG. GPR91 knockdown abolished the effect of AKG on protein synthesis but failed to inhibit protein degradation. These findings demonstrated that AKG promoted skeletal muscle hypertrophy via Akt/mTOR signaling pathway. In addition, GPR91 might be partially attributed to AKG-induced skeletal muscle protein synthesis.

Lessons from mammalian hibernators: molecular insights into striated muscle plasticity and remodeling

Striated muscle shows an amazing ability to adapt its structural apparatus based on contractile activity, loading conditions, fuel supply, or environmental factors. Studies with mammalian hibernators have identified a variety of molecular pathways which are strategically regulated and allow animals to endure multiple stresses associated with the hibernating season. Of particular interest is the observation that hibernators show little skeletal muscle atrophy despite the profound metabolic rate depression and mechanical unloading that they experience during long weeks of torpor. Additionally, the cardiac muscle of hibernators must adjust to low temperature and reduced perfusion, while the strength of contraction increases in order to pump cold, viscous blood. Consequently, hibernators hold a wealth of knowledge as it pertains to understanding the natural capacity of myocytes to alter structural, contractile and metabolic properties in response to environmental stimuli. The present review outlines the molecular and biochemical mechanisms which play a role in muscular atrophy, hypertrophy, and remodeling. In this capacity, four main networks are highlighted: (1) antioxidant defenses, (2) the regulation of structural, contractile and metabolic proteins, (3) ubiquitin proteosomal machinery, and (4) macroautophagy pathways. Subsequently, we discuss the role of transcription factors nuclear factor (erythroid-derived 2)-like 2 (Nrf2), Myocyte enhancer factor 2 (MEF2), and Forkhead box (FOXO) and their associated posttranslational modifications as it pertains to regulating each of these networks. Finally, we propose that comparing and contrasting these concepts to data collected from model organisms able to withstand dramatic changes in muscular function without injury will allow researchers to delineate physiological versus pathological responses.

Flavones Inhibit LPS-Induced Atrogin-1/MAFbx Expression in Mouse C2C12 Skeletal Myotubes

Muscle atrophy is a complex process that occurs as a consequence of various stress events. Muscle atrophy-associated genes (atrogenes) such as atrogin-1/MAFbx and MuRF-1 are induced early in the atrophy process, and the increase in their expression precedes the loss of muscle weight. Although antioxidative nutrients suppress atrogene expression in skeletal muscle cells, the inhibitory effects of flavonoids on inflammation-induced atrogin-1/MAFbx expression have not been clarified. Here, we investigated the inhibitory effects of flavonoids on lipopolysaccharide (LPS)-induced atrogin-1/MAFbx expression. We examined whether nine flavonoids belonging to six flavonoid categories inhibited atrogin-1/MAFbx expression in mouse C2C12 myotubes. Two major flavones, apigenin and luteolin, displayed potent inhibitory effects on atrogin-1/MAFbx expression. The pretreatment with apigenin and luteolin significantly prevented the decrease in C2C12 myotube diameter caused by LPS stimulation. Importantly, the pretreatment of LPS-stimulated myoblasts with these flavones significantly inhibited LPS-induced JNK phosphorylation in C2C12 myotubes, resulting in the significant suppression of atrogin-1/MAFbx promoter activity. These results suggest that apigenin and luteolin, prevent LPS-mediated atrogin-1/MAFbx expression through the inhibition of the JNK signaling pathway in C2C12 myotubes. Thus, these flavones, apigenin and luteolin, may be promising agents to prevent LPS-induced muscle atrophy.

Inhibitors of c-Jun phosphorylation impede ovine primordial follicle activation

STUDY HYPOTHESIS

Is the c-Jun-N-terminal kinase (JNK) pathway implicated in primordial follicle activation?

STUDY FINDING

Culture of ovine ovarian cortex in the presence of two different c-Jun phosphorylation inhibitors impeded pre-antral follicle activation.

WHAT IS KNOWN ALREADY

Despite its importance for fertility preservation therapies, the mechanisms of primordial follicle activation are poorly understood. Amongst different signalling pathways potentially involved, the JNK pathway has been previously shown to be essential for cell cycle progression and pre-antral follicle development in mice.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

Ovine ovarian cortex pieces were cultured with varying concentrations of SP600125, JNK inhibitor VIII or anti-Mullerian hormone (AMH) in the presence of FSH for 9 days. Follicular morphometry and immunohistochemistry for proliferating cell nuclear antigen (PCNA), apoptosis and follicle activation (Foxo3a) were assessed.

MAIN RESULTS AND THE ROLE OF CHANCE

Inhibition of primordial follicle activation occurred in the presence of SP600125, JNK inhibitor VIII and AMH when compared with controls (all P < 0.05) after 2 days of culture. However, only in the highest concentrations used was the inhibition of activation associated with induction of follicular apoptosis (P < 0.05). In growing follicles, PCNA antigen expression was reduced when the JNK inhibitors or AMH were used (P < 0.05 versus control), indicating reduced proliferation of the somatic compartment.

LIMITATIONS, REASONS FOR CAUTION

Although we evaluated the effects of inhibition of c-Jun phosphorylation on primordial follicle development, we did not determine the cellular targets and mechanism of action of the inhibitors.

WIDER IMPLICATIONS OF THE FINDINGS

These results are the first to implicate the JNK pathway in primordial follicle activation and could have significant consequences for the successful development of fertility preservation strategies and our understanding of primordial follicle activation.

LARGE SCALE DATA

n/a.

STUDY FUNDING AND COMPETING INTERESTS

Dr Michael J. Bertoldo and the laboratories involved in the present study were supported by a grant from 'Région Centre' (CRYOVAIRE, Grant number #320000268). There are no conflicts of interest to declare.

F-BOX proteins in cancer cachexia and muscle wasting: Emerging regulators and therapeutic opportunities

Cancer cachexia is a debilitating metabolic syndrome accounting for fatigue, an impairment of normal activities, loss of muscle mass associated with body weight loss eventually leading to death in majority of patients with advanced disease. Cachexia patients undergoing skeletal muscle atrophy show consistent activation of the SCF ubiquitin ligase (F-BOX) family member Atrogin-1 (also known as MAFBx/FBXO32) alongside the activation of the muscle ring finger protein1 (MuRF1). Other lesser known F-BOX family members are also emerging as key players supporting muscle wasting pathways. Recent work highlights a spectrum of different cancer signaling mechanisms impacting F-BOX family members that feed forward muscle atrophy related genes during cachexia. These novel players provide unique opportunities to block cachexia induced skeletal muscle atrophy by therapeutically targeting the SCF protein ligases. Conversely, strategies that induce the production of proteins may be helpful to counter the effects of these F-BOX proteins. Through this review, we bring forward some novel targets that promote atrogin-1 signaling in cachexia and muscle wasting and highlight newer therapeutic opportunities that can help in the better management of patients with this devastating and fatal disorder.

The p66Shc protein controls redox signaling and oxidation-dependent DNA damage in human liver cells

The p66Shc protein mediates oxidative stress-related injury in multiple tissues. Steatohepatitis is characterized by enhanced oxidative stress-mediated cell damage. The role of p66Shc in redox signaling was investigated in human liver cells and alcoholic steatohepatitis. HepG2 cells with overexpression of wild-type or mutant p66Shc, with Ser36 replacement by Ala, were obtained through infection with recombinant adenoviruses. Reactive oxygen species and oxidation-dependent DNA damage were assessed by measuring dihydroethidium oxidation and 8-hydroxy-2'-deoxyguanosine accumulation into DNA, respectively. mRNA and protein levels of signaling intermediates were evaluated in HepG2 cells and liver biopsies from control and alcoholic steatohepatitis subjects. Exposure to H2O2 increased reactive oxygen species and phosphorylation of p66Shc on Ser36 in HepG2 cells. Overexpression of p66Shc promoted reactive oxygen species synthesis and oxidation-dependent DNA damage, which were further enhanced by H2O2. p66Shc activation also resulted in increased Erk-1/2, Akt, and FoxO3a phosphorylation. Blocking of Erk-1/2 activation inhibited p66Shc phosphorylation on Ser36. Increased p66Shc expression was associated with reduced mRNA levels of antioxidant molecules, such as NF-E2-related factor 2 and its target genes. In contrast, overexpression of the phosphorylation defective p66Shc Ala36 mutant inhibited p66Shc signaling, enhanced antioxidant genes, and suppressed reactive oxygen species and oxidation-dependent DNA damage. Increased p66Shc protein levels and Akt phosphorylation were observed in liver biopsies from alcoholic steatohepatitis compared with control subjects. In human alcoholic steatohepatitis, increased hepatocyte p66Shc protein levels may enhance susceptibility to DNA damage by oxidative stress by promoting reactive oxygen species synthesis and repressing antioxidant pathways.

Genetic inhibition of JNK3 ameliorates spinal muscular atrophy

Mutation of the Survival Motor Neuron 1 (SMN1) gene causes spinal muscular atrophy (SMA), an autosomal recessive neurodegenerative disorder that occurs in early childhood. Degeneration of spinal motor neurons caused by SMN deficiency results in progressive muscle atrophy and death in SMA. The molecular mechanism underlying neurodegeneration in SMA is unknown. No treatment is available to prevent neurodegeneration and reduce the burden of illness in SMA. We report that the c-Jun NH2-terminal kinase (JNK) signaling pathway mediates neurodegeneration in SMA. The neuron-specific isoform JNK3 is required for neuron degeneration caused by SMN deficiency. JNK3 deficiency reduces degeneration of cultured neurons caused by low levels of SMN. Genetic inhibition of JNK pathway in vivo by Jnk3 knockout results in amelioration of SMA phenotype. JNK3 deficiency prevents the loss of spinal cord motor neurons, reduces muscle degeneration, improves muscle fiber thickness and muscle growth, improves motor function and overall growth and increases lifespan of mice with SMA that shows a systemic rescue of phenotype by a SMN-independent mechanism. JNK3 represents a potential (non-SMN) therapeutic target for the treatment of SMA.

Alpha B-crystallin induction in skeletal muscle cells under redox imbalance is mediated by a JNK-dependent regulatory mechanism

The small heat shock protein α-B-crystallin (CRYAB) is critically involved in stress-related cellular processes such as differentiation, apoptosis, and redox homeostasis. The up-regulation of CRYAB plays a key role in the cytoprotective and antioxidant response, but the molecular pathway driving its expression in muscle cells during oxidative stress still remains unknown. Here we show that noncytotoxic exposure to sodium meta-arsenite (NaAsO2) inducing redox imbalance is able to increase the CRYAB content of C2C12 myoblasts in a transcription-dependent manner. Our in silico analysis revealed a genomic region upstream of the Cryab promoter containing two putative antioxidant-responsive elements motifs and one AP-1-like binding site. The redox-sensitive transcription factors Nrf2 and the AP-1 component c-Jun were found to be up-regulated in NaAsO2-treated cells, and we demonstrated a specific NaAsO2-mediated increase of c-Jun and Nrf2 binding activity to the genomic region identified, supporting their putative involvement in CRYAB regulation following a shift in redox balance. These changes also correlated with a specific phosphorylation of JNK and p38 MAPK kinases, the well-known molecular mediators of signaling pathways leading to the activation of these transcription factors. Pretreatment of C2C12 cells with the JNK inhibitor SP600125 induced a decrease in c-Jun and Nrf2 content and was able to counteract the NaAsO2-mediated increase in CRYAB expression. Thus these data show a direct role of JNK in CRYAB regulation under redox imbalance and also point to a previously unrecognized link between c-Jun and Nrf2 transcription factors and redox-induced CRYAB expression in muscle cells.

Redox regulation of FoxO transcription factors

Transcription factors of the forkhead box, class O (FoxO) family are important regulators of the cellular stress response and promote the cellular antioxidant defense. On one hand, FoxOs stimulate the transcription of genes coding for antioxidant proteins located in different subcellular compartments, such as in mitochondria (i.e. superoxide dismutase-2, peroxiredoxins 3 and 5) and peroxisomes (catalase), as well as for antioxidant proteins found extracellularly in plasma (e.g., selenoprotein P and ceruloplasmin). On the other hand, reactive oxygen species (ROS) as well as other stressful stimuli that elicit the formation of ROS, may modulate FoxO activity at multiple levels, including posttranslational modifications of FoxOs (such as phosphorylation and acetylation), interaction with coregulators, alterations in FoxO subcellular localization, protein synthesis and stability. Moreover, transcriptional and posttranscriptional control of the expression of genes coding for FoxOs is sensitive to ROS. Here, we review these aspects of FoxO biology focusing on redox regulation of FoxO signaling, and with emphasis on the interplay between ROS and FoxOs under various physiological and pathophysiological conditions. Of particular interest are the dual role played by FoxOs in cancer development and their key role in whole body nutrient homeostasis, modulating metabolic adaptations and/or disturbances in response to low vs. high nutrient intake. Examples discussed here include calorie restriction and starvation as well as adipogenesis, obesity and type 2 diabetes.