Catabolic Signaling Research Articles

A role of zinc finger ccch type containing 12A (ZC3H12A) In osteoarthritis pathogenesis

Purpose: Osteoarthritis is the most common degenerative disease and it leads to enormous social and economic consequences. However, there is currently no effective disease modifying therapy. This total joint disease involves cartilage destruction, synovitis, osteophyte formation, and subchondral bone remodeling. Among those conditions, cartilage destruction is a hallmark of OA caused by the imbalance of catabolic-anabolic homeostasis. Recently, various studies have been carried out to find the molecular mechanisms of disturbing the cartilage homeostasis in OA pathogenesis. Herein, we focused on RNases as regulatory factors that disrupt cartilage homeostasis. Methods: Expression profiles of genes involved RNases in primary-culture mouse chondrocytes was examined by microarray analysis. Expression patterns of ZC3H12A mRNA levels are confirmed by qRTPCR. Experimental OA was induced by DMM surgery or intra-articular (IA) injection of adenoviruses in C57BL/6 12-week-old male mice. Homozygous Zc3h12a-/- mice exhibit dwarfism and short life-span but heterozygous Zc3h12a+/- mice exhibit normal development, therefore we used Zc3h12a+/- mice for operating DMM surgery. To overexpression or knockdown ZC3H12A in whole-joint tissues and chondrocytes, we used adenoviruses (Ad-ZC3H12A and Ad-shZC3H12A). The mice were sacrificed for analysis 6 weeks after the DMM surgery and 3 weeks after the first IA injection. Results: ZC3H12A is specifically upregulated in chondrocytes stimulated with OA-associated catabolic signaling. Because the role of ZC3H12A in OA pathogenesis has not been investigated, we explored the molecular targets of ZC3H12A which may act as RNase in OA pathogenesis. Adenovirus-mediated overexpression of ZC3H12A in mouse chondrocytes or joint tissues had no effect on cartilage tissue. However, when ZC3H12A was overexpressed in post-traumatic damaged-mouse joint tissue via DMM surgery, cartilage destruction was markedly alleviated. On the other hand, genetic deletion of ZC3H12A in mice (Zc3h12a+/-) accelerated cartilage damage of DMM-induced OA. Consistently, shRNA-mediated Zc3h12a (Ad-shZC3H12A) silencing in mouse joint tissue also promoted DMM-induced cartilage destruction. Conclusions: In conclusion, ZC3H12A has been shown to play a role in suppressing OA pathogenesis in the experimental OA model. We anticipate that the target gene of ZC3H12A as RNase may cause disrupting chondrocytes homeostasis, and our findings suggest that ZC3H12A is a potential therapeutic target for treatment of OA.

A Hyaluronan-binding Peptide (P15-1) Reduces Inflammatory and Catabolic Events in IL-1\u03b2-treated Human Articular Chondrocytes

Inflammation plays a critical role in osteoarthritis (OA). It stimulates catabolic events in articular chondrocytes and prevents chondrogenic precursor cells from repairing cartilage lesions, leading to accelerated cartilage degradation. Therefore, the identification of novel factors that reduce catabolic events in chondrocytes and enhances chondrogenic differentiation of precursor cells in an inflammatory environment may provide novel therapeutic strategies for the treatment of OA. The goal of this study was to determine whether a hyaluronan (HA)-binding peptide (P15-1), via interacting with high molecular weight (HMW)HA can enhance the anti-inflammatory properties of HMWHA and decrease catabolic events in interleukin-1beta (IL-1β)-treated human articular chondrocytes. Treatment with P15-1 decreased catabolic events and stimulated anabolic events in articular chondrocytes cultured in an inflammatory environment. P15-1 pre-mixed with HMWHA was more effective in inhibiting catabolic events and stimulating anabolic events than P15-1 or HMWHA alone. Our findings suggest that P15-1 together with HMWHA inhibits catabolic events in articular chondrocytes via the inhibition of p38 mitogen-activated protein kinases (MAPK) and increasing the thickness of the pericellular matrix (PCM) around chondrocytes thereby decreasing catabolic signaling. Finally, conditioned medium from IL-1β and P15-1-treated human articular chondrocytes was less inhibitory for chondrogenic differentiation of precursor cells than conditioned medium from chondrocytes treated with IL-1β alone. In conclusion, P15-1 is proposed to function synergistically with HMWHA to enhance the protective microenvironment for chondrocytes and mesenchymal stem cells during inflammation and regeneration.

Exploring vitamin D signalling within skin cancer.

Sunlight exposure of the skin is associated with both risks and benefits. On one hand, sunlight ultraviolet (UV) radiation can cause skin cancer through signature DNA mutations. On the other hand, it can be absorbed in the skin by 7-dehydrocholesterol to instigate endogenous synthesis of vitamin D to regulate anticancer effects. Thus, protecting one's skin from sunlight to avoid skin cancer may lead to impaired vitamin D levels arguing for sensible sun exposure practices. To limit cancer, vitamin D metabolites can promote uncharacterized and diverse sets of events such as repair responses to DNA damage, apoptosis of malignant cells, and suppression of immune surveillance, proliferation and angiogenesis. Recent findings also suggest that part of the anticancer effects of vitamin D within squamous cell carcinoma-a type of skin cancer most directly linked to sun exposure-involves the DDIT4-mTOR catabolic signalling pathway to enhance cell autophagy. As mTOR activity and cellular metabolism are modulated as part of the DNA damage response, insights into the means by which mTOR can be controlled by vitamin D to suppress cancer is of molecular and clinical importance. Overall, the research so far suggests that presence of vitamin D through sunlight exposure and supplementation are beneficial for human health in the face of cancer.

Proteasome activity and expression of mammalian target of rapamycin signaling factors in skeletal muscle of dairy cows supplemented with conjugated linoleic acids during early lactation

The mammalian target of rapamycin (mTOR) is a major regulator of protein synthesis via its main downstream effectors, ribosomal protein S6 kinase (S6K1) and eukaryotic initiation factor 4E binding protein (4EBP1). The ubiquitin-proteasome system (UPS) is the main proteolytic pathway in muscle, and the muscle-specific ligases tripartite motif containing 63 (TRIM63; also called muscle-specific ring-finger protein 1, MuRF-1) and F-box only protein 32 (FBXO32; also called atrogin-1) are important components of the UPS. We investigated 20S proteasome activity and mRNA expression of key components of mTOR signaling and UPS in skeletal muscle of dairy cows during late gestation and early lactation and tested the effects of dietary supplementation (from d 1 in milk) with conjugated linoleic acids (sCLA; 100 g/d; n = 11) compared with control fat-supplemented cows (CTR; n = 10). Blood and muscle tissue (semitendinosus) samples were collected on d -21, 1, 21, and 70 relative to parturition. Dry matter intake increased with time of lactation in both groups. It was lower in sCLA than in CTR on d 21, which resulted in a reduced calculated metabolizable protein balance. Most serum and muscle concentrations of AA followed time-related changes but were unaffected by CLA supplementation. In both groups, serum and muscle 3-methylhistidine (3-MH) concentrations and the ratio of 3-MH:creatinine increased from d -21 to d 1, followed by a decline on d 21. The mRNA abundance of MTOR on d 21 and 70 was greater in sCLA than in CTR. The abundance of 4EBP1 mRNA did not differ between groups but was upregulated in both on d 1. The mRNA abundance of S6K1 on d 70 was greater in CTR than in sCLA, but remained unchanged over time in both groups. The mRNA abundance of FBXO32 (encoding atrogin-1) on d 21 was greater in sCLA than in CTR. The mRNA abundance of TRIM63 (also known as MuRF1) showed a similar pattern as FBXO32 in both groups: an increase from d -21 to d 1, followed by a decline. The mRNA for the α (BCKDHA) and β (BCKDHB) polypeptide of branched-chain α-keto acid dehydrogenase was elevated in sCLA and CTR cows on d 21, respectively, suggesting a role of CLA in determining the metabolic fate of branched-chain AA. For the mTOR protein, no group differences were observed. The abundance of S6K1 protein was greater across all time points in sCLA versus CTR. The antepartum 20S proteasome activity in muscle was elevated in both groups compared with postpartum, probably reflecting the start of protein mobilization before parturition. Plasma insulin concentrations decreased in both groups postpartum but to a greater extent in CTR than in sCLA, resulting in greater insulin concentrations in sCLA than in CTR. Thus, the greater abundance of MTOR mRNA and S6K1 protein in sCLA compared with CTR might be mediated by the greater plasma insulin postpartum. The upregulation of MTOR mRNA in sCLA cows on d 21, despite greater FBXO32 mRNA abundance, may reflect a simultaneous activation of both anabolic and catabolic signaling pathways, likely resulting in greater protein turnover.

Sestrin prevents atrophy of disused and aging muscles by integrating anabolic and catabolic signals

A unique property of skeletal muscle is its ability to adapt its mass to changes in activity. Inactivity, as in disuse or aging, causes atrophy, the loss of muscle mass and strength, leading to physical incapacity and poor quality of life. Here, through a combination of transcriptomics and transgenesis, we identify sestrins, a family of stress-inducible metabolic regulators, as protective factors against muscle wasting. Sestrin expression decreases during inactivity and its genetic deficiency exacerbates muscle wasting; conversely, sestrin overexpression suffices to prevent atrophy. This protection occurs through mTORC1 inhibition, which upregulates autophagy, and AKT activation, which in turn inhibits FoxO-regulated ubiquitin–proteasome-mediated proteolysis. This study reveals sestrin as a central integrator of anabolic and degradative pathways preventing muscle wasting. Since sestrin also protected muscles against aging-induced atrophy, our findings have implications for sarcopenia.

Overcoming resistance to anabolic SARM therapy in experimental cancer cachexia with an HDAC inhibitor

No approved therapy exists for cancer‐associated cachexia. The colon‐26 mouse model of cancer cachexia mimics recent late‐stage clinical failures of anabolic anti‐cachexia therapy and was unresponsive to anabolic doses of diverse androgens, including the selective androgen receptor modulator (SARM) GTx‐024. The histone deacetylase inhibitor (HDACi) AR‐42 exhibited anti‐cachectic activity in this model. We explored combined SARM/AR‐42 therapy as an improved anti‐cachectic treatment paradigm. A reduced dose of AR‐42 provided limited anti‐cachectic benefits, but, in combination with GTx‐024, significantly improved body weight, hindlimb muscle mass, and grip strength versus controls. AR‐42 suppressed the IL‐6/GP130/STAT3 signaling axis in muscle without impacting circulating cytokines. GTx‐024‐mediated β‐catenin target gene regulation was apparent in cachectic mice only when combined with AR‐42. Our data suggest cachectic signaling in this model involves catabolic signaling insensitive to anabolic GTx‐024 therapy and a blockade of GTx‐024‐mediated anabolic signaling. AR‐42 mitigates catabolic gene activation and restores anabolic responsiveness to GTx‐024. Combining GTx‐024, a clinically established anabolic therapy, with AR‐42, a clinically evaluated HDACi, represents a promising approach to improve anabolic response in cachectic patients.

Anabolic SIRT4 Exerts Retrograde Control over TORC1 Signaling by Glutamine Sparing in the Mitochondria.

Anabolic and catabolic signaling mediated via mTOR and AMPK (AMP-activated kinase) have to be intrinsically coupled to mitochondrial functions for maintaining homeostasis and mitigate cellular/organismal stress. Although glutamine is known to activate mTOR, whether and how differential mitochondrial utilization of glutamine impinges on mTOR signaling has been less explored. Mitochondrial SIRT4, which unlike other sirtuins is induced in a fed state, is known to inhibit catabolic signaling/pathways through the AMPK-PGC1α/SIRT1-peroxisome proliferator-activated receptor α (PPARα) axis and negatively regulate glutamine metabolism via the tricarboxylic acid cycle. However, physiological significance of SIRT4 functions during a fed state is still unknown. Here, we establish SIRT4 as key anabolic factor that activates TORC1 signaling and regulates lipogenesis, autophagy, and cell proliferation. Mechanistically, we demonstrate that the ability of SIRT4 to inhibit anaplerotic conversion of glutamine to α-ketoglutarate potentiates TORC1. Interestingly, we also show that mitochondrial glutamine sparing or utilization is critical for differentially regulating TORC1 under fed and fasted conditions. Moreover, we conclusively show that differential expression of SIRT4 during fed and fasted states is vital for coupling mitochondrial energetics and glutamine utilization with anabolic pathways. These significant findings also illustrate that SIRT4 integrates nutrient inputs with mitochondrial retrograde signals to maintain a balance between anabolic and catabolic pathways.

The Effect of β-GPA on the Markers of Anabolic and Catabolic Signaling Pathways in Rat Soleus Muscle at the Initial Stage of Hindlimb Unloading

Molecular mechanisms initiating the development of atrophic changes in a mammalian postural muscle remain unclear. We have suggested that AMP-activated protein kinase (AMPK) may play an important role in the regulation of anabolic and catabolic signaling pathways in postural muscle at the initial stage of mechanical unloading, since skeletal muscle inactivation can lead to changes in the balance of intramuscular high-energy phosphates. Beta-guanidinopropionic acid (β-GPA) can act as a modulator of the balance of high-energy phosphates, application of which can reduce the content of intracellular high-energy phosphates. The purpose of this study was to assess signaling pathways of protein synthesis and degradation in rat soleus muscle after preliminary treatment with β-GPA followed by 1-day hindlimb unloading. The experiments were performed on male Wistar rats, which were divided into the following groups: (1) vivarium control (C); (2) vivarium control + β-GPA (C + GPA); (3) 1-day hindlimb unloading (HU); and (4) 1-day hindlimb unloading + β-GPA (HU + GPA). β-GPA was administered daily by intraperitoneal injections (400 mg/kg). The content of the key signaling proteins (AMPK, ACC, p70S6K, 4E-BP1, and FOXO3) was determined by gel electrophoresis followed by immunoblotting. The expression of mRNA of ubiquitin ligases (MuRF1 and MAFbx) was evaluated by real-time PCR. A prevention of reduction in phosphorylation of AMPK, ACC and 4E-BP1 and the return to control values of the increased level of p70S6K phosphorylation were observed in the group with 1-day unloading and β-GPA pretreatment. The phosphorylation of AKT and FOXO3, as well as the expression levels of MuRF1 and MAFbx in the HU + GPA group did not differ from the HU group. The obtained data indicate that the AMPK activity may play an important role in the modulation of anabolic mTORC1-signaling in rat soleus muscle at the early stage of simulated microgravity.

Effects of bathing in hot water after resistance exercise on muscle anabolic and catabolic signaling pathways in rat skeletal muscle

Effects of bathing in hot water after resistance exercise on muscle anabolic and catabolic signaling pathways in rat skeletal muscle

Human Pluripotent Stem Cell Modeling of Tuberous Sclerosis Complex Reveals Lineage-Specific Therapeutic Vulnerabilities

mTORC1 hyperactivation resulting from inactivating TSC2 mutations underlie the multi-system tumor disorder tuberous sclerosis complex (TSC) and the rare pulmonary neoplasm lymphangioleiomyomatosis (LAM). Mutation-bearing neural precursor cells (NPCs) lead to the formation of TSC brain tumors during development, while the cell of origin of TSC mesenchymal tumors such as LAM is unknown. We report the first model of multi-system TSC cell types, characterized by NPCs and neural crest cells (NCCs) differentiated in parallel from multiple engineered TSC2-/- human pluripotent stem cell (hPSC) lines. These cells successfully model defining phenotypes of neural and mesenchymal TSC, with transcriptomic signatures reflecting those observed in patient tumors, thus establishing TSC2-/- NCCs as a powerful model of LAM. Employing this rich cellular and transcriptomic resource, we identified lineage-specific catabolic signaling mechanisms that drive divergent cell behavior and therapeutic sensitivities that, in turn, demonstrate the power of employing lineage-specific stem cell models to dissect multi-system diseases.

Vitamin D repletion ameliorates adipose tissue browning and muscle wasting in infantile nephropathic cystinosis-associated cachexia.

BackgroundCtns−/− mice, a mouse model of infantile nephropathic cystinosis, exhibit hypermetabolism with adipose tissue browning and profound muscle wasting. Ctns−/− mice are 25(OH)D3 and 1,25(OH)2D3 insufficient. We investigated whether vitamin D repletion could ameliorate adipose tissue browning and muscle wasting in Ctns−/− mice.MethodsTwelve‐month‐old Ctns−/− mice and wild‐type controls were treated with 25(OH)D3 and 1,25(OH)2D3 (75 μg/kg/day and 60 ng/kg/day, respectively) or an ethylene glycol vehicle for 6 weeks. Serum chemistry and parameters of energy homeostasis were measured. We quantitated total fat mass and studied expression of molecules regulating adipose tissue browning, energy metabolism, and inflammation. We measured lean mass content, skeletal muscle fibre size, in vivo muscle function (grip strength and rotarod activity), and expression of molecules regulating muscle metabolism. We also analysed the transcriptome of skeletal muscle in Ctns−/− mice using RNAseq.ResultsSupplementation of 25(OH)D3 and 1,25(OH)2D3 normalized serum concentration of 25(OH)D3 and 1,25(OH)2D3 in Ctns−/− mice, respectively. Repletion of vitamin D partially or fully normalized food intake, weight gain, gain of fat, and lean mass, improved energy homeostasis, and attenuated perturbations of uncoupling proteins and adenosine triphosphate content in adipose tissue and muscle in Ctns−/− mice. Vitamin D repletion attenuated elevated expression of beige adipose cell biomarkers (UCP‐1, CD137, Tmem26, and Tbx1) as well as aberrant expression of molecules implicated in adipose tissue browning (Cox2, Pgf2α, and NF‐κB pathway) in inguinal white adipose tissue in Ctns−/− mice. Vitamin D repletion normalized skeletal muscle fibre size and improved in vivo muscle function in Ctns−/− mice. This was accompanied by correcting the increased muscle catabolic signalling (increased protein contents of IL‐1β, IL‐6, and TNF‐α as well as an increased gene expression of Murf‐2, atrogin‐1, and myostatin) and promoting the decreased muscle regeneration and myogenesis process (decreased gene expression of Igf1, Pax7, and MyoD) in skeletal muscles of Ctns−/− mice. Muscle RNAseq analysis revealed aberrant gene expression profiles associated with reduced muscle and neuron regeneration, increased energy metabolism, and fibrosis in Ctns−/− mice. Importantly, repletion of 25(OH)D3 and 1,25(OH)2D3 normalized the top 20 differentially expressed genes in Ctns−/− mice.ConclusionsWe report the novel findings that correction of 25(OH)D3 and 1,25(OH)2D3 insufficiency reverses cachexia and may improve quality of life by restoring muscle function in an animal model of infantile nephropathic cystinosis. Mechanistically, vitamin D repletion attenuates adipose tissue browning and muscle wasting in Ctns−/− mice via multiple cellular and molecular mechanisms.

Interactions of the super complexes: When mTORC1 meets the proteasome.

Homeostatic regulation of energy and metabolic status requires that anabolic and catabolic signaling pathways be precisely regulated and coordinated. Mammalian/mechanistic target of rapamycin complex 1 (mTORC1) is a mega protein complex that promotes energy-consuming anabolic processes of protein and nucleic acid synthesis as well lipogenesis in times of energy and nutrient abundance. However, it is best characterized as the regulator of steps leading to protein synthesis. The ubiquitin-proteasome proteolytic system (UPS) is a major intracellular proteolytic system whose activity is increased during periods of nutrient scarcity and in muscle wasting conditions such as cachexia. Recent studies have examined the impact of mTORC1 on levels and functions of the 26S proteasome, the mega protease complex of the UPS. Here we first briefly review current understanding of the regulation of mTORC1, the UPS, and the 26S proteasome complex. We then review evidence of the effect of each complex on the abundance and functions of the other. Given the fact that drugs that inhibit either complex are either in clinical trials or are approved for treatment of cancer, a muscle wasting condition, we identify studying the effect of combinatory mTORC1-proteasome inhibition on skeletal muscle mass and health as a critical area requiring investigation.

Effects of Plantar Mechanical Stimulation on Anabolic and Catabolic Signaling in Rat Postural Muscle Under Short-Term Simulated Gravitational Unloading.

It is known that plantar mechanical stimulation (PMS) is able to attenuate unloading-induced skeletal muscle atrophy and impaired muscle function. However, molecular mechanisms underlying the effect of PMS on skeletal muscle during unloading remain undefined. The aim of the study was to evaluate the effects of PMS on anabolic and catabolic signaling pathways in rat soleus at the early stages of mechanical unloading. Wistar rats were randomly assigned to ambulatory control, hindlimb suspension (HS) for 1 or 3 days, and HS for 1 or 3 days with PMS. The key anabolic and catabolic markers were assessed by western blotting and RT-PCR. Protein synthesis (PS) rate was estimated using SUnSET technique. PMS attenuated a 1-day HS-induced decrease in 4E-BP1, GSK-3β, and AMPK phosphorylation. PMS also partially prevented a decrease in PS, phosphorylation of GSK-3β, nNOS, and an increase in eEF2 phosphorylation after 3-day HS. PMS during 1- and 3-day HS prevented MuRF-1, but not MAFbx, upregulation but did not affect markers of ribosome biogenesis (18S + 28S rRNA, c-myc) as well as AKT phosphorylation. Thus, PMS during 3-day HS partially prevented a decrease in the global rate of PS in rat soleus muscle, which was accompanied by attenuation of MuRF-1 mRNA expression as well as changes in GSK-3β, nNOS, and eEF2 phosphorylation.

A novel nutritional supplement prevents muscle loss and accelerates muscle mass recovery in caloric-restricted mice

BackgroundMuscle atrophy is defined as decreased muscle mass, associated with aging as well as with various chronic diseases and is a fundamental cause of frailty, functional decline and disability. Frailty represents a huge potential public health issue worldwide with high impact on healthcare costs. A major clinical issue is therefore to devise new strategies preventing muscle atrophy. In this study, we tested the efficacy of Vital01, a novel oral nutritional supplement (ONS), on body weight and muscle mass using a caloric restriction-induced mouse model for muscle atrophy. MethodsMice were calorically restricted for 2 weeks to induce muscle atrophy: one control group received 60% kcal of the normal chow diet and one intervention group received 30% kcal chow and 30 kcal% Vital01. The effects on body weight, lean body mass, muscle histology and transcriptome were assessed. In addition, the effects of Vital01, in mice with established muscle atrophy, were assessed and compared to a standard ONS. To this end, mice were first calorically restricted on a 60% kcal chow diet and then refed with either 100 kcal% chow, a mix of Vital01 (receiving 60% kcal chow and 40 kcal% Vital01) or with a mix of standard, widely prescribed ONS (receiving 60 kcal% chow and 40 kcal% Fortisip Compact). ResultsVital01 attenuated weight loss (−15% weight loss for Vital01 vs. −25% for control group, p < 0.01) and loss of muscle mass (Vital01 with −13%, −12% and −18%, respectively, for gastrocnemius, quadriceps and tibialis vs. 25%, −23% and −28%, respectively, for control group, all p < 0.05) and also restored body weight, fat and muscle mass more efficiently when compared to Fortisip Compact. As assessed by transcriptome analysis and Western blotting of key proteins (e.g. phospoAKT, mTOR and S6K), Vital01 attenuated the catabolic and anabolic signaling pathways induced by caloric restriction and modulated inflammatory and mitochondrial pathways. In addition, Vital01 affected pathways related to matrix proteins/collagens homeostasis and tended to reduce caloric restriction-induced collagen fiber density in the quadriceps (with −27%, p = 0.051). ConclusionsWe demonstrate that Vital01 preserves muscle mass in a calorically restricted mouse model for muscle atrophy. Vital01 had preventive effects when administered during development of muscle atrophy. Furthermore, when administered in a therapeutic setting to mice with established muscle atrophy, Vital01 rapidly restored body weight and accelerated the recurrence of fat and lean body mass more efficiently than Fortisip Compact. Bioinformatics analysis of gene expression data identified regulatory pathways that were specifically influenced by Vital01 in muscle.

Mechanobiological osteocyte feedback drives mechanostat regulation of bone in a multiscale computational model.

Significant progress has been made to identify the cells and signaling molecules involved in the mechanobiological regulation of bone remodeling. It is now well accepted that osteocytes act as mechanosensory cells in bone expressing several signaling molecules such as nitric oxide (NO) and sclerostin (Scl) which are able to control bone remodeling responses. In this paper, we present a comprehensive multiscale computational model of bone remodeling which incorporates biochemical osteocyte feedback. The mechanostat theory is quantitatively incorporated into the model using mechanical feedback to control expression levels of NO and Scl. The catabolic signaling pathway RANK-RANKL-OPG is co-regulated via (continuous) PTH and NO, while the anabolic Wnt signaling pathway is described via competitive binding reactions between Wnt, Scl and the Wnt receptors LRP5/6. Using this novel model of bone remodeling, we investigate the effects of changes in the mechanical loading and hormonal environment on bone balance. Our numerical simulations show that we can calibrate the mechanostat anabolic and catabolic regulatory mechanisms so that they are mutually exclusive. This is consistent with previous models that use a Wolff-type law to regulate bone resorption and formation separately. Furthermore, mechanical feedback provides an effective mechanism to obtain physiological bone loss responses due to mechanical disuse and/or osteoporosis.

High-Frequency Stimulation on Skeletal Muscle Maintenance in Female Cachectic Mice.

The purpose of this study was to determine whether high-frequency electric stimulation (HFES) could attenuate muscle mass loss during the progression of cancer cachexia in female tumor-bearing mice. Female wild-type (WT) and Apc (Min) mice (16-18 wk old) performed either repeated bouts or a single bout of HFES (10 sets of 6 repetitions, ~22 min), which eccentrically contracts the tibialis anterior (TA) muscle. TA myofiber size, oxidative capacity, anabolic signaling, and catabolic signaling were examined. Min had reduced TA muscle mass and type IIa and type IIb fiber sizes compared with WT. HFES increased the muscle weight and the mean cross-sectional area of type IIa and type IIb fibers in WT and Min mice. HFES increased mTOR signaling and myofibrillar protein synthesis and attenuated cachexia-induced AMPK activity. HFES attenuated the cachexia-associated decrease in skeletal muscle oxidative capacity. HFES in female mice can activate muscle protein synthesis through mTOR signaling and repeated bouts of contraction can attenuate cancer-induced muscle mass loss.

Cellular and molecular signatures of alcohol-induced myopathy in women.

Alcoholic myopathy is characterized by the reduction in cross-sectional area (CSA) of muscle fibers and impaired anabolic signaling. The goal of the current study was to investigate the causes and compare the changes in CSA and fiber type composition with the modifications of anabolic and catabolic signaling pathways at the early stages of chronic alcohol consumption in women. Skeletal muscle samples from 5 female patients with alcohol abuse (AL; 43 ± 5 yr old; alcohol abuse duration 5,6 ± 0,6 yr) were compared with the muscle from the control group of 8 healthy women (C; 35 ± 4 yr old). The average daily dose of alcohol consumption was 110 ± 10 ml of pure ethanol. In women patients, a significant decrease in CSA of type I and II muscle fibers, titin and nebulin content, plasma IGF-1 level and total IRS-1, p-Akt and p-4E-BP1 in vastus lateralis was found in comparison with the control group. The p-AMPK level was found to be increased versus the control group. In women patients with chronic alcoholic myopathy 1) both fast and slow muscle fibers are subjected to atrophy; 2) impairments in IGF-I-dependent signaling and pathways controlling translation initiation (AMPK/mTOR/4E-BP1), but not translation elongation, are observed; 3) the level of calpain-1 and ubiquitinated proteins increases, unlike E3 ligases content.

Gene Expression Pattern and Regulatory Network of α-Toxin Treatment in Bombyx mori.

Bacillus bombyseptieus is a pathogen of Bombyx mori; it can cause bacterial septicemia in silkworm. One of the components of the parasporal crystal toxin of B. bombyseptieus, α-toxin, plays an important role in the process of infection in silkworm. In this study, we investigated the immune response of silkworm induced by α-toxin by using RNA-seq. We compared the changes in gene expression in the midgut, fatbody, and hemocytes of silkworm and in the B. mori embryonic cell line (BmE) after treatment with α-toxin and identified 952 differentially expressed genes and 353 differentially expressed long noncoding RNAs (lncRNAs). These regulated genes in different tissues were found to be enriched in different pathways. The upregulated genes in the midgut were mainly involved in peptidoglycan catabolic process and tyrosine kinase signaling pathway, whereas the downregulated genes were mainly involved in chitin metabolic pathways. The upregulated genes in fatbody were also involved in peptidoglycan catabolic process, but they were for a different peptidoglycan subtype. Further, genes encoding cecropins were enriched in the fatbody. The downregulated genes were mainly involved in the metabolic pathways of fundamental substances such as cellular protein metabolic process and nucleobase-containing compound metabolic process. These results suggest that α-toxin can induce various immune responses in silkworm, and further studies are warranted to understand the mechanism of α-toxin action in silkworm. Further, lncRNAs and differentially expressed genes were correlated using coexpression network analysis. Our findings revealed potential candidate genes and lncRNAs that might play important physiological functions in the immune response to α-toxins in silkworm.

Inhibition of Proteasomes by Bortezomib Decreases MuRF-1 and MAFbx mRNA Expression in Rat Soleus during Hindlimb Unloading

Skeletal muscle atrophy caused by unloading is accompanied by increased proteolysis and decreased protein synthesis. It is established that in conditions of muscle unloading, concentration of free amino acids is increased. We hypothesized that proteasome inhibition may decrease amino acid accumulation in skeletal muscle and prevent the atrophy. To test this hypothesis, we treated rats with bortezomib (a proteasome inhibitor) during 7-day hindlimb suspension. Content of key signaling proteins of various signaling pathways was measured by Western-blotting; mRNA level of E3 ligases by RT-PCR, rate of protein synthesis by SUnSET technique. Soleus muscle weight and intensity of the protein synthesis in the groups of “hindlimb suspension” (HS) and “HS + bortezomib” (HSB) were equally reduced as compared to control. Levels of MuRF-1 and MAFbx mRNAs, content of MuRF-1 and calpain-1 proteins, and level of the protein ubiquitination were increased only in the HS group and remained unchanged in the HSB group as compared to the control group. We conclude that inhibition of proteasomes during m. soleus unloading prevents increase in activity of some components of catabolic signaling pathways. However, this is not sufficient to reduce rate of the atrophic processes in skeletal muscle.

Muscle Loss in Chronic Liver Diseases: The Example of Nonalcoholic Liver Disease.

Recent publications highlight a frequent loss of muscle mass in chronic liver diseases, including nonalcoholic fatty liver disease (NAFLD), and its association with a poorer prognosis. In NAFLD, given the role of muscle in energy metabolism, muscle loss promotes disease progression. However, liver damage may be directly responsible of this muscle loss. Indeed, muscle homeostasis depends on the balance between peripheral availability and action of anabolic effectors and catabolic signals. Moreover, insulin resistance of protein metabolism only partially explains muscle loss during NAFLD. Interestingly, some data indicate specific alterations in the liver–muscle axis, particularly in situations such as excess fructose/sucrose consumption, associated with increased hepatic de novo lipogenesis (DNL) and endoplasmic reticulum stress. In this context, the liver will be responsible for a decrease in the peripheral availability of anabolic factors such as hormones and amino acids, and for the production of catabolic effectors such as various hepatokines, methylglyoxal, and uric acid. A better understanding of these liver–muscle interactions could open new therapeutic opportunities for the management of NAFLD patients.