The E3 ubiquitin ligase TRIM62 and inflammation-induced skeletal muscle atrophy

Elevated levels of S100A8 and S100A9 exacerbate muscle mitochondrial fragmentation in sepsis-induced muscle atrophy

Sepsis-induced skeletal muscle atrophy is common in septic patients with the increases risk of mortality and is associated with myocellular mitochondrial dysfunction. Nevertheless, the specific mechanism of sepsis muscle atrophy remains unclear. Here we conducted a clinical retrospective analysis and observed the elevation of skeletal muscle index (ΔSMI) was an independent risk factor for 60-day mortality in septic patients. Moreover, in mouse model of sepsis, the skeletal muscle atrophy was also observed, which was associated with the upregulation of S100a8/a9-mediated mitochondrial dysfunction. Inhibition of S100a8/a9 significantly improved mitochondrial function and alleviated muscle atrophy. Conversely, administration of recombinant S100a8/a9 protein exacerbated mitochondrial energy exhaustion and myocyte atrophy. Mechanistically, S100a8/a9 binding to RAGE induced Drp1 phosphorylation and mitochondrial fragmentation, resulting in muscle atrophy. Additionally, RAGE ablation or administration of Drp1 inhibitor significantly reduced Drp1-mediated mitochondrial fission, improved mitochondrial morphology and function. Our findings indicated the pivotal role of S100a8/a9 in driving the mitochondrial fragmentation in septic muscle atrophy. Targeting S100a8/a9-RAGE-initiated mitochondrial fission might offer a promising therapeutic intervention against septic muscle atrophy.

Inflammation and Fatty Infiltration Correlates with Rotator Cuff Muscle Atrophy in Hypercholesterolemic Yucatan Microswine

Rotator cuff injuries are the most common injuries among active and training astronauts. According to the CDC, 1 in 4 adults in the U.S. experience rotator cuff injuries, particularly affecting the supraspinatus muscle. Hypercholesterolemia, a condition characterized by high levels of LDL cholesterol, is prevalent in approximately 2 in 5 adults in the US and is a risk factor for worsened outcomes in shoulder inflammation and rotator cuff injury repairs. Chronic inflammation, a prolonged low-grade inflammatory state, can arise from conditions like hypercholesterolemia and contribute to muscle atrophy. Skeletal muscle atrophy can be caused by factors such as disuse, aging, malnutrition, and microgravity, and currently lacks approved drug therapies. Thus, gaining a comprehensive understanding of the associations between hypercholesterolemia, chronic inflammation, and skeletal muscle atrophy is imperative for developing effective strategies to manage this condition. We conducted an animal study in Yucatan miniswine to investigate the impact of a high-cholesterol diet on rotator cuff muscle. The results suggested the presence of chronic inflammation in rotator cuff muscle hypercholesterolemic swine, associated with elevated pro-inflammatory cytokines and intramuscular adipocytes, and skeletal muscle atrophy. The results also revealed upregulation of the FOXO3/TRIM63/Titin axis in a hyperlipidemic state. These findings open new perspectives for developing better treatment strategies by targeting the FOXO3/TRIM63/Titin axis to manage rotator cuff muscle atrophy in the context of hypercholesterolemia.

Glucocorticoid treatment increases cholesterol availability during critical illness: effect on adrenal and muscle function

BACKGROUND

Hypocholesterolemia hallmarks critical illness though the underlying pathophysiology is incompletely understood. As low circulating cholesterol levels could partly be due to an increased conversion to cortisol/corticosterone, we hypothesized that glucocorticoid treatment, via reduced de novo adrenal cortisol/corticosterone synthesis, might improve cholesterol availability and as such affect adrenal gland and skeletal muscle function.

METHODS

In a matched set of prolonged critically ill patients (n = 324) included in the EPaNIC RCT, a secondary analysis was performed to assess the association between glucocorticoid treatment and plasma cholesterol from ICU admission to day five. Next, in a mouse model of cecal ligation and puncture-induced sepsis, septic mice were randomized to receive either hydrocortisone (1.2 mg/day) (n = 17) or placebo (n = 15) for 5 days, as compared with healthy mice (n = 18). Plasma corticosterone, cholesterol, and adrenocortical and myofiber cholesterol were quantified. Adrenal structure and steroidogenic capacity were evaluated. Muscle force and markers of atrophy, fibrosis and regeneration were quantified. In a consecutive mouse study with identical design (n = 24), whole body composition was assessed by EchoMRI to investigate impact on lean mass, fat mass, total and free water.

RESULTS

In human patients, glucocorticoid treatment was associated with higher plasma HDL- and LDL-cholesterol from respectively ICU day two and day three, up to day five (P < 0.05). Plasma corticosterone was no longer elevated in hydrocortisone-treated septic mice compared to placebo, whereas the sepsis-induced reduction in plasma HDL- and LDL-cholesterol and in adrenocortical cholesterol was attenuated (P < 0.05), but without improving the adrenocortical ACTH-induced CORT response and with increased adrenocortical inflammation and apoptosis (P < 0.05). Total body mass was further decreased in hydrocortisone-treated septic mice (P < 0.01) compared to placebo, with no additional effect on muscle mass, force or myofiber size. The sepsis-induced rise in markers of muscle atrophy and fibrosis was unaffected by hydrocortisone treatment, whereas markers of muscle regeneration were suppressed compared to placebo (P < 0.05). An increased loss of lean body mass and total and free water was observed in hydrocortisone-treated septic mice compared to placebo (P < 0.05).

CONCLUSIONS

Glucocorticoid treatment partially attenuated critical illness-induced hypocholesterolemia, but at a cost of impaired adrenal function, suppressed muscle regeneration and exacerbated loss of body mass.

Dynamic alternations of three-dimensional chromatin architecture contribute to phenotypic characteristics of breast muscle in chicken

Breast muscle growth rate and intramuscular fat (IMF) content show apparent differences between fast-growing broilers and slow-growing indigenous chickens. However, the underlying genetic basis of these phenotypic characteristics remains elusive. In this study, we investigate the dynamic alterations of three-dimensional genome architecture and chromatin accessibility in breast muscle across four key developmental stages from embryo to starter chick in Arbor Acres (AA) broilers and Yufen (YF) indigenous chickens. The limited breed-specifically up-regulated genes (Bup-DEGs) are embedded in breed-specific A compartment, while a majority of the Bup-DEGs involving myogenesis and adipogenesis are regulated by the breed-specific TAD reprogramming. Chromatin loops allow distal accessible regions to interact with myogenic genes, and those loops share an extremely low similarity between chicken with different growth rate. Moreover, AA-specific loop interactions promote the expression of 40 Bup-DEGs, such as IGF1, which contributes to myofiber hypertrophy. YF-specific loop interactions or distal accessible regions lead to increased expression of 5 Bup-DEGs, including PIGO, PEMT, DHCR7, TMEM38B, and DHDH, which contribute to IMF deposition. These results help elucidate the regulation of breast muscle growth and IMF deposition in chickens.

A critical discussion on the relationship between E3 ubiquitin ligases, protein degradation, and skeletal muscle wasting: it's not that simple

Ubiquitination is an important post-translational modification (PTM) for protein substrates, whereby ubiquitin is added to proteins through the coordinated activity of activating (E1), ubiquitin-conjugating (E2), and ubiquitin ligase (E3) enzymes. The E3s provide key functions in the recognition of specific protein substrates to be ubiquitinated and aid in determining their proteolytic or nonproteolytic fates, which has led to their study as indicators of altered cellular processes. MuRF1 and MAFbx/Atrogin-1 were two of the first E3 ubiquitin ligases identified as being upregulated in a range of different skeletal muscle atrophy models. Since their discovery, the expression of these E3 ubiquitin ligases has often been studied as a surrogate measure of changes to bulk protein degradation rates. However, emerging evidence has highlighted the dynamic and complex regulation of the ubiquitin proteasome system (UPS) in skeletal muscle and demonstrated that protein ubiquitination is not necessarily equivalent to protein degradation. These observations highlight the potential challenges of quantifying E3 ubiquitin ligases as markers of protein degradation rates or ubiquitin proteasome system (UPS) activation. This perspective examines the usefulness of monitoring E3 ubiquitin ligases for determining specific or bulk protein degradation rates in the settings of skeletal muscle atrophy. Specific questions that remain unanswered within the skeletal muscle atrophy field are also identified, to encourage the pursuit of new research that will be critical in moving forward our understanding of the molecular mechanisms that govern protein function and degradation in muscle.

Activin A level is associated with physical function in critically ill patients

BACKGROUND

Activin A is a potent negative regulator of muscle mass elevated in critical illness. It is unclear whether muscle strength and physical function in critically ill humans are associated with elevated activin A levels.

OBJECTIVES

The objective of this study was to investigate the relationship between serum activin A levels, muscle strength, and physical function at discharge from the intensive care unit (ICU) and hospital.

METHODS

Thirty-six participants were recruited from two tertiary ICUs in Melbourne, Australia. Participants were included if they were mechanically ventilated for >48 h and expected to have a total ICU stay of >5 days. The primary outcome measure was the Six-Minute Walk Test distance at hospital discharge. Secondary outcome measures included handgrip strength, Medical Research Council Sum Score, Physical Function ICU Test Scored, Six-Minute Walk Test, and Timed Up and Go Test assessed throughout the hospital admission. Total serum activin A levels were measured daily in the ICU.

RESULTS

High peak activin A was associated with worse Six-Minute Walk Test distance at hospital discharge (linear regression coefficient, 95% confidence interval, p-value: -91.3, -154.2 to -28.4, p = 0.007, respectively). Peak activin A concentration was not associated with the secondary outcome measures.

CONCLUSIONS

Higher peak activin A may be associated with the functional decline of critically ill patients. Further research is indicated to examine its potential as a therapeutic target and a prospective predictor for muscle wasting in critical illness.

STUDY REGISTRATION

ACTRN12615000047594.

TRIM62 knockdown by inhibiting the TLR4/NF-κB pathway and NLRP3 inflammasome attenuates cognitive impairment induced by diabetes in mice

The tripartite motif 62 is an E3 ubiquitin ligase protein that regulates cellular processes, including differentiation, immunity, development and apoptosis, leading to various disease states, such as cancer and inflammatory diseases. However, the role and mechanism of the tripartite motif 62 in the process of diabetic-induced cognitive impairment have not been reported. Therefore, the aim of this study was to investigate the role and mechanism of the tripartite motif 62 in diabetic-induced cognitive impairment. The results showed that the expression of the tripartite motif 62 was up-regulated in diabetic mice. Silencing of TRIM62 increased body weight and decreased fasting blood glucose in diabetic mice. In addition, knockdown of the tripartite motif 62 inhibited STZ-induced inflammation, apoptosis and oxidative stress. Further studies showed that the TLR4/NF-κB pathway and NLRP3 inflammasomes were involved in the regulation of diabetic mice by the tripartite motif 62. More importantly, inhibition of the tripartite motif 62 improved cognitive impairment and learning ability in mice. In conclusion, inhibition of TRIM62 inhibits STZ-induced inflammation, cell apoptosis and oxidative stress, and improves the cognitive ability of mice. Therefore, the tripartite motif 62 may be an important target for the treatment of diabetes-induced cognitive impairment.

Tripartite Motif Protein Family in Central Nervous System Diseases

Tripartite motif (TRIM) protein superfamily is a group of E3 ubiquitin ligases characterized by the conserved RING domain, the B-box domain, and the coiled-coil domain (RBCC). It is widely involved in various physiological and pathological processes, such as intracellular signal transduction, cell cycle regulation, oncogenesis, and innate immune response. Central nervous system (CNS) diseases are composed of encephalopathy and spinal cord diseases, which have a high disability and mortality rate. Patients are often unable to take care of themselves and their life quality can be seriously declined. Initially, the function research of TRIM proteins mainly focused on cancer. However, in recent years, accumulating attention is paid to the roles they play in CNS diseases. In this review, we integrate the reported roles of TRIM proteins in the pathological process of CNS diseases and related signaling pathways, hoping to provide theoretical bases for further research in treating CNS diseases targeting TRIM proteins. TRIM proteins participated in CNS diseases. TRIM protein family is characterized by a highly conserved RBCC domain, referring to the RING domain, the B-box domain, and the coiled-coil domain. Recent research has discovered the relations between TRIM proteins and various CNS diseases, especially Alzheimer's disease, Parkinson's disease, and ischemic stroke.

M2 macrophage-derived exosomal miR-193b-3p promotes progression and glutamine uptake of pancreatic cancer by targeting TRIM62

BACKGROUND

Pancreatic cancer (PC) is a highly lethal malignancy that requires effective novel therapies. M2 macrophages are abundant in the PC microenvironment and promote cancer progression. Exosomes are emerging mediators of the crosstalk between cancer cells and the microenvironment. This study was conducted to explore the role of M2 macrophage-derived exosomes in PC.

METHODS

Exosomes derived from M2 macrophages were extracted. miR-193b-3p and TRIM62 were overexpressed or silenced to examine their function in PC. Luminescence assays were used to investigate the interaction between miR-193b-3p and TRIM62. Cell proliferation was examined by EdU staining. Would healing and transwell assays were applied to evaluate cell migration and invasion. Co-immunoprecipitation was used to assess the interaction between TRIM62 and c-Myc. Gene and protein expressions were analyzed by quantitative RT-PCR and immunoblotting, respectively.

RESULTS

M2 macrophage-derived exosomal miR-193b-3p promoted the proliferation, migration, invasion, and glutamine uptake of SW1990 cells. Mechanism study revealed that TRIM62 is a target of miR-193b-3p. TRIM62 inhibited the proliferation, migration, invasion, and glutamine uptake of SW1990 cells by promoting c-Myc ubiquitination. Our data also suggested that TRIM62 expression negatively correlated with miR-193b-3p and c-Myc expression. High-expression of miR-193b-3p and c-Myc predicts poor prognosis, whereas low-expression of TRIM62 predicts poor prognosis in patients with PC.

CONCLUSION

M2 macrophage-derived exosomal miR-193b-3p enhances the proliferation, migration, invasion, and glutamine uptake of PC cells by targeting TRIM62, resulting in the decrease of c-Myc ubiquitination. This study not only reveals the mechanism underlying the crosstalk between M2 macrophages and PC cells but also suggests a promising therapeutic target for PC.

Long-term epigenetic and metabolomic changes in the mouse ventricular myocardium after exertional heat stroke

Evidence from human epidemiological studies suggests that exertional heat stroke (EHS) results in an elevated risk of long-term cardiovascular and systemic disease. Previous results using a preclinical mouse model of EHS demonstrated severe metabolic imbalances in ventricular myocardium developing at 9-14 days of recovery. Whether this resolves over time is unknown. We hypothesized that the long-term effects of EHS on the heart reflect retained maladaptive epigenetic responses. In this study, we evaluated genome-wide DNA methylation, RNA-Seq, and metabolomic profiles of the left ventricular myocardium in female C57BL/6 mice, 30 days after EHS (exercise in 37.5°C; n = 7-8), compared with exercise controls. EHS mice ran to loss of consciousness, reaching core temperatures of 42.4 ± 0.2°C. All mice recovered quickly. After 30 days, the left ventricles were rapidly frozen for DNA methyl sequencing, RNA-Seq, and untargeted metabolomics. Ventricular DNA from EHS mice revealed >13,000 differentially methylated cytosines (DMCs) and >900 differentially methylated regions (DMRs; ≥5 DMCs with ≤300 bp between each CpG). Pathway analysis using DMRs revealed alterations in genes regulating basic cell functions, DNA binding, transcription, and metabolism. Metabolomics and mRNA expression revealed modest changes that are consistent with a return to homeostasis. Methylation status did not predict RNA expression or metabolic state at 30 days. We conclude that EHS induces a sustained DNA methylation memory lasting over 30 days of recovery, but ventricular gene expression and metabolism return to a relative homeostasis at rest. Such long-lasting alterations to the DNA methylation landscape could alter responsiveness to environmental or clinical challenges later in life.

microRNA-181a Promotes Mitochondrial Dysfunction and Inflammatory Reaction in a Rat Model of Intensive Care Unit-Acquired Weakness by Inhibiting IGFBP5 Expression

This study investigated mechanisms by which microRNA (miR)-181a orchestrates mitochondrial dysfunction and inflammation in a rat model of intensive care unit-acquired weakness (ICU-AW). Expression of miR-181a and insulin-like growth factor binding protein 5 (IGFBP5) was detected and then miR-181a was overexpressed or inhibited and IGFBP5 was overexpressed in the ICU-AW rats. The expression of UCP-3, metaphase chromosome protein 1 (MCP1), mitochondrial DNA (mtDNA), inflammatory factors, phosphorylation (p)-JAK1, p-STAT1, and p-STAT2 were measured in skeletal muscle tissues; binding of miR-181a to IGFBP5 was evaluated by a dual-luciferase reporter assay. The results demonstrated high expression of miR-181a and low expression of IGFBP5 in ICU-AW versus control rats; IGFBP5 was identified as a target gene of miR-181a. Further experiments demonstrated that ICU-AW rats suffered from marked loss of grip strength and decreased adenosine triphosphate production, mtDNA content, and UCP-3 mRNA expression in skeletal muscles; this was accompanied by elevated TNF-α, IL-6, IL-1β, MCP1, p-JAK1, p-STAT1, and p-STAT2 levels. Importantly, miR-181a suppression alleviated strength loss, inflammatory reaction, and mitochondrial dysfunction and diminished the phosphorylation levels of JAK1, STAT1, and STAT2 whereas IGFBP5 upregulation rescued the effect of miR-181a overexpression in ICU-AW rats. These results indicate that miR-181a promotes mitochondrial dysfunction and inflammation by activating the JAK/STAT pathway via IGFBP5 in ICU-AW model rats.

The Transcription Factor EB (TFEB) Sensitizes the Heart to Chronic Pressure Overload

The transcription factor EB (TFEB) promotes protein degradation by the autophagy and lysosomal pathway (ALP) and overexpression of TFEB was suggested for the treatment of ALP-related diseases that often affect the heart. However, TFEB-mediated ALP induction may perturb cardiac stress response. We used adeno-associated viral vectors type 9 (AAV9) to overexpress TFEB (AAV9-Tfeb) or Luciferase-control (AAV9-Luc) in cardiomyocytes of 12-week-old male mice. Mice were subjected to transverse aortic constriction (TAC, 27G; AAV9-Luc: n = 9; AAV9-Tfeb: n = 14) or sham (AAV9-Luc: n = 9; AAV9-Tfeb: n = 9) surgery for 28 days. Heart morphology, echocardiography, gene expression, and protein levels were monitored. AAV9-Tfeb had no effect on cardiac structure and function in sham animals. TAC resulted in compensated left ventricular hypertrophy in AAV9-Luc mice. AAV9-Tfeb TAC mice showed a reduced LV ejection fraction and increased left ventricular diameters. Morphological, histological, and real-time PCR analyses showed increased heart weights, exaggerated fibrosis, and higher expression of stress markers and remodeling genes in AAV9-Tfeb TAC compared to AAV9-Luc TAC. RNA-sequencing, real-time PCR and Western Blot revealed a stronger ALP activation in the hearts of AAV9-Tfeb TAC mice. Cardiomyocyte-specific TFEB-overexpression promoted ALP gene expression during TAC, which was associated with heart failure. Treatment of ALP-related diseases by overexpression of TFEB warrants careful consideration.

Hidden Agenda - The Involvement of Endoplasmic Reticulum Stress and Unfolded Protein Response in Inflammation-Induced Muscle Wasting

Critically ill patients at the intensive care unit (ICU) often develop a generalized weakness, called ICU-acquired weakness (ICUAW). A major contributor to ICUAW is muscle atrophy, a loss of skeletal muscle mass and function. Skeletal muscle assures almost all of the vital functions of our body. It adapts rapidly in response to physiological as well as pathological stress, such as inactivity, immobilization, and inflammation. In response to a reduced workload or inflammation muscle atrophy develops. Recent work suggests that adaptive or maladaptive processes in the endoplasmic reticulum (ER), also known as sarcoplasmic reticulum, contributes to this process. In muscle cells, the ER is a highly specialized cellular organelle that assures calcium homeostasis and therefore muscle contraction. The ER also assures correct folding of proteins that are secreted or localized to the cell membrane. Protein folding is a highly error prone process and accumulation of misfolded or unfolded proteins can cause ER stress, which is counteracted by the activation of a signaling network known as the unfolded protein response (UPR). Three ER membrane residing molecules, protein kinase R-like endoplasmic reticulum kinase (PERK), inositol requiring protein 1a (IRE1a), and activating transcription factor 6 (ATF6) initiate the UPR. The UPR aims to restore ER homeostasis by reducing overall protein synthesis and increasing gene expression of various ER chaperone proteins. If ER stress persists or cannot be resolved cell death pathways are activated. Although, ER stress-induced UPR pathways are known to be important for regulation of skeletal muscle mass and function as well as for inflammation and immune response its function in ICUAW is still elusive. Given recent advances in the development of ER stress modifying molecules for neurodegenerative diseases and cancer, it is important to know whether or not therapeutic interventions in ER stress pathways have favorable effects and these compounds can be used to prevent or treat ICUAW. In this review, we focus on the role of ER stress-induced UPR in skeletal muscle during critical illness and in response to predisposing risk factors such as immobilization, starvation and inflammation as well as ICUAW treatment to foster research for this devastating clinical problem.

Out of Control: The Role of the Ubiquitin Proteasome System in Skeletal Muscle during Inflammation

The majority of critically ill intensive care unit (ICU) patients with severe sepsis develop ICU-acquired weakness (ICUAW) characterized by loss of muscle mass, reduction in myofiber size and decreased muscle strength leading to persisting physical impairment. This phenotype results from a dysregulated protein homeostasis with increased protein degradation and decreased protein synthesis, eventually causing a decrease in muscle structural proteins. The ubiquitin proteasome system (UPS) is the predominant protein-degrading system in muscle that is activated during diverse muscle atrophy conditions, e.g., inflammation. The specificity of UPS-mediated protein degradation is assured by E3 ubiquitin ligases, such as atrogin-1 and MuRF1, which target structural and contractile proteins, proteins involved in energy metabolism and transcription factors for UPS-dependent degradation. Although the regulation of activity and function of E3 ubiquitin ligases in inflammation-induced muscle atrophy is well perceived, the contribution of the proteasome to muscle atrophy during inflammation is still elusive. During inflammation, a shift from standard- to immunoproteasome was described; however, to which extent this contributes to muscle wasting and whether this changes targeting of specific muscular proteins is not well described. This review summarizes the function of the main proinflammatory cytokines and acute phase response proteins and their signaling pathways in inflammation-induced muscle atrophy with a focus on UPS-mediated protein degradation in muscle during sepsis. The regulation and target-specificity of the main E3 ubiquitin ligases in muscle atrophy and their mode of action on myofibrillar proteins will be reported. The function of the standard- and immunoproteasome in inflammation-induced muscle atrophy will be described and the effects of proteasome-inhibitors as treatment strategies will be discussed.

Global alternative splicing landscape of skeletal muscle atrophy induced by hindlimb unloading

Background

Long-term exposure to microgravity will cause skeletal muscle atrophy, which can cause serious harm to astronauts in space travel. Therefore, it is important to explore skeletal muscle atrophy’s molecular mechanism for its prevention and treatment. However, as an important regulatory approach of skeletal muscle physiology, the role of alternative splicing in skeletal muscle atrophy, especially skeletal muscle atrophy caused by disuse, is unclear.

Methods

We established a rat hindlimb unloading model and performed RNA sequencing on soleus muscle, which was seriously atrophied during unloading. Several bioinformatics methods were used to identify alternative splicing events and determine their gene functions.

Results

Many alternative splicing events were found to occur at different time points (12 h, 24 h, 36 h, 3 days, and 7 days) after hindlimb unloading. These differential alternative splicing events mainly occurred in the gene's coding domain sequence region, and 59% of the alternative splicing events caused open reading frameshift. Bioinformatics analysis results showed that genes with different alternative splicing events were enriched in multiple pathways related to muscle atrophy, including the insulin signaling pathway, endocytosis, mitophagy, and ubiquitin-proteasome pathway. Moreover, alternative splicing of several deubiquitinase genes persisted during skeletal muscle atrophy induced by unloading. Additionally, we identified 10 differentially expressed RNA binding proteins during skeletal muscle atrophy induced by unloading, mainly containing Xpo4, Eif4e2, P4ha1, Lrrfip1, Zc3h14, Emg1, Hnrnp h1, Mbnl2, RBfox1, and Mbnl1. Hnrnp h1 and Mbnl2 were significantly downregulated, and RBfox1 and Mbnl1 were significantly upregulated during skeletal muscle atrophy caused by unloading.

Conclusions

To the best of our knowledge, the present study is the first to propose alternative splicing alterations related to disuse-induced muscle atrophy, emphasizing that alternative splicing is a new focus of attention in the occurrence of muscle atrophy.

Activation of Tripartite Motif Containing 63 Expression by Transcription Factor EB and Transcription Factor Binding to Immunoglobulin Heavy Chain Enhancer 3 Is Regulated by Protein Kinase D and Class IIa Histone Deacetylases

Rationale

The ubiquitin–proteasome system (UPS) is responsible for skeletal muscle atrophy. We showed earlier that the transcription factor EB (TFEB) plays a role by increasing E3 ubiquitin ligase muscle really interesting new gene-finger 1(MuRF1)/tripartite motif-containing 63 (TRIM63) expression. MuRF 1 ubiquitinates structural proteins and mediates their UPS-dependent degradation. We now investigated how TFEB-mediated TRIM63 expression is regulated.

Objective

Because protein kinase D1 (PKD1), histone deacetylase 5 (HDAC5), and TFEB belong to respective families with close structural, regulatory, and functional properties, we hypothesized that these families comprise a network regulating TRIM63 expression.

Methods and Results

We found that TFEB and transcription factor for immunoglobulin heavy-chain enhancer 3 (TFE3) activate TRIM63 expression. The class IIa HDACs HDAC4, HDAC5, and HDAC7 inhibited this activity. Furthermore, we could map the HDAC5 and TFE3 physical interaction. PKD1, PKD2, and PKD3 reversed the inhibitory effect of all tested class IIa HDACs toward TFEB and TFE3. PKD1 mediated nuclear export of all HDACs and lifted TFEB and TFE3 repression. We also mapped the PKD2 and HDAC5 interaction. We found that the inhibitory effect of PKD1 and PKD2 toward HDAC4, HDAC5, and HDAC7 was mediated by their phosphorylation and 14-3-3 mediated nuclear export.

Conclusion

TFEB and TFE3 activate TRIM63 expression. Both transcription factors are controlled by HDAC4, HDAC5, HDAC7, and all PKD-family members. We propose that the multilevel PKD/HDAC/TFEB/TFE3 network tightly controls TRIM63 expression.

Ubiquitin Ligases at the Heart of Skeletal Muscle Atrophy Control

Skeletal muscle loss is a detrimental side-effect of numerous chronic diseases that dramatically increases mortality and morbidity. The alteration of protein homeostasis is generally due to increased protein breakdown while, protein synthesis may also be down-regulated. The ubiquitin proteasome system (UPS) is a master regulator of skeletal muscle that impacts muscle contractile properties and metabolism through multiple levers like signaling pathways, contractile apparatus degradation, etc. Among the different actors of the UPS, the E3 ubiquitin ligases specifically target key proteins for either degradation or activity modulation, thus controlling both pro-anabolic or pro-catabolic factors. The atrogenes MuRF1/TRIM63 and MAFbx/Atrogin-1 encode for key E3 ligases that target contractile proteins and key actors of protein synthesis respectively. However, several other E3 ligases are involved upstream in the atrophy program, from signal transduction control to modulation of energy balance. Controlling E3 ligases activity is thus a tempting approach for preserving muscle mass. While indirect modulation of E3 ligases may prove beneficial in some situations of muscle atrophy, some drugs directly inhibiting their activity have started to appear. This review summarizes the main signaling pathways involved in muscle atrophy and the E3 ligases implicated, but also the molecules potentially usable for future therapies.

TRIM62 knockout protects against cerebral ischemic injury in mice by suppressing NLRP3-regulated neuroinflammation

Cerebral stroke is a leading global cause for mortality and disability. However, its pathogenesis is still unclear. Most tripartite motif (TRIM) family proteins, including TRIM62, have E3 ubiquitin ligase activities, and have multiple functions in regulating cellular processes. Nevertheless, the effects of TRIM62 on cerebral stroke still remain vague. Here, we reported that TRIM62 expression was markedly up-regulated in oxygen and glucose deprivation (OGD)-treated microglial cells. After cerebral ischemia, significantly elevated expression of TRIM62 was detected in peri-infarct area of wild type (WT) mice. The TRIM62 knockout (KO) mice exhibited alleviated apoptosis and neuroinflammation in the ischemic brain, eventually attenuating the stroke outcomes. Both in vitro and in vivo studies showed that nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome was dramatically activated in cerebral ischemia/reperfusion (I/R) conditions, while being ameliorated in TRIM62-KO mice, contributing to the suppression of neuroinflammatory response. Importantly, the in vitro experiments showed that OGD could induce the K63-ubiquitination of TRIM62 and the interaction between TRIM62 and NLRP3. In addition, adenovirus-regulated TRIM62 over-expression promoted the NLRP3 and nuclear factor κB (NF-κB) signaling, along with elevated interleukin-1β (IL-1β) and IL-18 transcriptional activities. Together, our results demonstrated that TRIM62 suppression was strongly protective in ischemic stroke through inhibiting NLRP3-regulated neuroinflammation.

Serum amyloid A1 mediates myotube atrophy via Toll-like receptors

BACKGROUND

Critically ill patients frequently develop muscle atrophy and weakness in the intensive-care-unit setting [intensive care unit-acquired weakness (ICUAW)]. Sepsis, systemic inflammation, and acute-phase response are major risk factors. We reported earlier that the acute-phase protein serum amyloid A1 (SAA1) is increased and accumulates in muscle of ICUAW patients, but its relevance was unknown. Our objectives were to identify SAA1 receptors and their downstream signalling pathways in myocytes and skeletal muscle and to investigate the role of SAA1 in inflammation-induced muscle atrophy.

METHODS

We performed cell-based in vitro and animal in vivo experiments. The atrophic effect of SAA1 on differentiated C2C12 myotubes was investigated by analysing gene expression, protein content, and the atrophy phenotype. We used the cecal ligation and puncture model to induce polymicrobial sepsis in wild type mice, which were treated with the IкB kinase inhibitor Bristol-Myers Squibb (BMS)-345541 or vehicle. Morphological and molecular analyses were used to investigate the phenotype of inflammation-induced muscle atrophy and the effects of BMS-345541 treatment.

RESULTS

The SAA1 receptors Tlr2, Tlr4, Cd36, P2rx7, Vimp, and Scarb1 were all expressed in myocytes and skeletal muscle. Treatment of differentiated C2C12 myotubes with recombinant SAA1 caused myotube atrophy and increased interleukin 6 (Il6) gene expression. These effects were mediated by Toll-like receptors (TLR) 2 and 4. SAA1 increased the phosphorylation and activity of the transcription factor nuclear factor 'kappa-light-chain-enhancer' of activated B-cells (NF-κB) p65 via TLR2 and TLR4 leading to an increased binding of NF-κB to NF-κB response elements in the promoter region of its target genes resulting in an increased expression of NF-κB target genes. In polymicrobial sepsis, skeletal muscle mass, tissue morphology, gene expression, and protein content were associated with the atrophy response. Inhibition of NF-κB signalling by BMS-345541 increased survival (28.6% vs. 91.7%, P < 0.01). BMS-345541 diminished inflammation-induced atrophy as shown by a reduced weight loss of the gastrocnemius/plantaris (vehicle: -21.2% and BMS-345541: -10.4%; P < 0.05), tibialis anterior (vehicle: -22.7% and BMS-345541: -17.1%; P < 0.05) and soleus (vehicle: -21.1% and BMS-345541: -11.3%; P < 0.05) in septic mice. Analysis of the fiber type specific myocyte cross-sectional area showed that BMS-345541 reduced inflammation-induced atrophy of slow/type I and fast/type II myofibers compared with vehicle-treated septic mice. BMS-345541 reversed the inflammation-induced atrophy program as indicated by a reduced expression of the atrogenes Trim63/MuRF1, Fbxo32/Atrogin1, and Fbxo30/MuSA1.

CONCLUSIONS

SAA1 activates the TLR2/TLR4//NF-κB p65 signalling pathway to cause myocyte atrophy. Systemic inhibition of the NF-κB pathway reduced muscle atrophy and increased survival of septic mice. The SAA1/TLR2/TLR4//NF-κB p65 atrophy pathway could have utility in combatting ICUAW.

Biochemical characterization of TRIM72 E3 ligase and its interaction with the insulin receptor substrate 1

TRIM family of E3 ubiquitin ligases have an amino-terminal conserved tripartite motif consisting of RING, B-Box, coiled-coil domain and different C-terminal domain leading it to classification into 11 subclasses. TRIM72 is an E3 ligase of class IV and subclass 1 with its role in a multitude of cellular processes. Despite being crucial in multiple cellular processes, TRIM72 still hasn't been biochemically characterized. In the present study, we have characterized the oligomeric status of TRIM72 and found that it forms both monomers, dimers, and tetramers. We have screened a set of 12 E2s and identified two novel E2 enzymes (Ubch5c and Ubch10) that work in cooperation with TRIM72. Nevertheless, E3 ligase activity is minimal and we propose that additional regulation is required to enhance its E3 ligase activity. We have also used surface plasmon resonance to study interaction with one of its substrate proteins, IRS1, and identified the PH domain of IRS1 is mediating interaction with the TRIM72 E3 ligase while the PTB domain of IRS1, does not show any interaction.

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TRIM72 exist as tetramer and monomer.

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UbcH5c and Ubch10 are the new E2s identified for TRIM72.

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The PH domain of the IRS1 interacts with the TRIM72.

TRIM62-mediated restriction of avian leukosis virus subgroup J replication is dependent on the SPRY domain

Emerging evidence suggests that some members of the tripartite motif (TRIM) family play a crucial role in antiretroviral. However, the chicken TRIM62 antiretroviral activity is unknown. Avian leukosis virus subgroup J (ALV-J) is an avian retrovirus mainly inducing tumor formation and immunosuppression. The purpose of the study was to explore chicken TRIM62's role in ALV-J replication. In this study, we first tested the RNA expression of ALV-J and TRIM62 in chicken embryo fibroblasts (CEFs) cells infected with ALV-J by qRT-PCR. The result showed that ALV-J infection affected TRIM62 RNA expression, first upregulation and then downregulation, with the time course infection of ALV-J. Then, we silenced and overexpressed the TRIM62 to evaluate the effect of TRIM62 on ALV-J replication by qRT-PCR. We found that the knockdown of TRIM62 in CEF cells with shRNA targeting SPRY domain enhanced the viral replication more significantly than that with shRNA targeting coiled coil/unstructured domain, and overexpression of TRIM62 inhibited the viral replication. Further, we detected the effect of the domain deletion on TRIM62's antiviral activity. The result demonstrated that deletion of RING, B-box, coiled-coil domains partially abolished TRIM62's antiviral activity, while SPRY domain deletion resulted in the disappearance of antiviral activity of TRIM62. Taken together, our findings strongly suggested that TRIM62 plays an important role in the restriction of ALV-J replication, and SPRY domain is a prerequisite for the antiviral activity of TRIM62.

Muscle weakness: Understanding the principles of myopathy and neuropathy in the critically ill patient and the management options

Myo-neuropathy of the critically ill patient is a difficult nosological entity to understand and manage. It appears soon after injury, and it is estimated that 20-30% of patients admitted to Intensive Care Units will develop it in some degree. Although muscular and nervous involvement are related, the former has a better prognosis. Myo-neuropathy associates to more morbidity, longer stay in Intensive Care Unit and in hospital, and also to higher costs and mortality. It is considered part of the main determinants of the new entities: the Chronic Critical Patient and the Post Intensive Care Syndrome. This update focuses on aetiology, pathophysiology, diagnosis and strategies that can prevent, alleviate and/or improve muscle (or muscle-nerve) weakness.

Carboxyl-terminal modulator protein regulates Akt signaling during skeletal muscle atrophy in vitro and a mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neuromuscular disease involving motor neuron death, paralysis and, ultimately, respiratory failure. Motor neuron dysfunction leads to target skeletal muscle atrophy involving dysregulation of downstream cell survival, growth and metabolic signaling. Decreased Akt activity is linked to muscle atrophy in ALS and is associated with increased atrophy gene expression. Unfortunately, the regulating mechanism of Akt activity in atrophic muscle remains unclear. Recent research indicates a role of carboxyl-terminal modulator protein (CTMP) in Akt-signaling related neurologic dysfunction and skeletal muscle metabolism. CTMP is known to bind and reduce Akt phosphorylation and activation. We hypothesized that CTMP expression might progressively increase in ALS skeletal muscle as the disease progresses, downregulating Akt activity. We found that CTMP protein expression significantly increased in hindlimb skeletal muscle in the mSOD1^G93A mouse model of ALS in late stages of the disease (P < 0.05), which negatively correlated with Akt phosphorylation over this period (R² = -0.77). Co-immunoprecipitation of Akt revealed CTMP binding in pre-symptomatic and end-stage skeletal muscle, suggesting a possible direct role in reduced Akt signaling during disease progression. Inflammatory TNFα and downstream cellular degradation process markers for autophagy, lysosome production, and atrophy significantly increased in a pattern corresponding to increased CTMP expression and reduced Akt phosphorylation. In an in vitro model of skeletal muscle atrophy, differentiated C2C12 cells exhibited reduced Akt activity and decreased FOXO1 phosphorylation, a process known to promote transcription of atrophy genes in skeletal muscle. These results corresponded with  increased  Atrogin-1 expression  compared to healthy control cells  (P < 0.05). Transfection with CTMP siRNA significantly increased Akt phosphorylation in atrophic C2C12 cells, corresponding to significantly decreased CTMP expression. In conclusion, this is the first study to provide evidence for a link between elevated CTMP expression, downregulated Akt phosphorylation and muscle atrophy in ALS and clearly demonstrates a direct influence of CTMP on Akt phosphorylation in an in vitro muscle cell atrophy model.

DCAF8, a novel MuRF1 interaction partner, promotes muscle atrophy

The muscle-specific RING-finger protein MuRF1 constitutes a bona fide ubiquitin ligase that routes proteins like Myosin heavy chain (MyHC) to proteasomal degradation during muscle atrophy. In two unbiased screens we identified DCAF8 as a new MuRF1 binding partner. MuRF1 physically interacts with DCAF8 and both proteins localize to overlapping structures in muscle cells. Noteworthy, similar to MuRF1, DCAF8 levels increase during atrophy and the down-regulation of either protein substantially impedes muscle wasting and MyHC degradation in C2C12 myotubes, a model system for muscle differentiation and atrophy. DCAF proteins typically serve as substrate receptors in Cullin 4-type (Cul4) ubiquitin ligases (CRL) and we demonstrate that DCAF8 and MuRF1 associate with the subunits of such a protein complex. Because genetic downregulation of DCAF8 and inhibition of Cullin activity also impair myotube atrophy in C2C12 cells, our data imply that the DCAF8 promotes muscle wasting by targeting proteins like MyHC as an integral substrate receptor of a CRL4A ubiquitin ligase.

Conserved structural and functional aspects of the tripartite motif gene family point towards therapeutic applications in multiple diseases

The tripartite motif (TRIM) gene family is a highly conserved group of E3 ubiquitin ligase proteins that can establish substrate specificity for the ubiquitin-proteasome complex and also have proteasome-independent functions. While several family members were studied previously, it is relatively recent that over 80 genes, based on sequence homology, were grouped to establish the TRIM gene family. Functional studies of various TRIM genes linked these proteins to modulation of inflammatory responses showing that they can contribute to a wide variety of disease states including cardiovascular, neurological and musculoskeletal diseases, as well as various forms of cancer. Given the fundamental role of the ubiquitin-proteasome complex in protein turnover and the importance of this regulation in most aspects of cellular physiology, it is not surprising that TRIM proteins display a wide spectrum of functions in a variety of cellular processes. This broad range of function and the highly conserved primary amino acid sequence of family members, particularly in the canonical TRIM E3 ubiquitin ligase domain, complicates the development of therapeutics that specifically target these proteins. A more comprehensive understanding of the structure and function of TRIM proteins will help guide therapeutic development for a number of different diseases. This review summarizes the structural organization of TRIM proteins, their domain architecture, common and unique post-translational modifications within the family, and potential binding partners and targets. Further discussion is provided on efforts to target TRIM proteins as therapeutic agents and how our increasing understanding of the nature of TRIM proteins can guide discovery of other therapeutics in the future.

Regulation of Akt-mTOR, ubiquitin-proteasome and autophagy-lysosome pathways in locomotor and respiratory muscles during experimental sepsis in mice

Sepsis induced loss of muscle mass and function contributes to promote physical inactivity and disability in patients. In this experimental study, mice were sacrificed 1, 4, or 7 days after cecal ligation and puncture (CLP) or sham surgery. When compared with diaphragm, locomotor muscles were more prone to sepsis-induced muscle mass loss. This could be attributed to a greater activation of ubiquitin-proteasome system and an increased myostatin expression. Thus, this study strongly suggests that the contractile activity pattern of diaphragm muscle confers resistance to atrophy compared to the locomotor gastrocnemius muscle. These data also suggest that a strategy aimed at preventing the activation of catabolic pathways and preserving spontaneous activity would be of interest for the treatment of patients with sepsis-induced neuromyopathy.

Intensive Care Unit-Acquired Weakness: Implications for Case Management

PURPOSE

The purpose of this case study is to provide a specific example of the disease trajectory for one patient's experience with intensive care unit-acquired weakness (ICUAW). This case study provides those in case management with an overview of some of the common signs and symptoms of ICUAW, as well as the possible prognosis and recovery from ICUAW.

PRIMARY PRACTICE SETTING

The events in this case study take place in the acute care setting including the intensive care unit of a mid-sized health center, a general medical-surgical (med-surg) unit, and a long-term acute care facility.

CONCLUSIONS

ICUAW affects the clinical, functional, and financial outcomes of patients. If the patient survives, their quality of life and the quality of life of their family members could be severely impacted. Case management practice has a significant role in coordinating care for those diagnosed with ICUAW. Case managers can use knowledge about ICUAW to improve the patient's transition throughout the hospital stay, improve discharge recommendations, and improve the patient's short-term and long-term outcomes. This may reduce unnecessary utilization of health care resources.

Secreted Frizzled-Related Protein 2 and Inflammation-Induced Skeletal Muscle Atrophy

OBJECTIVE

In sepsis, the disease course of critically ill patients is often complicated by muscle failure leading to ICU-acquired weakness. The myokine transforming growth factor-β1 increases during inflammation and mediates muscle atrophy in vivo. We observed that the transforming growth factor-β1 inhibitor, secreted frizzled-related protein 2, was down-regulated in skeletal muscle of ICU-acquired weakness patients. We hypothesized that secreted frizzled-related protein 2 reduction enhances transforming growth factor-β1-mediated effects and investigated the interrelationship between transforming growth factor-β1 and secreted frizzled-related protein 2 in inflammation-induced atrophy.

DESIGN

Observational study and prospective animal trial.

SETTING

Two ICUs and research laboratory.

PATIENTS/SUBJECTS

Twenty-six critically ill patients with Sequential Organ Failure Assessment scores greater than or equal to 8 underwent a skeletal muscle biopsy from the vastus lateralis at median day 5 in ICU. Four patients undergoing elective orthopedic surgery served as controls. To search for signaling pathways enriched in muscle of ICU-acquired weakness patients, a gene set enrichment analysis of our recently published gene expression profiles was performed. Quantitative reverse transcriptase-polymerase chain reaction, Western blot, and immunohistochemistry were used to analyze secreted frizzled-related protein 2 expression and protein content. A mouse model of inflammation-induced skeletal muscle atrophy due to polymicrobial sepsis and cultured myocytes were used for mechanistic analyses.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Gene set enrichment analysis uncovered transforming growth factor-β1 signaling activation in vastus lateralis from ICU-acquired weakness patients. Muscular secreted frizzled-related protein 2 expression was reduced after 5 days in ICU. Likewise, muscular secreted frizzled-related protein 2 expression was decreased early and continuously in mice with inflammation-induced atrophy. In muscle, secreted frizzled-related protein 2 was predominantly contained in fast twitch/type II myofibers. Secreted frizzled-related protein 2 physically interacted and colocalized with transforming growth factor-β1 through its cysteine-rich domain. Finally, secreted frizzled-related protein 2 prevented transforming growth factor-β1-induced atrophy in C2C12 myotubes.

CONCLUSIONS

Muscular secreted frizzled-related protein 2 is down-regulated in ICU-acquired weakness patients and mice with inflammation-induced muscle atrophy. Decreased secreted frizzled-related protein 2 possibly establishes a positive feedback loop enhancing transforming growth factor-β1-mediated atrophic effects in inflammation-induced atrophy.

Chinese Herbal Medicine Baoyuan Jiedu Decoction Inhibited Muscle Atrophy of Cancer Cachexia through Atrogin-l and MuRF-1

The aim of this study is to investigate the mechanisms of Chinese herbal medicine called “Baoyuan Jiedu” (BYJD for short) decoction, improving life quality and preventing muscle atrophy of cancer cachexia model mice. We showed that the effect of BYJD decoction increased body weights of mice and reduced tumor volume and tumor mass. Furthermore, BYJD decoction increased the gastrocnemii mass and the transverse diameter of muscle fiber morphology. Moreover, BYJD reduced the expression of Atrogin-1 and MuRF-1 protein. Collectively, our results show that BYJD decoction improves the life quality of cancer cachexia mice and prevents muscle atrophy by downregulating expression of Atrogin-1 and MuRF-1.

Deletion of Nlrp3 protects from inflammation-induced skeletal muscle atrophy

Background

Critically ill patients develop atrophic muscle failure, which increases morbidity and mortality. Interleukin-1β (IL-1β) is activated early in sepsis. Whether IL-1β acts directly on muscle cells and whether its inhibition prevents atrophy is unknown. We aimed to investigate if IL-1β activation via the Nlrp3 inflammasome is involved in inflammation-induced atrophy.

Methods

We performed an experimental study and prospective animal trial. The effect of IL-1β on differentiated C2C12 muscle cells was investigated by analyzing gene-and-protein expression, and atrophy response. Polymicrobial sepsis was induced by cecum ligation and puncture surgery in Nlrp3 knockout and wild type mice. Skeletal muscle morphology, gene and protein expression, and atrophy markers were used to analyze the atrophy response. Immunostaining and reporter-gene assays showed that IL-1β signaling is contained and active in myocytes.

Results

Immunostaining and reporter gene assays showed that IL-1β signaling is contained and active in myocytes. IL-1β increased Il6 and atrogene gene expression resulting in myocyte atrophy. Nlrp3 knockout mice showed reduced IL-1β serum levels in sepsis. As determined by muscle morphology, organ weights, gene expression, and protein content, muscle atrophy was attenuated in septic Nlrp3 knockout mice, compared to septic wild-type mice 96 h after surgery.

Conclusions

IL-1β directly acts on myocytes to cause atrophy in sepsis. Inhibition of IL-1β activation by targeting Nlrp3 could be useful to prevent inflammation-induced muscle failure in critically ill patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s40635-016-0115-0) contains supplementary material, which is available to authorized users.

When and how should sepsis patients be fed?

PURPOSE OF REVIEW

To provide an overview on the recent literature regarding metabolism during sepsis and outcome-related effects of nutrition therapy in septic patients. The question when and how these patients should be fed with respect to macronutrient intake is elaborated.

RECENT FINDINGS

Although the incidence of severe sepsis has steadily increased over the past years, still no strong evidence is available with respect to the role of energy and protein provision in these patients. On the basis of recent large randomized trials in mixed patient populations, the updated sepsis guidelines recommend early but limited nutrition via the enteral route rather than targeted feeding. Lately, the results of a large trial challenged the importance of the route of feeding on the clinical outcome of critically ill patients. Four post-hoc analyses of prospective randomized trials including a large number of severely septic patients yielded conflicting results. One reported significant mortality reduction with near-target calorie and protein intake by exclusive enteral nutrition, whereas the second showed an advantage of enteral compared to combined nutrition, albeit resulting in a lower calorie and protein provision. The other two analyses found no association at all of either lower or higher daily caloric or protein intake, respectively, with clinical outcomes.

SUMMARY

In the absence of strong clinical evidence, pathophysiological findings are discussed and nutritional strategies for septic patients derived. Future studies should explore the individual response to specific exogenous supply of macronutrients and micronutrients in the acute and persistent phase of severe systemic inflammation.