CCAAT/enhancer binding protein beta protects muscle satellite cells from apoptosis after injury and in cancer cachexia

CEBPA as a potential hub gene for cutaneous inflammation in type 2 diabetes mellitus

BACKGROUND

The role of inflammation in the development of type 2 diabetes mellitus (T2DM) related skin complications necessitates further investigation. This study aims to explore the correlation between inflammation and cutaneous alterations in T2DM, enhancing comprehension of underlying mechanism involved.

METHODS

Utilizing bioinformatics, the GSE38396 and GSE92724 datasets were employed to identify differentially expressed genes (DEGs) and potential hub genes in T2DM-related skin inflammation. Subsequently, gene functional enrichment analysis was employed for functional annotation. Finally, we validated the regulatory impact of hub gene on inflammation during high glucose incubation using the in vitro model.

RESULTS

A comprehensive analysis identified 742 DEGs, including 9 hub genes and 4 potential biomarkers. Compared to the CON group, the expression of M2 macrophages was significantly upregulated in the T2DM group, while resting dendritic cells and eosinophils showed notable decreases, indicating a significant correlation with CEBPA. Furthermore, functional enrichment analysis revealed significant enrichment of DEGs in pathways linked to immunity and diabetes pathogenesis. Interestingly, overexpression of CEBPA demonstrated anti-inflammatory effects under hyperglycemic conditions, while silencing CEBPA expression appeared to worsen inflammation.

CONCLUSION

CEBPA emerges as a potential hub gene for skin inflammation in T2DM, shedding light on the underlying mechanisms of this condition.

CEBPA Overexpression Enhances β-Cell Proliferation and Survival

A commonality between type 1 and type 2 diabetes is the decline in functional β-cell mass. The transcription factor Nkx6.1 regulates β-cell development and is integral for proper β-cell function. We have previously demonstrated that Nkx6.1 depends on c-Fos mediated upregulation and the nuclear hormone receptors Nr4a1 and Nr4a3 to increase β-cell insulin secretion, survival, and replication. Here, we demonstrate that Nkx6.1 overexpression results in upregulation of the bZip transcription factor CEBPA and that CEBPA expression is independent of c-Fos regulation. In turn, CEBPA overexpression is sufficient to enhance INS-1 832/13 β-cell and primary rat islet proliferation. CEBPA overexpression also increases the survival of β-cells treated with thapsigargin. We demonstrate that increased survival in response to ER stress corresponds with changes in expression of various genes involved in the unfolded protein response, including decreased Ire1a expression. These data show that CEBPA is sufficient to enhance functional β-cell mass by increasing β-cell proliferation and modulating the unfolded protein response.

PARP1 mediated PARylation contributes to myogenic progression and glucocorticoid transcriptional response

The ADP-ribosyltransferase, PARP1 enzymatically generates and applies the post-translational modification, ADP-Ribose (ADPR). PARP1 roles in genome maintenance are well described, but recent work highlights roles in many fundamental processes including cellular identity and energy homeostasis. Herein, we show in both mouse and human skeletal muscle cells that PARP1-mediated PARylation is a regulator of the myogenic program and the muscle transcriptional response to steroid hormones. Chemical PARP1 modulation impacts the expression of major myocellular proteins, including troponins, key in dictating muscle contractile force. Whilst PARP1 in absence of DNA damage is often assumed to be basally inactive, we show PARylation to be acutely sensitive to extracellular glucose concentrations and the steroid hormone class, glucocorticoids which exert considerable authority over muscle tissue mass. Specifically, we find during myogenesis, a transient and significant rise in PAR. This early-stage differentiation event, if blocked with PARP1 inhibition, reduced the abundance of important muscle proteins in the fully differentiated myotubes. This suggests that PAR targets during early-stage differentiation are central to the proper development of the muscle contractile unit. We also show that reduced PARP1 in myoblasts impacts a variety of metabolic pathways in line with the recorded actions of glucocorticoids. Currently, as both regulators of myogenesis and muscle mass loss, glucocorticoids represent a clinical conundrum. Our work goes on to identify that PARP1 influences transcriptional activation by glucocorticoids of a subset of genes critical to human skeletal muscle pathology. These genes may therefore signify a regulatory battery of targets through which selective glucocorticoid modulation could be achieved. Collectively, our data provide clear links between PARP1-mediated PARylation and skeletal muscle homeostatic mechanisms crucial to tissue mass maintenance and endocrine response.

Pathological features of tissues and cell populations during cancer cachexia

Cancers remain among the most devastating diseases in the human population in spite of considerable advances in limiting their impact on lifespan and healthspan. The multifactorial nature of cancers, as well as the number of tissues and organs that are affected, have exposed a considerable diversity in mechanistic features that are reflected in the wide array of therapeutic strategies that have been adopted. Cachexia is manifested in a number of diseases ranging from cancers to diabetes and ageing. In the context of cancers, a majority of patients experience cachexia and succumb to death due to the indirect effects of tumorigenesis that drain the energy reserves of different organs. Considerable information is available on the pathophysiological features of cancer cachexia, however limited knowledge has been acquired on the resident stem cell populations, and their function in the context of these diseases. Here we review current knowledge on cancer cachexia and focus on how tissues and their resident stem and progenitor cell populations are individually affected.

Shared and Divergent Epigenetic Mechanisms in Cachexia and Sarcopenia

Significant loss of muscle mass may occur in cachexia and sarcopenia, which are major causes of mortality and disability. Cachexia represents a complex multi-organ syndrome associated with cancer and chronic diseases. It is often characterized by body weight loss, inflammation, and muscle and adipose wasting. Progressive muscle loss is also a hallmark of healthy aging, which is emerging worldwide as a main demographic trend. A great challenge for the health care systems is the age-related decline in functionality which threatens the independence and quality of life of elderly people. This biological decline can also be associated with functional muscle loss, known as sarcopenia. Previous studies have shown that microRNAs (miRNAs) play pivotal roles in the development and progression of muscle wasting in both cachexia and sarcopenia. These small non-coding RNAs, often carried in extracellular vesicles, inhibit translation by targeting messenger RNAs, therefore representing potent epigenetic modulators. The molecular mechanisms behind cachexia and sarcopenia, including the expression of specific miRNAs, share common and distinctive trends. The aim of the present review is to compile recent evidence about shared and divergent epigenetic mechanisms, particularly focusing on miRNAs, between cachexia and sarcopenia to understand a facet in the underlying muscle wasting associated with these morbidities and disclose potential therapeutic interventions.

Aerobic exercise-mediated changes in the expression of glucocorticoid responsive genes in skeletal muscle differ across the day

Glucocorticoids are released in response to acute aerobic exercise. The objective was to define changes in the expression of glucocorticoid target genes in skeletal muscle in response to acute aerobic exercise at different times of day. We identified glucocorticoid target genes altered in skeletal muscle by acute exercise by comparing data sets from rodents subjected to acute aerobic exercise in the light or dark cycles to data sets from C2C12 myotubes treated with glucocorticoids. The role of glucocorticoid receptor signaling and REDD1 protein in mediating gene expression was assessed in exercised mice. Changes to expression of glucocorticoid genes were greater when exercise occurred in the dark cycle. REDD1 was required for the induction of genes induced at both times of day. In all, the time of day at which aerobic exercise is conducted dictates changes to the expression of glucocorticoid target genes in skeletal muscle with REDD1 contributing to those changes.

C/EBPβ promotes the expression of atrophy-inducing factors by tumours and is a central regulator of cancer cachexia

BACKGROUND

CCAAT/enhancer-binding protein β (C/EBPβ) is a transcription factor whose high expression in human cancers is associated with tumour aggressiveness and poor outcomes. Most advanced cancer patients will develop cachexia, characterized by loss of skeletal muscle mass. In response to secreted factors from cachexia-inducing tumours, C/EBPβ is stimulated in muscle, leading to both myofibre atrophy and the inhibition of muscle regeneration. Involved in the regulation of immune responses, C/EBPβ induces the expression of many secreted factors, including cytokines. Because tumour-secreted factors drive cachexia and aggressive tumours have higher expression of C/EBPβ, we examined a potential role for C/EBPβ in the expression of tumour-derived cachexia-inducing factors.

METHODS

We used gain-of-function and loss-of-function approaches in vitro and in vivo to evaluate the role of tumour C/EBPβ expression on the secretion of cachexia-inducing factors.

RESULTS

We report that C/EBPβ overexpression up-regulates the expression of 260 secreted protein genes, resulting in a secretome that inhibits myogenic differentiation (-31%, P < 0.05) and myotube maturation [-38% (fusion index) and -25% (myotube diameter), P < 0.05]. We find that knockdown of C/EBPβ in cachexia-inducing Lewis lung carcinoma cells restores myogenic differentiation (+25%, P < 0.0001) and myotube diameter (+90%, P < 0.0001) in conditioned medium experiments and, in vivo, prevents muscle wasting (-51% for small myofibres vs. controls, P < 0.01; +140% for large myofibres, P < 0.01). Conversely, overexpression of C/EBPβ in non-cachectic tumours converts their secretome into a cachexia-inducing one, resulting in reduced myotube diameter (-41%, P < 0.0001, EL4 model) and inhibition of differentiation in culture (-26%, P < 0.01, EL4 model) and muscle wasting in vivo (+98% small fibres, P < 0.001; -76% large fibres, P < 0.001). Comparison of the differently expressed transcripts coding for secreted proteins in C/EBPβ-overexpressing myoblasts with the secretome from 27 different types of human cancers revealed ~18% similarity between C/EBPβ-regulated secreted proteins and those secreted by highly cachectic tumours (brain, pancreatic, and stomach cancers). At the protein level, we identified 16 novel secreted factors that are present in human cancer secretomes and are up-regulated by C/EBPβ. Of these, we tested the effect of three factors (SERPINF1, TNFRSF11B, and CD93) on myotubes and found that all had atrophic potential (-33 to -36% for myotube diameter, P < 0.01).

CONCLUSIONS

We find that C/EBPβ is necessary and sufficient to induce the secretion of cachexia-inducing factors by cancer cells and loss of C/EBPβ in tumours attenuates muscle atrophy in an animal model of cancer cachexia. Our findings establish C/EBPβ as a central regulator of cancer cachexia and an important therapeutic target.

Skeletal muscle transcriptomics identifies common pathways in nerve crush injury and ageing

Motor unit remodelling involving repeated denervation and re-innervation occurs throughout life. The efficiency of this process declines with age contributing to neuromuscular deficits. This study investigated differentially expressed genes (DEG) in muscle following peroneal nerve crush to model motor unit remodelling in C57BL/6 J mice. Muscle RNA was isolated at 3 days post-crush, RNA libraries were generated using poly-A selection, sequenced and analysed using gene ontology and pathway tools. Three hundred thirty-four DEG were found in quiescent muscle from (26mnth) old compared with (4-6mnth) adult mice and these same DEG were present in muscle from adult mice following nerve crush. Peroneal crush induced 7133 DEG in muscles of adult and 699 DEG in muscles from old mice, although only one DEG (ZCCHC17) was found when directly comparing nerve-crushed muscles from old and adult mice. This analysis revealed key differences in muscle responses which may underlie the diminished ability of old mice to repair following nerve injury.

From quiescence to repair: C/EBPβ as a regulator of muscle stem cell function in health and disease

CCAAT/Enhancer Binding protein beta (C/EBPβ) is a transcriptional regulator involved in numerous physiological processes. Herein, we describe a role for C/EBPβ as a regulator of skeletal muscle stem cell function. In particular, C/EBPβ is expressed in muscle stem cells in healthy muscle where it inhibits myogenic differentiation. Downregulation of C/EBPβ expression at the protein and transcriptional level allows for differentiation. Persistence of C/EBPβ promotes stem cell self-renewal and C/EBPβ expression is required for mitotic quiescence in this cell population. As a critical regulator of skeletal muscle homeostasis, C/EBPβ expression is stimulated in pathological conditions such as cancer cachexia, which perturbs muscle regeneration and promotes myofiber atrophy in the context of systemic inflammation. C/EBPβ is also an important regulator of cytokine expression and immune response genes, a mechanism by which it can influence muscle stem cell function. In this viewpoint, we describe a role for C/EBPβ in muscle stem cells and propose a functional intersection between C/EBPβ and NF-kB action in the regulation of cancer cachexia.

Trabectedin and Lurbinectedin Extend Survival of Mice Bearing C26 Colon Adenocarcinoma, without Affecting Tumor Growth or Cachexia

Trabectedin (ET743) and lurbinectedin (PM01183) limit the production of inflammatory cytokines that are elevated during cancer cachexia. Mice carrying C26 colon adenocarcinoma display cachexia (i.e., premature death and body wasting with muscle, fat and cardiac tissue depletion), high levels of inflammatory cytokines and subsequent splenomegaly. We tested whether such drugs protected these mice from cachexia. Ten-week-old mice were inoculated with C26 cells and three days later randomized to receive intravenously vehicle or 0.05 mg/kg ET743 or 0.07 mg/kg PM01183, three times a week for three weeks. ET743 or PM01183 extended the lifespan of C26-mice by 30% or 85%, respectively, without affecting tumor growth or food intake. Within 13 days from C26 implant, both drugs did not protect fat, muscle and heart from cachexia. Since PM01183 extended the animal survival more than ET743, we analyzed PM01183 further. In tibialis anterior of C26-mice, but not in atrophying myotubes, PM01183 restrained the NF-κB/PAX7/myogenin axis, possibly reducing the pro-inflammatory milieu, and failed to limit the C/EBPβ/atrogin-1 axis. Inflammation-mediated splenomegaly of C26-mice was inhibited by PM01183 for as long as the treatment lasted, without reducing IL-6, M-CSF or IL-1β in plasma. ET743 and PM01183 extend the survival of C26-bearing mice unchanging tumor growth or cachexia but possibly restrain muscle-related inflammation and C26-induced splenomegaly.

Interaction between C/EBPβ and RUNX2 promotes apoptosis of chondrocytes during human lumbar facet joint degeneration

The pathophysiological changes in cartilage are a crucial feature of lumbar facet joint (LFJ) degeneration and arthritis. However, the molecular mechanism of human LFJ degeneration remains largely defined. This study aimed to examine the changes in chondrocytes at different stages of degenerative LFJ using hematoxylin and eosin and Safranin O staining. The significant loss of chondrocytes in grades 2 and 3 of LFJs was observed. The expression levels of CCAAT enhancer binding protein β (C/EBPβ), Runt-related transcription factor 2 (RUNX2), and matrix metalloproteinase 13 (MMP13) also increased with the aggravation of degeneration (4.89, 5.77, and 6.3 times by Western blot). In vitro, chondrocytes scraped from the LFJs during surgery were stimulated by interleukin (IL)-1β to establish the injury model. The association of C/EBPβ and RUNX2 with active caspase-3 on chondrocytes was analyzed. The high expression level of C/EBPβ, RUNX2, and MMP13 was consistent with that of caspase-3, which reached a peak after 36 h of stimulation. Immunofluorescence suggested that C/EBPβ, RUNX2, and MMP13 co-labeled with active caspase-3. Moreover, immunoprecipitation data prompted that C/EBPβ was able to interact with RUNX2. The knockdown of C/EBPβ significantly decreased the expression levels of MMP13 and active caspase-3 (2.48 and 2.89 times as detected by Western blot analysis) and inhibited chondrocyte apoptosis, which was further demonstrated using flow cytometry. Taken together, the findings of this study uncovered that C/EBPβ could interact with RUNX2 to induce chondrocyte apoptosis in human LFJ degeneration by regulating the expression of MMP13.

Molecular cloning, characterisation, and expression patterns of pigeon CCAAT/enhancer binding protein-α and -β genes

1. CCAAT/enhancer binding proteins (C/EBPs), as a family of transcription factors, consists of six functionally and structurally related proteins which share a conserved basic leucine zipper (bZIP) DNA-binding domain. The aim of this study was to clone the full-length coding sequences (CDS) of C/EBP-α and -β genes, and determine the abundance of these two genes in various tissues of white king pigeon (C. livia). 2. The complete cDNA sequences of C/EBP-α and -β genes were cloned from pigeons by using PCR combined with rapid amplification of cDNA ends (RACE). The sequences were bioinformatically analysed, and the tissue distribution determined by quantitative real-time RT-PCR (qRT-PCR). 3. The results showed that the full-length cDNA sequences of pigeon C/EBP-α and -β genes were 2,807bp and 1,778bp, respectively. The open reading frames of C/EBP-α (978 bp) and -β (987bp) encoded 325 amino acids and 328 amino acids, respectively. The pigeon C/EBP-α and C/EBP-β proteins were predicted to have a conserved basic leucine zipper (bZIP) domain, which is a common structure feature of the C/EBP family. Multiple sequence alignments indicated that pigeon C/EBP-α and -β shared more than 90% amino-acid identity with their corresponding homologues in other avian species. Phylogenetic analysis revealed that these two proteins were highly conserved across different species and evolutionary processes. QRT-PCR results indicated that the pigeon C/EBP-α and -β mRNA transcripts were expressed in all investigated organs. The mRNA expression levels of pigeon C/EBP-α in descending order, were in spleen, heart, liver, lung, kidney and muscle. The pigeon C/EBP-β gene had the most abundant expression in lung, followed by the kidney, with minimal expression detected in muscle. 4. This study investigated the full-length cDNA sequences, genetic characteristics and tissue distribution of pigeon C/EBP-α and -β genes and found that they may have functions in various tissues of pigeon. This provides a foundation for further study for regulatory mechanisms of these two genes in birds.

Immunohistochemical phenotyping of T cells, granulocytes, and phagocytes in the muscle of cancer patients: association with radiologically defined muscle mass and gene expression

BACKGROUND

Inflammation is a recognized contributor to muscle wasting. Research in injury and myopathy suggests that interactions between the skeletal muscle and immune cells confer a pro-inflammatory environment that influences muscle loss through several mechanisms; however, this has not been explored in the cancer setting. This study investigated the local immune environment of the muscle by identifying the phenotype of immune cell populations in the muscle and their relationship to muscle mass in cancer patients.

METHODS

Intraoperative muscle biopsies were collected from cancer patients (n = 30, 91% gastrointestinal malignancies). Muscle mass was assessed histologically (muscle fiber cross-sectional area, CSA; μm²) and radiologically (lumbar skeletal muscle index, SMI; cm²/m² by computed tomography, CT). T cells (CD4 and CD8) and granulocytes/phagocytes (CD11b, CD14, and CD15) were assessed by immunohistochemistry. Microarray analysis was conducted in the muscle of a second cancer patient cohort.

RESULTS

T cells (CD3+), granulocytes/phagocytes (CD11b+), and CD3-CD4+ cells were identified. Muscle fiber CSA (μm²) was positively correlated (Spearman's r = > 0.45; p = < 0.05) with the total number of T cells, CD4, and CD8 T cells and granulocytes/phagocytes. In addition, patients with the smallest SMI exhibited fewer CD8 T cells within their muscle. Consistent with this, further exploration with gene correlation analyses suggests that the presence of CD8 T cells is negatively associated (Pearson's r = ≥ 0.5; p = <0.0001) with key genes within muscle catabolic pathways for signaling (ACVR2B), ubiquitin proteasome (FOXO4, TRIM63, FBXO32, MUL1, UBC, UBB, UBE2L3), and apoptosis/autophagy (CASP8, BECN1, ATG13, SIVA1).

CONCLUSION

The skeletal muscle immune environment of cancer patients is comprised of immune cell populations from the adaptive and innate immunity. Correlations of T cells, granulocyte/phagocytes, and CD3-CD4+ cells with muscle mass measurements indicate a positive relationship between immune cell numbers and muscle mass status in cancer patients. Further exploration with gene correlation analyses suggests that the presence of CD8 T cells is negatively correlated with components of muscle catabolism.

Inflammation-associated miR-155 activates differentiation of muscular satellite cells

Tissue renewal and muscle regeneration largely rely on the proliferation and differentiation of muscle stem cells called muscular satellite cells (MuSCs). MuSCs are normally quiescent, but they are activated in response to various stimuli, such as inflammation. Activated MuSCs proliferate, migrate, differentiate, and fuse to form multinucleate myofibers. Meanwhile, inappropriate cues for MuSC activation induce premature differentiation and bring about stem cell loss. Recent studies revealed that stem cell regulation is disrupted in various aged tissues. We found that the expression of microRNA (miR)-155, which is an inflammation-associated miR, is upregulated in MuSCs of aged muscles, and this upregulation activates the differentiation process through suppression of C/ebpβ, which is an important molecule for maintaining MuSC self-renewal. We also found that Notch1 considerably repressed miR-155 expression, and loss of Notch1 induced miR-155 overexpression. Our findings suggest that miR-155 can act as an activator of muscular differentiation and might be responsible for accelerating aging-associated premature differentiation of MuSCs.

Epigenetics of cancer-associated muscle catabolism

Cancer patients are commonly affected by cachexia, a wasting process involving muscle and fat. Specifically, loss of the muscle compartment has been associated with poor prognosis and suboptimal response to therapy. Nutritional support has been ineffective in treating this process leading to investigations into the underlying molecular processes governing muscle catabolism. In this commentary, we discuss the molecular mechanisms of cancer-associated muscle metabolism and the epigenetic processes responsible for the muscle wasting phenotype. Ultimately, we highlight how the epigenome may serve as a promising therapeutic target in reversing cancer-associated muscle catabolism.

SOX7 Is Required for Muscle Satellite Cell Development and Maintenance

Satellite cells are skeletal-muscle-specific stem cells that are activated by injury to proliferate, differentiate, and fuse to enable repair. SOX7, a member of the SRY-related HMG-box family of transcription factors is expressed in quiescent satellite cells. To elucidate SOX7 function in skeletal muscle, we knocked down Sox7 expression in embryonic stem cells and primary myoblasts and generated a conditional knockout mouse in which Sox7 is excised in PAX3⁺ cells. Loss of Sox7 in embryonic stem cells reduced Pax3 and Pax7 expression. In vivo, conditional knockdown of Sox7 reduced the satellite cell population from birth, reduced myofiber caliber, and impaired regeneration after acute injury. Although Sox7-deficient primary myoblasts differentiated normally, impaired myoblast fusion and increased sensitivity to apoptosis in culture and in vivo were observed. Taken together, these results indicate that SOX7 is dispensable for myogenesis but is necessary to promote satellite cell development and survival.

CCAAT/enhancer binding protein β is required for satellite cell self-renewal

Background

Postnatal growth and repair of skeletal muscle relies upon a population of quiescent muscle precursor cells, called satellite cells that can be activated to proliferate and differentiate into new myofibers, as well as self-renew to replenish the satellite cell population. The balance between differentiation and self-renewal is critical to maintain muscle tissue homeostasis, and alterations in this equilibrium can lead to chronic muscle degeneration. The transcription factor CCAAT/enhancer binding protein beta (C/EBPβ) is expressed in Pax7⁺ satellite cells of healthy muscle and is downregulated during myoblast differentiation. Persistent expression of C/EBPβ upregulates Pax7, inhibits MyoD, and blocks myogenic differentiation.

Methods

Using genetic tools to conditionally abrogate C/EBPβ expression in Pax7⁺ cells, we examined the role of C/EBPβ in self-renewal of satellite cells during muscle regeneration.

Results

We find that loss of C/EBPβ leads to precocious differentiation at the expense of self-renewal in primary myoblast and myofiber cultures. After a single muscle injury, C/EBPβ-deficient satellite cells fail to self-renew resulting in a reduction of satellite cells available for future rounds of regeneration. After a second round of injury, muscle regeneration is impaired in C/EBPβ conditional knockout mice compared to wild-type control mice. We find that C/EBPβ can regulate Notch2 expression and that restoration of Notch activity in myoblasts lacking C/EBPβ prevents precocious differentiation.

Conclusions

These findings demonstrate that C/EBPβ is a novel regulator of satellite cell self-renewal during muscle regeneration acting at least in part through Notch2.