CREG1 improves the capacity of the skeletal muscle response to exercise endurance via modulation of mitophagy

Creg1 Regulates Erythroid Development via TGF-β/Smad2-Klf1 Axis in Zebrafish

Understanding the regulation of normal erythroid development will help to develop new potential therapeutic strategies for disorders of the erythroid lineage. Cellular repressor of E1A-stimulated genes 1 (CREG1) is a glycoprotein that has been implicated in the regulation of tissue homeostasis. However, its role in erythropoiesis remains largely undefined. In this study, it is found that CREG1 expression increases progressively during erythroid differentiation. In zebrafish, creg1 mRNA is preferentially expressed within the intermediate cell mass (ICM)/peripheral blood island (PBI) region where primitive erythropoiesis occurs. Loss of creg1 leads to anemia caused by defective erythroid differentiation and excessive apoptosis of erythroid progenitors. Mechanistically, creg1 deficiency results in reduced activation of TGF-β/Smad2 signaling pathway. Treatment with an agonist of the Smad2 pathway (IDE2) could significantly restore the defective erythroid development in creg1-/- mutants. Further, Klf1, identified as a key target gene downstream of the TGF-β/Smad2 signaling pathway, is involved in creg1 deficiency-induced aberrant erythropoiesis. Thus, this study reveals a previously unrecognized role for Creg1 as a critical regulator of erythropoiesis, mediated at least in part by the TGF-β/Smad2-Klf1 axis. This finding may contribute to the understanding of normal erythropoiesis and the pathogenesis of erythroid disorders.

Mitochondrial heterogeneity and adaptations to cellular needs

Although it is well described that mitochondria are at the epicentre of the energy demands of a cell, it is becoming important to consider how each cell tailors its mitochondrial composition and functions to suit its particular needs beyond ATP production. Here we provide insight into mitochondrial heterogeneity throughout development as well as in tissues with specific energy demands and discuss how mitochondrial malleability contributes to cell fate determination and tissue remodelling.

HIF-1α is Required to Differentiate the Neonatal Macrophage Secretome from Adults

The immune response to stress diverges with age, with neonatal macrophages implicated in tissue regeneration versus tissue scarring and maladaptive inflammation in adults. Integral to the macrophage stress response is the recognition of hypoxia and pathogen-associated molecular patterns (PAMPs), which are often coupled. The age-specific, cell-intrinsic nature of this stress response remains vague. To uncover age-defined divergences in macrophage crosstalk potential after exposure to hypoxia and PAMPs, we interrogated the secreted proteomes of neonatal versus adult macrophages via non-biased mass spectrometry. Through this approach, we newly identified age-specific signatures in the secretomes of neonatal versus adult macrophages in response to hypoxia and the prototypical PAMP, lipopolysaccharide (LPS). Neonatal macrophages polarized to an anti-inflammatory, regenerative phenotype protective against apoptosis and oxidative stress, dependent on hypoxia inducible transcription factor-1α ( HIF-1α). In contrast, adult macrophages adopted a pro-inflammatory, glycolytic phenotypic signature consistent with pathogen killing. Taken together, these data uncover fundamental age and HIF-1α dependent macrophage programs that may be targeted to calibrate the innate immune response during stress and inflammation.

CREG1 deficiency impaired myoblast differentiation and skeletal muscle regeneration

BACKGROUND

CREG1 (cellular repressor of E1A-stimulated genes 1) is a protein involved in cellular differentiation and homeostasis regulation. However, its role in skeletal muscle satellite cells differentiation and muscle regeneration is poorly understood. This study aimed to investigate the role of CREG1 in myogenesis and muscle regeneration.

METHODS

RNA sequencing data (GSE8479) was analysed from the Gene Expression Omnibus database (GEO, https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi). We generated Creg1 knockdown and skeletal muscle satellite cells specific Creg1 overexpression mice mediated by adeno-associated virus serotype 9 (AAV9), skeletal muscle mature myofibre Creg1 knockout mice (myoblast/Creg1MKO), and control mice Creg1flox/flox (Creg1fl/fl) as in vivo models. The mice were injected into tibialis anterior (TA) muscle with 100 μL of 10 μM cardiotoxin to establish a muscle regeneration model. Creg1fl/fl and Creg1MKO mice were treated with AAV-sh-C-Cbl (2 × 1010 genomic copies/mouse) to silence C-Cbl in the TA muscle. 293T and C2C12 cells were transfected with plasmids using lipofectamine RNAi MAX in vitro. Mass spectrometry analyses and RNA sequencing transcriptomic assay were performed.

RESULTS

We analysed the transcriptional profiles of the skeletal muscle biopsies from healthy older (N = 25) and younger (N = 26) adult men and women in GSE8479 database, and the results showed that Creg1 was associated with human sarcopenia. We found that Creg1 knockdown mice regenerated less newly formed fibres in response to cardiotoxin injection (~30% reduction, P < 0.01); however, muscle satellite cells specific Creg1 overexpression mice regenerated more newly formed fibres (~20% increase, P < 0.05). AMPKa1 is known as a key mediator in the muscle regeneration process. Our results revealed that CREG1 deficiency inhibited AMPKa1 signalling through C-CBL E3-ubiquitin ligase-mediated AMPKa1 degradation (P < 0.01). C-CBL-mediated AMPKa1 ubiquitination was attributed to the K48-linked polyubiquitination of AMPKa1 at K396 and that the modification played an important role in the regulation of AMPKa1 protein stability. We also found that Creg1MKO mice regenerated less newly formed fibres compared with Creg1fl/fl mice (~30% reduction, P < 0.01). RNA-seq analysis showed that CREG1 deletion in impaired muscles led to the upregulation of inflammation and DKK3 expression. The TA muscles of Creg1MKO mice were injected with AAV-vector or AAV-shC-Cbl, silencing C-CBL (P < 0.01) in the skeletal muscles of Creg1MKO mice significantly improved muscle regeneration induced by CTX injury (P < 0.01).

CONCLUSIONS

Our findings suggest that CREG1 may be a potential therapeutic target for skeletal muscle regeneration.

Kaempferol Improves Exercise Performance by Regulating Glucose Uptake, Mitochondrial Biogenesis, and Protein Synthesis via PI3K/AKT and MAPK Signaling Pathways

Kaempferol is a natural flavonoid with reported bioactivities found in many fruits, vegetables, and medicinal herbs. However, its effects on exercise performance and muscle metabolism remain inconclusive. The present study investigated kaempferol's effects on improving exercise performance and potential mechanisms in vivo and in vitro. The grip strength, exhaustive running time, and distance of mice were increased in the high-dose kaempferol group (p < 0.01). Also, kaempferol reduced fatigue-related biochemical markers and increased the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) related to antioxidant capacity. Kaempferol also increased the glycogen and adenosine triphosphate (ATP) content in the liver and skeletal muscle, as well as glucose in the blood. In vitro, kaempferol promoted glucose uptake, protein synthesis, and mitochondrial function and decreased oxidative stress in both 2D and 3D C2C12 myotube cultures. Moreover, kaempferol activated the PI3K/AKT and MAPK signaling pathways in the C2C12 cells. It also upregulated the key targets of glucose uptake, mitochondrial function, and protein synthesis. These findings suggest that kaempferol improves exercise performance and alleviates physical fatigue by increasing glucose uptake, mitochondrial biogenesis, and protein synthesis and by decreasing ROS. Kaempferol's molecular mechanism may be related to the regulation of the PI3K/AKT and MAPK signaling pathways.

Identification of Active Components for Sports Supplements: Machine Learning-Driven Classification and Cell-Based Validation

The identification of active components is critical for the development of sports supplements. However, high-throughput screening of active components remains a challenge. This study sought to construct prediction models to screen active components from herbal medicines via machine learning and validate the screening by using cell-based assays. The six constructed models had an accuracy of >0.88. Twelve randomly selected active components from the screening were tested for their active potency on C2C12 cells, and 11 components induced a significant increase in myotube diameters and protein synthesis. The effect and mechanism of luteolin among the 11 active components as potential sports supplements were then investigated by using immunofluorescence staining and high-content imaging analysis. It showed that luteolin increased the skeletal muscle performance via the activation of PGC-1α and MAPK signaling pathways. Thus, high-throughput prediction models can be effectively used to screen active components as sports supplements.

Effects of Lactiplantibacillus plantarum on oxidative stress, mitophagy, and NLRP3 inflammasome activation in broiler breast meat

Poultry meat has a high polyunsaturated fatty acids content, making it vulnerable to oxidative stress. Mitophagy participates in the regulation of oxidative stress and the nucleotide-binding and oligomerization domain (NOD)-like receptor family as well as pyrin domain-containing protein 3 (NLRP3) inflammasome activation. Lactiplantibacillus plantarum P8 (P8) is a probiotic strain with an antioxidant capacity. In the present study, we investigated the effects of P8 on oxidative stress, mitochondrial function, mitophagy, and NLRP3 inflammasome in the breast meat of oxidatively stressed broilers. Four hundred 1-day-old male broilers were assigned to a 2 × 2 factorial design with 2 P8 levels (0 or 1 × 108 cfu/g), either with or without dexamethasone (DEX) injection, for a 21-day experimental period. DEX was injected intraperitoneally once daily from d 16 to 21. The breast meat was collected on d 21. The results showed that P8 supplementation decreased malondialdehyde (MDA) levels, increased superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), and activated the Keap1-Nrf2 pathway in DEX-injected broilers. Moreover, P8 supplementation downregulated mitochondrial DNA (mtDNA) copy number and increased the expressions of peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α), silent information regulator 1 (SIRT1), mitochondrial fusion protein 1 (Mfn1), and optic atrophy protein 1 (OPA1) in DEX-treated broilers. In addition, the decreased mitophagy level in DEX-treated broilers was elevated with P8 supplementation, as reflected by the increased gene expression of autophagy-related gene 5 (ATG5), Bcl-2-interacting protein (Becline-1), Parkin, PTEN-induced kinase 1 (PINK1), light chain 3 II (LC3II)/LC31, and the protein expression of Parkin as well as decreased p62 expression. In addition, P8 supplementation inhibited NLRP3 inflammasome activation by decreasing the transcription of NLRP3, IL-18, cysteinyl aspartate-specific proteinase-1 (Caspase-1), and the expression of NLRP3 and IL-18 in DEX-treated broilers. In conclusion, dietary P8 supplementation alleviates oxidative stress, improves mitophagy, and inhibits NLRP3 inflammasome activation in the breast meat of oxidatively stressed broilers.

High-intensity interval training alleviates exhaustive exercise-induced HSP70-assisted selective autophagy in skeletal muscle

This study was designed to probe the effect of chaperone-assisted selective autophagy (CASA) on the maintenance of proteostasis during exhaustive exercise and uncover the alteration of CASA in muscle fibers with pre-high-intensity interval training (HIIT) intervention-induced muscle adaptation in response to exhaustive exercise. Rats were randomly divided into a control group; an exhaustive exercise group; and an HIIT + exhaustive exercise group. Results show myofibril damage and BiP levels were increased after exhaustive exercise, and the levels of the HSP70, BAG3, ubiquitin, autophagy-related proteins, and their interactions were increased. HIIT intervention before exhaustive exercise could decrease myofibril injury and BiP levels, accompanied by down-regulation of HSP70/BAG3 complex and selective autophagy. In conclusion, exhaustive exercise promotes CASA to clear protein aggregation for keeping proteostasis in muscle fibers; pre-HIIT intervention improves myofibril injury and unfold protein response caused by exhaustive exercise, which might contribute to inhibit the augmentation of CASA.

Exercise mitigates age-related metabolic diseases by improving mitochondrial dysfunction

The benefits of regular physical activity are related to delaying and reversing the onset of ageing and age-related disorders, including cardiomyopathy, neurodegenerative diseases, cancer, obesity, diabetes, and fatty liver diseases. However, the molecular mechanisms of the benefits of exercise or physical activity on ageing and age-related disorders remain poorly understood. Mitochondrial dysfunction is implicated in the pathogenesis of ageing and age-related metabolic diseases. Mitochondrial health is an important mediator of cellular function. Therefore, exercise alleviates metabolic diseases in individuals with advancing ageing and age-related diseases by the remarkable promotion of mitochondrial biogenesis and function. Exerkines are identified as signaling moieties released in response to exercise. Exerkines released by exercise have potential roles in improving mitochondrial dysfunction in response to age-related disorders. This review comprehensive summarizes the benefits of exercise in metabolic diseases, linking mitochondrial dysfunction to the onset of age-related diseases. Using relevant examples utilizing this approach, the possibility of designing therapeutic interventions based on these molecular mechanisms is addressed.

The CREG1-FBXO27-LAMP2 axis alleviates diabetic cardiomyopathy by promoting autophagy in cardiomyocytes

Autophagy plays an important role in the development of diabetic cardiomyopathy. Cellular repressor of E1A-stimulated genes 1 (CREG1) is an important myocardial protective factor. The aim of this study was to investigate the effects and mechanisms of CREG1 in diabetic cardiomyopathy. Male C57BL/6 J mice, Creg1 transgenic mice and cardiac-specific knockout mice were used to establish a type 2 diabetes model. Small animal ultrasound, Masson's staining and western blotting were used to evaluate cardiac function, myocardial fibrosis and autophagy. Neonatal mouse cardiomyocytes (NMCMs) were stimulated with palmitate, and the effects of CREG1 on NMCMs autophagy were examined. CREG1 deficiency exacerbated cardiac dysfunction, cardiac hypertrophy and fibrosis in mice with diabetic cardiomyopathy, which was accompanied by exacerbated autophagy dysfunction. CREG1 overexpression improved cardiac function and ameliorated cardiac hypertrophy and fibrosis in diabetic cardiomyopathy by improving autophagy. CREG1 protein expression was decreased in palmitate-induced NMCMs. CREG1 knockdown exacerbated cardiomyocyte hypertrophy and inhibited autophagy. CREG1 overexpression inhibited cardiomyocyte hypertrophy and improved autophagy. LAMP2 overexpression reversed the effect of CREG1 knockdown on palmitate-induced inhibition of cardiomyocyte autophagy. CREG1 inhibited LAMP2 protein degradation by inhibiting the protein expression of F-box protein 27 (FBXO27). Our findings indicate new roles of CREG1 in the development of diabetic cardiomyopathy.

CREG1 stimulates AMPK phosphorylation and glucose uptake in skeletal muscle cells

The cellular repressor of adenovirus early region 1A-stimulated gene 1 (CREG1) is a secreted glycoprotein involved in cell differentiation and energy metabolism. It also binds to insulin-like growth factor 2 receptor (IGF2R), a protein implicated in muscle regeneration. However, whether CREG1 regulates the regeneration and metabolism of skeletal muscles via IGF2R remains unclear. This study investigates the role of CREG1 in skeletal muscle regeneration and glucose uptake in C2C12 myotubes and a cardiotoxin (CTX)-induced mouse skeletal muscle regeneration model. CTX-treated skeletal muscle showed significantly higher levels of IGF2R, CREG1, phospho-AMPKα Thr¹⁷², and GLUT4 proteins. Similarly, treatment of myotubes with CREG1 also stimulated AMPKα phosphorylation and GLUT4 expression. CREG1-induced AMPKα phosphorylation and 2DG uptake in myotubes were suppressed by IGF2R knockdown and Compound C, an AMPK inhibitor. These results suggest that CREG1 stimulates glucose uptake in skeletal muscles partially through AMPK activation. Hence, CREG1 plays an essential role in muscle regeneration by affecting glucose metabolism in skeletal muscles.

TLR4-Mediated Inflammatory Responses Regulate Exercise-Induced Molecular Adaptations in Mouse Skeletal Muscle

Endurance exercise induces various adaptations that yield health benefits; however, the underlying molecular mechanism has not been fully elucidated. Given that it has recently been accepted that inflammatory responses are required for a specific muscle adaptation after exercise, this study investigated whether toll-like receptor (TLR) 4, a pattern recognition receptor that induces proinflammatory cytokines, is responsible for exercise-induced adaptations in mouse skeletal muscle. The TLR4 mutant (TLR4m) and intact TLR4 control mice were each divided into 2 groups (sedentary and voluntary wheel running) and were housed for six weeks. Next, we removed the plantaris muscle and evaluated the expression of cytokines and muscle regulators. Exercise increased cytokine expression in the controls, whereas a smaller increase was observed in the TLR4m mice. Mitochondrial markers and mitochondrial biogenesis inducers, including peroxisome proliferator-activated receptor beta and heat shock protein 72, were increased in the exercised controls, whereas this upregulation was attenuated in the TLR4m mice. In contrast, exercise increased the expression of molecules such as peroxisome proliferator-activated receptor-gamma coactivator 1-alpha and glucose transporter 4 in both the controls and TLR4m mice. Our findings indicate that exercise adaptations such as mitochondrial biogenesis are mediated via TLR4, and that TLR4-mediated inflammatory responses could be involved in the mechanism of adaptation.

CREG1 improves diet-induced obesity via uncoupling protein 1-dependent manner in mice

Thermogenic brown and beige adipocytes express uncoupling protein 1 (UCP1) and stimulate energy metabolism, protecting against obesity and metabolic diseases such as type 2 diabetes and hyperlipidemia. Cellular repressor of E1A-stimulated genes 1 (CREG1) can stimulate thermogenic fat formation, induce UCP1, and reduce diet-induced obesity (DIO) in mice at normal room temperature. In this study, we investigated the effect of CREG1 administration and the importance of UCP1 in DIO inhibition under thermoneutral conditions at 30°C, which attenuate thermogenic fat formation. Interestingly, subcutaneous administration of recombinant CREG1 protein via an osmotic pump in C57BL/6J mice for four weeks increased UCP1 expression in interscapular brown adipose tissue (IBAT), inhibited visceral white fat hypertrophy with partial browning, and reduced DIO compared with that in PBS-treated mice. The mRNA expression of energy metabolism-related genes was significantly increased in the IBAT of CREG1-treated mice compared to that in PBS-treated mice. In contrast, adipocyte-specific overexpression of CREG1 failed to improve DIO in UCP1-knockout mice at thermoneutrality. Our results indicate the therapeutic potential of CREG1 administration for obesity under thermogenic fat-attenuating conditions and highlight the indispensable role of UCP1 in the DIO-inhibitory effect of CREG1.

Epigenetics of Mitochondria-Associated Genes in Striated Muscle

Striated muscle has especially large energy demands. We identified 97 genes preferentially expressed in skeletal muscle and heart, but not in aorta, and found significant enrichment for mitochondrial associations among them. We compared the epigenomic and transcriptomic profiles of the 27 genes associated with striated muscle and mitochondria. Many showed strong correlations between their tissue-specific transcription levels, and their tissue-specific promoter, enhancer, or open chromatin as well as their DNA hypomethylation. Their striated muscle-specific enhancer chromatin was inside, upstream, or downstream of the gene, throughout much of the gene as a super-enhancer (CKMT2, SLC25A4, and ACO2), or even overlapping a neighboring gene (COX6A2, COX7A1, and COQ10A). Surprisingly, the 3' end of the 1.38 Mb PRKN (PARK2) gene (involved in mitophagy and linked to juvenile Parkinson's disease) displayed skeletal muscle/myoblast-specific enhancer chromatin, a myoblast-specific antisense RNA, as well as brain-specific enhancer chromatin. We also found novel tissue-specific RNAs in brain and embryonic stem cells within PPARGC1A (PGC-1α), which encodes a master transcriptional coregulator for mitochondrial formation and metabolism. The tissue specificity of this gene's four alternative promoters, including a muscle-associated promoter, correlated with nearby enhancer chromatin and open chromatin. Our in-depth epigenetic examination of these genes revealed previously undescribed tissue-specific enhancer chromatin, intragenic promoters, regions of DNA hypomethylation, and intragenic noncoding RNAs that give new insights into transcription control for this medically important set of genes.

A novel function of CREG in metabolic disorders

Metabolic disorders are public health problems that require prevention and new efficient drugs for treatment. Cellular repressor of E1A-stimulated genes (CREG) is ubiquitously expressed in mature tissues and cells in mammals and plays a critical role in keeping cells or tissues in a mature, homeostatic state. Recently, CREG turns to be an important mediator in the development of metabolic disorders. Here in this review, we briefly discuss the structure and molecular regulation of CREG along with the therapeutic strategy to combat the metabolic disorders.