Meteorin-Like (METRNL) Attenuates Myocardial Ischemia/Reperfusion Injury-Induced Cardiomyocytes Apoptosis by Alleviating Endoplasmic Reticulum Stress via Activation of AMPK-PAK2 Signaling in H9C2 Cells

Downregulation of miR-410-3p via the METRNL-mediated AMPK/SIRT1/NF-κB signaling axis inhibits oxidative stress and inflammation in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF), a fatal pulmonary condition, is marked by fibrosis and is devoid of efficacious treatments. The aim of our research was to explore the influence of miR-410-3p on the advancement of IPF. For creating a model of lung fibrosis, tracheal injections of 5 mg/kg bleomycin (BLM) were administered to mice, and added 10 ng/mL of TGF-β1 into MRC-5 cell medium. The evaluation of gene and protein expression was conducted using RT-qPCR and western blotting techniques. The assessment of fibrosis in MRC-5 cells and mouse pulmonary tissue involved the use of CCK-8, ELISA, flow cytometry, and HE staining methods. The results of our study revealed a rise in miR-410-3p levels in both TGF-β1-stimulated MRC-5 cells and BLM-exposed mouse pulmonary tissue. Inhibiting miR-410-3p decreased cell viability, lessened oxidative stress (MDA, ROS), decreased levels of inflammatory cytokines (TNF-α, IL-1β, IL-6), curtailed fibrosis-associated proteins (α-SMA, Collagen I, Collagen III, FN1), and amplified the expression of SOD and E-cadherin. The treatment effectively reduced cell fibrosis and improved lung tissue health, thus hindering the advancement of IPF. Mechanically, knocking down miR-410-3p activates AMPK/SIRT1 molecular axis to inhibit NF-κB signaling by up-regulating METRNL expression, thereby inhibiting oxidative stress and inflammation levels, and ultimately improving IPF. In summary, our research indicates that focusing on miR-410-3p might be an effective approach in IPF treatment.

Meteorin-like protein (Metrnl): a key exerkine in exercise-mediated cardiovascular health

CONTEXT

Cardiovascular diseases (CVDs) remain a leading global cause of mortality, necessitating non‑pharmacological interventions such as exercise. Meteorin‑like protein (Metrnl), an exercise‑induced myokine and adipokine, has emerged as a critical mediator of exercise‑mediated cardiovascular benefits, though its specific mechanisms and clinical implications remain underexplored.

OBJECTIVE

This review synthesizes current evidence on Metrnl's role as a key exerkine in cardiovascular health, focusing on its exercise‑induced regulatory mechanisms, tissue‑specific effects, and therapeutic potential for CVD management.

METHODS

A comprehensive analysis of preclinical and clinical studies was conducted, encompassing molecular, metabolic, and anti‑inflammatory pathways linked to Metrnl. Literature from PubMed, Scopus, and Web of Science was systematically reviewed to evaluate Metrnl's role in exercise‑mediated cardiovascular adaptations.

RESULTS

Exercise‑induced Metrnl enhances endothelial function, vascular remodeling, and metabolic regulation via AMPK, PPARγ, and KIT receptor signaling. It promotes glucose/lipid metabolism, angiogenesis, and anti‑inflammatory responses, reducing atherosclerotic risks and improving cardiac repair post‑infarction. Clinically, Metrnl levels correlate with CVD severity, acting as a biomarker for risk stratification. Acute exercise elevates Metrnl, while chronic training effects vary by modality and population. Paradoxically, elevated plasma Metrnl in acute cardiac events predicts adverse outcomes, whereas reduced levels in chronic conditions (e.g., diabetes, heart failure) reflect metabolic dysregulation.

DISCUSSION

Metrnl bridges exercise benefits to cardiovascular health through inter‑organ crosstalk, yet discrepancies exist in its chronic exercise‑mediated regulation. Its dual role as a protective mediator and stress‑responsive biomarker underscores context‑dependent interpretations. Unresolved questions include receptor specificity, tissue autonomy, and therapeutic delivery strategies.

CONCLUSION

Metrnl is a pivotal exerkine with promising diagnostic and therapeutic potential for CVDs. Translating its exercise‑mediated benefits into clinical applications requires further human trials to validate mechanisms and optimize interventions. Harnessing Metrnl could revolutionize strategies for CVD prevention and rehabilitation, leveraging exercise's molecular advantages.

Exploring METRNL as a novel biomarker in sepsis: diagnostic potential and secretion mechanism

BACKGROUND

Sepsis is a life-threatening condition with a high mortality rate in intensive care unit (ICU). However, rapid and accurate diagnostic criteria are still lacking. This pilot study explored the role of METRNL as a novel biomarker for sepsis by focusing on its diagnostic potential and rapid secretion mechanism.

METHODS

METRNL levels were measured in cell and animal models of sepsis. Serum samples from 107 sepsis patients and 95 non-septic controls in ICU were collected. Diagnostic performance of METRNL, Procalcitonin (PCT) and C-reactive protein (CRP) were assessed using ROC analysis. Endothelial cell-specific Metrnl gene knockout mice (EC-Metrnl-/- mice) were used to identify the source of METRNL secretion. Chemical inhibitors and RNA interference were used to explore the secretion pathways.

RESULTS

In lipopolysaccharide (LPS)-induced cell and mouse models of sepsis, METRNL levels significantly increased in a dose- and time-dependent manner. Similarly, in the cecal ligation and puncture mouse models, serum METRNL levels were elevated over time and correlated with sepsis severity. In animals, serum METRNL increased within 1 h post-modeling, preceding PCT and CRP. Clinically, sepsis patients had significantly higher serum METRNL levels. ROC analysis showed area under the curves [95% confidence intervals] of 0.943 [0.91-0.975] for METRNL, 0.955 [0.929-0.981] for PCT and 0.873 [0.825-0.921] for CRP. At the optimal cutoff value, METRNL (91.6%) exhibited relatively greater diagnostic specificity than PCT (88.4%) and CRP (69.5%). EC-Metrnl-/- reduced majority of serum Metrnl levels in sepsis mouse models. Inhibition of the endoplasmic reticulum-Golgi (ER-Golgi) pathway through chemical inhibitors or RNA interference significantly reduced METRNL levels in the supernatant of sepsis cell models compared to control groups. Similar results were obtained with Toll-like receptor 4 (TLR4) and ERK inhibitors.

CONCLUSIONS

This pilot study demonstrates that METRNL is a novel potential biomarker for sepsis with diagnostic capability comparable to that of PCT. Serum METRNL rapidly increased during the early phase of sepsis. Mechanistically, it mainly originates from the endothelium during sepsis, and TLR4-ERK signaling mediates the rapid secretion of METRNL via the classical ER-Golgi pathway in response to LPS stimulation.

Meteorin-like protein plasma levels are associated with worse outcomes in de novo heart failure

BACKGROUND AND AIMS

Meteorin-like protein (Metrnl) has been recently suggested as a new adipokine with protective cardiovascular effects. Its circulating levels in patients seem to be associated with heart failure (HF), although with contradictory results. Our aim was to ascertain whether this adipokine could estimate the prognosis of HF in de novo HF (DNHF) patients.

METHODS

Metrnl plasma levels of 400 patients hospitalized with DNHF (55% of patients with HF with reduced ejection fraction, 17.3% HF with mid-range ejection fraction, 27.8% HF with preserved ejection fraction) were measured by enzyme-linked immunosorbent assay. We performed both sex-pooled and sex-specific analyses. A 12-month follow-up was conducted, during which clinical outcomes such as all-cause mortality, cardiovascular death and re-hospitalization due to HF were collected.

RESULTS

After a 12-month follow up, higher plasma Metrnl levels were associated with an increased risk for all-cause death and cardiovascular death after adjusting by sex, age, LVEF, hypertension, diabetes, ischemic aetiology, chronic renal failure, NT-proBNP and troponin (hazard ratio [HR] = 1.003, 95% confidence interval [CI] = 1.000-1.005; p-value<.05 and HR = 1.004, 95% CI = 1.001-1.007, p-value<.05, respectively). In line with this, DNHF patients with increased levels of circulating Metrnl had a higher number of occurrences of cardiovascular events. Regarding Metrnl associations with parameters implicated in the development and progression of HF, we found that Metrnl circulating levels were positively correlated with age (r = .322, p-value<.0001), NT-proBNP (r = .281, p-value<.0001) and with the renal dysfunction markers urea (r = .322, p-value<.0001) and creatinine (r = .353, p-value<.0001) and higher in women than men (473.7 [385.9-594.0] pg/mL vs. 428.7 [349.1-561.3] pg/mL, p-value<.006). Finally, concerning the subtype of HF, Metrnl plasma levels were higher in HF with preserved ejection fraction.

CONCLUSION

Patients with higher Metrnl levels have a worse prognosis in DNHF. Our results reinforce the association of Metrnl plasma levels with HF progression and outcomes.

Metrnl ameliorates myocardial ischemia-reperfusion injury by activating AMPK-mediated M2 macrophage polarization

BACKGROUND

Meteorin-like hormone (Metrnl) is prominently expressed in activated M2 macrophages and has demonstrated potential therapeutic effects in a range of cardiovascular diseases by modulating inflammatory responses. Nevertheless, its precise role and the underlying mechanisms in myocardial ischemia/reperfusion injury (MI/RI) are not fully understood. This study examined whether Metrnl can mitigate MI/RI through the AMPK-mediated polarization of M2 macrophages.

METHODS

In vivo, adeno-associated virus 9 containing the F4/80 promoter (AAV9-F4/80) was utilized to overexpress Metrnl in mouse cardiac macrophages before MI/RI surgery. In vitro, mouse bone marrow-derived macrophages (BMDMs) were treated with recombinant protein Metrnl, and the human cardiomyocyte cell line AC16 was subjected to hypoxia/reoxygenation (H/R) after co-culture with the supernatant of these macrophages. Cardiac function was assessed via echocardiography, H&E staining, and Evans blue-TTC staining. Inflammatory infiltration was evaluated by RT-qPCR and ELISA, apoptosis by Western blotting and TUNEL staining, and macrophage polarization by immunofluorescence staining and flow cytometry.

RESULTS

In vivo, Metrnl overexpression in cardiac macrophages significantly attenuated MI/RI, as evidenced by reduced myocardial infarct size, enhancement of cardiac function, diminished inflammatory cell infiltration, and decreased cardiomyocyte apoptosis. Furthermore, Metrnl overexpression promoted M1 to M2 macrophage polarization. In vitro, BMDMs treated with Metrnl shifted towards M2 polarization, characterized by decreased expression of inflammatory cytokines (IL-1β, MCP-1, TNF-α) and increased expression of the anti-inflammatory cytokine IL-10. Additionally, supernatant from Metrnl-treated macrophages protected AC16 cells from apoptosis under H/R conditions, as evidenced by decreased BAX expression and increased BCL-2 expression. However, these effects of Metrnl were inhibited by the AMPK inhibitor Compound C.

CONCLUSIONS

Metrnl alleviates MI/RI by activating AMPK-mediated M2 macrophage polarization to attenuate inflammatory response and cardiomyocyte apoptosis. This study highlights the therapeutic potential of Metrnl in MI/RI, and identifies it as a promising target for the treatment of ischemic heart disease.

Targeting P21-Activated Kinase 2 as a Novel Therapeutic Approach to Mitigate Endoplasmic Reticulum Stress in Heart Failure With Preserved Ejection Fraction

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF) is linked to prolonged endoplasmic reticulum (ER) stress. P21-activated kinase 2 (Pak2) facilitates a protective ER stress response. This study explores the mechanism and role of Pak2 in HFpEF pathology.

METHODS AND RESULTS

The HFpEF mouse model was established using a high-fat diet combined with the nitric oxide synthase inhibitor Nω-Nitro-l-arginine methyl ester (high-fat diet+Nω-Nitro-l-arginine methyl ester). The model exhibited the typical characteristics of HFpEF (cardiac hypertrophy, diastolic dysfunction with preserved systolic function, and lung edema) as determined by echocardiography and hemodynamic analysis. Terminal deoxynucleotidyl transferase dUTP nick end labeling and dihydroethidium staining results showed that cell death and reactive oxygen species generation were higher in the high-fat diet+Nω-Nitro-l-arginine methyl ester-treated group. Transmission electron microscopy revealed disruption of the ER subcellular structures in the HFpEF mouse model, while western blot analysis confirmed reduced Pak2 phosphorylation and impaired inositol-requiring enzyme 1/X-box binding protein 1 splicing ER stress response signaling. Furthermore, H9c2 cells subjected to the palmitic acid-mediated metabolic stress developed temporal changes in unfolded protein response proteins and Pak2 activity. The inositol requiring enzyme 1/X-box binding protein 1 splicing branch of unfolded protein response was impaired earlier than other branches. Overexpression of Pak2 by adenovirus in H9c2 cells sustained the activation of inositol requiring enzyme 1/X-box binding protein 1 splicing. Pak2 deficiency in the mouse heart accelerated the HFpEF progression, and this phenomenon occurred as early as 10 weeks in Pak2 cardiomyocyte-specific knockout mice. Conversely, adeno-associated virus serotype 9-mediated Pak2 overexpression mitigated HFpEF symptoms, underscoring its protective role against HFpEF progression.

CONCLUSIONS

Pak2 prevents HFpEF progression, exerting cardioprotective effects against ER stress. These insights underscore the therapeutic value of Pak2 in HFpEF.

Metrnl as a secreted protein: Discovery and cardiovascular research

Secreted proteins have gained more and more attentions, since they can become therapeutic targets, drugs and biomarkers for prevention, diagnosis and treatment of disease and aging. In 2014, Metrnl (also named Meteorin-like, Cometin, Subfatin, Interleukin-39, Interleukin-41, Meteorin-β, and Metrn-β/Metrnβ), as a novel secreted protein released from a certain tissue, was reported by us and others. During the past decade, the number of articles on Metrnl has continued to increase. Different sources of Metrnl have been described with different functions, including Metrnl as an adipokine for insulin sensitization, a cardiokine against cardiac hypertrophy and dysfunction, an endothelium-derived factor against endothelial dysfunction and atherosclerosis, etc. Especially, we show that endothelial Metrnl is a major source for circulating Metrnl levels. Meanwhile, lots of clinical studies have investigated the relationship between blood Metrnl levels and metabolic, inflammatory and cardiovascular diseases. Metrnl appears a protective factor and a promising therapeutic target and/or drug against these diseases, given the relatively consistent conclusion from the preclinical studies. In addition to graphically demonstrating the role of Metrnl in various organs and diseases, this review will mainly describe the discovery of Metrnl, summarize the role of Metrnl in cardiovascular system that is a recently major progress in Metrnl research, and highlight several perspectives for future basic and translational research. Also, we suggest using one name Metrnl instead of other multiple names for the same protein.

Characterization of the Metabolic Proteome of Serum From Patients With Diabetic Distal Symmetric Polyneuropathy

AIMS

The pathophysiological of diabetic distal symmetric polyneuropathy (DSPN) remains to be elucidated and there are no diagnostic or prognostic biomarkers for the condition. In this explorative proteomic study, metabolic proteome profiling of serum in patients with/without DSPN was analyzed. We aimed to discover proteins with different abundance ranges through proximity extension assay (PEA) technology.

METHODS

Temperature quantitative sensory testing (QST) and electromyography (EMG) were used to access the small- and large-fiber function of all participants, respectively. The metabolic proteome profile of serum was analyzed using PEA technology (Olink Target 96 METABOLISM panel).

RESULTS

We evaluated serum from patients without DSPN (n = 27), with small-fiber neuropathy (SFN, n = 25) and with mixed small- and large-fiber neuropathy (MSLFN, n = 24). Fifteen proteins, which were especially related to immune response, insulin resistance, and lipid metabolism, were significantly different between patients without DSPN and with MSLFN. Besides, seven proteins, especially related to extracellular structure organization, were significantly different between serum from patients with SFN and with MSLFN. What's more, serum from patients without DSPN showed that three proteins, related to immune response, altered significantly compared to serum from patients with SFN.

CONCLUSIONS

This was the first study that characterized the metabolic proteomic profile of serum in DSPN patients by analyzing a panel of 92 metabolic proteins using PEA technology.

Metrnl: a promising biomarker and therapeutic target for cardiovascular and metabolic diseases

Modern human society is burdened with the pandemic of cardiovascular and metabolic diseases. Metrnl is a widely distributed secreted protein in the body, involved in regulating glucose and lipid metabolism and maintaining cardiovascular system homeostasis. In this review, we present the predictive and therapeutic roles of Metrnl in various cardiovascular and metabolic diseases, including atherosclerosis, ischemic heart disease, cardiac remodeling, heart failure, hypertension, chemotherapy-induced myocardial injury, diabetes mellitus, and obesity.

Increased serum interleukin-41 correlates with disease severity in myasthenia gravis

BACKGROUND

Myasthenia gravis (MG) is an autoimmune disease mediated by pathogenic antibodies produced by abnormally activated B cells, resulting in neuromuscular junction transmission dysfunction. Interleukin-41 (IL-41) is a novel immunomodulatory cytokine that has been implicated in various metabolic, inflammatory, and autoimmune diseases. The role of IL-41 in MG is still unclear up to now, our study aimed to investigate the level of IL-41 in MG patients and its correlation with clinical features and inflammatory indicators.

METHODS

Totally, 60 MG patients and 30 healthy controls (HC) were recruited. Baseline data and laboratory parameters were routinely recorded through electronic medical systems. IL-41 levels were measured by enzyme-linked immunosorbent assay. Proportions of T-cell and B-cell subsets and natural killer cells were analyzed by flow cytometry. The correlation between serum IL-41 and MG related parameters was investigated, and the clinical value of IL-41 in the diagnosis of MG was evaluated by receiver operator characteristic curve (ROC) analysis.

RESULTS

Serum IL-41 levels in MG patients were higher than in HC, and were higher in Myasthenia Gravis Foundation of America (MGFA) III + IV group than that in MGFA I + II group. Serum IL-41 was positively correlated with MG-specific activities of daily living scale (MG-ADL), MGFA classification, platelet to lymphocyte ratio (PLR), and proportion of CD19+ B cells, while it was negatively correlated with high-sensitive C-reactive protein (hs-CRP) and circulatory plasma cells in MG patients. Serum IL-41 levels increased in patients who were treated with efgartigimod during the first cycle of therapy. However, compared to disease initiation, serum IL-41 levels decreased when clinical features steadily improved. ROC analysis showed that IL-41 had a diagnostic value for MG.

CONCLUSION

The present findings suggested that serum IL-41 was increased in MG patients and was positively associated with the severity of the disease. IL-41 may be essential to the immunopathological mechanism of MG and a potential biomarker for MG.

Differential expression of miR-140-3p and its potential role during the development of the acute coronary syndrome

BACKGROUND

Acute coronary syndrome (ACS) is a category of cardiovascular disease with a high fatality rate.

AIMS

We searched the differential expressed miRNAs (DEmiRNAs) in ACS based on bioinformatic analysis and investigated the diagnostic value of plasma miR-140-3p in patients with ACS and its potential functional role in ACS.

METHODS

The miRNAs (GSE94605, GSE49823, and GSE185729) microarray datasets of ACS were downloaded from the GEO datasets. After integrating the miRNA and mRNA interaction, a protein-protein interaction (PPI) network was constructed with 36 overlapped target mRNAs using STRING database. The plasma levels of miR-140-3p were detected by RT-qPCR, and its clinical diagnostic value was evaluated using the ROC curve. The potential effects of the miR-140-3p/RHOA axis in ACS were explored using human coronary endothelial cells (HCAECs).

RESULTS

After overlapping the GEO datasets, miR-140-3p was identified in the microarray datasets of ACS. The plasma miR-140-3p expression levels were highly expressed in ACS patients than in healthy control and had diagnostic significance. The target mRNAs of miR-140-3p were predicted using TargetScan, miRWalk, TarBase, and miRDB databases. The PPI network identified ten hub genes. miR-140-3p could decrease the HCAECs' cell viability, while RHOA reversed the inhibition effect of miR-140-3p.

CONCLUSIONS

The plasma expression of miR-140-3p was upregulated in ACS patients. miR-140-3p could decrease the HCAECs' cell viability, while RHOA reversed the inhibition effect of miR-140-3p. The miR-140-3p may be a potential diagnostic biomarker for the early detection of ACS.

MG53: A new protagonist in the precise treatment of cardiomyopathies

Cardiomyopathies (CMs) are highly heterogeneous progressive heart diseases characterised by structural and functional abnormalities of the heart, whose intricate pathogenesis has resulted in a lack of effective treatment options. Mitsugumin 53 (MG53), also known as Tripartite motif protein 72 (TRIM72), is a tripartite motif family protein from the immuno-proteomic library expressed primarily in the heart and skeletal muscle. Recent studies have identified MG53 as a potential cardioprotective protein that may play a crucial role in CMs. Therefore, the objective of this review is to comprehensively examine the underlying mechanisms mediated by MG53 responsible for myocardial protection, elucidate the potential role of MG53 in various CMs as well as its dominant status in the diagnosis and prognosis of human myocardial injury, and evaluate the potential therapeutic value of recombinant human MG53 (rhMG53) in CMs. It is expected to yield novel perspectives regarding the clinical diagnosis and therapeutic treatment of CMs.

Meteorin-like (METRNL) attenuates hypertensive induced cardiac hypertrophy by inhibiting autophagy via activating BRCA2

Hypertension, a prevalent cardiovascular ailment globally, can precipitate numerous complications, notably hypertensive cardiomyopathy. Meteorin-like (METRNL) is demonstrated to possess potential protective properties on cardiovascular diseases. However, its specific role and underlying mechanism in hypertensive myocardial hypertrophy remain elusive. Spontaneously hypertensive rats (SHRs) served as hypertensive models to explore the effects of METRNL on hypertension and its induced myocardial hypertrophy. The research results indicate that, in contrast to Wistar-Kyoto (WKY) rats, SHRs exhibit significant symptoms of hypertension and myocardial hypertrophy, but cardiac-specific overexpression (OE) of METRNL can partially ameliorate these symptoms. In H9c2 cardiomyocytes, METRNL suppresses Ang II-induced autophagy by controlling the BRCA2/Akt/mTOR signaling pathway. But when BRCA2 expression is knocked down, this effect will be suppressed. Collectively, METRNL emerges as a potential therapeutic target for hypertensive cardiomyopathy.

The Function and Mechanism of Anti-Inflammatory Factor Metrnl Prevents the Progression of Inflammatory-Mediated Pathological Bone Osteolytic Diseases

Metrnl, recently identified as an adipokine, is a secreted protein notably expressed in white adipose tissue, barrier tissues, and activated macrophages. This adipokine plays a pivotal role in counteracting obesity-induced insulin resistance. It enhances adipose tissue functionality by promoting adipocyte differentiation, activating metabolic pathways, and exerting anti-inflammatory effects. Extensive research has identified Metrnl as a key player in modulating inflammatory responses and as an integral regulator of muscle regeneration. These findings position Metrnl as a promising biomarker and potential therapeutic target in treating inflammation-associated pathologies. Despite this, the specific anti-inflammatory mechanisms of Metrnl in immune-mediated osteolysis and arthritis remain elusive, warranting further investigation. In this review, we will briefly elaborate on the role of Metrnl in anti-inflammation function in inflammation-related osteolysis, arthritis, and pathological bone resorption, which could facilitate Metrnl's clinical application as a novel therapeutic strategy to prevent bone loss. While the pathogenesis of elbow stiffness remains elusive, current literature suggests that Metrnl likely exerts a pivotal role in its development.

Low Levels of Metrnl are Linked to the Deterioration of Diabetic Kidney Disease

Objective

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease. Metrnl is a secreted protein that plays an important role in kidney disease. The aim of this study was to investigate DKD-related factors and the correlation between serum Metrnl levels and the severity of DKD.

Methods

Ninety-six type 2 diabetes mellitus (T2DM) patients and 45 DKD patients were included in the study. A range of parameters were measured simultaneously, including waist-to-hip ratio (WHR), body mass index (BMI), urinary albumin/creatinine ratio (UACR), monocyte-lymphocyte ratio (MLR), albumin/globulin (A/G), liver and kidney function, blood lipid profile, islet function, and others. Subsequently, the related factors and predictive significance of DKD were identified. The correlation between the relevant factors of DKD and serum Metrnl levels with DKD was evaluated.

Results

The duration of the disease (OR: 1.12, 95% CI: 1.01-1.24, P=0.031), hypertension (OR: 4.86, 95% CI: 1.16-20.49, P=0.031), fasting blood glucose (OR: 1.23, 95% CI: 1.03-1.48, P=0.025), WHR (OR: 2.53, 95% CI: 1.03-6.22, P=0.044), and MLR (OR: 1.91, 95% CI: 1.18-3.08, P=0.008) are independent risk factors for DKD (P < 0.05). Conversely, A/G (OR: 0.13, 95% CI: 0.02-0.76, P=0.024) and Metrnl (OR: 0.99, 95% CI: 0.98-1.00, P=0.001) have been identified as protective factors against DKD. Furthermore, the level of Metrnl was negatively correlated with the severity of DKD (rs=-0.447, P<0.001). The area under receiver operating characteristic (ROC) curves for the diagnostic accuracy of Metrnl for DKD is 0.765 (95% CI: 0.686-0.844).

Conclusion

The duration of the disease, hypertension, fasting blood glucose, WHR, and MLR are major risk factors for DKD. Metrnl and A/G are protective factors for DKD. Serum Metrnl concentrations are inversely correlated with DKD severity.

Interleukin-41 as a biomarker of the anti-inflammatory response associated with hyperuricemia

BACKGROUND

Interleukin (IL)-41 is a recently discovered secreted protein that is expressed in a variety of tissues, and it is associated with several immune and metabolic diseases. However, IL-41 has not been studied in hyperuricemia (HUA).

METHODS

Forty-four HUA patients and 44 healthy controls (HCs) were included in this study, and we collected theirgeneral and biochemical parameters, including white blood cell, neutrophil, lymphocyte, and platelet counts, mean platelet volume, platelet distribution width, serum creatinine, blood urea nitrogen, fasting blood glucose, total triglyceride, total cholesterol, high-density lipoprotein, low-density lipoprotein, total protein, albumin, alkaline phosphatase, gamma-glutamyltransferase, and hemoglobin concentration. The level of serum IL-41 was determined using an enzyme-linked immunosorbent assay. Multivariate logistic regression analysis was exploited to identify the independent risk factors associated with HUA, and the clinical diagnostic value of IL-41 was analyzed by applying the receiver operating characteristic (ROC) curve. We assessed the association between IL-41 and clinical parameters with Spearman's rank correlation.

RESULTS

Circulating IL-41 levels were significantly higher in HUA patients than in the HCs group (460.3 pg/mL vs. 261.3 pg/mL, respectively; P < 0.001). The area under the ROC curve (AUC) for IL-41 in HUA patients was 0.7443 (with a cut-off value of 311.055 pg/mL, a sensitivity of 68.18 %, and a specificity of 72.73 %), while the AUC for IL-41 combined with the platelet count was 0.8109. Correlation analysis revealed that the circulating IL-41 level was positively correlated with age in HCs and HUA patients.

CONCLUSIONS

We herein demonstrated that serum IL-41 was elevated in HUA patients and that it may constitute a novel biomarker of anti-inflammatory response related to HUA.

AMPK Signalling Pathway: A Potential Strategy for the Treatment of Heart Failure with Chinese Medicine

Heart failure (HF) is a complex clinical syndrome that represents the advanced stage of cardiovascular disease, characterized by systolic and diastolic dysfunction of the heart. Despite continuous updates in HF treatment drugs, the morbidity and mortality rates remain high, necessitating ongoing exploration for new therapeutic targets. Adenosine monophosphate-activated protein kinase (AMPK) is the serine/threonine protein kinase which responds to adenosine monophosphate (AMP) levels.Activation of AMPK shifts cellular metabolic patterns from synthesis to catabolism, enhancing energy metabolism in pathological conditions such as inflammation, ischemia, obesity, and aging. Numerous studies have identified AMPK as a vital target for HF treatment, with herbal monomers/extracts and compounds affecting key signaling factors including rapamycin targeting protein (mTOR), silencing regulator protein 1 (SIRT1), nuclear transcription factor E2-related factor 2 (Nrf2), and nuclear transcription factor-κB (NF-κB) through regulation of the AMPK signaling pathway.This modulation can achieve the effects of improving metabolism, autophagy, reducing oxidative stress and inflammatory response in the treatment of heart failure, with the advantages of multi-targeting, comprehensive action and low toxicity.The modulation of the AMPK pathway by Traditional Chinese Medicine (TCM) has emerged as a crucial research direction for the prevention and treatment of HF, but a systematic summary and generalization in this field is lacking. This article provides an overview of the composition, regulation, and mechanism of the AMPK signaling pathway's influence on HF, as well as a summary of current research on the regulation of the AMPK pathway by TCM for HF prevention and treatment. The aim is to serve as a reference for the diagnosis and treatment of HF using TCM and the development of new drugs.

Accelerating Wound Closure With Metrnl in Normal and Diabetic Mouse Skin

Impaired wound healing and ulcer complications are major causes of morbidity in patients with diabetes. Impaired wound healing is associated with increased inflammation and poor angiogenesis in diabetes patients. Here, we demonstrate that topical administration of a secreted recombinant protein (Meteorin-like [Metrnl]) accelerates wound epithelialization and angiogenesis in mice. We observed a significant increase in Metrnl expression during physiological wound healing; however, its expression remained low during diabetic wound healing. Functionally, the recombinant protein Metrnl significantly accelerated wound closure in normal and diabetic mice models including db/db, high-fat diet/streptozotocin (HFD/STZ), and STZ mice. Mechanistically, keratinocytes secrete quantities of Metrnl to promote angiogenesis; increase endothelial cell proliferation, migration, and tube formation; and enhance macrophage polarization to the M2 type. Meanwhile, M2 macrophages secrete Metrnl to further stimulate angiogenesis. Moreover, the keratinocyte- and macrophage-produced cytokine Metrnl drives postinjury angiogenesis and reepithelialization through activation of AKT phosphorylation (S473) in a KIT receptor tyrosine kinase (c-Kit)-dependent manner. In conclusion, our study suggests that Metrnl has a biological effect in accelerating wound closure through c-Kit-dependent angiogenesis and epithelialization.

ARTICLE HIGHLIGHTS

N-Acetylcysteine may exert hepatoprotective effect by regulating Meteorin-Like levels in Adriamycin-induced liver injury

Adriamycin (ADR) is an important chemotherapeutic drug, but it has serious side effects such as hepatotoxicity. This study aimed to evaluate whether N-acetylcysteine (NAC) has hepatoprotective effects against ADR-induced hepatotoxicity in rats. In addition, it was aimed to determine how Meteorin-Like (MtrnL), which has pleiotropic effects on immunology, inflammation, and metabolism, is affected by ADR and/or NAC applications in liver tissue. 28 rats were randomly assigned to one of four equal groups in the study: control (no treatment), NAC (150 mg/kg/day of NAC intraperitoneally (i.p), ADR (15 mg/kg only on the first day of the experiment), and ADR + NAC (ADR 15 mg/kg on the first day of the experiment + 150 mg/kg/day NAC i.p). After 15 days, liver enzyme levels in serum, oxidant/antioxidant parameters in liver tissue, histopathological changes, caspase 3 (Casp3) and heat shock protein 70 (HSP-70) immunoreactivities, and MtrnL levels were examined. Histopathological changes, liver enzyme levels, as well as HSP-70, and Casp3 immunoreactivities increased due to ADR application. Additionally, MtrnL levels in liver tissue were significantly increased as a result of ADR application. However, it was detected that the NAC application significantly regulated the ADR-induced changes. Furthermore, it was determined that NAC administration regulated the changes in ADR-induced oxidative stress parameters. We propose that NAC may exert a hepatoprotective effect by regulating ADR-induced altered oxidative stress parameters, MtrnL levels, Casp3, and HSP-70 immunoreactivities in the liver.

Metrnl deficiency retards skin wound healing in mice by inhibiting AKT/eNOS signaling and angiogenesis

Meteorin-like (Metrnl) is a novel secreted protein with various biological activities. In this study, we investigated whether and how Metrnl regulated skin wound healing in mice. Global Metrnl gene knockout mice (Metrnl-/-) and endothelial cell-specific Metrnl gene knockout mice (EC-Metrnl-/-) were generated. Eight-mm-diameter full-thickness excisional wound was made on the dorsum of each mouse. The skin wounds were photographed and analyzed. In C57BL/6 mice, we observed that Metrnl expression levels were markedly increased in skin wound tissues. We found that both global and endothelial cell-specific Metrnl gene knockout significantly retarded mouse skin wound healing, and endothelial Metrnl was the key factor affecting wound healing and angiogenesis. The proliferation, migration and tube formation ability of primary human umbilical vein endothelial cells (HUVECs) were inhibited by Metrnl knockdown, but significantly promoted by addition of recombinant Metrnl (10 ng/mL). Metrnl knockdown abolished the proliferation of endothelial cells stimulated by recombinant VEGFA (10 ng/mL) but not by recombinant bFGF (10 ng/mL). We further revealed that Metrnl deficiency impaired VEGFA downstream AKT/eNOS activation in vitro and in vivo. The damaged angiogenetic activity in Metrnl knockdown HUVECs was partly rescued by addition of AKT activator SC79 (10 μM). In conclusion, Metrnl deficiency retards skin wound healing in mice, which is related to impaired endothelial Metrnl-mediated angiogenesis. Metrnl deficiency impairs angiogenesis by inhibiting AKT/eNOS signaling pathway.

Meteorin-like protein overexpression ameliorates fulminant hepatitis in mice by inhibiting chemokine-dependent immune cell infiltration

Myokines, which are recently identified cytokines secreted by skeletal muscle in response to stimulation, are crucial for the maintenance of liver function. Fulminant hepatitis (FH) is a life-threatening pathological condition with severe hepatic dysfunction. In this study, we investigated the role of meteorin-like (METRNL), a new myokine, in the pathogenesis of FH. We compared serum samples and liver tissues from FH patients and healthy controls and found that hepatic and serum METRNL levels were significantly increased in FH patients, and serum METRNL levels were related to disease severity in FH patients. We then established a concanavalin A-induced FH model in METRNL-overexpressing and control mice. We found that hepatic METRNL levels in FH mice were significantly increased, and METRNL in the liver was mainly derived from macrophages. In the cultured mouse macrophage line (RAW264.7 cells) and mouse primary peritoneal macrophages (PMs), METRNL overexpression significantly inhibited the release of the proinflammatory cytokines TNF and IL-1β. In METRNL-overexpressing mice, concanavalin A-induced liver injury was significantly ameliorated. Moreover, METRNL overexpression significantly reduced chemokine-dependent inflammatory cell infiltration into the liver. METRNL overexpression also suppressed liver CD4+ T cell differentiation into Th 1 cells and inhibited the secretion of Th 1 cytokines. Taken together, these data suggest that METRNL overexpression effectively ameliorates FH. Therefore, METRNL may serve as a potential biomarker and therapeutic target for FH.

Meteorin-like/Metrnl, a novel secreted protein implicated in inflammation, immunology, and metabolism: A comprehensive review of preclinical and clinical studies

Meteorin-like, also known as Metrnl, Meteorin-β, Subfatin, and Cometin, is a novel secreted protein exerting pleiotropic effects on inflammation, immunology, and metabolism. Earlier research on this hormone focused on regulating energy expenditure and glucose homeostasis. Consequently, several studies attempted to characterize the molecule mechanism of Metrnl in glucose metabolism and obesity-related disorders but reported contradictory clinical results. Recent studies gradually noticed its multiple protective functions in inflammatory immune regulations and cardiometabolic diseases, such as inducing macrophage activation, angiogenesis, tissue remodeling, bone formation, and preventing dyslipidemias. A comprehensive understanding of this novel protein is essential to identify its significance as a potential therapeutic drug or a biomarker of certain diseases. In this review, we present the current knowledge on the physiology of Metrnl and its roles in inflammation, immunology, and metabolism, including animal/cell interventional preclinical studies and human clinical studies. We also describe controversies regarding the data of circulation Metrnl in different disease states to determine its clinical application better.

Panax notoginseng Saponins Alleviate Coronary Artery Disease Through Hypermethylation of the miR-194-MAPK Pathway

Background:Panax notoginseng saponins (PNS) may have an inhibitory effect against coronary artery disease (CAD); however, the mechanism is unclear. Recent research has begun to evaluate the role of epigenetics in CAD. Our team found that hypomethylation of miR-194 could be an important mechanism of CAD.

Purpose: The aim of this study was to investigate the effect of PNS against CAD and evaluate whether the mechanism is related to methylation of mi-R194.

Methods: We conducted a randomized controlled trial with a double-blind placebo design on 84 patients with CAD. Treatment was continued for 4 weeks, and the clinical effect of PNS on CAD was observed. Methylation of miR-194, its promoter, and the key nodes of the MAPK pathway were measured by pyrosequencing and qRT-PCR. We then conducted a pharmacological analysis of the active components of PNS. The effects of PNS on oxidized human umbilical vein endothelial cells and the methylation of miR-194, its promoter, and the key nodes of the MAPK pathway were measured in vitro through methylation-specific PCR (MSPCR), qRT-PCR, Western blot analysis, and annexin V/propidium iodide apoptosis assay.

Results: PNS improved symptoms of CAD. High-density lipoprotein and white blood cell count demonstrated significant changes after treatment in the PNS group. No significant difference was observed between miR-194 and mRNA MAPK, FAS, RAS, and FOS in the PNS group after treatment. However, some notable trends were observed in these genes. The targets of PNS were predicted by the pharmacological components. Some targets were found to be differentially expressed genes in CAD sequencing. Six genes, including MAPK1, RAS, and FASL, were common targets of PNS in CAD sequencing. Correlations were observed between genes in the interaction network and clinical parameters. In vitro experiments confirmed that PNS could change the methylation of miR-194, its promoter, and MAPK, FAS, RAS, and FOS. Intervention with PNS is likely to improve apoptosis.

Conclusion: We reported the regulation of miR-194 promoter, miR-194, and MAPK methylation by PNS through cell experiments and a randomized controlled trial. PNS can be used for intervention in CAD by targeting the miR-194 promoter-miR-194-MAPK signaling pathway.

Clinical Trial Registration: https://www.clinicaltrials.gov/, NCT03083119.

Subfatin concentration decreases in acute coronary syndrome

Introduction

We investigated the association of serum subfatin concentration and acute myocardial infarction (AMI) in patients with ST-elevation myocardial infarction (STEMI) and non-STEMI (NSTEMI).

Materials and methods

In this study, patients who presented with chest pain (STEMI, NSTEMI, or non-cardiac chest pain) were included, i.e. 49 patients with non-cardiac chest pain (control) and 66 patients hospitalised with AMI. In the AMI group, 35 patients had NSTEMI and 31 had STEMI. Serum subfatin concentrations were determined via enzyme-linked immunosorbent assay (ELISA). Descriptive data on the patients and their comorbidities were recorded, and subfatin concentrations were analysed.

Results

Subfatin concentrations were significantly different in the control, STEMI and NSTEMI groups (P = 0.002). In addition, subfatin concentrations were significantly lower in patients in the NSTEMI group than those in the control group (P < 0.001), but there was no significant difference between STEMI and the control group (P = 0.143). The receiver operating characteristic (ROC) analysis performed for differentiating the AMI and control groups found that subfatin had 64% sensitivity and 69% specificity, whereas troponin had 59% sensitivity and 95% specificity. In patients with AMI, the ROC analysis for differentiating NSTEMI from STEMI found that subfatin had 94% sensitivity and 41% specificity, while troponin had 65% sensitivity and 88% specificity.

Conclusions

Subfatin concentrations were lower in patients without STEMI than in patients with STEMI. Subfatin concentration is associated with NSTEMI.

MicroRNA-194-5p Attenuates Doxorubicin-Induced Cardiomyocyte Apoptosis and Endoplasmic Reticulum Stress by Targeting P21-Activated Kinase 2

Objective

Many studies have reported that microRNAs (miRs) are involved in the regulation of doxorubicin (DOX)-induced cardiotoxicity. MiR-194-5p has been reported significantly upregulated in patients with myocardial infarction; however, its role in myocardial diseases is still unclear. Various stimuluses can trigger the endoplasmic reticulum (ER) stress and it may activate the apoptosis signals eventually. This study aims to explore the regulatory role of miR-194-5p in DOX-induced ER stress and cardiomyocyte apoptosis.

Methods

H9c2 was treated with 2 μM DOX to induce apoptosis, which is to stimulate the DOX-induced cardiotoxicity model. The expression of miR-194-5p was detected by quantitative real-time PCR (qRT-PCR); the interaction between miR-194-5p and P21-activated kinase 2 (PAK2) was tested by dual luciferase reporter assay; terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay and caspase-3/7 activity were used to assess apoptosis; trypan blue staining was applied to measure cell death; Western blotting was performed to detect protein expressions; and ER-related factors splicing X-box binding protein 1 (XBP1s) was detected by polyacrylamide gel electrophoresis and immunofluorescence to verify the activation of ER stress.

Results

MiR-194-5p was upregulated in cardiomyocytes and mouse heart tissue with DOX treatment, while the protein level of PAK2 was downregulated. PAK2 was predicted as the target of miR-194-5p; hence, dual luciferase reporter assay indicated that miR-194-5p directly interacted with PAK2 and inhibited its expression. TUNEL assay, caspase-3/7 activity test, and trypan blue stain results showed that either inhibition of miR-194-5p or overexpression of PAK2 reduced DOX-induced cardiomyocyte apoptosis. Silencing of miR-194-5p also improved DOX-induced cardiac dysfunction. In addition, DOX could induce ER stress in H9c2, which led to XBP1 and caspase-12 activation. The expression level of XBP1s with DOX treatment increased first then decreased. Overexpression of XBP1s suppressed DOX-induced caspase-3/7 activity elevation as well as the expression of cleaved caspase-12, which protected cardiomyocyte from apoptosis. Additionally, the activation of XBP1s was regulated by miR-194-5p and PAK2.

Conclusion

Our findings revealed that silencing miR-194-5p could alleviate DOX-induced cardiotoxicity via PAK2 and XBP1s in vitro and in vivo. Thus, the novel miR-194-5p/PAK2/XBP1s axis might be the potential prevention/treatment targets for cancer patients receiving DOX treatment.

Serum Meteorin-like is associated with weight loss in the elderly patients with chronic heart failure

BACKGROUND

Unintentional weight loss (cachexia) has been associated with poor outcomes in chronic heart failure (CHF). Meteorin-like (Metrnl) is a novel myokine with protective effects on cardiovascular diseases. However, the change of Metrnl concentrations and its role in elderly patients with CHF remains unclear. The aim of this study was to evaluate the association of serum Metrnl with weight loss and outcomes in elderly patients with CHF.

METHODS

A total of 931 consecutive elderly patients (aged 60 years and older) with CHF and 135 age-matched and sex-matched control subjects were enrolled. Serum Metrnl concentration was measured by enzyme-linked immunosorbent assay. Body weight was measured at baseline and 12 months.

RESULTS

Median of serum Metrnl levels was lower in CHF patients when compared with controls [201.31 (184.95-261.16) pg/mL vs. 168.68 (103.15-197.54) pg/mL, P < 0.001]. Patients with the lowest levels of Metrnl had higher N-terminal pro brain natriuretic peptide (NT-proBNP) levels but lower left ventricular eject fraction (LVEF) and estimated glomerular filtration rate (P < 0.001). Lower serum Metrnl was associated with a higher risk of >5% weight loss from baseline to 12 months [odds ratio = 6.13, 95% confidence interval (CI) = 2.57-14.62 per log decrease; P < 0.001]. Serum Metrnl levels were decreased as LVEF decreased (P < 0.001) and were positively correlated with LVEF (r = 0.267, P < 0.001) but negatively correlated with NT-proBNP levels (r = -0.257, P < 0.001). Cox regression analysis suggested that lower serum Metrnl was associated with higher cardiovascular mortality [hazard ratio (HR) = 6.71, 95% CI = 3.41-13.18 per log decrease; P < 0.001], CHF rehospitalization (HR = 3.07, 95% CI = 1.82-5.17 per log decrease; P < 0.001), and the combined major adverse cardiac event(s) (MACEs) (HR = 5.38, 95% CI = 3.51-8.25 per log decrease; P < 0.001). The Kaplan-Meier survival curves showed that low concentration of Metrnl was a prognostic indicator of MACEs in patients with CHF.

CONCLUSIONS

Our study suggests that lower serum Metrnl level is correlated with weight loss and the severity of cardiac dysfunction in elderly patients with CHF.

Dysregulated Circulating Apoptosis- and Autophagy-Related lncRNAs as Diagnostic Markers in Coronary Artery Disease

Objective

Increasing evidence emphasizes the implications of dysregulated apoptosis and autophagy cellular processes in coronary artery disease (CAD). Herein, we aimed to explore apoptosis- and autophagy-related long noncoding RNAs (lncRNAs) in peripheral blood of CAD patients.

Methods

The mRNA and lncRNA expression profiles were retrieved from the Gene Expression Omnibus (GEO) database. With ∣fold change | >1.5 and adjusted p value < 0.05, differentially expressed apoptosis- and autophagy-related mRNAs were screened between CAD and healthy blood samples. Also, differentially expressed lncRNAs were identified for CAD. Using the psych package, apoptosis- and autophagy-related lncRNAs were defined with Spearson's correlation analysis. Receiver operating characteristic (ROC) curves were conducted for the assessment of the diagnosed efficacy of these apoptosis- and autophagy-related lncRNAs.

Results

Our results showed that 24 apoptosis- and autophagy-related mRNAs were abnormally expressed in CAD than normal controls. 12 circulating upregulated and 1 downregulated apoptosis- and autophagy-related lncRNAs were identified for CAD. The ROCs confirmed that AC004485.3 (AUC = 0.899), AC004920.3 (AUC = 0.93), AJ006998.2 (AUC = 0.776), H19 (AUC = 0.943), RP5-902P8.10 (AUC = 0.956), RP5-1114G22.2 (AUC = 0.883), RP11-247A12.1 (AUC = 0.885), RP11-288L9.4 (AUC = 0.928), RP11-344B5.2 (AUC = 0.858), RP11-452C8.1 (AUC = 0.929), RP11-565A3.1 (AUC = 0.893), and XXbac-B33L19.4 (AUC = 0.932) exhibited good performance in differentiating CAD from healthy controls.

Conclusion

Collectively, our findings proposed that circulating apoptosis- and autophagy-related lncRNAs could become underlying diagnostic markers for CAD in clinical practice.

Adipokines and Inflammation: Focus on Cardiovascular Diseases

It is well established that adipose tissue, apart from its energy storage function, acts as an endocrine organ that produces and secretes a number of bioactive substances, including hormones commonly known as adipokines. Obesity is a major risk factor for the development of cardiovascular diseases, mainly due to a low grade of inflammation and the excessive fat accumulation produced in this state. The adipose tissue dysfunction in obesity leads to an aberrant release of adipokines, some of them with direct cardiovascular and inflammatory regulatory functions. Inflammation is a common link between obesity and cardiovascular diseases, so this review will summarise the role of the main adipokines implicated in the regulation of the inflammatory processes occurring under the scenario of cardiovascular diseases.

Meteorin-like protein attenuates doxorubicin-induced cardiotoxicity via activating cAMP/PKA/SIRT1 pathway

Meteorin-like (METRNL) protein is a newly identified myokine that functions to modulate energy expenditure and inflammation in adipose tissue. Herein, we aim to investigate the potential role and molecular basis of METRNL in doxorubicin (DOX)-induced cardiotoxicity. METRNL was found to be abundantly expressed in cardiac muscle under physiological conditions that was decreased upon DOX exposure. Cardiac-specific overexpression of METRNL by adeno-associated virus serotype 9 markedly improved oxidative stress, apoptosis, cardiac dysfunction and survival status in DOX-treated mice. Conversely, knocking down endogenous METRNL by an intramyocardial injection of adenovirus exacerbated DOX-induced cardiotoxicity and death. Meanwhile, METRNL overexpression attenuated, while METRNL silence promoted oxidative damage and apoptosis in DOX-treated H9C2 cells. Systemic METRNL depletion by a neutralizing antibody aggravated DOX-related cardiac injury and dysfunction in vivo, which were notably alleviated by METRNL overexpression within the cardiomyocytes. Besides, we detected robust METRNL secretion from isolated rodent hearts and cardiomyocytes, but to a less extent in those with DOX treatment. And the beneficial effects of METRNL in H9C2 cells disappeared after the incubation with a METRNL neutralizing antibody. Mechanistically, METRNL activated SIRT1 via the cAMP/PKA pathway, and its antioxidant and antiapoptotic capacities were blocked by SIRT1 deficiency. More importantly, METRNL did not affect the tumor-killing action of DOX in 4T1 breast cancer cells and tumor-bearing mice. Collectively, cardiac-derived METRNL activates SIRT1 via cAMP/PKA signaling axis in an autocrine manner, which ultimately improves DOX-elicited oxidative stress, apoptosis and cardiac dysfunction. Targeting METRNL may provide a novel therapeutic strategy for the prevention of DOX-associated cardiotoxicity.

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METRNL is abundant in the heart, yet decreased upon DOX treatment.

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METRNL overexpression improves, while METRNL deficiency exacerbates DOX-induced cardiotoxicity in vivo and in vitro.

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METRNL activates SIRT1 via cAMP/PKA signaling axis in an autocrine manner.

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METRNL does not affect the tumor-killing action of DOX in cancer cells.