Metrnl deficiency decreases blood HDL cholesterol and increases blood triglyceride

Higher serum Metrnl levels are associated with increased vascular calcification in hemodialysis patients

BACKGROUND

Meteorin-like (Metrnl) is a newly identified secreted protein that plays important roles in metabolic and inflammation-related diseases. Our study aimed to evaluate serum Metrnl levels and establish their relationship with vascular calcification (VC) in hemodialysis (HD) patients.

METHODS

In total, 313 HD patients and 41 healthy individuals, as controls, were included. Serum levels of Metrnl and other clinical and laboratory parameters were compared. VC was evaluated based on the abdominal aortic calcification (AAC) scores. HD patients were divided into a high-AAC score group (AAC score ≥ 4) and a low-AAC score group (AAC score < 4).

RESULTS

HD patients had higher serum Metrnl levels than the controls (0.52 ± 0.26 ng/ml vs. 0.24 ± 0.11 ng/ml, p < 0.001). Serum Metrnl concentrations were significantly higher in HD patients in the high-AAC score group than in those in the low-AAC score group (0.55 ± 0.27 vs. 0.49 ± 0.24 ng/ml, p = 0.041). Multivariate logistic regression revealed that serum Metrnl, age, diabetes mellitus, serum total carbon dioxide (tCO2) and serum intact parathyroid hormone (iPTH) were significant independent determinants of high AAC scores.

CONCLUSION

The results herein provide the first clinical evidence of the association between serum Metrnl and VC in HD patients. Higher Metrnl levels, older age, diabetes mellitus, and higher serum tCO2 and iPTH levels are independent determining factors for high AAC scores in HD patients.

Naringenin cationic lipid-modified nanoparticles mitigate MASLD progression by modulating lipid homeostasis and gut microbiota

Naringenin (NAR) possesses various pharmacological activities including antioxidant, anti-inflammatory, and hepatoprotective effects. However, its therapeutic efficacy is limited by its hydrophobic and crystalline nature. This study aimed to investigate the therapeutic potential and molecular mechanisms of NAR efficiently loaded into cationic nanoparticles (NP-NAR) for treating metabolic dysfunction-associated steatotic liver disease (MASLD) in a mouse model. The results demonstrated that NP-NAR effectively ameliorated lipid metabolism dysbiosis, oxidative stress, insulin resistance, and inflammation in MASLD mice. Transcriptomic analysis and molecular data revealed that NP-NAR promoted fatty acid oxidation via activation of the PPAR signaling pathway, reduced hepatic lipid uptake and lipogenesis by inhibiting the expressions of key genes including CD36, ACC, and FASN. Moreover, NP-NAR modulated cholesterol metabolism by inhibiting the classical bile acid synthesis pathway. 16 S rDNA gene sequencing revealed a disbalanced gut microbiota in MASLD mice, whereas NP-NAR treatment statistically reversed the abundance changes of several intestinal bacteria at the phylum and genus levels, which partly contributed to the balance in intestinal metabolite production, including short-chain fatty acids. In conclusion, these findings suggest that NP-NAR may be a promising candidate for the treatment of obesity-associated MASLD, offering new insight into the mechanisms underlying NAR's efficacy against MASLD.

Specific muscle targeted delivery of miR-130a loaded lipid nanoparticles: a novel approach to inhibit lipid accumulation in skeletal muscle and obesity

BACKGROUND

Skeletal muscle lipid deposition is a key manifestation of obesity, often accompanied by decreased exercise capacity and muscle atrophy. Skeletal muscle as the largest organ in the body, makes it challenges for designing targeted drug delivery systems. Lipid nanoparticles (LNPs) are widely used as a safe and efficient delivery carrier, there is limited research on LNPs that specifically target skeletal muscle.

RESULTS

A LNP designed with five specific receptor complements on its surface, which specifically targets skeletal muscle in vivo in mice, without off-target effects on other tissues and organs. MiR-130a, a regulator of PPARG, which is a key factor in skeletal muscle lipid deposition, was encapsulated with LNP (LNP@miR-130a). In high-fat diet (HFD) mice, LNP@miR-130a effectively reduced skeletal muscle lipid deposition, increased exercise activity and enhanced muscle mass. Interestingly, the myokines in skeletal muscle have also changed which may leading to reduce the adipose tissue weight and liver lipid deposition in HFD mice.

CONCLUSIONS

These results indicated LNP@miR-130a is a promising inhibitor of skeletal muscle lipid deposition and may help alleviate obesity. This study provides new insights for obesity treatment and lays foundation for the development of targeted skeletal muscle therapeutics.

β-Carotene-loaded cationic nanoparticles ameliorate MASLD via modulating lipid homeostasis and gut microbiome

Metabolic dysfunction-associated steatotic liver disease (MASLD) is, increasingly, a major threat to human health, yet without any approved drug. β-carotene (BC) contributes to alleviating several metabolic diseases. However, the bioavailability of BC is hindered by hydrophobicity and environmental sensitivity. Herein, we explore the utilization of cationic lipid-assisted nanoparticles to achieve efficient delivery of BC. In the MASLD model, NP-BC ameliorated the development of metabolic disorders, insulin resistance, inflammatory injury and hepatic steatosis. Transcriptomic analysis showed that NP-BA rectifies various pathways involved in steatosis development by inhibiting the PI3K/AKT/mTOR pathway and PPARγ gene expression. Meanwhile, NP-BC also reshaped the composition of gut microbiota in MASLD mice by reducing the Firmicutes/Bacteroidetes ratio and increasing the abundance of beneficial bacteria. Taken together, our study demonstrates that NP-BC can improve MASLD and may be a promising candidate for treating MASLD.

Meteorin-like alleviates hepatic steatosis by regulating hepatic triglyceride secretion and fatty acid oxidation

Amid a rising prevalence of non-alcoholic fatty liver disease (NAFLD), there is still an unmet need to better treat it. We identified a secreted factor, Meteorin-like (Metrnl), with decreased levels in livers with hepatic steatosis. Notably, recombinant Metrnl ameliorated hepatic steatosis in NAFLD mouse models. Mechanistically, Metrnl exerted dual effects by promoting triglyceride (TG) transportation by the phosphatidylinositol 3-kinase (PI3K)/Akt/Sp1/cytidylyltransferase α (CCTα) axis, thereby increasing the biosynthesis of phosphatidylcholine (PC) to facilitate TG secretion from the liver while facilitating AMP-activated protein kinase (AMPK)-dependent fatty acid oxidation (FAO). Exogenous injection of cytidine diphosphocholine (CDP)-choline, the production of CCTα, to increase PC synthesis, was shown to restore the inhibition of TG secretion in hepatic Metrnl-deficient (LKO-Met) mice. Combining CDP-choline and an AMPK activator was sufficient to rescue hepatic steatosis in LKO-Met mice. Collectively, these findings reveal unexpected roles of Metrnl as a factor in PC biosynthesis, TG secretion, and FAO, suggesting potential therapeutic application for NAFLD.

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.

Association of serum Metrnl levels and high-density lipoprotein cholesterol in patients with type 2 diabetes mellitus: a cross-sectional study

Purpose

Meteorin-like (Metrnl) is a novel adipokine which is highly expressed in adipose tissue and has a beneficial effect on glucose and lipid metabolism. High density lipoprotein cholesterol (HDL-C) is well recognized to be inversely associated with cardiovascular events. However, the relationship between serum Metrnl levels and HDL-C in the type 2 diabetes mellitus (T2DM) remains unclear. Therefore, the present study aimed to evaluate the association of serum Metrnl with HDL-C levels in T2DM.

Materials and Methods

Eighty participants with T2DM were included in this cross-sectional study. They were divided into two groups according to HDL-C levels: Group1 (lower HDL-C group): HDL-C < 1.04 mmol/L; Group2 (higher HDL-C group): HDL-C ≥ 1.04 mmol/L. Serum Metrnl levels were measured by enzyme-linked immunosorbent assay (ELISA).

Results

As compared with lower HDL-C levels groups, serum Metrnl levels were significantly higher in the group with higher HDL-C. Binary logistic regression analysis showed serum Metrnl levels were positively associated with HDL-C group after adjustment with sex, age, body mass index (BMI), mean arterial pressure (MAP), fasting blood glucose (FPG), triglyceride (TG). Furthermore, serum Metrnl levels were inversely correlated with insulin resistance index (HOMA-IR). HDL-C levels were lowest in the group with the lowest Metrnl levels group and remained positively associated with Metrnl after adjustment for sex, age, BMI, TG, and HOMA-IR by using multivariate logistic regression analysis.

Conclusion

Serum Metrnl levels were positively associated with HDL-C levels in patients with T2DM.This suggests that increasing serum Metrnl levels maybe a candidate for improving lipid metabolism and preventing cardiovascular events in T2DM.

Registry and the Registration No of the Study/Trial

The study was registered in the Chinese clinical trial registry (ChiCTR- 2100047148).

Homotherapy for heteropathy: Interleukin-41 and its biological functions

Interleukin-41 (IL-41) is a newly discovered cytokine, named Cometin, Subfatin, meteorin-like transcription (Metrnl), and so forth. It is widely expressed in animals and can exert its biological roles through autocrine and paracrine forms. It has functions such as anti-inflammatory, improving body metabolism, regulating immunity, regulating fat metabolism and participates in the process of autoimmune disease or inflammatory injury. It plays an important role in psoriasis, diabetes, Crohn's disease (CD), osteoarthritis, Kawasaki disease (KD), Graves' disease, autoimmune hepatitis, infertility, obesity, sepsis, cardiovascular diseases and respiratory diseases. This paper reviews the biological functions of IL-41, the relationship between IL-41 and diseases, the effects of IL-41 in the cytokine network and the possible signalling pathways. In order to explore the same target or the same drug for the treatment of different diseases from the perspective of homotherapy for heteropathy, cytokine strategies based on IL-41 have been put forward for the precise treatment of immune diseases and inflammatory diseases. It is worth noting that IL-41 related preparations for lung protection and smoking cessation are interesting research fields.

De novo structure prediction of meteorin and meteorin-like protein for identification of domains, functional receptor binding regions, and their high-risk missense variants

Meteorin (Metrn) and Meteorin-like (Metrnl) are homologous secreted proteins involved in neural development and metabolic regulation. In this study, we have performed de novo structure prediction and analysis of both Metrn and Metrnl using Alphafold2 (AF2) and RoseTTAfold (RF). Based on the domain and structural homology analysis of the predicted structures, we have identified that these proteins are composed of two functional domains, a CUB domain and an NTR domain, connected by a hinge/loop region. We have identified the receptor binding regions of Metrn and Metrnl using the machine-learning tools ScanNet and Masif. These were further validated by docking Metrnl with its reported KIT receptor, thus establishing the role of each domain in the receptor interaction. Also, we have studied the effect of non-synonymous SNPs on the structure and function of these proteins using an array of bioinformatics tools and selected 16 missense variants in Metrn and 10 in Metrnl that can affect the protein stability. This is the first study to comprehensively characterize the functional domains of Metrn and Metrnl at their structural level and identify the functional domains, and protein binding regions. This study also highlights the interaction mechanism of the KIT receptor and Metrnl. The predicted deleterious SNPs will allow further understanding of the role of these variants in modulating the plasma levels of these proteins in disease conditions such as diabetes.Communicated by Ramaswamy H. Sarma.

Chronic vascular pathogenesis results in the reduced serum Metrnl levels in ischemic stroke patients

Metrnl is a secreted protein involved in neurite outgrowth, insulin sensitivity, immunoinflammatory responses, blood lipids and endothelial protection. In this study, we investigated the role of Metrnl in ischemic stroke. Fifty-eight ischemic stroke patients (28 inpatient patients within 2 weeks of onset and 30 emergency patients within 24 h of onset) and 20 healthy controls were enrolled. Serum Metrnl was measured by enzyme-linked immunosorbent assay. We showed that serum Metrnl levels were significantly reduced in both inpatient and emergency patient groups compared with the controls. Different pathological causes for ischemic stroke such as large artery atherosclerosis and small artery occlusion exhibited similar reduced serum Metrnl levels. Transient ischemic attack caused by large artery atherosclerosis without brain infarction also had lower serum Metrnl levels. Metrnl was correlated with some metabolic, inflammatory and clotting parameters. Reduced serum Metrnl was associated with the severity of intracranial arterial stenosis and the presence of ischemic stroke. In order to elucidate the mechanisms underlying the reduced serum Metrnl levels, we established animal models of ischemic stroke in normal mice, atherosclerotic apolipoprotein E-knockout mice and Metrnl-knockout mice by middle cerebral artery occlusion (MCAO) using intraluminal filament or electrocoagulation. We demonstrated that serum Metrnl levels were significantly lower in atherosclerosis mice than normal mice, whereas acute ischemic stroke injury in normal mice and atherosclerosis mice did not alter serum Metrnl levels. Metrnl knockout did not affect acute ischemic stroke injury and death. We conclude that reduced serum Metrnl levels are attributed to the chronic vascular pathogenesis before the onset of ischemic stroke. Metrnl is a potential target for prevention of ischemic stroke.

Immunomodulation through Nutrition Should Be a Key Trend in Type 2 Diabetes Treatment

An organism's ability to function properly depends not solely on its diet but also on the intake of nutrients and non-nutritive bioactive compounds that exert immunomodulatory effects. This principle applies both to healthy individuals and, in particular, to those with concomitant chronic conditions, such as type 2 diabetes. However, the current food industry and the widespread use of highly processed foods often lead to nutritional deficiencies. Numerous studies have confirmed the occurrence of immune system dysfunction in patients with type 2 diabetes. This article elucidates the impact of specific nutrients on the immune system function, which maintains homeostasis of the organism, with a particular emphasis on type 2 diabetes. The role of macronutrients, micronutrients, vitamins, and selected substances, such as omega-3 fatty acids, coenzyme Q10, and alpha-lipoic acid, was taken into consideration, which outlined the minimum range of tests that ought to be performed on patients in order to either directly or indirectly determine the severity of malnutrition in this group of patients.

The role of adipokines in osteoporosis management: a mini review

The prevalence of osteoporosis has been on the rise globally. With ageing populations, research has sought therapeutic solutions in novel areas. One such area is that of the adipokines. Current literature points to an important role for these chemical mediators in relation to bone metabolism. Well-established adipokines have been broadly reported upon. These include adiponectin and leptin. However, other novel adipokines such as visfatin, nesfatin-1, meteorin-like protein (Metrnl), apelin and lipocalin-2 are starting to be addressed pre-clinically and clinically. Adipokines hold pro-inflammatory and anti-inflammatory properties that influence the pathophysiology of various bone diseases. Omentin-1 and vaspin, two novel adipokines, share cardioprotective effects and play essential roles in bone metabolism. Studies have reported bone-protective effects of omentin-1, whilst others report negative associations between omentin-1 and bone mineral density. Lipocalin-2 is linked to poor bone microarchitecture in mice and is even suggested to mediate osteoporosis development from prolonged disuse. Nesfatin-1, an anorexigenic adipokine, has been known to preserve bone density. Animal studies have demonstrated that nesfatin-1 treatment limits bone loss and increases bone strength, suggesting exogenous use as a potential treatment for osteopenic disorders. Pre-clinical studies have shown adipokine apelin to have a role in bone metabolism, mediated by the enhancement of osteoblast genesis and the inhibition of programmed cell death. Although many investigations have reported conflicting findings, sufficient literature supports the notion that adipokines have a significant influence on the metabolism of bone. This review aims at highlighting the role of novel adipokines in osteoporosis while also discussing their potential for treating osteoporosis.

Meteorin-like protein elevation post-exercise improved vascular inflammation among coronary artery disease patients by downregulating NLRP3 inflammasome activity

BACKGROUND

Coronary artery disease (CAD) has become the most common cause of death worldwide. However, the negative effects of CAD are able to be alleviated via exercises, possibly via increased production of meteorin-like protein (Metrnl). In this study, we aim to evaluate the connection between Metrnl production during exercise with lowered CAD risk and severity.

METHODS

Two age and gender-matched groups of 60 human patients, one with CAD, and one without were randomly recruited. The CAD group were subjected to continuous training exercises. Mice were exercised by using a treadmill, establishing an animal exercise model. ELISA was used to measure plasma Metrnl and inflammatory factors. To determine the impact of Metrnl on glucose metabolism, oxygen consumption and extracellular acid rates were taken for untreated, palmitic acid (PA)-treated, and PA+Metrnl co-treated human umbilical vein endothelial cells. Western blot was used to measure expression levels for the NLR family pyrin domain containing 3 inflammasome.

RESULTS

CAD patients had lower Metrnl levels compared to non-CAD controls. Furthermore, higher Metrnl levels post-exercise were inversely associated with LDL, inflammatory cytokines, and CAD severity, as well as being positively associated with HDL. Metrnl was able to counteract against PA-induced HUVEC glucose metabolic dysfunction via reducing ROS production, which in turn lowered NLRP3 inflammasome expression, thereby serving as the basis behind the inverse correlation between Metrnl and inflammatory cytokines.

CONCLUSIONS

Exercise was able to increase Metrnl production from skeletal muscle among CAD patients, and subsequently improve patient atherosclerosis via counteracting against endothelial metabolic dysfunction and pro-inflammatory activities.

Meteorin-like protein is associated with a higher risk profile and predicts a worse outcome in patients with STEMI

INTRODUCTION AND OBJECTIVES

Meteorin-like protein (Metrnl) is a cytokine involved in the attenuation of inflammation. In patients with heart failure, high levels of this biomarker are associated with a worse outcome. In this study, we evaluated the circulating levels and prognostic value of Metrnl in patients with ST-segment elevation myocardial infarction (STEMI).

METHODS

We enrolled STEMI patients undergoing primary percutaneous coronary intervention. Circulating Metrnl levels were measured in peripheral blood 12hours after symptom onset. The primary endpoint was a composite of all-cause mortality or nonfatal myocardial infarction (MI) at 3 years.

RESULTS

We studied 381 patients (mean age 61 years, 21% female, 8% Killip class III/IV). Metrnl levels were associated with age, cardiovascular risk factors and the extent of coronary artery disease, as well as with STEMI complications, particularly heart failure and cardiogenic shock. Multivariable Cox regression analysis revealed that Metrnl independently predicted all-cause death or nonfatal MI at 3 years (HR, 1.86; 95%CI, 1.23-2.81; P=.003). Moreover, patients in the highest tertile (> 491.6 pg/mL) were at higher risk for the composite endpoint than those in the lowest tertiles (HR, 3.24; 95%CI, 1.92-5.44; P <.001), even after adjustment by age, diabetes mellitus, cardiac arrest, Killip-Kimball III/IV class, left ventricular ejection fraction, and creatinine clearance (HR, 1.90; 95%CI, 1.10-3.29; P=.021).

CONCLUSIONS

Circulating Metrnl levels are associated with complications during the acute phase of STEMI and independently predict a worse outcome in these patients.

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.

Potential clinical value of serum interleukin-41 levels in patients with acute gout

BACKGROUND

Gout is a common metabolic rheumatic disease, and there have been no reports on the serum levels of interleukin (IL)-41 in gout patients. The purpose of this study was to therefore determine the expression of IL-41 in the serum of gout patients.

METHODS

Eighty-one participants were enrolled in this study, including 34 patients with acute gout, 27 gout patients in remission, and 20 healthy controls (HCs). Baseline data were obtained through interviews and laboratory parameters were acquired via blood sample testing. We measured serum IL-41 concentrations with an enzyme-linked immunosorbent assay, and executed Spearman's correlation analysis to investigate the correlation between IL-41 and other parameters, and the diagnostic value for IL-41 was demonstrated using a receiver operating characteristic curve. Multivariate analysis was conducted by adopting logistic regression.

RESULTS

Serum IL-41 concentrations in acute-gout patients were higher than those in HCs and there was no significant difference in serum IL-41 levels between remission gout patients and HCs. In addition, IL-41 was positively correlated with white blood cell count, erythrocyte sedimentation rate, and C-reactive protein and serum amyloid A concentrations, while it was negatively correlated with triglyceride levels. IL-41 showed good diagnostic value for gout, and the combination of IL-41 and uric acid produced a superior diagnostic value. We also noted that IL-41 was an independent risk factor for acute gout.

CONCLUSIONS

This study revealed that serum IL-41 was elevated in patients with acute gout, and suggests that IL-41 may constitute a novel diagnostic marker for acute gout.

Machine-learning-based analysis of the sensitivity and specificity on lipid-lowering effect of one-month-administered statins

Few predictive studies have been reported on the efficacy of atorvastatin in reducing lipoprotein cholesterol to be qualified after 1-month course of treatment in different individuals. A total of 14,180 community-based residents aged ≥ 65 received health checkup, 1013 of whom had low-density lipoprotein (LDL) higher than 2.6mmol/L so that they were put on 1-month course of treatment with atorvastatin. At its completion, lipoprotein cholesterol was measured again. With < 2.6 mmol/L considered as the treatment standard, 411 individuals were judged as the qualified group, and 602, and as the unqualified group. The basic sociodemographic features covered 57 items. The data were randomly divided into train sets and test ones. The recursive random-forest algorithm was applied to predicting the patients response to atorvastatin, the recursive feature elimination method, to screening all the physical indicators. The overall accuracy, sensitivity and specificity were calculated, respectively, and so were the receiver operator characteristic curve and the area under the curve of the test set. In the prediction model on the efficacy of 1-month treatment of statins for LDL, the sensitivity, 86.86%; and the specificity, 94.83%. In the prediction model on the efficacy of the same treatment for triglyceride, the sensitivity, 71.21%; and the specificity, 73.46%. As to the prediction of total cholesterol, the sensitivity, 94.38%; and the specificity, 96.55%. And in the case of high-density lipoprotein (HDL), the sensitivity, 84.86%; and the specificity, 100%. recursive feature elimination analysis showed that total cholesterol was the most important feature of atorvastatin efficacy of reducing LDL; that HDL was the most important one of its efficacies of reducing triglycerides; that LDL was the most important one of its efficacies of reducing total cholesterol; and that triglyceride was the most important one of its efficacies of reducing HDL. Random-forest can help predict whether atorvastatin efficacy of reducing lipoprotein cholesterol to be qualified after 1-month course of treatment in different individuals.

Hepatic Nampt Deficiency Aggravates Dyslipidemia and Fatty Liver in High Fat Diet Fed Mice

Nicotinamide phosphoribosyltransferase (Nampt) is the rate-limiting enzyme in the salvage pathway of nicotinamide adenine dinucleotide (NAD) biosynthesis. Thus far, hepatic Nampt has not been extensively explored in terms of its effects on serum lipid stability and liver lipids metabolism. In this study, hepatocyte-specific Nampt knockout (HC-Nampt^-/-) mice were generated by Cre/loxP system. Nampt mRNA expression was reduced in the liver, but not in other tissues, in HC-Nampt^-/- mice compared with wild-type (WT) mice. Hepatic Nampt deficiency had no effect on body weight and fasting blood glucose, and it did not induce atherosclerosis in mice under both normal chow diet (NCD) and high fat diet (HFD). At baseline state under NCD, hepatic Nampt deficiency also did not affect liver weight, liver function index, including alanine aminotransferase, aspartate aminotransferase, albumin and alkaline phosphatase, and serum levels of lipids, including triglycerides (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and non-esterified fatty acids (NEFA). However, under HFD, deficiency of hepatic Nampt resulted in increased liver weight, liver function index, and serum levels of TG, TC, HDL-C, and NEFA. Meanwhile, histopathological examination showed increased fat accumulation and fibrosis in the liver of HC-Nampt^-/- mice compared with WT mice. Taken together, our results show that hepatic Nampt deficiency aggravates dyslipidemia and liver damage in HFD fed mice. Hepatocyte Nampt can be a protective target against dyslipidemia and fatty liver.

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.

Endothelial METRNL determines circulating METRNL level and maintains endothelial function against atherosclerosis

METRNL is a recently identified secreted protein with emerging functions. This study is to find major cellular source of circulating METRNL and to determine METRNL novel function. Here, we show METRNL is abundant in human and mouse vascular endothelium and released by endothelial cells using endoplasmic reticulum-Golgi apparatus pathway. By creating endothelial cell-specific Metrnl knockout mice, combined with bone marrow transplantation to produce bone marrow-specific deletion of Metrnl, we demonstrate that most of circulating METRNL (approximately 75%) originates from the endothelial cells. Both endothelial and circulating METRNL decrease in atherosclerosis mice and patients. By generating endothelial cell-specific Metrnl knockout in apolipoprotein E-deficient mice, combined with bone marrow-specific deletion of Metrnl in apolipoprotein E-deficient mice, we further demonstrate that endothelial METRNL deficiency accelerates atherosclerosis. Mechanically, endothelial METRNL deficiency causes vascular endothelial dysfunction including vasodilation impairment via reducing eNOS phosphorylation at Ser1177 and inflammation activation via enhancing NFκB pathway, which promotes the susceptibility of atherosclerosis. Exogenous METRNL rescues METRNL deficiency induced endothelial dysfunction. These findings reveal that METRNL is a new endothelial substance not only determining the circulating METRNL level but also regulating endothelial function for vascular health and disease. METRNL is a therapeutic target against endothelial dysfunction and atherosclerosis.

Serum Metrnl levels are decreased in subjects with overweight or obesity and are independently associated with adverse lipid profile

Background

Meteorin-like (Metrnl), a novel adipokine, is highly expressed in adipose tissue and has a beneficial effect on energy metabolism. However, data on circulating Metrnl levels in obesity are scarce and inconsistent. This study aimed to evaluate the serum levels of Metrnl in adults with obesity and its association with glucose and lipid metabolism.

Methods

182 subjects were included in the cross-sectional study. The participants were divided into three groups according to BMI: normal (n = 95), overweight (n = 46), and obesity (n = 41). Serum Metrnl concentrations were measured by enzyme-linked immunosorbent assay.

Results

Serum Metrnl levels in overweight or obese subjects were significantly lower than in the normal group. Circulating Metrnl levels were negatively correlated with TG, TC, LDL-C, and sdLDL and positively correlated with HDL-C before and after adjusting for age, sex, BMI, diabetes, HOMA-IR, and eGFR (all P < 0.05). Furthermore, logistic regression analysis indicated that compared with the highest tertile, the lowest tertile of Metrnl levels were significantly associated with the presence of hyper-TG, hyper-TC, and Hyper-LDL after full adjustment (all P for trend < 0.05).

Conclusions

Serum Metrnl levels were reduced in individuals with overweight or obesity and were independently associated with adverse lipid profile, suggesting that modifying circulating Metrnl levels may serve as a potential therapeutic target for atherogenic dyslipidemia.

Meteorin-like protein (Metrnl): A metabolic syndrome biomarker and an exercise mediator

Metrnl is a secreted protein able to activate different intracellular signaling pathways in adipocytes, macrophages, myocytes and cardiomyocytes with physiological effects of the browning of white adipose tissue (BWT), insulin sensitivity, inflammation inhibition, skeletal muscle regeneration and heart protection. Shown to be regulated by obesity, diabetes, caloric restriction, weight loss and heart diseases, Metrnl is definitely involved in metabolic turbulences, and may play roles in metabolic syndrome (MetS). However, due to the conflicting data yielded, Metrnl is still far from clinical application as a diagnostic and/or a therapeutic agent or even a therapeutic target in MetS-related diseases such as type 2 diabetes (T2D) and obesity. Nevertheless, blood Metrnl levels as well as Metrnl as a cardiokine have been reported to play cardioprotective roles against heart diseases. Considering the established metabolic and anti-inflammatory hallmarks, exercise-induced Metrnl (as a myokine) is regarded as an exercise mediator in improving obesity-induced complications such as insulin resistance, T2D and inflammation. Besides, due to its healing role in muscle damage, Metrnl is also a potential therapeutic candidate to enhance regeneration with ageing or other inflammatory myopathies like Duchenne muscular dystrophy (DMD). Therefore, there are still many exercise-related questions unanswered on Metrnl, such as Metrnl-mediated fat browning in humans, exercise effects on heart Metrnl production and secretion and the effects of other exercise-induced skeletal muscle stressors like hypoxia and oxidative in Metrnl production other than exercise-induced muscle damage.

Role of circulating molecules in age-related cardiovascular and metabolic disorders

Studies analyzing heterochronic parabiosis mice models showed that molecules in the blood of young mice rejuvenate aged mice. Therefore, blood-based therapies have become one of the therapeutic approaches to be considered for age-related diseases. Blood includes numerous biologically active molecules such as proteins, metabolites, hormones, miRNAs, etc. and accumulating evidence indicates some of these change their concentration with chronological aging or age-related disorders. The level of some circulating molecules showed a negative or positive correlation with all-cause mortality, cardiovascular events, or metabolic disorders. Through analyses of clinical/translation/basic research, some molecules were focused on as therapeutic targets. One approach is the supplementation of circulating anti-aging molecules. Favorable results in preclinical studies let some molecules to be tested in humans. These showed beneficial or neutral results, and some were inconsistent. Studies with rodents and humans indicate circulating molecules can be recognized as biomarkers or therapeutic targets mediating their pro-aging or anti-aging effects. Characterization of these molecules with aging, testing their biological effects, and finding mimetics of young systemic milieu continue to be an interesting and important research topic to be explored.

New Discovered Adipokines Associated with the Pathogenesis of Obesity and Type 2 Diabetes

Obesity is defined as abnormal or excessive accumulation of adipose tissue, closely associated with the increased risk of various comorbidities, especially type 2 diabetes mellitus (T2DM). Adipose tissue is a complex structure responsible for not only fat storage but also releasing adipokines which may play roles in the pathogenesis and could be developed into biomarkers for diagnosis, treatment and prognosis of obesity-related metabolic diseases. This review aims to summarize several adipokines discovered recently that have promising functions in obesity and T2DM. Among them, the levels of FSTL1, WISP1 and Asprosin in subjects with obesity or diabetes are commonly higher than in normal controls, suggesting that they may be pathogenic. Inversely, SFRP5, Metrnl, NRG4 and FAM19A5 may serve as the protective factors.

Meteorin-Like Protein (Metrnl) in Obesity, during Weight Loss and in Adipocyte Differentiation

Meteorin-like protein (Metrnl) is an adipo-myokine with pleiotropic effects in adipose tissue (AT). Its systemic regulation in obesity and under weight loss is unclear. Circulating Metrnl concentrations were analyzed by ELISA in severely obese patients undergoing bariatric surgery (BS) or low calorie diet (LCD). Metrnl mRNA expression was analyzed in human and murine tissues and cell lines by quantitative real-time PCR. About 312 morbidly obese individuals underwent BS (n = 181; BMI 53.4 + 6.8 kg/m²) or LCD (n = 131; BMI 43.5 + 6.7 kg/m²). Serum samples were obtained at baseline and 3, 6, and 12 months after intervention. AT specimen from subcutaneous and visceral adipose tissue were resected during BS. Serum Metrnl levels were lower in type 2 diabetic patients and negatively correlated with HbA1c. In BS and LCD patients, Metrnl concentrations significantly increased after 3 months and returned to baseline levels after 12 months. There was no gender-specific effect. Metrnl mRNA expression did not differ between visceral and subcutaneous AT in n = 130 patients. In contrast, Metrnl gene expression in mice was highest in intra-abdominal AT followed by subcutaneous, peri-renal, and brown AT. In the murine 3T3-L1 cell line, Metrnl expression was high in pre-adipocytes and mature adipocytes with a transient downregulation during adipocyte differentiation. Metrnl expression remained unaffected upon treatment with glucose, insulin, fatty acids, bile acids, and incretins. Polyunsaturated omega-3 and omega-6 fatty acids downregulated Metrnl expression. Systemic Metrnl is transiently upregulated during massive weight loss and gene expression in adipocytes is differentially regulated.

Allisartan isoproxil reduces mortality of stroke-prone rats and protects against cerebrovascular, cardiac, and aortic damage

Stroke is a common cause of death and disability. Allisartan isoproxil (ALL) is a new angiotensin II receptor blocker and a new antihypertensive drug discovered and developed in China. In the present study we investigated the therapeutic effects of ALL in stroke-prone renovascular hypertensive rats (RHR-SP) and the underlying mechanisms. The model rats were generated via two-kidney two-clip (2K2C) surgery, which led to 100% of hypertension, 100% of cerebrovascular damage as well as 100% of mortality 1 year after the surgery. Administration of ALL (30 mg · kg-1 · d-1 in diet, for 55 weeks) significantly decreased stroke-related death and prolonged lifespan in RHR-SP, but the survival ALL-treated RHR-SP remained of hypertension and cardiovascular hypertrophy compared with sham-operated normal controls. In addition to cardiac, and aortic protection, ALL treatment for 10 or 12 weeks significantly reduced cerebrovascular damage incidence and scoring, along with a steady reduction of blood pressure (BP) in RHR-SP. Meanwhile, it significantly decreased serum aldosterone and malondialdehyde levels and cerebral NAD(P)H oxidase expressions in RHR-SP. We conducted 24 h continuous BP recording in conscious freely moving RHR-SP, and found that a single intragastric administration of ALL produced a long hypotensive effect lasting for at least 12 h on systolic BP. Taken together, our results in RHR-SP demonstrate that ALL can be used for stroke prevention via BP reduction and organ protection, with the molecular mechanisms related to inhibition of angiotensin-aldosterone system and oxidative stress. This study also provides a valuable scoring for evaluation of cerebrovascular damage and drug efficacy.

Involvement of the secreted protein Metrnl in human diseases

Metrnl, a secreted protein expressed in white adipose tissue, has been identified as a novel adipokine. It is also highly expressed in barrier tissues, including the skin, intestinal and respiratory tract epithelium in both mice and humans. Research shows that its expression is upregulated by inflammation, chronic high-fat diets, exercise, cold exposure, etc., and it plays important roles in promoting neurite extension, enhancing white fat browning, improving insulin sensitivity, modulating lipid metabolism and regulating inflammatory response, the latter implying Metrnl is a new cytokine. These studies suggest that Metrnl could be a promising biomarker and a potential therapeutic target for the related diseases. For proving this, clinical studies need to be performed to bridge the gap between bench and bedside. In this paper, we summarize the progress in recent clinical research on Metrnl. Most of these clinical studies are designed to confirm the relationship between circulating Metrnl and metabolic or cardiovascular disease (type 2 diabetes and coronary heart disease), or immune inflammation-related diseases, such as colitis, psoriasis and arthritis. Although blood Metrnl seems to fluctuate and are affected by many factors, such as drugs, physical exercise, and cold exposure, these clinical studies provide reliable clues that Metrnl is associated with coronary heart disease, inflammation-related diseases, etc. Nevertheless, the roles of Metrnl in some diseases such as nervous system diseases remain unclear, and its putative involvement should be further clarified. These studies could promote the application of Metrnl in clinic as a new therapeutic target.