Maternal obesity and gestational diabetes decrease Metrnl concentrations in cord plasma

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.

Decreased serum interleukin-41/Metrnl levels in patients with Graves' disease

Background

Interleukin (IL)‐41, also known as Metrnl, is a novel immunomodulatory cytokine, which is involved in the pathogenesis of many inflammatory and metabolic diseases, but its role in thyroid autoimmune diseases is not clear. The aim of this study was to evaluate the serum IL‐41 levels in patients with Graves' disease (GD) and its relationship with GD.

Methods

This study included a total of 49 GD patients and 47 age‐ and sex‐matched healthy individuals. All baseline data were obtained by physical examination. Free triiodothyronine 3 (FT3), free triiodothyronine 4 (FT4), thyroid‐stimulating hormone (TSH), anti‐thyroglobulin antibodies (TgAb), thyroid peroxidase antibody (TPOAb), and thyrotropin receptor antibody (TRAb) levels in plasma of GD patients were measured by chemiluminescence. The high‐sensitivity C‐reactive protein (CRP) and white blood cell count (WBC) were detected using automated biochemical analyzer. Serum IL‐41 levels were measured by enzyme‐linked immunosorbent assay.

Results

Serum IL‐41 levels in patients with GD were significantly lower than those in healthy controls (201.0 vs. 260.8 pg/mL, p < 0.05). There was a significant positive correlation between IL‐41 level and CRP (r = 0.2947, p = 0.0385) and WBC (r = 0.4104, p = 0.0034) in GD patients. CRP was positively correlated with TRAb (r = 0.2874, p = 0.0452) and TSH (r = 0.3651, p = 0.0099) levels in GD patients.

Conclusions

This study demonstrates that GD patients have decreased serum IL‐41 levels, and IL‐41 plays a potential role in abnormal immune response of GD patients.

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.