Biochemical and Biophysical Research Communications
High circulating levels of S100A8/A9 complex (calprotectin) in male Japanese with abdominal adiposity and dysregulated expression of S100A8 and S100A9 in adipose tissues of obese mice
Highlights
► High serum levels of S100A8/A9 complex in obesity. ► Circulating S100A8/A9 complex levels correlated significantly with abdominal adiposity. ► High S100A8 mRNA levels in mature adipocyte fraction of obese mice. ► High S100A9 mRNA levels in stromal vascular cell fraction of obese mice.
Introduction
The S100A8/A9 complex (also known as calprotectin), a heterodimer of two calcium-binding proteins [1]; calcranulin A (S100A8) and B (S100A9), or myeloid-related protein (MRP)-8 (S100A8) and MRP-14 (S100A9), is actively secreted into blood during stress response of phagocytes [2]. High serum levels of S100A8/A9 are associated with inflammatory disorders, such as autoimmune diseases [3] and acute coronary syndrome [4], [5], [6], [7], [8]. S100A8 and S100A9 are expressed in a tissue/cell-specific manner mainly in cells of the myeloid lineage, including monocytes, neutrophils and early-differentiated macrophages [9], and are abundantly expressed in inflammatory [10] or atherosclerotic lesions [11], [12]. Several functions for these proteins have described, including activation of NADPH oxidase [13], binding toll-like receptor 4 (TLR4) [14] and association with the receptor for advanced glycation end-products (RAGE) [15], which are vital signaling pathways involved in the pathogenesis of atherosclerosis. S100A8 and S100A9 induced serum amyloid A (SAA) three in pre-metastatic lungs through the TLR4-NF-kappaB signaling pathway [16]. We recently reported that, (1) overexpression of S100A8 mRNA was expressed highly in murine white adipose tissue and differentiated 3T3-L1 adipocytes, as well as in macrophage-associated tissues (i.e., lung, spleen) and RAW cells [17], (2) the mRNA expression level of S100A8 in adipose tissue is significantly elevated in obese mice [17], (3) peroxisome proliferator-activated receptor (PPAR) γ agonists reduced the high S100A8 mRNA expression level in obese mice [17], and (4) 3-month treatment with pioglitazone, a PPARγ agonist, reduced circulating calprotectin levels in subjects with abdominal obesity [18]. However, the relationship between blood levels of calprotectin and adiposity in the general population and regulation of S100A9 expression in murine adipose tissue remains to be elucidated.
The aims of the present study were to; (1) determine the relationship between circulating levels of S100A8/A9 complex (calprotectin) and adiposity including body mass index (BMI), visceral and subcutaneous fat areas (VFA, SFA), in Japanese men, and (2) measure S100A8 and S100A9 expression levels in tissues of B6.V-Lepob/J (ob/ob) mice and 3T3-L1 cells.
Section snippets
Study population
The study subjects were 500 consecutive Japanese male employees who underwent the 2010 annual health checkup at Hitachi Ltd., Ibaraki Prefecture, including computed tomography (CT). The present study was approved by the human ethics committees of Osaka University and Hitachi Health Care Center. A written informed consent was obtained from each subject. This trial (Victor-J study) is registered under No. #UMIN 000004318.
Anthropometry and Laboratory tests
Height and weight were measured in the standing position. BMI was calculated
Human studies
The baseline characteristics of the subjects are listed in Table 1. Table 2 lists the correlation coefficients for the relationship between calprotectin and various clinical features. The IRI, triglyceride, adiponectin and calprotectin values showed skewed distribution, and were therefore log-transformed before analysis. Simple linear regression analysis showed that log-calprotectin correlated positively with BMI (Fig. 1A), WC, VFA (Fig. 1B), SFA (Fig. 1C), SBP, HR, log-IRI (Fig. 1D),
Discussion
The major findings of the present study were: (1) high circulating levels of S100A8/A9 complex (calprotectin) correlated with VFA as well as BMI, SFA, and leukocyte count in Japanese men, and (2) higher levels of S100A8 mRNA in MAF and S100A9 mRNA in SVF of obese mice, compared with those of lean mice.
Mortesen et al. [20] suggested that circulating calprotectin level is a marker of obesity, but did not investigate its relation with adiposity, i.e., VFA and SFA measured by CT. The present study
Conflict of interest statement
K.K. and T.F. are members of the “Department of Metabolism and Atherosclerosis”, a sponsored course endowed by Kowa Co. Ltd. A researcher from the same company is a member of the same course. All other authors declare no competing interests.
Contributions
R.S. and K.K. researched and analyzed data. K.K. also participated in the concept and design of the study, interpretation of data and reviewed/edited the manuscript. H.N. collected the data. T.N. recruited the patients and collected the data. T.F. and I.S. contributed to the discussion and wrote the manuscript. All authors read and approved the final version of the manuscript.
Acknowledgments
We thank Mrs. Miyuki Nakamura for the excellent technical assistance. This research was supported in part by a Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area) “Molecular Basis and Disorders of Control of Appetite and Fat Accumulation” (#22126008, to T.F. and K.K.).
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