Clinical ScienceAccumulation of adiponectin in inflamed adipose tissues of obese mice
Introduction
Visceral obesity associated with multiple cardiometabolic risk factors is a common basis of atherosclerotic vascular diseases. Obesity correlates with chronic inflammation of the adipose tissues, which is characterized by progressive infiltration of macrophages [1] and overproduction of reactive oxygen species (ROS) [2], [3]. The chronic inflammation state results in adipocyte dysfunction and dysregulated production of adipocytokines, leading to systemic metabolic disorders and atherosclerosis [4], [5]. The inflamed adipose tissue in obesity is also characterized histopathologically by the presence of "crown-like structures", representing macrophages around dead adipocytes [6], [7].
The normal blood level of adiponectin [also known as adipocyte complement-related protein of 30 kDa (ACRP30), adipoQ and gelatin binding protein of 28 kDa (GBP28)], an adipocytokine discovered by our laboratory and three other groups, independently [8], [9], [10], [11], [12], ranges from 3 to 30 μg/mL, but decreases in obese individuals [13]. However, the mechanism of plasma adiponectin reduction in obesity has not been fully elucidated. Adiponectin is exclusively synthesized by adipocytes and exhibits anti-diabetic, anti-atherosclerotic, and anti-inflammatory properties [14]. These actions are supposed to be mediated through the interaction of adiponectin with cell surface binding receptors. The first identified adiponectin receptor, AdipoR1, was isolated from a human skeletal muscle cDNA library while screening for globular adiponectin binding [15]. AdipoR2 was found based on its homology with AdipoR1. Both AdipoR1 and AdipoR2 are surface membrane proteins with seven transmembrane domains, with similar molecular structures, and are expressed in the liver, muscle, and adipose tissue in humans. Adiponectin also binds to calreticulin on the macrophage cell surface, and opsonizes apoptotic cells [16]. T-cadherin, a GPI-anchored molecule that lacks a cytoplasmic region, also binds with adiponectin on vascular endothelial cells and smooth muscle [17], [18].
Studies from our laboratories have demonstrated the severer tissue damage in the heart and kidney of adiponectin-deficient (APN-KO) mice compared to wild type mice, by various pathological overload. Administration of adenovirus-induced adiponectin ameliorates such tissue injury and also suppressed progression of fatty streak lesion in apoE KO mice [19], [20], [21]. The anti-proinflammatory property of adiponectin [14] might be mediated partly through the release of IL-10 by macrophages [22]. Adiponectin also promotes macrophage polarization toward the M2 phenotype and reduces ROS generation [23]. Here, in this study, we postulate adiponectin may stay or return to interstitial space of adipose tissue adipose tissue, and may play a role in the control of adipose tissue inflammation in obesity. The present study was designed to localize adiponectin in adipose tissues of obese and lean mice, and the mechanisms involved in such distribution pattern.
Section snippets
Materials
Rabbit polyclonal antibody to mouse adiponectin was generated at Otsuka Pharmaceutical (Tokyo, Japan). Monoclonal antibodies to mouse F4/80 (Abcam, Cambridge, MA) and T-cadherin (Santa Cruz Biotechnology, Santa Cruz, CA) were purchased. Goat anti-rabbit IgG horseradish peroxidase (HRP) conjugate and Goat anti-rat IgG HRP conjugate were purchased from GE Healthcare (Uppsala, Sweden).
Animal models
Male BKS.Cg-+LeprDB/+ Leprdb/J (db/db) mice and their respective lean control male BKS.Cg-m +/m +/J (+ m/+ m) mice were
Adiponectin protein in lean and obese mice
Body weight, tissue weight of WATsub and WATmes were significantly higher and plasma adiponectin concentrations were significantly lower in obese db/db mice than lean control + m/+ m mice (body weight: db/db; 45.2 ± 1.6 g, + m/+ m; 24.4 ± 1.2 g, p < 0.0001, WATsub: db/db; 3.7 ± 0.5 g, + m/+ m; 0.4 ± 0.1 g, p < 0.0001, WATmes: db/db; 1.6 ± 0.2 g, + m/+ m; 0.3 ± 0.1 g, p < 0.0001, plasma adiponectin: db/db; 14.2 ± 2.2 μg/mL, + m/+ m; 19.0 ± 2.1 μg/mL, p < 0.0001). Next, we examined the tissue distribution of adiponectin protein in lean
Discussion
The major findings of the present study were 1) adiponectin protein existed in SVF, which lacks adiponectin mRNA expression, as well as MAF of WATsub and WATmes, 2) adiponectin protein levels were significantly higher in SVFsub and SVFmes of obese mice than in lean mice, 3) using fluorescent immunostaining, adiponectin protein was observed not only in adipocytes, but also in interstitium of WATsub and WATmes. The present study also demonstrated that 1) by a single injection of WT-plasma
Author contributions
HN and KK researched and analyzed the data, participated in the concept and design of the study. KK also participated in interpretation of data and reviewed/edited the manuscript. RS analyzed the data. NK and SK contributed to the discussion. TF and IS contributed to the discussion and wrote the manuscript. All authors read and approved the final version of the manuscript.
Funding
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 TF and KK).
Conflict of interest
TF is a member of the “Department of Metabolism and Atherosclerosis”, a sponsored course endowed by Kowa Co. Ltd. The company has a scientific officer who oversees the program. All other authors declare no competing interests.
Acknowledgments
We thank Dr. Yoshihiro Tochino, Mrs. Miyuki Nakamura, Mr. Yugo Miyata and Takuya Mori (members of our laboratory) for the excellent technical assistance.
References (46)
- et al.
Adipocyte death defines macrophage localization and function in adipose tissue of obese mice and humans
J Lipid Res
(2005) - et al.
Dead adipocytes, detected as crown-like structures, are prevalent in visceral fat depots of genetically obese mice
J Lipid Res
(2008) - et al.
cDNA cloning and expression of a novel adipose specific collagen-like factor, apM1 (AdiPose Most abundant gene transcript 1)
Biochem Biophys Res Commun
(1996) - et al.
Analysis of an expression profile of genes in the human adipose tissue
Gene
(1997) - et al.
A novel serum protein similar to C1q, produced exclusively in adipocytes
J Biol Chem
(1995) - et al.
AdipoQ is a novel adipose-specific gene dysregulated in obesity
J Biol Chem
(1996) - et al.
Paradoxical decrease of an adipose-specific protein, adiponectin, in obesity
Biochem Biophys Res Commun
(1999) - et al.
Adiponectin promotes macrophage polarization toward an anti-inflammatory phenotype
J Biol Chem
(2010) - et al.
Adiponectin-AdipoR1/2-APPL1 signaling axis suppresses human foam cell formation: differential ability of AdipoR1 and AdipoR2 to regulate inflammatory cytokine responses
Atherosclerosis
(2012) - et al.
Adiponectin inhibits Toll-like receptor family-induced signaling
FEBS Lett
(2005)