Macrophages regulate tumor necrosis factor-alpha expression in adipocytes through the secretion of matrix metalloproteinase-3

Roles of Matrix Metalloproteinases and Their Natural Inhibitors in Metabolism: Insights into Health and Disease

Matrix metalloproteinases (MMPs) are a family of zinc-activated peptidases that can be classified into six major classes, including gelatinases, collagenases, stromelysins, matrilysins, membrane type metalloproteinases, and other unclassified MMPs. The activity of MMPs is regulated by natural inhibitors called tissue inhibitors of metalloproteinases (TIMPs). MMPs are involved in a wide range of biological processes, both in normal physiological conditions and pathological states. While some of these functions occur during development, others occur in postnatal life. Although the roles of several MMPs have been extensively studied in cancer and inflammation, their function in metabolism and metabolic diseases have only recently begun to be uncovered, particularly over the last two decades. This review aims to summarize the current knowledge regarding the metabolic roles of metalloproteinases in physiology, with a strong emphasis on adipose tissue homeostasis, and to highlight the consequences of impaired or exacerbated MMP actions in the development of metabolic disorders such as obesity, fatty liver disease, and type 2 diabetes.

Expression of genes associated with inflammation and iron metabolism in 3T3-L1 cells induced with macrophages-conditioned medium, glucose and iron

Obesity is characterized by a chronic inflammatory process, with an increased volume of total adipose tissue, especially visceral, which secretes pro-inflammatory cytokines such as TNF-α and IL-6. Hepcidin (Hpc), a main iron metabolism regulator, is synthetized by an IL-6 stimuli, among others, in liver and adipose tissue, favoring an association between the inflammatory process and iron metabolism. Still there are questions remain regarding the interaction of these factors. Our aim was to study the effect of a macrophage-conditioned medium (MCM) on adipocyte cells challenged with glucose and/or iron. We studied the mRNA relative abundance of genes related to inflammation in differentiated 3T3-L1 cells challenged with Fe (40 µM), glucose (20 mM) or Fe/glucose (40 µM/20 mM) with or without MCM for 24 h. We also measured the intracellular iron levels under these conditions. Our results showed that when adipocytes were challenged with MCM, glucose and/or Fe, the intracellular iron and mRNA levels of pro-inflammatory cytokines increased. These responses were higher when all the stimuli were combined with MCM from macrophages. Thus, we showed that combined high glucose/high Fe alone or with MCM may contribute to an increase on intracellular iron and inflammatory response in 3T3-L1 differentiated cells, by increased mRNA levels of IL-6, TNF-α, MCP-1, Hpc and reducing adiponectin levels, enhancing the inflammatory processes.

Incorporating Refractory Period in Mechanical Stimulation Mitigates Obesity-Induced Adipose Tissue Dysfunction in Adult Mice

OBJECTIVE

The aim of this study was to determine whether inclusion of a refractory period between bouts of low-magnitude mechanical stimulation (LMMS) can curb obesity-induced adipose tissue dysfunction and sequelae in adult mice.

METHODS

A diet-induced obesity model that included a diet with 45% of kilocalories from fat was employed with intention to treat. C57BL/6J mice were weight matched into four groups: low-fat diet (LFD, n = 8), high-fat diet (HFD, n = 8), HFD with one bout of 30-minute LMMS (HFDv, n = 9), and HFD with two bouts of 15-minute LMMS with a 5-hour separation (refractory period, RHFDv, n = 9). Two weeks of diet was followed by 6 weeks of diet plus LMMS.

RESULTS

HFD and HFDv mice continued gaining body weight and visceral adiposity throughout the experiment, which was mitigated in RHFDv mice. Compared with LFD mice, HFD and HFDv mice had increased rates of adipocyte hypertrophy, increased immune cell infiltration (B cells, T cells, and macrophages) into adipose tissue, increased adipose tissue inflammation (tumor necrosis factor alpha gene expression), and a decreased proportion of mesenchymal stem cells in adipose tissue, all of which were rescued in RHFDv mice. Glucose intolerance and insulin resistance were elevated in HFD and HFDv mice, but not in RHFDv mice, as compared with LFD mice.

CONCLUSIONS

Incorporating a 5-hour refractory period between bouts of LMMS attenuates obesity-induced adipose tissue dysfunction and improves glucose metabolism.

Adipocyte-secreted chemerin is processed to a variety of isoforms and influences MMP3 and chemokine secretion through an NFkB-dependent mechanism

Obesity is associated with white adipose tissue (WAT) remodelling characterized by changes in cellular composition, size, and adipokine secretion. Levels of the adipokine chemerin are positively associated with obesity; however, the biological function of chemerin in WAT is poorly understood. We identified factors involved in WAT remodelling, including matrix metalloproteinase (Mmp)3 and chemokines (Ccl2, 3, 5, 7), as novel targets of chemerin signalling in mature adipocytes. Inhibition of chemerin signalling increased MMP activity and the recruitment of macrophages towards adipocyte-conditioned media. These effects were mediated through increases in NFkB signalling, suggesting that chemerin exerts an anti-inflammatory influence. We also demonstrate that multiple chemerin isoforms are present in adipocyte-conditioned media and that adipocyte-secreted chemerin, but not synthetic chemerin, recapitulates the activity of endogenous chemerin. Considered altogether, this suggests that endogenously secreted chemerin plays an autocrine/paracrine role in WAT, identifying chemerin as a therapeutic target to modulate adipose remodelling.

Serotonin-Exacerbated DSS-Induced Colitis Is Associated with Increase in MMP-3 and MMP-9 Expression in the Mouse Colon

Background. 5-HT enhances dextran sulfate sodium- (DSS-) induced colitis and is involved in inflammatory bowel disease (IBD). Matrix metalloproteinases (MMPs) play roles in the process of intestinal inflammation. Aims. To examine whether 5-HT induces MMPs expression in mouse colon to enhance DSS-induced colitis. Materials and Methods. C57BL/6J (B6) mice were treated with either low-dose (1.0 mg/kg) or high-dose (2.0 mg/kg) 5-HT by enema, low-dose (1.0%) or high-dose (2.5%) DSS, or combined low-dose (1.0%) DSS and (1.0 mg/kg) 5-HT. Mouse colitis was analyzed. MMPs and tissue inhibitors of MMPs (TIMPs) mRNA were measured by real-time quantitative RT-PCR in mouse colon and in human Caco-2 cells and neutrophils. MMP-3 and MMP-9 protein levels were quantified from immunohistochemistry (IHC) images of mouse colons. Results. 5-HT exacerbated DSS-induced colitis, low-dose 5-HT induces both MMP-3 and MMP-9, and high-dose 5-HT only increased MMP-3 mRNA expression in mouse colon. Mouse colon MMP-3 and MMP-9 protein levels were also elevated by 5-HT treatment. The MMP-2, TIMP-1, and TIMP-2 mRNA levels were increased in the inflamed colon. 5-HT induced MMP-3 and MMP-9 mRNA expression in Caco-2 and human neutrophils, respectively, in vitro. Conclusion. 5-HT induced MMP-3 and MMP-9 expression in mouse colon; these elevated MMPs may contribute to DSS-induced colitis.

Macrophage-induced expression and release of matrix metalloproteinase 1 and 3 by human preadipocytes is mediated by IL-1β via activation of MAPK signaling

Obesity is associated with a chronic low-grade inflammation and increased macrophage infiltration in adipose tissue. Matrix metalloproteinases (MMPs) are involved in adipose tissue remodeling and inflammatory responses in obesity. This study investigated whether macrophage-derived factors modulate expression and secretion of MMP1 and MMP3 in human preadipocytes. The potential mediators and signaling pathways were also explored. MMP1 and MMP3 were primarily expressed and secreted by preadipocytes and dramatically reduced post-differentiation. Preadipocytes were incubated with RPMI 1640 medium (control) or THP-1 macrophage-conditioned (MC) medium (25% and 100%) for 24 h. MC medium markedly increased mRNA levels of MMP1 (up to 122-fold) and MMP3 (up to 59-fold), as well as protein release of MMP1 (up to 378-fold) and MMP3 (up to 10-fold) in a dose-dependent manner. Treatment with IL-1β or TNFα, the major products of macrophages, also induced MMP1 and MMP3 secretion by preadipocytes. Neutralizing IL-1β abolished the induction of MMP1 and MMP3 in preadipocytes by MC medium while the effects of TNFα neutralization were modest. Furthermore, MC medium or IL-1β led to the phosphorylation of p38, ERK and JNK MAPKs. Inhibition of p38, ERK and JNK reversed the stimulatory effects of MC or IL-1β on MMP1 and MMP3 production. MC medium and IL-1β also activated NF-κB p65 whereas reduced IκBα protein expression in preadipocytes. These results suggest that macrophage accumulation in adipose tissue has a central role in stimulating MMP1 and MMP3 production by preadipocytes, and this is partially mediated by IL-1β via activation of the MAPK and NF-κB signaling pathways.

The use of THP-1 cells as a model for mimicking the function and regulation of monocytes and macrophages in the vasculature

Since their establishment thirty years ago, THP-1 cells have become one of most widely used cell lines to investigate the function and regulation of monocytes and macrophages in the cardiovascular system. However, because this cell line was derived from the blood of a patient with acute monocytic leukemia, the extent to which THP-1 cells mimic monocytes and macrophages in the vasculature is not entirely known. This article serves as a meaningful attempt to address this question by reviewing the recent publications. The interactions between THP-1 cells and various vascular cells (such as endothelial cells, smooth muscle cells, adipocytes, and T cells) provide insight into the roles of the interconnection of monocytes-macrophages with other vascular cells during vascular inflammation, particularly atherogenesis and obesity. Transcriptome, microRNA profile, and histone modifications of THP-1 cells shed new light on the regulatory mechanism of the monocytes-macrophages in response to various inflammatory mediators, such as oxidized low density lipoprotein, lipopolysaccharide, and glucose. These studies hint that under certain defined conditions, THP-1 cells not only resemble primary monocytes-macrophages isolated from healthy donors or donors with disease, such as diabetes mellitus, but also mimic the in situ alteration of macrophages in the adipose tissue of obese subjects and in atherosclerotic lesions. A potential trajectory is to use this cell line to study the novel molecular mechanisms in monocytes and macrophages in relation to the physiology and pathophysiology of the cardiovascular system, however, the conclusion of studies employing THP-1 cells requires further verification using primary cells and/or in vivo models to be generalized to monocytes and macrophages.

THP-1 Macrophages and SGBS Adipocytes - A New Human in vitro Model System of Inflamed Adipose Tissue

Obesity is associated with an accumulation of macrophages in adipose tissue. This inflammation of adipose tissue is a key event in the pathogenesis of several obesity-related disorders, particularly insulin resistance. Here, we summarized existing model systems that mimic the situation of inflamed adipose tissue in vitro, most of them being murine. Importantly, we introduce our newly established human model system which combines the THP-1 monocytic cell line and the preadipocyte cell strain Simpson-Golabi-Behmel syndrome (SGBS). THP-1 cells, which originate from an acute monocytic leukemia, differentiate easily into macrophages in vitro. The human preadipocyte cell strain SGBS was recently introduced as a unique tool to study human fat cell functions. SGBS cells are characterized by a high capacity for adipogenic differentiation. SGBS adipocytes are capable of fat cell-specific metabolic functions such as insulin-stimulated glucose uptake, insulin-stimulated de novo lipogenesis and β-adrenergic-stimulated lipolysis and they secrete typical adipokines including leptin, adiponectin, and RBP4. Applying either macrophage-conditioned medium or a direct co-culture of macrophages and fat cells, our model system can be used to distinguish between paracrine and cell-contact dependent effects. In conclusion, we propose this model as a useful tool to study adipose inflammation in vitro. It represents an inexpensive, highly reproducible human system. The methods described here can be easily extended for usage of primary human macrophages and fat cells.

Innate immunity and adipose tissue biology

The understanding of the role of adipose tissue has changed from a lipid storage organ to an endocrine and immunologically active organ. Here, we summarize the evidence for an important role of adipose tissue in innate immunity. The review focuses on the expression and function of Toll-like receptors (TLRs) in adipocytes and on the role of adipose tissue macrophages. The dual activation of TLR4 in adipocytes by lipopolysaccharide and fatty acids represents a molecular gate that connects innate immunity with metabolism. Dichotomic molecules derived from ancient precursor molecules control metabolism and immune function. Visceral adipose tissue is infiltrated by macrophages in obesity, and there is local crosstalk between these two types of cells, leading to an inflammatory transformation of adipose tissue.

Adipocyte extracellular matrix composition, dynamics and role in obesity

The central role of the adipose tissue in lipid metabolism places specific demands on the cell structure of adipocytes. The protein composition and dynamics of the extracellular matrix (ECM) is of crucial importance for the functioning of those cells. Adipogenesis is a bi-phasic process in which the ECM develops from a fibrillar to a laminar structure as cells move from the commitment phase to the growth phase characterized by storage of vast amounts of triglycerides. Mature adipocytes appear to spend a lot of energy on the maintenance of the ECM. ECM remodeling is mediated by a balanced complement of constructive and destructive enzymes together with their enhancers and inhibitors. ECM remodeling is an energy costing process regulated by insulin, by the energy metabolism, and by mechanical forces. In the obese, overgrowth of adipocytes may lead to instability of the ECM, possibly mediated by hypoxia.

Anti-inflammatory effects of nicotinic acid in adipocytes demonstrated by suppression of fractalkine, RANTES, and MCP-1 and upregulation of adiponectin

OBJECTIVE

A major site of action for the atheroprotective drug nicotinic acid (NA) is adipose tissue, via the G-protein-coupled receptor, GPR109A. Since, adipose tissue is an active secretory organ that contributes both positively and negatively to systemic inflammatory processes associated with cardiovascular disease, we hypothesized that NA would act directly upon adipocytes to alter the expression of pro-inflammatory chemokines, and the anti-inflammatory adipokine adiponectin.

METHODS AND RESULTS

TNF-alpha treatment (1.0ng/mL) of 3T3-L1 adipocytes resulted in an increase in gene expression of fractalkine (9+/-3.3-fold, P<0.01); monocyte chemoattractant protein-1 (MCP-1) (24+/-1.2-fold, P<0.001), 'regulated upon activation, normal T cell expressed and secreted' (RANTES) (500+/-55-fold, P<0.001) and inducible nitric oxide synthase (iNOS) (200+/-70-fold, P<0.05). The addition of NA (10(-4)M) to TNF-alpha-treated adipocytes attenuated expression of fractalkine (50+/-12%, P<0.01); MCP-1 (50+/-6%, P<0.01), RANTES (70+/-3%, P<0.01) and iNOS (60+/-16%). This pattern was mirrored in protein released from the adipocytes into the surrounding media. The effect on gene expression was neutralised by pre-treatment with pertussis toxin. NA attenuated macrophage chemotaxis (by 27+/-3.5%, P<0.001) towards adipocyte conditioned media. By contrast, NA, (10(-6)-10(-3)M) increased, in a dose-dependent manner, mRNA of the atheroprotective hormone adiponectin (3-5-fold n=6, P<0.01).

CONCLUSIONS

NA suppresses pro-atherogenic chemokines and upregulates the atheroprotective adiponectin through a G-protein-coupled pathway. Since adipose tissue has the potential to contribute to both systemic and local (perivascular) inflammation associated with atherosclerosis our results suggest a new "pleiotropic" role for NA.

Intracellular infections enhance interleukin-6 and plasminogen activator inhibitor 1 production by cocultivated human adipocytes and THP-1 monocytes

Obesity is associated with a chronic inflammatory state, and adipocyte dysfunction is thought to play a crucial role in this. Infection of adipose tissue may trigger the production of inflammatory cytokines, leading to increased recruitment of macrophages into adipose tissue, which in turn may exacerbate the inflammatory state in obesity. Low-grade inflammation was mimicked in an in vitro coculture model with human adipocytes and THP-1 monocytes. Adipocytes and monocytes were infected with adenovirus, cytomegalovirus (CMV), or influenza A virus. After 48 h, transinfection was evaluated and interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-alpha), adiponectin, and plasminogen activator inhibitor 1 (PAI-1) were measured. IL-6 production was upregulated in cocultures of uninfected adipocytes and THP-1 macrophages in a THP-1 cell number-dependent fashion. IL-6 production by CMV-infected adipocytes was increased relative to that of uninfected adipocytes (P < 0.01). IL-6 production by CMV-infected cocultures was 16- to 37-fold higher than that of uninfected adipocytes (P < 0.001). IL-6 production in influenza A virus-infected cocultures was increased 12- to 20-fold (P < 0.05). Only CMV infection increased levels of PAI-1 in cocultures (fourfold; P < 0.05). Soluble factors produced by THP-1 macrophages rather than by adipocytes were responsible for the increased production of IL-6 in cocultures. Infection of cocultivated human adipocytes and THP-1 monocytes with CMV or influenza A virus led to increased production of IL-6 and PAI-1. Thus, infection of adipose tissue evokes an inflammatory response, leading to adipose tissue dysfunction and subsequent overproduction of IL-6 and PAI-1. This may further compound the atherogenic effects of obesity.

Matrix metalloproteinase 2 improves the transplanted adipocyte survival in mice

BACKGROUND

Fat tissue is a common material for autologous transplantation in plastic and reconstructive surgery. Basic fibroblast growth factor (bFGF) ameliorates the fat graft survival. A transplantation model has shown the gene expression of matrix metalloproteinases (MMPs) to increase in adipocytes. The aim of this study is to investigate the role of MMPs in the amelioration of survival by bFGF.

MATERIALS AND METHODS

3T3-L1 adipocytes were incubated with or without 10 microg mL(-1) bFGF for 8 h in the presence or absence of the MMP inhibitor GM6001, vascular endothelial growth factor (VEGF), MMP-2 or anti-bFGF antibody to study the effect of bFGF on MMP-2 mRNA expression, MMP-2 activity, fat accumulation or 2-deoxyglucose uptake. Collagen sheets containing l x l0(7) adipocytes with or without bFGF in the presence or absence of GM6001 were subcutaneously transplanted into mice, and the appearance, histology, mRNA expression and fat accumulation of the grafts were analysed 4 weeks after transplantation.

RESULTS

The MMP-2 expression was drastically induced by bFGF among MMPs in 3T3-L1 adipocytes. MMP-2 accelerated fat accumulation, peroxisome proliferator-activated receptor gamma (PPAR gamma) mRNA expression, and glucose uptake to an extent similar to those induced by bFGF, respectively. The bFGF-induced increases were inhibited by the blocking of MMP-2. The transplantation of adipocytes into mice showed that bFGF ameliorates the appearance and fat accumulation, as well as mRNA expression in grafts. These effects were almost or partly inhibited by a MMP blockade.

CONCLUSIONS

MMP-2 may be involved in the mechanism by which bFGF ameliorates the survival of fat grafts.

Matrix metalloproteinase-3 enhances the free fatty acids-induced VEGF expression in adipocytes through toll-like receptor 2

Infiltrated macrophages (Mphi) are believed to cause pathological changes in the surrounding adipocytes through the secretion of active molecules in visceral fat. Matrix metalloproteinase (MMP)-3 is secreted from Mphi, and enhances expression of the inflammatory cytokines through the activation of toll-like receptor (TLR) 2. Visceral adipocytes express high levels of vascular endothelial growth factor (VEGF), and the degree of visceral fat accumulation is associated with the plasma VEGF concentration in obese subjects. The aim of the study is to clarify the role of MMP-3 in the enhancement of the free fatty acids (FFAs)-induced VEGF expression through TLR2 in visceral adipocytes. One mM FFAs induced VEGF mRNA and protein expression in 3T3-L1 adipocytes. The FFAs-induced VEGF expression was mostly mediated by TLR2. A high fat intake increased the VEGF mRNA expression in visceral fat and the VEGF concentration in plasma, accompanied with the increase in the plasma FFAs concentration in mice. These increases were largely inhibited in TLR2-deficient mice. The FFAs-induced VEGF expression was increased in the presence of Mphi-conditioned medium (CM) in adipocytes, and the enhancement was inhibited by a MMP-3 inhibitor or a neutralizing antibody against MMP-3. The active form of MMP-3 induced the VEGF mRNA expression, as well as TLR2, in adipocytes. The increase in the VEGF expression by MMP-3 was inhibited by the treatment with siRNA for TLR2. The enhancement of FFAs-induced TLR2 expression by Mphi-CM was inhibited by blocking of the MMP-3. The increase in the VEGF mRNA expression by Mphi-CM or MMP-3 was partially inhibited by a neutralizing antibody against TNF-alpha. These results indicate that MMP-3 in Mphi-CM enhances the FFAs-induced VEGF expression in adipocytes through the increase in the TLR2 expression. The MMP-3 secreted from the infiltrated Mphi may be a regulator of the VEGF expression in visceral adipocytes.