DNA microarray analyses of genes expressed differentially in 3T3-L1 adipocytes co-cultured with murine macrophage cell line RAW264.7 in the presence of the toll-like receptor 4 ligand bacterial endotoxin

The bidirectional association between diabetes and periodontitis, from basic to clinical

The prevalence and severity of periodontitis are increased and advanced in diabetes. Severe periodontitis elicits adverse effects on diabetes by impairing insulin actions due to systemic microinflammation. Recent studies unveil the emerging findings and molecular basis of the bidirectional relationship between periodontitis and diabetes. In addition to conventional mechanisms such as hyperglycemia, hyperlipidemia, and chronic inflammation, deficient insulin action may play a pathogenic role in the progression of periodontitis under diabetes. Epidemiologically, from the viewpoint of the adverse effect of periodontitis on diabetes, recent studies have suggested that Asians including Japanese and Asian Americans with diabetes and mild obesity (BMI <25 kg/m2) should pay more attention to their increased risk for cardiovascular diseases. In this review, we summarize recent findings on the effect of diabetes on periodontitis from the viewpoint of abnormalities in metabolism and insulin resistance with novel mechanisms, and the influence of periodontitis on diabetes mainly focused on micro-inflammation related to mature adipose tissue and discuss future perspectives about novel approaches to interrupt the adverse interrelationship.

Role of bone marrow adipocytes in bone metastasis development and progression: a systematic review

Purpose

Bone marrow adipocytes (BMAs) are the most plentiful cells in the bone marrow and function as an endocrine organ by producing fatty acids, cytokines, and adipokines. Consequently, BMAs can interact with tumor cells, influencing both tumor growth and the onset and progression of bone metastasis. This review aims to systematically evaluate the role of BMAs in the development and progression of bone metastasis.

Methods

A comprehensive search was conducted on PubMed, Web of Science, and Scopus electronic databases, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement standards, to identify studies published from March 2013 to June 2023. Two independent reviewers assessed and screened the literature, extracted the data, and evaluated the quality of the studies. The body of evidence was evaluated and graded using the ROBINS-I tool for non-randomized studies of interventions and the Systematic Review Centre for Laboratory Animal Experimentation (SYRCLE) tool for in vivo studies. The results were synthesized using descriptive methods.

Results

The search yielded a total of 463 studies, of which 17 studies were included in the final analysis, including 15 preclinical studies and two non-randomized clinical studies. Analysis of preclinical studies revealed that BMAs play a significant role in bone metastasis, particularly in prostate cancer followed by breast and malignant melanoma cancers. BMAs primarily influence cancer cells by inducing a glycolytic phenotype and releasing or upregulating soluble factors, chemokines, cytokines, adipokines, tumor-derived fatty acid-binding protein (FABP), and members of the nuclear receptor superfamily, such as chemokine (C-C motif) ligand 7 (CCL7), C-X-C Motif Chemokine Ligand (CXCL)1, CXCL2, interleukin (IL)-1β, IL-6, FABP4, and peroxisome proliferator-activated receptor γ (PPARγ). These factors also contribute to adipocyte lipolysis and regulate a pro-inflammatory phenotype in BMAs. However, the number of clinical studies is limited, and definitive conclusions cannot be drawn.

Conclusion

The preclinical studies reviewed indicate that BMAs may play a crucial role in bone metastasis in prostate, breast, and malignant melanoma cancers. Nevertheless, further preclinical and clinical studies are needed to better understand the complex role and relationship between BMAs and cancer cells in the bone microenvironment. Targeting BMAs in combination with standard treatments holds promise as a potential therapeutic strategy for bone metastasis.

Effects of co-incubation of LPS-stimulated RAW 264.7 macrophages on leptin production by 3T3-L1 adipocytes: a method for co-incubating distinct adipose tissue cell lines

BACKGROUND

Adipose tissue is a major endocrine organ capable of releasing inflammatory adipokines that are linked to changes occurring in the overfed state, where tissue remodeling results in hypertrophic adipocytes that recruit monocytes to infiltrate the tissue and take on an inflammatory phenotype. Increases in macrophage-specific inflammatory mediator levels contribute to the inflamed state and worsen the inflammatory loop between the macrophages and adipocytes. Although most inflammatory adipokines are released by macrophages, adipocytes can also release immunomodulatory adipokines, such as leptin. The objective of this research was to determine if co-incubation of activated macrophages with mature adipocytes, using transwell inserts, affected adipocyte leptin release. We also examined if there were differences in levels of cell-secreted products quantified in cell-conditioned media collected from macrophage-containing (transwell insert) and adipocyte-containing (well) compartments.

METHODS

Mature adipocytes were co-incubated with control and lipopolysaccharide-stimulated (0.01 mg/ml) murine macrophages, and nitric oxide, interleukin-6, and leptin levels were quantified in the cell-conditioned media from both compartments.

RESULTS

Activation status of the macrophages did not affect leptin release by the adipocytes. We observed higher amounts of leptin in wells compared to transwells. Nitric oxide and interleukin-6 levels were similar between transwells and wells, suggesting that these adipokines travel through the transwell inserts and are reaching equilibrium between the two compartments.

CONCLUSION

Our results suggest that co-incubating activated macrophages and adipocytes using transwell inserts can result in distinct microenvironments in the different cellular compartments and that separate sampling of these compartments is required to detect the subtle signaling dynamics that exist between these cells.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1186/s42269-022-00747-7.

The Link Between Periodontal Inflammation and Obesity

Purpose of Review

Obesity is a trigger for multiple diseases such as diabetes mellitus, hypertension, and cardiovascular diseases. Epidemiological studies have shown that obesity may be a risk factor for periodontal disease. Recently, there have been reports of presumed mechanisms of the associations between periodontitis and lipid metabolism or thermogenesis. This review aims to discuss the link between periodontal disease and energy regulatory function based on recent findings.

Recent Findings

It has been demonstrated that activation of the C–C motif chemokine ligand/C–C chemokine receptor 7 pathway in adipose tissue induces inflammation and impairment of lipid metabolism and energy regulation in mice. Porphyromonas gingivalis administration has been shown to induce further weight gain and increased adipose tissue in diet-induced obese mice. Additionally, it has been reported that Porphyromonas gingivalis–induced endotoxemia potentially affect obesity by altering endocrine functions in brown adipose tissue in mice. Several cohort studies have shown that obesity is associated with tooth loss 5 years later, and periodontal conditions of obese individuals are significantly worse 2 and 6 months after the treatment compared with those of non-obese individuals. It has also been reported that body mass index is positively associated with the periodontal inflamed surface area index, a measure of periodontal inflammation. These results suggest that not only the enhancement of inflammation due to obesity but also the activation of inflammatory signaling may affect energy regulation.

Summary

Loss of adipose tissue homeostasis induces increase and activation of immune cells in adipose tissue, leading to impaired immune function in obesity. Various cytokines and chemokines are secreted from obese adipose tissue and promote inflammatory signaling. Some of these signaling pathways have been suggested to affect energy regulation. The combination of obesity and periodontitis amplifies inflammation to levels that affect the whole body through the adipose tissue. Obesity, in turn, accelerates the exacerbation of periodontitis.

Inhibition of γ-secretase in adipocytes leads to altered IL-6 secretion and adipose inflammation

Adipocyte-mediated inflammatory signalling has been proposed to alter adipose physiology in obesity and Type 2 diabetes mellitus. Novel targets for alteration of inflammatory signalling are needed to improve obesity-related outcomes. The γ-secretase enzyme complex has been suggested to play a role both in adipocyte function as well as in immune regulation. We hypothesized that adipocyte-specific γ-secretase inhibition could alter the inflammatory makeup of adipose tissue. We found that genetic blockade of γ-secretase in adipocytes leads to a decrease in EMR1 (F4/80) expression, as a marker of macrophage presence, in adipose tissue without changes in expression of markers of other inflammatory cell types. To explore the mechanism by which adipocytes can alter macrophage function in vitro, fully differentiated 3T3-L1 adipocytes were treated with a γ-secretase inhibitor in the presence of lipopolysaccharide (LPS) and transcription of IL6 and ccl2 (MCP1) were quantified. IL-6 expression and secretion were significantly inhibited by γ-secretase blockade, with little effect on MCP1. Preconditioned media from 3T3-L1 adipocytes treated with a γ-secretase inhibitor also alters macrophage activation but did not affect macrophage translocation in vitro. Therefore, γ-secretase inhibition in fully differentiated adipocytes can alter IL-6 signalling to macrophages, consistent with our hypothesis that that γ-secretase is involved in adipocyte-initiated inflammatory signalling cascades.

Anti-inflammatory effects of miRNA-146a induced in adipose and periodontal tissues

MicroRNA (miRNA) plays an important role in diverse cellular biological processes such as inflammatory response, differentiation and proliferation, and carcinogenesis. miR-146a has been suggested as a negative regulator of the inflammatory reaction. Although, it has been reported as expressed in inflamed adipose and periodontal tissues, however, miR-146a's inhibitory effects against inflammatory response in both the tissues, are not well understood. Therefore, in this study, the inhibitory effects of miR-146a on both adipose and periodontal inflammation, was investigated. In vitro study has revealed that miR-146a transfection into either adipocytes or gingival fibroblasts, has resulted in a reduced cytokine gene expression, observed on co-culturing the cells with macrophages in the presence of lipopolysaccharides (LPS), in comparison to the control miRNA transfected. Similarly, miR-146a transfection into macrophages resulted in a reduced expression of TNF-α gene and protein in response to LPS stimulation. In vivo study revealed that a continuous intravenous miR-146a administration into mice via tail vein, protected the mice from developing high-fat diet-induced obesity and the inflammatory cytokine gene expression was down-regulated in both adipose and periodontal tissues. miR-146a appeared to be induced by macrophage-derived inflammatory signals such as TNF-α by negative feed-back mechanism, and it suppressed inflammatory reaction in both adipose and periodontal tissues. Therefore, miR-146a could be suggested as a potential therapeutic molecule and as a common inflammatory regulator for both obesity-induced diabetes and related periodontal diseases.

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miR-146a induced by adipose and periodontal inflammation via macrophage mediators.

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miR-146a is a negative inflammation regulator in adipose and periodontal tissues.

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miR-146a is a potential therapeutic target against obesity and periodontal diseases.

Ccr7 null mice are protected against diet-induced obesity via Ucp1 upregulation and enhanced energy expenditure

Background

The chemokine receptor CCR7, expressed on various immune cells, is associated with cell migration and lympho-node homing. Mice lacking Ccr7 are protected from diet-induced obesity and subsequent insulin resistance. We evaluated the mechanism underlying these protective effects from the standpoint of energy expenditure.

Methods

Wild-type and Ccr7 null mice were fed a high-fat diet, and the regulation of energy metabolism and energy metabolism-related molecules, e.g., Ucp1, Cidea, and Pgc1α, were evaluated.

Results

Food intake did not differ between groups. O₂ consumption and CO₂ production were higher in Ccr7 null mice than in wild-type mice, despite a similar respiratory quotient and glucose and lipid utilization, suggesting that energy expenditure increased in Ccr7 null mice via enhanced metabolism. In white adipose tissues of Ccr7 null mice, Prdm16, Cd137, Tmem26, Th, and Tbx1 expression increased. Similarly, in brown adipose tissues of Ccr7 null mice, Dio2, Pgc1α, Cidea, Sirt1, and Adiponectin expression increased. In both white and brown adipose tissues, Ucp1 gene and protein expression levels were higher in null mice than in wild-type mice.

Conclusions

In Ccr7 null mice, browning of white adipocytes as well as the activation of brown adipocytes cause enhanced energy metabolism, resulting in protection against diet-induced obesity.

Electronic supplementary material

The online version of this article (10.1186/s12986-019-0372-5) contains supplementary material, which is available to authorized users.

Dental pulp cell-derived powerful inducer of TNF-α comprises PKR containing stress granule rich microvesicles

It is well known that dental pulp tissue can evoke some of the most severe acute inflammation observed in the human body. We found that dental pulp cells secrete a factor that induces tumor necrosis factor-α production from macrophages, and designated this factor, dental pulp cell-derived powerful inducer of TNF-α (DPIT). DPIT was induced in dental pulp cells and transported to recipient cells via microvesicles. Treatment of dental pulp cells with a PKR inhibitor markedly suppressed DPIT activity, and weak interferon signals were constitutively activated inside the cells. In recipient macrophages, stimulation with DPIT-containing supernatants from pulp cells resulted in activation of both nuclear factor-κB and MAP kinases like JNK and p38. Proteomics analyses revealed that many stress granule-related proteins were present in supernatants from dental pulp cells as well as microvesicle marker proteins like GAPDH, β-actin, HSPA8, HSPB1, HSPE1, and HSPD1. Furthermore, giant molecule AHNAK and PKR were detected in microvesicles derived from dental pulp cells, and gene silencing of AHNAK in dental pulp cells led to reduced DPIT activity. Thus, it appeared that the core protein of DPIT was PKR, and that PKR was maintained in an active state in stress granule aggregates with AHNAK and transported via microvesicles. The activity of DPIT for TNF-α induction was far superior to that of gram-negative bacterial endotoxin. Therefore, we, report for the first time, that active PKR is transported via microvesicles as stress granule aggregates and induces powerful inflammatory signals in macrophages.

Kavain Reduces Porphyromonas gingivalis-Induced Adipocyte Inflammation: Role of PGC-1α Signaling

A link between obesity and periodontitis has been suggested because of compromised immune response and chronic inflammation in obese patients. In this study, we evaluated the anti-inflammatory properties of Kavain, an extract from Piper methysticum, on Porphyromonas gingivalis-induced inflammation in adipocytes with special focus on peroxisome proliferation-activated receptor γ coactivator α (PGC-1α) and related pathways. The 3T3-L1 mouse preadipocytes and primary adipocytes harvested from mouse adipose tissue were infected with P. gingivalis, and inflammation (TNF-α; adiponectin/adipokines), oxidative stress, and adipogenic marker (FAS, CEBPα, and PPAR-γ) expression were measured. Furthermore, effect of PGC-1α knockdown on Kavain action was evaluated. Results showed that P. gingivalis worsens adipocyte dysfunction through increase of TNF-α, IL-6, and iNOS and decrease of PGC-1α and adiponectin. Interestingly, although Kavain obliterated P. gingivalis-induced proinflammatory effects in wild-type cells, Kavain did not affect PGC-1α-deficient cells, strongly advocating for Kavain effects being mediated by PGC-1α. In vivo adipocytes challenged with i.p. injection of P. gingivalis alone or P. gingivalis and Kavain displayed the same phenotype as in vitro adipocytes. Altogether, our findings established anti-inflammatory and antioxidant effects of Kavain on adipocytes and emphasized protective action against P. gingivalis-induced adipogenesis. The use of compounds such as Kavain offer a portal to potential therapeutic approaches to counter chronic inflammation in obesity-related diseases.

Integrated Immunomodulatory Mechanisms through which Long-Chain n-3 Polyunsaturated Fatty Acids Attenuate Obese Adipose Tissue Dysfunction

Obesity is a global health concern with rising prevalence that increases the risk of developing other chronic diseases. A causal link connecting overnutrition, the development of obesity and obesity-associated co-morbidities is visceral adipose tissue (AT) dysfunction, characterized by changes in the cellularity of various immune cell populations, altered production of inflammatory adipokines that sustain a chronic state of low-grade inflammation and, ultimately, dysregulated AT metabolic function. Therefore, dietary intervention strategies aimed to halt the progression of obese AT dysfunction through any of the aforementioned processes represent an important active area of research. In this connection, fish oil-derived dietary long-chain n-3 polyunsaturated fatty acids (PUFA) in the form of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have been demonstrated to attenuate obese AT dysfunction through multiple mechanisms, ultimately affecting AT immune cellularity and function, adipokine production, and metabolic signaling pathways, all of which will be discussed herein.

Adipose tissue complement factor B promotes adipocyte maturation

OBJECTIVES

It is well-known that the complement system plays an essential role in host immunity. Observational studies have indicated that complement system-related molecules such as complement factor B (CfB) and other components are correlated with obesity and/or insulin resistance parameters. In this study, we investigated the role of adipocyte-derived CfB in adipose tissue metabolism.

METHODS

We investigated the expression level of complement system-related genes in adipocytes. To understand the role of CfB in adipocyte, we performed Cfb overexpression in 3T3-L1 preadipocytes and generated adipocyte-specific Cfb transgenic mice.

RESULTS

Cfb expression was markedly enhanced in 3T3-L1 adipocytes co-cultured with macrophages following endotoxin stimulation. In Cfb-overexpressing cells, the expression of adipocyte differentiation/maturation-related genes encoding peroxisome proliferator-activated receptor γ (Pparγ), adipocyte Protein 2 and perilipin was significantly enhanced. Cfb transgenic mice showed a marked increase in the expression of genes encoding Pparγ, perilipin, sterol regulatory element-binding protein 1 c, and Cd36 in the subcutaneous adipose tissue.

CONCLUSIONS

CfB plays a crucial role in late-phase of adipocyte differentiation and subsequent lipid droplet formation.

Epicatechin downregulates adipose tissue CCL19 expression and thereby ameliorates diet-induced obesity and insulin resistance

BACKGROUND AND AIMS

Epicatechin (EC) intake has been suggested to be beneficial for the prevention of cardiovascular disorders, and it is well known that adipose tissue inflammation is one of the major risk factors for coronary heart diseases. The purpose of the present study was to determine the in vitro and in vivo effects of EC on adipose tissue inflammation and obesity.

METHODS AND RESULTS

DNA microarray analysis was performed to evaluate the effects of EC on gene expression in adipocytes co-cultured with bacterial endotoxin-stimulated macrophages. To determine the in vivo effects of the catechin, C57BL/6 mice were fed either a high-fat diet (HFD) or HFD combined with EC, and metabolic changes were observed EC suppressed the expression of many inflammatory genes in the adipocytes co-cultured with endotoxin-stimulated macrophages. Specifically, EC markedly suppressed chemokine (CC motif) ligand 19 (CCL19) expression. The target cell of EC appeared to macrophages. The in vivo study indicated that mice fed the EC-supplemented HFD were protected from diet-induced obesity and insulin resistance. Accordingly, the expression levels of genes associated with inflammation in adipose tissue and in the liver were downregulated in this group of mice.

CONCLUSIONS

EC exerts beneficial effects for the prevention of adipose tissue inflammation and insulin resistance. Since we previously reported that mice deficient in the CCL19 receptor were protected from diet-induced obesity and insulin resistance, it can be concluded that the beneficial effects of EC could be mediated, at least in part, by marked suppression of CCL19 expression.

Serum Amyloid A3 Gene Expression in Adipocytes is an Indicator of the Interaction with Macrophages

The infiltration of macrophages into adipose tissue and their interaction with adipocytes are essential for the chronic low-grade inflammation of obese adipose tissue. In this study, we identified the serum amyloid A3 (Saa3) gene as a key adipocyte-derived factor that is affected by interaction with macrophages. We showed that the Saa3 promoter in adipocytes actually responds to activated macrophages in a co-culture system. Decreasing C/EBPβ abundance in 3T3-L1 adipocytes or point mutation of C/EBPβ elements suppressed the increased promoter activity in response to activated macrophages, suggesting an essential role of C/EBPβ in Saa3 promoter activation. Bioluminescence based on Saa3 promoter activity in Saa3-luc mice was promoted in obese adipose tissue, showing that Saa3 promoter activity is most likely related to macrophage infiltration. This study suggests that the level of expression of the Saa3 gene could be utilized for the number of infiltrated macrophages in obese adipose tissue.

IL-17A synergistically enhances TNFα-induced IL-6 and CCL20 production in 3T3-L1 adipocytes

Interleukin-17A (IL-17A) is known to induce inflammatory responses and to be involved in the pathogenesis of not only autoimmune diseases, but also several metabolic and infectious diseases. In this study, IL-17A is shown to induce IL-6 expression in 3T3-L1 mature adipocytes. Interestingly, we found that IL-17A synergistically amplified TNFα-induced secretion of IL-6 and upregulation of IL-17RA expression in 3T3-L1 adipocytes. Its synergistic effects on IL-6 production were inhibited by pre-treatment with inhibitors of IκBα and JNK. Furthermore, IL-17A cooperatively enhanced LPS-mediated IL-6 production in 3T3-L1 adipocytes co-cultured with RAW264.7 macrophages. In addition, IL-17A also enhanced CCL20 production in 3T3-L1 adipocytes stimulated with TNFα or co-cultured with LPS-stimulated RAW macrophages. In high-fat diet-fed mouse epididymal adipose tissues, IL-17RA and RORγt mRNA levels were significantly increased and the serum level of CCL20 was also upregulated. Taken together, these data show that, in adipose tissues, IL-17A contributes to exacerbating insulin resistance-enhancing IL-6 production and promotes the infiltration of Th17 cells in cooperation with TNFα; these findings represent a novel hypothesis for the association between IL-17A-producing cells and type 2 diabetes.

Protection from diet-induced obesity and insulin resistance in mice lacking CCL19-CCR7 signaling

OBJECTIVE

Several chemokines play important roles in recruiting the monocyte/macrophage lineage into adipose tissues. We previously found CCL19 was highly expressed in adipocytes cocultured with macrophages stimulated by endotoxin. This study aimed to evaluate the role of CCL19-CCR7 axis on obesity and insulin resistance.

METHODS

Serum CCL19 concentration was examined in obese model mice challenged by endotoxin. CCL19 receptor-null, Ccr7(-/-), mice and wild-type mice fed a high-fat diet or normal diet were used to investigate the role of CCL19 signals on obesity-associated inflammation.

RESULTS

CCL19 protein was elevated in the sera of obese model mice challenged by endotoxin. Ccr7(-/-) mice were protected from diet-induced obesity and insulin resistance. The adipose tissue and liver expression of inflammatory genes of Ccr7(-/-) mice was much lower than in diet-induced obese mice. Ccr7(-/-) mice were protected from fatty liver and dyslipidemia and exhibited increased thermogenesis on high-fat feeding. CCL19 attracts activated dendritic cells (DC). The expression of the DC markers, CD11b and 11c, was not observed in the adipose tissues of Ccr7(-/-) mice fed a high-fat diet, which might be closely associated with the protection of these mice from obesity.

CONCLUSIONS

The CCL19-CCR7 pathway associates with the development of high-fat-induced obesity and insulin resistance.

MAP kinase phosphatase 2 regulates macrophage-adipocyte interaction

Objective

Inflammation is critical for the development of obesity-associated metabolic disorders. This study aims to investigate the role of mitogen-activated protein kinase phosphatase 2 (MKP-2) in inflammation during macrophage-adipocyte interaction.

Methods

White adipose tissues (WAT) from mice either on a high-fat diet (HFD) or normal chow (NC) were isolated to examine the expression of MKP-2. Murine macrophage cell line RAW264.7 stably expressing MKP-2 was used to study the regulation of MKP-2 in macrophages in response to saturated free fatty acid (FFA) and its role in macrophage M1/M2 activation. Macrophage-adipocyte co-culture system was employed to investigate the role of MKP-2 in regulating inflammation during adipocyte-macrophage interaction. c-Jun N-terminal kinase (JNK)- and p38-specific inhibitors were used to examine the mechanisms by which MKP-2 regulates macrophage activation and macrophage-adipocytes interaction.

Results

HFD changed the expression of MKP-2 in WAT, and MKP-2 was highly expressed in the stromal vascular cells (SVCs). MKP-2 inhibited the production of proinflammatory cytokines in response to FFA stimulation in macrophages. MKP-2 inhibited macrophage M1 activation through JNK and p38. In addition, overexpression of MKP-2 in macrophages suppressed inflammation during macrophage-adipocyte interaction.

Conclusion

MKP-2 is a negative regulator of macrophage M1 activation through JNK and p38 and inhibits inflammation during macrophage-adipocyte interaction.

Marrow adipocyte-derived CXCL1 and CXCL2 contribute to osteolysis in metastatic prostate cancer

Increased bone marrow adiposity is a common feature of advanced age, obesity and associated metabolic pathologies. Augmented numbers of marrow adipocytes positively correlate with dysregulated bone remodeling, also a well-established complication of metastatic disease. We have shown previously that marrow adiposity accelerates prostate tumor progression in the skeleton and promotes extensive destruction of the bone; however, the factors behind adipocyte-driven osteolysis in the skeletal tumor microenvironment are not currently known. In this study, utilizing in vivo diet-induced models of bone marrow adiposity, we reveal evidence for positive correlation between increased marrow fat content, bone degradation by ARCaP(M) and PC3 prostate tumors, and augmented levels of host-derived CXCL1 and CXCL2, ligands of CXCR2 receptor. We show by in vitro osteoclastogenesis assays that media conditioned by bone marrow adipocytes is a significant source of CXCL1 and CXCL2 proteins. We also demonstrate that both the adipocyte-conditioned media and the recombinant CXCL1 and CXCL2 ligands efficiently accelerate osteoclast maturation, a process that can be blocked by neutralizing antibodies to each of the chemokines. We further confirm the contribution of CXCR2 signaling axis to adiposity-driven osteoclastogenesis by blocking fat cell-induced osteoclast differentiation with CXCR2 antagonist or neutralizing antibodies. Together, our results link CXCL1 and CXCL2 chemokines with bone marrow adiposity and implicate CXCR2 signaling in promoting effects of marrow fat on progression of skeletal tumors in bone.

IκB kinase epsilon expression in adipocytes is upregulated by interaction with macrophages

Macrophage infiltration in the adipose tissue, and the interaction with adipocytes, is well documented to be involved in fat inflammation and obesity-associated complications. In this study, we isolated IκB kinase ε (IKKε) as a key adipocyte factor that is potentially affected by interaction with macrophages in adipose tissue in vivo. We showed that IKKε mRNA expression levels in white adipose tissue were increased in both genetic and diet-induced obese mouse. Furthermore, IKKε mRNA expression was decreased by the administration of vitamin B6, an anti-inflammatory vitamin, and that IKKε expression levels in adipose tissue were closely correlated with the numbers of infiltrating macrophages. In a co-culture system, we showed that IKKε expression in adipocytes was upregulated by interaction with activated macrophages. This study provides novel insight into IKKε, which is involved in adipose tissue inflammation during the development of obesity.

Alliin, a garlic (Allium sativum) compound, prevents LPS-induced inflammation in 3T3-L1 adipocytes

Garlic (Allium sativum L.) has been used to alleviate a variety of health problems due to its high content of organosulfur compounds and antioxidant activity. The main active component is alliin (S-allyl cysteine sulfoxide), a potent antioxidant with cardioprotective and neuroprotective actions. In addition, it helps to decrease serum levels of glucose, insulin, triglycerides, and uric acid, as well as insulin resistance, and reduces cytokine levels. However its potential anti-inflammatory effect is unknown. We examined the effects of alliin in lipopolysaccharide- (LPS-) stimulated 3T3-L1 adipocytes by RT-PCR, Western blot, and microarrays analysis of 22,000 genes. Incubation of cells for 24 h with 100 μmol/L alliin prevented the increase in the expression of proinflammatory genes, IL-6, MCP-1, and Egr-1 in 3T3-L1 adipocytes exposed to 100 ng/mL LPS for 1 h. Interestingly, the phosphorylation of ERK1/2, which is involved in LPS-induced inflammation in adipocytes, was decreased following alliin treatment. Furthermore, the gene expression profile by microarrays evidentiate an upregulation of genes involved in immune response and downregulation of genes related with cancer. The present results have shown that alliin is able to suppress the LPS inflammatory signals by generating an anti-inflammatory gene expression profile and by modifying adipocyte metabolic profile.

Angiotensin receptor 1 blocker valsartan normalizes gene expression profiles of 3T3-L1 adipocytes altered by co-culture with LPS-treated RAW264.7 macrophages

SUMMARY

Macrophages in adipose tissue reportedly play a major role in the development of insulin resistance and chronic inflammation associated with obesity. On the other hand, several clinical trials have revealed angiotensin II receptor blockers (ARBs) to improve insulin resistance. In this study, we analyzed the gene expression profile of 3T3-L1 adipocytes co-cultured with LPS-treated RAW264.7 macrophages in the presence or the absence of the angiotensin receptor 1 blocker valsartan, for 4, 8, 12 and 24 h. The genes of which expressions were affected by LPS-treated RAW macrophages but normalized by co-addition of valsartan were analyzed using KeyMolnet Lite. They included many NF-κB, thyroid receptor and AP-1 target transcripts. In addition, the expression patterns of caspases, integrins, matrix metallopeptidases and adipogenic genes, altered by co-culture with LPS-treated RAW cells, were generally normalized by valsartan treatment. In light of these data, it is reasonable to consider valsartan to normalize altered gene expression patterns in adipose tissue infiltrated by macrophages, and to ameliorate inflammation, apoptosis and fibrotic changes of adipose tissue. Although there may be multiple mechanisms by which ARBs ameliorate insulin resistance, for example, through effects on muscle or other tissues via the circulatory system, this is the first report demonstrating that a favorable effect of valsartan involves normalization of the interaction between adipocytes and macrophages. This mechanism of valsartan action holds promise for developing treatments for obesity-related insulin resistance.:

The inflammation-lipocalin 2 axis may contribute to the development of chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) is an important risk factor for coronary heart disease, and previous studies indicated the involvement of low-grade inflammation in the pathogenesis of CKD.

METHODS

The study was designed to (i) identify and confirm genes and their products upregulated in mesangial cells cocultured with endotoxin-stimulated macrophages and (ii) determine the clinical relevance of genes and proteins upregulated in mesangial cells under inflammatory conditions by an epidemiological approach.

RESULTS

DNA microarray analysis revealed upregulated expression of many genes and their products including several cytokines and chemokines, as well as the inflammatory marker, lipocalin 2 gene. The gene expression and protein upregulation of lipocalin 2 were synergistically affected by endotoxin and tumor necrosis factor (TNF)-α stimulation. In human studies, lipocalin 2 level was significantly associated with creatinine (r = 0.419, P < 0.001) and negatively associated with eGFR (r = -0.365, P < 0.001). Multiple logistic regression analysis revealed a significant association between lipocalin 2 and soluble tumor necrosis factor receptor 2 (sTNF-R2), eGFR and uric acid in general subjects attending regular annual medical check-up (n = 420). When subjects with diabetes were excluded from the analysis, lipocalin 2 remained associated with sTNF-R2, eGFR and uric acid.

CONCLUSIONS

Since an activated TNF system, as demonstrated by elevated sTNF-R2, and elevated uric acid were recently implicated in an elevated CKD risk, we conclude that inflammation could play an important role in the pathogenesis of CKD, and that lipocalin 2 is a potential universal marker for impaired kidney function. Furthermore, the results obtained by the current microarray analysis could improve the understanding of gene profiles associated with the pathophysiology of CKD under inflammatory conditions.

The FLS (fatty liver Shionogi) mouse reveals local expressions of lipocalin-2, CXCL1 and CXCL9 in the liver with non-alcoholic steatohepatitis

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) encompasses a wide spectrum of diseases, ranging from simple steatosis to nonalcoholic steatohepatitis (NASH), which carries a significant risk of progression to cirrhosis and hepatocellular carcinoma. Since NASH is a progressive but reversible condition, it is desirable to distinguish NASH from simple steatosis, and to treat NASH patients at an early stage. To establish appropriate diagnosis and therapy, the pathological mechanisms of the disease should be elucidated; however, these have not been fully clarified for both NASH and simple steatosis. This study aims to reveal the differences between simple steatosis and NASH.

METHODS

This study used fatty liver Shionogi (FLS) mice as a NASH model, for comparison with dd Shionogi (DS) mice as a model of simple steatosis. Genome-wide gene expression analysis was performed using Affymetrix GeneChip Mouse Genome 430 2.0 Array, which contains 45101 probe sets for known and predicted genes. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) and immunohistochemistry were used to investigate gene expression changes and protein localizations.

RESULTS

DNA microarray analysis of the liver transcriptomes and qRT-PCR of both types of mice revealed that LCN2, CXCL1 and CXCL9 mRNAs were overexpressed in FLS mouse livers. Immunohistochemistry showed that CXCL1 protein was mainly localized to steatotic hepatocytes. CXCL9 protein-expressing hepatocytes and sinusoidal endothelium were localized in some areas of inflammatory cell infiltration. Most interestingly, hepatocytes expressing LCN2, a kind of adipokine, were localized around almost all inflammatory cell clusters. Furthermore, there was a positive correlation between the number of LCN2-positive hepatocytes in the specimen and the number of inflammatory foci.

CONCLUSIONS

Overexpression and distinct localization of LCN2, CXCL1 and CXCL9 in the liver of fatty liver Shionogi mice suggest significant roles of these proteins in the pathogenesis of NASH.

RASSF6 expression in adipocytes is down-regulated by interaction with macrophages

Macrophage infiltration into adipose tissue is associated with obesity and the crosstalk between adipocytes and infiltrated macrophages has been investigated as an important pathological phenomenon during adipose tissue inflammation. Here, we sought to identify adipocyte mRNAs that are regulated by interaction with infiltrated macrophages in vivo. An anti-inflammatory vitamin, vitamin B6, suppressed macrophage infiltration into white adipose tissue and altered mRNA expression. We identified >3500 genes whose expression is significantly altered during the development of obesity in db/db mice, and compared them to the adipose tissue mRNA expression profile of mice supplemented with vitamin B6. We identified PTX3 and MMP3 as candidate genes regulated by macrophage infiltration. PTX3 and MMP3 mRNA expression in 3T3-L1 adipocytes was up-regulated by activated RAW264.7 cells and these mRNA levels were positively correlated with macrophage number in adipose tissue in vivo. Next, we screened adipose genes down-regulated by the interaction with macrophages, and isolated RASSF6 (Ras association domain family 6). RASSF6 mRNA in adipocytes was decreased by culture medium conditioned by activated RAW264.7 cells, and RASSF6 mRNA level was negatively correlated with macrophage number in adipose tissue, suggesting that adipocyte RASSF6 mRNA expression is down-regulated by infiltrated macrophages in vivo. Finally, this study also showed that decreased RASSF6 expression up-regulates mRNA expression of several genes, such as CD44 and high mobility group protein HMGA2. These data provide novel insights into the biological significance of interactions between adipocytes and macrophages in adipose tissue during the development of obesity.

Smoking and adipose tissue inflammation suppress leptin expression in Japanese obese males: potential mechanism of resistance to weight loss among Japanese obese smokers

BACKGROUND

The effect of smoking on leptin regulation is controversial. Smoking may induce low-grade inflammation. Recent series of studies indicated the critical role of macrophage migration in the establishment of adipose tissue inflammation. In this study, we aimed to see the effects of smoking and inflammation on leptin regulation both at cellular and epidemiological levels.

METHODS

We compared the concentration of inflammatory markers and serum leptin levels among Japanese male subjects. Additionally, leptin and intercellular adhesion molecule (ICAM) -1 gene expression was assessed in adipocytes co-cultured with or without macrophages in the presence or absence of nicotine and/or lipopolysaccharide (LPS).

RESULTS

In subjects with BMI below 25 kg/m2, both WBC counts and soluble-ICAM-1 levels are significantly higher in smokers than in non-smokers. However, leptin concentration did not differ according to smoking status. However, in subjects with BMI over 25 kg/m2, smokers exhibited significantly lower serum leptin level as well as higher WBC counts and s-ICAM-1 concentration as compared with non-smokers. Leptin gene expression was markedly suppressed in adipocytes co-cultured with macrophages than in adipocyte culture alone. Furthermore, nicotine further suppressed leptin gene expression. ICAM-1 gene expression was markedly up-regulated in adipocytes co-cultured with macrophages when stimulated with LPS.

CONCLUSIONS

Adipose tissue inflammation appears to down-regulate leptin expression in adipose tissues. Nicotine further suppresses leptin expression. Thus, both smoking and inflammation may diminish leptin effect in obese subjects. Therefore, obese, but not normal weight, smokers might be more resistant to weight loss than non-smokers.

Stimulation of inflammatory gene expression in human preadipocytes by macrophage-conditioned medium: upregulation of IL-6 production by macrophage-derived IL-1β

The aim of this study was to examine the effects of macrophage secretions on global gene expression in human preadipocytes using microarrays. Preadipocytes were cultured with unconditioned or conditioned medium from U937 macrophages, and gene expression examined with Agilent arrays (43,000 probes). 472 transcripts were differentially regulated (>2-fold difference; P<0.05) between preadipocytes in the conditioned medium compared to the unconditioned; 401 were upregulated and 71 downregulated. The upregulated transcripts were particularly linked to inflammation, including IL-1β, IL-6, and CCL20 (16.8-, 10.0-, and 8.9-fold increases, respectively) together with matrix metalloproteinases (MMP3, MMP9 and MMP12). Major pathways regulated by the conditioned medium were linked to inflammation, macrophage infiltration and lipid accumulation. Network analysis identified NFkB and IL-1β as central nodes in the upregulation of multiple inflammation-related genes. Treatment with an IL-1β neutralising antibody abolished the stimulation of IL-6 secretion by conditioned medium, indicating that IL-1β is a key regulator of preadipocyte IL-6 production. Macrophages evoke extensive changes in preadipocyte gene expression.

Human monocytes accelerate proliferation and blunt differentiation of preadipocytes in association with suppression of C/EBPΑ mRNA

Obesity, type 2 diabetes, and HIV-associated lipodystrophy are associated with abnormalities in adipocyte growth and differentiation. In persons with these conditions, adipose depots contain increased numbers of macrophages, but the origins of these cells and their specific effects are uncertain. Peripheral blood mononuclear cells (PBMC)-derived monocytes, but not T cells, cocultured via transwells with primary subcutaneous preadipocytes, increased proliferation (approximately twofold) and reduced differentiation (~50%) of preadipocytes. Gene expression analyses in proliferating preadipocytes (i.e., prior to hormonal induction of terminal differentiation) revealed that monocytes down-regulated mRNA levels of CCAAT/enhancer binding protein, alpha (C/EBPα) and up-regulated mRNA levels of G0/G1 switch 2 (G0S2) message, genes important for the regulation of adipogenesis and the cell cycle. These data indicate that circulating peripheral blood monocytes can disrupt adipogenesis by interfering with a critical step in C/EBPα and G0S2 transcription required for preadipocytes to make the transition from proliferation to differentiation. Interactions between preadipocytes and monocytes also increased the inflammatory cytokines IL-6 and IL-8, as well as a novel chemotactic cytokine, CXCL1. Additionally, the levels of both IL-6 and CXCL1 were highest when preadipocytes and monocytes were cultured together, compared to each cell in culture alone. Such cross-talk amplifies the production of mediators of tissue inflammation.

Adipocyte-macrophage interaction may mediate LPS-induced low-grade inflammation: Potential link with metabolic complications

Chronic low-grade infection has been suggested to be associated with metabolic disorder such as diabetes. However, the molecular mechanism underlying this important association is largely unknown. The only clue established so far is that many subjects exhibit elevated levels of C-reactive protein as measured by highly sensitive assay. Here, we hypothesized that adipocyte–macrophage interaction plays a key role in amplifying such low grade infection to the level of influencing metabolic disorders. The presence of macrophages in abdominal adipose tissues was investigated by immunohistochemistry. To see whether molecules associated with acute phase protein, LPS signaling, and persistent recruitment of monocytes, are produced at higher amounts in adipocytes co-cultured with macrophages stimulated with low concentration of LPS (1 ng/ml), we measured serum amyloid A (SAA), LPS binding protein (LBP), soluble CD14 (sCD14), and RANTES levels in culture supernatant of co-cultures. Lastly, we investigated in vivo effect of low-grade LPS infusion on the production of these molecules using obese model mice. The macrophages were certainly identified in abdominal adipose tissues. Investigated molecules, especially LBP, SAA, and RANTES were produced at higher amounts in co-cultures stimulated with LPS compared with the cells without LPS. The ob/ob, and high-fat diet-induced obesity mice produced higher amounts of LBP, SAA, and RANTES one day after LPS infusion (1 ng/ml/g body weight) compared with ob/– and normal-fat fed control mice. Thus, adipocytes and infiltrated macrophages, and their interaction with low endotoxin stimulation appear to play an important role in amplifying and maintaining LPS-induced low-grade inflammation.

Interactions of overweight, poor oral health, and stress related to chronic disease in an aging population

The prevalence of excess body mass (XBM), poor oral health (POH), and stress in a secluded population of aged (≥60 years) Hmong immigrants was surveyed. The findings were related to the prevalence of diabetes in the same population. Diabetes was associated separately with POH (OR 2.4; CL 1.3, 4.2) or with XBM (OR 2.5; CL 1.4, 4.8). The association of diabetes with the combination of XBM and POH was striking (OR 5.1; CL 3.4, 7.5); that apparent synergism has not been fully appreciated. We describe a mechanism that explains the synergism. The concept of “thrifty genotype” is a plausible explanation of XBM in the elderly Hmong immigrants and possibly the current older Laotian population. POH is common among elderly Laotians as it is in most developing countries. We conclude that synergism of XBM and POH significantly elevates the prevalence of diabetes among aging populations and probably other age groups as well.

Macrophage-secreted factors inhibit ZAG expression and secretion by human adipocytes

Zinc-alpha2-glycoprotein (ZAG), a novel adipokine, is downregulated in adipose tissue in obesity, a state characterized by increased adipose tissue macrophage infiltration and chronic low-grade inflammation. This study investigated whether macrophage-secreted factors and TNF-alpha, a major product of macrophages, modulate ZAG expression and secretion by human adipocytes. ZAG was produced primarily by adipocytes, and not by preadipocytes and macrophages. Incubation of preadipocytes with macrophage-conditioned medium for up to 12 days decreased ZAG mRNA and protein release, and the expression of adipogenic markers (PPARgamma and C/EBPalpha). Adipocytes treated with macrophage-conditioned medium for 24h displayed significant reductions in ZAG mRNA and release. Chronic TNF-alpha treatment let to significant decreases in ZAG expression and secretion, but marked upregulation of pro-inflammatory cytokines and chemokines (IL-6, leptin, IL-8, MCP-1 and RANTES) in adipocytes. These findings suggest that macrophage-associated inflammation may play a significant role in the downregulation of ZAG in adipose tissue in obesity.

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.

Adipose tissue depots of Holstein cows are immune responsive: inflammatory gene expression in vitro

The transcriptional response of adipose tissue depots with respect to their immune responsiveness in dairy cows remains largely unknown. Thus, we examined mRNA expression and responsiveness of subcutaneous (SUB) and mesenteric (MES) adipose tissue from nonpregnant dairy cows to a short-term (2 h), in vitro lipopolysaccharide (LPS) challenge (20 microg/mL in physiological saline). Abundance of mRNA for tumor necrosis factor-alpha (TNFA), interleukin-6 (IL6), serum amyloid A3 (SAA3), toll-like receptor 4 (TLR4), monocyte chemoattractant protein-1 (CCL2), and RANTES/chemokine C-C motif ligand 5 (CCL5) were analyzed using quantitative polymerase chain reaction (PCR) from tissue samples collected at slaughter from 5 nonpregnant/nonlactating Holstein cows. Prior to LPS challenge, SAA3 mRNA abundance was greater in MES than SUB tissue. Regardless of depot site, LPS led to greater mRNA abundance of TNFA and IL6 and was more pronounced for IL6 in MES. We also observed a marked increased in expression of CCL2, CCL5, TLR4, IL6, and TNFA in both MES and SUB during the 2-h incubation with saline alone (ie, the control). Because mRNA expression of the apoptotic markers B-cell CLL/lymphoma 2 (BCL2) and tumor protein p53 (TP53) did not differ during the 2-h incubation, it is less likely that the response to saline was a result of increased rate of cell death during incubation. Analysis using semiquantitative PCR of the 16s rRNA gene in cDNA from tissue explants revealed the presence of bacteria likely arising from contamination during sample collection. Furthermore, surfactant medium from about 50% of explant cultures had viable aerobic bacteria without differences between treatments or tissue samples. Thus, the presence of bacteria could partly explain the large increase in inflammatory-related genes after 2-h incubation with saline. The higher SAA3 expression in MES suggests that this acute-phase protein has a role in lipid metabolism and/or transport during an immune challenge. Overall, results provided evidence that adipose depots of dairy cows are capable of synthesizing chemokines and are immune responsive when exposed to inflammatory conditions that can arise from a pathogenic insult or during and soon after parturition.

Microarray analysis identifies matrix metalloproteinases (MMPs) as key genes whose expression is up-regulated in human adipocytes by macrophage-conditioned medium

White adipose tissue exhibits inflammation as tissue mass expands in obesity, involving macrophage infiltration and a direct inflammatory response by adipocytes. DNA microarrays and conditioned medium have been used to examine the effects of macrophages on global gene expression in human adipocytes. SGBS adipocytes, differentiated in culture, were treated with macrophage-conditioned medium (U937 cells) for 4 or 24 h; control cells received unconditioned medium. Agilent arrays comprising 44,000 probes were used to analyse gene expression. Microarray analysis identified 1,088 genes differentially expressed in response to the conditioned medium at both 4 and 24 h (754 up-regulated, 334 down-regulated at 24 h); these included genes associated with inflammation and macrophage infiltration. A cluster of matrix metalloproteinase genes were highly up-regulated at both time-points, including MMP1, MMP3, MMP9, MMP10, MMP12 and MMP19. At 4 and 24 h, MMP1 was the most highly up-regulated gene (>2,400-fold increase in mRNA at 24 h). ELISA measurements indicated that substantial quantities of MMP1 and MMP3 were released from adipocytes incubated with conditioned medium, with little release by control adipocytes. Treatment with TNFalpha induced substantial increases in MMP1 (>100-fold) and MMP3 (27-fold) mRNA level and MMP1 and MMP3 release in adipocytes, suggesting that this cytokine could contribute to the stimulation of MMP expression by macrophages. In conclusion, macrophage-secreted factors induce a major inflammatory response in human adipocytes, with expression of MMP family members being strongly up-regulated. The induction of MMP1 and other MMPs suggests that macrophages stimulate tissue remodelling during adipose tissue expansion in obesity.