Macrophage-induced preadipocyte survival depends on signaling through Akt, ERK1/2, and reactive oxygen species

HnRNPA2B1 Aggravates Inflammation by Promoting M1 Macrophage Polarization

Macrophages have critical contributions to both acute and chronic inflammatory diseases, for example, bowel disease and obesity, respectively. However, little is known about the post-transcriptional regulatory mechanisms in macrophage-mediated inflammatory diseases. hnRNPA2B1 (A2B1) is an RNA binding protein for mRNA fate determination. We showed that hnRNPA2B1 mRNA levels were increased in colon in dextran sodium sulfate (DSS)-induced colitis mice and in epididymal white adipose tissue (eWAT) and spleen of high-fat-diet (HFD)-induced obese mice. Consistently, mice with haploinsufficiency of A2B1 (A2B1 HET) are protected against DSS-induced acute colitis and HFD-induced obesity, with decreased M1 macrophages polarization in colon, eWAT and spleen. Mechanistically, A2B1 mRNA and protein levels were increased in LPS-stimulated RAW 264.7 macrophages, and A2B1 enhanced RNA stability of pro-inflammatory genes Tnfα, Il-6 and Il-1β for the regulation of macrophages polarization. Interestingly, A2B1 HET mice exhibited reduced white fat expansion, which was influenced by macrophages, since conditioned medium from macrophages with A2B1 manipulation significantly changed preadipocyte proliferation. Our data demonstrate that A2B1 plays a vital role in macrophage-mediated inflammation via regulating mRNA stability, suggesting that A2B1 may be served as a promising target for the intervention of acute and chronic inflammatory diseases.

Immune Cell Regulation of White Adipose Progenitor Cell Fate

Adipose tissue is essential for energy storage and endocrine regulation of metabolism. Imbalance in energy intake and expenditure result in obesity causing adipose tissue dysfunction. This alters cellular composition of the stromal cell populations and their function. Moreover, the individual cellular composition of each adipose tissue depot, regulated by environmental factors and genetics, determines the ability of the depots to expand and maintain its endocrine and storage function. Thus, stromal cells modulate adipocyte function and vice versa. In this mini-review we discuss heterogeneity in terms of composition and fate of adipose progenitor subtypes and their interactions with and regulation by different immune cell populations. Immune cells are the most diverse cell populations in adipose tissue and play essential roles in regulating adipose tissue function via interaction with adipocytes but also with adipocyte progenitors. We specifically discuss the role of macrophages, mast cells, innate lymphoid cells and T cells in the regulation of adipocyte progenitor proliferation, differentiation and lineage commitment. Understanding the factors and cellular interactions regulating preadipocyte expansion and fate decision will allow the identification of novel mechanisms and therapeutic strategies to promote healthy adipose tissue expansion without systemic metabolic impairment.

Effects of macrophage regulation on fat grafting survival: Improvement, mechanisms, and potential application-A review

BACKGROUND

Autologous fat grafting has become a popular tool in plastic surgery to solve soft tissue defects and achieve skin rejuvenation, but the volume loss after transplantation remains a disturbing problem. In recent years, some new strategies have improved the outcome to some extent, but the fat graft retention is still far from ideal, so there remains a wide development prospect in this field. Macrophages are closely related to the local microenvironment and tissue regeneration, and their role in fat grafting has been increasingly highlighted.

AIMS

This article was aimed to review the efficacy, possible mechanisms, and potential application of macrophage regulation on fat grafting, as well as concerns and future perspectives of this filed.

METHODS

A retrospective review of the published data was conducted.

RESULTS

Most studies indicated that up-regulating M2 macrophages during fat grafting would improve fat retention via promoting neovascularization. M2 macrophages could secrete several pro-angiogenic factors, accelerate extracellular matrix (ECM) remodeling, and directly function on endothelial cells to encourage vascular expansion. In addition, macrophages could influence the proliferation, apoptosis, and adipogenic differentiation of preadipocytes.

CONCLUSIONS

During autologous fat grafting, appropriately regulating macrophages may become a promising method to increase fat retention. Nevertheless, the M2 macrophage polarizing agents, treatment opportunity, and contraindications require further discussion. We hope our work could promote more in-depth studies in this field, and we are looking forward to a standard procedure for the macrophage therapy in clinical practice.

Human macrophages stimulate expression of inflammatory mediators in adipocytes; effects of second-generation antipsychotics and glucocorticoids on cellular cross-talk

OBJECTIVE

Adipose tissue inflammation and distorted macrophage-adipocyte communication are positively associated with metabolic disturbances. Some pharmacological agents, such as second-generation antipsychotics (SGAs) and synthetic glucocorticoid (GC) dexamethasone, tend to induce adverse metabolic side effects and the underlying mechanisms are not fully understood. Our work aimed to study whether SGAs and dexamethasone affect macrophage phenotype and macrophage-adipocyte communication on gene expression level. We selected the model involving THP-1-derived macrophages, polarized into M0, M1, and M2 phenotypes, and primary human mature subcutaneous adipocytes.

METHODS

Abdominal subcutaneous adipose tissue needle biopsies were obtained from 6 healthy subjects (4F/2M; age: 22-64 yr; BMI: 21.7-27.6 kg/m2) followed by isolation of mature adipocytes. THP-1-human monocytic cell line was used for the study. THP-1 monocytes were differentiated and polarized into M0 (naïve), M1 (classically activated), and M2 (alternatively activated) macrophages. During and after polarization the macrophages were treated for 24 h without (control) or with therapeutic and supra-therapeutic concentrations of olanzapine (0.2 µM and 2.0 µM), aripiprazole (1.0 µM and 10 µM) and its active metabolite dehydroaripiprazole (0.4 µM and 4.0 µM). Isolated mature human adipocytes were co-incubated with THP-1-derived polarized macrophages pre-treated with SGAs after their polarization. Adipocytes and macrophages were collected before and after co-culture for mRNA expression analysis of genes involved in inflammation.

RESULTS

Co-incubation of mature human adipocytes with human macrophages, regardless of polarization, resulted in a marked induction of pro-inflammatory cytokines in adipocytes, including IL1B, IL6, TNFA, and IL10. Remarkably, it did not affect the expression of adipokines and genes involved in the regulation of energy, lipid, and glucose metabolism in adipocytes. Dexamethasone markedly reduced gene expression of pro-inflammatory cytokines in macrophages and prevented macrophage-induced inflammatory response in adipocytes. In contrast, SGAs did not affect macrophage-adipocyte communication and had a minute anti-inflammatory effect in macrophages at supra-therapeutic concentrations. Interestingly, the adipocytes co-incubated with M1 macrophages pre-treated with dexamethasone and SGAs particularly the supra-therapeutic concentration of olanzapine, reduced expression of LPL, LIPE, AKT1, and SLC2A4, suggesting that the expression of metabolic genes in adipocytes was dependent on the presence of pro-inflammatory M1 macrophages.

CONCLUSION

Together, these data suggest that macrophages induce expression of pro-inflammatory genes in human subcutaneous adipocytes without affecting the expression of adipokines or genes involved in energy regulation. Furthermore, our findings demonstrated that SGAs and dexamethasone had a mild effect on macrophage-adipocyte communication in M1 macrophage phenotype.

Impact of Conventional and Atypical MAPKs on the Development of Metabolic Diseases

The family of mitogen-activated protein kinases (MAPKs) consists of fourteen members and has been implicated in regulation of virtually all cellular processes. MAPKs are divided into two groups, conventional and atypical MAPKs. Conventional MAPKs are further classified into four sub-families: extracellular signal-regulated kinases 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK1, 2 and 3), p38 (α, β, γ, δ), and extracellular signal-regulated kinase 5 (ERK5). Four kinases, extracellular signal-regulated kinase 3, 4, and 7 (ERK3, 4 and 7) as well as Nemo-like kinase (NLK) build a group of atypical MAPKs, which are activated by different upstream mechanisms than conventional MAPKs. Early studies identified JNK1/2 and ERK1/2 as well as p38α as a central mediators of inflammation-evoked insulin resistance. These kinases have been also implicated in the development of obesity and diabetes. Recently, other members of conventional MAPKs emerged as important mediators of liver, skeletal muscle, adipose tissue, and pancreatic β-cell metabolism. Moreover, latest studies indicate that atypical members of MAPK family play a central role in the regulation of adipose tissue function. In this review, we summarize early studies on conventional MAPKs as well as recent findings implicating previously ignored members of the MAPK family. Finally, we discuss the therapeutic potential of drugs targeting specific members of the MAPK family.

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.

Macrophage-induced adipose tissue dysfunction and the preadipocyte: should I stay (and differentiate) or should I go?

Adipose tissue can be regarded as a multidepot organ responsible for metabolic homeostasis by managing sophisticated energy transactions as well as by producing bioactive molecules that regulate insulin sensitivity and immune and vascular responses. Chronic nutrient excess expands adipose tissue, and concomitant variations in its cellular and matrix remodeling can affect the extent of the metabolic dysfunction that is associated with obesity. Preadipocytes, also termed adipose progenitor cells, play a pivotal role in determining whether a dysfunctional hypertrophic state arises as opposed to a hyperplastic process in which mature adipocytes remain relatively responsive. Obesity is associated with infiltration of macrophages, and these immune cells have been shown to communicate with preadipocytes to influence how they differentiate, survive, and proliferate. Understanding macrophage-preadipocyte interactions and their effect on adipose remodeling mechanisms may identify potential therapeutic molecular targets to improve adipose tissue function, even in the face of obesity.

The activation state of macrophages alters their ability to suppress preadipocyte apoptosis

Adipose tissue contains macrophages whose state of activation is regulated as obesity develops. Macrophage-secreted factors influence critical processes involved in adipose tissue homeostasis, including preadipocyte proliferation and differentiation into adipocytes. Macrophage-conditioned medium (MacCM) from J774A.1 macrophages protects 3T3-L1 preadipocytes from apoptosis through platelet-derived growth factor (PDGF) signaling. Here, we investigated the effect of macrophage activation on MacCM-dependent preadipocyte survival. MacCM was prepared following activation of either J774A.1 macrophages with lipopolysaccharide (LPS) or human primary monocyte-derived macrophages (MD-macrophages) with LPS or interleukin 4 (IL4). 3T3-L1 and human primary preadipocytes were induced to undergo apoptosis in MacCM, and apoptosis was quantified by cell enumeration or Hoechst nuclear staining. Preadipocyte PDGF signaling was assessed by immunoblot analysis of phosphorylated PDGF receptor, Akt, and ERK1/2. Pro-inflammatory activation of J774A.1 macrophages with LPS inhibited the pro-survival activity of MacCM on 3T3-L1 preadipocytes, despite intact PDGF signaling. Upregulation of macrophage tumor necrosis factor a (TNFα) expression occurred in response to LPS, and TNFα was demonstrated to be responsible for the inability of LPS-J774A.1-MacCM to inhibit preadipocyte apoptosis. Furthermore, MacCM from human MD-macrophages (MD-MacCM) inhibited apoptosis of primary human preadipocytes. MD-MacCM from LPS-treated macrophages, but not IL4-treated anti-inflammatory macrophages, was unable to protect human preadipocytes from cell death. In both murine cell lines and human primary cells, pro-inflammatory activation of macrophages inhibits their pro-survival activity, favoring preadipocyte death. These findings may be relevant to preadipocyte fate and adipose tissue remodeling in obesity.

An inflammatory micro-environment promotes human adipocyte apoptosis

Obesity-associated macrophage infiltration into adipose tissue is responsible for both local and systemic inflammation. Recent findings suggest fat cell apoptosis as an initiator of macrophage recruitment. Here, we investigated the effects of an inflammatory micro-environment on fat cells using human THP-1 macrophages and SGBS adipocytes. Macrophage-secreted factors induced insulin resistance, inhibited insulin-stimulated Akt phosphorylation, and induced apoptosis of adipocytes. The apoptosis-inducing effect was even more pronounced in direct co-cultures of adipocytes and macrophages. Our data suggest a link between insulin resistance and apoptosis sensitivity. Accordingly, pharmacological and genetic inhibition of insulin signaling at the level of Akt2 sensitized adipocytes to apoptosis induction by macrophage-secreted factors. In conclusion, we describe here a novel interaction of macrophages and fat cells, i.e. induction of apoptosis. Our data suggest a feed-forward cycle in which macrophages further drive the inflammatory process by inducing insulin resistance and concomitant apoptosis of adipocytes.

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.