Blockade of fatty acid signalling inhibits lipopolysaccharide-induced macrophage recruitment and progression of apical periodontitis

27-Hydroxycholesterol contributes to hypercholesterolemia-associated aggravation of apical periodontitis in ovariectomized rats and raloxifene counteracts its action

AIM

The influence of hypercholesterolemia on the development of apical periodontitis (AP) is inconclusive. Recent studies revealed that cholesterol metabolite 27-hydoxycholesterol (27HC) can affect cellular responses to bacterial infections and oestrogen status and raloxifene may influence its action. Herein, we aimed to examine the impact of 27HC on production of inflammatory mediators by macrophages and the regulatory function of raloxifene. The contribution of 27HC to AP development and the therapeutic effect of raloxifene were evaluated in a rat model.

METHODS

Murine macrophages J774 cells were used. The expression of inducible nitric oxide synthase (iNOS) was examined by Western blot. The concentrations of C-C motif chemokine ligand (CCL) 2 and 27HC were assessed by enzyme-linked immunosorbent assay. Colorimetric assay was used to evaluate cholesterol levels. Experimental AP was induced in ovariectomized (OVX) or un-operated rats receiving high-fat/high-cholesterol diet (HFHCD) or normal diet (ND). Micro-computed tomography and immunohistochemistry were employed to evaluate disease severity and the therapeutic effect of raloxifene.

RESULTS

Cholesterol enhanced 27HC production in macrophages. 27HC induced iNOS and CCL2 synthesis by macrophages and estradiol suppressed the responses. In our animal model of AP, HFHCD plus OVX significantly augmented serum and lesion tissue levels of 27HC (p < .05 versus the ND group). Lesion size, infiltration of CD68+ cells, and iNOS+ monocytes were increased in parallel with 27HC accumulation. Raloxifene inhibited pro-inflammatory effects of 27HC on macrophages and suppressed AP progression in HFHCD/OVX rats (p < .05 versus the vehicle control group).

CONCLUSIONS

Our results suggested that 27HC contributes to AP aggravation associated with hypercholesterolemia. Oestrogen deficiency may both enhance 27HC production and exacerbate its downstream action.

P. Gingivalis induce macrophage polarization by regulating hepcidin expression in chronic apical periodontitis

INTRODUCTION

Hepcidin, a central regulatory molecule of iron metabolism, is upregulated through the IL-6/STAT3 signaling pathway in inflammatory and infectious states, contributing to the pathogenesis of various diseases. In chronic apical periodontitis (CAP), Porphyromonas gingivalis (P. gingivalis) and its lipopolysaccharides (LPS) activate various immune responses in vivo, contributing to disease progression. This study evaluated the role and mechanism of hepcidin in P. gingivalis-induced bone tissue damage in CAP, focusing on its promotion of macrophage M1 polarization via the IL-6/STAT3 signaling pathway.

METHODS

We analyzed a GSE77459 dataset from the GEO database, containing data from inflammatory and normal dental pulp tissues. RT-qPCR and immunofluorescence staining were used to detect the expression of hepcidin in human CAP tissues and its relationship with macrophages. Mouse bone marrow derived macrophages (BMDMs) were cultured in vitro and stimulated with P. gingivalis LPS. The effects of Stattic on macrophage hepcidin expression, IL-6 expression, STAT3 phosphorylation, and macrophage polarization were detected by ELISA, western blotting, RT-qPCR, and flow cytometry, respectively.

RESULTS

Hepcidin expression in human inflammatory dental pulp tissues was upregulated via the IL-6/STAT3 pathway and correlated with macrophage polarization. Hepcidin-encoding genes were found to be highly expressed and primarily associated with M1 macrophages in CAP tissues. In vitro experiments revealed that P. gingivalis LPS stimulation induced macrophages to express hepcidin through the IL-6/STAT3 pathway and polarize to M1. Additionally, the IL-6/STAT3 pathway inhibitor Stattic suppressed these changes.

CONCLUSIONS

Our study demonstrates that in CAP, macrophages highly express hepcidin, which subsequently alters macrophage metabolism, regulates M1 polarization, and leads to bone tissue destruction.

FASN contributes to the pathogenesis of lupus by promoting TLR-mediated activation of macrophages and dendritic cells

Hyper-activations of monocytes/macrophages and dendritic cells (DCs) contribute to the pathogenesis of various autoimmune diseases, such as systemic lupus erythematosus (SLE). Fatty acid synthase (FASN) is essential for the de novo synthesis of long-chain fatty acids, which play a key role in controlling the activation, differentiation, and function of immune cells. However, the role of FASN in regulating the activations of monocytes/macrophages and DCs has not been studied. In this study, we investigated the involvement of the FASN in modulating the activations of macrophages and DCs, as well as the pathogenesis of SLE. Importantly, we observed a significant upregulation of FASN expression in monocytes and DCs from patients with SLE. This increase is strongly correlated with disease severity and activation status of the immune cells. Furthermore, overexpression of FASN significantly boosts the TLR4/7/9-mediated activation of macrophages and DCs, while knockdown of FASN markedly inhibits this activation. Notably, knockdown of FASN alleviates TLR7 agonist imiquimod (IMQ)-induced lupus in mice and the activation of macrophages and DCs. It makes more sense that pharmaceutical targeting of FASN by using TVB-2640 significantly alleviates IMQ-induced lupus in mice and the activation of macrophages and DCs, as well as in spontaneous lupus MRL/lpr mice. Thus, FASN contributes to the TLRs-mediated activation of macrophages and DCs, as well as the pathogenesis of SLE. More importantly, FASN inhibitor TVB-2640 is expected to be an effective drug in the treatment of SLE.

The Role of Autophagy on Osteogenesis of Dental Follicle Cells Under Inflammatory Microenvironment

OBJECTIVE

This study investigated the role of autophagy on osteogenesis of DFCs under inflammatory microenvironment during tooth eruption.

METHODS

DFCs were isolated and identified. Lipopolysaccharide (LPS) was used to construct the inflammatory microenvironment in vitro and in vivo. Cell viability was examined by CCK-8 assay. Osteogenic differentiation was evaluated by alkaline phosphatase (ALP) staining, alizarin red S (ARS) staining. The gene and protein levels were examined using qRT-PCR and western blot analysis, respectively. We observed the process of tooth eruption after local LPS injection by micro-CT and HE staining. Osteogenesis and autophagy were monitored through qRT-PCR, western blot and histological staining of specific markers.

RESULTS

LPS at the indicated concentrations did not produce toxic effects on DFCs, and significantly promoted the inflammatory gene expression. LPS inhibited osteogenic differentiation and activated autophagy in DFCs. Blocking autophagy with 3-MA reversed the expression of osteogenic markers in LPS-treated DFCs. Additionally, the eruption of LPS-treated teeth was accelerated and their DFs exhibited an increased expression of TNF-α and Beclin1, and decreased expression of ALP and RUNX2.

CONCLUSIONS

Autophagy was involved in the suppression of the DFCs osteogenesis in an LPS-induced inflammatory condition, suggesting the pivotal role of autophagy in inflammation-induced premature tooth eruption.

Blocking Gremlin1 inhibits M1 macrophage polarization through Notch1/Hes1 signaling pathway in apical periodontitis

BACKGROUND

Gremlin1 is a multifunctional protein whose expression is demonstrated to be involved in a series of physiology and pathological processes. The association between Gremlin1 and apcial periodontitis (AP) has been established. M1-polarized macrophages are crucial immune cells that exacerbate the progression of apical periodontal inflammatory response, but the function of Gremlin1 during macrophages activation in periapical lesions is still unclear. This study attempts to explore the regulatory effects of Gremlin1 on macrophage polarization on apical periodontitis microenviroment.

METHODS

Clinical specimens were used to determine the expression of Gremlin1 in periapical tissues by immunohistochemical (IHC) staining. Then, the disease models of periapical inflammation in rats were established, and adenovirus- associated virus (AAVs) was used to blockade Gremlin1 expression. Lentivirus carrying sh-Gremlin1 particles were used to transfect THP-1 induced M1-subtype macrophages. To assess the expression of associated molecules, Western blot, immunofluorescence staining were performed.

RESULTS

Gremlin1 was significantly up-regulated in the periapical tissues of subjects with AP as identified by IHC staining, and positively correlated with levels of M1 macrophage-associated genes. Rats AP model with inhibition of Gremlin1 in periapical lesions exhibited limited infiltration of macrophages and decreased expression of M1 macrophage-related genes in periapical lesions. Furthermore, Gremlin1 blockade substantially decreased the Notch1/Hes1 signaling pathway activation level. The in vitro experiments confirmed the above results.

CONCLUSION

Taken together, current study illustrated that the Gremlin1 suppression in periapical lesions inhibited M1 macrophage polarization through Notch1/Hes1 axis. Moreover, Gremlin1 may act as a potential candidate in the treatment of AP.

NLRP3 Cys126 palmitoylation by ZDHHC7 promotes inflammasome activation

Nucleotide oligomerization domain (NOD)-like receptor protein 3 (NLRP3) inflammasome hyperactivation contributes to many human chronic inflammatory diseases, and understanding how NLRP3 inflammasome is regulated can provide strategies to treat inflammatory diseases. Here, we demonstrate that NLRP3 Cys126 is palmitoylated by zinc finger DHHC-type palmitoyl transferase 7 (ZDHHC7), which is critical for NLRP3-mediated inflammasome activation. Perturbing NLRP3 Cys126 palmitoylation by ZDHHC7 knockout, pharmacological inhibition, or modification site mutation diminishes NLRP3 activation in macrophages. Furthermore, Cys126 palmitoylation is vital for inflammasome activation in vivo. Mechanistically, ZDHHC7-mediated NLRP3 Cys126 palmitoylation promotes resting NLRP3 localizing on the trans-Golgi network (TGN) and activated NLRP3 on the dispersed TGN, which is indispensable for recruitment and oligomerization of the adaptor ASC (apoptosis-associated speck-like protein containing a CARD). The activation of NLRP3 by ZDHHC7 is different from the termination effect mediated by ZDHHC12, highlighting versatile regulatory roles of S-palmitoylation. Our study identifies an important regulatory mechanism of NLRP3 activation that suggests targeting ZDHHC7 or the NLRP3 Cys126 residue as a potential therapeutic strategy to treat NLRP3-related human disorders.

The implications of FASN in immune cell biology and related diseases

Fatty acid metabolism, particularly fatty acid synthesis, is a very important cellular physiological process in which nutrients are used for energy storage and biofilm synthesis. As a key enzyme in the fatty acid metabolism, fatty acid synthase (FASN) is receiving increasing attention. Although previous studies on FASN have mainly focused on various malignancies, many studies have recently reported that FASN regulates the survival, differentiation, and function of various immune cells, and subsequently participates in the occurrence and development of immune-related diseases. However, few studies to date systematically summarized the function and molecular mechanisms of FASN in immune cell biology and related diseases. In this review, we discuss the regulatory effect of FASN on immune cells, and the progress in research on the implications of FASN in immune-related diseases. Understanding the function of FASN in immune cell biology and related diseases can offer insights into novel treatment strategies for clinical diseases.

Ferroptosis of macrophages facilitates bone loss in apical periodontitis via NRF2/FSP1/ROS pathway

Apical periodontitis (AP) is an infectious disease that causes periapical tissue inflammation and bone destruction. Ferroptosis, a novel type of regulated cell death, is closely associated with inflammatory diseases and the regulation of bone homeostasis. However, the exact involvement of ferroptosis in the bone loss of AP is not fully understood. In this study, human periapical tissues were collected, and a mouse model was established to investigate the role of ferroptosis in AP. Colocalization staining revealed that ferroptosis in macrophages contributes to the inflammatory bone loss associated with AP. A cell model was constructed using RAW 264.7 cells stimulated with LPS to further explore the mechanism underlying ferroptosis in macrophages upon inflammatory conditions, which exhibited ferroptotic characteristics. Moreover, downregulation of NRF2 was observed in ferroptotic macrophages, while overexpression of NRF2 upregulated the level of FSP1, leading to a reduction in reactive oxygen species (ROS) in macrophages. Additionally, ferroptotic macrophages released TNF-α, which activated the p38 MAPK signaling pathway and further increased ROS accumulation in macrophages. In vitro co-culture experiments demonstrated that the osteogenic ability of mouse bone marrow stromal cells (BMSCs) was suppressed with the stimulation of TNF-α from ferroptotic macrophages. These findings suggest that the TNF-α autocrine-paracrine loop in ferroptotic macrophages can inhibit osteogenesis in BMSCs through the NRF2/FSP1/ROS signaling pathway, leading to bone loss in AP. This study highlights the potential therapeutic value of targeting ferroptosis in the treatment of inflammatory bone diseases.

Pathophysiology of cellulite: Possible involvement of selective endotoxemia

The most relevant hallmarks of cellulite include a massive protrusion of superficial adipose tissue into the dermis, reduced expression of the extracellular glycoprotein fibulin-3, and an unusually high presence of MUSE cells in gluteofemoral white adipose tissue (gfWAT) that displays cellulite. Also typical for this condition is the hypertrophic nature of the underlying adipose tissue, the interaction of adipocytes with sweat glands, and dysfunctional lymph and blood circulation as well as a low-grade inflammation in the areas of gfWAT affected by cellulite. Here, we propose a new pathophysiology of cellulite, which connects this skin condition with selective accumulation of endogenous lipopolysaccharides (LPS) in gfWAT. The accumulation of LPS within a specific WAT depot has so far not been considered as a possible pathophysiological mechanism triggering localized WAT modifications, but may very well be involved in conditions such as cellulite and, secondary to that, lipedema.