STAT6 Signaling Mediates PPARγ Activation and Resolution of Acute Sterile Inflammation in Mice

PPAR-γ in Melanoma and Immune Cells: Insights into Disease Pathogenesis and Therapeutic Implications

Changes in skin pigmentation, like hyperpigmentation or moles, can affect appearance and social life. Unlike locally containable moles, malignant melanomas are aggressive and can spread rapidly, disproportionately affecting younger individuals with a high potential for metastasis. Research has shown that the peroxisome proliferator-activated receptor gamma (PPAR-γ) and its ligands exhibit protective effects against melanoma. As a transcription factor, PPAR-γ is crucial in functions like fatty acid storage and glucose metabolism. Activation of PPAR-γ promotes lipid uptake and enhances sensitivity to insulin. In many cases, it also inhibits the growth of cancer cell lines, like breast, gastric, lung, and prostate cancer. In melanoma, PPAR-γ regulates cell proliferation, differentiation, apoptosis, and survival. During tumorigenesis, it controls metabolic changes and the immunogenicity of stromal cells. PPAR-γ agonists can target hypoxia-induced angiogenesis in tumor therapy, but their effects on tumors can be suppressive or promotional, depending on the tumor environment. Published data show that PPAR-γ-targeting agents can be effective in specific groups of patients, but further studies are needed to understand lesser-known biological effects of PPAR-γ and address the existing safety concerns. This review provides a summary of the current understanding of PPAR-γ and its involvement in melanoma.

FABP7 in Hepatic Macrophages Promotes Fibroblast Activation and CD4+ T-Cell Migration by Regulating M2 Polarization During Liver Fibrosis

Hepatic macrophages respond to various microenvironmental signals and play a central role in maintaining hepatic homeostasis, dysregulation of which leads to various liver diseases. Fatty acid-binding protein 7 (FABP7), an intracellular lipid chaperone for polyunsaturated fatty acids (PUFAs), is highly expressed in liver macrophages. However, the mechanisms by which FABP7 regulates hepatic macrophage activation remain unclear. Therefore, we aimed to elucidate the mechanisms underlying the effects of FABP7 on the functions of hepatic macrophages in metabolic dysfunction-associated steatohepatitis (MASH) and liver fibrosis models. In this study, we found that FABP7-deficient macrophages exhibited impaired M2 polarization, which reduced the fibrotic response of myofibroblasts and CD4+ T-cell infiltration into the liver tissues in a carbon tetrachloride (CCl4)-induced hepatic fibrosis model. In vitro, FABP7-deficient macrophages exhibited decreased levels of peroxisome proliferator-activated receptor (PPAR)-γ and its target genes, including C-C motif chemokine ligand (CCL)-17 and transforming growth factor-β (TGF-β), compared to the wild-type (WT) macrophages post-interleukin (IL)-4 stimulation. However, these effects were inhibited by a PPARγ inhibitor. IL-4-stimulated WT macrophages also promoted CD4+ T-cell migration and hepatic fibroblast (TWNT-1 hepatic stellate cell [HSC]) activation, indicated by increased mRNA levels of actin alpha 2, smooth muscle (ACTA2), and collagen type I alpha 1 (COL1A1); however, these effects were inhibited in FABP7-deficient macrophages. Overall, FABP7 in hepatic macrophages modulated the crosstalk between hepatic fibroblasts and T cells by regulating M2 polarization. Therefore, regulation of hepatic macrophage function by FABP7 is a potential therapeutic target for liver fibrosis.

Efferocytosis in atherosclerosis

Cardiovascular disease is the leading cause of death worldwide, and it commonly results from atherosclerotic plaque progression. One of the increasingly recognized drivers of atherosclerosis is dysfunctional efferocytosis, a homeostatic mechanism responsible for the clearance of dead cells and the resolution of inflammation. In atherosclerosis, the capacity of phagocytes to participate in efferocytosis is hampered, leading to the accumulation of apoptotic and necrotic tissue within the plaque, which results in enlargement of the necrotic core, increased luminal stenosis and plaque inflammation, and predisposition to plaque rupture or erosion. In this Review, we describe the different forms of programmed cell death that can occur in the atherosclerotic plaque and highlight the efferocytic machinery that is normally implicated in cardiovascular physiology. We then discuss the mechanisms by which efferocytosis fails in atherosclerosis and other cardiovascular and cardiometabolic diseases, including myocardial infarction and diabetes mellitus, and discuss therapeutic approaches that might reverse this pathological process.

The role of foam cells in spinal cord injury: challenges and opportunities for intervention

Spinal cord injury (SCI) results in a large amount of tissue cell debris in the lesion site, which interacts with various cytokines, including inflammatory factors, and the intrinsic glial environment of the central nervous system (CNS) to form an inhibitory microenvironment that impedes nerve regeneration. The efficient clearance of tissue debris is crucial for the resolution of the inhibitory microenvironment after SCI. Macrophages are the main cells responsible for tissue debris removal after SCI. However, the high lipid content in tissue debris and the dysregulation of lipid metabolism within macrophages lead to their transformation into foamy macrophages during the phagocytic process. This phenotypic shift is associated with a further pro-inflammatory polarization that may aggravate neurological deterioration and hamper nerve repair. In this review, we summarize the phenotype and metabolism of macrophages under inflammatory conditions, as well as the mechanisms and consequences of foam cell formation after SCI. Moreover, we discuss two strategies for foam cell modulation and several potential therapeutic targets that may enhance the treatment of SCI.

Sesquiterpene from Artemisia argyi seed extracts: A new anti-acute peritonitis agent that suppresses the MAPK pathway and promotes autophagy

To find novel anti-inflammatory drugs, we screened anti-inflammatory compounds from 18 different types of Artemisia argyi seed extracts. The in vitro and in vivo anti-inflammatory activities of the screened compounds and their mechanisms were characterized. We first detected the cytotoxic effect of the compounds on RAW264.7 cells and the inhibitory effect on LPS-induced NO release. It was found that sesquiterpenoids CA-2 and CA-4 had low cytotoxic and strong NO inhibitory activity with an IC50 of 4.22 ± 0.61 μM and 2.98 ± 0.23 μM for NO inhibition, respectively. Therefore, compound CA-4 was studied in depth. We found that compound CA-4 inhibited LPS-induced pro-inflammatory factor production and M1 macrophage differentiation in RAW264.7 cells. Additionally, CA-4 inhibited the expression of p-ERK1/2, p-JNK, iNOS, and COX-2 by blocking the MAPK signaling pathway. CA-4 also promoted the expression of autophagy-related proteins such as LC3 II and Beclin-1 by inhibiting activation of the PI3K/AKT/mTOR signaling pathway, and promoted the generation of autophagosomes. Finally, CA-4 significantly inhibited the degree of inflammation in mice with acute peritonitis, showing good anti-inflammatory activity in vivo. Consequently, compound CA-4 may be a promising drug for the treatment of acute inflammatory diseases and provide new ideas for the synthesis of novel anti-inflammatory compounds.

Anti-inflammatory and immunomodulating effects of rilpivirine: Relevance for the therapeutics of chronic liver disease

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease (CLD) worldwide and inflammation is key to its progression/resolution. As we have previously described that rilpivirine (RPV) is hepatoprotective in murine models of CLD, here we determine the molecular mechanisms involved, focusing on its anti-inflammatory and immunomodulating properties. They were evaluated in vitro (human hepatic cell lines of the major hepatic cell types), in vivo (liver samples from a murine nutritional model of NAFLD) and ex vivo (peripheral blood mononuclear cells -PBMC- from patients with CLD). Transcriptomic analysis of liver samples from NAFLD mice showed RPV down-regulated biological processes associated with the inflammatory response (NF-κB/IκB signaling and mitogen-activated protein kinase -MAPK- activity) and leukocyte chemotaxis and migration. We observed a decrease in Adgre1 and Ccr2 expression and in the number of CCR2 + cells in the periportal areas of RPV-treated NAFLD mice. This RPV-induced effect on the CCL2/CCR2 axis was confirmed in vitro. A similar result was also obtained with CXCL10/IP10, one of the main chemokines in the liver. RPV also diminished activation of MAP kinases p38 and JNK. In addition, RPV inhibited the NLRP3 inflammasome pathway in vitro, decreasing NLRP3 protein expression, caspase-1 activation and IL-1β gene expression. RPV was also proven anti-inflammatory in PBMC from patients with CLD treated ex vivo. In conclusion, beyond its well-described role in antiretroviral therapy, RPV manifests anti-inflammatory and immunoregulatory effects, a finding that could be of great relevance for the search of novel targets or repositioning strategies for CLD.

Investigation of effective components and action mechanism of Yiguanjian in treatment of liver fibrosis based on network pharmacology

BACKGROUND

Traditional Chinese medicine compounds are characterized by the comprehensive adjustment of multiple components and show unique advantages in the prevention and treatment of liver fibrosis. Yiguanjian (YGJ) is a famous prescription for nourishing Yin to soothe the liver, which can improve the symptoms of liver fibrosis, and understanding its anti-liver fibrosis mechanism can promote its development and use.

AIM

To explore the mechanism of YGJ in the treatment of liver fibrosis through network pharmacology and to experi-mentally validate the initial results obtained.

METHODS

Components of YGJ and potentially targeted proteins were downloaded from the Traditional Chinese Medicine Systems Pharmacology (TCMSP) database. The targets of liver fibrosis were accessed from GeneCard and OMIM databases. STRING database was utilized to construct a protein-protein interaction (PPI) network based on the components of YGJ and the targets of liver fibrosis. The PPI network was subjected to random walk with restart (RWR) to obtain key genes, and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were performed based on the DAVID database. For animal experimental validation, eighteen SD rats were randomly assigned to a normal group, a model group, and a YGJ group. The rats in the model group and YGJ group were intraperitoneally injected with 50% CCl₄ olive oil solution for 6 wk to induce liver fibrosis, and rats in the normal group were intraperitoneally injected with the same amount of olive oil solution. Then, the rats of the YGJ group were given YGJ decoction (6.67 g/kg) daily for 4 weeks. Meanwhile, rats in the other groups were given distilled water. Blood and liver samples were collected, and the levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in the serum of rats were detected with an automated analyzer. Pathological changes in liver tissue were observed by hematoxylin-eosin (HE) and Masson staining. Western blot and qRT-PCR were used to detect the expression of key proteins and genes in the liver.

RESULTS

A total of 52 components and 186 potential targets of YGJ were obtained, and 1080 targets of liver fibrosis were screened. The top 10 genes with the high-affinity scores to the drug targets were STAT6, SRC, MAPK3, STX1A, EP300, STAT3, PLG, CTNNB1, CDKN1B, and CANX. The top 50 genes were mainly enriched in response to PI3K- Akt signaling pathway and FoxO signaling pathway, etc. In CCl4-induced liver fibrosis rats, YGJ decoction could significantly improve liver lesions and reduce fibrosis. YGJ decoction could reduce α-SMA expression, promote the expression of phosphorylated STAT6, increase the protein expression of PPAR-γ and CD163 and the mRNA expression of Arg-1, CD206, and CD163, and inhibit the gene expression of IL-6.

CONCLUSION

The therapeutic effect of YGJ decoction for liver fibrosis involves multiple components and multiple pathways, including the STAT6/PPAR-γ pathway.

Inhibition of STAT6 with Antisense Oligonucleotides Enhances the Systemic Antitumor Effects of Radiotherapy and Anti-PD-1 in Metastatic Non-Small Cell Lung Cancer

Diverse factors contribute to the limited clinical response to radiotherapy (RT) and immunotherapy in metastatic non-small cell lung cancer (NSCLC), among which is the ability of these tumors to recruit a retinue of suppressive immune cells-such as M2 tumor-associated macrophages (TAM)-thereby establishing an immunosuppressive tumor microenvironment that contributes to tumor progression and radio resistance. M2 TAMs are activated by the STAT6 signaling pathway. Therefore, we targeted STAT6 using an antisense oligonucleotide (ASO) along with hypofractionated RT (hRT; 3 fractions of 12 Gy each) to primary tumors in three bilateral murine NSCLC models (Lewis lung carcinoma, 344SQ-parental, and anti-PD-1-resistant 344SQ lung adenocarcinomas). We found that STAT6 ASO plus hRT slowed growth of both primary and abscopal tumors, decreased lung metastases, and extended survival. Interrogating the mechanism of action showed reduced M2 macrophage tumor infiltration, enhanced TH1 polarization, improved T-cell and macrophage function, and decreased TGFβ levels. The addition of anti-PD-1 further enhanced systemic antitumor responses. These results provide a preclinical rationale for the pursuit of an alternative therapeutic approach for patients with immune-resistant NSCLC.

Delayed revascularization in acute ischemic stroke patients

Stroke shares a significant burden of global mortality and disability. A significant decline in the quality of life is attributed to the so-called post-stroke cognitive impairment including mild to severe cognitive alterations, dementia, and functional disability. Currently, only two clinical interventions including pharmacological and mechanical thrombolysis are advised for successful revascularization of the occluded vessel. However, their therapeutic effect is limited to the acute phase of stroke onset only. This often results in the exclusion of a significant number of patients who are unable to reach within the therapeutic window. Advances in neuroimaging technologies have allowed better assessment of salvageable penumbra and occluded vessel status. Improvement in diagnostic tools and the advent of intravascular interventional devices such as stent retrievers have expanded the potential revascularization window. Clinical studies have demonstrated positive outcomes of delayed revascularization beyond the recommended therapeutic window. This review will discuss the current understanding of ischemic stroke, the latest revascularization doctrine, and evidence from clinical studies regarding effective delayed revascularization in ischemic stroke.

Zymosan-Induced Murine Peritonitis Is Associated with an Increased Sphingolipid Synthesis without Changing the Long to Very Long Chain Ceramide Ratio

Sphingolipids are key molecules in inflammation and defense against pathogens. Their role in dectin-1/TLR2-mediated responses is, however, poorly understood. This study investigated the sphingolipidome in the peritoneal fluid, peritoneal cells, plasma, and spleens of mice after intraperitoneal injection of 0.1 mg zymosan/mouse or PBS as a control. Samples were collected at 2, 4, 8, and 16 h post-injection, using a total of 36 mice. Flow cytometry analysis of peritoneal cells and measurement of IL-6, IL-1β, and TNF-α levels in the peritoneal lavages confirmed zymosan-induced peritonitis. The concentrations of sphingoid bases, dihydroceramides, ceramides, dihydrosphingomyelins, sphingomyelins, monohexosylceramides, and lactosylceramides were increased after zymosan administration, and the effects varied with the time and the matrix measured. The greatest changes occurred in peritoneal cells, followed by peritoneal fluid, at 8 h and 4 h post-injection, respectively. Analysis of the sphingolipidome suggests that zymosan increased the de novo synthesis of sphingolipids without change in the C14-C18:C20-C26 ceramide ratio. At 16 h post-injection, glycosylceramides remained higher in treated than in control mice. A minor effect of zymosan was observed in plasma, whereas sphinganine, dihydrosphingomyelins, and monohexosylceramides were significantly increased in the spleen 16 h post-injection. The consequences of the observed changes in the sphingolipidome remain to be established.

Trihydroxyxanthones from the heartwood of Maclura cochinchinensis modulate M1/M2 macrophage polarisation and enhance surface TLR4

The anti-inflammatory actions of phytochemicals have attracted much attention due to the current state of numerous inflammatory disorders. Thai traditional medicine uses Maclura cochinchinensis (Lour.) Corner to treat chronic fever and various inflammatory diseases, as well as to maintain normal lymphatic function. Five flavonoids and five xanthones were isolated from the heartwood of M. cochinchinensis and we investigated the anti-inflammatory properties of the isolated compounds. All isolated compounds possessed an anti-inflammatory effect by decreasing prostaglandin E₂ (PGE₂) synthesis in lipopolysaccharide (LPS)-activated murine macrophages with varying degrees of potency. The greatest decrease in M1 inflammatory mediators, nitric oxide, PGE₂, and proinflammatory cytokines was observed with 1,3,7-trihydroxyxanthone and 1,3,5-trihydroxyxanthone treatment of LPS-activated macrophages. The anti-inflammatory mechanism of the two xanthones is mediated by the suppression of inducible nitric oxide synthase, cyclooxygenase-2, and phosphatidylinositol 3-kinase/protein kinase B expression and the upregulation of M2 anti-inflammatory signalling proteins phosphorylated signal transducer and activator of transcription 6 and peroxisome proliferator-activated receptors-γ. 1,3,7-Trihydroxyxanthone exhibits superior induction of anti-inflammatory M2 mediator of LPS-activated macrophages by upregulating arginase1 expression. Following the resolution of inflammation, the two xanthones enhanced surface TLR4 expression compared to LPS-stimulated cells, possibly preserving macrophage function. Our research highlights the role of the two xanthones in modulating the M1/M2 macrophage polarisation to reduce inflammation and retain surface TLR4 once inflammation has been resolved. These findings support the use of xanthones for their anti-inflammatory effects in treating inflammatory dysregulation.

Dual targeting of mTOR/IL-17A and autophagy by fisetin alleviates psoriasis-like skin inflammation

Psoriasis is a chronic autoimmune inflammatory skin disorder characterized by epidermal hyperplasia and aberrant immune response. In addition to aberrant cytokine production, psoriasis is associated with activation of the Akt/mTOR pathway. mTOR/S6K1 regulates T-lymphocyte activation and migration, keratinocytes proliferation and is upregulated in psoriatic lesions. Several drugs that target Th1/Th17 cytokines or their receptors have been approved for treating psoriasis in humans with variable results necessitating improved therapies. Fisetin, a natural dietary polyphenol with anti-oxidant and anti-proliferative properties, covalently binds mTOR/S6K1. The effects of fisetin on psoriasis and its underlying mechanisms have not been clearly defined. Here, we evaluated the immunomodulatory effects of fisetin on Th1/Th17-cytokine-activated adult human epidermal keratinocytes (HEKa) and anti-CD3/CD28-stimulated inflammatory CD4+ T cells and compared these activities with those of rapamycin (an mTOR inhibitor). Transcriptomic analysis of HEKa revealed 12,713 differentially expressed genes (DEGs) in the fisetin-treated group compared to 7,374 DEGs in the rapamycin-treated group, both individually compared to a cytokine treated group. Gene ontology analysis revealed enriched functional groups related to PI3K/Akt/mTOR signaling pathways, psoriasis, and epidermal development. Using in silico molecular modeling, we observed a high binding affinity of fisetin to IL-17A. In vitro, fisetin significantly inhibited mTOR activity, increased the expression of autophagy markers LC3A/B and Atg5 in HEKa cells and suppressed the secretion of IL-17A by activated CD4+ T lymphocytes or T lymphocytes co-cultured with HEKa. Topical administration of fisetin in an imiquimod (IMQ)-induced mouse psoriasis model exhibited a better effect than rapamycin in reducing psoriasis-like inflammation and Akt/mTOR phosphorylation and promoting keratinocyte differentiation and autophagy in mice skin lesions. Fisetin also significantly inhibited T-lymphocytes and F4/80+ macrophage infiltration into skin. We conclude that fisetin potently inhibits IL-17A and the Akt/mTOR pathway and promotes keratinocyte differentiation and autophagy to alleviate IMQ-induced psoriasis-like disease in mice. Altogether, our findings suggest fisetin as a potential treatment for psoriasis and possibly other inflammatory skin diseases.

Aurantiamide promotes M2 polarization of microglial cells to improve the cognitive ability of mice with Alzheimer's disease

This work aimed to investigate the effect of aurantiamide (Aur) in promoting the M2 polarization of microglial cells to improve the cognitive ability of mice with Alzheimer's disease (AD). The M2 polarization of BV2 cells was induced by interleukin-4 (IL-4) treatment.Aur promoted the M2 polarization of BV2 cells, and up-regulated the expression of CD206 and SOCS3. In the meantime, it increased TGF-β1, Arg-1 and IL-10 levels, and promoted the polarization of JAK1-STAT6. Treatment with STAT6 inhibitor antagonized the effect of Aur. Besides, the cognitive ability of AD mice was improved after Aur treatment, meanwhile, the expression of CD206 was up-regulated, while that of IBA-1 was down-regulated. Aur promotes the M2 polarization of microglial cells to improve the cognitive ability of AD mice, and such effect is related to the STAT6 signal.

Adipose tissue aging is regulated by an altered immune system

Adipose tissue is a widely distributed organ that plays a critical role in age-related physiological dysfunctions as an important source of chronic sterile low-grade inflammation. Adipose tissue undergoes diverse changes during aging, including fat depot redistribution, brown and beige fat decrease, functional decline of adipose progenitor and stem cells, senescent cell accumulation, and immune cell dysregulation. Specifically, inflammaging is common in aged adipose tissue. Adipose tissue inflammaging reduces adipose plasticity and pathologically contributes to adipocyte hypertrophy, fibrosis, and ultimately, adipose tissue dysfunction. Adipose tissue inflammaging also contributes to age-related diseases, such as diabetes, cardiovascular disease and cancer. There is an increased infiltration of immune cells into adipose tissue, and these infiltrating immune cells secrete proinflammatory cytokines and chemokines. Several important molecular and signaling pathways mediate the process, including JAK/STAT, NFκB and JNK, etc. The roles of immune cells in aging adipose tissue are complex, and the underlying mechanisms remain largely unclear. In this review, we summarize the consequences and causes of inflammaging in adipose tissue. We further outline the cellular/molecular mechanisms of adipose tissue inflammaging and propose potential therapeutic targets to alleviate age-related problems.

Tofacitinib enhances IGF1 via inhibiting STAT6 transcriptionally activated-miR-425-5p to ameliorate inflammation in RA-FLS

Rheumatoid arthritis (RA) is a systemic autoimmune disease, which has been reported closely associated with the dysfunction of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway. This study aims to explore the potential therapeutic effect of Tofacitinib, a putative JAK/STAT inhibitor, in RA. Tofacitinib suppressed proliferation and accelerated apoptosis of rheumatoid arthritis synovial fibroblasts (RA-FLS) as confirmed by CCK-8, EdU and Western blot assays. Tofacitinib significantly inhibited expression of pro-inflammatory factors including tumor necrosis factor-α (TNF-α), vascular endothelial growth factor A, matrix metalloproteinase 1, matrix metalloproteinase 3, interleukin-6 and interferon gamma in RA-FLS cells. mechanistically, tofacitinib decreased signal transducer and activator of transcription 6 (STAT6), which transcriptionally activates miR-425-5p, and thus increased insulin like growth factor 1 (IGF1) expression, a target of miR-425-5p in RA-FLS. Overexpression of STAT6 restored the expression of pro-inflammatory factors and proliferation inhibited by Tofacitinib in RA-FLS. Overall, Tofacitinib exerted inhibitory effect on proliferation and inflammation of RA-FLS through modulating STAT6/miR-425-5p/IGF1 signal axis. These findings shed light on the novel strategies for improving RA.

Inhibition of STAT6 Activation by AS1517499 Inhibits Expression and Activity of PPARγ in Macrophages to Resolve Acute Inflammation in Mice

Signal transducer and activator of transcription 6 (STAT6) promotes an anti-inflammatory process by inducing the development of M2 macrophages. We investigated whether modulating STAT6 activity in macrophages using AS1517499, the specific STAT6 inhibitor, affects the restoration of homeostasis after an inflammatory insult by regulating PPARγ expression and activity. Administration of AS1517499 suppressed the enhanced STAT6 phosphorylation and nuclear translocation observed in peritoneal macrophages after zymosan injection. In addition, AS1517499 delayed resolution of acute inflammation as evidenced by enhanced secretion of pro-inflammatory cytokines, reduced secretion of anti-inflammatory cytokines in PLF and supernatants from peritoneal macrophages, and exaggerated neutrophil numbers and total protein levels in PLF. We demonstrate temporal increases in annexin A1 (AnxA1) protein and mRNA levels in peritoneal lavage fluid (PLF), peritoneal macrophages, and spleen in a murine model of zymosan-induced acute peritonitis. In vitro priming of mouse bone marrow-derived macrophages (BMDM) and peritoneal macrophages with AnxA1 induced STAT6 activation with enhanced PPARγ expression and activity. Using AS1517499, we demonstrate that inhibition of STAT6 activation delayed recovery of PPARγ expression and activity, as well as impaired efferocytosis. Taken together, these results suggest that activation of the STAT6 signaling pathway mediates PPARγ expression and activation in macrophages to resolve acute inflammation.

Transcriptional and Histochemical Signatures of Bone Marrow Mononuclear Cell-Mediated Resolution of Synovitis

Osteoarthritis (OA) may result from impaired ability of synovial macrophages to resolve joint inflammation. Increasing macrophage counts in inflamed joints through injection with bone marrow mononuclear cells (BMNC) induces lasting resolution of synovial inflammation. To uncover mechanisms by which BMNC may affect resolution, in this study, differential transcriptional signatures of BMNC in response to normal (SF) and inflamed synovial fluid (ISF) were analyzed. We demonstrate the temporal behavior of co-expressed gene networks associated with traits from related in vivo and in vitro studies. We also identified activated and inhibited signaling pathways and upstream regulators, further determining their protein expression in the synovium of inflamed joints treated with BMNC or DPBS controls. BMNC responded to ISF with an early pro-inflammatory response characterized by a short spike in the expression of a NF-ƙB- and mitogen-related gene network. This response was associated with sustained increased expression of two gene networks comprising known drivers of resolution (IL-10, IGF-1, PPARG, isoprenoid biosynthesis). These networks were common to SF and ISF, but more highly expressed in ISF. Most highly activated pathways in ISF included the mevalonate pathway and PPAR-γ signaling, with pro-resolving functional annotations that improve mitochondrial metabolism and deactivate NF-ƙB signaling. Lower expression of mevalonate kinase and phospho-PPARγ in synovium from inflamed joints treated with BMNC, and equivalent IL-1β staining between BMNC- and DPBS-treated joints, associates with accomplished resolution in BMNC-treated joints and emphasize the intricate balance of pro- and anti-inflammatory mechanisms required for resolution. Combined, our data suggest that BMNC-mediated resolution is characterized by constitutively expressed homeostatic mechanisms, whose expression are enhanced following inflammatory stimulus. These mechanisms translate into macrophage proliferation optimizing their capacity to counteract inflammatory damage and improving their general and mitochondrial metabolism to endure oxidative stress while driving tissue repair. Such effect is largely achieved through the synthesis of several lipids that mediate recovery of homeostasis. Our study reveals candidate mechanisms by which BMNC provide lasting improvement in patients with OA and suggests further investigation on the effects of PPAR-γ signaling enhancement for the treatment of arthritic conditions.

Cross-regulation of notch/AKT and serum/glucocorticoid regulated kinase 1 (SGK1) in IL-4-stimulated human macrophages

Notch signaling regulates the responses of macrophages to different stimuli in a context-dependent manner. The roles of Notch signaling in proinflammatory macrophages are well characterized, whereas its involvement, if any, in IL-4-stimulated macrophages (M(IL-4)) is still unclear. We observed that Notch signaling is functional in human M(IL-4). We performed transcriptome analysis of the Notch1 intracellular domain (NIC1)-overexpressing human monocytic cell line THP-1 with or without IL-4 stimulation to understand the global impact of Notch signaling in M(IL-4). The results revealed that NIC1-overexpressing THP-1 upregulated proinflammatory-associated genes and target genes of IL-4 signaling. We identified serum/glucocorticoid regulated kinase 1 (SGK1) as one of the genes increased by NIC1 overexpression in M(IL-4). To dissect the signaling pathway leading to SGK1 upregulation, we pretreated THP-1-derived macrophages with specific inhibitors of Notch (DAPT), AKT (LY294002) or ERK (U0126). Among these inhibitors, only LY294002 decreased the SGK1 mRNA levels in M(IL-4), indicating that the AKT pathway plays a key role in SGK1 transcription in M(IL-4). Furthermore, treatment of THP-1-derived macrophages with the SGK1 inhibitor (GSK650394) suppressed AKT phosphorylation, but not STAT6, in response to IL-4, indicating that SGK1 positively regulates AKT pathway in M(IL-4). Finally, GSK650394 treatment of human M(IL-4) increased the levels of PPARG mRNA and its protein, indicating a negative role of SGK1 in M(IL-4) function. Overall, we report that the Notch signaling and AKT pathways cooperatively regulate SGK1 expression in M(IL-4) where SGK1, in turn, plays an important role in suppressing IL-4-induced PPAR_γ expression.