STAT4 knockout protects LPS-induced lung injury by increasing of MDSC and promoting of macrophage differentiation

Myeloid-Derived Suppressor-like Cells as a Prognostic Marker in Critically Ill Patients: Insights from Experimental Endotoxemia and Intensive Care Patients

Patients admitted to the intensive care unit (ICU) often experience endotoxemia, nosocomial infections and sepsis. Polymorphonuclear and monocytic myeloid-derived suppressor cells (PMN-MDSCs and M-MDSCs) can have an important impact on the development of infectious diseases, but little is known about their potential predictive value in critically ill patients. Here, we used unsupervised flow cytometry analyses to quantify MDSC-like cells in healthy subjects challenged with endotoxin and in critically ill patients admitted to intensive care units and at risk of developing infections. Cells phenotypically similar to PMN-MDSCs and M-MDSCs increased after endotoxin challenge. Similar cells were elevated in patients at ICU admission and normalized at ICU discharge. A subpopulation of M-MDSC-like cells expressing intermediate levels of CD15 (CD15int M-MDSCs) was associated with overall mortality (p = 0.02). Interestingly, the high abundance of PMN-MDSCs and CD15int M-MDSCs was a good predictor of mortality (p = 0.0046 and 0.014), with area under the ROC curve for mortality of 0.70 (95% CI = 0.4-1.0) and 0.86 (0.62-1.0), respectively. Overall, our observations support the idea that MDSCs represent biomarkers for sepsis and that flow cytometry monitoring of MDSCs may be used to risk-stratify ICU patients for targeted therapy.

Lung cancer treatment potential and limits associated with the STAT family of transcription factors

Lung cancer is one of the mortal cancers and the leading cause of cancer-related mortality, with a cancer survival rate of fewer than 5% in developing nations. This low survival rate can be linked to things like late-stage detection, quick postoperative recurrences in patients receiving therapy, and chemoresistance developing against various lung cancer treatments. Signal transducer and activator of transcription (STAT) family of transcription factors are involved in lung cancer cell proliferation, metastasis, immunological control, and treatment resistance. By interacting with specific DNA sequences, STAT proteins trigger the production of particular genes, which in turn result in adaptive and incredibly specific biological responses. In the human genome, seven STAT proteins have been discovered (STAT1 to STAT6, including STAT5a and STAT5b). Many external signaling proteins can activate unphosphorylated STATs (uSTATs), which are found inactively in the cytoplasm. When STAT proteins are activated, they can increase the transcription of several target genes, which leads to unchecked cellular proliferation, anti-apoptotic reactions, and angiogenesis. The effects of STAT transcription factors on lung cancer are variable; some are either pro- or anti-tumorigenic, while others maintain dual, context-dependent activities. Here, we give a succinct summary of the various functions that each member of the STAT family plays in lung cancer and go into more detail about the advantages and disadvantages of pharmacologically targeting STAT proteins and their upstream activators in the context of lung cancer treatment.

Phosphodiesterase 4B is required for NLRP3 inflammasome activation by positive feedback with Nrf2 in the early phase of LPS- induced acute lung injury

Acute lung injury (ALI) is associated with overproduction of inflammatory mediators in lung tissue. Previous studies have revealed that inflammation induces activation of phosphodiesterase 4B (PDE4B) accompanied by the production of inflammatory mediators, but the detailed mechanism remains unclear. Here, we focused on the NOD-, LRR- and pyrin domain-containing protein 3(NLRP3) inflammasome complexes to study the crosstalk between PDE4B and NF-E2-related factor 2 (Nrf2). We used global knockout PDE4B or Nrf2 mice to prepare LPS induced acute lung injury model by intratracheally administration, and LPS primed bone marrow-derived macrophages (BMDMs), following overexpression of PDE4B or Nrf2, luciferase activity analysis, and chIP-qPCR analyses. We found that deficiency of PDE4B could potently attenuate the lung histopathological changes, suppress the secretion of pro-inflammatory mediators such as tumor necrosis factor α (TNF-α), interleukin (IL)-1β, IL-6, IL-18, and cleaved caspase-1, 8, and GSDMD accompanied with defective activation of the ROS/Nrf2/NLRP3. Meanwhile deficiency of Nrf2 showed the similar results. Furtherly, overexpression by PDE4B or Nrf2 plasmid transfection in MH-S cells could enhance the Nrf2 or PDE4B expression. Luciferase analysis suggested that Nrf2 activated PDE4B promoter activity, while PDE4B could increase Nrf2 substrate ARE activity in MH-S cells in dose dependent manners. ChIP-qPCR analyses showed that Nrf2 bound to the PDE4B promoter region at ̴ 1532 to ̴1199 position in macrophages. Altogether, deficiency of PDE4B inhibit the inflammasome activation and pyroptosis in LPS stimulated lung injury model and macrophages by regulating ROS/Nrf2/NLRP3 activation. The study provides new insight that PDE4B is required for NLRP3 inflammasome activation by positive feedback with Nrf2.

The diverse roles of myeloid derived suppressor cells in mucosal immunity

The mucosal immune system plays a vital role in protecting the host from the external environment. Its major challenge is to balance immune responses against harmful and harmless agents and serve as a 'homeostatic gate keeper'. Myeloid derived suppressor cells (MDSCs) are a heterogeneous population of undifferentiated cells that are characterized by an immunoregulatory and immunosuppressive phenotype. Herein we postulate that MDSCs may be involved in shaping immune responses related to mucosal immunity, due to their immunomodulatory and tissue remodeling functions. Until recently, MDSCs were investigated mainly in cancerous diseases, where they induce and contribute to an immunosuppressive and inflammatory environment that favors tumor development. However, it is now becoming clear that MDSCs participate in non-cancerous conditions such as chronic infections, autoimmune diseases, pregnancy, aging processes and immune tolerance to commensal microbiota at mucosal sites. Since MDSCs are found in the periphery only in small numbers under normal conditions, their role is highlighted during pathologies characterized by acute or chronic inflammation, when they accumulate and become activated. In this review, we describe several aspects of the current knowledge characterizing MDSCs and their involvement in the regulation of the mucosal epithelial barrier, their crosstalk with commensal microbiota and pathogenic microorganisms, and their complex interactions with a variety of surrounding regulatory and effector immune cells. Finally, we discuss the beneficial and harmful outcomes of the MDSC regulatory functions in diseases affecting mucosal tissues. We wish to illuminate the pivotal role of MDSCs in mucosal immunity, the limitations in our understanding of all the players and the intricate challenges stemming from the complex interactions of MDSCs with their environment.

Janus Kinase/Signal Converters, and the Transcriptional Activator Signaling Pathway Promotes Lung Cancer Through Increasing M2 Macrophage

Accumulating evidence highlights the salient function of JAK/STAT signaling pathway in tumorigenesis and development. But the mechanism of JAK/STAT signaling in lung cancer remains elusive. This study assessed the impact of JAK/STAT on lung tumorigenesis and its interaction with microenvironment. Mouse model of primary lung cancer was established and then treated with JAK/STAT inhibitor. Immunofluorescence was performed to analyze fluorescent labels. Transwell assay determined the cell migration ability, and Western blot, immunohistochemistry, and immunofluorescence to detect the expression of JAK/STAT key proteins. Cell proliferation was measured by Kit-8 and colony formation. JAK/STAT key proteins were upregulated in lung cancer models. Inhibition of JAK/STAT led to a decrease in proliferative, migratory and invasive capability of lung cancer cells and macrophages from bone marrow and spleen. The cell invasion ability in the bone marrow and the proliferation of macrophages in the treatment group was weakened. When co-cultured with the treated macrophages, the proliferation of LLC1 cells was inhibited. Furthermore, in vitro flow cytometry indicated that JAK/STAT affected lung cancer progression by affecting the polarization of M1/M2 macrophages. Taken altogether, JAK/STAT signal enhances M2 macrophage expression and promotes lung cancer progression.

M-CSF, IL-6, and TGF-β promote generation of a new subset of tissue repair macrophage for traumatic brain injury recovery

Traumatic brain injury (TBI) leads to high mortality rate. We aimed to identify the key cytokines favoring TBI repair and found that patients with TBI with a better outcome robustly increased concentrations of macrophage colony-stimulating factor, interleukin-6, and transforming growth factor-β (termed M6T) in cerebrospinal fluid or plasma. Using TBI mice, we identified that M2-like macrophage, microglia, and endothelial cell were major sources to produce M6T. Together with the in vivo tracking of mCherry+ macrophages in zebrafish models, we confirmed that M6T treatment accelerated blood-borne macrophage infiltration and polarization toward a subset of tissue repair macrophages that expressed similar genes as microglia for neuroprotection, angiogenesis and cell migration. M6T therapy in TBI mice and zebrafish improved neurological function while blocking M6T-exacerbated brain injury. Considering low concentrations of M6T in some patients with poor prognostic, M6T treatment might repair TBI via generating a previously unidentified subset of tissue repair macrophages.

Immune Suppression Mediated by STAT4 Deficiency Promotes Lymphatic Metastasis in HNSCC

Head and neck squamous cell carcinoma (HNSCC) is a prevalent form of cancer with 5-years survival rates around 57%, and metastasis is a leading cause of mortality. Host-derived immunological factors that affect HNSCC tumor development and metastasis are not completely understood. We investigated the role of host-derived signal transducer and activator of transcription 4 (STAT4) during experimental HNSCC using an aggressive and metastatic HNSCC cell line, LY2, which was orthotopically injected into the buccal sulcus of wild type (WT) and STAT4 deficient (Stat4-/-) BALB/c mice. Necropsies performed at terminal sacrifice revealed that Stat4-/- mice displayed comparable primary tumor growth to the WT mice. However, the rate and extent of lymph node and lung metastasis among Stat4-/- mice was significantly higher. Downstream analyses performed on primary tumors, draining lymph nodes, spleens and bone marrow revealed significant upregulation of lymphocytic immunosuppressive biomarkers as well as an accumulation of granulocytic MDSC subpopulations in draining lymph nodes of metastatic Stat4-/- mice. Further, we observed a significant decrease in TH1, TH17, and cytotoxic activity in tumor bearing Stat4-/- compared to WT mice. Our results demonstrate that STAT4 mediates resistance to HNSCC metastasis, and activation of STAT4 could potentially mitigate lymphatic metastasis in HNSCC patients.

SOD2 ameliorates pulmonary hypertension in a murine model of sleep apnea via suppressing expression of NLRP3 in CD11b+ cells

Background

High prevalence of obstructive sleep apnea (OSA) in the pulmonary hypertension (PH) population suggests that chronic intermittent hypoxia (CIH) is an important pathogenic factor of PH. However, the exact mechanism of CIH induced PH is not clear. One of the molecules that plays a key role in regulating pulmonary artery function under hypoxic conditions is superoxide dismutase 2 (SOD₂).

Methods

Our study utilized heterozygous SOD₂^−/+ mice firstly in CIH model to explore the exact role of SOD₂ in CIH causing PH. Expression of SOD2 was analyzed in CIH model. Echocardiography and pulmonary hypertension were measured in wild type (WT) and SOD2^−/+ mice under normal air or CIH condition. Hematoxylin–Eosin (H&E) staining and masson staining were carried out to evaluate pulmonary vascular muscularization and remodeling. Micro-PET scanning of in vivo ^99mTc-labelled- MAG3-anti-CD11b was applied to assess CD11b in quantification and localization. Level of nod-like receptor pyrin domain containing 3 (NLRP3) was analyzed by real time PCR and immunohistochemistry (IHC).

Results

Results showed that SOD₂ was down-regulated in OSA/CIH model. Deficiency of SOD2 aggravated CIH induced pulmonary hypertension and pulmonary vascular hypertrophy. CD11b⁺ cells, especially monocytic myeloid cell line-Ly6C⁺Ly6G⁻ cells, were increased in the lung, bone marrow and the blood under CIH condition, and down-regulated SOD2 activated NLRP3 in CD11b⁺ cells. SOD₂-deficient-CD11b⁺ myeloid cells promoted the apoptosis resistance and over-proliferation of human pulmonary artery smooth muscle cells (PASMCs) via up-regulating NLRP3.

Conclusion

CIH induced down-regulating of SOD2 increased pulmonary hypertension and vascular muscularization. It could be one of the mechanism of CIH leading to PH.

Activation of the IL-4/STAT6 Signaling Pathway Promotes Lung Cancer Progression by Increasing M2 Myeloid Cells

Emerging evidence shows that signal transducer and activator of transcription 6 (STAT6) plays critical roles in tumor development. We previously found high-level expression of STAT6 in human lung adenocarcinoma and squamous cell carcinoma, specifically in infiltrated immune cells located in the lung interstitium. Nevertheless, the role of STAT6 signaling in lung carcinogenesis and lung cancer proliferation and its underlying mechanisms remain unclear. This study aimed to investigate the role of STAT6 and the interaction between STAT6 and the tumor microenvironment in pulmonary tumorigenesis. We established a murine model of primary lung carcinogenesis in STAT6-deficient (STAT6^−/−) and STAT6 wild-type (WT) BALB/c mice using the carcinogen urethane. Two-month-old male mice were intraperitoneally injected with urethane (1 g/kg) dissolved in phosphate buffered saline (PBS). Primary tumors were monitored in vivo by positron emission tomography scanning. At 4, 6, and 9 months after urethane injection, lung tumors were harvested from the STAT6^−/− and WT mice for analysis. Small interfering RNA was used to downregulate the expression of STAT6 in tumor cells. Fluorescence activated cell sorting analysis was used to analyze fluorescence-conjugated cell markers. Transwell assays were used in coculturing experiments. STAT6 protein expression was detected by Western blotting, immunohistochemistry, and immunofluorescence. STAT6 mRNA expression was detected by quantitative real time-polymerase chain reaction. Cell Counting Kit-8 and colony formation assays were performed to evaluate cell proliferation. We detected high expression of STAT6 in CD11b⁺ cells of lung carcinoma. Our results indicate that STAT6 deficiency inhibits carcinogen-induced tumor growth and improves prognosis. STAT6 deficiency also decreased the mobilization and differentiation of CD11b⁺ cells. STAT6 deficiency in CD11b⁺ cells but not tumor cells decreased interleukin (IL)-4 secretion and the differentiation of CD11b⁺ cells into M2 macrophage cells. In conclusion, our findings indicate that IL-4/STAT6 signaling in CD11b⁺ cells promotes lung cancer progression by triggering an IL-4 positive feedback loop and increasing M2 myeloid cells. STAT6 may be a new therapeutic target for the prevention and treatment of lung cancer.

Abnormal aggregation of myeloid-derived suppressor cells in a mouse model of cyclophosphamide-induced premature ovarian failure

Oocytes are extremely sensitive to radiation and chemotherapy, and premature ovarian failure (POF) is one of the side effects of anti-tumor therapy. The pathogenesis of POF is very complex and still not fully elucidated. A mouse POF model was established after 14 days of cyclophosphamide injection. POF mice presented ovarian atrophy, destroyed follicular structure, a reduction in the number of primordial and mature follicles, and an decrease in the number of corpora luteal along with increased level of follicle-stimulating hormone (FSH), decreased levels of estradiol (E2), and anti-Mullerian hormone (AMH). Additionally, the proportion of bone marrow myeloid-derived suppressor cells (MDSCs) in peripheral blood, spleen, and ovarian tissue increased. MDSCs were mainly distributed around follicles and corpora luteal. Levels of mTOR and p-mTOR increased in ovarian tissue and inhibition of mTOR with rapamycin reduced the aggregation of MDSCs in peripheral blood, spleen, and ovarian tissue. This investigation sheds new light on the modulatory role of mTOR and demonstrates that an increase in MDSC number may play a key role in the pathological reaction during POF. Inhibition of mTOR and reduction of MDSCs in the ovary may represent a novel strategy for the treatment of POF.

Activation of SIRT1 ameliorates LPS-induced lung injury in mice via decreasing endothelial tight junction permeability

The integrity of the endothelial barrier is a determinant of the prognosis of lipopolysaccharide (LPS)-induced acute lung injury (ALI). In this study, we investigated whether and how Sirtuin 1 (SIRT1) maintained the vascular integrity during ALI. An experimental model of ALI was established in mice through intratracheal administration of LPS (10 mg/kg). LPS stimulation significantly increased the pulmonary permeability and decreased the expression of SIRT1 and tight junction proteins (TJs), including occludin, claudin-5, tight junction protein 1 and tight junction protein 2. Morphological studies showed that LPS induced obvious lung injury with inflammatory cell infiltration in the interstitial and alveolar space, hemorrhage, edema, and the thickened alveolar wall compared to the control mice. Intratracheal administration of the selective SIRT1 activator SRT1720 (6.25 mg/kg) significantly attenuated LPS-induced lung injury, lung hyper-permeability and increased TJs expression, whereas intratracheal administration of the selective SIRT1 inhibitor EX527 (6.25 mg/kg) aggravated LPS-induced ALI. Similar protective effects of SIRT1 on pulmonary cellular permeability were observed in primary human pulmonary microvascular endothelial cells treated with LPS (2 mg/mL) in vitro. We further demonstrated that the RhoA/ROCK signaling pathway was activated in SIRT1 regulation of tight junction permeability. The RhoA/ROCK inhibitor Y-27632 (10 μM) increased the expression of TJs and reversed LPS- or EX527-induced hyper-permeability. In conclusion, SIRT1 ameliorates LPS-induced lung injury via decreasing endothelial tight junction permeability, possibly via RhoA/ROCK signaling pathway. This finding may contribute to the development of new therapeutic approaches for lung injury.

The mTOR signal regulates myeloid-derived suppressor cells differentiation and immunosuppressive function in acute kidney injury

The mammalian target of rapamycin (mTOR) signal controls innate and adaptive immune response in multiple immunoregulatory contexts. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of myeloid cells of potent immunosuppressive capacity. In this study, we aimed to investigate the role of MDSCs in the protection of acute kidney injury (AKI) and the regulation of mTOR signal on MDSC's protective role in this context. In mice AKI model, rapamycin administration was associated with improved renal function, restored histological damage and decreased CD4⁺ and CD8⁺ T-cell infiltration in kidney tissue. MDSCs, especially CD11b⁺Ly6G⁺Ly6C^low G-MDSCs were recruited to the injured kidney following the interaction of CXCL1, CXCL2 and their receptor CXCR2 after inhibiting mTOR signal with rapamycin treatment. The adoptive transfer of rapamycin-treated MDSCs into the mice with AKI significantly improved the renal function, ameliorated histologic damages and limited the infiltration of T cells in kidney tissue. In addition, the expression of pro-inflammatory cytokines IL-1β and IFN-γ mRNA was downregulated while the expression of TGF-β1 and Foxp3 mRNA was upregulated in kidney tissue after transferring rapamycin-treated MDSCs. Adoptive transfer of rapamycin-treated MDSCs also downregulated the serum levels of IL-1β, IL-6 and IFN-γ and upregulated the serum levels of TGF-β1 compared with the IR group and PBS-treated MDSC group. In in vitro study, inhibiting mTOR signal regulated the induction of MDSC towards the CD11b⁺Ly6G⁺Ly6C^low G-MDSC subset. The ability to suppress T-cell proliferation of both bone marrow–derived CD11b⁺Ly6G⁺Ly6C^low G-MDSCs and CD11b⁺Ly6G^-Ly6C^high M-MDSCs was enhanced by mTOR signal inhibition via upregulating the expression of Arginase-1 and iNOS. Accordingly, both G-MDSCs and M-MDSCs presented downregulated runx1 gene expression after rapamycin treatment. Taken together, our results demonstrated that MDSCs ameliorated AKI and the protective effect was enhanced by mTOR signal inhibition via promoting MDSCs recruitment, regulating the induction of MDSCs and strengthening their immunosuppressive activity.