Acute respiratory distress syndrome (ARDS) is a serious lung condition characterized by severe hypoxemia leading to limitations of oxygen needed for lung function. In this study, we investigated the effect of anandamide (AEA), an endogenous cannabinoid, on Staphylococcal enterotoxin B (SEB)-mediated ARDS in female mice. Single-cell RNA sequencing data showed that the lung epithelial cells from AEA-treated mice showed increased levels of antimicrobial peptides (AMPs) and tight junction proteins. MiSeq sequencing data on 16S RNA and LEfSe analysis demonstrated that SEB caused significant alterations in the microbiota, with increases in pathogenic bacteria in both the lungs and the gut, while treatment with AEA reversed this effect and induced beneficial bacteria. AEA treatment suppressed inflammation both in the lungs as well as gut-associated mesenteric lymph nodes (MLNs). AEA triggered several bacterial species that produced increased levels of short-chain fatty acids (SCFAs), including butyrate. Furthermore, administration of butyrate alone could attenuate SEB-mediated ARDS. Taken together, our data indicate that AEA treatment attenuates SEB-mediated ARDS by suppressing inflammation and preventing dysbiosis, both in the lungs and the gut, through the induction of AMPs, tight junction proteins, and SCFAs that stabilize the gut-lung microbial axis driving immune homeostasis.

Acute Respiratory Distress Syndrome (ARDS) causes up to 40% mortality in humans and is difficult to treat. ARDS is also one of the major triggers of mortality associated with coronavirus-induced disease (COVID-19). We used a mouse model of ARDS induced by Staphylococcal enterotoxin B (SEB), which triggers 100% mortality, to investigate the mechanisms through which Δ9-tetrahydrocannabinol (THC) attenuates ARDS. SEB was used to trigger ARDS in C3H mice. These mice were treated with THC and analyzed for survival, ARDS, cytokine storm, and metabolome. Additionally, cells isolated from the lungs were used to perform single-cell RNA sequencing and transcriptome analysis. A database analysis of human COVID-19 patients was also performed to compare the signaling pathways with SEB-mediated ARDS. The treatment of SEB-mediated ARDS mice with THC led to a 100% survival, decreased lung inflammation, and the suppression of cytokine storm. This was associated with immune cell apoptosis involving the mitochondrial pathway, as suggested by single-cell RNA sequencing. A transcriptomic analysis of immune cells from the lungs revealed an increase in mitochondrial respiratory chain enzymes following THC treatment. In addition, metabolomic analysis revealed elevated serum concentrations of amino acids, lysine, n-acetyl methionine, carnitine, and propionyl L-carnitine in THC-treated mice. THC caused the downregulation of miR-185, which correlated with an increase in the pro-apoptotic gene targets. Interestingly, the gene expression datasets from the bronchoalveolar lavage fluid (BALF) of human COVID-19 patients showed some similarities between cytokine and apoptotic genes with SEB-induced ARDS. Collectively, this study suggests that the activation of cannabinoid receptors may serve as a therapeutic modality to treat ARDS associated with COVID-19.

We previously reported that an aryl hydrocarbon receptor (AhR) ligand, indole-3-carbinol (I3C), was effective at reducing colitis severity through immune cell-mediated interleukin-22 (IL-22) production. Intestinal epithelial cells (IECs) are also involved in regulating colitis, so we investigated their AhR-mediated mechanisms in the current report. A transcriptome analysis of IECs in wildtype (WT) mice revealed that during colitis, I3C regulated select mucin proteins, which could be attributed to goblet cell development. To address this, experiments under in vivo colitis (mice) or in vitro colon organoid conditions were undertaken to determine how select mucin proteins were altered in the absence or presence of AhR in IECs during I3C treatment. Comparing WT to IEC-specific AhR knockout mice (AhR^ΔIEC), the results showed that AhR expression was essential in IECs for I3C-mediated protection during colitis. AhR-deficiency also impaired mucin protein expression, particularly mucin 2 (Muc2), independently of IL-22. Collectively, this report highlights the important role of AhR in direct regulation of Muc2. These results provide justification for future studies aimed at determining how AhR might regulate select mucins through mechanisms such as direct transcription binding to enhance production.

During endotoxin-induced acute lung injury (ALI), immune cell recruitment resulting from chemotaxis is mediated by CXC and CC chemokines and their receptors. In this study, we investigated the role of chemokines and their receptors in the regulation of myeloid cell populations in the circulation and the lungs of C57BL/6J mice exhibiting LPS-mediated ALI using single-cell RNA sequencing. During ALI, there was an increase in the myeloid cells, M1 macrophages, monocytes, neutrophils, and other granulocytes, whereas there was a decrease in the residential alveolar macrophages and M2 macrophages. Interestingly, LPS triggered the upregulation of CCL3, CCL4, CXCL2/3, and CXCL10 genes associated with cellular migration of various subsets of macrophages, neutrophils, and granulocytes. Furthermore, there was an increase in the frequency of myeloid cells expressing CCR1, CCR3, CCR5, and CXCR2 receptors during ALI. MicroRNA sequencing studies of vehicle versus LPS groups identified several dysregulated microRNAs targeting the upregulated chemokine genes. This study suggests that chemokine ligand–receptors interactions are responsible for myeloid cell heterogenicity and cellular recruitment to the lungs during ALI. The single-cell transcriptomics allowed for an in-depth assessment and characterization of myeloid cells involved in immune cell trafficking during ALI.

Previously, we showed that 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), an aryl hydrocarbon receptor (AhR) ligand and a potent and persistent toxicant and carcinogenic agent, induces high levels of murine myeloid-derived suppressor cell (MDSC) when injected into mice. In the current study, we demonstrate that Resveratrol (3,4,5-trihydroxy-trans-stilbene; RSV), an AhR antagonist, reduces TCDD-mediated MDSC induction. RSV decreased the number of MDSCs induced by TCDD in mice but also mitigated the immunosuppressive function of TCDD-induced MDSCs. TCDD caused a decrease in F4/80+ macrophages and an increase in CD11C+ dendritic cells, while RSV reversed these effects. TCDD caused upregulation in CXCR2, a critical molecule involved in TCDD-mediated induction of MDSCs, and Arginase-1 (ARG-1), involved in the immunosuppressive functions of MDSCs, while RSV reversed this effect. Transcriptome analysis of Gr1⁺ MDSCs showed an increased gene expression profile involved in the metabolic pathways in mice exposed to TCDD while RSV-treated mice showed a decrease in such pathways. The bio-energetic profile of these cells showed that RSV treatment decreased the energetic demands induced by TCDD. Overall, the data demonstrated that RSV decreased TCDD-induced MDSC induction and function by altering the dynamics of various myeloid cell populations involving their numbers, phenotype, and immunosuppressive potency. Because MDSCs play a critical role in tumor growth and metastasis, our studies also support the potential use of RSV to attenuate the immunosuppressive properties of MDSC.

Macrophages are vital components of the immune system and serve as the first line of defense against pathogens. Macrophage colony-stimulating factor (M-CSF) induces macrophage differentiation from bone marrow-derived cells (BMDCs). Δ9-tetrahydrocannabiol (THC), a phytocannabinoid from the Cannabis plant, has profound anti-inflammatory properties with significant effects on myeloid cells. To investigate the effect of THC on macrophage differentiation, we cultured BMDCs with M-CSF in the presence of THC. Interestingly, THC markedly blocked the differentiation of BMDCs into CD45 + CD11b + F4/80+ macrophages. The effect of THC was independent of cannabinoid receptors CB1, and CB2, as well as other potential receptors such as GPR18, GPR55, and Adenosine 2A Receptor. RNA-seq analysis revealed that the THC-treated BMDCs displayed a significant increase in the expression of NRF2-ARE-related genes. KEGG pathway analysis revealed that the expression profiles of THC-treated cells correlated with ferroptosis and glutathione metabolism pathways. Fluorescence-based labile iron assays showed that the THC-treated BMDCs had significantly increased iron levels. Finally, THC-exposed BMDCs showed decreased levels of intracellular ROS. THC has the unique molecular property to block the Fenton Reaction, thus preventing the increase in intracellular ROS that is normally induced by high iron levels. Together, these studies demonstrated that THC blocks M-CSF-induced macrophage differentiation by inhibiting ROS production through both the induction of NRF2-ARE-related gene expression and the prevention of ROS formation via the Fenton Reaction.