Sphingosine 1-Phosphate- and C-C Chemokine Receptor 2-Dependent Activation of CD4+ Plasmacytoid Dendritic Cells in the Bone Marrow Contributes to Signs of Sepsis-Induced Immunosuppression

Unraveling the genetic and molecular landscape of sepsis and acute kidney injury: A comprehensive GWAS and machine learning approach

OBJECTIVES

This study aimed to explore the underlying mechanisms of sepsis and acute kidney injury (AKI), including sepsis-associated AKI (SA-AKI), a frequent complication in critically ill sepsis patients.

METHODS

GWAS data was analyzed for genetic association between AKI and sepsis. Then, we systematically applied three distinct machine learning algorithms (LASSO, SVM-RFE, RF) to rigorously identify and validate signature genes of SA-AKI, assessing their diagnostic and prognostic value through ROC curves and survival analysis. The study also examined the functional and immunological aspects of these genes, potential drug targets, and ceRNA networks. A mouse model of sepsis was created to test the reliability of these signature genes.

RESULTS

LDSC confirmed a positive genetic correlation between AKI and sepsis, although no significant shared loci were found. Bidirectional MR analysis indicated mutual increased risks of AKI and sepsis. Then, 311 key genes common to sepsis and AKI were identified, with 42 significantly linked to sepsis prognosis. Six genes, selected through LASSO, SVM-RFE, and RF algorithms, showed excellent predictive performance for sepsis, AKI, and SA-AKI. The models demonstrated near-perfect AUCs in both training and testing datasets, and a perfect AUC in a sepsis mouse model. Significant differences in immune cells, immune-related pathways, HLA, and checkpoint genes were found between high- and low-risk groups. The study identified 62 potential drug treatments for sepsis and AKI and constructed a ceRNA network.

CONCLUSIONS

The identified signature genes hold potential clinical applications, including prognostic evaluation and targeted therapeutic strategies for sepsis and AKI. However, further research is needed to confirm these findings.

The role of sphingosine-1-phosphate in the gut mucosal microenvironment and inflammatory bowel diseases

Sphingosine-1-phosphate (S1P), a type of bioactive sphingolipid, can regulate various cellular functions of distinct cell types in the human body. S1P is generated intracellularly by the catalysis of sphingosine kinase 1/2 (SphK1/2). S1P is transferred to the extracellular environment via the S1P transporter, binds to cellular S1P receptors (S1PRs) and subsequently activates S1P-S1PR downstream signaling. Dysbiosis of the intestinal microbiota, immune dysregulation and damage to epithelial barriers are associated with inflammatory bowel disease (IBD). Generally, S1P mainly exerts a proinflammatory effect by binding to S1PR1 on lymphocytes to facilitate lymphocyte migration to inflamed tissues, and increased S1P was found in the intestinal mucosa of IBD patients. Notably, there is an interaction between the distribution of gut bacteria and SphK-S1P signaling in the intestinal epithelium. S1P-S1PR signaling can also regulate the functions of intestinal epithelial cells (IECs) in mucosa, including cell proliferation and apoptosis. Additionally, increased S1P in immune cells of the lamina propria aggravates the inflammatory response by increasing the production of proinflammatory cytokines. Several novel drugs targeted at S1PRs have recently been used for IBD treatment. This review provides an overview of the S1P-S1PR signaling pathway and, in particular, summarizes the various roles of S1P in the gut mucosal microenvironment to deeply explore the function of S1P-S1PR signaling during intestinal inflammation and, more importantly, to identify potential therapeutic targets for IBD in the SphK-S1P-S1PR axis.

TLR2-induced CD8+ T-cell deactivation shapes dendritic cell differentiation in the bone marrow during sepsis

Sepsis is associated with profound immune dysregulation that increases the risk for life-threatening secondary infections: Dendritic cells (DCs) undergo functional reprogramming due to yet unknown changes during differentiation in the bone marrow (BM). In parallel, lymphopenia and exhaustion of T lymphocytes interfere with antigen-specific adaptive immunity. We hypothesized that there exists a link between T cells and the modulation of DC differentiation in the BM during murine polymicrobial sepsis. Sepsis was induced by cecal ligation and puncture (CLP), a model for human bacterial sepsis. At different time points after CLP, the BM and spleen were analyzed in terms of T-cell subpopulations, activation, and Interferon (IFN)-γ synthesis as well as the number of pre-DCs. BM-derived DCs were generated in vitro. We observed that naïve and virtual memory CD8⁺ T cells, but not CD4⁺ T cells, were activated in an antigen-independent manner and accumulated in the BM early after CLP, whereas lymphopenia was evident in the spleen. The number of pre-DCs strongly declined during acute sepsis in the BM and almost recovered by day 4 after CLP, which required the presence of CD8⁺ T cells. Adoptive transfer experiments and in vitro studies with purified T cells revealed that Toll-like receptor 2 (TLR2) signaling in CD8⁺ T cells suppressed their capacity to secrete IFN-γ and was sufficient to change the transcriptome of the BM during sepsis. Moreover, the diminished IFN-γ production of CD8⁺ T cells favored the differentiation of DCs with increased production of the immune-activating cytokine Interleukin (IL)-12. These data identify a novel role of CD8⁺ T cells in the BM during sepsis as they sense TLR2 ligands and control the number and function of de novo differentiating DCs.

Disparate Recruitment and Retention of Plasmacytoid Dendritic Cells to The Small Intestinal Mucosa between Young and Aged Mice

Plasmacytoid dendritic cells (pDC), a highly specialized class of innate immune cells that serve as rapid sensors of danger signals in circulation or in lymphoid tissue are well studied. However, there remains knowledge gaps about age-dependent changes of pDC function in the intestinal mucosa. Here, we report that under homeostatic conditions, the proportion of pDC expressing C-C chemokine receptor 9 (CCR9) in the intestinal intraepithelial cell (iIEC) population is comparable between young (2-4 months) and aged (18-24 months) mice, but the absolute numbers of iIEC and pDC are significantly lower in aged mice. Employing the classic model of acute endotoxemia induced by lipopolysaccharide (LPS), we found a decrease in the proportion and absolute number of intraepithelial pDC in both young and aged mice despite the LPS-induced increased expression of the chemokine C-C ligand 25 (CCL25), the ligand of CCR9, in the intestinal mucosa of young mice. In adoptive transfer experiments, a significantly lower number of pDC was retained into the intestinal layer of aged host mice after LPS administration. This was associated with recoverable pDC numbers in the intestinal lumen. Furthermore, co-adoptive transfer of young and aged pDC into young hosts also showed significantly lower retention of aged pDC in the epithelial layer compared to the co-transferred young pDC. Collectively, these data show age-associated changes in mucosal CCL25 gene expression and in pDC number. These may underlie the reported inadequate responses to gastrointestinal pathogens during chronologic aging.

Cytokines CCL2 and CXCL1 may be potential novel predictors of early bone loss

Osteoporosis is a common disorder characterized by decreased bone mineral density (BMD) and increased fracture risk. The current techniques detect real-time BMD precisely but do not provide adequate information to predict early bone loss. If bone loss could be diagnosed and predicted early, severe osteoporosis and unexpected fractures could be prevented, allowing for an improved quality of life for individuals. In the present study, an ovariectomized rat model of bone loss was established and the serum levels of 78 potential cytokines were determined using a protein array. The BMD of ovariectomized rats was dynamically measured by micro-CT and the early stage of bone loss was defined at the fourth week after surgery. The expression of several serum protein cytokines was indicated to be altered in the ovariectomized rats during an 8-week time-course of bone loss. Linear regression analysis revealed that the serum levels of C-C motif chemokine ligand 2 (CCL2, also known as monocyte chemoattractant protein 1) and C-X-C motif chemokine ligand 1 (CXCL1) were significantly associated with a reduction in BMD. The significance of these two factors in indicating bone mass reduction was further verified by analyzing serum samples from 24 patients with BMD using ELISA and performing a linear regression analysis. The serum levels of CCL2 and CXCL1 were inversely correlated with the bone mass. Therefore, the cytokines CCL2 and CXCL1 may be potential novel predictors of early bone loss and may be clinically relevant for the early diagnosis and prevention of osteoporosis.

Impaired dendritic cell functions in lung cancer: a review of recent advances and future perspectives

Lung cancer is the leading cause of cancer mortality worldwide. Dendritic cells (DCs) are the key factors providing protective immunity against lung tumors and clinical trials have proven that DC function is reduced in lung cancer patients. It is evident that the immunoregulatory network may play a key role in the failure of the immune response to terminate tumors. Lung tumors likely employ numerous strategies to suppress DC-based anti-tumor immunity. Here, we summarize the recent advances in our understanding on lung tumor-induced immunosuppression in DCs, which affects the initiation and development of T-cell responses. We also describe which existing measures to restore DC function may be useful for clinical treatment of lung tumors. Furthering our knowledge of how lung cancer cells alter DC function to generate a tumor-supportive environment will be essential in order to guide the design of new immunotherapy strategies for clinical use.