Exposure to space environment induces alterations in glucose and lipid metabolism that contribute to muscular atrophy, bone loss, and cardiovascular disorders. Intestinal microbiota is also changed, but its impact on spaceflight‐related metabolic disorder is not clear. We investigated the relationship between glucose metabolic changes and gut dysbiosis in a hind limb‐unloading (HU) mouse model, a well‐accepted ground‐based spaceflight analog. Impaired body weight gain, glucose intolerance, and peripheral insulin resistance were found in 2–4‐wk HU mice. Reduced abundance of gut Bifidobacterium spp. and Akkermansia muciniphila was observed within 3 d of HU. The ground‐based control (Ctrl) mice that were cohoused with HU mice showed similar patterns of dysbiosis and metabolic changes. Compared with the Ctrls, higher levels of plasma LPS‐binding protein and altered transcription of Tnfa and glucose metabolism‐related genes in the liver were observed in HU mice. The supplementation of Bifidobacterium spp. suppressed endotoxemia and liver inflammation and improved glucose tolerance in HU mice. The results indicate a close relationship between dysbiosis and altered glucose metabolism in the HU model and also emphasize the importance of evaluating intestinal microbiota in astronauts and its effect on glucose metabolism.—Wang, Y., Zhao, W., Shi, J., Wang, J., Hao, J., Pang, X., Huang, X., Chen, X., Li, Y., Jin, R., Ge, Q. Intestinal microbiota contributes to altered glucose metabolism in simulated microgravity mouse model. FASEB J. 33, 10140–10151 (2019). www.fasebj.org

Mature naive T cells circulate through the secondary lymphoid organs in an actively enforced quiescent state. Impaired cell survival and cell functions could be found when T cells have defects in quiescence. One of the key features of T cell quiescence is low basal metabolic activity. It remains unclear at which developmental stage T cells acquire this metabolic quiescence. We compared mitochondria among CD4 single-positive (SP) T cells in the thymus, CD4⁺ recent thymic emigrants (RTEs), and mature naive T cells in the periphery. The results demonstrate that RTEs and naive T cells had reduced mitochondrial content and mitochondrial reactive oxygen species when compared with SP thymocytes. This downregulation of mitochondria requires T cell egress from the thymus and occurs early after young T cells enter the circulation. Autophagic clearance of mitochondria, but not mitochondria biogenesis or fission/fusion, contributes to mitochondrial downregulation in RTEs. The enhanced apoptosis signal-regulating kinase 1/MAPKs and reduced mechanistic target of rapamycin activities in RTEs relative to SP thymocytes may be involved in this mitochondrial reduction. These results indicate that the gain of metabolic quiescence is one of the important maturation processes during SP–RTE transition. Together with functional maturation, it promotes the survival and full responsiveness to activating stimuli in young T cells.

The liver is a unique lymphoid organ whose microenvironment is biased towards tolerance induction. We previously found that a proportion of CD4⁺ autoreactive recent thymic emigrants (RTEs) retained in the liver after thymic egress and acquired IL-10 producing capability. To investigate the tolerance of these liver persisting CD4⁺ RTEs in more detail and to study the liver stromal cell types that facilitate the tolerogenic changes in young T cells, the phenotype and function of liver RTEs were further characterized and the impact of liver sinusoidal endothelial cells (LSECs) and Kupffer cells on RTEs were examined using an in vitro co-culture system. More than 70% of CD4⁺ CD44^hi RTEs in the liver acquired Foxp3^-LAG3⁺ CD49b⁻ regulatory phenotype and function. But higher ratio of apoptosis with enhanced FasL and Bim expression was also found in these CD4⁺ liver RTEs when compared to those in the lymph nodes and spleen. LSECs played an important role in RTEs’ acquisition of tolerogenic and regulatory phenotype. These results indicate an important role of liver microenvironment in enforcing peripheral tolerance to CD4⁺ thymic emigrants against self- and gut-derived antigens.

Background: The diagnosis, severity assessment, and development of therapeutic strategies for asthma are crucial aspects of disease management. Since biomarkers are reliable tools in disease management, we aimed to identify and explore asthma-associated biomarkers and investigate their mechanisms.Methods: Lipidomics was used to profile serum glycerophospholipids in asthmatic patients and controls. The absolute concentration of lysophosphatidylglycerol (LPG) 18:0 was quantified in various asthma subtypes. Mouse asthma models were used to confirm its potential as a biomarker and investigate its mechanismsin vivo.The effects of LPG 18:0 on CD4⁺T-cell differentiation, proliferation and apoptosis were assessedin vitroby flow cytometry, while mitochondrial dysfunction was evaluated through mitochondrial membrane potential, reactive oxygen species and ATP production measurements. The intracellular mechanism of LPG 18:0 in regulatory T-cells (Tregs) was investigated using small-molecule inhibitors.Results: The serum glycerophospholipid profile varied between asthmatic patients and control group, with LPG 18:0 levels being notably higher in asthmatic patients, correlating with asthma severity and control level.In vivoandin vitrostudies revealed that LPG 18:0 impaired naïve CD4⁺T-cell differentiation into Tregs and compromised their suppressive function. Further investigation demonstrated that LPG 18:0 treatment reduced the FOXP3 protein levelviaSIRT1-mediated deacetylation during Treg differentiation.Conclusions: This study identifies that serum levels of LPG 18:0 are generally elevated in asthmatics and serve as a biomarker for asthma. LPG 18:0 impairs Treg functionviathe NAD⁺/SIRT1/FOXP3 pathway. Our research reveals the potential of LPG 18:0 as a biomarker for asthma, elucidating its role in asthma diagnosis and treatment.

Anti-PD-1/L1 immunotherapy has been intensively used in heavily treated population with advanced gastric adenocarcinoma. However, the immunotherapeutic efficacy is low even in PD-L1 positive patients. We aimed to establish a new strategy based on the co-expression of CMTM6/4 and PD-L1 for patient stratification before immunotherapy. By analyzing the data obtained from TCGA and single-cell RNA sequencing at the mRNA level, and 6-color multiplex immunofluorescence staining of tumor tissues in tissue array and 48-case pre-immunotherapy patients at the protein level, we found that CMTM6/4 and PD-L1 co-expressed in both epithelial and mesenchymal regions of gastric adenocarcinoma. The tumor tissues had higher levels of CMTM6/4 expression than their adjacent ones. A positive correlation was found between the expression of CMTM6/4 and the expression of PD-L1 in tumor epithelium. Epithelial co-expression of CMTM6/4 and PD-L1 in gastric tumor region was associated with shorter overall survival but better short-term response to anti-PD-1/L1 immunotherapy. Thus, we developed a predictive model and three pathological patterns based on the membrane co-expression of CMTM6/4 and PD-L1 in tumor epithelial cells for pre-immunotherapy patient screening in gastric adenocarcinoma.

The signal mediated by sphingosine-1-phosphate receptor 1 (S1P1) is essential but seemingly insufficient for thymic export of newly generated T cells. Here, we reported the identification of CCR2 as an additional regulator of this process. CCR2 showed a markedly increased expression in the most mature subset of single-positive (SP) thymocytes. Its deficiency led to a reduction of recent thymic emigrants in the periphery and a simultaneous accumulation of mature SP cells in the thymus. The CCR2 signaling promoted thymic emigration primarily through modulating the chemotactic responses to S1P1 engagement. On the one hand, the chemokinesis induced by CCR2 activation endowed thymocytes with enhanced capacity to respond to S1P-induced migration. On the other hand, CCR2 signaling through Stat3 augmented forkhead box O1 activity, leading to increased expression of S1P1. Taken together, the present study highlights a unique and novel function of CCR2 signaling in the regulation of thymic egress.