CD137L Inhibition Ameliorates Hippocampal Neuroinflammation and Behavioral Deficits in a Mouse Model of Sepsis-Associated Encephalopathy

Anxiety manifestations and cognitive dysfunction are common sequelae in patients with sepsis-associated encephalopathy (SAE). Microglia-mediated inflammatory signaling is involved in anxiety, depression, and cognitive dysfunction during acute infection with bacterial lipopolysaccharide (LPS). However, the molecular mechanisms underlying microglia activation and behavioral and cognitive deficits in sepsis have not been in fully elucidated. Based on previous research, we speculated that the CD137 receptor/ligand system modulates microglia function during sepsis to mediate classical neurological SAE symptoms. A murine model of SAE was established by injecting male C57BL/6 mice with LPS, and cultured mouse BV2 microglia were used for in vitro assays. RT-qPCR, immunofluorescence staining, flow cytometry, and ELISA were used to assess microglial activation and the expression of CD137L and inflammation-related cytokines in the mouse hippocampus and in cultured BV2 cells. In addition, behavioral tests were conducted in assess cognitive performance and behavioral distress. Immunofluorescence and RT-qPCR analyses showed that hippocampal expression of CD137L was upregulated in activated microglia following LPS treatment. Pre-treatment with the CD137L neutralizing antibody TKS-1 significantly reduced CD137L levels, attenuated the expression of M1 polarization markers in microglia, and inhibited the production of TNF-α, IL-1β, and IL-6 in both LPS-treated mice and BV2 cells. Conversely, stimulation of CD137L signaling by recombinant CD137-Fc fusion protein activated the synthesis and release of pro-inflammatory cytokines in cultures BV2 microglia. Importantly, open field, elevated plus maze, and Y-maze spontaneous alternation test results indicated that TKS-1 administration alleviated anxiety-like behavior and spatial memory decline in mice with LPS-induced SAE. These findings suggest that CD137L upregulation in activated microglia critically contributes to neuroinflammation, anxiety-like behavior, and cognitive dysfunction in the mouse model of LPS-induced sepsis. Therefore, therapeutic modulation of the CD137L/CD137 signaling pathway may represent an effective way to minimize brain damage and prevent cognitive and emotional deficits associated with SAE.

Study of Relieving Graft-versus-Host Disease by Blocking CD137-CD137 Ligand Costimulatory Pathway in Vitro

Engagement of the TCR without appropriate costimulation will result in the inability of T-cells to respond to the alloantigen as described earlier. We made a further investigation into the effect of relieving graft-versus-host disease (GVHD) and its mechanism in mice by blocking CD137-CD137L pathway in vitro. Responder cells (spleen cells) from BALB/C donor mice (H-2d) were incubated with stimulator cells (spleen cells) from C57BL/6 recipient mice (H-2b), with or without anti-CD137L monoclonal antibodies (MoAbs). Donor bone marrow cells plus mixed lymphocyte culture (MLC) T-cells were transplanted into lethally irradiated C57BL/6 mice. C57BL/6 mice were divided into 3 groups: group A (allogeneic bone marrow transplantation control group), group B (cyclosporine + methotrexate group), and group C (donor T-cells were treated with anti-CD137L MoAbs). The percentage of CD3+CD4+ and CD3+CD8+ T-cells were detected by flow cytometry, and the levels of cytokines (IFN-gamma, interleukin [IL]-2, IL-10, IL-4) by reverse-transcriptase polymerase chain reaction. The incidence of GVHD in group C was 70%, while the incidence of GVHD was 100% in group A and group B. The survival rate of group C was higher than that of group A and B, and the median survival time was longer than that of group A and B (P < .01). Clinical symptoms and histological signs of GVHD in group C were the mildest among all 3 groups. The percentage of CD3+CD8+T-cells in group C was lower than that in group A and B (P < .01). The levels of IFN-gamma in group C were markedly lower than those in group A and B (P < .01), and the levels of IL-10 in group C were significantly higher than those in group A and B (P < .01). The results suggest that treatment of donor T-cells by anti-CD137L MoAbs in vitro may relieve GVHD, thereby improve the survival time and survival rate of recipient mice, which might be related to the increased TH1 cytokine (IFN-gamma) and decreased TH2 cytokine (IL-10) as well as the reduced CD3+CD8+T-cells.