Upregulation of proBDNF in the Mesenteric Lymph Nodes in Septic Mice

The immune status in the lymphatic system, especially mesenteric lymph nodes (MLNs), is critical to regulate the septic shock. Brain-derived neurotrophic factor (BDNF) in the enteric system has been reported to regulate enteric immunity. However, the role of its precursor, proBDNF, in the immune status of MLNs under sepsis condition is still unclear. This study aimed to characterize the expression pattern of proBDNF in MLNs after lipopolysaccharide (LPS) stimulation, and to investigate the association of pathogenesis of sepsis. LPS (20 mg/kg) was intraperitoneally injected to induce sepsis in mice. Survival curve analysis, routine blood tests, and liver and kidney function tests were performed to evaluate the severity of sepsis. QPCR and histological staining were performed to assess the mRNA levels of proinflammatory cytokines and degree of immune-inflammatory response in the MLNs. Furthermore, Western blotting, flow cytometry, and immunofluorescence were performed to examine the key molecules expression of proBDNF signaling. Intraperitoneal LPS injection significantly decreased the number of lymphocytes in blood but increased the number of T lymphocytes in MLNs. Serum alanine transaminase, aspartate transaminase, and blood urea nitrogen levels were increased in LPS-challenged mice compared to control mice. LPS administration upregulated proinflammatory cytokine gene expression and induced histological changes in the MLNs. LPS injection increased BDNF, proBDNF, and its receptor pan neutrophin receptor 75 (p75^NTR) expression in MLNs. The increased proBDNF was mainly localized on CD3⁺ and CD4⁺ T cells in the medulla of MLNs. LPS-induced sepsis upregulated proBDNF expression in medulla T cells of MLNs. ProBDNF upregulation may be involved in the pathogenesis of septic shock.