Pyruvate enhances M1 microglial polarization via NF-κB/MCT1/iNOS signaling axis under low glucose condition

Background Proinflammatory microglia rely predominantly on glycolysis to maintain cytokine production during an inflammatory response. However, during ischemia, where glucose supply is low, inducible nitric oxide synthase (iNOS) production remains high accompanied by an increase in monocarboxylate transporter 1 (MCT1) expression. In this study, we explored whether there is a link between iNOS and MCT1 expressions, and whether pyruvate can act as an energy source to sustain the M1 phenotype. Methods Using a mouse model with laser-induced brain ischemia and cell culture with low-glucose treatment, we examined responses from microglia. Results The expressions of iNOS and MCT1, as well as arginase-1 (ARG1), were increased in the brain of the ischemic mouse model. In the BV2 microglial cell line and primary microglia treated under low glucose condition, iNOS and MCT1 also increased, while ARG1 decreased. The addition of pyruvate under low-glucose or lipopolysaccharide (LPS) treatment enhanced iNOS and MCT1 expressions compared with groups without pyruvate. MCT1 knockdown resulted in decreased iNOS while MCT1 overexpression increased iNOS. Furthermore, inhibitor of nuclear factor-kappaB (NF-κB) reduced both iNOS and MCT1. Conclusion Our data suggested that after proinflammatory microglial polarization, MCT1 is upregulated through the NF-κB signaling pathway, which leads to iNOS production. We speculate that microglia may continuously pick up monocarboxylates such as pyruvate through MCT1 to sustain the M1 phenotype.

The expression of Kruppel-like factor 2 in mice with collagen-induced arthritis and its role in the induction of nitric oxide synthase production

Kruppel-like factor 2 (KLF2) is associated with acute and chronic inflammation. However, the role of KLF2 in rheumatoid arthritis (RA) remains unknown. Here, we investigated the expression of KLF2 in mice with collagen-induced arthritis (CIA) to determine whether KLF2 levels correlate with inducible nitric oxide synthase (iNOS) production in vitro. Hematoxylin and eosin staining was used to assess the synovitis and bone destruction in mice. The concentration of tumor necrosis factor (TNF)-α, interleukin (IL)-6, and nitric oxide (NO) in synovial fluid was determined by enzyme-linked immunosorbent assay, while western blot (WB) analysis was employed to detect the expression of KLF2 and iNOS in the synovium, heart, and kidneys. The expression of iNOS in MH7A cells was analyzed by quantitative polymerase chain reaction (PCR) and WB. The expression of KLF2 and iNOS was significantly elevated in the synovium, heart, and kidneys of CIA mice. This was correlated to an increase in the severity of arthritis and the concentration of inflammatory mediators including TNF-α, IL-6, and NO in joint fluid. KLF2 and iNOS expression in vitro was induced by TNF-α and KLF2 knockdown significantly reduced the TNF-α-induced iNOS expression. These findings indicate that KLF2 influences synovial inflammation in CIA mice by regulating iNOS production in synoviocytes.

Association ofHelicobacter pyloriand iNOS Production by Macrophages and Lymphocytes in the Gastric Mucosa in Chronic Gastritis

Helicobacter pyloriis one of the most common causes of chronic gastritis. With the development of the disease cellular inflammatory infiltrates composed of lymphocytes, plasma cells, and macrophages are formed in epithelium and lamina propria of the stomach. These cells are capable of secreting a number of active substances, including inducible nitric oxide synthase (iNOS). We examined the relationship betweenH. pyloriand secretion of iNOS by cells of inflammatory infiltrates in chronic gastritis by light microscopy and immunohistochemistry. The data obtained indicate that stimulation ofH. pyloriimmune system cells of the host organism during development of chronic gastritis causes increase in number of macrophages and lymphocytes in the inflammatory infiltrate of the gastric mucosa. This is accompanied with increased expression of inducible NO-synthase with excess free radicals in the tissues, which leads to secondary alterations and exacerbates the inflammation with impaired regeneration processes.