Transglutaminase 2 induces nitric oxide synthesis in BV-2 microglia.

A hallmark of brain inflammation is the activation of microglia. Excessive production of nitric oxide (NO), as a consequence of increased inducible nitric oxide synthase (iNOS) in glia, contributes to neurodegeneration. Transglutaminase 2 (TGase 2) is a cross-linking enzyme, which is increased in neurodegeneration. TGase 2 is also considered to be a useful and reliable marker for activation levels in resident and inflammatory macrophages. Therefore, an increase of TGase 2 expression may contribute to activation of microglia. To test this hypothesis, we analyzed the expression of TGase 2 in BV-2 microglia activated with lipopolysaccharide (LPS). Total TGase activity was increased about 5-fold after 24h exposure to LPS. The increase of NO synthesis is correlated with increase of TGase 2 expression. Secretion of NO was reduced between 40 and 80% by TGase inhibition in a dose-dependent manner. This suggests that TGase 2 appears to control iNOS transcription.