Abstract
Over-activation of Toll-like receptor 4 (TLR4) is the key mechanism in Gram-negative bacterial infection-induced sepsis. SAM and HD domain-containing deoxynucleoside triphosphate triphosphohydrolase 1 (SAMHD1) inhibits multiple viruses, but whether it plays a role during bacterial invasion remains unelucidated. Monocyte-macrophage specific Samhd1 knockout (Samhd1-/-) mice and Samhd1-/- macrophage cell line RAW264.7 were constructed and used as research models to evaluate the role of SAMHD1 in TLR4-activated inflammation. In vivo, LPS-challenged Samhd1-/- mice showed higher serum inflammatory factors, accompanied with more severe inflammation infiltration and lower survival rate. In vitro, Samhd1-/- peritoneal macrophages had more activated TLR4 pathway upon LPS-stimulation, accompanied with mitochondrial depolarization and dysfunction and a higher tendency to be M1-polarized. These results could be rescued by overexpressing full-length wild-type SAMHD1 or its phospho-mimetic T634D mutant into Samhd1-/- RAW264.7 cells, whereas the mutants, dNTP hydrolase-function-deprived H238A and phospho-ablative T634A, did not exert the same effect. Lastly, co-IP and immunofluorescence assays confirmed that SAMHD1 interacted with an outer mitochondrial membrane-localized protein, voltage-dependent anion channel-1 (VDAC1). SAMHD1 inhibits TLR4-induced acute inflammation and M1 polarization of macrophages by interacting with VDAC1 and maintaining mitochondria function, which outlines a novel regulatory mechanism of TLR signaling upon LPS stimulation.