Protein disulfide isomerase integrates toll-like receptor 4 and P2X7 receptor signaling pathways during lipopolysaccharide-induced neuroinflammation

P2X7 receptor (P2X7R) augments lipopolysaccharide (LPS)-toll-like receptor 4 (TLR4)-mediated neuroinflammation. These roles of P2X7R in neuroinflammation are relevant to nitrosative stress through nuclear factor-κB (NF-κB)-inducible nitric oxide synthase (iNOS) pathway, while the underlying mechanisms are largely unknown. In the present study, we investigated whether protein disulfide isomerase (PDI) is involved in the integration of TLR4-P2X7R functions in response to LPS in vivo. The present study showed that LPS elicited NF-κB-mediated PDI upregulation, iNOS induction and S-nitrosylated PDI (SNO-PDI) level, independent of S-nitrosylation of NF-κB p65 subunit, in P2X7R^+/+ mice more than P2X7R^-/- mice. SN50 (an NF-κB inhibitor) effectively diminished LPS-induced PDI upregulation in both P2X7R^+/+ and P2X7R^-/- mice. PDI knockdown attenuated LPS-induced p65 S276 phosphorylation and iNOS induction in both strains. Of interest, S-nitroso-N-acetyl-DL-penicillamine (SNAP, a NO donor) increased SNO-PDI level, surface P2X7R expression and p65 S276 phosphorylation in P2X7R^+/+ mice under physiological condition. In P2X7R^-/- mice, SNAP was less effective on NF-κB S276 phosphorylation, although SNO-PDI level was similar to that in P2X7R^+/+ mice. Taken together, the present data demonstrate that PDI may be an intermediator to integrate TLR4- and P2X7R-mediated signaling pathways in a positive feedback loop, which would exert NF-κB-iNOS-mediated nitrosative stress during LPS-induced neuroinflammation.