PPARγ activation suppresses the expression of MMP9 by downregulating NF-κB post intracerebral hemorrhage

Peroxisome proliferator-activated receptor-gamma (PPARγ) is critical in protecting against inflammatory and oxidative stresses post brain injury. We have previously reported that rosiglitazone, an agonist of PPARγ, was effective to prevent microglia from apoptosis and ameliorate neuronal injuries post intracerebral hemorrhage (ICH) with suppression of matrix metalloproteinase-9 (MMP9) expression. However, molecular mechanisms linking how PPARγ decreases MMP9 remain unknown. Here, we hypothesize that PPARγ downregulates MMP9 expression post hemorrhage by inhibiting nuclear factor kappa B (NF-κB), an upstream regulator of MMPs gene and also key transcription factor involved in the control of immune and neuroinflammatory responses. We found both in vivo and in vitro that PPARγ was significantly downregulated post ICH with prominent increases of NF-κB and MMP9. Activation of PPARγ using rosiglitazone decreased the expression of both NF-κB and MMP9, while reversed effects were observed when administrating the PPARγ antagonist GW9662. Besides, inhibiting NF-κB by JSH-23 also suppressed the expression of MMP9, with only limited effect on PPARγ. Further studies revealed prominent colocalizations of NF-κB with PPARγ and MMP9, respectively. Finally, direct interactions of NF-κB with PPARγ and MMP9 gene were also confirmed, respectively, by protein and chromatin immunoprecipitations. These results suggested a role of NF-κB in mediating the reduction of MMP9 by PPARγ, potentially providing a new therapeutic target for brain hemorrhage.