PPARγ-Dependent and -Independent Inhibition of the HMGB1/TLR9 Pathway by Eicosapentaenoic Acid Attenuates Ischemic Brain Damage in Ovariectomized Rats

High mobility group box 1 (HMGB1) elevation after cerebral ischemia activates inflammatory pathways via receptors such as the receptor for advanced glycation end products (RAGE) and toll-like receptors (TLRs) and leads to brain damage. Eicosapentaenoic acid (EPA), a peroxisome proliferator-activated receptor gamma (PPAR gamma) agonist, attenuates postischemic inflammation and brain damage in male animals. However, postischemic HMGB1 signaling and the effects of EPA on ovariectomized (OVX+) rats remain unclear. We hypothesized that EPA attenuates brain damage in OVX+ rats via the inhibition of HMGB1 signaling in a PPAR gamma-dependent manner. Seven-week-old female Sprague-Dawley rats were divided into 3 groups; nonovariectomized (OVX-) rats and EPA-treated and EPA-untreated OVX+ rats before cerebral ischemia induction. Another set of EPA-treated OVX+ rats was injected with the PPAR gamma inhibitor GW9662. OVX+ decreased the messenger RNA level of PPAR gamma and increased that of HMGB1, RAGE, TLR9, and tumor necrosis factor alpha (TNF alpha) in parallel with ischemic brain damage. EPA restored the PPAR gamma expression, downregulated the HMGB1 signal-related molecules, and attenuated the ischemic brain damage. Neither OVX+ nor EPA affected the expression of TLR2 or TLR4. Interestingly, GW9662 partially abrogated the EPA-induced neuro-protection and the downregulation of RAGE and TLR9. In contrast, GW9662 did not affect HMGB1 or TNF alpha. These results suggest that EPA exerts PPAR gamma-dependent and PPAR gamma-independent effects on postischemic HMGB1/TLR9 pathway. The cortical infarct volume exacerbated by OVX+ is associated with the upregulation of the HMGB1/TLR9 pathway. Suppression of this pathway may help to limit ischemic brain damage in postmenopausal women.