Abstract Body: [Background] The neuroinflammation triggered by acute cerebral ischemia can be mediated through inflammasome such as NLRP3 (NOD-like receptor family, pyrin domain containing 3) and ASC (apoptosis-associated speck-like protein). The NLRP3 inflammasome complex triggers caspase1-mediated maturation of cytokine. Chronic cerebral hypoperfusion induces upregulation of NLRP3 inflammasome and neuroinflammation. This study was undertaken to test our hypothesis that chronic cerebral ischemia in triggered inflammasome-mediated neuroinflammation, resulting in increased chronic ischemic injury. Furthermore, we undertook this study to demonstrate that NLRP3 inhibitor treatment reduces inflammasome-derived neuroinflammation and white matter damage caused by chronic ischemia.

[Methods] We used eight-week-old male C.B-17/Icr-Jcl mice in this experiment. The mice were subjected to sham or bilateral common carotid artery stenosis (BCAS) operation using microcoils with an internal diameter of 0.18 mm. At 3weeks after BCAS, these mice were sacrificed and examined by immunohistochemistry and western blotting (n = 5 for each group). In a separate set of experiments, mice were administered with 40 mg/kg of a NLRP3 inhibitor or vehicle daily for 3 weeks after BCAS. As before, the NLRP3 inhibitor and vehicle groups were compared by immunohistochemistry and western blotting (n = 5 for each group).

[Results] Cerebral hypoperfusion in BCAS mice induce upregulation of NLRP3, ASC, and upregulation of inflammasome-dependent IL-1β in the splenium of corpus callosum. In immunoblots and quantification of inflammasome proteins, the expression of NLRP3, ASC and IL-1β in ipsilateral brain lysates was increased after BCAS compared to the sham surgery group. Furthermore, the results of immunoreactivity showed that NLRP3 inhibitor treatment for BCAS mice reduced upregulation of NLRP3, caspase1 and IL-1β.

[Conclusions] These results suggest that chronic cerebral hypoperfusion induces upregulation of NLRP3 in the white matter lesion, likely leading to an increase of IL-1β. We also identified NLRP3 inflammasome inhibition as a novel mechanism to protective against chronic ischemic damage, can become a potential clinical benefit of therapeutic interventions.