NP-23 Cascade Events for Delayed Postoperative Cognitive Dysfunction

摘要

Background:Postoperative cognitive dysfunction(POCD)can occur in patients with cardiac and non-cardiac surgeries.About 20%to 40%patients develop POCD at hospital discharge(a few days after surgery,acute POCD)and 10%elderly patients(>60 years old)have POCD at 3 months after surgery(delayed POCD).Age and degree of education are risk factors for delayed POCD.It has been shown that POCD is associated with increased mortality.Patients with POCD have a longer hospital stay and an increased rate of leaving job market.Thus,POCD is a very significant clinical syndrome during the perioperative period,which is recognized only in recent years.We and others have shown that neuroinflammation is a critical neuropathological process for POCD.However,neuroinflammation lasts for a few days after surgery.It is not known how such a short-lived neuropathological process lead to POCD a few months after surgery.To address this issue,a series of experiments were performed in my laboratory.Methods:Rats or mice were subjected to common carotid arterial exposure,a surgical component of carotid endarterectomy that is often performed in elderly patients.Their learning and memory were assessed at least one week after surgery.Their blood and brain tissues were harvested at various time after surgery for biochemical and structural analyses.Results:The surgery induced an increase of proinflammatory cytokines in the blood.The surgery also increased the expression of active matrix metallopeptidase 9(MMP-9)and its activity in the brain.This surgery induced POCD and neuroinflammation in wild-type mice but not in the MMP-9 knockout mice.P2X7 receptors and inflammasome were activated by the surgery.Inhibition of P2X7 receptors and P2X7 receptor knockout abolished POCD and neuroinflammation after surgery.The surgery decreased growth factor production and inhibition of neuroinflammation attenuated this decrease.The decreased growth factor expression occurred at 3 to 5 days after the surgery.Surgery increased histone deacetylase activity and inhibition of histone deacetylase attenuated the decrease of growth factor expression and the development of POCD.The surgery decreased neurogenesis in the hippocampus and application of growth factors to the brain attenuated this decrease and POCD.This decreased neurogenesis was observed 3 weeks after surgery.Finally,surgery impaired dendritic arborization that was assessed 3 weeks after surgery.Inhibition of histone deacetylases attenuated this impairment and POCD.Conclusion:Surgery induces a delayed POCD in rodents.Surgery results in systemic inflammation,which then activates MMP-9 to damage the brain-blood barrier to facilitate the systemic inflammation to be transmitted to the brain.Proinflammatory signals in the blood activate P2X7 receptors to induce neuroinflammation that inhibits growth factor expression through epigenetic regulation.Reduced growth factor expression results in decreased neurogenesis and dendritic arborization that then ultimately lead to the delayed POCD.Thus,surgery activates a series of cascade events to induce the delayed POCD.