General Anesthetics Regulate Autophagy via Modulating the Inositol 1,4,5-Trisphosphate Receptor: Implications for Dual Effects of Cytoprotection and Cytotoxicity

Abstract

General anesthetics are both neuroprotective and neurotoxic with unclear mechanisms. General anesthetics may control cell survival via their effects on autophagy by activation of type 1 inositol triphosphate receptor (InsP ₃R-1). DT40 or SH-SY5Y cells with only or over 99% expression of InsP ₃R-1 were treated with isoflurane or propofol. Cell viability was determined by MTT reduction or LDH release assays. Apoptosis was determined by measuring Caspase-3 or by TUNEL assay. Autophagy activity was determined by measuring LC3 II and P62. We evaluated mitochondrial integrity using MitoTracker Green and cytosolic ATP levels. Fura2-AM was used to measure the concentrations of cytosolic calcium ([Ca ²⁺] _c). Propofol significantly increased peak and integrated calcium response (P < 0.001) in cells with InsP ₃R-1 but not in cells with triple knockout of InsP ₃R. Both propofol and isoflurane increased autophagy induction (P < 0.05) in an mTOR- and InsP ₃R- activity dependent manner. Short exposure to propofol adequately activated InsP ₃-1 to provide sufficient autophagy for cytoprotection, while prolonged exposure to propofol induced cell apoptosis via impairment of autophagy flux through over activation of InsP ₃-1. Propofol damaged mitochondria and decreased cytosolic ATP. The effects of general anesthetics on apoptosis and autophagy are closely integrated; both are caused by differential activation of the type 1 InsP ₃R.