Brief isoflurane anesthesia regulates striatal AKT-GSK3β signaling and ameliorates motor deficits in a rat model of early-stage Parkinson's disease

Abstract

Parkinson's disease (PD) is a progressive neurodegenerative movement disorder primarily affecting the nigrostriatal dopaminergic system. The link between heightened activity of glycogen synthase kinase 3β (GSK3β) and neurodegene-rative processes has encouraged investigation into the potential disease-modifying effects of novel GSK3β inhibitors in experimental models of PD. Therefore, the intriguing ability of several anesthetics to readily inhibit GSK3β within the cortex and hippocampus led us to investigate the effects of brief isoflurane anesthesia on striatal GSK3β signaling in naïve rats and in a rat model of early-stage PD. Deep but brief (20-min) isoflurane anesthesia exposure increased the phosphorylation of GSK3β at the inhibitory Ser9 residue, and induced phosphorylation of AKT^Thr308 (protein kinase B; negative regulator of GSK3β) in the striatum of naïve rats and rats with unilateral striatal 6-hydroxydopamine (6-OHDA) lesion. The 6-OHDA protocol produced gradual functional deficiency within the nigrostriatal pathway, reflected as a preference for using the limb ipsilateral to the lesioned striatum at 2 weeks post 6-OHDA. Interestingly, such motor impairment was not observed in animals exposed to four consecutive isoflurane treatments (20-min anesthesia every 48 h; treatments started 7 days after 6-OHDA delivery). However, isoflurane had no effect on striatal or nigral tyrosine hydroxylase (a marker of dopaminergic neurons) protein levels. This brief report provides promising results regarding the therapeutic potential and neurobiological mechanisms of anesthetics in experimental models of PD and guides development of novel disease-modifying therapies.

Keywords: anesthesia; dopamine; neurodegeneration; phosphorylation; sensorimotor test.

Figure 1

Isoflurane anesthesia exposure increases GSK3β^Ser9 and AKT^Thr308 phosphorylation in the adult rat cortex and striatum. Representative cortical EEG spectrogram demonstrating the burst suppression pattern during isoflurane administration (4% induction for 2 min, 2% maintenance) (a). Effect of a single brief isoflurane anesthesia exposure (4% induction for 2 min, 2% maintenance for 20 min; N = 4/group) on GSK3β^Ser9 phosphorylation (b) and AKT^Thr308 phosphorylation (c) in the adult rat cortex and striatum. Striatal GSK3β^Ser9 and AKT^Thr308 phosphorylation after repeated (20‐min anesthesia exposure every 48 h for total of five consecutive times; N = 6/group) isoflurane administration (d–f). *p < 0.05; **p < 0.01; ***p < 0.005, Student t‐test. EEG, electroencephalogram; GAPDH, glyceraldehyde 3‐phosphate dehydrogenase; GSK3β, glycogen synthase 3β; AKT, protein kinase B; ISO, isoflurane; Sham, rats in the induction chamber for 2 min with continuous O₂ flow (with no anesthetics).

Figure 2

Isoflurane anesthesia exposure regulates striatal AKT‐GSK3β signaling and ameliorates motor deficits in an animal model of early‐stage Parkinson′s disease. (a) Experimental workflow. Unilateral intrastriatal 6‐hydroxydopamine (10 μg) administration was performed on day 0. Animals were exposed to isoflurane (4% induction for 2 min, 2% maintenance for 20 min; N = 9) or sham conditions (rats in the induction chamber for 2 min with O₂ flow on; N = 9) on days 7, 9, 11, and 13. On day 14 (24 h after previous anesthesia exposure), animals were subjected to behavioral tests, assessing sensorimotor functions (cylinder, vibrissae, movement initiation, and adjusting step tests). The animals were exposed to an additional isoflurane/sham anesthesia treatment on day 15, after which the striata were collected for analyses. (b) Effect of repeated isoflurane anesthesia exposure on motor functions (combined ipsilateral limb use score of sensorimotor performance); (c) Phospho‐GSK3β^Ser9/total‐GSK3β ratio and total GSK3β normalized to GAPDH; (d) Phospho‐AKT^Thr308/total‐AKT ratio and total AKT normalized to GAPDH; (e) The ratio of TH protein in lesioned versus intact striatum. (f) The ratio of TH protein in lesioned versus intact substantia nigra area. ^#/*p < 0.05; ^###/***p < 0.005, Student t‐test (b, e–f) or two‐way anova followed by Newmann–Keuls post hoc test (c–d). GAPDH, Glyceraldehyde 3‐phosphate dehydrogenase; GSK3β, glycogen synthase 3β; AKT, protein kinase B; ISO, isoflurane; I, intact hemisphere; L, lesioned hemisphere; TH, tyrosine hydroxylase.