Insufficient Astrocyte-Derived Brain-Derived Neurotrophic Factor Contributes to Propofol-Induced Neuron Death Through Akt/Glycogen Synthase Kinase 3β/Mitochondrial Fission Pathway

Abstract

BACKGROUND Growing animal evidence demonstrates that prolonged exposure to propofol during brain development induces widespread neuronal cell death, but there is little information on the role of astrocytes. Astrocytes can release neurotropic growth factors such as brain-derived neurotropic factor (BDNF), which can exert the protective effect on neurons in paracrine fashion. We hypothesize that during propofol anesthesia, BDNF released from developing astrocytes may not be sufficient to prevent propofol-induced neurotoxicity. METHODS Hippocampal astrocytes and neurons isolated from neonatal Sprague Dawley rats were exposed to propofol at a clinically relevant dose of 30 μM or dimethyl sulfoxide as control for 6 h. Propofol-induced cell death was determined by propidium iodide (PI) staining in astrocyte-alone cultures, neuron-alone cultures, or co-cultures containing either low or high density of astrocytes [1:9 or 1:1 ratio of astrocytes to neurons (ANR), respectively)]. The astrocyte-conditioned medium was collected 12 h following propofol exposure and measured by protein array assay. BDNF concentration in astrocyte-conditioned medium was quantified using ELISA. Neuron-alone cultures were treated with BDNF, tyrosine receptor kinase B (TrkB) inhibitor Cyclotraxin-B, glycogen synthase kinase 3β (GSK3β) inhibitor CHIR99021, or mitochondrial fission inhibitor Mdivi-1 prior to propofol exposure. Western blot was performed for quantification of the level of Akt and GSK3β. Mitochondrial shape was visualized through TOM20 staining. RESULTS Propofol increased cell death in neurons by 1.8 fold [% of PI-positive cells (PI%) =18.6, 95% CI=15.2–21.9, P<0.05], but did not influence astrocyte viability. The neuronal death was attenuated by a high ANR (1:1 co-cultures) [fold change (FC) =1.17, 95% CI=0.96–1.38, P<0.05), but not with a low ANR (1:9 co-cultures)] (FC=1.87, 95% CI=1.48–2.26, P>0.05). Astrocytes secreted BDNF in a cell density-dependent way and propofol decreased BDNF secretion from astrocytes. Administration of BDNF, CHIR99021, or Mdivi-1 significantly attenuated the propofol-induced neuronal death and aberrant mitochondria in neuron-alone cultures (FC=0.8, 95% CI=0.62–0.98; FC=1.22, 95% CI=1.11–1.32; FC=1.35, 95% CI=1.16–1.54 respectively, P<0.05) and the co-cultures with a low ANR (1:9) (FC=0.85, 95% CI=0.74–0.97; FC=1.08, 95% CI=0.84–1.32; FC=1.25, 95% CI=1.1–1.39 respectively, P<0.05) Blocking BDNF receptor or Akt activity abolished astrocyte-induced neuroprotection in the co-cultures with a high ANR (1:1). CONCLUSIONS Astrocytes attenuate propofol-induced neurotoxicity through BDNF-mediated cell survival pathway suggesting multiple neuroprotective strategies such as administration of BDNF, astrocyte-conditioned medium, decreasing mitochondrial fission, or inhibition of GSK3β.

Propofol Alters Long Non-Coding RNA Profiles in the Neonatal Mouse Hippocampus: Implication of Novel Mechanisms in Anesthetic-Induced Developmental Neurotoxicity

“…In addition to the neuroapoptosis observed in our study (Fig. 1), several reports suggest other propofol-induced side effects (e.g., dysregulated neurogenesis, abnormal dendritic development, and decreased neurotrophic factor expression) [12, 18, 19, 30, 32, 33]. Thus, the current study on the analysis of the signaling pathways based on altered lncRNA and mRNA involvement was not limited to focus on apoptosis alone but predicted pathways linked to multiple neurological outcomes.…”

Propofol Induces Apoptosis of Neurons but Not Astrocytes, Oligodendrocytes, or Neural Stem Cells in the Neonatal Mouse Hippocampus

“…In addition, although propofol did not induce apoptosis in astrocytes, oligodendrocytes, or NSCs in seven-day-old mice, we cannot exclude other toxic effects on these cells. Our previous rat study showed that propofol did not induce the apoptosis of cultured hippocampal astrocytes but decreased the secretion of nine growth factors and cytokines such as brain-derived neurotrophic factor and vascular endothelial growth factor C [ 24 ]. These downregulated paracrine factors have been shown to play important roles in neuron survival, learning, and memory [ 25 ].…”

Alfaxalone activates Human Pregnane-X Receptors with greater efficacy than Allopregnanolone: an in-vitro study with implications for neuroprotection during anesthesia

“…There are reports citing precise mechanisms for neurotoxicity of anesthetic drugs per se. Liu et al showed that propofol causes dose-dependent neuronal cell death at clinically relevant concentrations through a mitochondrial pathway; Akt (protein kinase B)/glycogen synthase kinase-3 (GSK3) 26 . See Figure 3.…”