Insufficient Astrocyte-Derived BDNF Contributes to Propofol-Induced Neuron Death through Akt/GSK3β/Mitochondrial Fission Pathway

Zeljko J. Bosnjak, Ph.D., Yanan Liu, Ph.D., Sarah Logan, B.S., Yasheng Yan, B.S., Xiaowen Bai, M.D., Ph.D.

Background: Propofol causes neuron death in developing animals and there is little information regarding the role of astrocytes. Relative numbers of astrocytes to neurons are much less in neonatal rodent brains compared with adults. We hypothesize that insufficient levels of astrocyte-derived brain-derived neurotrophic factor (BDNF) may contribute to propofol-induced neuron death. 
Methods: Hippocampal astrocytes and neurons isolated from neonatal rats were either cultured alone or co-cultured at 1:9 and 1:1 ratios. The cultures were treated with propofol (3, 10, or 30 μM) for 6 h with BDNF, TrkB inhibitor Cyclotraxin-B, GSK3β inhibitor CHIR99021, or mitochondrial fission inhibitor Mdivi-1. Cell death was measured by propidium iodide staining. BDNF concentration in astrocyte-conditioned medium was quantified using ELISA. Western blot was performed for Akt and GSK3β assay. Mitochondrial shape was visualized through TOM20 staining. 
Results: Propofol (10 and 30 μM) increased cell death, mitochondrial fission, and activated GSK3β; and decreased activated Akt in neurons, but did not influence astrocyte viability. The neuron death was attenuated by co-culturing with astrocytes at high-density (1:1) but not low-density (1:9). Administration of BDNF, CHIR99021, or Mdivi-1 prevented the increases of cell death and mitochondrial fission of neurons in neuron-alone cultures and 1:9 co-cultures. Blocking BDNF receptor and Akt activities abolished astrocyte-induced neuroprotection. 
Conclusions: We demonstrate for the first time that 1) astrocytes are more resistant to propofol than neurons and 2) insufficient BDNF secretion, due to low-density of astrocytes, contributes to propofol-induced neuron death through Akt/GSK3β/mitochondrial fission pathway, suggesting potential neuroprotective strategies against propofol such as administration of BDNF or astrocyte-conditioned medium, decreasing mitochondrial fission, or inhibiting GSK3β.

Insufficient astrocyte-derived BDNF contributes to propofol-induced neuron death through Akt/GSK3&#946;/mitochondrial fission pathway

Insufficient astrocyte-derived BDNF contributes to propofol-induced neuron death through Akt/GSK3β/mitochondrial fission pathway