Necroptotic astrocytes induced neuronal apoptosis partially through EVs-derived pro-BDNF

Our previous study showed that neuronal apoptosis was significantly increased upon treatment of conditioned medium (CM) from necroptotic astrocytes (NAS), leaving the underlying mechanism unclear. Considering the nutritive and supportive roles of astrocytes, we first examined the neurotrophic phenotype of necroptotic astrocytes with focus on glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF), two important neurotrophic factors, and it was unexpectedly found that the expression of GDNF and BDNF were up-regulated in necroptotic astrocytes in vitro. A question was raised as to whether the functional secreted forms of neurotrophic factors were increased. Considering that extracellular vesicles (EVs) were carriers of secreted substances and their roles in cellular interaction, we isolated EVs from astrocytes and found EVs from normal and necroptotic astrocytes (EVs-NAS) had characteristics of exosomes. We then examined GDNF and BDNF in EVs-NAS, and BDNF was interestingly found as an immature form of pro-BDNF. The expression of pro-BDNF was found to be increased in EVs-NAS, and EVs-NAS had a negative effect on neuronal survival. To verify that whether pro-BDNF was involved in the detrimental effect of EVs-NAS, anti-pro-BDNF antibody was applied, and we found that neuronal apoptosis-induced by EVs-NAS could be significantly attenuated by blocking pro-BDNF, which suggested that necroptotic astrocytes induced neuronal apoptosis partially through EVs-derived pro-BDNF. The data expand our understanding in neurotrophic phenotype of necroptotic astrocytes, and may provide us new strategies targeting on EVs-NAS in treatment of neurological diseases.