BACKGROUND: Glioblastoma multiforme (GBM) is characterized by lethal 
aggressiveness and patients with GBM are in urgent need for new therapeutic 
avenues to improve quality of life. Current studies on tumor invasion focused on 
roles of cytokines in tumor microenvironment and numerous evidence suggests that 
TGF-β2 is abundant in glioma microenvironment and vital for glioma invasion. 
Autopagy is also emerging as a critical factor in aggressive behaviors of cancer 
cells; however, the relationship between TGF-β2 and autophagy in glioma has been 
poorly understood.
METHODS: U251, T98 and U87 GBM cell lines as well as GBM cells from a primary 
human specimen were used in vitro and in vivo to evaluate the effect of TGF-β2 
on autophagy. Western blot, qPCR, immunofluorescence and transmission-electron 
microscope were used to detect target molecular expression. Lentivirus and siRNA 
vehicle were introduced to establish cell lines, as well as mitotracker and 
seahorse experiment to study the metabolic process in glioma. Preclinical 
therapeutic efficacy was evaluated in orthotopic xenograft mouse models.
RESULTS: Here we demonstrated that TGF-β2 activated autophagy in human glioma 
cell lines and knockdown of Smad2 or inhibition of c-Jun NH2-terminal kinase, 
attenuated TGF-β2-induced autophagy. TGF-β2-induced autophagy is important for 
glioma invasion due to the alteration of epithelial-mesenchymal transition and 
metabolism conversion, particularly influencing mitochondria trafficking and 
membrane potential (△Ψm). Autopaghy also initiated a feedback on TGF-β2 in 
glioma by keeping its autocrine loop and affecting Smad2/3/7 expression. A 
xenograft model provided additional confirmation on combination of TGF-β 
inhibitor (Galunisertib) and autophagy inhibitor (CQ) to better "turn off" tumor 
growth.
CONCLUSION: Our findings elucidated a potential mechanism of 
autophagy-associated glioma invasion that TGF-β2 could initiate autophagy via 
Smad and non-Smad pathway to promote glioma cells' invasion.