Glioblastoma is the most common and aggressive brain tumor and it is characterized by a high mortality rate. Temozolomide (TMZ) is an effective chemotherapy drug for glioblastoma, but the resistance to TMZ has come to represent a major clinical problem, and its underlying mechanism has yet to be elucidated. In the present study, the role of exosomal connexin 43 (Cx43) in the resistance of glioma cells to TMZ and cell migration was investigated. First, higher expression levels of Cx43 were detected in TMZ-resistant U251 (U251r) cells compared with those in TMZ-sensitive (U251s) cells. Exosomes from U251s or U251r cells (sExo and rExo, respectively) were isolated. It was found that the expression of Cx43 in rExo was notably higher compared with that in sExo, whereas treatment with rExo increased the expression of Cx43 in U251s cells. Additionally, exosomes stained with dioctadecyloxacarbocyanine (Dio) were used to visualized exosome uptake by glioma cells. It was observed that the uptake of Dio-stained rExo in U251s cells was more prominent compared with that of Dio-stained sExo, while 37,43 Gap27, a gap junction mimetic peptide directed against Cx43, alleviated the rExo uptake by cells. Moreover, rExo increased the IC 50 of U251s to TMZ, colony formation and Bcl-2 expression, but decreased Bax and cleaved caspase-3 expression in U251s cells. 37,43 Gap27 efficiently inhibited these effects of rExo on U251s cells. Finally, the results of the wound healing and Transwell assays revealed that rExo significantly enhanced the migration of U251s cells, whereas 37,43 Gap27 significantly attenuated rExo-induced cell migration. Taken together, these results indicate the crucial role of exosomal Cx43 in chemotherapy resistance and migration of glioma cells, and suggest that Cx43 may hold promise as a therapeutic target for glioblastoma in the future.

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Cathepsins are families of proteases that have been reported to play the key roles in neuroexcitotoxicity. The present study was sought to determine the effect of CBI, a cathepsin B inhibitor, in the prevention of neurobehavioral deficits after inhalant flurothyl-induced recurrent neonatal seizures in rats. We examined the expression pattern of autophagy-related genes at acute phase after the last seizures using western blot method, and evaluated behavioral deficits during postnatal day 28 (P28) to P35. The results showed improved neurological scores and learning ability in CBI-treated rats compared with the nontreated control. Flurothyl-induced increases in the ratio of LC3-II/LC3-I, Beclin-1 and Cathepsin-B were blocked by pre-treatment with CBI at 1.5, 3, 6 and 24 h after the last seizures in hippocampus and cerebral cortex by western blot analysis. Meanwhile, CBI also reversed flurothyl-induced down-regulation of Bcl-2 protein levels. Furthermore, in the long-term time point of 35 days (P35), PRG-1 mRNA and protein level in hippocampus and cerebral cortex of recurrent seizure group were up-regulated when compared to the control rats; meanwhile, the up-regulated expression of PRG-1 were robustly inhibited by CBI. These date demonstrated, for the first time, that lysosomal enzymes participate in neonatal seizure-induced brain damage and that modulation of cathepsin B may offer a new strategy for the development of therapeutic interventions for treatment of developmental seizure-induced brain damage.

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Glioblastoma multiform (GBM) is a highly aggressive primary brain tumor. Exosomes derived from glioma cells under a hypoxic microenvironment play an important role in tumor biology including metastasis, angiogenesis and chemoresistance. However, the underlying mechanisms remain to be elucidated. In this study, we aimed to explore the role of connexin 43 on exosomal uptake and angiogenesis in glioma under hypoxia. U251 cells were exposed to 3% oxygen to achieve hypoxia, and the expression levels of HIF-1α and Cx43, involved in the colony formation and proliferation of cells were assessed. Exosomes were isolated by differential velocity centrifugation from U251 cells under normoxia and hypoxia (Nor-Exos and Hypo-Exos), respectively. Immunofluorescence staining, along with assays for CCK-8, tube formation and wound healing along with a transwell assay were conducted to profile exosomal uptake, proliferation, tube formation, migration and invasion of HUVECs, respectively. Our results revealed that Hypoxia significantly up-regulated the expression of HIF-1α in U251 cells as well as promoting proliferation and colony number. Hypoxia also increased the level of Cx43 in U251 cells and in the exosomes secreted. The uptake of Dio-stained Hypo-Exos by HUVECs was greater than that of Nor-Exos, and inhibition of Cx43 by 37,43 gap27 or lenti-Cx43-shRNA efficiently prevented the uptake of Hypo-Exos by recipient endothelial cells. In addition, the proliferation and total loops of HUVECs were remarkably increased at 24 h, 48 h, and 10 h after Hypo-Exos, respectively. Notably, 37,43 gap27, a specific Cx-mimetic peptide blocker of Cx37 and Cx43, efficiently alleviated Hypo-Exos-induced proliferation and tube formation by HUVECs. Finally, 37,43 gap27 also significantly attenuated Hypo-Exos-induced migration and invasion of HUVECs. These findings demonstrate that exosomal Cx43 contributes to glioma angiogenesis mediated by Hypo-Exos, and suggests that exosomal Cx43 might serve as a potential therapeutic target for glioblastoma.