High energy ionizing radiation can cause DNA damage and cell death. During clinical radiation therapy, the radiation dose could range from 15 to 60 Gy depending on targets. While 2 Gy radiation has been shown to cause cancer cell death, studies also suggest a protective potential by low dose radiation. In this study, we examined the effect of 0.2-2 Gy radiation on hippocampal neurons. Low dose 0.2 Gy radiation treatment increased the levels of MTT. Since hippocampal neurons are post-mitotic, this result reveals a possibility that 0.2 Gy irradiation may increase mitochondrial activity to cope with stimuli. Maintaining neural plasticity is an energy-demanding process that requires high efficient mitochondrial function. We thus hypothesized that low dose radiation may regulate mitochondrial dynamics and function to ensure survival of neurons. Our results showed that five days after 0.2 Gy irradiation, no obvious changes on neuronal survival, neuronal synapses, membrane potential of mitochondria, reactive oxygen species levels, and mitochondrial DNA copy numbers. Interestingly, 0.2 Gy irradiation promoted the mitochondria fusion, resulting in part from the increased level of a mitochondrial fusion protein, Mfn2, and inhibition of Drp1 fission protein trafficking to the mitochondria. Accompanying with the increased mitochondrial fusion, the expressions of complexes I and III of the electron transport chain were also increased. These findings suggest that, hippocampal neurons undergo increased mitochondrial fusion to modulate cellular activity as an adaptive mechanism in response to low dose radiation.

Due to the inhibitory microenvironment and reduced intrinsic growth capacity of neurons, neuronal regeneration of central nervous system remains challenging. Neurons are highly energy demanding and require sufficient mitochondria to support cellular activities. In response to stimuli, mitochondria undergo fusion/fission cycles to adapt to environment. It is thus logical to hypothesize that the plasticity of mitochondrial dynamics is required for neuronal regeneration. In this study, we examined the role of mitochondrial dynamics during regeneration of rat hippocampal neurons. Quantitative analysis showed that injury induced mitochondrial fission. As mitochondrial dysfunction has been implicated in neurodegenerative diseases, we tested the possibility that the mitochondrial therapy may promote neuronal regeneration. Supplying freshly isolated mitochondria to the injured hippocampal neurons not only significantly increased neurite re-growth but also restored membrane potential of injured hippocampal neurons. Together, our findings support the importance of mitochondrial dynamics during regeneration of injured hippocampal neurons and highlight the therapeutic prospect of mitochondria to the injured central nervous system.

Toona sinensis (TS) is a type of deciduous tree, which is distributed widely in Asia and used as a traditional herb medicine. Previously, we demonstrated that aqueous extracts of TS leaves (TSL-1) induce apoptosis in two clear types of human renal carcinoma cells (ccRCC) via mitochondria-dependent pathway. In this study, we further investigated the more detailed mechanism of TSL-1-induced antitumor effects on ccRCCs. TSL-1 treatment arrested ccRCC cells in G0/G1 phase through the decrease of cyclin D1, cyclin-dependent kinase (CDK)2, and CDK4 as well as induction of p53 and FOXO3a protein expressions. On the other hand, the inhibitory effects of TSL-1 on migration were also observed in 786-O and A-498 cells. Mechanically, we presented that TSL-1 could suppress cell cycle progression and motility via inhibiting the phosphorylation of JAK2/stat3, Akt, MEK/ERK, and mTOR in a concentration- and time-dependent manner. Moreover, we found that TSL-1 inhibited p21, HIF-2α, c-Myc, VEGF, and MMP9 protein expressions in both cell lines. In conclusion, these findings suggested that TS-induced apoptosis and its antimigration activity in ccRCC cells were accompanied by inactivation of several oncogenic pathways.

No abstract