Our recent study showed that quiescent G0 cells are more resistant to ionizing radiation than G1 cells; however, the underlying mechanism for this increased radioresistance is unknown. Based on the relatively lower DNA damage induced in G0 cells, we hypothesize that these cells are exposed to less oxidative stress during exposure. As a catalytic subunit of NADPH oxidase, Ras-related C3 botulinum toxin substrate 2 (RAC2) may be involved in the cellular response to ionizing radiation. Here, we show that RAC2 was expressed at low levels in G0 cells but increased substantially in G1 cells. Relative to G1 cells, the total antioxidant capacity in G0 phase cells increased upon exposure to X-ray radiation, whereas the intracellular concentration of ROS and malondialdehyde increased only slightly. The induction of DNA single- and double-stranded breaks in G1 cells by X-ray radiation was inhibited by knockdown of RAC2. P38 MAPK interaction with RAC2 resulted in a decrease of functional RAC2. Increased phosphorylation of P38 MAPK in G0 cells also increased cellular radioresistance; however, excessive production of ROS caused P38 MAPK dephosphorylation. P38 MAPK, phosphorylated P38 MAPK, and RAC2 regulated in mutual feedback and negative feedback regulatory pathways, resulting in the radioresistance of G0 cells.
DNA methylation is a central epigenetic event that regulates cellular differentiation, reprogramming, and pathogenesis. DNA demethylation occurs in preimplantation embryos and primordial germ cells. Recent studies suggest that TET3‐mediated oxidation of 5‐methylcytosine (5‐mC) contributes to genome‐wide loss of DNA methylation, yet the mechanism of this process in bovine preimplanted embryos has remained unknown. In this study, we analyzed the expression of Tet gene family at different stages of embryo development. The results revealed that Tet3 was highly expressed in bovine oocytes and in vitro fertilization preimplantation embryos. Knockdown of Tet3 by injection of siRNA in germinal vesicle oocytes was used to assess its role in epigenetic remodeling and embryo development. The results showed that knockdown of Tet3 significantly inhibited oocyte development, maturation, fertilization, and decreased subsequently cleavage and blastocyst rates. Tet3 knockdown significantly increased 5‐mC levels, whereas the 5‐hmC levels slightly declined. The quantitative polymerase chain reaction data showed that expression levels of the pluripotency genes ( POU5F1 and NANOG ) were significantly decreased, but the imprinted gene H19 did not change in the Tet3 knockdown group. In addition, some pluripotency genes ( POU5F1 and NANOG ) and repeated elements ( satellite I and α‐satellite ) promoter regions showed hypermethylation in the Tet3 knockdown group, except the imprinted gene H19 . Furthermore, the percentage of apoptotic cells and the expression levels of the proapoptotic gene BAX were significantly increased, whereas the antiapoptotic gene BCL‐2 messenger RNA levels were decreased in the Tet3 knockdown group. Our results indicated that Tet3 could influence the expression level of the pluripotency genes through regulating the methylation status of the promoter region, thus affect embryonic development.
All the living organisms originate, evolve and live under geomagnetic field (GMF, 20-70 µT). With rapid development in science and technology, exposure to various static magnetic fields (SMFs) from natural and man-made sources remains a public environmental topic in consideration of its probable health risk for humans. Many animal studies related to health effect have demonstrated that SMF could improve bone formation and enhance bone healing. Moreover, most of the studies focused on local SMF generated by rod-type magnet. It was difficult to come to a conclusion that how SMF affected bone metabolism in mice. The present study employed hypomagnetic field (HyMF, 500 nT), and moderate SMF (MMF, 0.2 T) to systematically investigate the effects of SMF with continuous exposure on microstructure and mechanical properties of bone. Our results clearly indicated that 4-week MMF exposure did not affect bone biomechanical properties or bone microarchitecture, while HyMF significantly inhibited the growth of mice and elasticity of bone. Furthermore, mineral elements might mediate the biological effect of SMF.
Long noncoding RNAs (lncRNAs) are important regulators of bone metabolism. In this study, lncRNA microarray analysis was used to identify differentially expressed lncRNAs in differentiated osteoclasts. lncRNA-Gm5532 is highly expressed during osteoclast differentiation. lncRNA-Gm5532 knockdown impairs osteoclast formation and bone resorption. Mechanistic experiments show that lncRNA-Gm5532 functions as a competing endogenous RNA (ceRNA) and acts as a sponge for miR-125a-3p, which promotes TNF receptor-associated factor 6 (TRAF6) expression. miR-125a-3p mimics suppress osteoclast differentiation and TAK1/NF-κB/MAPK signaling. The miR-125a-3p inhibitor reverses the negative effects of siGm5532 on osteoclast differentiation. In summary, our study reveals that lncRNA-Gm5532 functions as an activator in osteoclast differentiation by targeting the miR-125a-3p/TRAF6 axis, making it a novel biomarker and potential therapeutic target for osteoporosis.
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