SUMMARY Long interspersed elements 1 (LINE-1) occupy at least 17% of the human genome and are its only active autonomous retrotransposons. However, the host factors that regulate LINE-1 retrotransposition are not fully understood. Here, we demonstrate that the Aicardi-Goutières syndrome gene product SAMHD1, recently revealed to be an inhibitor of HIV/simian immunodeficiency virus (SIV) infectivity and neutralized by the viral Vpx protein, is also a potent regulator of LINE-1 and LINE-1-mediated Alu/SVA retrotransposition. We also found that mutant SAMHD1s of Aicardi-Goutières syndrome patients are defective in LINE-1 inhibition. Several domains of SAMHD1 are critical for LINE-1 regulation. SAMHD1 inhibits LINE-1 retrotransposition in dividing cells. An enzymatic active site mutant SAMHD1 maintained substantial anti-LINE-1 activity. SAMHD1 inhibits ORF2p-mediated LINE-1 reverse transcription in isolated LINE-1 ribonucleoproteins by reducing ORF2p level. Thus, SAMHD1 may be a cellular regulator of LINE-1 activity that is conserved in mammals.

BackgroundEndothelial dysfunction has been suggested as a possible causal link between hyperglycemia and microvascular complications in diabetes mellitus. The effect of metformin on endothelial progenitor cells (EPCs) is still unclear. This study was designed to test the hypothesis that metformin could accelerate wound healing by improving the impaired EPC functions in streptozotocin-induced diabetic mice.MethodsStreptozotocin (STZ, 60 mg/kg/d × 5 d, i.p.) was injected to induce type 1 diabetes in male C57BL/6 mice. Mice were treated with metformin (250 mg/kg/d, i.g.) for consecutive 14 days. Wound closure was evaluated by wound area and number of CD31 stained capillaries. Functions of bone marrow-endothelial progenitor cells (BM-EPCs) were assessed by tube formation and migration assays, and expression of AMP-activated protein kinase (AMPK) and endothelial nitric oxide synthase (eNOS) was determined by western blot analysis.ResultsMetformin accelerated wound closure and stimulated angiogenesis in diabetic mice. The number of circulating EPCs was increased significantly in metformin treated diabetic mice. Abilities of tube formation and migration of BM-EPCs were impaired in diabetic mice, which were improved by metformin. Expression of both phosphorylated-AMPK and phosphorylated-eNOS was significantly increased, and nitric oxide (NO) production was enhanced by metformin in BM-EPCs of diabetic mice. In vitro, metformin improved impaired BM-EPC functions, and increased phosphorylated-eNOS expression and NO production in cultured BM-EPCs caused by high glucose, which was prevented by the AMPK inhibitor compound C.ConclusionsOur results suggest that metformin could improve BM-EPC functions in STZ-induced diabetic mice, which was possibly dependent on the AMPK/eNOS pathway.Electronic supplementary materialThe online version of this article (doi:10.1186/s12933-016-0408-3) contains supplementary material, which is available to authorized users.

Prolonged exposure to volatile anesthetics, such as isoflurane and sevoflurane, causes neurodegeneration in the developing animal brains. Recent studies showed that dexmedetomidine, a selective α2-adrenergic agonist, reduced isoflurane-induced cognitive impairment and neuroapoptosis. However, the mechanisms for the effect are not completely clear. Thus, we investigated whether exposure to isoflurane or sevoflurane at an equivalent dose for anesthesia during brain development causes different degrees of neuroapoptosis and whether this neuroapoptosis is reduced by dexmedetomidine via effects on PI3K/Akt pathway that can regulate cell survival. Seven-day-old (P7) neonatal Sprague-Dawley rats were randomly exposed to 0.75% isoflurane, 1.2% sevoflurane or air for 6 h. Activated caspase-3 was detected by immunohistochemistry and Western blotting. Phospho-Akt, phospho-Bad, Akt, Bad and Bcl-xL proteins were detected by Western blotting in the hippocampus at the end of exposure. Also, P7 rats were pretreated with various concentrations of dexmedetomidine alone or together with PI3K inhibitor LY294002, and then exposed to 0.75% isoflurane. Terminal deoxyribonucleotide transferase-mediated dUTP nick end labeling (TUNEL) and activated caspase-3 were used to detect neuronal apoptosis in their hippocampus. Isoflurane, not sevoflurane at the equivalent dose, induced significant neuroapoptosis, decreased the levels of phospho-Akt and phospho-Bad proteins, increased the expression of Bad protein and reduced the ratio of Bcl-xL/Bad in the hippocampus. Dexmedetomidine pretreatment dose-dependently inhibited isoflurane-induced neuroapoptosis and restored protein expression of phospho-Akt and Bad as well as the Bcl-xL/Bad ratio induced by isoflurane. Pretreatment with single dose of 75 µg/kg dexmedetomidine provided a protective effect similar to that with three doses of 25 µg/kg dexmedetomidine. Moreover, LY294002, partly inhibited neuroprotection of dexmedetomidine. Our results suggest that dexmedetomidine pretreatment provides neuroprotection against isoflurane-induced neuroapoptosis in the hippocampus of neonatal rats by preserving PI3K/Akt pathway activity.