Titration of mitochondrial fusion rescues Mff-deficient cardiomyopathy

Defects in mitochondrial fusion or fission are associated with many pathologies, raising the hope that pharmacological manipulation of mitochondrial dynamics may have therapeutic benefit. This approach assumes that organ physiology can be restored by rebalancing mitochondrial dynamics, but this concept remains to be validated. We addressed this issue by analyzing mice deficient in Mff, a protein important for mitochondrial fission. Mff mutant mice die at 13 wk as a result of severe dilated cardiomyopathy leading to heart failure. Mutant tissue showed reduced mitochondrial density and respiratory chain activity along with increased mitophagy. Remarkably, concomitant deletion of the mitochondrial fusion gene Mfn1 completely rescued heart dysfunction, life span, and respiratory chain function. Our results show for the first time that retuning the balance of mitochondrial fusion and fission can restore tissue integrity and mitochondrial physiology at the whole-organ level. Examination of liver, testis, and cerebellum suggest, however, that the precise balance point of fusion and fission is cell type specific.     

Insufficient glucose supply is linked to hypothermia upon cold exposure in high-fat diet-fed mice lacking PEMT

Mice that lack phosphatidylethanolamine N-methyltransferase (Pemt^−/− mice) are protected from high-fat (HF) diet-induced obesity. HF-fed Pemt^−/− mice show higher oxygen consumption and heat production, indicating that more energy might be utilized for thermogenesis and might account for the resistance to diet-induced weight gain. To test this hypothesis, HF-fed Pemt^−/− and Pemt^+/+ mice were challenged with acute cold exposure at 4°C. Unexpectedly, HF-fed Pemt^−/− mice developed hypothermia within 3 h of cold exposure. In contrast, chow-fed Pemt^−/− mice, possessing similar body mass, maintained body temperature. Lack of PEMT did not impair the capacity for thermogenesis in skeletal muscle or brown adipose tissue. Plasma catecholamines were not altered by Pemt genotype, and stimulation of lipolysis was intact in brown and white adipose tissue of Pemt^−/− mice. HF-fed Pemt^−/− mice also developed higher systolic blood pressure, accompanied by reduced cardiac output. Choline supplementation reversed the cold-induced hypothermia in HF-fed Pemt^−/− mice with no effect on blood pressure. Plasma glucose levels were ∼50% lower in HF-fed Pemt^−/− mice compared with Pemt^+/+ mice. Choline supplementation normalized plasma hypoglycemia and the expression of proteins involved in gluconeogenesis. We propose that cold-induced hypothermia in HF-fed Pemt^−/− mice is linked to plasma hypoglycemia due to compromised hepatic glucose production.     

Distinct Cellular Assembly Stoichiometry of Polycomb Complexes on Chromatin Revealed by Single-molecule Chromatin Immunoprecipitation Imaging

Epigenetic complexes play an essential role in regulating chromatin structure, but information about their assembly stoichiometry on chromatin within cells is poorly understood. The cellular assembly stoichiometry is critical for appreciating the initiation, propagation, and maintenance of epigenetic inheritance during normal development and in cancer. By combining genetic engineering, chromatin biochemistry, and single-molecule fluorescence imaging, we developed a novel and sensitive approach termed single-molecule chromatin immunoprecipitation imaging (Sm-ChIPi) to enable investigation of the cellular assembly stoichiometry of epigenetic complexes on chromatin. Sm-ChIPi was validated by using chromatin complexes with known stoichiometry. The stoichiometry of subunits within a polycomb complex and the assembly stoichiometry of polycomb complexes on chromatin have been extensively studied but reached divergent views. Moreover, the cellular assembly stoichiometry of polycomb complexes on chromatin remains unexplored. Using Sm-ChIPi, we demonstrated that within mouse embryonic stem cells, one polycomb repressive complex (PRC) 1 associates with multiple nucleosomes, whereas two PRC2s can bind to a single nucleosome. Furthermore, we obtained direct physical evidence that the nucleoplasmic PRC1 is monomeric, whereas PRC2 can dimerize in the nucleoplasm. We showed that ES cell differentiation induces selective alteration of the assembly stoichiometry of Cbx2 on chromatin but not other PRC1 components. We additionally showed that the PRC2-mediated trimethylation of H3K27 is not required for the assembly stoichiometry of PRC1 on chromatin. Thus, these findings uncover that PRC1 and PRC2 employ distinct mechanisms to assemble on chromatin, and the novel Sm-ChIPi technique could provide single-molecule insight into other epigenetic complexes.     

Ablation of the Ferroptosis Inhibitor Glutathione Peroxidase 4 in Neurons Results in Rapid Motor Neuron Degeneration and Paralysis

Glutathione peroxidase 4 (GPX4), an antioxidant defense enzyme active in repairing oxidative damage to lipids, is a key inhibitor of ferroptosis, a non-apoptotic form of cell death involving lipid reactive oxygen species. Here we show that GPX4 is essential for motor neuron health and survival in vivo. Conditional ablation of Gpx4 in neurons of adult mice resulted in rapid onset and progression of paralysis and death. Pathological inspection revealed that the paralyzed mice had a dramatic degeneration of motor neurons in the spinal cord but had no overt neuron degeneration in the cerebral cortex. Consistent with the role of GPX4 as a ferroptosis inhibitor, spinal motor neuron degeneration induced by Gpx4 ablation exhibited features of ferroptosis, including no caspase-3 activation, no TUNEL staining, activation of ERKs, and elevated spinal inflammation. Supplementation with vitamin E, another inhibitor of ferroptosis, delayed the onset of paralysis and death induced by Gpx4 ablation. Also, lipid peroxidation and mitochondrial dysfunction appeared to be involved in ferroptosis of motor neurons induced by Gpx4 ablation. Taken together, the dramatic motor neuron degeneration and paralysis induced by Gpx4 ablation suggest that ferroptosis inhibition by GPX4 is essential for motor neuron health and survival in vivo.     

甲硫氨酸诱导高Hcy血症的抗氧化作用研究

为探讨甲硫氨酸在诱导高Hcy血症过程中的抗氧化作用,将Wistar大鼠随机分为正常组和1%甲硫氨酸组,喂养6周后,采用高效液相色谱法测定血清中同型半胱氨酸(Hcy)和谷胱甘肽含量(GSH),全自动氨基酸分析仪测定蛋氨酸和牛磺酸含量,转氨酶活性采用试剂盒测定。肝组织丙二醛(MDA)含量采用硫代巴比妥酸法,黄嘌呤氧化酶法和比色法测定肝组织超氧化物歧化酶(SOD)活性、总抗氧化能力(FRAP值)和还原性谷胱甘肽含量。结果表明,1%甲硫氨酸组血清Hcy和牛磺酸含量分别为3.56±0.68μmol·L-1和568.68±57.02μmol·L-1,较正常组显著升高(p<0.05)。1%甲硫氨酸组肝组织GSH含量和SOD活性分别为132.19±25.49mg·g-1和6.86±1.46U·mg-1,较正常组103.97±16.30mg·g-1和5.01±1.24U·mg-1显著升高(p<0.05)。1%甲硫氨酸组较正常组肝组织FRAP值亦升高而MDA含量降低。结果表明,甲硫氨酸在诱导高Hcy血症过程中同时具有抗氧化作用。     

Arabidopsis Cell Division Cycle 20.1 Is Required for Normal Meiotic Spindle Assembly and Chromosome Segregation

Cell division requires proper spindle assembly; a surveillance pathway, the spindle assembly checkpoint (SAC), monitors whether the spindle is normal and correctly attached to kinetochores. The SAC proteins regulate mitotic chromosome segregation by affecting CDC20 (Cell Division Cycle 20) function. However, it is unclear whether CDC20 regulates meiotic spindle assembly and proper homolog segregation. Here, we show that the Arabidopsis thaliana CDC20.1 gene is indispensable for meiosis and male fertility. We demonstrate that cdc20.1 meiotic chromosomes align asynchronously and segregate unequally and the metaphase I spindle has aberrant morphology. Comparison of the distribution of meiotic stages at different time points between the wild type and cdc20.1 reveals a delay of meiotic progression from diakinesis to anaphase I. Furthermore, cdc20.1 meiocytes exhibit an abnormal distribution of a histone H3 phosphorylation mark mediated by the Aurora kinase, providing evidence that CDC20.1 regulates Aurora localization for meiotic chromosome segregation. Further evidence that CDC20.1 and Aurora are functionally related was provided by meiosis-specific knockdown of At-Aurora1 expression, resulting in meiotic chromosome segregation defects similar to those of cdc20.1. Taken together, these results suggest a critical role for CDC20.1 in SAC-dependent meiotic chromosome segregation.