ASL

Researchers have succeeded in correcting a gene defect that causes a hereditary liver disease and its adverse effects on cells. Researchers at the University of Helsinki and HUS Helsinki University Hospital have succeeded in correcting a gene defect that causes a hereditary liver disease and its adverse effects on cells. Argininosuccinate lyase deficiency (ASLD), also known as argininosuccinic aciduria, is a disease that has been enriched in the Finnish genetic heritage. In this severe metabolic disease, the body does not process proteins normally, instead resulting in a very dangerous accumulation of argininosuccinic acid and ammonia. Excess ammonia causes disturbances of consciousness, coma and even death. In Finland, infants are screened for ASLD to determine the disease risk before symptoms develop. The treatment is an extremely strict lifelong diet and, in severe cases, a liver transplant. Researchers from the University of Helsinki and HUS Helsinki University Hospital have succeeded in correcting the gene defect associated with argininosuccinic aciduria and demonstrated that the harmful metabolism caused by the disease can be cured. In their recently completed study, they initially modified the skin cells of patients with ASLD into stem cells. Subsequently, the researchers reprogrammed the disease-causing gene defects in the stem cells using the CRISPR-Cas9 technique, known as gene scissors. Finally, the researchers guided the corrected stem cells to differentiate into liver cells to see whether the disease that impairs hepatic function was actually cured and that the fixed cells no longer produced the harmful argininosuccinic acid. "In our study, we demonstrated for the first time that the gene defect causing ASLD can be corrected with gene scissors without any adverse effects visible in the cells. The gene-corrected cells were also metabolically improved," says Docent of Stem Cell Biology Kirmo Wartiovaara, specialist in medical genetics, from the University of Helsinki and HUS. The study was published in the American Journal of Human Genetics. Researchers discover a suitable "gene mixture" in a drug already in use In the study, the researchers used mRNA encapsulated inside lipid nanoparticles to get the gene scissors inside the cultured cells. "This 'gene mixture' we produced is based on the formula of a pharmaceutical product already in use, which may facilitate its clinical use in the future. Our next goal is to cure ASLD in mice," says Doctoral Researcher Timo Keskinen from the University of Helsinki. "The same gene editing technique works on living animals and humans, but we don't yet know how safe it is. This is why the matter has to be investigated first in laboratory animals," Keskinen adds. Therapeutic potential at last for hereditary diseases There are already more than 7,000 hereditary diseases in the world. Finns, as well as other populations originating in small groups of people, have their own genetic disease variants that are more common in the population than elsewhere in the world. Many of these gene variants of our distant ancestors are such that if a child inherits the same variant from both parents, they may develop a severe disease. Treatments are available for only a handful of hereditary diseases, and curative therapies are even more rare. "However, a cure could be possible if the gene defect causing the disease is eliminated entirely. Thanks to basic research carried out with the help of gene scissors and other precise gene-editing techniques, permanent fixes are gradually starting to emerge," Wartiovaara says. The study is part of the doctoral theses of Sami Jalil and Timo Keskinen, supervised at the Biomedicum Stem Cell Center of the Biomedicum Helsinki research institute by Docent Kirmo Wartiovaara and Mervi Hyvönen, DMedSc.

综上所述，该研究揭示了TET2通过催化mRNA氧化的非经典功能来调控mTORC1信号转导和自噬，同时证明mTORC1能够反馈调节TET2表达，表明营养信号能够通过mTORC1-TET2轴调控表观遗传。 近日，复旦大学基础医学院生化系代谢分子医学教育部重点实验室吕雷团队与同济大学生命科学与技术学院徐艳萍团队合作，在 Cell Discovery 期刊发表了题为：TET2 is required to suppress mTORC1 signaling through urea cycle with therapeutic potential 的研究论文。 该研究揭示了DNA双加氧酶TET2通过催化尿素循环代谢酶mRNA的5mC氧化来影响其稳定性，并通过调控细胞内精氨酸含量来抑制mTORC1信号转导。进一步研究发现TET2缺失的肿瘤细胞对于mTORC1抑制剂更加敏感，为临床个性化治疗提供了理论依据。 首先，研究人员通过HE染色分析发现Tet2 KO小鼠肝脏细胞相较于对照组显著增大，而且mTORC1抑制剂Rapamycin能够逆转由TET2 KO引起的细胞体积变化。WB分析发现细胞和小鼠组织中TET2参与调控mTORC1底物（S6K, S6和4-EBP1）磷酸化和自噬。 RNA-seq分析揭示精氨酸合成在TET2 KO细胞中显著变化，而尿素循环是细胞内合成精氨酸的主要途径。研究人员发现小鼠组织和细胞中多种尿素循环代谢酶（ARG1, ASL, ASS1, CPS1和OTC）表达量被TET2抑制。LC-MS检测显示尿素循环相关代谢物含量，细胞代谢氨的能力和尿素生成在Tet2 KO细胞和小鼠组织中显著升高。敲除ASL或ASS1，或回补精氨酸能够逆转TET2对mTORC1信号转导的调控，表明TET2通过尿素循环参与mTORC1信号调控。同时，研究还揭示mTORC1对TET2表达量具有反馈调节作用。激活或抑制mTORC1信号能够显著改变TET2蛋白水平。 进一步体内和体外实验发现TET2通过催化尿素循环代谢酶mRNA氧化促进其降解，从而抑制精氨酸合成及mTORC1信号通路。过去的研究已证明mTORC1信号异常激活的细胞常出现生长活性过度依赖mTORC1通路的现象，因此研究人员尝试探索mTORC1抑制剂对TET2 KO细胞增殖的影响。体内和体外实验都证实TET2 KO细胞和肿瘤对于mTORC1抑制剂更敏感，该研究为临床治疗提供了理论依据。 综上所述，该研究揭示了TET2通过催化mRNA氧化的非经典功能来调控mTORC1信号转导和自噬，同时证明mTORC1能够反馈调节TET2表达，表明营养信号能够通过mTORC1-TET2轴调控表观遗传。最后，在临床意义方面，该研究揭示TET2低表达或失活的细胞对mTORC1抑制剂更加敏感，为肿瘤的临床治疗提供了新策略。