Abstract：
Thymidine phosphorylase (TP), encoded by the TYMP gene, is a cytosolic enzyme essential for the nucleotide salvage pathway. TP catalyzes the phosphorylation of the deoxyribonucleosides, thymidine and 2\'-deoxyuridine, to thymine and uracil. Biallelic TYMP variants are responsible for Mitochondrial NeuroGastroIntestinal Encephalomyopathy (MNGIE), an autosomal recessive disorder characterized in most patients by gastrointestinal and neurological symptoms, ultimately leading to death. Studies on the impact of TYMP variants in cellular systems with relevance to the organs affected in MNGIE are still scarce and the role of TP in adipose tissue remains unexplored.
Deep phenotyping was performed in three patients from two families carrying homozygous TYMP variants and presenting with lipoatrophic diabetes. The impact of the loss of TP expression was evaluated using a CRISPR-Cas9-mediated TP knockout (KO) strategy in human adipose stem cells (ASC), which can be differentiated into adipocytes in vitro. Protein expression profiles and cellular characteristics were investigated in this KO model.
All patients had TYMP loss-of-function variants and first presented with generalized loss of adipose tissue and insulin-resistant diabetes. CRISPR-Cas9-mediated TP KO in ASC abolished adipocyte differentiation and decreased insulin response, consistent with the patients\' phenotype. This KO also induced major oxidative stress, altered mitochondrial functions, and promoted cellular senescence. This translational study identifies a new role of TP by demonstrating its key regulatory functions in adipose tissue.
The implication of TP variants in atypical forms of monogenic diabetes shows that genetic diagnosis of lipodystrophic syndromes should include TYMP analysis. The fact that TP is crucial for adipocyte differentiation and function through the control of mitochondrial homeostasis highlights the importance of mitochondria in adipose tissue biology.
Deep phenotyping was performed in three patients from two families carrying homozygous TYMP variants and presenting with lipoatrophic diabetes. The impact of the loss of TP expression was evaluated using a CRISPR-Cas9-mediated TP knockout (KO) strategy in human adipose stem cells (ASC), which can be differentiated into adipocytes in vitro. Protein expression profiles and cellular characteristics were investigated in this KO model.
All patients had TYMP loss-of-function variants and first presented with generalized loss of adipose tissue and insulin-resistant diabetes. CRISPR-Cas9-mediated TP KO in ASC abolished adipocyte differentiation and decreased insulin response, consistent with the patients\' phenotype. This KO also induced major oxidative stress, altered mitochondrial functions, and promoted cellular senescence. This translational study identifies a new role of TP by demonstrating its key regulatory functions in adipose tissue.
The implication of TP variants in atypical forms of monogenic diabetes shows that genetic diagnosis of lipodystrophic syndromes should include TYMP analysis. The fact that TP is crucial for adipocyte differentiation and function through the control of mitochondrial homeostasis highlights the importance of mitochondria in adipose tissue biology.
摘要：
胸苷磷酸化酶（TP），由TYMP基因编码，是核苷酸补救途径所必需的细胞溶质酶。TP催化脱氧核糖核苷的磷酸化，胸苷和2'-脱氧尿苷，胸腺嘧啶和尿嘧啶.双等位基因TYMP变体负责线粒体神经胃肠道脑肌病（MNGIE），一种常染色体隐性遗传疾病，在大多数患者中以胃肠道和神经症状为特征，最终导致死亡。关于TYMP变体在细胞系统中与MNGIE中受影响的器官相关的影响的研究仍然很少，并且TP在脂肪组织中的作用仍未被探索。
对来自两个家庭的三名患者进行了深度表型分析，这些患者携带纯合TYMP变体并表现为脂肪萎缩性糖尿病。在人脂肪干细胞（ASC）中使用CRISPR-Cas9介导的TP敲除（KO）策略评估了TP表达缺失的影响。可以在体外分化为脂肪细胞。在该KO模型中研究了蛋白质表达谱和细胞特征。
所有患者均有TYMP功能丧失变异，首先表现为全身脂肪组织丧失和胰岛素抵抗糖尿病。在ASC中CRISPR-Cas9介导的TPKO消除了脂肪细胞分化并降低了胰岛素反应，与患者表型一致。该KO还诱导了主要的氧化应激，改变了线粒体功能，促进细胞衰老。这项翻译研究通过证明其在脂肪组织中的关键调节功能，确定了TP的新作用。
TP变异在非典型形式的单基因糖尿病中的意义表明，脂肪营养不良综合征的遗传诊断应包括TYMP分析。TP通过控制线粒体稳态对脂肪细胞分化和功能至关重要这一事实突出了线粒体在脂肪组织生物学中的重要性。
对来自两个家庭的三名患者进行了深度表型分析，这些患者携带纯合TYMP变体并表现为脂肪萎缩性糖尿病。在人脂肪干细胞（ASC）中使用CRISPR-Cas9介导的TP敲除（KO）策略评估了TP表达缺失的影响。可以在体外分化为脂肪细胞。在该KO模型中研究了蛋白质表达谱和细胞特征。
所有患者均有TYMP功能丧失变异，首先表现为全身脂肪组织丧失和胰岛素抵抗糖尿病。在ASC中CRISPR-Cas9介导的TPKO消除了脂肪细胞分化并降低了胰岛素反应，与患者表型一致。该KO还诱导了主要的氧化应激，改变了线粒体功能，促进细胞衰老。这项翻译研究通过证明其在脂肪组织中的关键调节功能，确定了TP的新作用。
TP变异在非典型形式的单基因糖尿病中的意义表明，脂肪营养不良综合征的遗传诊断应包括TYMP分析。TP通过控制线粒体稳态对脂肪细胞分化和功能至关重要这一事实突出了线粒体在脂肪组织生物学中的重要性。
