Department of Medicine, Lunenfeld-Tanenbaum Research Institute, Mt. Sinai Hospital, University of Toronto, Toronto, ON, M5G1X5, Canada.
Department of Medicine, Lunenfeld-Tanenbaum Research Institute, Mt. Sinai Hospital, University of Toronto, Toronto, ON, M5G1X5, Canada.
Mol Metab. 2021 Jun;48:101213. doi: 10.1016/j.molmet.2021.101213. Epub 2021 Mar 17.
Glucose-dependent insulinotropic polypeptide (GIP) and Glucagon-like peptide-1 (GLP-1) are incretin hormones that exert overlapping yet distinct actions on islet β-cells. We recently observed that GIP, but not GLP-1, upregulated islet expression of Transcription Factor 7 (TCF7), a gene expressed in immune cells and associated with the risk of developing type 1 diabetes. TCF7 has also been associated with glucose homeostasis control in the liver. Herein we studied the relative metabolic importance of TCF7 expression in hepatocytes vs. islet β-cells in mice.
Tcf7 expression was selectively inactivated in adult mouse hepatocytes using adenoviral Cre expression and targeted in β-cells using two different lines of insulin promoter-Cre mice. Glucose homeostasis, plasma insulin and triglyceride responses, islet histology, hepatic and islet gene expression, and body weight gain were evaluated in mice fed regular chow or high fat diets. Tcf7 expression within pancreatic islets and immune cells was evaluated using published single cell RNA-seq (scRNA-seq) data, and in islet RNA from immunodeficient Rag2Il2rg mice.
Reduction of hepatocyte Tcf7 expression did not impair glucose homeostasis, lipid tolerance or hepatic gene expression profiles linked to control of metabolic or immune pathways. Similarly, oral and intraperitoneal glucose tolerance, plasma insulin responses, islet histology, body weight gain, and insulin tolerance were not different in mice with targeted recombination of Tcf7 in insulin-positive β-cells. Surprisingly, islet Tcf7 mRNA transcripts were not reduced in total islet RNA containing endocrine and associated non-endocrine cell types from Tcf7 mice, despite Cre-mediated recombination of islet genomic DNA. Furthermore, glucose tolerance was normal in whole body Tcf7 mice. Analysis of scRNA-seq datasets localized pancreatic Tcf7 expression to islet progenitors during development, and immune cells, but not within differentiated islet β-cells or endocrine lineages within mature islets. Moreover, the expression of Tcf7 was extremely low in islet RNA from Rag2Il2rg mice and, consistent with expression within immune cells, Tcf7 was highly correlated with levels of Cd3g mRNA transcripts in RNA from wild type mouse islets.
These findings demonstrate that Tcf7 expression is not a critical determinant of glucose homeostasis in mice. Moreover, the detection of Tcf7 expression within islet mRNA is attributable to the expression of Tcf7 RNA in islet-associated murine immune cells, and not in islet β-cells.
葡萄糖依赖性胰岛素多肽（GIP）和胰高血糖素样肽-1（GLP-1）是肠促胰岛素激素，它们对胰岛β细胞发挥重叠但不同的作用。我们最近观察到，GIP 但不是 GLP-1，可上调胰岛转录因子 7（TCF7）的表达，该基因在免疫细胞中表达，并与 1 型糖尿病的发病风险相关。TCF7 也与肝脏葡萄糖稳态控制有关。在此，我们研究了 TCF7 在肝细胞和胰岛β细胞中的相对代谢重要性。
使用腺病毒 Cre 表达选择性地在成年小鼠肝细胞中失活 Tcf7 表达，并用两种不同的胰岛素启动子-Cre 小鼠系靶向β细胞中的 Tcf7。在给予常规饮食或高脂肪饮食的小鼠中评估葡萄糖稳态、血浆胰岛素和甘油三酯反应、胰岛组织学、肝和胰岛基因表达以及体重增加。使用已发表的单细胞 RNA-seq（scRNA-seq）数据和免疫缺陷 Rag2Il2rg 小鼠的胰岛 RNA 评估胰岛内 Tcf7 的表达，并评估免疫细胞中的 Tcf7 表达。
减少肝细胞 Tcf7 表达不会损害葡萄糖稳态、脂质耐受性或与代谢或免疫途径控制相关的肝基因表达谱。同样，靶向胰岛素阳性β细胞中 Tcf7 重组也不会导致口服和腹腔内葡萄糖耐量、血浆胰岛素反应、胰岛组织学、体重增加和胰岛素耐量不同。令人惊讶的是，尽管胰岛基因组 DNA 发生了 Cre 介导的重组，但在包含内分泌和相关非内分泌细胞类型的总胰岛 RNA 中，胰岛 Tcf7 mRNA 转录本并未减少。此外，全身 Tcf7 小鼠的葡萄糖耐量正常。scRNA-seq 数据集的分析将胰腺 Tcf7 表达定位在发育过程中的胰岛祖细胞和免疫细胞中，但不在成熟胰岛中的分化胰岛β细胞或内分泌谱系内。此外，Rag2Il2rg 小鼠胰岛 RNA 中的 Tcf7 表达极低，与免疫细胞中的表达一致，Tcf7 与野生型小鼠胰岛 RNA 中的 Cd3g mRNA 转录物水平高度相关。
这些发现表明 Tcf7 表达不是小鼠葡萄糖稳态的关键决定因素。此外，胰岛 mRNA 中 Tcf7 表达的检测归因于胰岛相关的鼠免疫细胞中 Tcf7 RNA 的表达，而不是胰岛β细胞中的表达。
