Institute of Biochemistry and Microbiology, Science Faculty, Universidad Austral de Chile, Valdivia, Chile.
Nephrology Service Fundació Puigvert, Biomedical Research Institute Sant Pau (IIB Sant Pau), Universitat Autònoma de Barcelona (UAB), Barcelona, Spain.
Biochim Biophys Acta Mol Basis Dis. 2024 Jan;1870(1):166890. doi: 10.1016/j.bbadis.2023.166890. Epub 2023 Sep 19.
Progression of diabetic nephropathy (DN) is linked to the dysregulated increase of adenosine and altered signaling properties. A major contribution to the maintenance of physiological extracellular adenosine levels relies on cellular uptake activity through plasma membrane nucleoside transporters. Because kidney cells are responsive to insulin, this study aims to determine how DN affects insulin regulation of the equilibrative nucleoside transporter-2 (ENT2).
Human Podocytes and rat glomeruli were used to study ENT2 regulation. The effects of diabetes and insulin on ENT2 mediated transport activity were determined measuring the fraction of total adenosine uptake in sodium-free medium which is inhibitable by hypoxanthine. Alterations in ENT2 subcellular distribution were assessed in the kidney of people affected with DN and diabetic rats. The consequences of impaired ENT2 activity on the kidney were evaluated using dipyridamole in an animal model.
Insulin upregulates ENT2 uptake activity by increasing the V, thus counteracting decreased adenosine uptake due to high d-glucose and achieving extracellular adenosine homeostasis. Insulin promoted ENT2 translocation to the plasma membrane dependent on PI3-kinase/Akt signaling and actin cytoskeleton integrity. However, in diabetic rats, the insulin-mediated induction of ENT2 activity was lost. Additionally, reduced Akt activation in response to insulin correlated with decreased ENT2 distribution at the plasma membrane. Kidney tissues from diabetic rats and human DN biopsies showed ENT2 redistribution to an intracellular pattern, evidencing dysfunctional adenosine uptake. Through ENT inhibition, we evidenced increased proteinuria and induced alpha-smooth muscle actin as a result of profibrotic activation of cells in the kidney.
Deficient insulin regulation of ENT2 activity contributes to chronically high adenosine levels and glomerular alterations that underline diabetic kidney disease progression.
糖尿病肾病（DN）的进展与腺苷的失调增加和信号转导特性改变有关。通过质膜核苷转运体的细胞摄取活性，维持生理细胞外腺苷水平的主要贡献。由于肾脏细胞对胰岛素有反应，因此本研究旨在确定 DN 如何影响胰岛素对平衡核苷转运体-2（ENT2）的调节。
使用人足细胞和大鼠肾小球来研究 ENT2 调节。通过测量钠自由介质中总腺苷摄取的分数来确定糖尿病和胰岛素对 ENT2 介导的转运活性的影响，该分数可被次黄嘌呤抑制。评估了人 DN 患者肾脏中 ENT2 亚细胞分布的改变和糖尿病大鼠。使用双嘧达莫在动物模型中评估 ENT2 活性受损对肾脏的影响。
胰岛素通过增加 V 来上调 ENT2 摄取活性，从而抵消由于高 d-葡萄糖导致的腺苷摄取减少，并实现细胞外腺苷的动态平衡。胰岛素促进 ENT2 向质膜易位，这依赖于 PI3-激酶/Akt 信号转导和肌动蛋白细胞骨架的完整性。然而，在糖尿病大鼠中，胰岛素介导的 ENT2 活性诱导丧失。此外，胰岛素反应性 Akt 激活的减少与质膜上 ENT2 分布的减少相关。糖尿病大鼠的肾脏组织和人 DN 活检显示 ENT2 重新分布到细胞内模式，表明腺苷摄取功能障碍。通过 ENT 抑制，我们证明了蛋白尿增加，并诱导了α-平滑肌肌动蛋白，这是由于肾脏细胞中纤维化激活的结果。
ENT2 活性的胰岛素调节不足导致慢性高腺苷水平和肾小球改变，这是糖尿病肾病进展的基础。
