Fong Shelley, Chiorini John A, Sneyd James, Suresh Vinod
Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand;
Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland.
Am J Physiol Gastrointest Liver Physiol. 2017 Feb 1;312(2):G153-G163. doi: 10.1152/ajpgi.00374.2016. Epub 2016 Dec 8.
Previous studies have shown that localized delivery of the aquaporin-1 (AQP1) gene to the parotid duct can restore saliva flow in minipigs following irradiation-induced salivary hypofunction. The resulting flow rate and electrochemistry of secreted saliva contradicts current understanding of ductal fluid transport. We hypothesized that changes in expression of ion transport proteins have occurred following AQP1 transfection. We use a mathematical model of ion and fluid transport across the parotid duct epithelial cells to predict the expression profile of ion transporters that are consistent with the experimental measurements of saliva composition and secretion rates. Using a baseline set of parameters, the model reproduces the data for the irradiated, non-AQP1-transfected case. We propose three scenarios which may have occurred after transfection, which differ in the location of the AQP1 gene. The first scenario places AQP1 within nonsecretory cells, and requires that epithelial sodium channel (ENaC) expression is greatly reduced (1.3% of baseline), and ductal bicarbonate concentration is increased from 40.6 to 137.0 mM, to drive water secretion into the duct. The second scenario introduces the AQP1 gene into all ductal cells. The final scenario has AQP1 primarily in the proximal duct cells which secrete water under baseline conditions. We find the change in the remaining cells includes a 95.8% reduction in ENaC expression, enabling us to reproduce all experimental ionic concentrations within 9 mM. These findings provide a mechanistic basis for the observations and will guide the further development of gene transfer therapy for salivary hypofunction.
NEW & NOTEWORTHY: Following transfection of aquaporin into the parotid ducts of minipigs with salivary hypofunction, the resulting increase in salivary flow rates contradicts current understanding of ductal fluid transport. We show that the change in saliva electrochemistry and flow rate can be explained by changes in expression of ion transporters in the ductal cell membranes, using a mathematical model replicating a single parotid duct.
先前的研究表明，将水通道蛋白-1（AQP1）基因局部递送至腮腺导管可恢复小型猪在辐射诱导的唾液功能减退后的唾液流量。所产生的分泌唾液的流速和电化学性质与当前对导管液体转运的理解相矛盾。我们推测，AQP1转染后离子转运蛋白的表达发生了变化。我们使用一个跨腮腺导管上皮细胞的离子和液体转运数学模型来预测与唾液成分和分泌速率的实验测量结果一致的离子转运体表达谱。使用一组基线参数，该模型再现了照射后未转染AQP1的情况的数据。我们提出了转染后可能发生的三种情况，这三种情况在AQP1基因的位置上有所不同。第一种情况是将AQP1置于非分泌细胞内，并且要求上皮钠通道（ENaC）的表达大幅降低（降至基线的1.3%），导管碳酸氢盐浓度从40.6 mM增加到137.0 mM，以驱动水分泌到导管中。第二种情况是将AQP1基因引入所有导管细胞。最后一种情况是AQP1主要存在于在基线条件下分泌水的近端导管细胞中。我们发现其余细胞的变化包括ENaC表达降低95.8%，这使我们能够在9 mM范围内再现所有实验离子浓度。这些发现为这些观察结果提供了一个机制基础，并将指导唾液功能减退的基因转移治疗的进一步发展。
在将水通道蛋白转染到患有唾液功能减退的小型猪的腮腺导管后，唾液流速的增加与当前对导管液体转运的理解相矛盾。我们表明，使用复制单个腮腺导管的数学模型，唾液电化学性质和流速的变化可以通过导管细胞膜中离子转运体表达的变化来解释。
