目的:双孔通道(TPCs)构成了一个在内溶酶体区室中表达的小家族阳离子通道。TPC已被表征为控制Ca2介导的囊泡膜融合并从而调节内溶酶体囊泡运输的关键元件。胞外和内吞运输和溶酶体降解是适应上皮运输的主要机制。高度调节的上皮运输的一个主要例子是肾脏的肾小管系统。因此,我们研究了TPC蛋白1(TPC1)在肾脏中的定位及其在肾小管运输动态调节中的功能作用。
方法:免疫组化结合肾小管标记物研究TPC1在近端和远端肾小管中的表达。磷酸盐和铵的排泄,以及在体内研究尿液体积和pH值,为了应对连续输注NaCl引起的甲状旁腺激素推注或酸碱转换引起的动态挑战,Na2CO3,和NH4Cl.
结果:在TPC1缺陷小鼠中,PTH诱导的磷酸盐排泄增加被延长和夸大,与野生型同窝动物相比,其恢复延迟。在酸碱转变实验中,与野生型相比,缺乏TPC1的小鼠对Na2CO3的反应显示出相同的磷酸盐排泄增加,而是NH4Cl诱导的复苏延迟。用Na2CO3减少铵排泄,并随NH4Cl增加,但基因型之间没有差异。
结论:我们得出的结论是,TPC1在近端而不是远端小管的根尖下表达,并且在近端小管磷酸盐重吸收向增强的动态适应中起重要作用。但不减少吸收。
Two-pore channels (TPCs) constitute a small family of cation channels expressed in endo-lysosomal compartments. TPCs have been characterized as critical elements controlling Ca2+ -mediated vesicular membrane fusion and thereby regulating endo-lysosomal vesicle trafficking. Exo- and endocytotic trafficking and lysosomal degradation are major mechanisms of adaption of epithelial transport. A prime example of highly regulated epithelial transport is the tubular system of the kidney. We therefore studied the localization of TPC protein 1 (
TPC1) in the kidney and its functional role in the dynamic regulation of tubular transport.
Immunohistochemistry in combination with tubular markers were used to investigate
TPC1 expression in proximal and distal tubules. The excretion of phosphate and ammonium, as well as urine volume and pH were studied in vivo, in response to dynamic challenges induced by bolus injection of parathyroid hormone or acid-base transitions via consecutive infusion of NaCl, Na2 CO3 , and NH4 Cl.
In
TPC1-deficient mice, the PTH-induced rise in phosphate excretion was prolonged and exaggerated, and its recovery delayed in comparison with wildtype littermates. In the acid-base transition experiment,
TPC1-deficient mice showed an identical rise in phosphate excretion in response to Na2 CO3 compared with wildtypes, but a delayed NH4Cl-induced recovery. Ammonium-excretion decreased with Na2 CO3 , and increased with NH4 Cl, but without differences between genotypes.
We conclude that
TPC1 is expressed subapically in the proximal but not distal tubule and plays an important role in the dynamic adaptation of proximal tubular phosphate reabsorption towards enhanced, but not reduced absorption.