Eaton Amity F, Danielson Elizabeth C, Tu Leona J, Brown Dennis, Merkulova Maria
Division of Nephrology, Program in Membrane Biology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States.
Am J Physiol Renal Physiol. 2025 Jun 1;328(6):F890-F906. doi: 10.1152/ajprenal.00363.2024. Epub 2025 May 13.
Intercalated cells (ICs) are acid-base regulatory cells in the kidney collecting duct that excrete either acid or base into the urine in response to systemic cues. A-ICs deliver protons into the tubule lumen via an apical proton pump (V-ATPase) and reabsorb base (bicarbonate) using the anion exchanger 1 (AE1) anion exchanger. B-ICs function in the opposite direction. They have basolateral V-ATPase and secrete bicarbonate into the lumen via the anion exchange protein pendrin. The function of a third IC subtype: the non-A, non-B IC, which has apical pendrin and apical V-ATPase, is less well understood. We previously reported that members of the TLDc protein family interact with the V-ATPase and may regulate its function. TLDc proteins exhibit a distinct expression pattern in the kidney with RNAseq showing high, differential expression of Tldc2 in B-ICs. Here, we show by RNAscope imaging that Tldc2 is indeed expressed in B-ICs but also in some non-A, non-B ICs. Using knockout () mice, we found that males and females had significantly lower urine pH than wild-type littermates and their ability to increase urine pH in response to a bicarbonate load was impaired. In addition, males developed hyperbicarbonatemia. kidneys contained fewer B-ICs than wild-type mice, but they were replaced by more non-A, non-B ICs; the number of A-ICs was unchanged. Finally, there was decreased basolateral accumulation of V-ATPase in B-ICs. These findings suggest that is a novel gene involved in renal acid-base regulation and in addition, may serve as a differentiation marker for B-ICs. Acid-base balance in the body is constantly changing but must be tightly controlled to be compatible with life. The kidney contains specialized cells that can excrete excess acid or base (bicarbonate) into the urine to maintain normal blood pH. The key protein involved in this process is called the V-ATPase. Here, we report that a novel V-ATPase interacting protein Tldc2 is critical for kidney bicarbonate secretion and is, therefore, a previously unrecognized acid-base regulatory gene.
闰细胞（ICs）是肾集合管中的酸碱调节细胞，可根据全身信号向尿液中排泄酸或碱。A型闰细胞通过顶端质子泵（V-ATP酶）将质子输送到肾小管管腔，并利用阴离子交换蛋白1（AE1）重吸收碱（碳酸氢盐）。B型闰细胞的功能则相反。它们具有基底外侧V-ATP酶，并通过阴离子交换蛋白pendrin将碳酸氢盐分泌到管腔中。第三种闰细胞亚型，即非A非B型闰细胞，其顶端有pendrin和顶端V-ATP酶，其功能尚不太清楚。我们之前报道过，TLDc蛋白家族成员与V-ATP酶相互作用，并可能调节其功能。TLDc蛋白在肾脏中呈现出独特的表达模式，RNA测序显示Tldc2在B型闰细胞中有高度差异表达。在这里，我们通过RNAscope成像显示，Tldc真的在B型闰细胞中表达，但在一些非A非B型闰细胞中也有表达。使用基因敲除（）小鼠，我们发现雄性和雌性小鼠的尿液pH值显著低于野生型同窝小鼠，并且它们对碳酸氢盐负荷增加尿液pH值的能力受损。此外，雄性小鼠出现了高碳酸氢盐血症。基因敲除小鼠的肾脏中B型闰细胞比野生型小鼠少，但被更多的非A非B型闰细胞取代；A型闰细胞的数量没有变化。最后，基因敲除小鼠B型闰细胞中V-ATP酶的基底外侧积累减少。这些发现表明，基因敲除是一个参与肾脏酸碱调节的新基因，此外，它可能作为B型闰细胞的分化标志物。体内的酸碱平衡不断变化，但必须严格控制以维持生命。肾脏含有专门的细胞，可以将多余的酸或碱（碳酸氢盐）排泄到尿液中，以维持正常的血液pH值。参与这个过程的关键蛋白叫做V-ATP酶。在这里我们报道，一种新的与V-ATP酶相互作用的蛋白Tldc2对肾脏碳酸氢盐分泌至关重要，因此，它是一个以前未被认识的酸碱调节基因。
