Tubular ATP release is regulated by mechanosensation of fluid shear stress (FSS). Polycystin-1/polycystin-2 (PC1/PC2) functions as a mechanosensory complex in the kidney. Extracellular ATP is... Show moreTubular ATP release is regulated by mechanosensation of fluid shear stress (FSS). Polycystin-1/polycystin-2 (PC1/PC2) functions as a mechanosensory complex in the kidney. Extracellular ATP is implicated in polycystic kidney disease (PKD), where PC1/PC2 is dysfunctional. This study aims to provide new insights into the ATP signaling under physiological conditions and PKD. Microfluidics, pharmacologic inhibition, and loss-of-function approaches were combined to assess the ATP release in mouse distal convoluted tubule 15 (mDCT15) cells. Kidney-specific Pkd1 knockout mice (iKsp-Pkd1(-/-)) and zebrafish pkd2 morphants (pkd2-MO) were as models for PKD. FSS-exposed mDCT15 cells displayed increased ATP release. Pannexin-1 inhibition and knockout decreased FSS-modulated ATP release. In iKsp-Pkd1(-/-) mice, elevated renal pannexin-1 mRNA expression and urinary ATP were observed. In Pkd1(-/-) mDCT15 cells, elevated ATP release was observed upon the FSS mechanosensation. In these cells, increased pannexin-1 mRNA expression was observed. Importantly, pannexin-1 inhibition in pkd2-MO decreased the renal cyst growth. Our results demonstrate that pannexin-1 channels mediate ATP release into the tubular lumen due to pro-urinary flow. We present pannexin-1 as novel therapeutic target to prevent the renal cyst growth in PKD. Show less
The kidneys are essential for water and electrolyte homeostasis. This Review outlines the effect of tubular flow on renal electrolyte transport along the nephron and the current challenges in the... Show moreThe kidneys are essential for water and electrolyte homeostasis. This Review outlines the effect of tubular flow on renal electrolyte transport along the nephron and the current challenges in the emerging field of tubular flow dynamics in the kidney.The kidney is a remarkable organ that accomplishes the challenge of removing waste from the body and simultaneously regulating electrolyte and water balance. Pro-urine flows through the nephron in a highly dynamic manner and adjustment of the reabsorption rates of water and ions to the variable tubular flow is required for electrolyte homeostasis. Renal epithelial cells sense the tubular flow by mechanosensation. Interest in this phenomenon has increased in the past decade since the acknowledgement of primary cilia as antennae that sense renal tubular flow. However, the significance of tubular flow sensing for electrolyte handling is largely unknown. Signal transduction pathways regulating flow-sensitive physiological responses involve calcium, purinergic and nitric oxide signalling, and are considered to have an important role in renal electrolyte handling. Given that mechanosensation of tubular flow is an integral role of the nephron, defective tubular flow sensing is probably involved in renal disease. Studies investigating tubular flow and electrolyte transport differ in their methodology, subsequently hampering translational validity. This Review provides the basis for understanding electrolyte disorders originating from altered tubular flow sensing as a result of pathological conditions. Show less
Magnesium (Mg2+) is an important cofactor of many enzymes crucial for life; therefore, maintaining a Mg2+ balance in the body is essential. In the kidney, the distal convoluted tubule (DCT)... Show moreMagnesium (Mg2+) is an important cofactor of many enzymes crucial for life; therefore, maintaining a Mg2+ balance in the body is essential. In the kidney, the distal convoluted tubule (DCT) determines the final urinary Mg2+ excretion. The nephron is subjected to variable urinary flow, but little is known about the influence of flow on Mg2+ transport. Primary cilia, which are mechanosensory organelles that sense changes in flow, are expressed on tubular epithelial cells. This study aimed to elucidate whether urinary flow facilitates DCT Mg2+ transport. To this end, mouse DCT15 cells, with and without primary cilia, were exposed to physiologic fluid flow generating 0.3, 0.6, and 1.2 dyn/cm(2) fluid shear stress (FSS). FSS stimulated Mg2+ uptake significantly. Net Mg2+ uptake (i.e., the difference between static and FSS) followed a single component saturable first-order transport function and was independent of FSS magnitude and primary cilia. FSS did not affect the expression of magnesiotropic genes, including Cnnm2, Kcna1, Proegf, Trpm6, and Trpm7. Transient receptor potential cation channel subfamily melastatin (TRPM) member 7 (Trmp7) inhibition by 2-aminoethyl diphenyl borinate or knockout of TRPM6 did not alter net Mg2+ uptake, suggesting that TRPM6/TRPM7 homo/heterodimeric channels are not involved in FSS-activated Mg2+ transport. In summary, FSS generated by physiologic fluid flow is a new factor activating Mg2+ transport in DCT independent of primary cilia. Show less
