Na Transport in Autosomal Recessive Polycystic Kidney Disease (ARPKD) Cyst Lining Epithelial Cells

Abstract

Abstract. Autosomal dominant (ADPKD) and recessive (ARPKD) polycystic kidney disease are characterized by the progressive growth and expansion of cysts or ectatic collecting ducts, respectively, that ultimately destroy the normal renal parenchyma. Evidence from experimental models of ADPKD suggests that transepithelial Na and fluid secretion contribute to cyst growth, yet little is known about solute transport in ARPKD. This purpose of this study was to begin to characterize the expression and polarity of transport proteins involved in vectorial Na movement in ARPKD epithelium. Immunodetectable ␣1 and ␤2 subunits of the Na/K-ATPase localized to the apical membrane of collecting duct cysts in tissue sections of human fetal ARPKD nephrectomy specimens and conditionally immortalized cells derived from these cysts. Measurements of transepithelial 22 Na transport performed on monolayers of ARPKD and age-matched collecting tubule (HFCT) cells grown on permeable supports revealed net Na absorption in both models. However, ARPKD cells absorbed Na at a rate approximately 50% greater than that of HFCT. Furthermore, Na absorption in ARPKD cells was partially inhibited by 100 M apical amiloride or 1 mM basolateral but not apical ouabain. Northern blot analyses of ARPKD whole kidney and Western immunoblot of ARPKD cells showed approximately twofold greater expression of the ␣-subunit of the epithelial Na channel (ENaC) compared with age-matched controls. These results suggest that, despite the presence of apical Na/K-ATPase, ARPKD cyst-lining cells absorb Na by a pathway that is modestly amiloride-sensitive. Whether Na absorption is mediated by ENaC, perhaps of nonclassical subunit composition, or another amiloride-sensitive transporter remains to be determined.

Increased Na+/H+ exchanger activity on the apical surface of a cilium-deficient cortical collecting duct principal cell model of polycystic kidney disease

“…Na ϩ -pump subunits and growth factor receptors are normally, if not exclusively, basolateral membrane proteins in renal collecting duct epithelia. However, individual Na ϩ -pump subunits have been found in the apical membrane of cystic epithelial cells (31,44), although it is not clear if they support Na ϩ -pump activity (31,32). There is more uniform agreement that growth factor receptors appear on both the apical surface, as well as the basolateral surface of cystic epithelia.…”

Expression of Components of the Renin-angiotensin System in Autosomal Recessive Polycystic Kidney Disease

“…If available, additional studies such as mRNA analysis and more quantitative protein analysis by Western blotting could be performed. An immortalized cell line derived from AR-PKD kidneys was recently described (Rohatgi et al 2003). Attempts at demonstrating renin staining in these cells were unsuccessful.…”

Peroxisome Proliferator-Activated Receptor γ Antagonists Decrease Na+Transport via the Epithelial Na+Channel

“…In contrast, loss-of-function mutations in ENaC and its regulatory pathways lead to inappropriate renal salt-wasting (Hummler and Horisberger, 1999;Rossier et al, 2002;Schild, 2004;Rossier and Schild, 2008). Abnormal ENaC activity, moreover, is beginning to be recognized as contributing to the disease processes associated with cystic fibrosis and polycystic kidney disease, as well as several other disorders with abnormal epithelial cell transport (Rohatgi et al, 2003;Mall et al, 2004;Veizis et al, 2004). Peroxisome proliferator-activated receptor gamma (PPAR␥)…”