GRHL2 Is Required for Collecting Duct Epithelial Barrier Function and Renal Osmoregulation

Abstract

Collecting ducts make up the distal-most tubular segments of the kidney, extending from the cortex, where they connect to the nephron proper, into the medulla, where they release urine into the renal pelvis. During water deprivation, body water preservation is ensured by the selective transepithelial reabsorption of water into the hypertonic medullary interstitium mediated by collecting ducts. The collecting duct epithelium forms tight junctions composed of barrier-enforcing claudins and exhibits a higher transepithelial resistance than other segments of the renal tubule exhibit. However, the functional relevance of this strong collecting duct epithelial barrier is unresolved. Here, we report that collecting duct-specific deletion of an epithelial transcription factor, grainyhead-like 2 (GRHL2), in mice led to reduced expression of tight junction-associated barrier components, reduced collecting duct transepithelial resistance, and defective renal medullary accumulation of sodium and other osmolytes. ,-deficient collecting duct cells displayed increased paracellular flux of sodium, chloride, and urea. Consistent with these effects, -deficient mice had diabetes insipidus, produced dilute urine, and failed to adequately concentrate their urine after water restriction, resulting in susceptibility to prerenal azotemia. These data indicate a direct functional link between collecting duct epithelial barrier characteristics, which appear to prevent leakage of interstitial osmolytes into urine, and body water homeostasis.

Epac1 null mice have nephrogenic diabetes insipidus with deficient corticopapillary osmotic gradient and weaker collecting duct tight junctions

“…The corticopapillary osmotic gradient perturbation of Epac1 null mice (Figures and ) resembled that reported in mice with genetically induced CD TJ ‘leakiness’ associated with less E‐cadherin expression . The striking CD clustering of mRNA coding for Avpr2, Epac1 and the downstream Epac1 target E‐cadherin (Table ) prompted a study of the CD junctions.…”

“…Epac1 therefore appears to be required to maintain a steep medullary osmotic gradient to prevent water loss under antidiuretic conditions. A similar osmotic gradient deficiency was observed in mice with lowered CD paracellular TJ resistance due to CD‐specific deletion of the transcription factor GRHL2 . The similar decrease of Na + and osmolarity in the renal papilla and urine in GRHL2‐ and Epac1‐targeted mice ( and Figures and ), as compared to Wt mice, argues that water can equilibrate between the papillary tissue and the pre‐urine in the CD lumen.…”

“…The importance of E‐cadherin for an intact CD barrier and ability to concentrate urine are demonstrated by mice with downregulated Grainyhead‐like protein 2 homolog (GRHL2). They express less key junctional proteins and have diabetes insipidus as well as decreased renal medullary Na + content . We therefore determined the Na + content in snap‐frozen renal papillae from Wt and Epac1 −/− mice and studied the CD junctions by transmission electron microscopy (TEM).…”

Claudins in the Renal Collecting Duct

“…A recent study has demonstrated the importance of an intact epithelial barrier in the renal collecting duct for efficient water reabsorption [43]. Deletion of the transcriptional regulator Grainyhead-like 2 (Grhl2), an epithelial transcription factor that induces the expression of barrier-enforcing molecular TJ components including Cldn-4 [44], results in a leaky collecting duct epithelium and a decreased TER across the collecting duct epithelium.…”

“…Leakage of interstitial osmolytes across the Grhl2-deficient collecting duct epithelium is associated with defective retention of osmolytes in the interstitium of the inner medulla. Grhl2-deficient mice show signs of diabetes insipidus and fail to concentrate their urine adequately, although AQP-mediated water transport across the apical and basolateral membranes of Grhl2-deficient collecting ducts is intact [43]. This indicates that a tight collecting duct epithelial barrier is crucial for the maintenance of osmolality gradients and for effective collecting duct water reabsorption.…”