The Cap1–claudin-4 regulatory pathway is important for renal chloride reabsorption and blood pressure regulation

Abstract

The paracellular pathway through the tight junction provides an important route for transepithelial chloride reabsorption in the kidney, which regulates extracellular salt content and blood pressure. Defects in paracellular chloride reabsorption may in theory cause deregulation of blood pressure. However, there is no evidence to prove this theory or to demonstrate the in vivo role of the paracellular pathway in renal chloride handling. Here, using a tissue-specific KO approach, we have revealed a chloride transport pathway in the kidney that requires the tight junction molecule claudin-4. The collecting duct-specific claudin-4 KO animals developed hypotension, hypochloremia, and metabolic alkalosis due to profound renal wasting of chloride. The claudin-4-mediated chloride conductance can be regulated endogenously by a proteasechannel-activating protease 1 (cap1). Mechanistically, cap1 regulates claudin-4 intercellular interaction and membrane stability. A putative cap1 cleavage site has been identified in the second extracellular loop of claudin-4, mutation of which abolished its regulation by cap1. The cap1 effects on paracellular chloride permeation can be extended to other proteases such as trypsin, suggesting a general mechanism may also exist for proteases to regulate the tight junction permeabilities. Together, we have discovered a theory that paracellular chloride permeability is physiologically regulated and essential to renal salt homeostasis and blood pressure control.chloride channel | epithelium | hypertension C hloride is the most abundant extracellular anion and thereby determines extracellular fluid volume (ECFV) and blood pressure (BP) (1, 2). The kidney plays a vital role in ECFV and BP control through complex regulatory mechanisms acting upon ion channels and transporters located in the aldosterone-sensitive distal nephron (ASDN) (3, 4). The ASDN comprises the distal convoluted tubule (DCT), the connecting tubule (CNT), and the collecting duct (CD). The primary chloride transport mechanism in the DCT is through the thiazide-sensitive Na + /Cl − cotransporter (NCC) to reabsorb Cl − coupled with equal moles of Na + (5). The chloride transport mechanism in the CNT and CD, on the other hand, has been under debate for many years. Recent advances have identified an electroneutral transport pathway for chloride using the Cl − /bicarbonate exchanger (Slc26a4; pendrin) (6) and the Na + -driven Cl − /bicarbonate exchanger (Slc4a8; NDCBE) (7) in the β-intercalated cells (ICs) of CNT and CD. However, such an electroneutral pathway is not able to couple Cl − reabsorption with epithelial sodium channel (ENaC)-based Na + reabsorption that takes place in the principal cells (PCs) of CNT and CD (8), despite many efforts to connect ENaC and pendrin gene expression through endocrine or paracrine mechanisms (9, 10). We and others have previously demonstrated the presence of a paracellular Cl − pathway or "chloride shunt" in vitro in the CNT and CD cells (11,12). The paracellular Cl − channel is made of a key claud...

Astrocytic tight junctions control inflammatory CNS lesion pathogenesis

“…Previous studies have shown that constitutive Cldn1 inactivation in mice results in perinatal death due to loss of epidermal TJ integrity (23), while CLDN4 is also expressed in kidney and lung, and constitutive or conditional Cldn4 inactivation has been linked to urothelial hyperplasia and hydronephrosis (53), failure of chloride reabsorption (54), and susceptibility to lung injury (33). Our results thus suggest that the BBB and GL represent a coordinated double barrier to CNS entry.…”

KLHL3 regulates paracellular chloride transport in the kidney by ubiquitination of claudin-8

“…The mean BP in KO was 17.6 mmHg lower than in control animals (P = 0.0007) ( Table 1). To record BP in awake and unrestrained animals, sex-(male) and age-matched (12-wk-old) KO and littermate control mice were implanted with radiotelemetric transducers in the carotid artery (11). The 24-h telemetric traces showed that the mean BP in KO was consistently lower than in control animals throughout the 24-h period, with statistical significance reached for each time point (SI Appendix, Fig.…”

“…Although the PHA-II mechanism in the DCT has been extensively studied, the CNT/CD's role remains largely elusive. The predominant NaCl transport pathway in the CNT/CD is through epithelial Na + channel (ENaC) mediated Na + reabsorption and electrically coupled paracellular Cl − reabsorption (also known as the chloride shunt) (10,11). WT WNK4 inhibits ENaC conductivity, whereas PHA-II-causing mutations eliminate WNK4's inhibition of ENaC, thereby promoting Na + reabsorption in the CNT/CD (12).…”

Claudin-4 is required for modulation of paracellular permeability by muscarinic acetylcholine receptor in epithelial cells

“…The extracellular loops of claudins interact with each other to seal the cellular sheet and regulate paracellular transport between luminal and basolateral spaces (Lal-Nag and Morin, 2009). Claudin-4 has been detected in diverse epithelia, such as salivary, renal, lung, intestinal and epidermal cells (Akazawa et al, 2013;Cong et al, 2013;Gong et al, 2014;Kage et al, 2014;Shrestha et al, 2014). In rat submandibular SMIE cells, overexpression of claudin-4 increases TER and decreases the epithelial permeability of 70 kDa dextran (Michikawa et al, 2008).…”