Aliskiren restores renal AQP2 expression during unilateral ureteral obstruction by inhibiting the inflammasome

Abstract

Ureteral obstruction is associated with reduced expression of renal aquaporins (AQPs), urinary concentrating defects, and an enhanced inflammatory response, in which the renin-angiotensin system (RAS) may play an important role. We evaluated whether RAS blockade by a direct renin inhibitor, aliskiren, would prevent the decreased renal protein expression of AQPs in a unilateral ureteral obstruction (UUO) model and what potential mechanisms may be involved. UUO was performed for 3 days (3UUO) and 7 days (7UUO) in C57BL/6 mice with or without aliskiren injection. In 3UUO and 7UUO mice, aliskiren abolished the reduction of AQP2 protein expression but not AQP1, AQP3, and AQP4. mRNA levels of renal AQP2 and vasopressin type 2 receptor were decreased in obstructed kidneys of 7UUO mice, which were prevented by aliskiren treatment. Aliskiren treatment was also associated with a reduced inflammatory response in obstructed kidneys of UUO mice. Aliskiren significantly decreased mRNA levels of several proinflammatory factors, such as transforming growth factor-β and tumor necrosis factor-α, seen in obstructed kidneys of UUO mice. Interestingly, mRNA and protein levels of the NOD-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome components apoptosis-associated speck-like protein containing a caspase recruitment domain, caspase-1, and IL-1β were dramatically increased in obstructed kidneys of 7UUO mice, which were significantly suppressed by aliskiren. In primary cultured inner medullary collecting duct cells, IL-1β significantly decreased AQP2 expression. In conclusions, RAS blockade with the direct renin inhibitor aliskiren increased water channel AQP2 expression in obstructed kidneys of UUO mice, at least partially by preventing NLRP3 inflammasome activation in association with ureteral obstruction.

Molecular mechanisms regulating aquaporin-2 in kidney collecting duct

“…In particular, for the AQP2 trafficking, the main underlying signaling pathways are AQP2 phosphorylation, RhoA phosphorylation, intracellular Ca 2ϩ mobilization, and actin depolymerization. Additional signaling pathways including angiotensin II, aldosterone, prostaglandins, and vesicle-targeting receptors have been reported in previous studies and reviews (18,34,64,68,80,98,100,102,103,112,145,150). Detailed studies on the AQP2 in the kidney collecting ducts will provide new insights in the treatment of patients with body water balance disorders, including NDI, and water retention conditions, such as congestive heart failure and liver cirrhosis.…”

Inflammasomes in the Pathophysiology of Kidney Diseases

“…Renin-angiotensin system blockade inhibited NLRP3 inflammasome activation and then increased water channel AQP2 expression in the UUO mouse model [27]. Vilaysane et al [23] observed less tubular injury, inflammation and fibrosis in association with a reduction in caspase-1 activation, as well as maturation of IL-1β and IL-18 in NLRP3 kidney-specific knockout mice 2 weeks after UUO operation.…”

Hydrogen sulfide upregulates renal AQP‐2 protein expression and promotes urine concentration

“…Upon completion of the incubation, the protein was isolated by using RIPA buffer containing a proteinase cocktail, and the samples were used for immunoblot analysis as described by Wang et al (19). All in vitro experiments were repeated 3 times.…”

“…Primary rat IMCD cells were cultured as described by Wang et al (19). The samples were incubated with GYY4137 (10 25 M) for 0.5, 1, and 2 h. Immunofluorescence was performed to examine AQP-2 expression and trafficking in IMCD cells.…”

“…Western blot analysis and immunohistochemistry were performed, as previously described (19). The Western blot analysis membranes were visualized with Pierce ECL (Thermo Fisher Scientific, Waltham, MA, USA) and processed for signal detection by using the 5200 Luminescent Imaging Workstation (Tanon, Shanghai, China).…”