Acute kidney injury (AKI) is a major complication of hepatic surgeries. The primary cilium protrudes to the lumen of kidney tubules and plays an important role in renal functions. Disruption of primary cilia homeostasis is highly associated with human diseases including AKI. Here, we investigated whether transient hepatic ischemia induces length change and deciliation of kidney primary cilia, and if so, whether reactive oxygen species (ROS)/oxidative stress regulates those. HIR induced damages to the liver and kidney with increases in ROS/oxidative stress. HIR shortened the cilia of kidney epithelial cells and caused them to shed into the urine. This shortening and shedding of cilia was prevented by Mn(III) tetrakis(1-methyl-4-pyridyl) porphyrin (MnTMPyP, an antioxidant). The urine of patient undergone liver resection contained ciliary proteins. These findings indicate that HIR induces shortening and deciliation of kidney primary cilia into the urine via ROS/oxidative stress, suggesting that primary cilia is associated with HIR-induced AKI and that the presence of ciliary proteins in the urine could be a potential indication of kidney injury.
Background: The primary cilium, a microtubule-based cellular organelle present in certain kidney cells, functions as a mechano-sensor to monitor fluid flow in addition to various other biological functions. In kidneys, the primary cilia protrude into the tubular lumen and are directly exposed to pro-urine flow and components. However, their effects on urine concentration remain to be defined. Here, we investigated the association between primary cilia and urine concentration. Methods: Mice either had free access to water (normal water intake, NWI) or were not allowed access to water (water deprivation, WD). Some mice received tubastatin, an inhibitor of histone deacetylase 6 (HDAC6), which regulates the acetylation of α-tubulin, a core protein of microtubules. Results: WD decreased urine output and increased urine osmolality, concomitant with apical plasma membrane localization of aquaporin 2 (AQP2) in the kidney. After WD, compared with after NWI, the lengths of primary cilia in renal tubular epithelial cells were shortened and HDAC6 activity decreased. WD induced deacetylation of α-tubulin without altering α-tubulin levels in the kidney. Tubastatin prevented the shortening of cilia through increasing HDAC6 activity and consequently increasing acetylated α-tubulin expression. Furthermore, tubastatin prevented the WD-induced reduction of urine output, urine osmolality increase, and apical plasma membrane localization of AQP2. Conclusions: WD shortens primary cilia length through HDAC6 activation and α-tubulin deacetylation, while HDAC6 inhibition blocks the WD-induced changes in cilia length and urine output. This suggests that cilia length alterations are involved, at least in part, in the regulation of body water balance and urine concentration.
Background: The primary cilium, a microtubule-based cellular organelle, acts as a mechano-sensor for monitoring the fluid flow in cells. In kidneys, the primary cilia protrude into the tubular lumen from the tubular cells and therefore, directly contact pro-urine flow and components. However, it remains to be defined how the cilia are associated with kidney function and diseases. Here, we investigated whether water access restriction affects the cilia length in the renal tubular cells, whether cilia length changes are associated with kidney functions, and how cilia lengths are regulated. Methods: C57BL/6 mice were provided free access to water (control), but water supply was stopped for some mice for 24 to 48 h (water restriction). Among each group, some mice were administered with tubastatin A (10 mg/kg BW), a specific inhibitor of histone deacetylase 6 (HDAC6), daily from 2 days before water restriction. Cultured tubular epithelial cells were treated with either 10 or 20 mM NaCl or 20 mM mannitol with or without tubastatin A. Primary cilia were determined by immunofluorescence staining using acetylated-α-tubulin antibody or scanning electron microscope. Results: Water restriction shortened the primary cilia of kidney tubular epithelial cells along with increasing urine osmolality. Water restriction increased the activity of HDAC6 with increased the deacetylation of α-tubulin, a substrate of HDAC6 and a major comprising protein of microtubule of primary cilia. HDAC6 inhibitor blocked water restriction-induced primary cilia shortening along with the inhibition of α-tubulin deacetylation. In addition, HDAC6 inhibitor blocked the increase in water restriction-induced urine osmolality. Increases of NaCl or mannitol concentration in the medium for Madin-Darby canine kidney tubule cell culture shortened the cilia length and increased HDAC6 activity and α-tubulin deacetylation. HDAC6 inhibitor blocked those NaCl and mannitol-induced effects. Conclusions: Our data have demonstrated that water restriction shortened the primary cilia of kidney tubular cells via HDAC6 activation and α-tubulin deacetylation along with increasing urine osmolality, suggesting that the alteration of primary cilia length is an adaptive response to the water intake to maintain body water balance and that the primary cilia length regulation may be a therapeutic strategy of kidney diseases related to the body water and electrolyte imbalances.
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