Shortening of primary cilia length is associated with urine concentration in the kidneys

Abstract

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.

Excessive F-Actin and Microtubule Formation Mediates Primary Cilia Shortening and Loss in Response to Increased Extracellular Osmotic Pressure

“…4), which also excludes the possibility of artifacts as urine osmolarity should be altered gradually in vivo. A recently published work further supports our in vitro findings and above-mentioned idea, as water deprivation causes shortening of renal primary cilia in vivo (Kong et al, 2023).…”

The miR‐669a‐5p/G3BP/HDAC6/AKAP12 Axis Regulates Primary Cilia Length

“…[3] For instance, leptin treatment increases the cilium length of hypothalamic neuronal cells; [4] insulin mediates negative feedback mechanisms that regulate cilium length during adipogenic differentiation; [5] and cilia on renal tubular epithelial cells are shortened upon water deprivation. [6] A recent study elegantly demonstrated that cilium length in the hypothalamus undergoes periodic changes, which are associated with circadian rhythms. [7] Dysregulation of cilium length causes multiple types of organ dysfunction, leading to a class of diseases called ciliopathies.…”

Primary cilia of the kidney: from ciliopathy to urinary concentration

“…In the current issue of Kidney Research and Clinical Practice, Kong et al [6] reported an association between water balance and primary cilia length. As expected, they found that water deprivation enhanced urine concentration and 280 www.krcp-ksn.org Kidney Res Clin Pract 2023;42(3):279-281 aquaporin-2 (AQP2) in mice.…”

“…In particular, acetylation is a characteristic of α-tubulin in the cilia, but not in the cytoplasm [1]. Acetylated α-tubulin was also used in the current study [6] as the standard marker of cilia.…”

“…Regulators of cilium disassembly, such as the scaffolding protein HEF1, can activate Aurora A kinase, which in turn phosphorylates and stimulates HDAC6, thereby promoting the deacetylation of modified, stabilized tubulins within the axoneme [7]. According to Kong et al [6], water deprivation acted as a regulator of cilium disassembly in mice. Arginine vasopressin might be a critical initiator of this process (Fig.…”