Disease relevance of Aqp5

• CONCLUSIONS: Ischemic acute renal failure leads to down regulation of pulmonary ENaC, Na,K-ATPase and aquaporin-5, but not aquaporin-1 [1].
• Subcellular distribution of aquaporin 5 in salivary glands in primary Sjögren's syndrome [2].
• These results suggest that AQP5 may be one of the candidates for inducing the intracranial edema in the CNS after ischemia injury [3].
• Interestingly, AQP5 showed a transient up-regulation (about 3-fold) and subsequent down-regulation of its expression within 20 h of reoxygenation after hypoxia [3].
• However, at 32 degrees C (mild hypothermia), the expression of AQP5 mRNA was restored to its basal level [4].

High impact information on Aqp5

• Our results suggest that the distribution and density of aquaporin 5 in salivary glands does not differ between patients with PSS and those without [2].
• Since aquaporin 5 is involved in transport of water and is present in salivary and lacrimal glands, this protein was thought to have a major role in the pathogenesis of PSS [2].
• These studies have identified a new mammalian member of the Aquaporin water channel family (gene symbol AQP5) which is implicated in the generation of saliva, tears, and pulmonary secretions [5].
• The muscarinic acetylcholine receptor-stimulated increase in aquaporin-5 levels in the apical plasma membrane in rat parotid acinar cells is coupled with activation of nitric oxide/cGMP signal transduction [6].
• These results suggest that NO/cGMP signal transduction has a crucial role in Ca(2+) homeostasis in the mAChR-stimulated increase in AQP5 levels in the APM of rat parotid glands [6].

Biological context of Aqp5

• Our present study suggests the existence of genetic variation in the expression of a water channel protein, AQP5, in rats [7].
• Keratinocyte growth factor modulates alveolar epithelial cell phenotype in vitro: expression of aquaporin 5 [8].
• AECs monolayers express AQP5 only on their apical surfaces as determined by cell surface biotinylation studies [8].
• These results suggest that VIP induced the exocytosis of granule contents and simultaneously caused translocation of AQP5 but not of AQP1 to the apical membrane in Brunner's gland cells [9].
• A naturally occurring point mutation in the rat aquaporin 5 gene, influencing its protein production by and secretion of water from salivary glands [10].

Anatomical context of Aqp5

• Under control conditions, >90% of AQP-5 was associated with the apical plasma membrane of acinar and intercalated duct cells, with only rare gold particles associated with intracellular membrane domains [11].
• However, it remains unknown whether AQP-5 in salivary glands is subject to regulated trafficking in vivo [11].
• However, the increased salivary secretion was associated with luminal dilation and the appearance of a markedly punctate AQP-5 labeling pattern due to clustering of AQP-5 at the microvilli (especially evident in the parotid gland) after 10 min of drug injection [11].
• To examine this possibility, we have investigated the subcellular localization of AQP-5 in rat parotid and submandibular glands fixed in vivo under conditions of stimulated or inhibited salivary secretion [11].
• In the human pancreas, secretion occurs mainly in the intercalated ducts, where the epithelial cells express abundant AQP1 and AQP5 at the apical membrane and AQP1 alone at the basolateral membrane [12].

Associations of Aqp5 with chemical compounds

• Pilocarpine treatment dramatically increased saliva production but had no discernible effect on AQP-5 distribution [11].
• No changes in the subcellular localization of AQP-5 were seen in response to epinephrine, atropine, or phentolamine treatment compared with control tissues [11].
• Furthermore, apical, but not basolateral, application of Hg(2+) significantly reduces the transepithelial osmotic permeability, suggesting that apical AQP1 and AQP5 may contribute significantly to fluid secretion [12].
• Pretreatment of rat parotid tissue with the NO scavenger 2-(4carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide potassium inhibited both acetylcholine (ACh)- and pilocarpine-induced increases in AQP5 in the APM [6].
• BAPTA-AM inhibited the cGMP-induced increase in AQP5 in the APM [6].

Other interactions of Aqp5

• Under these conditions, cultured AT2 cells display AT2 type morphology, express the AT2-specific marker surfactant protein C, and do not express AT1-specific cell marker aquaporin 5, all consistent with maintenance of AT2 phenotype [13].
• Involvement of aquaporin-5 water channel in osmoregulation in parotid secretory granules [14].
• Aquaporin 5 was detected in the apical membranes of acinar cells, while the cystic fibrosis transmembrane conductance regulator was found only in apical membranes of intralobular duct cells [15].

Analytical, diagnostic and therapeutic context of Aqp5

• RESULTS: Renal I/R injury and bilateral nephrectomy both led to marked down-regulation of pulmonary ENaC, Na,K-ATPase and aquaporin-5 but not aquaporin-1 compared to sham surgery [1].
• Such a diverse localization of AQP5 was confirmed by Western blotting as well [7].
• We used indirect immunofluorescence and an immunoperoxidase technique to assess expression and subcellular localisation of aquaporin 5 in patients and controls [2].
• A large amount of AQP1 and small amounts of AQP5 transcripts were detected in the isolated duct cells by RT-PCR [16].
• M(3) muscarinic acetylcholine receptor (mAChR)-induced changes in AQP5 localization in rat parotid glands were investigated with immunofluorescence or immunoelectron microscopy, detergent solubility, and gradient density floatation assays [17].

References