Disease relevance of Aqp8

• After 21 days on a 50% fat diet, wild-type and AQP8-null mice had similar weight gain ( approximately 15 g), with no evidence of steatorrhea or abnormalities in blood chemistries, except for mild hypertriglyceridemia in the null mice [1].
• Our findings suggest that aquaporin-8 in fetal membranes may be involved in the regulation of AFV, especially when oligohydramnios occurs [2].

High impact information on Aqp8

• AQP6 is present in intracellular vesicles in collecting duct intercalated cells, and AQP8 is present intracellularly at low abundance in proximal tubules and collecting duct principal cells, but the physiological function of these two channels remains undefined [3].
• AQP8 may have evolved separately to feature these intracellular roles as no other known aquaporin shows this specialization [4].
• As seen by reverse-transcription polymerase chain reaction (RT-PCR) and immunohistochemistry, fasting was accompanied by remarkable down-regulation of hepatic AQP8 that paralleled the expected depletion of glycogen content [4].
• Immunoelectron microscopy confirmed AQP8 in hepatocytes where labeling was over smooth endoplasmic reticulum (SER) membranes adjacent to glycogen granules and in canalicular membranes, subapical vesicles, and some mitochondria [4].
• Immunoblot analysis of mouse liver mitochondria failed to detect AQP8 expression, with liver homogenates from wild-type/AQP8 null mice as positive/negative controls [5].

Biological context of Aqp8

• Fluorescence in situ hybridization localized the Aqp8 locus to mouse chromosome 7F3 [6].
• Aqp8 consists of six exons with boundaries at amino acids 1-4, 5-87, 88-129, 130-201, 202-246 and 247-261 which partially correspond to those of other known aquaporin genes [6].
• Phenotype analysis of aquaporin-8 null mice [1].
• A 1447 bp cDNA was sequenced (designated AQP8) with a 783 bp open reading frame encoding a 261 amino acid hydrophobic protein which contained the conserved NPA motifs of MIP family members [7].
• In additional experiments, similar downregulation of AQP1 and AQP8 mRNA expression occurred in farnesoid X receptor (FXR)-deficient mice after 1 week on the lithogenic diet, without any difference from corresponding wild-type mice [8].

Anatomical context of Aqp8

• AQP8-knockout mice lacked detectable AQP8 transcript and protein, and had reduced water permeability in plasma membranes from testes [1].
• Aquaporin-8 (AQP8) is a water-transporting protein expressed in organs of the mammalian gastrointestinal tract (salivary gland, liver, pancreas, small intestine, and colon) and in the testes, heart, kidney, and airways [1].
• We also observed expression of AQP8 in the inner-cell mass and AQP9 in the mural trophectoderm of the implanting blastocyst [9].
• Expression of AQP8 cRNA in Xenopus oocytes increased osmotic water permeability from (0.8 +/- 0.1) x 10(-3) cm/s to (22 +/- 3) x 10(-3) cm/s (10 degrees C) in a mercurial-sensitive manner [7].
• RT-PCR with AQP8-specific primers and Southern blot analysis showed AQP8 transcript in the above tissues and in pancreas, lung, kidney, submandibular gland, diaphragm, testis, spleen, stomach and brain [7].

Associations of Aqp8 with chemical compounds

• Mice lacking AQP7 and AQP8 can concentrate their urine fully, although AQP7 null mice manifest an interesting defect in glycerol reabsorption [10].
• Normalization for oocyte plasma membrane expression using cMyc-tagged AQP8 indicated a single channel water permeability of 8.2 x 10(-14) cm3/s. AQP8 is unique among the water channels in terms of its urea permeability and its strong expression in gastrointestinal organs, placenta and heart [7].

Other interactions of Aqp8

• AQP5 and AQP8 expression were significantly increased on d 12-15 but fell to nongravid/baseline by d 19 and PP1 [11].
• In conclusion, during murine lithogenesis, altered gallbladder histology is associated with impaired motility, reduced concentrating function, and decreased AQP1 and AQP8 expression, the latter without the involvement of the FXR [8].
• AQP-3 was expressed at low levels in the epithelial cells and myometrium, whereas AQP-8 was found in both the stromal cells and myometrium [12].
• Reduction of aquaporin-8 on fetal membranes under oligohydramnios in mice lacking prostaglandin F2 alpha receptor [2].

Analytical, diagnostic and therapeutic context of Aqp8

• Organ weight and serum/urine chemistries were similar in wild-type and AQP8-null mice, except for increased testicular weight in the null mice (4.8 +/- 0.7 vs. 7.3 +/- 0.3 mg/g body wt) [1].
• Northern blotting showed strong AQP8 expression between fetal day 17 and birth as well as at weaning and thereafter [4].
• AQP8-facilitated NH(3) transport was confirmed in mammalian cell cultures expressing rat or mouse AQP8, in which the fluorescence of a pH-sensing yellow fluorescent protein was measured in response to ammonia (NH(3)/NH(4)(+)) gradients [13].
• Immunoblotting with subcellular membrane fractions of ANSCs showed predominant expression of AQP8 in the mitochondria-enriched fraction [14].
• Immunohistochemistry and immunoblot analysis showed that aquaporin-8 was expressed in the basal component of fetal membranes, and that the protein level was significantly decreased to 60% at 20 GD compared with that at 14 GD [2].

References