Immunolocalization of aquaporin-8 in rat kidney, gastrointestinal tract, testis, and airways

Elkjær, Marie-Louise; Nejsum, Lene N.; Gresz, Veronika; Kwon, Tae‐Hwan; Jensen, Uffe Birk; Frøkiær, Jørgen; Nielsen, Søren

doi:10.1152/ajprenal.0158.2001

Cited by 197 publications

(153 citation statements)

References 27 publications

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“…Also the intestinal cholesterol transporters Abcg5 and Abcg8 as well as the short chain peptide transporter Pept1 and the glucose transporters Sglt1 and Glu5 were not significantly altered. However, the down-regulation of the membrane integral protein Aqp8, which has been described to function on the apical side of duodenum, jejunum, and colon (38), was accompanied by a lower intestinal water absorption associated with a significant increase of hematocrit levels in Ugcg f/f/VilCreERT2 mice (data not shown). Reduced expression and activity of Aqp8 water channels may have been one factor for the extreme soft stools observed in mutant mice.…”

Section: Discussionmentioning

confidence: 86%

Glycosphingolipids are essential for intestinal endocytic function

Jennemann¹,

Kaden²,

Sandhoff³

et al. 2012

Exp Clin Endocrinol Diabetes

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Background:The intestine contains high concentrations of glycosphingolipids, but their function remained unclear. Results: In newborn mice lacking glycosphingolipids, intestinal epithelia were indistinguishable from control littermates. However, a few days after birth, severe defects in epithelial differentiation occurred. Conclusion: Glycosphingolipid expression in the intestinal epithelium is quintessential for maintenance of resorptive function. Significance: Glycosphingolipids are essential for enterocyte function but not for brush border formation.

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Section: Discussionmentioning

confidence: 86%

Glycosphingolipids are essential for intestinal endocytic function

Jennemann¹,

Kaden²,

Sandhoff³

et al. 2012

Exp Clin Endocrinol Diabetes

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show abstract

“…However, conflicting data have been reported for the subcellular localization of AQP8 expression in liver, perhaps because of the poor available AQP8 antibodies. Immunohistochemistry in rat shows AQP8 protein expression in intracellular vesicles in hepatocytes (21,25). Garcia et al (26) report a cAMP agonist-induced relocalization of intracellular AQP8 to the plasma membrane in rat hepatocytes.…”

Section: Discussionmentioning

confidence: 99%

Evidence against Functionally Significant Aquaporin Expression in Mitochondria

Yang

Zhao

Verkman

2006

Journal of Biological Chemistry

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where they were speculated to be involved in metabolism, apoptosis, and Parkinson disease. Here, we systematically examined the functional consequence of AQP expression in mitochondria by measurement of water and glycerol permeabilities in mitochondrial membrane preparations from rat brain, liver, and kidney and from wild-type versus knock-out mice deficient in AQPs -1, -4, or -8. Osmotic water permeability, measured by stopped-flow light scattering, was similar in all mitochondrial preparations, with a permeability coefficient P f ϳ 0.009 cm/s. Glycerol permeability was also similar (ϳ5 ؋ 10 ؊6 cm/s) in the various preparations. HgCl 2 slowed osmotic equilibration comparably in mitochondria from wild-type and AQP-deficient mice, although the slowing was explained by altered mitochondrial size rather than reduced P f . Immunoblot analysis of mouse liver mitochondria failed to detect AQP8 expression, with liver homogenates from wild-type/AQP8 null mice as positive/negative controls. Our results provide evidence against functionally significant AQP expression in mitochondria, which is consistent with the high mitochondrial surface-to-volume ratio producing millisecond osmotic equilibration, even when intrinsic membrane water permeability is not high.Functionally significant expression of aquaporin (AQP) 2 -type water channels has been demonstrated in plasma membranes in various cell types in kidney, brain, eye, glandular epithelia, endothelia, epidermis, fat, and other tissues. As demonstrated by phenotype comparisons of wild-type and AQP knock-out mice, plasma membrane AQPs are important in the urinary concentration mechanism, glandular fluid secretion, regulation of intraocular and intracranial pressures, cell migration, brain swelling, epidermal hydration, adipocyte metabolism, and other functions (1). Whether AQPs play a role in intracellular organellar functions is less clear. The vasopressin-regulated water channel AQP2 is expressed in both the plasma membrane and in a recycling endosomal compartment in kidney collecting cells (2, 3). Although endosomes in the kidney collecting duct are highly water-permeable (4), it is likely that their high water permeability is a consequence of dense AQP2 expression rather than a need for high endosomal water permeability. Indeed, the high surface-to-volume ratio of endosomes and other organelles, generally Ͼ3 ϫ 10 5 cm Ϫ1 (diameter Ͻ 200 nm) predicts very rapid osmotic equilibration times of Ͻ100 ms, even when osmotic water permeability (P f ) is low (Ͻ0.005 cm/s). Other AQPs have been reported in endosomes in some cell types, including AQP6 in the renal proximal tubule and collecting duct epithelial cells (5) and various AQPs in liver cells (6), although data are lacking on their possible cellular functions. Two recent studies reported AQP expression in mitochondria and suggested possible involvement of mitochondrial AQPs in many functions, including metabolism and apoptosis, and in the pathogenesis of neurological diseases such as Parkinson disease. Calamita et al. (7)...

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“…The role of AQP7 in male reproductive physiology is unclear as knockout mice are fertile, producing normal functional spermatozoa , whereas an association with sperm motility has been suggested in infertile men (Saito et al 2004). Although there are many studies on AQP8 in the testis, reports on the cellular localisation are inconsistent, ranging from spermatogenic cells in general (Elkjaer et al 2001, Kageyama et al 2001, Yang et al 2005, in elongated spermatids (ES), residual bodies and primary spermatocytes (Calamita et al 2001) and exclusively in Sertoli cells (Badran & Hermo 2002). Our recent work has demonstrated localisation only in ES and provides evidence suggesting a role of AQP8 in sperm volume regulation (Yeung et al 2009).…”

Section: Introductionmentioning

confidence: 99%

Aquaporin AQP11 in the testis: molecular identity and association with the processing of residual cytoplasm of elongated spermatids

Yeung

Cooper²

2010

Reproduction

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AQP11 is one of the latest aquaporin (AQP) family members found, which differs from the other AQPs by its intracellular localisation and unusual water pore nucleotides with unclear function. Despite the highest mRNA expression among organs having been reported in the testis, the testicular molecule has not been studied in detail. Immunohistochemistry of rat adult testis localised AQP11 to the elongated spermatids (ES) and no other cell types except residual bodies inside Sertoli cells. It was absent from early ES at least until stage 13, and after a first diffuse appearance in the caudal cytoplasm became concentrated in intracellular organelles by stage 17, was strongest in vesicles in the anterior cytoplasm at the final ES stages and appeared in residual bodies. Staining was detected on the distal quarter of the sperm tail only immediately before spermiation. A similar localisation was found in the mouse and developmental profiles for both the open reading frame mRNA and protein expression in 8-50 dpp testis pinpointed its first appearance coinciding with late stage ES. Sequencing of PCR products of testicular Aqp11 containing the open reading frames confirmed a full match with GenBank databases for rat, mouse and human. Western blotting revealed two or more molecular forms with the 26/27 kDa species dominating in the rat/mouse testis and the 33/34 kDa form selectively allocated to the spermatozoa. In view of intracellular vacuolation leading to polycystic kidney in Aqp11-null mice, a possible role of testicular AQP11 in the recycling of surplus cytoplasmic components of the ES and sustaining Sertoli cell capacity in the support of spermatogenesis was discussed.

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Immunolocalization of aquaporin-8 in rat kidney, gastrointestinal tract, testis, and airways

Cited by 197 publications

References 27 publications

Glycosphingolipids are essential for intestinal endocytic function

Glycosphingolipids are essential for intestinal endocytic function

Evidence against Functionally Significant Aquaporin Expression in Mitochondria

Aquaporin AQP11 in the testis: molecular identity and association with the processing of residual cytoplasm of elongated spermatids

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