Human aquaporin adipose (AQPap) gene. Genomic structure, promoter analysis and functional mutation

Abstract

Aquaporin adipose (AQPap), which we identified from human adipose tissue, is a glycerol channel in adipocyte [Kishida et al. (2000) J. Biol. Chem. 275, 20896-20902]. In the current study, we determined the genomic structure of the human AQPap gene, and identified three AQPap-like genes that resembled ( 95%) AQPap, with little expression in human tissues. The AQPap promoter contained a putative peroxisome proliferator response element (PPRE) at )46 to )62, and a putative insulin response element (IRE) at )542/)536. Deletion of the PPRE abolished the pioglitazone-mediated induction of AQPap promoter activity in 3T3-L1 adipocytes. Deletion and single base pair substitution analysis of the IRE abolished the insulin-mediated suppression of the human AQPap gene. Analysis of AQPap sequence in human subjects revealed three missense mutations (R12C, V59L and G264V), and two silent mutations (A103A and G250G). The cRNA injection of the missense mutants into Xenopus oocytes revealed the absence of the activity to transport glycerol and water in the AQPap-G264V protein. In the subject homozygous for AQPap-G264V, exercise-induced increase in plasma glycerol was not observed in spite of the increased plasma noradrenaline. We suggest that AQPap is responsible for the increase of plasma glycerol during exercise in humans.

Adaptation to fasting by glycerol transport through aquaporin 7 in adipose tissue

“…In this regard, epinephrine-stimulated glycerol release from 3T3-L1 adipocytes and plasma glycerol concentrations in rodents increased in parallel with the induction of Aqp7 mRNA in the cells and adipose tissue, respectively. Based on genetic screening, we found a subject carrying loss of function mutation in the AQP7 gene with a substitution of Gly-264 to Val, which is located in the center of GXXGXXG motif in the sixth transmembrane domain and crucial for functional confirmation (14). Expression study in Xenopus oocytes revealed AQP7 with G264V mutation lost both water and glycerol transport.…”

“…The molecular mechanism involved in the transport of glycerol from adipocytes remains unclear. Previously, we reported that exercise-induced increase of plasma glycerol was impaired in a subject carrying a loss of function mutation of AQP7 (14). We postulated that AQP7 might function as a glycerol channel molecule in adipose tissue.…”

“…Some of AQPs are known to permeabilize glycerol as well as water (9,10) and are subcategorized as aquaglyceroporins. We previously cloned a cDNA belonging to aquaglyceroporin from a human adipose tissue cDNA library, designated as AQP adipose (AQPap) (11)(12)(13)(14)(15). Subsequently, other groups demonstrated that AQPap was a human homologue of Aqp7.…”

Aquaporins in spermatozoa and testicular germ cells: identification and potential role

“…In this respect, reanalysis of sperm motility in Aqp7 −/− mice using various energy substrates is warranted. Nevertheless, in line with fertile Aqp7 −/− mice, an Aqp7-null man has been reported as fertile [77].…”

The Sir David Cuthbertson Medal Lecture Hunting for new pieces to the complex puzzle of obesity

“…AQP7 belongs to the subcategory termed aquaglyceroporins, which comprise channels known to permeabilise glycerol as well as water (King et al 2004;Hara-Chikuma & Verkman, 2006). Originally named AQPap, this water-glycerol pore was cloned from human adipose tissue (Kuriyama et al 1997;Kishida et al 2001;Kondo et al 2002). AQP7 deficiency in adipocytes has been associated with adult-onset obesity in mice; thus, providing evidence that AQP7 functions as a glycerol channel in vivo whereby adipocyte glycerol permeability exerts a key role in the regulation of fat accumulation (Maeda et al 2004;Hara-Chikuma et al 2005;Hibuse et al 2005;Wintour & Henry 2006).…”