Aquaporin-1—a water channel on the move**Comment on Saadoun S, Papadopoulos MC, Hara-Chikuma M, Verkman AS. Impairment of angiogenesis and cell migration by targeted aquaporin-1 gene disruption. Nature 2005; 434: 786–792

Aquaporin-1 plays a key role in erythropoietin-induced endothelial cell migration

Water influx through aquaporin-1 (AQP-1) has been linked to the ability of different cell types to migrate, and therefore plays an important part in processes like metastasis and angiogenesis. Since the erythroid growth factor erythropoietin (Epo) is now recognized as an angiogenesis promoter, we investigated the participation of AQP-1 as a downstream effector of this cytokine in the migration of endothelial cells. Inhibition of AQP-1 with either mercury ions (Hg²⁺) or a specific siRNA led to an impaired migration of EA.hy926 endothelial cells exposed to Epo (wound-healing assays). Epo also induced the expression of AQP-1 at mRNA and protein levels, an effect which was dependent on the influx of extracellular calcium through L-type calcium channels as well as TRPC3 channels. The relationship between Epo and AQP-1 was further confirmed at shorter exposure times, as the cytokine was unable to trigger calcium influxes in cells where AQP-1 had previously been knocked down. Moreover, Epo promoted changes in the subcellular localization of AQP-1 as well as rearrangements in the actin cytoskeleton, which are consistent with a migratory phenotype. Worthy of note, carbamylated erythropoietin (cEpo), the non-erythropoietic and non-promigratory derivative of Epo, was incapable of AQP-1 modulation. The therapeutical implications of aquaporin targeting in angiogenesis-related diseases highlight the importance of the present results in the context of the relationship between AQP-1 and Epo.

Evaluation of The Protective Effect of Hydro-Alcoholic Extract of Raspberry Fruit on Aquaporin1 Expression in Rats Kidney Treated by Methotrexate

OBJECTIVE

Methotrexate (MTX) is an antimetabolite drug commonly prescribed for the various cancers and autoimmune diseases. Despite its considerable therapeutic effects, nephrotoxicity is the most important side-effect of treatment with MTX. Aquaporin1 (AQP1) is a water channel proteins which is present in mammalian kidney. Raspberry fruit with antioxidant properties is able to protect biological systems from the harmful effects of free radicals. The purpose of this study was to investigate the effect of raspberry extract on expression of AQP1 and the MTX-induced nephrotoxicity in rats.

MATERIALS AND METHODS

In this experimental study, 60 adult male Wistar rats were divided into nine groups including control, sham, MTX treated group [single dose of 20 mg/kg of body weight (BW) MTX at the third day], raspberry treated groups [intraperitoneal (I.P) injection of 100, 200, 400 mg/kg of BW raspberry extract for ten consecutive days], MTX and raspberry treated groups. At day 11, rats were sacrificed via chloroform inhalation and kidney tissues were fixed in formalin solution for histological and immunohistochemistry analysis. The serological assays for urea, creatinine, uric acid and interleukin-6 (IL-6) levels were also performed.

RESULTS

MTX elevated serum level of the urea, creatinine, uric acid, IL-6, renal tissue damage and decreased the AQP1 expression level. Raspberry fruit extract improved the kidney function and reduced side effects of MTX in treated rats. Expression of AQP1, in a dose dependent manner was also ameliorated, as compared to control group.

CONCLUSION

According to the findings of this study, it can be concluded that biological activity of compounds presented in raspberry fruit extract especially anthocyanins may have chemo-protective effect on kidney function and AQP1 expression in rats treated by MTX.

Regulation of macrophage motility by the water channel aquaporin-1: crucial role of M0/M2 phenotype switch

The water channel aquaporin-1 (AQP1) promotes migration of many cell types. Although AQP1 is expressed in macrophages, its potential role in macrophage motility, particularly in relation with phenotype polarization, remains unknown. We here addressed these issues in peritoneal macrophages isolated from AQP1-deficient mice, either undifferentiated (M0) or stimulated with LPS to orientate towards pro-inflammatory phenotype (classical macrophage activation; M1). In non-stimulated macrophages, ablation of AQP1 (like inhibition by HgCl2) increased by 2-3 fold spontaneous migration in a Src/PI3K/Rac-dependent manner. This correlated with cell elongation and formation of lamellipodia/ruffles, resulting in membrane lipid and F4/80 recruitment to the leading edge. This indicated that AQP1 normally suppresses migration of resting macrophages, as opposed to other cell types. Resting Aqp1-/- macrophages exhibited CD206 redistribution into ruffles and increased arginase activity like IL4/IL13 (alternative macrophage activation; M2), indicating a M0-M2 shift. In contrast, upon M1 orientation by LPS in vitro or peritoneal inflammation in vivo, migration of Aqp1-/- macrophages was reduced. Taken together, these data indicate that AQP1 oppositely regulates macrophage migration, depending on stimulation or not by LPS, and that macrophage phenotypic and migratory changes may be regulated independently of external cues.

Aquaporin-1 channel function is positively regulated by protein kinase C

Aquaporin-1 (AQP1) channels contribute to osmotically induced water transport in several organs including the kidney and serosal membranes such as the peritoneum and the pleura. In addition, AQP1 channels have been shown to conduct cationic currents upon stimulation by cyclic nucleotides. To date, the short term regulation of AQP1 function by other major intracellular signaling pathways has not been studied. In the present study, we therefore investigated the regulation of AQP1 by protein kinase C. AQP1 wild type channels were expressed in Xenopus oocytes. Water permeability was assessed by hypotonic challenges. Activation of protein kinase C (PKC) by 1-oleoyl-2-acetyl-sn-glycerol (OAG) induced a marked increase of AQP1-dependent water permeability. This regulation was abolished in mutated AQP1 channels lacking both consensus PKC phosphorylation sites Thr(157) and Thr(239) (termed AQP1 DeltaPKC). AQP1 cationic currents measured with double-electrode voltage clamp were markedly increased after pharmacological activation of PKC by either OAG or phorbol 12-myristate 13-acetate. Deletion of either Thr(157) or Thr(239) caused a marked attenuation of PKC-dependent current increases, and deletion of both phosphorylation sites in AQP1 DeltaPKC channels abolished the effect. In vitro phosphorylation studies with synthesized peptides corresponding to amino acids 154-168 and 236-250 revealed that both Thr(157) and Thr(239) are phosphorylated by PKC. Upon stimulation by cyclic nucleotides, AQP1 wild type currents exhibited a strong activation. This regulation was not affected after deletion of PKC phosphorylation sites in AQP1 DeltaPKC channels. In conclusion, this is the first study to show that PKC positively regulates both water permeability and ionic conductance of AQP1 channels. This new pathway of AQP1 regulation is independent of the previously described cyclic nucleotide pathway and may contribute to the PKC stimulation of AQP1-modulated processes such as endothelial permeability, angiogenesis, and urine concentration.