AQP9 Membrane Protein Introduction

Introduction of AQP9

AQP9, encoded by the AQP9 gene, is an aquaglyceroporin membrane channel shown biophysically to conduct water, glycerol, and other small solutes. Sharing greater sequence identity with AQP3, AQP7 and AQP10, AQP9 is predicted to comprise 295 amino acids, containing 6 transmembrane regions and an intracellular N- and C-termini. AQP9 is widely expressed in different tissues with high levels in peripheral leukocytes, and lower levels in liver, lung, and spleen. AQP9 gene is mapped to chromosome 15.

Function of AQP9 Membrane Protein

As a member of the aquaglyceroporin subfamily of aquaporins, AQP9 can transport not only water, but also small uncharged molecules like glycerol, monocarboxylates, urea, purines, and pyrimidines. In addition, AQP9 has been proposed to transport a variety of neutral and ionic arsenic species, including arsenic trioxide, monomethyl arsenate (MAsIII) and dimethyl arsenate (DMAV). AQP9 expression has also been shown to be regulated by testosterone and estrogen. The expression of AQP9 in the male reproductive tract has been shown to be involved in sperm maturation, concentration, and storage, respectively. Moreover, AQP9 expression in the liver is down-regulated by insulin, potentially via an “insulin-responsive element” in the AQP9 promoter. In the patients with astrocytoma, it is documented that AQP9 can promote the invasion and motility of cells via the AKT pathway, indicating that AQP9 may represent a potential target for therapeutic use of astrocytoma. AQP9 blockade can be an effective strategy to reduce dendritic cells (DCs) inflammatory response. However, it is not sufficient to protect from acute inflammatory insults such as dextra sulfate sodium (DSS) induced colitis.

Fig.1 The role of AQP9 in islet secreting cells. (Lebeck, 2014)

Application of AQP9 Membrane Protein in Literature

1. Takeuchi K., et al. Downregulation of aquaporin 9 decreases catabolic factor expression through nuclear factor kappaB signaling ins chondrocytes. Int J Mol Med. 2018, 42(3):1548-1558. PubMed ID: 29901079
   
   

   This article reveals that AQP9 is highly expressed in OA cartilage and the downregulation of AQP9 in cultured chondrocytes can decrease the catabolic gene expression in response to IL-1β stimulation via NF-κB signaling, suggesting AQP9 may be a promising target for the treatment of OA.

2. Stahl K., et al. Targeted deletion of the aquaglyceroporin AQP9 is protective in a mouse model of Parkinson's disease. PLoS One. 2018, 13: e0194896. PubMed ID: 29566083
   
   

   These results show that AQP9 can selectively be expressed in catecholaminergic neurons, where it is permeable to MPP⁺, indicating that AQP9 contributes to the selective vulnerability of nigral dopaminergic neurons by providing an entry route for parkinsonogenic toxins.

3. Hou J., et al. Similar Aquaporin9 and MAPK Expression Profiles in the Liver of Types 1 and 2 Diabetes Mellitus. Horm Metab Res. 2018, 50: 414-421. PubMed ID: 29523003
   
   

   This study examines the expression patterns of AQP9 and mitogen-activated protein kinase (MAPK) in Types 1 and 2 diabetes mellitus (DM). And they clarify the roles and regulating mechanism of AQP9 in gluconeogenesis.

4. Han X., et al. Changes in the Expression of AQP4 and AQP9 in the Hippocampus Following Eclampsia-Like Seizure. Int J Mol Sci. 2018, 19(1). PubMed ID: 29351212
   
   

   These findings show that upregulation of AQP4 and AQP9 may be responsible for the cell death induced by eclamptic seizures.

5. Vilarino-Garcia T., et al. Leptin upregulates aquaporin 9 expression in human placenta in vitro. Gynecol Endocrinol 2018, 34: 175-177. PubMed ID: 28942694
   
   

   This article demonstrates that leptin can produce a dose-dependent increase of AQP9 gene expression, resulting in an increase in AQP9 protein in human trophoblast explants.

AQP9 Preparation Options

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Reference

1. Lebeck J. (2014). Metabolic impact of the glycerol channels AQP7 and AQP9 in adipose tissue and liver. Journal of molecular endocrinology. JME-13-0268.

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