AQP5

AQP5 Full Name

aquaporin 5

AQP5 Introduction

Aquaporin 5 (AQP5) is a vital transmembrane water channel protein belonging to the classical aquaporin superfamily, which is highly conserved across mammalian species and specialized for rapid, selective water permeation across biological membranes. Encoded by the AQP5 gene located on human chromosome 12q13.12, AQP5 shares close genetic homology with other classical aquaporin members including AQP0, AQP2, and AQP6, forming a clustered gene family with similar structural characteristics and membrane transport functions. Unlike ubiquitously expressed aquaporins, AQP5 exhibits highly tissue-specific expression patterns, primarily localized in secretory epithelial tissues, such as lacrimal glands, salivary glands, pulmonary alveolar epithelium, and epidermal keratinocytes. As a core regulator of exocrine fluid secretion and tissue osmotic balance, AQP5 exclusively transports water molecules while blocking ions, protons, and other small solutes, ensuring precise and efficient transmembrane water movement. Growing evidence confirms that AQP5 not only mediates basic physiological water transport but also participates in regulating epithelial cell proliferation, inflammatory responses, and tumor progression, making it a key biomarker and functional gene for multiple human diseases.

Figure 1. Schematic structure of AQP5.

Core Physiological Functions of AQP5
AQP5 is the primary functional protein responsible for exocrine gland fluid secretion and pulmonary water homeostasis in the human body. In lacrimal and salivary glands, AQP5-mediated transmembrane water transport directly drives the production and secretion of tears and saliva, maintaining ocular surface lubrication, oral cavity moistening, and normal digestive and defensive functions of mucosal tissues. Defective AQP5 expression or mislocalization is the leading cause of insufficient tear and saliva secretion, closely linked to dry eye syndrome and Sjögren's syndrome. In the respiratory system, AQP5 regulates rapid water exchange across alveolar epithelial membranes, prevents excessive fluid accumulation in alveolar cavities, and maintains normal pulmonary ventilation and gas exchange efficiency. Additionally, AQP5 participates in epidermal tissue hydration and skin barrier maintenance in human skin, and modulates cellular osmotic stress responses and epithelial tissue remodeling under physiological conditions. Its widespread regulatory roles in secretory function and tissue homeostasis ensure the stable operation of multiple organ systems throughout the body.

Pathophysiological and Clinical Significance of AQP5
Dysregulated expression, abnormal localization, or genetic mutation of AQP5 is closely associated with a variety of inflammatory diseases, autoimmune disorders, and malignant tumors, possessing important clinical diagnostic and therapeutic value. In autoimmune diseases, reduced AQP5 expression and impaired membrane polarization in lacrimal and salivary glands are classic pathological manifestations of Sjögren's syndrome, which directly leads to typical clinical symptoms of dry mouth and dry eyes. In respiratory diseases, downregulated AQP5 expression contributes to alveolar edema, acute lung injury, and asthma exacerbation by disrupting pulmonary water balance and aggravating inflammatory infiltration. Genetically, AQP5 gene polymorphisms and mutations are causally linked to Bothnian-type palmoplantar keratoderma, characterized by abnormal hyperplasia and thickening of palm and sole epidermis. Furthermore, aberrant overexpression of AQP5 is frequently detected in multiple malignant tumors including lung cancer, breast cancer, and gastric cancer, which promotes tumor cell proliferation, migration, and invasion by accelerating tumor microenvironment water metabolism and epithelial remodeling, indicating its potential as a prognostic biomarker and targeted therapeutic target for human malignancies.

Alternate Names for AQP5

AQP5; aquaporin 5; PPKB; AQP-5; aquaporin-5;