The Aquaporins: Regulator for Brain Pathophysiology

Water transport is a fundamental process contributing to human physiology and pathophysiology. Water is primarily needed for all cell types but the water does not sit in the cells it moves through in very organized way. This process of movement is occurring through aquaporins. Aquaporins (AQPs) are expressed in tissues in which edema and fluid imbalances are of major concern. Three major water-channel proteins (AQP1, AQP4, AQP9) are expressed in brain. Potential roles of AQPs in brain are water homeostasis, edema, angiogenesis, cell migration and development. Beside their physiological expression patterns in the brain, AQPs are abnormally expressed in some pathological conditions e.g. cancer, neuroinflammatory diseases and neurodegenerative diseases, in which preservation of brain homeostasis is at risk. In mammalian brain, AQP4 water channels are localised in astroglial cells at the blood-brain-barrier interface; AQP1 channels are expressed in choroid plexus and serve in cerebral spinal fluid secretion. Some of glial cells and neurons also show the expression of AQPs though the function is still not known. These aquaporins being integral membrane proteins have an important role in various neurodegenerative diseases, thereby signifying their therapeutic importance. Furthermore the enhanced expression of AQP4 increases the water permeability of blood vessels which could be an important aspect for understanding the ill effects of hypoxia. Research in this field has significantly in last few years, and the review focuses on functional roles of AQPs in brain related to physiology and pathophysiology.