Aquaglyceroporins in epithelial and endothelial barriers in the equine hoof

Abstract

Epidermal keratinocytes in the equine hoof rely on the transport of nutrients across an extracellular matrix (basement membrane), which separates the dermal lamellae from epidermal lamellae. Currently, nothing is known about how water and small solutes are transferred across this barrier. We hypothesize that specific aquaporin (AQP) water channels control fluid flow in equine epidermal hoof keratinocytes, small vessels in the dermis of the hoof, and the digital artery supplying the hoof. Using custom‐designed rabbit polyclonal anti‐sera, we have examined the cellular localization of AQP1, AQP3 and AQP9 within normal equine hoof tissues using immunohistochemistry. AQP3 and AQP9 immunoreactivity was observed in the cytoplasm and plasma membrane of lamellar keratinocytes, although AQP3 staining was stronger. AQP1 and AQP3 immunoreactivity was also demonstrated in the endothelium of small vessels within the dermal hoof tissue and digital artery, while AQP9 only stained smooth muscle of small vessels within the digital artery. Both AQP3 and AQP9 stained the smooth muscle of the digital artery, but only AQP3 demonstrated endothelial staining. These results confirm that aquaporins are present in epithelial and endothelial barriers in the equine hoof and may play a functional role in the transport of water and small solutes, such as glycerol and urea across these barriers. This research was supported by the University of Nottingham.