Expression and Function of ABC Proteins in Fish Intestine

BIECZYNSKI, FLAVIA; PAINEFILÚ, JULIO C.; VENTURINO, ANDRÉS; LUQUET, CARLOS M.

Frontiers in Physiology

Frontiers

Año: 2021 vol. 12

In fish, the intestine is fundamental for digestion, nutrient absorption, and otherfunctions like osmoregulation, acid-base balance, and excretion of some metabolicproducts. These functions require a large exchange surface area, which, in turn,favors the absorption of natural and anthropogenic foreign substances (xenobiotics)either dissolved in water or contained in the food. According to their chemical nature,nutrients, ions, and water may cross the intestine epithelium cells? apical and basolateralmembranes by passive diffusion or through a wide array of transport proteins andalso through endocytosis and exocytosis. In the same way, xenobiotics can cross thisbarrier by passive diffusion or taking advantage of proteins that transport physiologicalsubstrates. The entry of toxic substances is counterbalanced by an active effluxtransport mediated by diverse membrane proteins, including the ATP binding cassette(ABC) proteins. Recent advances in structure, molecular properties, and functionalstudies have shed light on the importance of these proteins in cellular and organismalhomeostasis. There is abundant literature on mammalian ABC proteins, while the studieson ABC functions in fish have mainly focused on the liver and, to a minor degree, onthe kidney and other organs. Despite their critical importance in normal physiology andas a barrier to prevent xenobiotics incorporation, fish intestine?s ABC transporters havereceived much less attention. All the ABC subfamilies are present in the fish intestine,although their functionality is still scarcely studied. For example, there are few studies ofABC-mediated transport made with polarized intestinal preparations. Thus, only a fewworks discriminate apical from basolateral transport activity. We briefly describe the mainfunctions of each ABC subfamily reported for mammals and other fish organs to helpunderstand their roles in the fish intestine. Our study considers immunohistochemical,histological, biochemical, molecular, physiological, and toxicological aspects of fishintestinal ABC proteins. We focus on the most extensively studied fish ABC proteins(subfamilies ABCB, ABCC, and ABCG), considering their apical or basolateral locationand distribution along the intestine. We also discuss the implication of fish intestinalABC proteins in the transport of physiological substrates and aquatic pollutants, suchas pesticides, cyanotoxins, metals, hydrocarbons, and pharmaceutical products.