POLARISATION: Polar cod, lipid metabolism and disruption by polycyclic aromatic hydrocarbons
This project is funded by the Norwegian Research Council (FRIMEDBIO) and the University´s “fellesløfte” for the period 2012-2015. It is led by Dr Jasmine Nahrgang at the University of Tromsø in close cooperation with the University Centre In Svalbard, Akvaplan-niva, Unilab Analyse AS, Norwegian Polar Institute, University of Bergen, Norwegian School of Veterinary Science, NIVA, University of the Basque Country (Spain), Università Politecnica delle Marche (Italy), University of Hull (UK), NOAA (USA) and Institute of Biology of the Karelian Research Centre, RAS (Russia).
This project is an integrated part of the ARCTOS network (http://www.arctosresearch.net/), a leading network for Arctic marine ecosystem research.
Polar cod (Boreogadus saida) is considered a key species in the arctic marine ecosystem. Although several studies have focused on its life cycle strategies, we still lack a broader insight into its ecological and physiological characteristics and sensitivity towards both environmental and anthropogenic stressors. Lipid metabolism in particular is highly important in polar organisms, but is a topic that has been poorly studied for the polar cod as well as its potential disruption by contaminants such as the polycyclic aromatic hydrocarbons (PAHs). Considering the crucial role lipids play for both survival during the polar night and for reproduction, the project aims at elucidating some key basic research questions regarding polar cod: Do PAHs disrupt lipid homeostasis in polar cod and is the peroxisome proliferator-activated receptor (PPAR) implicated in this toxicity? What are the long-term consequences of PAH exposure on key physiological processes such as growth and reproduction. Furthermore, the diet plays an important role as exposure route to contaminants; however the bioavailability of ingested PAHs and factors affecting it are largely misunderstood due to the primary focus given to waterborne exposures. Thus, the project will also determine the importance of exogenous and endogenous factors in the uptake of PAHs through this route of exposure.
Background and status of knowledge
Polar cod, a key species in the Arctic: The polar cod, a very abundant fish with a circumpolar distribution, is considered a key species in the arctic marine food web. In the highly seasonal arctic environment where food availability is restricted for long periods of time, the polar cod is relying on the accumulation of lipid reserves during the short productive season (June-August) for overwintering and reproduction during the polar night This small fish shows a high energy investment, with a weight loss of 30-50% during gonadal development.
Lipid metabolism – a key process in polar organisms: Lipids are undoubtedly an essential component of the physiology of organisms, being the principal form of stored energy, a major constituent of cellular membranes and serving among others as cofactors, detergents, transporters, hormones and cellular messengers. Lipids play an even more crucial role in polar marine organisms that are exposed to a high seasonality in food availability and constant low temperature. They have been the focus of exciting polar research for many decades, providing some understanding of adaptive biological mechanisms to extreme environments such as elevated membrane fluidity at low temperatures. The bulk of lipid research in arctic organisms however concerns mainly lipid composition as indicator of trophic interactions and the role of lipid reserves in the bioaccumulation and biomagnification of lipophilic contaminants along the arctic food chain. Few studies have provided fundamental knowledge on lipid homeostasis and associated physiological processes in arctic marine organisms. Furthermore, to the best of our knowledge no studies have reported on eventual disruptions of the lipid homeostasis by anthropogenic contaminants and their mode of actions in arctic species. Based on the extensive amount of data existing for mammals, it is known that polycyclic aromatic hydrocarbons (PAHs), a class of hundreds of ubiquitous contaminants, can disrupt lipid metabolism and lead to long-term biological effects. There is increasing evidence that this occurs also in fishes leading potentially to reduced growth and reduced reproduction success. However, the exact mechanisms involved in this toxicity are far from understood especially concerning Arctic fishes.
Objectives: Wild polar cod can be exposed to naturally occurring PAHs, as well as to anthropogenic discharges related to the presence of oil and gas industry and shipping routes. The waterborne route is the most investigated in toxicological studies, being a major source of PAH exposure following oil spills in marine organisms with a pelagic life cycle. However, the dietary route of exposure also plays a significant role in the exposure of marine fishes, and has been given considerably less focus.
POLARISATION combines advanced methodologies from several fields of science (molecular, cell biology, toxicology, physiology and chemistry) to attain the most complete understanding of the uptake and mechanisms of actions of ingested PAHs on the lipid metabolism and associated functions in polar cod and the long-term biological effects of exposure to PAHs.
The project is divided into work packages which objectives are to 1) determine the bioavailability of ingested PAHs in polar cod by testing the importance of some exogenous (energy density and quantity of the food) and endogenous (intestinal metabolism) factors, 2) identify the implication of the nuclear receptor PPAR in the toxicity of PAHs and the associated cellular cascade of events including disruption of lipid homeostasis and oxidative damage, 3) identify the long-term (several months) biological consequences (growth, reproduction and carcinogenicity) of a PAH exposure at the organismal level and 4) create a forum for sharing existing and new knowledge on polar cod and publish a special issue for this Arctic key-stone species that will represent the first comprehensive review covering all aspects of its ecotoxicology and biology.
This project is expected to increase our fundamental knowledge on lipid metabolism in polar cod and provide new knowledge on the uptake efficiency of PAHs via the food, their fate and mode of action on lipid metabolism in polar cod that is also relevant to other species. This project will also allow developing new molecular tools and in vitro methodologies adapted for this arctic fish species in order to further investigate the mode of action of PAHs toxicity in this species.