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.

Summary

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.