ORIGINAL RESEARCH published: 16 December 2020 doi: 10.3389/fmars.2020.589822 Edited by: Valerio Matozzo, University of Padua, Italy Reviewed by: Marco Gerdol, University of Trieste, Italy Francesco Dondero, Università del Piemonte Orientale, Italy *Correspondence: Alexandre Campos acampos@ciimar.up.pt † These authors have contributed equally to this work Specialty section: This article was submitted to Aquatic Physiology, a section of the journal Frontiers in Marine Science Received: 06 August 2020 Accepted: 23 November 2020 Published: 16 December 2020 Citation: Martins JC, Domínguez-Pérez D, Azevedo C, Braga AC, Costa PR, Osório H, Vasconcelos V and Campos A (2020) Molecular Responses of Mussel Mytilus galloprovincialis Associated to Accumulation and Depuration of Marine Biotoxins Okadaic Acid and Dinophysistoxin-1 Revealed by Shotgun Proteomics. Front. Mar. Sci. 7:589822. doi: 10.3389/fmars.2020.589822 Molecular Responses of Mussel Mytilus galloprovincialis Associated to Accumulation and Depuration of Marine Biotoxins Okadaic Acid and Dinophysistoxin-1 Revealed by Shotgun Proteomics José Carlos Martins 1† , Dany Domínguez-Pérez 1† , Catarina Azevedo 1 , Ana Catarina Braga 2 , Pedro Reis Costa 2 , Hugo Osório 3,4,5 , Vitor Vasconcelos 1,6 and Alexandre Campos 1 * 1 CIIMAR – Interdisciplinary Centre of Marine and Environmental Research, University of Porto, Terminal de Cruzeiros do Porto de Leixões, Porto, Portugal, 2 IPMA – Instituto Português do Mar e da Atmosfera, Lisbon, Portugal, 3 I3S – Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal, 4 Instituto de Patologia e Imunologia Molecular da Universidade do Porto, IPATIMUP, Porto, Portugal, 5 Faculdade de Medicina, Universidade do Porto, Porto, Portugal, 6 Biology Department, Faculty of Sciences, University of Porto, Porto, Portugal The molecular pathways behind the toxicity of diarrheic shellfish toxins (DSTs) in bivalves have been scarcely studied. Thus, a shotgun proteomics approach was applied in this work to understand bivalves’ molecular responses to the dinoflagellate Prorocentrum lima (1.0 × 10 6 cells/L). Protein expression along with toxins levels were analyzed in the gills and digestive gland of the mussel Mytilus galloprovincialis during and after exposure to this toxic strain. Results revealed an accumulation of OA and DTX1 only in the digestive gland with maximum amounts attained at the end of uptake phase (day 5; 2819.2 ± 522.2 μg OA/kg and 1107.1 ± 267.9 μg DTX1/kg). At the end of the depuration phase (day 20), 16% and 47% of total OA and DTX1 concentrations remained in the digestive gland tissues, respectively. The shotgun proteomic analyses yielded 3051 proteins in both organs. A total of 56 and 54 differentially expressed proteins (DEPs) were revealed in the digestive gland and gills, respectively. Both organs presented the same response dynamics along the experiment, although with tissue- specific features. The early response (3 days uptake) was characterized by a high number of DEPs, being more marked in gills, in relation to the latter time points (5 days uptake and depuration). Functional enrichment analysis revealed the up-regulation of carboxylic (GO:0046943) and organic acid transmembrane transporter activity (GO:0005342) pathways after 3 days uptake for digestive gland. Matching to these pathways are a group of proteins related to transmembrane transport and response to toxic substances and xenobiotics, namely P-glycoprotein (ABCB11), Sodium- dependent proline transporter (SLC6A7), and Sideroflexin-1 (SFXN1). According to Clusters of Orthologous Groups (GOs) categories, most of the DEPs found for digestive gland in all time-points were related with “cellular processes and signaling” Frontiers in Marine Science | www.frontiersin.org 1 December 2020 | Volume 7 | Article 589822