MAPK Pathway under Chronic Copper Excess in Green Macroalgae (Chlorophyta): Involvement in the Regulation of Detoxification Mechanisms.

Fernanda Rodríguez-Rojas,M Gabriela Lobos,Patricia Díaz,Lorena Méndez,Claudio A Sáez,Alejandra Moenne,José Luis Sánchez-Lizaso,Paula S M Celis-Plá,Pamela T Muñoz,Murray T Brown,Fabiola Moenne

doi:10.3390/ijms20184546

Abstract

Following the physiological complementary/parallel Celis-Plá et al., by inhibiting extracellular signal regulated kinases (ERK), c-Jun N-terminal kinases (JNK), and cytokinin specific binding protein (p38), we assessed the role of the mitogen-activated protein kinases (MAPK) pathway in detoxification responses mediated by chronic copper (10 µM) in U. compressa. Parameters were taken at 6, 24, and 48 h, and 6 days (d). H2O2 and lipid peroxidation under copper and inhibition of ERK, JNK, or p38 alone increased but recovered by the sixth day. By blocking two or more MAPKs under copper, H2O2 and lipid peroxidation decayed even below controls. Inhibition of more than one MAPK (at 6 d) caused a decrease in total glutathione (reduced glutathione (GSH) + oxidised glutathione (GSSG)) and ascorbate (reduced ascorbate (ASC) + dehydroascorbate (DHA)), although in the latter it did not occur when the whole MAPK was blocked. Catalase (CAT), superoxide dismutase (SOD), thioredoxin (TRX) ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), and glutathione synthase (GS), were downregulated when blocking more than one MAPK pathway. When one MAPK pathway was blocked under copper, a recovery and even enhancement of detoxification mechanisms was observed, likely due to crosstalk within the MAPKs and/or other signalling processes. In contrast, when more than one MAPK pathway were blocked under copper, impairment of detoxification defences occurred, demonstrating that MAPKs were key signalling mechanisms for detoxification in macroalgae.

Highlights

It has been recognised that besides metal exclusion/extrusion mechanisms, the main strategies by which macroalgae counteract metal excess in polluted environments are detoxification of bioavailable metals through the syntheses of chelating compounds and the inactivation of metal-mediated excess of reactive oxygen species (ROS) by the production and activities of antioxidants and antioxidant enzymes [1,2]
We demonstrated that under chronic copper excess when two or more mitogen-activated protein kinases (MAPK) pathways were inhibited, there was a general trend of decreasing intracellular copper concentrations when compared to exposure only to copper [1]
Similar patterns were observed at 24 h, the Cu + ERKi + p38i (T7) and Cu + ERKi + JNKi + p38i (T9) treatments were the ones with significantly higher levels of H2O2 (Figure 1B)

Summary

Introduction

It has been recognised that besides metal exclusion/extrusion mechanisms, the main strategies by which macroalgae counteract metal excess in polluted environments are detoxification of bioavailable metals through the syntheses of chelating compounds and the inactivation of metal-mediated excess of reactive oxygen species (ROS) by the production and activities of antioxidants and antioxidant enzymes [1,2]. GSH, in a recycling process with ascorbate (ASC), termed the Foyer–Halliwell–Asada cycle, is recognised as central to antioxidant metabolism in photoautotrophs, algae, and plants, and is one of the main mechanisms by which these organisms tolerate metal-mediated oxidative stress [2,4,5]. H2O2 is reduced to water by either ascorbate peroxidase (APX) using ASC as electron donor, or by the enzyme catalase (CAT) [7]. Another important group of enzymes within the antioxidant metabolism of photoautotrophs is thioredoxins (TRXs), which principally reduce oxidised cysteine residues and split disulfide bonds [8]

Methods

Results

Conclusion