Characterization of functional activity of ABCB1 and ABCC1 proteins in eggs and embryonic cells of the sea urchin Echinometra lucunter

Unraveling cellular and molecular mechanisms of acid stress tolerance and resistance in marine species: New frontiers in the study of adaptation to ocean acidification

Since the industrial revolution, fossil fuel combustion has led to a 30 %-increase of the atmospheric CO₂ concentration, also increasing the ocean partial CO₂ pressure. The consequent lowered surface seawater pH is termed ocean acidification (OA) and severely affects marine life on a global scale. Cellular and molecular responses of marine species to lowered seawater pH have been studied but information on the mechanisms driving the tolerance of adapted species to comparatively low seawater pH is limited. Such information may be obtained from species inhabiting sites with naturally low water pH that have evolved remarkable abilities to tolerate such conditions. This review gathers information on current knowledge about species naturally facing low water pH conditions and on cellular and molecular adaptive mechanisms enabling the species to survive under, and even benefit from, adverse pH conditions. Evidences derived from case studies on naturally acidified systems and on resistance mechanisms will guide predictions on the consequences of future adverse OA scenarios for marine biodiversity.

ABCB1 and ABCC1-like transporters in immune system cells from sea urchins Echinometra lucunter and Echinus esculentus and oysters Crassostrea gasar and Crassostrea gigas

ABC transporters activity and expression have been associated with the multixenobiotic resistance phenotype (MXR). The activity of these proteins leads to a reduction in the intracellular concentration of several xenobiotics, thus reducing their toxicity. However, little attention has been given to the expression of ABC transporters in marine invertebrates and few studies have investigated their role in immune system cells of sea urchins and shellfish bivalves. The aim of the present study was to investigate the activity of the ABC transporters ABCB1 and ABCC1 in immune system cells of sea urchins (coelomocytes) and oysters (hemocytes) from different climatic regions (Brazil and France). Sea urchins and oysters were collected at Paraíba coast; Brazil (Echinometra lucunter and Crassostrea gasar) and Rade of Brest; France (Echinus esculentus and Crassostrea gigas). Coelomocytes and hemocytes were stained with the ABC transporter substrate calcein-AM and dye accumulation analyzed under flow cytometry. Reversin 205 (ABCB1 transporter blocker) and MK571 (ABCC1 transporter blocker) were used as pharmacological tools to investigate ABC transporter activity. A different pattern of calcein accumulation was observed in coelomocytes: phagocytes > colorless spherulocytes > vibrate cells > red spherulocytes. The treatment with MK571 increased calcein fluorescence levels in coelomocytes from both species. However, reversin 205 treatment was not able to increase calcein fluorescence in E. esculentus coelomocytes. These data suggest that ABCC1-like transporter activity is present in both sea urchin species, but ABCB1-like transporter activity might only be present in E. lucunter coelomocytes. The activity of ABCC1-like transporter was observed in all cell types from both bivalve species. However, reversin 205 only increased calcein accumulation in hyalinocytes of the oyster C. gasar, suggesting the absence of ABCB1-like transporter activity in all other cell types, including hyalinocytes from the oyster C. gigas. Additionally, our results showed that C. gigas exhibited higher activity of ABCC1-like transporter in all hemocyte types than C. gasar. The present work is the first to characterize ABCB1 and ABCC1-like transporter activity in the immune system cells of sea urchins E. lucunter and E. esculentus and oysters. Our findings encourage the performing studies regarding ABC transporters activity/expression in immune system cells form marine invertebrates under stress conditions and the possible use of ABC transporters as biomarkers.

Investigating appearance and regulation of the MXR phenotype in early embryo stages of the Mediterranean mussel (Mytilus galloprovincialis)

Multixenobiotic resistance (MXR) efflux transporters constitute a broad-spectrum physiological defense system allowing marine bivalves to cope with environmental challenges. There is, however, scarce information on the type and role that different MXR transporters may have in embryos, which represent the most sensitive stages of bivalves to environmental stress. In this study regulation of MXR-related transporters was investigated in early developmental stages of the Mediterranean mussel (Mytilus galloprovincialis). In vitro fertilization experiments using gametes from naturally-spawning broodstocks were performed to follow embryo development from fertilized eggs (30min post fertilization, pf) to fully developed D-shape veligers (48hpf). Quantitative PCR analyses indicated that ABCB and ABCC transcripts encoding the MXR-related transporters P-glycoproteins (P-gp) and Multidrug resistance proteins (Mrp), respectively, were expressed soon after 30minpf, with ABCC being more expressed than ABCB. Copy numbers of both transcripts were increased in trochophorae and D-veligers. MXR efflux activity assessed using the fluorescent substrate rhodamine 123 and selective P-gp or Mrp inhibitors showed that the P-gp mediated efflux was detected only in D-veligers, while a significant Mrp mediated efflux was detected soon after 30minpf and remained almost unchanged in trochophorae and D-veligers. MXR modulation by propranolol and carbamazepine showed that the pharmaceuticals may act as transcriptional regulators and substrates. Results reported lead to hypothesize that while P-gp aids in xenobiotic efflux performing a prominent protective role, Mrp could be a dual-functioning transporter performing both protective and physiological functions in mussel development.

Mitochondrial permeability transition pore (MPTP) desensitization increases sea urchin spermatozoa fertilization rate

Mitochondrial permeability transition pore (MPTP) is a protein complex whose opening promotes an abrupt increase in mitochondrial inner membrane permeability. Calcium signaling pathways are described in gametes and are involved in the fertilization process. Although mitochondria may act as Ca(2+) store and have a fast calcium-releasing mechanism through MPTP, its contribution to fertilization remains unclear. The work aimed to investigate the MPTP phenomenon in sea urchin spermatozoa and its role on the fertilization. Several pharmacological tools were used to evaluate the MPTP's physiology. Our results demonstrated that MPTP occurs in male gametes in a Ca(2+) - and voltage-dependent manner and it is sensitive to cyclosporine A. Additionally, our data show that MPTP opening does not alter ROS generation in sperm cells. Inhibition of MPTP in spermatozoa strongly improved the fertilization rate, which may involve mechanisms that increase the spermatozoa lifespan. The present work is the first report of the presence of a voltage- and Ca(2+) -dependent MPTP in gametes of invertebrates and indicates MPTP opening as another evolutionary feature shared by sea urchins and mammals. Studies about MPTP in sea urchin male gametes may contribute to the elucidation of several mechanisms involved in sperm infertility.

Antimitotic activity of the pyrimidinone derivative py-09 on sea urchin embryonic development

Chemotherapy is the main cancer treatment and consists of drug administration that interferes with several metabolic pathways, leading to tumor cell death. Antimitotic drugs have a relevant role in chemotherapy. This study aimed to investigate the effect of a pyrimidinone derivative (6-(p-Anisyl)-2-(p-chlorophenyl)-4-oxo-3,4-dihydropyrimidine-5-carbonitrile, Py-09) on sea urchin embryonic development model. The effects of the compound were analyzed on fertilization, embryonic development, mitochondrial membrane potential (ΔΨm), production of reactive oxygen species (ROS) and ABC transporter activity. Py-09 inhibited the fertilization and the embryonic development in a time and dose-dependent pattern, with the maximum effect at 50 μM (EC50=12.5 μM). Py-09 induced the loss of ΔΨm without altering ROS intracellular levels. Morphological changes were observed in the pattern of embryo cleavage (unequal cleavage) and at larval stages (fissures of spicules and pigment cell leakage). We also demonstrated that Py-09 is not an ABC transporter substrate and the derivative does not circumvent the MXR phenomenon. Our study reports--for the first time--the antimitotic activity of Py-09 and stimulates new research on the potential of Py-09 as a pharmacological tool for in vitro studies, as well as its use as a new anticancer drug.

Transport in technicolor: mapping ATP-binding cassette transporters in sea urchin embryos

One quarter of eukaryotic genes encode membrane proteins. These include nearly 1,000 transporters that translocate nutrients, signaling molecules, and xenobiotics across membranes. While it is well appreciated that membrane transport is critical for development, the specific roles of many transporters have remained cryptic, in part because of their abundance and the diversity of their substrates. Multidrug resistance ATP-binding cassette (ABC) efflux transporters are one example of cryptic membrane proteins. Although most organisms utilize these ABC transporters during embryonic development, many of these transporters have broad substrate specificity, and their developmental functions remain incompletely understood. Here, we review advances in our understanding of ABC transporters in sea urchin embryos, and methods developed to spatially and temporally map these proteins. These studies reveal that multifunctional transporters are required for signaling, homeostasis, and protection of the embryo, and shed light on how they are integrated into ancestral developmental pathways recapitulated in disease.

ATP-binding cassette transporters protect sea urchin gametes and embryonic cells against the harmful effects of ultraviolet light

Embryos of marine organisms whose development occurs externally are particularly sensitive to ultraviolet (UV) light (bands A and B, respectively, UVA and UVB). ATP-binding cassette (ABC) transporters are the first line of cellular defense against chemical or physical stress. The present work investigated the involvement of ABC transporters on UVA or UVB effects on eggs, spermatozoa, and embryonic cells of the sea urchin Echinometra lucunter. Gametes or embryos were exposed to UVA (3.6-14.4 kJ m(-2)) or UVB (0.112-14.4 kJ m(-2)), and embryonic development was monitored by optical microscopy at different developmental stages in the presence or absence of the ABC-transporter blockers reversin205 (ABCB1 blocker) or MK571 (ABCC1 blocker). E. lucunter eggs, spermatozoa and embryos were resistant to UVA exposure. Resistance to the harmful effects of UVB was strongly associated to ABC transporter activity (embryos > eggs > spermatozoa). ABCB1 or ABCC1 blockage promoted the injurious effects of UVA on spermatozoa. ABCC1 transporter blockage increased UVB-dependent damage in eggs while ABCB1 transporter inhibition increased harmful effects of UVB in embryonic cells. ABC-transporter activity was not, however, affected by UVB exposure. In conclusion, the present study is the first report on the protective role of ABC transporters against harmful effects of UVA and UVB on sea urchin eggs and embryonic cells.

Inhibition of cellular efflux pumps involved in multi xenobiotic resistance (MXR) in echinoid larvae as a possible mode of action for increased ecotoxicological risk of mixtures

In marine organisms the multi xenobiotic resistance (MXR) mechanism via e.g. P-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP) is an important first line of defense against contaminants by pumping contaminants out of the cells. If compounds would impair the MXR mechanism, this could result in increased intracellular levels of other compounds, thereby potentiating their toxicity. A calcein-AM based larval cellular efflux pump inhibition assay (CEPIA) was developed for echinoid (Psammechinus miliaris) larvae and applied for several contaminants. The larval CEPIA revealed that triclosan (TCS) and the nanoparticles P-85(®) (P-85) were 124 and 155× more potent inhibitors (IC(50) 0.5 ± 0.05 and 0.4 ± 0.1 μM, respectively) of efflux pumps than the model inhibitor Verapamil (VER). PFOS (heptadecafluorooctane sulfonic acid) and pentachlorophenol also were more potent than VER, 24 and 5×, respectively. Bisphenol A and o,p'-dichlorodiphenyltrichloroethane (o,p'-DDT) inhibited efflux pumps with a potency 3× greater than VER. In a 48 h early life stage bioassay with P. miliaris, exposure to a non-lethal concentration of the inhibitors TCS, VER, the model MRP inhibitor MK-571, the nanoparticles P-85 and the model P-gp inhibitor PSC-833, increased the toxicity of the toxic model substrate for efflux pumps vinblastine by a factor of 2, 4, 4, 8 and 16, respectively. Our findings show that several contaminants accumulating in the marine environment inhibit cellular efflux pumps, which could potentiate toxic effects of efflux pumps substrates.

Involvement of ABCB1 and ABCC1 transporters in sea urchin Echinometra lucunter fertilization

Fertilization is an ordered sequence of cellular interactions that promotes gamete fusion to form a new individual. Since the pioneering work of Oskar Hertwig conducted on sea urchins, echinoderms have contributed to the understanding of cellular and molecular aspects of the fertilization processes. Studies on sea urchin spermatozoa reported the involvement of a plasma membrane protein that belongs to the ABC proteins superfamily in the acrosome reaction. ABC transporters are expressed in membranes of eukaryotic and prokaryotic cells, and are associated with the transport of several compounds or ions across biomembranes. We aimed to investigate ABCB1 and ABCC1 transporter activity in sea urchin spermatozoa and their involvement in fertilization. Our results indicate that Echinometra lucunter spermatozoa exhibit a low intracellular calcein accumulation (18.5% stained cells); however, the ABC blockers reversin205, verapamil, and MK571 increased dye accumulation (93.0-96.6% stained cells). We also demonstrated that pharmacologically blocking ABCB1 and ABCC1 decreased spermatozoa fertilizing capacity (70% inhibition), and this phenotype was independent of extracellular calcium. These data suggest that functional spermatozoa ABCB1 and ABCC1 transporters are crucial for a successful fertilization. Additional studies must be performed to investigate the involvement of membrane lipid homeostasis in the fertilization process.