Titanium dioxide nanoparticles temporarily influence the sea urchin immunological state suppressing inflammatory-relate gene transcription and boosting antioxidant metabolic activity

Titanium dioxide nanoparticles (TiO₂NPs) are revolutionizing biomedicine due to their potential application as diagnostic and therapeutic agents. However, the TiO₂NP immune-compatibility remains an open issue, even for ethical reasons. In this work, we investigated the immunomodulatory effects of TiO₂NPs in an emergent proxy to human non-mammalian model for in vitro basic and translational immunology: the sea urchin Paracentrotus lividus. To highlight on the new insights into the evolutionarily conserved intracellular signaling and metabolism pathways involved in immune-TiO₂NP recognition/interaction we applied a wide-ranging approach, including electron microscopy, biochemistry, transcriptomics and metabolomics. Findings highlight that TiO₂NPs interact with immune cells suppressing the expression of genes encoding for proteins involved in immune response and apoptosis (e.g. NF-κB, FGFR2, JUN, MAPK14, FAS, VEGFR, Casp8), and boosting the immune cell antioxidant metabolic activity (e.g. pentose phosphate, cysteine-methionine, glycine-serine metabolism pathways). TiO₂NP uptake was circumscribed to phagosomes/phagolysosomes, depicting harmless vesicular internalization. Our findings underlined that under TiO₂NP-exposure sea urchin innate immune system is able to control inflammatory signaling, excite antioxidant metabolic activity and acquire immunological tolerance, providing a new level of understanding of the TiO₂NP immune-compatibility that could be useful for the development in Nano medicines.

Different sizes of ZnO diversely affected the cytogenesis of the sea urchin Paracentrotus lividus

Today nanoparticles (NPs) have many applications in commercial products due to their small size and peculiar properties that, conversely, make them potentially toxic for humans and the environment. ZnO NPs are largely used in many personal care products, such as sunscreens and cosmetics. In this study the cytotoxic effects of ZnO particles with different sizes (ZnO Bulk, >100nm; ZnO NPs, 100nm and ZnO NPs, 14nm) upon the first developmental stages of the sea urchin Paracentrotus lividus, are evaluated. Morphological alterations are also assessed by embryotoxicity tests. The cytogenetic analysis highlighted that ZnO NPs interfere with cell cycle inducing a dose-dependent decrease of mitotic activity and chromosomal aberrations at higher concentrations (30μM). Moreover, the larval development was affected by ZnO NPs 100nm (EC50=0.46 [0.30-0.63] μM [Zn]) in a dose-dependent way. Size-dependent toxicity was instead not obtained for ZnO NPs. From our results could be highlighted that the presence of embryos, blocked in pre-larval stage, could be due to the induction of chromosome aberrations by ZnO particles, confirming that cytogenetic analyses allow evaluating possible NPs action mechanisms.

Sea urchin embryos exposed to cadmium as an experimental model for studying the relationship between autophagy and apoptosis

The sea urchin embryo is a suitable model that offers an excellent opportunity to investigate different defence strategies activated in stress conditions. We previously showed that cadmium accumulates in a dose- and time-dependent manner into embryonic cells, activating different stress and defence mechanisms, including the synthesis of HSPs and the onset of apoptosis and/or autophagy. In this paper we investigated the functional relationship between autophagy and apoptosis, evaluating apoptosis signals in cadmium-exposed Paracentrotus lividus embryos with inhibited autophagy. We found that the inhibition of autophagy produced the concurrent reduction of apoptosis, suggesting that the two phenomena are functionally related. Considering the catabolic role of autophagy, an energetic hypothesis to explain the relationship was evaluated. Using a substrate for ATP production, we found that apoptosis, assessed by TUNEL and cleaved caspase-3 immunocytochemistry, was substantially restored in cadmium-treated embryos where autophagy was inhibited by 3-Methyladenine. On the basis of these results, we propose that, autophagy could play a crucial role in stress response of this organism because autophagy could energetically contribute to apoptotic execution through its catabolic role.

Determination of sialic acids in immune system cells (coelomocytes) of sea urchin, Paracentrotus lividus, using capillary LC-ESI-MS/MS

Coelomocytes are considered to be immune effectors of sea urchins. Coelomocytes are the freely circulating cells in the body fluid contained in echinoderm coelom and mediate the cellular defence responses to immune challenges by phagocytosis, encapsulation, cytotoxicity and the production of antimicrobial agents. Coelomocytes have the ability to recognize self from non-self. Considering that sialic acids play important roles in immunity, we determined the presence of sialic acid types in coelomocytes of Paracentrotus lividus. Homogenized coelomocytes were kept in 2 M aqueous acetic acid at 80 °C for 3 h to liberate sialic acids. Sialic acids were determined by derivatization with 1,2-diamino-4,5-methylenediaoxy-benzene dihydrochloride (DMB) followed by capillary liquid-chromatography-electrospray ionization/tandem mass spectrometry (CapLC-ESI-MS/MS). Standard sialic acids; Neu5Ac, Neu5Gc, KDN and bovine submaxillary mucin showing a variety of sialic acids were used to confirm sialic acids types. We found ten different types of sialic acids (Neu5Gc, Neu5Ac, Neu5Gc9Ac, Neu5Gc8Ac, Neu5,9Ac2, Neu5,7Ac2, Neu5,8Ac2, Neu5,7,9Ac3, Neu5Gc7,9Ac2, Neu5Gc7Ac) isolated in limited amounts from total coelomocyte population. Neu5Gc type of sialic acids in coelomocytes was the most abundant type sialic acid when compared with other types. This is the first report on the presence of sialic acid types in coelomocytes of P. lividus using CapLC-ESI-MS/MS-Ion Trap system (Capillary Liquid Chromatography-Electrospray Ionization/Tandem Mass Spectrometry).

Toxicity of metal oxide nanoparticles in immune cells of the sea urchin

The potential toxicity of stannum dioxide (SnO₂), cerium dioxide (CeO₂) and iron oxide (Fe₃O₄) nanoparticles (NPs) in the marine environment was investigated using the sea urchin, Paracentrotus lividus, as an in vivo model. We found that 5 days after force-feeding of NPs in aqueous solutions, the three NPs presented different toxicity degrees, depending on the considered biomarkers. We examined: 1) the presence of the NPs in the coelomic fluid and the uptake into the immune cells (coelomocytes); 2) the cholinesterase activity and the expression of the stress-related proteins HSC70 and GRP78; 3) the morphological changes affecting cellular compartments, such as the endoplasmic reticulum (ER) and lysosomes. By Environmental Scanning Electron Microscope (ESEM) analysis, coupled with Energy Dispersive X-ray Spectroscopy (EDS) we found that NPs were uptaken inside coelomocytes. The cholinesterases activity, a well known marker of blood intoxication in vertebrates, was greatly reduced in specimens exposed to NPs. We found that levels of stress proteins were down-regulated, matching the observed ER and lysosomes morphological alterations. In conclusion, this is the first study which utilizes the sea urchin as a model organism for biomonitoring the biological impact of NPs and supports the efficacy of the selected biomarkers.

Cell cooperation in coelomocyte cytotoxic activity of Paracentrotus lividus coelomocytes

The coelomic fluid from the sea urchin Paracentrotus lividus contains several coelomocyte types including amoebocytes and uncoloured spherulocytes involved in immune defences. In the present paper, we show a Ca(2+)-dependent cytotoxic activity for the unfractionated coelomocytes assayed in vitro, with rabbit erythrocytes and the K562 tumour cell line. In a plaque-forming assay, whole coelomocyte preparations as well as density gradient separated coelomocyte populations revealed that cell populations enriched in uncoloured spherulocytes, exerted high cytotoxic activity by releasing lysins in the presence of amoebocytes. This cooperative effect could be dependent on soluble factors released by amoebocytes. With regard to this, we show that an enhanced cytotoxic activity was found by adding the supernatant from sonicated amoebocytes or hemocyte culture medium into spherulocyte preparations.

Regulatory sequences driving expression of the sea urchin Otp homeobox gene in oral ectoderm cells

PlOtp (Orthopedia), a homeodomain-containing transcription factor, has been recently characterized as a key regulator of the morphogenesis of the skeletal system in the embryo of the sea urchin Paracentrotus lividus. Otp acts as a positive regulator in a subset of oral ectodermal cells which transmit short-range signals to the underlying primary mesenchyme cells where skeletal synthesis is initiated. To shed some light on the molecular mechanisms involved in such a process, we begun a functional analysis of the cis-regulatory sequences of the Otp gene. Congruent with the spatial expression profile of the endogenous Otp gene, we found that while a DNA region from -494 to +358 is shown to drive in vivo GFP reporter expression in the oral ectoderm, but also in the foregut, a larger region spanning from -2044 to +358 is needed to give firmly established tissue specificity. Microinjection of PCR-amplified DNA constructs, truncated in the 5' regulatory region, and determination of GFP mRNA level in injected embryos allowed the identification of a 5'-flanking fragment of 184bp in length, essential for expression of the transgene in the oral ectoderm of pluteus stage embryos. Finally, we conducted DNAse I-footprinting assays in nuclear extracts for the 184bp region and detected two protected sequences. Data bank search indicates that these sites contain consensus binding sites for transcription factors.

Nemo-like kinase (NLK) acts downstream of Notch/Delta signalling to downregulate TCF during mesoderm induction in the sea urchin embryo

Studies in Caenorhabditis elegans and vertebrates have established that the MAP kinase-related protein NLK counteracts Wnt signalling by downregulating the transcription factor TCF. Here, we present evidence that during early development of the sea urchin embryo, NLK is expressed in the mesodermal precursors in response to Notch signalling and directs their fate by downregulating TCF. The expression pattern of nlk is strikingly similar to that of Delta and the two genes regulate the expression of each other. nlk overexpression, like ectopic activation of Notch signalling, provoked massive formation of mesoderm and associated epithelial mesenchymal transition. NLK function was found to be redundant with that of the MAP kinase ERK during mesoderm formation and to require the activity of the activating kinase TAK1. In addition, the sea urchin NLK, like its vertebrate counterpart, antagonizes the activity of the transcription factor TCF. Finally, activating the expression of a TCF-VP16 construct at blastula stages strongly inhibits endoderm and mesoderm formation, indicating that while TCF activity is required early for launching the endomesoderm gene regulatory network, it has to be downregulated at blastula stage in the mesodermal lineage. Taken together, our results indicate that the evolutionarily conserved TAK/NLK regulatory pathway has been recruited downstream of the Notch/Delta pathway in the sea urchin to switch off TCF-beta-catenin signalling in the mesodermal territory, allowing precursors of this germ layer to segregate from the endomesoderm.

Synthesis, structural investigations on organotin(IV) chlorin-e6 complexes, their effect on sea urchin embryonic development and induced apoptosis

Four new organotin(IV) chlorin derivatives, [chlorin=chlorin-e(6)=21H,23H-porphine-2-propanoic acid, 18-carboxy-20-(carboxymethyl)-8-ethenyl-13-ethyl-2,3-di-hydro-3,7,12,17-tetramethyl-(2S-trans)-], with formula (R(2)Sn)(3)(chlorin)(2).2H(2)O (R=Me, n-Bu) and (R(3)Sn)(3)chlorin.2H(2)O (R=Me, Ph) have been synthesized. The solid state and solution phase structures have been investigated by FT-IR, (119)Sn Mössbauer, (1)H and (13)C NMR spectroscopy. In the solid state, (R(2)Sn)(3)(chlorin)(2).2H(2)O complexes contain six coordinated Sn(IV), in a skew trapezoidal environment by forming trans-R(2)SnO(4) polymeric units. As far as (R(3)Sn)(3)chlorin.2H(2)O complexes are concerned, Sn(IV) is five coordinated in a polymeric (oligomeric) trigonal bipyramidal environment and eq-R(3)SnO(2) units, in the solid state. In saturated solutions, a polymeric structure comparable to the solid phase, with carboxylate groups of the ligand behaving in monoanionic bidentate fashion bridging Sn(IV) atoms, was detected for the (Me(3)Sn)(3)chlorin.2H(2)O complex, while in more diluted ones a tetrahedral configuration for the trimethyltin(IV) moieties was observed. Cytotoxic activity of the novel organotin(IV) chlorin was investigated in order to assay the effect on sea urchin embryonic development. The results obtained demonstrated that (n-Bu(2)Sn)(3)(chlorin)(2).2H(2)O and (Ph(3)Sn)(3)chlorin.2H(2)O exerted the antimitotic effect on the early stages of sea urchin development. In addition, the cytotoxic effect exerted by (n-Bu(2)Sn)(3)(chlorin)(2).2H(2)O appeared with necrosis of the blastomeres, which were clearly destroyed. After treatment with (Ph(3)Sn)(3)chlorin.2H(2)O, a programmed cell death was triggered, as shown by light microscope observations through morphological assays. The apoptotic events in 2-cell stage embryos revealed: (i) DNA fragmentation, with the TUNEL reaction (terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling); (ii) phosphatidylserine translocation in the membrane, with Annexin-V assay and (iii) cytoplasm blebbing, with the TUNEL reaction. The results demonstrated that the novel compound (Ph(3)Sn)(3)chlorin.2H(2)O was the most toxic derivative, by exerting antimitotic effect very early and by triggering apoptosis in the 2-cell stage of sea urchin embryonic development.