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Exposure to crystalline silica particles causes silicosis, an occupational disease leading to an overproduction of collagen in the lung. The first step of this pathology is characterized by the release of inflammatory mediators. Tumour necrosis factor (TNF) is a pro-inflammatory cytokine directly involved in silica-induced pulmonary fibrosis. The marine demosponge Chondrosia reniformis is able to incorporate silica grains and partially dissolve the crystalline forms apparently without toxic effects. In the present work, C. reniformis tissue explants were treated with fine quartz dust and the expression level of fibrogenic genes was assayed by qPCR, demonstrating an overexpression of a fibrillar and a non-fibrillar collagen and of prolyl-4-hydroxylase enzyme. The deposition of new collagen could also be documented in quartz-treated sponge explants. Furthermore, TNF pro-inflammatory cytokine overexpression and involvement in silica-induced sponge collagen biosynthesis was demonstrated in quartz-treated explants as compared with controls by means of specific TNF inhibitors affecting the fibrogenic gene response. As no documentable detrimental effect was observed in treated explants, we conclude that the C. reniformis unique quartz engulfment and erosion is physiological and beneficial to the animal, leading to new collagen synthesis and strengthening of the body stiffness. Thus, we put forward the hypothesis that an ancient physiological behaviour from the lowest of the Metazoa, persisting through evolution via the same molecular mediators such as TNF, may have become the cause of disease in the specialized tissues of higher animals such as mammals., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2017. Published by The Company of Biologists Ltd.)

Quartz is a well-known occupational fibrogenic agent able to cause fibrosis and other severe pulmonary diseases such as silicosis and lung cancer. The silicotic pathology owes its severity to the structural and chemo-physical properties of the particles such as shape, size and abundance of surface radicals. In earlier studies, we reported that significant amounts of surface radicals can be generated on crystalline silica by chemical aggression with ascorbic acid (AA), a vitamin naturally abundant in the lung surfactant, and this reaction led to enhanced cytotoxicity and production of inflammatory mediators in a macrophage cell line. However in the lung, other cells acting in the development of silicosis, like fibroblasts and endothelial cells, can come to direct contact with inhaled quartz. We investigated the cytotoxic/pro-inflammatory effects of AA-treated quartz microcrystals (QA) in human primary fibroblasts and endothelial cells as compared to unmodified microcrystals (Q). Our results show that, in fibroblasts, the abundance of surface radicals on quartz microcrystals (Q vs QA) significantly enhanced cell proliferation (with or without co-culture with macrophages), reactive oxygen species (ROS) production, NF-κB nuclear translocation, smooth muscle actin, fibronectin, Bcl-2 and tissue inhibitor of metalloproteinase-1 expression and collagen production. Contrariwise, endothelial cells reacted to the presence of quartz microcrystals independently from the abundance of surface radicals showing similar levels of cytotoxicity, ROS production, cell migration, MCP-1, ICAM-I and fibronectin gene expression when challenged with Q or QA. In conclusion, our in vitro experimental model demonstrates an important and quite unexplored direct contribute of silica surface radicals to fibroblast proliferation and fibrogenic responses., (Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.)

The major structural and enzymatically active protein in spicules from siliceous sponges, e.g., for Suberites domuncula studied here, is silicatein. Silicatein has been established to be the key enzyme that catalyzes the formation of biosilica, a polymer that represents the inorganic scaffold for the spicule. In the present study, it is shown, by application of high-resolution transmission and scanning transmission electron microscopy that, during the initial phase of spicule synthesis, nanofibrils with a diameter of around 10 nm are formed that comprise bundles of between 10 and 20 nanofibrils. In intracellular vacuoles, silicasomes, the nanofibrils form polar structures with a pointed tip and a blunt end. In a time-dependent manner, these nanofibrillar bundles become embedded into a Si-rich matrix, indicative for the formation of biosilica via silicatein molecules that form the nanofibrils. These biosilicified nanofibrillar bundles become extruded from the intracellular space, where they are located in the silicasomes, to the extracellular environment by an evagination process, during which a cellular protrusion forms the axial canal in the growing spicule. The nanofibrillar bundles condense and progressively form the axial filament that becomes localized in the extracellular space. It is concluded that the silicatein-composing nanofibrils act not only as enzymatic silica bio-condensing platforms but also as a structure-giving guidance for the growing spicule.

The interaction between mineral structures and living beings is increasingly attracting the interest of research. The formation of skeletons, geomicrobiology, the study of the origin of life, soil biology, benthos biology, human and mammalian diseases generated by the inhalation of dust and biomaterials are some examples of scientific areas where the topic has a relevance. In this chapter we focus on cell reactivity to siliceous rocks and to the various forms of silicon dioxide, in particular. The examples here reported carefully review how such minerals may strongly affect different living beings, from simple ones to humans. The biomineralogy concept is explained, focusing on the effects of rocks on cell growth and development. The toxic action of silicon dioxide in mammalian lungs is the oldest evidence of crystalline silica bioactivity. More recently, we could demonstrate that crystalline silica has a deep impact on cell biology throughout the whole animal kingdom. One of the most illustrative case studies is the marine sponge Chondrosia reniformis, which has the amazing ability to incorporate and etch crystalline silica releasing dissolved silicates in the medium. This specific and selective action is due to the chemical reaction of ascorbic acid with quartz surfaces. One consequence of this is an increased production of collagen. The discovery of this mechanism opened the door to a new understanding of silica toxicity for animal cells and mammalian cells in particular. The presence of silica in sea water and substrates also affects processes like the settlement of larvae and the growth of diatoms. The following sections review all such aspects.

Siliceous sponges, one of the few animal groups involved in a biosilicification process, deposit hydrated silica in discrete skeletal elements called spicules. A multidisciplinary analysis of the structural features of the protein axial filaments inside the spicules of a number of marine sponges, belonging to two different classes (Demospongiae and Hexactinellida), is presented, together with a preliminary analysis of the biosilicification process. The study was carried out by a unique combination of techniques: fiber diffraction using synchrotron radiation, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetric (DSC), Fourier transform infrared spectroscopy (FTIR), and molecular modeling. From a phylogenetic point of view, the main result is the structural difference between the dimension and packing of the protein units in the spicule filaments of the Demospongiae and the Hexactinellida species. Models of the protein organization in the spicule axial filaments, consistent with the various experimental evidences, are given. The three different species of demosponges analyzed have similar general structural features, but they differ in the degree of order. The structural information on the spicule axial filaments can help shed some light on the still unknown molecular mechanisms controlling biosilicification.

A synchrotron radiation fiber diffraction structural study of the axial filament of siliceous spicules from two species of marine sponges (the Demosponge Geodia cydonium and the Hexactinellid Scolymastra joubini) was carried out. The sharpness of the spots in the diffraction patterns indicated that the protein units in the filament of both samples were highly organized. A possible explanation is that the arrangement of the protein units is similar to that of the pores in highly ordered siliceous mesoporous materials. Nevertheless, the diffraction patterns are quite different for the two types of spicules. The pattern of G. cydonium is consistent with a regular 2D hexagonal lattice of protein units in the direction perpendicular to the spicule axis, with a repeating distance of 5.8 nm; the units are linked to form fibers along the axis. The pattern of S. joubini indicates the presence of two different 2D lattices in which the repeating protein units are inclined by +50 degrees and -50 degrees with respect to the elongation axis; the distance between the units increases to 8.4 nm. This 2D model is consistent with hexagonal packing of spirally oriented cylindrical protein units elongated along the filament axis., (Copyright 2003 Wiley-Liss, Inc.)

Several sponge species incorporate a wide range of foreign material. Whether such material is actively selected by the sponge is controversial. Here we compare the available suspended matter and the sediment incorporated in the tissue of the demosponge Chondrosia reniformis. Field observations and laboratory experiments indicate that this species selects and incorporates only siliceous materials, in particular quartz particles and opal sponge spicules, avoiding carbonate particles. The reaction of ectosome cells of Chondrosia depends on the forms of silica: after settlement of crystalline quartz particles on the sponge surface, the pinacocytes contract uniformly, giving rise to a ruffled surface that remains throughout the incorporation of foreign material. In contrast, the opal spicules elicit a motile response in pinacocytes, which cover the spicules as a result. After incorporation, while the opal spicules remain unaltered within sponge tissue, the engulfed quartz particles are quickly etched, reduced in size, and released from the sponge. The etching of quartz particles by C. reniformis is produced by ascorbic acid, and is the first evidence of such activity from the animal kingdom. Ascorbic acid has been found to change the quartz surface features, which leads to an increased radical production and a consequent dissolution of quartz. This process does not occur on opal spicules., (Copyright 2003 Wiley-Liss, Inc.)