EXPLORING THE POTENTIAL OF MARINE RESOURCES: ECHINODERMS AS VALID MODELS FOR REGENERATION STUDIES AND BIOTECHNOLOGICAL APPLICATIONS

The marine ecosystems have always been exploited by humans as source of food,
inspiration, bioactive compounds and biomaterials. Marine invertebrates especially
caught the interests of scientists for their potential in basic research and applied
biotechnology studies displaying the most spectacular variety of morphological,
physiological and behavioural adaptations to diverse environmental conditions. Among
them, echinoderms are interesting models for three main reasons: 1) their crucial
phylogenetic position, since they are the second largest group of deuterostomes after
chordates, 2) their striking regenerative abilities and 3) their peculiar dynamic
connective tissues (Mutable Collagenous Tissues or MCTs) capable of rapidly changing
their mechanical properties. These last two features are strongly related: indeed,
echinoderm connective tissues are considered one of the key characteristics that allows
their effective regeneration phenomena. In particular, the extracellular matrix (ECM), with
both its fibrous (mainly collagen) and cellular components, is primarily involved during
regeneration and can be regarded as a promising source of biomaterial (collagen) for
regenerative medicine applications.
Therefore, the present work followed two different but overlapping research lines whose
main aims were to: a) describe echinoderm arm regeneration after traumatic amputation
with a special focus on connective tissue and immune system in order to gain a better
comprehension of this fundamental biological process and to compare it with other
animals, especially with those with limited regenerative abilities (e.g. mammals), and b)
explore the biotechnological potential of echinoderm connective tissues as source of
fibrillar collagen to produce valuable tools for human biotechnological applications , such
as regenerative medicine.
The starfish Echinaster sepositus, the brittle star Amphiura filiformis, the sea urchin
Paracentrotus lividus and the sea cucumber Holothuria tubulosa were selected as
experimental models. For both research lines a multi-disciplinary approach was
employed mainly including microscopic anatomy, gene expression,
immunohistochemistry, ultrastructural and biomechanical characterisation and in vitro
tests.
Focusing on the first research line, starfish and brittle star were traumatically amputated
and the regenerates at different time points were analysed with a specific focus on the
ECM and immune system roles during the regenerative process. Our results showed that
echinoderm emergency reaction and wound healing after injury are faster that those
described in mammals and ECM fibrillar organisation at the wound site is delayed in
comparison to them. Absence of fibrosis (i.e. over-deposition of collagen) is shown as
well. In general, all these evidences can be regarded as key features to ensure their
subsequent effective regeneration. Gene expression analyses showed that the identified
collagen-like and ECM-related molecule genes in brittle star are differentially expressed
during regeneration, thus indicating that different tissues are involved in collagen and
ECM production/remodelling. The expression pattern of the collagen biosynthesis
enzyme gene here identified indicated that in both experimental models the regenerating
epidermis is involved in collagen production. Preliminary analyses on immune system
molecules showed that in brittle star TNF-α-like presence is comparable to that of
mammals during wound healing. Overall, the regenerat