Recombinant HvRNASET2 protein induces a marked connective tissue remodelling in the invertebrate model Hirudo verbana

The RNASET2 ribonuclease, belonging to the highly conserved RH/T2/s RNase gene family, has been recently shown to
modulate inflammatory processes in both vertebrates and invertebrates. Indeed, the RNASET2 protein acts as a chemoattractor
for macrophages in both in vitro and in vivo experimental settings and its expression significantly increases following bacterial
infections. Moreover, we recently observed that injection of human recombinant RNASET2 protein in the body wall of the
medicinal leech (a consolidated invertebrate model for both immune response and tissue regeneration) not only induced immune
cell recruitment but also apparently triggered massive connective tissue remodelling as well. Based on these data, we evaluate
here a possible role of leech recombinant RNASET2 protein (rHvRNASET2) in connective tissue remodelling by characterizing
the cell types involved in this process through histochemical, morphological and immunofluorescent assays. Moreover, a timecourse
expression analysis of newly synthesized pro-collagen1α1 (COL1α1) and basic FGF receptor (bFGFR, a known fibroblast
marker) following rHvRNASET2 injection in the leech body wall further supported the occurrence of rHvRNASET2-
mediated matrix remodelling. HumanMRC-5 fibroblast cells were also investigated in order to evaluate their pattern of collagen
neosynthesis driven by rHvRNASET2 injection.
Taken together, the data reported in this work provide compelling evidence in support of a pleiotropic role for RNASET2 in
orchestrating an evolutionarily conserved crosstalk between inflammatory response and regenerative process, based on macrophage
recruitment and fibroblast activation, coupled to a massive extracellular reorganization.