Planarians as a Model to Assess In Vivo the Role of Matrix Metalloproteinase Genes during Homeostasis and Regeneration

Abstract

Matrix metalloproteinases (MMPs) are major executors of extracellular matrix remodeling and, consequently, play key roles in the response of cells to their microenvironment. The experimentally accessible stem cell population and the robust regenerative capabilities of planarians offer an ideal model to study how modulation of the proteolytic system in the extracellular environment affects cell behavior in vivo. Genome-wide identification of Schmidtea mediterranea MMPs reveals that planarians possess four mmp-like genes. Two of them (mmp1 and mmp2) are strongly expressed in a subset of secretory cells and encode putative matrilysins. The other genes (mt-mmpA and mt-mmpB) are widely expressed in postmitotic cells and appear structurally related to membrane-type MMPs. These genes are conserved in the planarian Dugesia japonica. Here we explore the role of the planarian mmp genes by RNA interference (RNAi) during tissue homeostasis and regeneration. Our analyses identify essential functions for two of them. Following inhibition of mmp1 planarians display dramatic disruption of tissues architecture and significant decrease in cell death. These results suggest that mmp1 controls tissue turnover, modulating survival of postmitotic cells. Unexpectedly, the ability to regenerate is unaffected by mmp1(RNAi). Silencing of mt-mmpA alters tissue integrity and delays blastema growth, without affecting proliferation of stem cells. Our data support the possibility that the activity of this protease modulates cell migration and regulates anoikis, with a consequent pivotal role in tissue homeostasis and regeneration. Our data provide evidence of the involvement of specific MMPs in tissue homeostasis and regeneration and demonstrate that the behavior of planarian stem cells is critically dependent on the microenvironment surrounding these cells. Studying MMPs function in the planarian model provides evidence on how individual proteases work in vivo in adult tissues. These results have high potential to generate significant information for development of regenerative and anti cancer therapies.

Mechanics dictate where and how freshwater planarians fission

“…Our data on the distribution of the waist location argues against a permanent fission zone, but allows for the possibility that the animal locally prepares for fission before each event., e.g. via enzymatic digestion of extracellular matrix components by metalloproteinases, which have been shown to play a role in planarian tissue homeostasis and regeneration (29,30).…”

Reconsidering regeneration in metazoans: an evo-devo approach

“…Evolution of different components of the extracellular matrix can also directly foster or inhibit regenerative processes. For instance, the metalloproteinases, a family of proteinases conserved across metazoans, seem to have been co-opted to different roles in regeneration, e.g., maintaining cell identity during Hydra foot regeneration (Leontovich et al, 2000), sea cucumber intestine regeneration (Quiñones et al, 2002) and planarian body regeneration (Isolani et al, 2013). In vertebrates, Calve and collaborators suggested hyaluronic acid, tenascin-C and fibronectin as part of a regeneration-specific transitional extracellular matrix during muscle regeneration in newt (Calve et al, 2010).…”

Innate immune system and tissue regeneration in planarians: An area ripe for exploration

“…MMP-like proteins have been identified in a diverse array of invertebrates [107, 108]. Planarians have four MMP-like genes ( Smed-mmp1, Smed-mmp2, Smed-mt-mmpA and Smed-mt-mmpB ) with roles in proliferation, apoptosis and cell migration [109]. Two of these, Smed-mmp-1 and Dj-mmp-1 , are essential for homeostatic remodeling of extracellular matrix, but not wound repair [109].…”

“…Planarians have four MMP-like genes ( Smed-mmp1, Smed-mmp2, Smed-mt-mmpA and Smed-mt-mmpB ) with roles in proliferation, apoptosis and cell migration [109]. Two of these, Smed-mmp-1 and Dj-mmp-1 , are essential for homeostatic remodeling of extracellular matrix, but not wound repair [109]. Although gene expression was unchanged following wounding, knock-down of Smed-mt-mmpA resulted in a delay in blastema regeneration [109].…”

“…Two of these, Smed-mmp-1 and Dj-mmp-1 , are essential for homeostatic remodeling of extracellular matrix, but not wound repair [109]. Although gene expression was unchanged following wounding, knock-down of Smed-mt-mmpA resulted in a delay in blastema regeneration [109]. Smed-mmp1 was also found to be expressed during septic-wounding in planaria, suggesting a role for this MMP in innate immune responses in addition to structural homeostasis [63].…”