Historical step in Biomedical sciences: Limb regeneration in a non regerative species
Most of us think of limb regeneration as science fiction or futuristic dream, that could be achieved when we are able to import genes from regenerative species (as seen in a Spiderman blockbuster’s movie).
Yet, this has been recently carried out successfully by a team based in the Departments of Biology and Biomedical Engineering of Tufts University, Medford, MA, USA, in an adult non regenerative species, the Xenopus Leavis frog.
The paper was published in Science a few days ago and is freely accessible here.
Back to the 80’, previous attempts to induce limb regeneration in non regenerative species made use of electrical stimulation, tissue-guiding biomaterials, progenitor cell transplantation, and the direct simulation of key molecular pathways. Moreover, these projects of experimentally stimulated limb regeneration largely involved fully or partially regenerative biological systems or developmentally immature (i.e., nonadult) subjects. Restoring substantial growth and patterning of new functional limbs in nonregenerative adults has never been reported so far.
The models used in this clinical study involved an adult frog species individual with characteristics similar to Humans. Indeed, “like mammals, the authors wrote, adult X. laevis exhibits modest tissue renewal, few pluripotent stem cell pools, and an age- dependent decline of regenerative ability that is similar to that of human finger amputations.”
The authors designed their own limb regeneration roadmap protocol involving the development of a complex intervention for adult Xenopus hind-leg amputations. First, in order to control the local microenvironment of a wound in vivo, they used a wearable bioreactor (called “BioDome”). In addition, they made use of 24 hours immersion in a silk hydrogel containing specific compounds conceived to trigger a sustainable, endogenous morphogenetic cascade and induce complementary processes such as the modulation of inflammation, promotion of neural sparing, and tissue growth - doing so, no subsequent intervention or continuous micromanagement of the wound was needed.
This molecular cocktail involved a combination of five drugs (Multi Drugs Treatment or MDT) and was used in a group of amputees (MDT) and compared against a separate group of amputees that had not been exposed to this treatment (named BD or ND in the charts below) .
Results:
Regenerative soft tissue length, as measured by the distance from the amputation plane to the distal tip of the regenerate, increased for all groups over the 18-month regeneration period, but animals exposed to MDT displayed significantly greater and complex soft tissue growth when compared to the other groups.
Looking into more details, they observed that non MDT groups showed delayed wound closure at an early stage of the recovery process. They also analysed the macroscopic soft tissue and bone and observed that thicker tissue buds displaying early signs of pigmentation and morphological complexity in the MDT, but not in the other groups.
In parallel of the limb restoration analysis, the authors tracked the temporal pattern of gene expression underlying the regeneration process, by sampling and analysing the transcriptome (the product of gene transcription) at different time.
A bioinformatics approach was then used to identify significant clusters of gene expression underlying parallel biomolecular processes governing regeneration. Their analyses show that early MDT exposure lead to an increased transcriptional activity (i.e., gene expression) of a genetic network with inflammation, morphogenesis, and embryological development.
The technical details are available in the original paper for the readers wishing to dig into this further.
This is an outstanding work and according to me very promising, that not only reports a biomedical performance never reached so far, but also reports the underlying genetic expression pattern.
