Bioreactor device helps frogs regenerate their legs

A team of scientists has devised a device that can induce partial regeneration of the hind limbs in adult African aquatic claw frogs (Xenopus laevis) by "starting" the tissue repair at the site of amputation. Their conclusions, published November 6 in the newspaper Cell reports, introduce a new model for testing "electroceuticals", or cell-stimulating therapies.

"In the best of cases, adult frogs normally only grow back in the form of a thin, featureless cartilaginous spike," says lead author Michael Levin, a development biologist at Allen's Discovery Center. Tufts University. "Our procedure has induced a regenerative response that they never have, which has resulted in the creation of larger and more structured appendices." The bioreactor device generated very complex downstream results that bio-engineers can not yet manage directly. "

The 3-D scientists printed the silicon bioreactor and filled it with hydrogel, a sticky polymer globe. They combined moisturizing silk proteins with the hydrogel to promote healing and regeneration and then added progesterone. Progesterone is best known for its role in the preparation of the uterus for pregnancy, but it has also been shown that the hormone promotes the repair of nerves, blood vessels and bone tissue.

The researchers divided the frogs into three groups: experimental, control and sham. For the experimental and simulated group, they stitched the device on the frogs immediately after limb amputation. In the experimental group, the bioreactor released progesterone at the site of amputation. In any case, they removed the devices after 24 hours.

When they examined the frogs of the experimental group at different times during 9.5 months, they found that the bioreactor seemed to trigger a degree of limb regeneration not seen in the other groups. Instead of a typical tip-shaped structure, bioreactor treatment resulted in a blade-shaped formation closer to a fully formed limb that could not generate unassisted regeneration.

"The bioreactor device has created a favorable environment for the wound where the tissue could grow as during embryogenesis," Levin said. "A very brief application of the bioreactor and its payload triggered months of tissue growth and structuring."

Levin and his team took a closer look at the regenerated structures with the help of molecular and histological analyzes. They found that, unlike the control and dummy groups, the regenerating members of the bioreactor-treated frogs were thicker with more developed bones, innervation and vascularization. By analyzing video footage of frogs in their tanks, they also noticed that frogs could swim more like frogs without pretension.

RNA sequencing and transcriptome analysis revealed that the bioreactor had altered gene expression occurring in the cells at the amputation site. The genes involved in oxidative stress, serotonergic signaling, and white blood cell activity were upregulated, while other genes related to signaling were downregulated.

The researchers also observed that scars and immune responses were downregulated in bioreactor-treated frogs, suggesting that added progesterone attenuated the body's natural response to injury, thereby promoting the regeneration process.

"In reproduction and in its newly discovered role in the functioning of the brain, the actions of progesterone are local or tissue-specific," says the first author, Celia Herrera-Rincon, neuroscientist at Levin's lab at the University of Toronto. Tufts University. "What we demonstrate with this approach is that maybe reproduction, brain processing and regeneration are closer than we think, maybe they share paths and elements of a code. common bioelectric – and not yet fully understood. " "

Levin's lab will continue to target bioelectric processes to induce spinal cord regeneration and reprogramming of the tumor. They also hope to replicate their mammalian bioreactor experience. Previous research suggests that mice can partially regenerate amputated fingertips in the right conditions, but that their life on the ground prevents this process.

"Almost all good regenerators are aquatic," says Levin. "You can imagine why this is important: a mouse that loses a finger or a hand, and then grinds the delicate regenerative cells in the flooring material while it is moving, is unlikely to experience significant regeneration of the limb. "

Levin plans to add sensors to the device for remote monitoring and optogenetic stimulation, which he hopes will improve control of cellular decision making after injury.

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More information:
Cell reports, Herrera-Rincon et al .: "A short, local application of progesterone via a portable bioreactor induces a long-term regenerative response of the lower limb Xenopus Hindlimb" https://www.cell.com/cell-reports/fulltext/S2211- 1247 (18) 31573-0, DOI: 10.1016 / j.celrep.2018.10.010