1. Casey A Spencer1 and Thomas Leung1,2,3
Research Techniques Made Simple: Parabiosis to Elucidate Humoral Factors in Skin Biology
Casey A Spencer1 and Thomas Leung1,2,3
1Department of Dermatology, University of Pennsylvania School of Medicine, Philadelphia, PA, 19104, US.
2Corporal Michael Crescenz Veterans Affairs Medical Center, Philadelphia, PA, 19104, US.
3Institute for Regenerative Medicine, University of Pennsylvania, Philadelphia, PA, 19104, US.

2. Parabiosis
Two living animals are surgically conjoined and share a single circulatory system
Surgical union of skin causes formation of vascular anastomoses
150+ years of use
Led to advances in endocrinology, neurology, musculoskeletal biology, and dermatology

3. Selected History of Parabiosis
Sauerbruche and Heyde coin the term “parabiosis” and modify the technique by extending the length of the incision and adding an intestinal anastomosis.
Hervey uses parabiosis to demonstrate that the circulating factor leptin is involved in energy balance.
Villeda and Wyss-Coray uses parabiosis to study impact of aging on neurons and brain function.
1908
1959
2014
1864
1933
2018
French biologist Bert tests the viability of skin allografts by joining two rats together and attaching flaps of skin from one animal to another animal.
Bunster and Meyer improve on the technique by joining the skin, muscle layers, and abdominal wall together.
Nishiguchi uses parabiosis to show that the circulating factor, SDF1, is responsible for scar formation in skin.
2005
Conboy and Rando shows that the aged environment impairs muscular regenerative potential of older individuals.

4. Example of parabiosis experiment to test age-defined phenotypes
Pairings
Intervention
Observation
Conclusion
Both parabionts
maintain phenotype A
Parabiont B adopts phenotype A
Systemic
circulating factor
Parabiont A adopts
phenotype B
Wound
Both parabionts maintain individual phenotypes
Local
cell signaling
Both parabionts
maintain phenotype B

5. Basic Principles of Parabiosis
Standard aseptic technique used
Elbows and knee joints are sutured together
Left and right flanks of parabiont skin are sutured with single, interrupted stitches
Surgery length: minutes
Post-procedure care is critical
Treat with antibiotics, subcutaneous normal saline, meloxicam and buprenorphine hydrochloride
Monitor for recovery characteristics
Incisions are healed 2 weeks post-surgery
Additional skin wounding performed 4 weeks post-surgery

6. Technical Challenges
Background matched animals have best chance of survival
Perioperative mortality
90% + pairs recover from procedure
Parabiotic disease
1-2 weeks post-surgery
Likely represents underlying graft-versus-host disease, where the rejected “organ” is the anastomoses
Affects 20-30% of pairs in inbred mouse strains
Affects 60-70% of pairs in outbred mouse strains

7. Kinetic Considerations
Circulatory system anastomosis requires 2 weeks to mature before steady-state is reached
Use a reporter mouse (e.g. mTmG mouse) to determine level of blood exchange
Consider rate of clearance of factors from circulation
Rate of blood exchange in parabiosis is slow
Potential for a false negative result if circulating factor cannot reach the other parabiont

8. Applications
Test for a circulating factor involved in skin physiological processes (i.e. differentiation, neoplastic formation, wound healing)
Mice can vary in physiological condition:
Parabiont A
Parabiont B
Potential physiological conditions
Aged
Mutant
Wounded
Irradiated
Infected
Obese
Young
Wildtype
Unwounded
Non-irradiated
Non-infected
Lean

9. Applications
Answer questions about systemic regulation of cell and tissue aging in multiple organs
Use genetically altered mouse strains for direct testing of signaling pathways/networks involved in regulating an identified process