Subcutaneous Adipose Tissue-Derived Neural Stem Cells Promote Regeneration Following Peripheral Nerve Gap Injury
*Leah Ott , *Rhian Stavely , *Ahmed Rahman , *Christopher Han , *Abigail Leavitt , *Ryo Hotta , *Allan Goldstein
Pediatric Surgery, Massachusetts General Hospital, Brookline, MA
Background: Peripheral nerves (PN) have the capacity to repair themselves, but functional outcomes remain poor for transection injuries with large gaps. Schwann cells participate in PN repair by guiding regenerating axons, producing myelin, and secreting neurotrophic factors. Given difficulties expanding Schwann cells in vitro, neural stem cell (NSC) therapy has been proposed for the treatment of PN gap injuries. We have previously shown that Schwann cells in the subcutaneous adipose tissue (SAT) can adopt NSC properties in vitro, which then differentiate into functional neurons and glia after transplantation into the gastrointestinal tract. Whether SAT-NSCs can engraft and promote regeneration after PN injury is unknown.
Study Design: Randomized control trial. Fluorescent Schwann cells were isolated from the SAT of adult Wnt1tDT+ neural crest reporter mice and cultured in neuroproliferation media for 21 days, generating floating clusters of SAT-NSCs. Adult Plp1GFP+ pan-glial reporter mice underwent PN injury surgery, in which 5mm of the left sciatic nerve was sharply resected at the mid-thigh and repaired with a 7mm fenestrated silicone conduit. Nerve stumps were sutured inside the conduit to create a 5 mm defect. Conduits contained either SAT-NSC neurospheres (n=14) or media alone (n=8). On POD28 or 56, mice were sacrificed and conduits dissected to assess nerve repair. SAT-NSC engraftment and differentiation in the regenerated nerve were evaluated using immunofluorescence. Gastrocnemius muscle mass and leg circumference served as measures of muscle wasting. Sciatic functional index (SFI, a previously validated measure of sciatic nerve dysfunction calculated using paw print measurements) was used to quantify motor recovery (ranging from normal SFI 0 to complete dysfunction SFI -100).
Results: At POD28 and 56, SAT-NSCs survived within the conduit (Fig.1a) and integrated with the regenerating nerve (Fig.1b). Nerves demonstrated immunoreactivity to myelin protein zero around host Plp1GFP+ cells and transplanted SAT-NSCs, suggesting both populations participated in myelination (Fig.1c). At POD28, mice receiving SAT-NSCs had greater leg circumference (mean 17.0mm versus 16.0mm, p=0.002; Fig.1d) and gastrocnemius muscle mass (mean 56.8 mg versus 45.9 mg, p = 0.03; Fig.1e) than media controls, but these differences did not persist at POD56. Mice receiving SAT-NSCs had superior SFI scores at POD56 (mean -79.0 versus -103.5, p=0.04; Fig.1f), consistent with enhanced motor function.
Conclusions: Transplanted SAT-NSCs can integrate with regenerating nerves and enhance motor reinnervation following PN transection. These cells may represent a novel, easily accessible source of autologous NSCs for the treatment of PN injuries.
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