Repair and Reconstruction of Peripheral Nerve Injuries. Treatment with G-CSF and Stromal Vascular Fraction

Abstract: While surgery is a cornerstone in treatment of peripheral nerve injuries, it is not a comprehensive approach, and outcome is unsatisfactory, especially sensory function. The present aim was to translate recent findings about stem- and progenitor cells to improve regenerative outcome, where the cells have to be autologous, available within the same surgical procedure, and minimally manipulated. Granulocyte colony-stimulating factor (G-CSF) mobilizes hematopoietic stem cells from the bone marrow. Post-traumatic G-CSF therapy, evaluated in a rat sciatic nerve injurymodel with immediate repair, showed a 13% local decrease in Schwann cell apoptosis at the site of lesion, and a similar trend in the distal nerve segment in healthy rats, and at the site of lesion in diabetic Goto-Kakizaki rats. G-CSF had no effect on axonal outgrowth in short- or long term experiments.Stromal vascular fraction (SVF) of adipose tissue is a heterogenic mixture of cells, including small amounts of adipose derived stem cells. Electrospun multi-channeled nerve conduits, designed to mimic a native nerve, with longitudinal nanofibers inside the channels for axonal guidance +/- delivered SVF to the nerve conduit was used to bridge a 10 mm sciatic nerve gap in healthy rats. The nerve conduit supported axonal outgrowth and acted as a cell delivery vehicle during the observation time (four weeks). SVF did not improve axonal outgrowth, and adverse effects – gross encapsulation – was observed in 9/30 implants after SVF therapy. Schwann cell infiltration was inferior in nerve conduits supplemented with SVF cells, with a partially enhanced inflammatory response.Co-culture of SVF cells and peripheral nerve segments performed on aligned nanofibers, recreating in vitro the environment above, showed no change in expression of Schwann cell marker S-100 in SVF cells, but increased Sox10 in SVF cells exposed to a nerve segment compared to baseline. Pilot experiments with mass spectrometry indicated a SVF-nerve interplay in the local microenvironment.In conclusion, G-CSF and SVF therapy affected glial cells, but did not improve axonal outgrowth. G-CSF decreases Schwann cell apoptosis, but does not improve regenerative outcome. An electrospun nerve conduit can be used to bridge a nerve gap and act as a cell delivery vehicle. SVF delivered in micro-channels interferes with ingrowth of Schwann cells by unknown mechanisms.