# Assessment of Nerve Repair Augmented with Adipose-Derived Mast Cells in an Animal Model
## 4 Discussion  
In our study, rat sciatic neurornraphy augmented with a processed fat autograft led to less mast cells as determined by luxol fast blue and tryptase, compared to a simple end-to-end suture. There were more CD34+ blood vessels at 10 weeks and comparable ultrasonographic gastrocnemius muscle atrophy throughout. The involvement of mast cells in the inflammatory process and in immune reactions is well studied, but their implication in central and peripheral nervous system repair was only recently discovered. The role of mast cells in nerve regeneration is supported by their heterogeneous, morphological and functional characteristics [12; 13]. Post-traumatic nerve regeneration is a complex process which involves cellular interactions, growth factors, proteins and enzymes. These facts have been evaluated using an adult rat femoral nerve in a regeneration room type H [14]. [PERSON] et al. support the idea of a link between chemotaxis after nerve injury and the benefits of using a regeneration room to improve the motor functions of the injured nerve [15]. Our study found that vascular density starts to increase from the second part of the regeneration process, between 4 and 10 weeks, with a decrease in the mast cell subpopulation within the neural tissue. It seems that adipose tissue addition inhibits the mast cell subpopulation positive to tryptase, avoiding the inflammatory process which can appear nearby. The angiogenesis process involved in nervous regeneration may be an early event. At both 4 and 10 weeks the morphology of the CD34 blood vessels--immature, intermediate, and mature--suggests an active and continuous angiogenesis process. The results of our present study suggest multiple methods of mast cell involvement in nervous regeneration. The CD34-positive cells with different morphologies than the endothelial cells may be Schwan cell progenitors, but further studies are needed. Mast cells may stimulate CD34 fibrobl cells from the adipose tissue, which could be involved in repairing either an injured nerve or the muscle innervated by it. The participation of mast cells in muscle regeneration has been previously described. Different research groups showed that mast cell tryptase is involved in repairing an injured muscle by stimulating myoblasts [15; 16]. Regarding the tryptase mast cell subpopulation, we consider that they may have a limited effect on the angiogenesis process. It seems that adipose tissue addition has an anti-inflammatory effect, especially if we consider adipose tissue to be one of the sources of mast cells and of progenitor cells. The CD34 progenitor cells have been demonstrated to play a role in nerve repair, but not to such an intense degree as the vascular endothelial growth factor (VEGF) [17; 18]. The presence of the CD34 progenitor cells in the injured nerve has been associated with an increase in the regenerative process [19]. On the other hand, the increase in the CD34 progenitor cells may be involved in the nervous regeneration process independent of the mast cells. [PERSON] et al. demonstrated that adipose tissue has an anti-inflammatory effect by containing IL-1, which, when associated with IL-10, can produce IFN Beta [20]. In addition to heparin, histamine, interleukins, and granules, mast cells also contain NGF (the nerve growth factor), which is involved in immune and inflammatory processes [21]. Therefore, mast cells should be able to produce both nerve injury as well as repair, via their numerous degranulation factors. These biochemical and molecular processes remain unclear so far. Together with other inflammatory cells, the mast cells express the CD300f receptor, well known for its involvement in nerve injury but also in nerve repair [22]. Similar to our study, [PERSON] et al. have analyzed the accumulation of macrophages close to the injured sciatic nerve, but also the role of inflammatory mediators in injured nerve tissue [22]. The injured sciatic nerve repair process involves mast cells,