Modulation of the tissue composition of regenerative neuroma by dexamethasone and granulocyte colony-stimulating factor

Abstract

Aim. To evaluate the change of the content of mesenchymal (vimentin-positive) and reparative Schwann (GFAP-positive) cells in the regenerative neuroma of the rat sciatic nerve, taking into account the activity of local homeostasis regulation (CD73 expression) under the influence of dexamethasone (Dex) and granulocyte colony-stimulating factor (GCSF). Materials and methods. Vimentin-, GFAP-, and CD73-positive cells were detected immunohistochemically in the regenerative neuroma of 168 male Wistar rats, and their presence was quantified using statistical methods. Results. The regenerative neuroma of the sciatic nerve is characterized by a stereotypical cellular composition kinetics. Dexamethasone, during the initial stage of neuroma formation (1–7 days), led to a reduction in inflammatory infiltration and accumulation of vimentin+ mesenchymal cells. It significantly accelerated the accumulation of neural GFAP+ reparative Schwann cells and suppressed the expression of CD73. The granulocyte colony-stimulating factor (1–3 days) in the regenerative neuroma resulted in a slight reduction in inflammatory infiltration and an increase in the number of blood vessels penetrating into it. Under these conditions, the speed and quantity of vimentin+ cell accumulation and CD73 expression noticeably increased, as well as the speed of GFAP+ cell accumulation. The deviations in the expression of vimentin, GFAP, and CD73 in the neuroma under the administration of the mentioned substances gradually decreased and, after 8 weeks of the experiment, did not differ significantly from the control. When combined, dexamethasone and granulocyte colony-stimulating factor potentiated each other’s effects and, in addition, led to long-term maintenance of high CD73 expression. At the same time, the most pronounced approximation of the structure of the newly formed part of the nerve to the structure of the intact nerve trunk was observed. Conclusions. The simultaneous action of Dex and GCSF during the initial stages of regenerative neuroma formation, in contrast to their individual actions, not only alters the dynamics of mesenchymal and neural cell accumulation but also modifies the newly formed part of the nerve, bringing its structure closer to the intact state. This phenomenon is accompanied by increased reactivity of neurolemocytes during the axial cylinder germination stage of neuroma regeneration.