Bone marrow-derived cells response in proximal regions of nerves after peripheral nerve injury

In recent years, bone marrow-derived cells have been found to be crucial for peripheral nerve regeneration. After traumatic peripheral nerve injury, bone marrow-derived macrophages quickly infiltrate into the distal regions of nerves. To explore the changes caused by bone marrow-derived cells within the proximal regions of the nerves, sciatic nerves of chimeric mice carrying bone marrow cells expressing green fluorescent protein were crushed to observe the infiltration of invading bone marrow-derived cells. Seven days after surgery, abundant bone marrow-derived cells had infiltrated into the damaged proximal nerve segments. The numbers of these cells increased to a peak at 2 weeks and then gradually returned to normal levels within 30 weeks. Through immunofluorescence staining, many of these cells were identified as macrophages, and they showed a similar infiltration tendency toward distal nerve segments. However, fewer cells infiltrated proximal segments than distal nerve segments. In conclusion, these findings suggest that bone marrow-derived cells response not only occurs within the distal nerve segments but may also take place within the proximal segments of nerve tissues after nerve injury.