I fibroblasti del nervo colonizzano il condotto usato per riparare una lesione nervosa ed esprimono la Neuregulina1 solubile, un fattore che promuove la rigenerazione del nervo periferico

Despite the peripheral nervous system intrinsic regenerative capacity, following a severe injury characterised by the loss of nerve material, a surgical intervention is required. The tubulization technique has been proven as a good alternative to the autograft, the gold-standard technique currently used. In this study, chitosan tubes and autografts are used to repair 8 mm rat median nerve lesions and the expression of Schwann cell (SC) and nerve fibroblast markers at 7, 14 and 28 days following the surgery are analysed and compared between the two models. SC markers are barely detectable at all time points analysed in the chitosan tube, while nerve fibroblast markers are observed. This suggests that Schwann cells slowly colonize the hollow conduit, while nerve fibroblasts arrive earlier. We focused our attention on the expression of soluble Neuregulin1 (NRG1), a growth factor strongly involved in the process of peripheral nerve degeneration and regeneration. In particular, we observed that NRG1 is strongly detected in the chitosan tubes 7 days following the repair, while ErbB3 and ErbB2, NRG1 receptor and co-receptor respectively, typically expressed by SCs, are not present. We know that nerve fibroblasts are able to produce different NRG1 isoforms in vitro. For this reason, we hypothesized that the soluble NRG1 detected in the early time points might be expressed by these cells. We show that cells expressing CD34, a nerve fibroblast marker, are also positive for soluble NRG1 in vivo. The action of soluble NRG1 is widely studied. In particular, it is known that this factor influences SC behaviour and it is responsible for the down-regulation of myelination genes, an important step in the process of SC trans-differentiation. Since also c-Jun transcription factor is known to have a central role in this process, we hypothesized that these two molecules could be involved in a positive feed-back mechanism. We analysed some genes expressed following SC primary culture stimulation with soluble NRG1β1. Our result shows that c-Jun is up-regulated earlier in time, while soluble NRG1 is expressed later, thus supporting our hypothesis. To further validate the idea of a positive interplay between these two molecules, we imagined to perform a silencing of either c-Jun or soluble NRG1. To this purpose we analysed the suitability of the RT4-D6P2T schwannoma cell line, which can be more easily manipulated compared to SC primary cultures.