Sensory neurons influence the expression of cell adhesion factors by cutaneous cells in vitro and in vivo

Dorsal root ganglion (DRG) neurons co-cultured with skin-derived fibroblast-like cells (FLCs) show a strong neurite outgrowth. However, when physical contact between FLCs and neurons is prevented with membrane inserts, the DRG neurons exhibit a low survival and a deficient neurite growth. This indicates that cell adhesion molecules influence neuronal survival and neurite growth in co-cultures. The aim of the present study is to find out if selected adhesion molecules are expressed by cultivated FLCs with and without nervous influences, and/or by normal and denervated whole skin. RT-PCR data show that cultured FLCs and denervated skin express L1, N-CAM, N-cadherin and ninjurin, but not neurofascin or TAG-1. However, cultured FLCs exposed to DRG homogenates and innervated skin express N-cadherin only. Following application of neutralizing L1-, N-cadherin- and ninjurin-antibodies (but not N-CAM-antibodies) in the culture medium the mean number of surviving neurons is decreased. Co-cultures incubated with L1-, N-cadherin- or ninjurin-antibodies all show significantly less neurite outgrowth compared to controls. In conclusion, the findings in this paper indicate (i) that FLCs cultured in vitro and denervated whole skin express the cell adhesion factors L1, N-CAM, N-cadherin and ninjurin, (ii) that FLCs treated with neural molecules and innervated whole skin express N-cadherin only, (iii) that L1, N-cadherin and ninjurin are important for DRG neurons co-cultured with FLCs in vitro in terms of survival and neurite extension and (iv) that there may exist subpopulations of DRG-neurons with different sensitivities for N-cadherin- and ninjurin-antibodies.