Protease inhibitors influence the direction of neurite outgrowth.

Addition of protease inhibitors to the culture medium has been shown to enhance neurite outgrowth by cultured mouse dorsal root ganglia (DRG). Those results are now extended to show that a diffusible source of soybean trypsin inhibitor (STI) or zones of immobilized STI can orient the direction of outgrowth towards the region of STI. However, a high concentration of diffusible STI promotes outgrowth in the opposite direction from the STI source. Immobilized leupeptin, L-lysine, or D-Phe-Pro-Arg-chloromethyl ketone can also direct outgrowth towards their immobilized areas, as do zones of laminin or fibronectin. However, derivatized zones containing urokinase or thrombin preferentially direct outgrowth away from those zones. These data support the hypothesis that a balance between extracellular protease and inhibitor is important in mediating interactions between neurite growth cone and extracellular matrix.