Differentiation PC12 assay after 10 ng/ml NGF, 20/10 ng/ml proNGF/NGF, 20 ng/ml proNGF treatments. DIC (Differential Interference Contrast) images show differentiated PC12 cells after 5 days of treatment. The graph displays the mean neurite length for each group. Values are mean + Standard Deviation (SD) of three independent experiments and statistically significant differences were calculated by unpaired-two tailed t-Student’s test (*p < 0.05 versus proNGF/NGF group). Note the increase in neurite length in the proNGF/NGF group compared to the NGF or proNGF alone treatments. Scale bar 40 μm.