Figure 6.

Partial rescue of neurite outgrowth in SNS-gp130^−/− cultures through alternative STAT3 activation with leptin. A, Representative examples of control and gp130-deficient neurons treated with leptin and stained with Tuj-1. Scale bar, 30 μm. B, Leptin, that activates STAT3 via a gp130-independent pathway, increased the average length of control neurons (***p < 0.001; Mann–Whitney U test with Holm correction, n = 121 nontreated, n = 59 treated). Moreover, leptin partially restored neurite outgrowth in SNS-gp130^−/− neurons (*p < 0.05; Mann–Whitney U test with Holm correction, n = 11 nontreated, n = 36 treated). The number of neurite-bearing cells was increased in leptin treated compared with nontreated SNS-gp130^−/− cultures (***p = 0.000001; χ² test, for gp130^fl/fl n = 388 nontreated, n = 166 treated; for SNS-gp130^−/− n = 305 nontreated, n = 184 treated). C, SNS-gp130^−/− cultures were stimulated with the combination of NGF and leptin. This treatment recovered total neurite length to the levels of NGF-treated control neurons (p = 0.447; Mann–Whitney U test with Holm correction). This effect was in turn inhibited by Stattic (for SNS-gp130^−/− n = 11 nontreated, n = 51 NGF treated, n = 36 leptin treated, n = 95 NGF+leptin, n = 19 NGF+leptin+1.5 μm Stattic; for gp130^fl/fl n = 105 NGF treated). D, The percentage of neurite-bearing cells was largely recovered by coapplication of NGF and leptin in knock-out cultures and this effect was abolished by the addition of Stattic (for SNS-gp130^−/− n = 516 nontreated, n = 515 NGF treated, n = 184 leptin treated, n = 271 NGF+leptin, n = 280 NGF+leptin+1.5 μm Stattic; for gp130^fl/fl n = 391 NGF treated). Data are presented as mean ± SEM and analyzed by Mann–Whitney U test with Holm correction or χ² test; *p < 0.05, **p < 0.01, ***p < 0.001.