The miR-21–mediated repression of PTEN by STAT3 controls adhesion dynamics and astrocyte migration. (A) miR-21 levels are significantly reduced in STAT3-CKO astrocytes (Mann-Whitney U test, n = 6, P = 0.0022). (B) PTEN is significantly up-regulated in STAT3-CKO astrocytes in vitro, and activation of Akt is accordingly reduced in STAT3-CKO astrocytes (n = 5, Mann-Whitney U test, P = 0.079 and P = 0.079 for PTEN and p-Akt, respectively). (C) PTEN IR is increased in astrocytes devoid of STAT3 in vitro. Bars, 20 µm. (D) The reduction of miR-21 observed in the spinal cords of Nestin-Stat3^−/− mice at 3 d after contusive injury is not significant. (E) PTEN is up-regulated in injured spinal cords of both WT and Nestin-Stat3^−/− mice at 5 dpi compared with sham. (Sagittal sections) Z-stack tile series of images acquired with a KEYENCE BZ-9000 microscope was processed to full focus. Bar, 200 µm. (F) Confocal analysis shows that up-regulation of PTEN in reactive astrocytes after SCI is more pronounced in Nestin-Stat3^−/− mice. Bar, 50 µm. (G) Reduction of PTEN rescued the migration of STAT3^+/− astrocytes. (H) WT and STAT3-CKO astrocytes exhibit equivalent reductions of trans-well migration upon inhibition of PI3K. (I and J) The length of LPA-induced FA is rescued to WT values in STAT3^+/−/PTEN^+/− astrocytes (left histogram, n = 810, 793, and 975 FAs of 25 WT; 27 STAT3^+/−; and 27 STAT3^+/−/PTEN^+/− astrocytes, respectively). (I and K) FAs recover their sensitivity to Src kinase inhibition in STAT3^+/−/PTEN^+/− astrocytes (right histogram, n = 381 and 182 FAs of the LPA alone versus LPA/SU6656 groups, respectively; unpaired t test). Bars, 10 µm. Error bars indicate ±SEM. **, P < 0.01; ***, P < 0.001.