TH and Parkinson disease: As was shown in Figure 4a, in PD mouse substantia nigra, TH positive neurons were dramatically fewer than those in the sham group; lentivirus‐mediated overexpression of miR‐221 mimics in vivo significantly blocked the number of TH positive cells in the substantia nigra; and on this basis, overexpression of Bim blocked the increase of TH positive cells (F = 180.5).