Overexpression of miR669a ameliorates the dystrophic cardiac phenotype in Sgcb-null hearts. (A) Schematic representation of AAV2/9-TF-CBA-nLacZ-mi669a2×/miRdsRed2×. 2-d-old Sgcb-null mice were injected intraventricularly and analyzed 8 wk later (B–L). X-gal reaction, miR669a in situ hybridization, and H&E and Azan-Mallory (AM) staining on heart sections from miRdsRed (B–E)- and miR669a (F–I)-injected animals. miR669a was specifically expressed in miR669a-injected Sgcb-null hearts (C and G). Necrotic foci and fibrotic area extension were reduced in miR669a (H and I) compared with miRdsRed (D and E)-treated Sgcb-null hearts, assuming a benefic role of miR669a overexpression in cardiac pathology progression. Immunofluorescence analysis for MyHC and Cx43 expression in miRdsRed (J)- and miR669a (L)-injected Sgcb-null hearts. TUNEL assay analysis on miRdsRed (K and K′)- and miR669a (M and M′)-injected Sgcb-null hearts. Apoptotic nuclei are shown in green and highlighted by arrows in K and K′. (N) Percentage of apoptotic nuclei on cardiac sections from miRdsRed- and miR669a-injected Sgcb-null hearts. Three mice per each group of treatment were independently and statistically analyzed using Student’s t test (P < 0.01). (O) Percentage of necrotic foci on total cardiac section of miRdsRed- and miR669a-injected Sgcb-null hearts. Four mice per each group of treatment were independently and statistically analyzed. Bars, 50 µm.