Fig. 3

Transmission electron microscopy images of myocardial ultrastructure in control db/+ mice (A-B), 12w (C-D) and 20w (E-F) db/db mice. Figures A, C, E (×1500), Figures B, D, F (×5000). A-B: Myofibrils are regularly arranged and the sarcomere length is uniform. Mitochondria (M) structure is clear, with intact membrane and cristae; sarcoplasmic reticulum (Spr) has no obvious expansion; Z line (Z) is arranged continuously and regularly, without obvious asymmetric widening; complete and continuous H-band (H) structure can be seen; there are a few small and scattered lipid droplets (LD). C-D: Moderate hypertrophy of cardiomyocytes with mild steatosis, myofibril rupture and dissolution. Mitochondria (M) are slightly swollen, the electron density is slightly reduced, the intramembrane matrix is dissolved, and the cristae are broken and reduced; the sarcoplasmic reticulum (Spr) is slightly expanded; the Z line (Z) structure is blurred and discontinuous; the H band (H) structure disappears, and the structure of thick and thin myofilaments is loose; the number of lipid droplets (LD) is relatively high and widely distributed; there is a few autophagolysosomes (ASS) can be observed. E-F: Cardiomyocytes are obviously enlarged with steatosis, and myofibrils are disordered. Mitochondria (M) are moderately expanded, the outer membrane is blurred, the cristae disappear, and abnormal aggregation increases; the sarcoplasmic reticulum (Spr) is expanded; the structure of Z line (Z) and H band (H) is blurred and invisible, and some thick and thin filaments are broken; the number of lipid droplets (LD) is significantly increased; there are several autophagy lysosomes (ASS) can be seen in the field