Figure 3.

High Level of FXN-HA Overexpression in WT Mice Cardiomyocytes Leads to Mitochondrial Function and Structure Impairment

Representative histological observations from the correlative analysis of adjacent heart tissue sections/sample from WT mice treated at 7 weeks of age with AAVRh.10-CAG-hFXN-HA vector (5 × 10¹⁴ vg/kg, n = 4; 5 × 10¹³ vg/kg, n = 3) and sacrificed at 21 weeks. For controls, 21-week-old NaCl-injected WT mouse (n = 1) and 9-week-old untreated Mck mice (n = 2) were also analyzed. Each image series corresponds to the same individual for which dose of vector, VCN, and [hFXN] are reported. From left to right, co-staining and co-localization analysis of hFXN-HA protein expression and SDH enzymatic activity, cytochrome C oxidase (COX), and NADH-ubiquinone oxidoreductase (NADH) enzymatic activities assessed by in situ histoenzymatic assay are shown. Transmission electron microscopy (TEM) observations at low and high magnification of the LV myocardium is shown, following negative stain performed to assess cardiomyocyte and mitochondria ultrastructure. Finally, TEM observations of adjacent ultrathin sections at high magnification following bismuth sodium tartrate labeling of iron-ferritin complexes are shown. White arrows indicate non-iron mitochondrial electron-dense bodies, blue arrowheads indicate collapsed mitochondrial cristae, orange arrowheads indicate mitochondrial iron deposits, yellow arrowheads indicate mitochondrial iron-ferritin complex accumulation in mitochondria, and red arrowheads indicate ferritin sequestrated in the lysosome. myo, myofibrils; mito, mitochondria; nuc, nucleus. See also Figure S3 for extended histological analysis.