Figure 1: Mitophagy is impaired in aged and DOX-treated hearts.

(a) Ten-month-old adult mice and 20-month-old aged mice were treated with an intraperitoneal injection of 5 mg kg⁻¹ CCCP and their hearts were collected 12 h later. Representative electron micrographs of hearts from CCCP-treated adult and aged mice; original magnification × 5,000; scale bar, 2 μm. The magnified photograph represents an autophagic vacuole containing mitochondria; original magnification × 12,000; scale bar, 500 nm. Mitochondria incorporated into an autophagic vacuole in baseline and CCCP-treated conditions were quantified blindly from 8–10 images from different fields (original magnification × 5,000) (n=3 per group). (b,c) CCCP-induced recruitment of Parkin and p62 to mitochondria was determined by immunoblotting of the heart mitochondria-rich fraction in adult and aged mice (b), and DOX-treated mice (c). Representative immunoblots are shown from four independent experiments. (d) Parkin was overexpressed in young and senescent MEFs using adenovirus-mediated transduction for the in vitro cell-based bioassay to assess the ability to clear damaged mitochondria. Mitochondrial content after 24 h of treatment with 20 μM CCCP was assessed by flow cytometry for MitoTracker Green FM. Results from four independent experiments performed in duplicate are shown. MEFs at passage 3 and passage 9 were used as young and senescent MEFs, respectively. (e) Mitochondrial DNA content was assessed by real-time PCR. Results are shown from six-independent experiments. (f) Mitochondrial content was assessed by immunoblotting for the mitochondrial chaperone, GRP75 (matrix protein) and complex I subunit, NDUFA9 (inner membrane protein). MEFs were treated with 100 nM bafilomycin-A1, (Baf-A1, an inhibitor of the vacuolar-type proton ATPase) to inhibit autophagy. Representative immunoblots are shown from three independent experiments. (g) Representative images of GFP-LC3 expressing MEFs treated with 20 μM CCCP for 10 h before the immunostaining of mitochondria with anti-TOM20 (red); original magnification, × 400 and × 1,000; scale bar, 100 μm and scale bar, 15 μm. Line scans below the images indicate colocalization between LC3 (green) and mitochondria (red) and correlate to the arrows drawn in the images. WHL indicates whole-heart lysate. Data are shown as the means±s.d. *P<0.05; **P<0.01 (two-tailed unpaired Student’s t-test).