Table 9.
Additional mitochondrial fission and fusion studies in the heart using TEM.
| The models | Ultrastructural changes | Quantitative TEM? | References |
|---|---|---|---|
| i.v. injection of mdivi-1 (1.2 mg/kg) 15 min | Mdivi-1 did not change mitochondrial morphology as assessed by TEM, while ↑ percent mitochondria that are >2 μm or 1 sarcomere in length, after 20 min regional ischemia compared to vehicle control |
Percent mitochondria that are >2 μm or 1 sarcomere in length, 3.6% (vehicle) vs. 14.5% (with mdivi-1) | Ong et al., 2010 |
| Drp (Myh6-cre) KO in the early postnatal days | Compromised LV function at postnatal day 7, decreased mitochondrial respiratory activity. Myofibrils appeared unaffected. Heterogeneous mito morphology in the Drp1KO heart, with branched tubules and large ovals. There are also vacuolar structures suggestive of mitophagosomes. |
Tomography study with 3D reconstruction measurement demonstrated that Drp1 KO heart has: ↑ Mit volume by ~0.7 × 108 nm3 |
Kageyama et al., 2014 |
| Cardiac Drp1-KO (via myh6-MER-cre) | Dilated cardiomyopathy (DCM) and heart failure (HF) 6–8 weeks after KO. Mitochondria have preserved cristae; however, they were larger and more elongated. In this study, mitochondrial autophagy and mitochondrial stress were assessed using p62, LC3, LONP2, AFG3L2, and Hsp60 Western blots. | ↑Mean area ctl 0.9, 3 weeks 1.8, 6 weeks 1.8 μm2
↑Mito aspect ratio: clt 0.8, 3 weeks 1.7, 6 weeks 1.7 ↓Mito content: clt 48%, 3 weeks 35%, 6 weeks 30% |
Song et al., 2015a |
| Parkin and Drp1 DKO mice (via myh6-MER-cre) | Parkin KO or overexpression (OE) did not result in cardiac dysfunction over 20 weeks. TEM at 6 weeks after Parkin KO look normal, Myh6-Parkin transgenic mice at 30 weeks did not show abnormalities in mito content, mito area and aspect ratio. TEM showed that Drp1 KO exhibit loss of mitochondria 6 weeks after Drp1 deletion, Parkin/Drp1 DKO delays cardiomyopathy of the Drp1 KO, and partially restore mitochondrial content | Mito content (% total cell): WT: 50%, Parkin KO: 50%, Drp1 KO: 30%, DKO: 42% Mito area (μm2): WT: 0.75 Parkin KO: 0.75 Drp1 KO: 1.3, DKO: 1.55 Mito aspect ratio: WT: 0.4 Parkin KO: 0.4 Drp1 KO: 0.7, DKO: 0.6 |
Song et al., 2015b |
| Whole-body Opa1 heterozygous knockout (KO) (+/–) mice | Cardiac dysfunction at 12 months but not 3 months ↓ Complex IV activity and ↓ mtDNA have been seen at 3 months, and ↓ complex I activity seen at 12 months. Disruption of orderly arrays of mitochondria between myofilaments, and ↓ mitochondrial density even at 3 months. Loss of cristae has been visualized at 12 months. |
No | Chen L. et al., 2012 |
| Whole-body Opa1 heterozygous KO(+/–) mice | At 6 months, no change of cardiac function, but ↓of small mitochondria (<1 μm3 from 46% to 41%) and increase of large mitochondria (>1.8 m3 from 21% to 27%) by MitoTracker image analyses. TEM showed that mitochondria exhibited variability in size and shape at 3 months, with cristae deformation and the presence of dark material consistent with deficient fusion. No change in SR-mitochondrial contacts |
↑ Mean size of mitochondria: WT 0.5 μm2, +/– 0.7 μm2 ↑ mean surface of mitochondria % of a given surface: WT: 38%<0.4 μm2, 55% 0.4–0.8 μm2, 7%>0.8 μm2 +/–: 17%<0.4 μm2, 55% 0.4–0.8 μm2, 28%>0.8 μm2 |
Chen L. et al., 2012; Piquereau et al., 2012 |
| Cardiac specific Mfn2 KO hearts (via Mlc2v-cre) | Cardiac dysfunction at 17 months, and increased sensitivity to I/R injury at 6 months. At 4 months, ↑ LC3II and p62 protein levels and ↑ autophagosomes by TEM, ↑ mitochondrial area, while no changes of mitochondrial volume density, nor of mtDNA. |
↑ Mito area 0.65 μm2 WT, 1.05 μm2 in MFN2 CKO heart Mito volume density 0.4 μm3 /μm3 for both |
Zhao et al., 2012 |
| Mfn1 and Mfn2 KO (Myh6 “turbo” cre) | Mfn2 KO exhibit ↑ mito mean perimeter and area, ↓ contact length with jSR, ↓ Ca2+ uptake and Ca2+-induced change of NAD(P)H/FAD+, while Mfn1 KO is normal. |
Ctl vs. Mfn2 ↑ Mean mito perimeter (μm) 3 vs. 3.9 ↑ Mean mito area (μm2) 0.68 vs. 1.1 ↓ Contact length with jSR (%) 48 vs. 34 |
Chen Y. et al., 2012 |
| Using Myh6-cre to delete Mfn1 starting embryonic day 9.5 | ↑ Small, fragmented mitochondria; ↓ myofibril volume density; cardiac function and respiration in isolated mitochondria were maintained, but adult cardiac myocytes have better survival in response to H2O2 |
↓ Cross-sectional mito area 52–32 μm2
↓ Mean diameter 3.05–2.36 μm ↓ Mean maximum diameter 1.12–0.7 μm ↑ numbers of 58–98/100 μm2 Normal mito volume density 42%, ↓ Myofibril volume density 44%−40% |
Papanicolaou et al., 2012 |
| Cardiac Mfn1/2 DKO (via myh6-MER-cre) | While Drp1 KO heart has ↑ LV/wall thickness, Mfn DKO mice have enlarged heart but the LV/wall thickness is unchanged. While Drp1 KO has larger mitochondria, Mfn DKO has smaller mitochondria |
↓ Mito area ctl 0.75 μm2, 3 weeks 5 μm2, 6 weeks 0.4 μm2
Mito aspect ratio: 1.3 no change ↑ Mito content: clt 48%, 3 weeks 60%, 6 weeks 75% |
Song et al., 2015a |
| Cardiac (Myh6) OE of Mfn2, Mfn2-AA | Mfn2-AA mice have smaller, abnormally shaped mitochondria in the heart starting at 3 weeks of age, associated with ↓ succinate dehydrogenase (SDHB) complex II subunit protein compared to wild-type (WT) Mfn2 transgenics, at 5 weeks of age, the Mfn2-AA mutant mice develop DCM |
3 weeks: Mito content ↓ 46%−33%, Mito area ↓ 1.25–0.7 μm2, Mito aspect ratio ↑ 1.5–2.6 |
Gong et al., 2015 |
| Cardiac Mfn1/2 DKO (via myh6-MER-cre) | Mfn DKO mice are more resistant to I/R injury, have smaller mitochondria, the presence of cristae-disrupted and fragmented interfibrillar mitochondria, maximal respiration ↓ in isolated mitochondria |
↓ Mito area ctl 0.55–0.42 μm2 (5 weeks KO) | Hall et al., 2016 |
| Mfn2 KO (cardiac- Myh6 “turbo” cre) 8–10 weeks | Extensive 3D analyses of mito volume, roundness, elongation, flatness, minimum mito-jSR distance | ↑ Volume 0.6 vs. 0.85 μm3; ↓roundness 0.87 vs. 0.8; elongation similar at 0.40; ↑flatness 0.45 vs. 0.5; ↑ mito-jSR distance 12.5 vs. 17 nm; length of mito-jSR networks along Z-axis similar at 200 nm; ↓number of mito-jSR networks 18 vs. 9 nm |
Beikoghli Kalkhoran et al., 2017 |
| OE of Mfn2 (ad-Mfn2 vs. control of ad-ctl) in neonatal rat cardiomyocytes in vitro | No change of mitochondrial number, length, size, aspect ratio, or number of mitophagic vacuoles. However, addition of Ang II resulted in an accumulation of mitophagic vacuoles and increased mitochondrial size, indicative of increased mitochondrial damage | Mito autophagy (%) 0.05 ↑ by AngII to 0.12 in Ad-ctl, further ↑ 0.22 in Ad-Mfn2 by AngII, The number of mito/cell remains the same ~45 Aspect ratio 1.75 ↓ to 1.0 in Ad-ctl by AngII, to 1.25 in Ad-Mfn2 by AngII Av. mito area (μm2): ↓ 0.3–0.18 in Ad-ctl by Ang II, to 0.23 in Ad-Mfn2 by AngII Av. mito length (μm): ↓ 0.9–0.4 in Ad-ctl by AngII, to 0.6 in Ad-Mfn2 by AngII |
Xiong et al., 2019 |