Objective

2

To explore the mechanism of energy changes in the three stages of the formation of coronary heart disease due to blood stasis in rat model from the perspective of mitochondrial fusion-fission dynamic changes.

Method

2

Thirty healthy male rats were divided into the blank control group （

n

=6） and model group （

n

=24） using SPSS 21.0 simple random sampling method. The rats in the blank control group were fed an ordinary diet， while those in the model group a high-fat diet. After seven days of adaptive feeding， the rats were treated with intragastric administration of vitamin D

3

（VitD

3

） at 300 000 U·kg

-1

and then at 200 000 U·kg

-1

14 d later. The high-fat diet continued for 21 d， and six rats were randomly selected as samples for the pre-stage blood stasis syndrome group， followed by model verification and sampling. The remaining rats continued to receive the high-fat diet for 30 d， and six were randomly selected and categorized into the sub-stage blood stasis syndrome group， followed by model verification and sampling. The rest of rats were classified into the heart blood stasis syndrome group. While continuing the high-fat diet， they were also treated with multipoint subcutaneous injection of isoproterenol （ISO，5 mg·kg

-1

） for three consecutive days. One week later， the electrocardiogram （ECG） was recorded for determining whether the modeling was successful and the samples were taken at the same time. The changes in mitochondrial morphology and quantity were observed under a transmission electron microscope. The expression of mitochondrial dynamics-related proteins was measured by Western blot and the cellular localization of related proteins by immunofluorescence assay.

Result

2

The levels of total cholesterol and low-density lipoprotein cholesterol in the pre-stage and sub-stage blood stasis syndrome groups were significantly increased as compared with those in the blank control group （

P

<

0.05）. The blood rheology index in the pre-stage blood stasis syndrome group was significantly elevated in contrast to that in the blank control group （

P

<

0.05）. The three-layered membrane of the aorta in the blank group was intact. However， the tunica media of the pre-stage blood stasis syndrome group began to show obvious calcification， with a small number of inflammatory cells adhering to the intima. The subintima and media smooth muscles in the sub-stage blood stasis syndrome group exhibited cavity structures. The three-layered structure of the arterial wall in the heart blood stasis syndrome group was severely damaged. The ECG of the blank control group revealed the regular appearance of P wave，regular QRS waveform （no broadening or deformity）， and no obvious ST-segment depression or elevation. The ECG of the pre-stage blood stasis syndrome group showed no obvious abnormalities as compared with that of the blank control group. In the sub-stage blood stasis syndrome group， the ECG showed an upward trend of the J point and slight ST-segment elevation， with the elevation≤0.1 mV. The ECG in the heart blood stasis syndrome group displayed significant ST-segment depression （

>

0.1 mV） and J point depression

>

0.1 mV. The mitochondria in the blank control group were normal in size and morphology， with clear and dense cristae， whereas those in the pre-stage blood stasis syndrome group were fusiform with sparse cristae. Some mitochondria in the sub-stage blood stasis syndrome group were significantly elongated， and even vacuole-like changes were present. In the heart blood stasis syndrome group， the mitochondria were ruptured. As demonstrated by comparison with the blank control group， the expression levels of mitofusin 2 （Mfn2）， dynamin-related protein 1 （Drp1）， and fission protein 1 （Fis1） in the model group were significantly up-regulated （

P

<

0.05，

P

<

0.01）. Compared with the pre-stage blood stasis syndrome group， the heart blood stasis syndrome group exhibited down-regulated Mfn2 （

P<

0.05）. Compared with the blank control group and the pre-stage blood stasis syndrome group， the sub-stage blood stasis syndrome group and the heart blood stasis syndrome group displayed down-regulated optic atrophy 1（OPA1） （

P

<

0.05，

P

<

0.01）. The Drp1 and Fis1 protein expression declined significantly in the sub-stage blood stasis syndrome group in comparison with that in the pre-stage blood stasis syndrome group （

P

<

0.05，

P

<

0.01）. The expression levels of Mfn2 and Drp1 in the heart blood stasis syndrome group were lower than those in the sub-stage blood stasis syndrome group （

P<

0.01）. The comparison with the blank control group showed that Mfn2 and OPA1 were extensively accumulated in mitochondria of both the pre-stage and sub-stage blood stasis syndrome groups， while the red-stained Mfn2 was significantly reduced in the heart blood stasis syndrome group. The Drp1/Fis1 fluorescence was weak in the blank group and the pre-stage blood stasis syndrome group but strong in the sub-stage blood stasis syndrome group and heart blood stasis syndrome group.

Conclusion

2

The cardiomyocyte mitochondria dynamics changes with the change in energy demand of cardiomyocytes. Mfn2 is dominated by fusion effect in the early stage of the formation of coronary heart disease due to blood stasis. With the gradual development of this disease， Mfn2 begins to mediate mitochondrial autophagy. OPA1 plays a role in intimal fusion and cristae integrity. The decreased OPA1 expression is closely related to the accelerated progression of coronary heart disease differentiated into blood stasis syndrome. The process by which Drp1 and Fis1 separate damaged mitochondria to prepare for mitochondrial autophagy contributes to alleviating the imbalance between the energy demand and supply of human body.