Author(s): XU, Y., LU, J., SUN, W., YUAN, X., XIANG, M., XIAO, H., ZHANG, Y., Institution: NANJING INSTITUTE OF PHYSICAL, Country: CHINA, Abstract-ID: 927

INTRODUCTION:
Mitochondrial function is crucial for hepatic lipid metabolism. Current research identifies two types: peri-droplet mitochondria (PDM) excelling in fatty acid synthesis, and cytoplasmic mitochondria (CM) with superior oxidative metabolism. Yet, their roles in hepatic hyperenergetics and energetic stress are debated. This study examines CM and PDM respiratory changes in diet-induced NAFLD under fasting and acute exercise.
METHODS:
C57BL/6J mice were fed a normal diet or high-fat, fructose, and cholesterol diet for 12 weeks.Then they were equally divided into four groups (n=8 each): Normal Diet (ND), High-Fat Control (HC), High-Fat Fasting (HF), and High-Fat Exercise (HE).Primary hepatocytes (n=4) were isolated and stained with BODIPY 493/503 and MitoTracker Red CMXRos to study lipid accumulation and lipid droplet-mitochondria interaction. Liver tissues (n=4) were processed to separate PDM and CM, which were tested for mitochondrial respiration and fatty acid oxidation (FAO) capacity by using the MitoXpress Xtra Oxygen Consumption Assay(MX-200-4) kit. Mitochondrial Respiratory Control Ratio (RCR) was calculated as StateIII/StateIV were evaluated, and FAO capability was measured as the rate of increase of probe emission intensity.
RESULTS:
1)Compared to the ND group, the HC group showed significant increases in lipid droplet total area (615.4 ± 172.7 vs 47.37 ± 21.96 μm², p < 0.05), number (99.57 ± 16.98 vs 39.33 ± 10.29, p < 0.05), and size (9.679 ± 3.346 vs 0.9479 ± 0.5336 μm², p < 0.05). The HC group had higher CM content (17.42 ± 3.815 vs 11.93 ± 1.994 mg/g, p < 0.05), CM RCR (5.900 ± 0.8549 vs 3.639 ± 1.31, p < 0.05) and elevated CM FAO level (1047 ± 147.6 vs 589.6 ± 49.00 RFU/min, p < 0.05).
2)Compared to the HC group, the HF group had significantly increased lipid droplet number (204.5±67.63, p < 0.05) and total area (946.4±111.9μm², p < 0.05), but smaller size (5.399±2.882μm², p < 0.05). The HF group also showed a significant decline in CM RCR (3.491 ± 1.056, p < 0.05), but a significant increase in PDM RCR (8.741 ± 2.448 vs 3.678 ± 0.4140, p < 0.05) and CM FAO (1671 ± 326.7 RFU/min, p < 0.05), with a significant decrease in PDM FAO (986.4 ± 171.2 vs 505.9 ± 321.5, p < 0.05).
3)The HE group, relative to the HC group, demonstrated a significant increase in CM RCR (9.614 ± 2.628, p < 0.05) and CM FAO (1608 ± 422 RFU/min, p < 0.05), but a significant decrease in PDM FAO (380.6 ± 159.9 RFU/min, p < 0.05).
CONCLUSION:
1)CM respiration and FAO were adaptability increased in response to the high-fat diet induced hepatic accumulation of excess lipids.
2)Fasting induces energy shortage in hepatocytes, prompting PDM to elevate RCR for ATP provision, facilitating lipid droplet decomposition, while CM increases FAO levels, meeting intracellular energy demands.
3)Hepatocyte energy expenditure increases under exercise stress, and CM increases fatty acid involvement in energy supply by increasing FAO and RCR levels.