Mechanism of mitochondrial biogenesis regulated by PGC-1α/NR1D1 to increase the vulnerability of myocardial ischemia/reperfusion injury in diabetes.

BACKGROUND

Peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) regulates the expression of clock gene nuclear receptor subfamily 1 group D member 1 (NR1D1) and is closely related to diabetes mellitus and ischemic heart disease. However, the mechanism by which PGC-1α/NR1D1 increases the vulnerability of diabetic myocardium to ischemia/reperfusion (I/R) injury has yet to be elucidated. This study aimed to explore the roles of PGC-1α/NR1D1-mediated regulation of mitochondrial biogenesis in myocardial I/R injury of type 2 diabetic mice.

METHODS

Type 2 diabetes was induced in C57BL/6 mice by a high-fat diet and streptozotocin. Diabetic and nondiabetic mice underwent I/R injury, with subsets receiving the NR1D1 agonist SR9009 or cardiac-specific Nr1d1 knockout. In parallel, rat cardiomyocyte-derived cell line H9c2 cardiomyocytes were exposed to high glucose and high fat and hypoxia/reoxygenation insult, with or without Pgc-1α overexpression by Pgc-1α lentivirus. Cardiac function in mice was assessed using an animal ultrasound system. Myocardial infarction size was determined by 2% 2,3,5-triphenyltetrazolium chloride (TTC) staining. Serum levels of troponin I (cTn-I) and lactate dehydrogenase (LDH) were measured by enzyme-linked immunosorbent assay (ELISA). The expression levels of NR1D1, PGC-1α, nuclear respiratory factor 1 (NRF1), transcription factor A (TFAM), ‌autophagy-related protein 4 homolog B (ATG4B), and microtubule-associated protein 1 light chain 3 (LC3) in mouse myocardial tissue were detected by real-time quantitative polymerase chain reaction (RT-qPCR), Western blotting, and immunofluorescence. Meanwhile, the cell viability, apoptosis rate, mitochondrial reactive oxygen species (ROS), mitochondrial membrane potential (MMP), and mitochondrial morphology of H9c2 cardiomyocyte were evaluated using assay kits.

RESULTS

Compared with nondiabetic mice, diabetic mice exhibited larger infarct size, higher serum LDH and cTn-I, and severe ultrastructural damage. Cardiac PGC-1α and NR1D1 expression decreased significantly after I/R, accompanied by reduced NRF1 and TFAM levels and impaired mitochondrial biogenesis. Nr1d1 knockout further worsened injury, shown by increased infarct size and decreased left ventricular ejection fraction (LVEF), whereas SR9009 pretreatment restored PGC-1α expression, activated NRF1/TFAM signaling, and reduced infarct size. In vitro, high glucose and high fat plus hypoxia/reoxygenation increased LDH release and apoptosis while decreasing MMP and elevating ROS. Overexpression of Pgc-1α reversed these effects, improving cell viability and reducing ROS by upregulating NR1D1 and NRF1/TFAM.

CONCLUSIONS

These results indicate that disruption of PGC-1α/NR1D1 signaling impairs mitochondrial function, exacerbating diabetic myocardial I/R injury. Pharmacological activation of Nr1d1 or Pgc-1α overexpression alleviates injury by restoring mitochondrial function. Targeting this axis represents a promising strategy for cardioprotection in diabetes.