(P012) NOVEL ROLE OF RAB8B IN REGULATING AUTOPHAGY AGAINST MYOCARDIAL ISCHEMIA-REPERFUSION INJURY

Background: Reperfusion is a necessary medical therapy to save an ischemic heart, a severe disease threatening the health of nearly 1.72% of the global population. However, myocardial ischemia/reperfusion (I/R) injury ensues restoration of blood flow to an ischemic heart, complicating this therapy. The lack of clinical interventions further complicates I/R injury. Nevertheless, recent studies have revealed that autophagy is essential in I/R injury. Concurrently, our previous study found that the expression of Rab8B, a member of the Rab family protein, significantly decreased in the pathological state of I/R injury.

METHODS AND RESULTS: To examine the role of Rab8B following I/R, we established in vivo I/R and in vitro hypoxia/reoxygenation (H/R) models and used experimental techniques such as western blot, qPCR, and immunofluorescence to analyze its potential role in autophagy, including molecular pathways. In addition, plasmid transfection was used to overexpress the Rab8B genes in vitro.
Echocardiogram results showed reduced left ventricular myocardial contraction and myocardial tissue impairment following reperfusion in vivo. Mechanistic studies revealed significant downregulation of Rab8B and partial inhibition of the autophagy pathway in cardiomyocytes, including the conversion of LC3BI to LC3BII. Contrary to the protein expression of Rab8B, we observed an upregulation of p62 with a significantly diminished scavenging activity of the autophagic vacuole. In vitro results confirmed the downregulated expression of Rab8B protein and the autophagy pathway inhibition, leading to excessive autophagic vacuole accumulation and massive cardiomyocyte death. The overexpression of Rab8B alleviated these pathological alterations caused by I/R injury in cardiomyocytes.

Conclusion: This study suggests that during I/R injury, the upregulation of Rab8B can exert a cardioprotective effect in the myocardium through the autophagic pathway, potentially by increasing the number of myocardial lysosomes and reducing autophagic vacuole accumulation.