BECN1 regulates FADD/RIPK1/Caspase-8 complex formation via RIPK1 ubiquitination by downregulating OTUD1 in MI/R induced myocyte apoptosis.

Background: Cardiomyocyte apoptosis plays a vital role in myocardial ischemia-reperfusion (MI/R) injury; however, the role of beclin1 (BECN1) remains unclear. This study aimed at revealing the function of BECN1 during cardiomyocyte apoptosis after MI/R injury.

Methods: In vivo, TTC and Evan's blue double staining was applied to verify the gross morphological alteration in both wild type (WT) mice and BECN1 transgene mice (BECN1-TG), and TUNEL staining and western blot were adopted to evaluate the cardiomyocyte apoptosis. In vitro, a hypoxia/reoxygenation (H/R) model was established in H9c2 cells to simulate MI/R injury. Proteomics analysis was preformed to verify if apoptosis occurs in the H/R cellular model. And apoptosis factors, RIPK1, Caspase-1, Caspase-3, and cleaved Caspase-3, were investigated using western bolting. In addition, the mRNA level were verified using RT-PCR. To further investigate the protein interactions small interfering RNA and lentiviral transfection were used. To continue investigate the protein interactions, immunofluorescence and coimmunoprecipitation were applied.

Results: Morphologically, BECN1 significantly attenuated the apoptosis from TTC-Evan's staining, TUNEL, and cardiac tissue western blot. After H/R, a RIPK1-induced complex (complex II) containing RIPK1, Caspase-8, and FADD was formed. Thereafter, cleaved Caspase-3 was activated, and myocyte apoptosis occurred. However, BECN1 decreased the expression of RIPK1, Caspase-8, and FADD. Nevertheless, BECN1 overexpression increased RIPK1 ubiquitination before apoptosis by inhibiting OTUD1.

Conclusions: BECN1 regulates FADD/RIPK1/Caspase-8 complex formation via RIPK1 ubiquitination by downregulating OTUD1 in C-Caspase-3-induced myocyte apoptosis after MI/R injury. Therefore, BECN1 can function as a cardioprotective candidate.