Ischemic cardiomyopathy remains a globally prevalent disease characterized by high morbidity and mortality . At present, for patients who are subjected to myocardial infarction, rapid reconstruction of blood flow in ischemic myocardial tissue has been approved widely as the most effective treatment. However, a large amount of clinical and experimental evidence has confirmed that reconstructing the blood flow of ischemic myocardial tissue results in myocardial tissue injury, which is known as myocardial ischemia–reperfusion injury (MIRI) . MIRI causes a series of pathophysiological changes in the heart, and among these changes, excessive myocardial cell death is a principal and basic pathological symptom of MIRI . However, the mechanism underlying MIRI-induced cell death remains unclear.
Autophagy, as an evolutionarily conserved catabolic mechanism, plays an important role in the maintenance of energy and protein homeostasis, which digests and degrades damaged organelles and misfolded proteins to maintain normal cellular function by fusing with lysosomes . Emerging evidence has suggested that the disruption of autophagy contributes to the pathogenesis and progression of a variety of human diseases [5, 6]. Recent studies have demonstrated that autophagy is defective during ischemia/reperfusion (I/R) . However, the molecular underpinnings that regulate autophagy have not yet been fully elucidated. Beclin1, one of the earliest autophagy effectors discovered in mammals  and a core component of the class (III) phosphatidylinositol 3-kinase (PI3K)/Vps34 complex, is involved in the regulation of autophagosome formation as an autophagy initiation factor [9–11]. Despite the role of Beclin1 reported in MIRI, the beneficial and harmful effects of Beclin1 on MIRI remain controversial. Therefore, further analysis of the role and regulatory mechanism of Beclin1 in MIRI is of great value.
Accumulative evidence has demonstrated that autophagy and the ubiquitin–proteasome system (UPS) are two major degradation mechanisms in eukaryotic cells . Autophagy includes microautophagy, macroautophagy and chaperone-mediated autophagy. Here, we focus on macroautophagy/autophagy . The UPS is a selective proteolytic system in which the conjugation of ubiquitin to substrates induces degradation by the proteasome . Ubiquitination is mediated by the cooperative action of three enzymes: ubiquitin-activating enzyme (E1), ubiquitin-transferring enzyme (E2), and ubiquitin ligase (E3) . The ubiquitin chain can then be recognized by the proteasome, which degrades the target substrate in an ATP-dependent manner . A recent study from our lab demonstrated that increased UBE2D3 expression, one of the members of the ubiquitin-binding enzyme 2 family, increases the ubiquitination of p62/SQSTM, subsequently disrupting autophagic flux and exacerbating myocardial ischemia–reperfusion injury in a manner dependent on the mTOR-Beclin1 pathway . In addition, some studies from other groups have also demonstrated that ubiquitination plays a crucial role in the pathogenesis of cardiovascular diseases, such as ischemia–reperfusion injury . As a member of the tripartite motif-containing protein (TRIM) family of E3 ubiquitin ligases, TRIM9 plays a significant role in the central nervous system of developing adults and affects a variety of biological processes, such as inflammation, immunity, cell proliferation, apoptosis, and antiviral mechanisms [19, 20]. Several studies have demonstrated that TRIM proteins can recruit ULK1 and BECN1 complexes and bind to mammalian Atg8-family paralogs via an LC3-interacting region, acting as both autophagy cargo receptors and platforms assembling autophagosome-formation machinery [21, 22]. Moreover, in non-small-cell lung cancer, TRIM59 inhibits Beclin1 expression to block autophagy by inhibiting the NF-κB pathway . However, whether and how TRIM9 regulates autophagy remains unclear.
In this study, we found that TRIM9 expression was upregulated in in vivo and in vitro MIRI models. TRIM9 downregulated the expression of Beclin1 and promoted the ubiquitination of Beclin1, subsequently inhibiting the expression of LC3II and p62 and blocking autophagy to ameliorate MIRI. Taken together, our study revealed that TRIM9 can protect against MIRI and may represent a promising valuable therapeutic target for MIRI.