| BackgroundSmooth muscle cell(SMC)apoptosis is an important pathological feature that leads to various mechanisms regulating abdominal aortic aneurysm(AAA).The majority of these studies suggested that various proteins can be used as biomarkers and therapeutic targets in AAA diagnosis and treatment because of their role in the regulation of SMC apoptosis.In addition,evidence suggests that microRNA(miR)-21 may be a crucial protective factor that can be targeted to inhibit SMC proliferation and apoptosis,thereby preventing AAA formation.However,traditional methods of administering anti-protein or anti-miR-21 agents have limited applications due to their systemic effects on other organ systems,which are often affected to a greater extent than the aorta.Long noncoding RNAs(lncRNAs),a type of noncoding RNA transcript longer than 200 nucleotides,are often expressed in specific locations,thereby displaying the potential to target specific tissues/cells rather than having systemic effects as conventional treatments.Recently,multiple lncRNAs have been suggested to contribute to SMC apoptosis during AAA formation,among which lncRNA H19 has been demonstrated to participate in AAA development through its regulation of SMC survival.Nonetheless,the roles of other lncRNAs in AAA and their therapeutic potential against AAA formation remain elusive.LncRNA GAS5 is functionally associated with several biological processes,including cell proliferation,apoptosis,differentiation,and growth arrest.Recently,GAS5 has been identified as a critical regulator that can rescue the proliferative/migratory phenotype of vascular SMCs.Many studies have reported that GAS5 acts as a protein scaffold to regulate the downstream targets of p21and phosphatase and tensin homolog(PTEN),which are validated targets associated with SMC proliferation and apoptosis during aneurysm formation.Moreover,studies have reported that GAS5 acts as a "miRNA sponge" to regulate miR-21 expression in many other diseases,including cancer,osteoarthritis,and cardiac fibrosis.MiR-21 is one of the most commonly miRNAs in several cardiovascular diseases and is the only miRNA that has been demonstrated to play a central role in AAA formation through the regulation of SMC proliferation and apoptosis.Therefore,we hypothesized that GAS5 stimulates SMC apoptosis and proliferation via simultaneously regulating bothproteins and miR-21 and ultimately contributes to AAA formation.In this study,we used two AAA mouse models to investigate the role of GAS5 in AAA formation and its underlying mechanism.First,we examined the GAS5 expression level in two mouse AAA models.Second,we overexpressed and knockdowned the GAS5 content in the aorta and observed its correspondent effects on the development of AAA.In addition,we explored the molecular mechanism conducting GAS5 promoting the development of AAA.Methods and Results:Gain-and loss-of-function experimentsResults:(1)knockdown of GAS5 reduced the incidence of AAA formation,the rupture rate of AAA and the maximal abdominal aortic diameter,furthermore knockdown of GAS5 significantly inhibited SMC apoptosis in vivo.(2)In contrast,overexpression of GAS5 enhanced the maximal abdominal aortic diameter,the incidence of AAA formation and the rupture rate of AAA.Consistent with these results,voverexpression of GAS5 promoted apoptosis in SMCs(3)Similar trends of Gain-and loss-of-function experiments upon GAS5 dysregulation were obtained in CaCl2-induced mouse AAA model.Mechanism experiments(1)RNA-pull down results demonstrated that GAS5 can bind to YBX1.GAS5 could simultaneously promote the entry of YBX1 into the nucleus while inhibiting YBX1 degradation.(2)luciferase reporter gene assays indicating that GAS5 directly binds to miR-21 and acts as a sponge of miR-21 to release PTEN from miR-21-mediated suppression.(3)YBX1was identified as an upstream regulator of GAS5 and could thus regulate the transcription of GAS5.ConclusionGAS5 acts as a sponge of miR-21 to induce the upregulation of PTEN.Additionally,GAS5 and Y-box-binding protein 1(YBX1)form a positive feedback loop to promote downstream p21 expression.LncRNA GAS5 contributes to SMC survival during AAA formation. |
