Diabetic retinopathy (DR), a prevalent microvascular progressive complication of diabetes mellitus (DM), serves as a major cause of visual impairment and blindness among working-age adults worldwide and exerts an enormous financial burden on society [1]. The early lesions of DR are induced by breakdown of the blood−retina barrier (BRB) and enhanced vascular permeability, leading to vascular leakage, while the late stage of DR is characterized by retinal vascular remodeling and capillary nonperfusion, resulting in pathological angiogenesis [2]. As a pivotal component of RBR and neurovascular unit (NVU), damage to endothelial cell (EC) is considered a decisive factor in the occurrence and development of DR [3,4]. Despite the mainstream medication of VEGF for treatment, the nonresponse, relapse, and unsatisfactory long-term prognosis have harassed us [5]. Therefore, it is urgent to explore the pathological mechanism of EC dysfunction and to search for new therapeutic targets.

Growing evidence has verified the crucial function of inflammation in diabetes-induced vascular endothelial dysfunction [6]. Pyroptosis, a novel inflammatory form of programmed cell death, was newly discovered in recent years and reported to be involved in numerous diseases, including tumor metabolic diseases, cardiovascular diseases, and infectious diseases [7,8]. In the canonical CASP1-mediated pyroptosis pathway, after being activated by ligands of various inflammasomes, such as NLRP1 and NLRP3, CASP1 cleaves the downstream execution protein GSDMD into an N-terminal fragment (GSDMD-N), eliciting the cell membrane rupture with the release of inflammatory factors IL-1β and IL-18 [9,10]. Recent studies confirmed the significant influence of EC pyroptosis in EC death and vascular dysfunction in systemic blood vessels, including the retinal vascular system [11,12]. Meanwhile, CASP1 was uncovered to be a crucial molecule in the acceleration of EC pyroptosis in diverse diseases, including chronic kidney disease (CKD) [13] and atherosclerosis (AS) [14]. Clinical research revealed elevated expression of CASP1 and IL-18 in the vitreous of DR patients [15], as well as increased expression of NLRP3, CASP1, IL-1β and IL-18 in peripheral blood mononuclear cells (PBMCs) of adults with DR [16]. Furthermore, in our previous study, enhanced CASP1 activity and elevated NLRP3 expression were verified in HG-induced human retinal microvascular endothelial cells (HRMECs) [17]. Thus, further exploration on the molecular mechanism of aberrant CASP1 upregulation in EC pyroptosis might provide novel insight for DR treatment.

Circular RNAs (circRNAs), a novel class of noncoding RNAs, commonly originate from exons of protein-coding genes in a back-splicing manner and possess a covalently closed loop structure without 5′–3′ polarity or polyadenylated tails [18]. Genome-wide analyses exhibited their characteristics of high abundance, species conservation, cell type, and tissue-specific expression [19,20]. CircRNAs were reported to regulate target gene expression by adsorbing microRNAs (miRNAs) as ceRNA sponges, binding proteins as sequestering or recruiting agents and translating polypeptides [21,22]. Several studies have verified the aberrant expression and functional regulation of circRNAs in diverse vascular diseases, as well as the regulatory mechanism in EC dysfunction in DR [23,24]. However, whether circRNAs are involved in EC pyroptosis and the potential pathological mechanism is still unknown.

In this study, we explored the aberrant expression profiles of circRNAs in ECs of DR through circRNA microarray analysis and investigated the molecular mechanisms of circRNAs in CASP1-mediated EC pyroptosis. The results showed that circTHADA regulated CASP1 and accelerated EC pyroptosis by acting as a miRNA sponge, providing novel insights for DR treatment.