Introduction
High myopia, characterized by a refractive error exceeding -6.00 diopters (D) or an axial length greater than 26mm, stands as a significant contributor to visual impairment globally, with its prevalence steadily rising [1]. In 2020, approximately 399 million individuals, constituting 5.1% of the world’s population, were affected by high myopia. It is projected that this number could surge to nearly 938 million, accounting for 9.8% of the global population, by the year 2050 [2].
Early onset of cataract is one of the most prevalent complications associated with high myopia [3]. Many population-based studies have consistently shown a direct correlation between high myopia and an elevated risk of cataract formation, particularly with a three- to five-fold increase in the risk of nuclear cataract [4] and a 30% heightened risk of posterior subcapsular cataracts [5]. However, the exact mechanism of the precocious onset of cataract remains uncertain. One hypothesis suggests that the more pronounced vitreous liquefaction in eyes with high myopia may lead to increased exposure of the lens to oxygen from the retina, resulting in an imbalance in the oxygen defense system, and ultimately promoting cataract formation [6,7].
The lens is a transparent tissue comprising lens epithelial cells (LECs) and lens fibers cells, both enclosed with a collagenous basement membrane known as the lens capsule. Throughout its life, LECs play pivotal roles, including differentiating into lens fibers during embryonic development, maintaining lens transparency in adulthood, and contributing to cataract formation [8]. Any disruption to the transport mechanisms, morphology, or biochemistry of the lens epithelium can alter ion concentration both inside and outside the cells, leading to fluid accumulation in the lens and ultima result in cataract formation [9]. Additionally, the lens capsule,which functions as a semipermeable membrane allowing nutrients and antioxidants to enter the lens, is also implicated in the development of lens opacification. This membrane facilitates the passive exchange of metabolic substrates and wastes between the ocular environment and lens cells [10]. However, the exact mechanism by which the lens capsule influences cataract development remains unknown.
Extracellular vesicles (EVs), which are secreted by parental cells, holds pivotal significance in facilitating intercellular communication and molecular transport [11]. These EVs are abundantly present in almost all ocular biofluids, such as aqueous humor, providing insights into the physiological and pathological conditions of their parental cells. They have also been associated with many ocular diseases, including cataract [12-14]. However, ocular biofluids contain admixtures from various sources, including serum proteins or a blend of EVs originating from different parts of the eye [15]. Furthermore, the specific proportion of EVs in the ocular biofluids that originate from particular tissues is unknown [16].
In comparison, tissue-derived EVs (Ti-EVs) are present in the extracellular interstitium and serve as well-established mediators of intercellular signal transduction [17]. These EVs more precisely reflect the pathophysiological characteristics and behaviors of cells, as they preserve the three‐dimensional structure of tissues and cellular properties. Moreover, they are relatively uncontaminated due to their single-tissue origin, in contrast to biofluid‐derived EVs [18]. While proteomics and RNA sequencing can now routinely analyze EVs and their protein and RNA contents in bulk, the inherent heterogeneity of EVs necessitates examination at the single EV level to accurately decipher the encapsulated pathophysiological information and develop promising biomarkers. Here, we utilized the proximity barcoding assay (PBA), an innovative and rapid high-throughput technique for single-EV analysis, to profile more than a hundred surface proteins on a single EV simultaneously [19]. PBA enables us to differentiate EVs based on their highly heterogeneous surface protein compositions and identify subpopulations of EVs in the human lens capsule.
In this research, PBA was performed to detect a panel of 260 proteins at single-EV resolution and subsequently classified all detected individual EVs into 7 clusters according to their proteomic features. We examined the alteration of EV clusters in high myopic cataract compared to age-related cataract as the control group. This study is poised to shed light on the complex mechanism of cataract formation. By elucidating the specific roles of EVs and their proteomic features in the development and progression of high myopic cataract, we hope to pave the way for new therapeutic strategies and interventions.