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.