Nucleosomal association and altered interactome underlie the mechanism of cataract caused by the R54C mutation of αA-crystallin

A bibliometric and visualized analysis of the pathogenesis of cataracts from 1999 to 2023

Research on the pathogenesis of cataracts is ongoing and the number of publications on this topic is increasing annually. This study offers an overview of the research status, popular topics, and scholarly tendencies in the field of cataract pathogenesis over recent decades，which helps to guide future research directions, and optimize resource allocation. In the present study, we performed a bibliometric analysis of cataract pathogenesis. Publications from January 1, 1999, to December 20, 2023, were collected from the Web of Science Core Collection (WoSCC), and the extracted data were quantified and analyzed. We analyzed and presented the data using Microsoft Excel, VOSviewer, CiteSpace, and Python. In all, 4006 articles were evaluated based on various characteristics, including publication year, authors, countries, institutions, journals, citations, and keywords. This study utilized VOSviewer to conduct visualized analysis, including co-authorship, co-citation, co-occurrence, and network visualization. The CiteSpace software was used to identify keywords with significant bursts of activity. The number of annual global publications climbed from 76 to 277 between 1999 and 2023, a 264.47% rise. Experimental Eye Research published the most manuscripts (178 publications), whereas Investigative Ophthalmology & Visual Science received the most citations (6675 citations). The most influential and productive country, institution, and author were the United States (1244 publications, 54,456 citations), University of California system (136 publications, 5401 citations), and Yao Ke (49 publications, 838 citations), respectively. The top 100 ranked keywords are divided into four clusters through co-occurrence analysis: (1) secondary cataracts, (2) oxidative stress, (3) gene mutations and protein abnormalities, and (4) alteration of biological processes in lens epithelial cells. Further discussions on the four subtopics outline the research topics and trends. In conclusion, the specific mechanism of cataract formation remains a popular topic for future research and should be explored in greater depth.

Protein Aggregation and Cataract: Role of Age-Related Modifications and Mutations in α-Crystallins

* The article is published as a part of the Special Issue "Protein Misfolding and Aggregation in Cataract Disorders" (Vol. 87, No. 2). ** To whom correspondence should be addressed. Cataract is a major cause of blindness. Due to the lack of protein turnover, lens proteins accumulate age-related and environmental modifications that alter their native conformation, leading to the formation of aggregation-prone intermediates, as well as insoluble and light-scattering aggregates, thus compromising lens transparency. The lens protein, α-crystallin, is a molecular chaperone that prevents protein aggregation, thereby maintaining lens transparency. However, mutations or post-translational modifications, such as oxidation, deamidation, truncation and crosslinking, can render α-crystallins ineffective and lead to the disease exacerbation. Here, we describe such mutations and alterations, as well as their consequences. Age-related modifications in α-crystallins affect their structure, oligomerization, and chaperone function. Mutations in α-crystallins can lead to the aggregation/intracellular inclusions attributable to the perturbation of structure and oligomeric assembly and resulting in the rearrangement of aggregation-prone regions. Such rearrangements can lead to the exposure of hitherto buried aggregation-prone regions, thereby populating aggregation-prone state(s) and facilitating amorphous/amyloid aggregation and/or inappropriate interactions with cellular components. Investigations of the mutation-induced changes in the structure, oligomer assembly, aggregation mechanisms, and interactomes of α-crystallins will be useful in fighting protein aggregation-related diseases.

Cataract-causing allele in CRYAA (Y118D) proceeds through endoplasmic reticulum stress in mouse model

As small heat shock proteins, α-crystallins function as molecular chaperones and inhibit the misfolding and aggregation of β/γ-crystallins. Genetic mutations of CRYAA are associated with protein aggregation and cataract occurrence. One possible process underlying cataract formation is that endoplasmic reticulum stress (ERS) induces the unfolded protein response (UPR), leading to apoptosis. However, the pathogenic mechanism related to this remains unexplored. Here, we successfully constructed a cataract-causing CRYAA (Y118D) mutant mouse model, in which the lenses of the CRYAA-Y118D mutant mice showed severe posterior rupture, abnormal morphological changes, and aberrant arrangement of crystallin fibers. Histological analysis was consistent with the clinical pathological characteristics. We also explored the pathogenic factors involved in cataract development through transcriptome analysis. In addition, based on key pathway analysis, up-regulated genes in CRYAA-Y118D mutant mice were implicated in the ERS-UPR pathway. This study showed that prolonged activation of the UPR pathway and severe stress response can cause proteotoxic and ERS-induced cell death in CRYAA-Y118D mutant mice.

Crystallin gene expression: Insights from studies of transcriptional bursting

Cellular differentiation is marked by temporally and spatially regulated gene expression. The ocular lens is one of the most powerful mammalian model system since it is composed from only two cell subtypes, called lens epithelial and fiber cells. Lens epithelial cells differentiate into fiber cells through a series of spatially and temporally orchestrated processes, including massive production of crystallins, cellular elongation and the coordinated degradation of nuclei and other organelles. Studies of transcriptional and posttranscriptional gene regulatory mechanisms in lens provide a wide range of opportunities to understand global molecular mechanisms of gene expression as steady-state levels of crystallin mRNAs reach very high levels comparable to globin genes in erythrocytes. Importantly, dysregulation of crystallin gene expression results in lens structural abnormalities and cataracts. The mRNA life cycle is comprised of multiple stages, including transcription, splicing, nuclear export into cytoplasm, stabilization, localization, translation and ultimate decay. In recent years, development of modern mRNA detection methods with single molecule and single cell resolution enabled transformative studies to visualize the mRNA life cycle to generate novel insights into the sequential regulatory mechanisms of gene expression during embryogenesis. This review is focused on recent major advancements in studies of transcriptional bursting in differentiating lens fiber cells, analysis of nascent mRNA expression from bi-directional promoters, transient nuclear accumulation of specific mRNAs, condensation of chromatin prior lens fiber cell denucleation, and outlines future studies to probe the interactions of individual mRNAs with specific RNA-binding proteins (RBPs) in the cytoplasm and regulation of translation and mRNA decay.