Cataract 18 (CTRCT18) Cell Models for Research

Cataract is the leading cause of blindness worldwide, affecting over 65 million people and causing blindness in 20 million (WHO, 2020). Age-related cataract accounts for most cases, but congenital cataracts, including those linked to CTRCT18, are a significant cause of childhood blindness. The global burden is projected to rise with aging populations. In the US, cataract surgery is the most common surgical procedure among Medicare beneficiaries, with over 2 million procedures annually (NCI). The 5-year survival for cataract patients is generally good, but visual impairment impacts quality of life and increases mortality risk. Key risk factors include aging, UV exposure, diabetes, smoking, and genetic mutations.

CTRCT18 is an autosomal dominant congenital cataract disorder caused by mutations in the CRYBB2 gene, which encodes beta-crystallin B2, a major structural protein of the lens. This disease provides an ideal model for studying protein aggregation, chaperone function, and cellular stress responses. The lens is an avascular tissue, making it a unique system to study protein homeostasis and aging. Public datasets, such as the Human Gene Mutation Database and ClinVar, provide curated mutations, but functional validation is lacking. Gene-edited cell models allow researchers to investigate the molecular consequences of specific CRYBB2 mutations, screen for therapeutic agents, and explore gene therapy approaches.

While cataract is not a cancer, the molecular pathways involved in lens development and protein aggregation share similarities with oncogenic stress pathways. Key pathways include:

• • Protein Folding and Aggregation: Mutations in crystallins lead to misfolding and aggregation, causing light scattering and opacity.
• • Unfolded Protein Response (UPR): Accumulation of misfolded proteins activates UPR, leading to ER stress and apoptosis.
• • Oxidative Stress: Reactive oxygen species (ROS) can damage lens proteins and DNA, contributing to cataract formation.
• • Apoptosis and Autophagy: Impaired clearance of damaged proteins via autophagy can exacerbate aggregation.

Data from ClinVar and COSMIC.

In cataract, the primary deregulated networks involve:

• • Protein Quality Control: Heat shock proteins (HSPs) and chaperones like CRYAA and CRYAB are crucial. Mutations impair their function.
• • ER Stress Pathway: PERK, IRE1, and ATF6 are activated in response to misfolded proteins.
• • Apoptosis Signaling: Caspase activation and Bcl-2 family proteins are involved.
• • Autophagy Pathway: LC3 and p62 are key markers of autophagic flux.

Organoids derived from human induced pluripotent stem cells (iPSCs) can recapitulate lens development and are useful for studying cataract formation.

• • Genetically Engineered Mouse Models (GEMMs): Mice with CRYBB2 mutations (e.g., O377) exhibit cataracts.
• • Induced Models: UV or oxidative stress-induced cataract in rodents.
• • Patient-Derived Xenografts (PDX): Not applicable for cataract, but lens tissue explants can be used.

CRISPR-Cas9 gene editing enables the creation of isogenic cell lines with specific CRYBB2 mutations. For example, a CRYBB2 knockout line in HLE-B3 cells can model loss-of-function, while a knock-in of a common mutation (e.g., p.Q155X) can model dominant-negative effects. These models are commercially available from sources that provide sequence-verified, mycoplasma-free cells, accelerating research. They are essential for studying protein aggregation, screening anti-cataract drugs, and validating gene therapy approaches.

Knockout and knock-in lines allow functional validation of CRYBB2 mutations. For example, CRISPR knockout of CRYBB2 in lens epithelial cells can reveal changes in cell viability and protein aggregation. Knock-in of a disease-associated mutation can be used to study the molecular mechanisms of cataract formation.

Isogenic pairs (wild-type vs. mutant) are used to screen for compounds that prevent protein aggregation or reduce ER stress. Resistance to oxidative stress can be modeled by exposing cells to H2O2 and measuring survival.

CRISPR screens can identify genes that modify the phenotype of CRYBB2 mutations, revealing potential therapeutic targets. Synthetic lethality screens can identify genes essential for survival in mutant cells, which could be targeted by drugs.