USH2A-Mutated Human Retinal Organoids Model Rod-Cone Dystrophy.

Area of Science:

• Ophthalmology
• Genetics
• Stem Cell Biology

Background:

• Mutations in the USH2A gene are the primary cause of autosomal recessive retinitis pigmentosa (RP), a degenerative eye disease leading to blindness.
• Existing animal models do not accurately replicate human USH2A RP, hindering understanding of early disease mechanisms.
• The earliest pathogenic events in USH2A RP remain largely unknown.

Purpose of the Study:

• To establish a human-specific model for studying USH2A-related retinitis pigmentosa.
• To investigate the earliest cellular and molecular defects in USH2A RP using patient-derived and engineered stem cells.
• To elucidate the developmental origins and pathogenic timeline of USH2A RP.

Main Methods:

• Generation of retinal organoids from patient-derived induced pluripotent stem cells (iPSCs).
• Engineering of isogenic USH2A knockout (USH2A-/-) iPSCs using CRISPR-Cas9 technology.
• Assessment of organoids via serial live imaging, whole organoid analysis, and fixed section analysis for cellular, molecular, and morphological defects.

Main Results:

• Both patient-derived and isogenic USH2A-/- organoids exhibited preferential loss of rod photoreceptors, mirroring human RP phenotypes.
• Widespread degeneration of photoreceptors was observed in the developed organoid models.
• Isogenic USH2A-/- organoids displayed early-onset defects in cellular proliferation and structural integrity.

Conclusions:

• Molecular alterations precede overt photoreceptor degeneration in USH2A RP.
• Pathogenesis of USH2A RP may initiate prior to the onset of clinical symptoms.
• This model provides critical insights into early and late disease features, aiding the development of targeted therapies for USH2A RP.