TYROSINASE-Deficient Human Retinal Pigment Epithelium Exhibits Melanosome Maturation Defects

Area of Science:

• Genetics
• Cell Biology
• Ophthalmology

Background:

• Oculocutaneous albinism type 1A (OCA1A) is a genetic disorder characterized by reduced pigmentation due to mutations in the TYROSINASE (TYR) gene.
• Melanosome biogenesis and maturation are critical processes for pigmentation in skin, hair, and eyes.

Purpose of the Study:

• To investigate melanosome biogenesis and maturation defects in an in vitro model of OCA1A.
• To utilize retinal pigment epithelium (RPE) derived from TYR knockout human induced pluripotent stem cells (iPSC) for studying OCA1A.

Main Methods:

• Generated an isogenic pair of human induced pluripotent stem cells (iPSC) using CRISPR-Cas9 to knockout the TYR gene.
• Differentiated iPSC into RPE monolayer tissue using a developmentally guided protocol.
• Analyzed melanosome formation, maturation, TYR protein expression, RPE morphology, and junction integrity.

Main Results:

• TYR knockout RPE displayed significantly reduced TYR protein levels.
• An increase in immature pre-melanosomes and a complete absence of mature melanosomes were observed in TYR knockout RPE.
• Abnormal β-catenin localization at cell junctions was noted, consistent with previous findings in albino models.

Conclusions:

• TYR deficiency in iPSC-derived RPE leads to pigmentation defects and prevents the maturation of melanosomes, while biogenesis remains unaffected.
• The observed defects confirm the validity of this iPSC-derived RPE model for studying OCA1A.
• This model provides a valuable tool for understanding the cellular mechanisms underlying OCA1A.