In vitro Pigmentation of Human iPSC-Derived Retinal Pigment Epithelium Cells Does Not Reflect Their Functional Characteristics

Core Concepts

The degree of pigmentation in in vitro cultured human iPSC-derived retinal pigment epithelium (iPSC-RPE) cells does not correlate strongly with their gene expression profiles or functional characteristics.

Abstract

The study investigated the relationship between the pigmentation level and gene expression profiles of human iPSC-derived retinal pigment epithelium (iPSC-RPE) cells.
Key findings:

The iPSC-RPE cells showed diverse degrees of pigmentation, but this did not correspond to specific gene expression profiles or functional clusters when analyzed by single-cell transcriptomics.
Even for genes directly involved in melanin synthesis (TYRP1, TYR), their expression levels had only weak correlation with the pigmentation level of the iPSC-RPE cells.
Further analysis revealed that the pigmentation level was moderately correlated with the expression of genes related to lysosome and complement pathways, which are important for RPE function.
The authors hypothesized that the pigmentation of iPSC-RPE cells in vitro may be a temporal condition not strongly indicative of their functional maturity, as environmental cues play a key role in melanogenesis.
Compared to fetal-derived RPE cells, iPSC-RPE cells may be more plastic and their pigmentation may not necessarily reflect their functional characteristics.
Overall, the study suggests that the degree of pigmentation alone is not a reliable indicator of the quality or functional properties of iPSC-derived RPE cells for cell transplantation purposes.

Stats

The genes with the highest positive correlation between their expression and the pigmentation level of iPSC-RPE cells were:
CST3 (correlation coefficient 0.565)
C1R (correlation coefficient 0.31)
C1S (correlation coefficient 0.31)
C3 (correlation coefficient 0.27)
The genes with the highest negative correlation were not reported.

Quotes

"Intriguingly, the expressions of the genes directly related to the production of melanin were not the highest for the correlation with the color. For example, correlation coefficients between the expressions of the enzymes for melanin-synthesis, TYR and TYRP1, and color intensities were 0.434 and 0.458, respectively."
"This suggests the degree of pigmentation is dynamically regulated in each cell, and there is a time-lag between mRNA expression, production of the enzymes, and synthesis of melanin."

Key Insights Distilled From

Pigmentation level of human iPSC-derived retinal pigment epithelium cell does not indicate a specific gene expression profile

by Nakai-Futats... at www.biorxiv.org 09-29-2023

https://www.biorxiv.org/content/10.1101/2023.09.29.560095v2

Deeper Inquiries

What other functional or phenotypic characteristics of iPSC-RPE cells, besides pigmentation, could be better predictors of their quality and suitability for cell transplantation

In addition to pigmentation, several other functional and phenotypic characteristics of iPSC-RPE cells could serve as better predictors of their quality and suitability for cell transplantation. One crucial aspect is the expression levels of key RPE markers such as RPE65, Bestrophin, CRALBP, and MERTK. These markers are essential for the proper functioning of RPE cells in maintaining the visual system, and their expression levels can indicate the maturity and functionality of iPSC-RPE cells. Additionally, the phagocytic activity of RPE cells, their ability to secrete factors like VEGF and PEDF, and their capacity for retinoid recycling are all important functional characteristics that can determine the quality of iPSC-RPE cells for transplantation. Evaluating the morphology, polarization, and barrier function of the RPE monolayer can also provide valuable insights into the integrity and functionality of the cells.

How do the findings from this in vitro study translate to the behavior and properties of iPSC-RPE cells after transplantation in vivo

The findings from this in vitro study provide valuable insights into the behavior and properties of iPSC-RPE cells after transplantation in vivo. While the study focused on the correlation between pigmentation and gene expression profiles in cultured iPSC-RPE cells, the results suggest that the degree of pigmentation may not directly reflect the functional characteristics of the cells. Therefore, after transplantation in vivo, the dynamic regulation of pigmentation observed in iPSC-RPE cells may continue, indicating that the pigmentation level alone may not be a reliable indicator of the cells' behavior post-transplantation. Instead, it is essential to consider a combination of functional markers, gene expression profiles, and phenotypic characteristics to assess the quality and performance of iPSC-RPE cells in vivo.

Could the dynamic regulation of pigmentation in iPSC-RPE cells be leveraged to enhance their protective functions, such as by modulating the expression of complement or lysosome-related genes

The dynamic regulation of pigmentation in iPSC-RPE cells presents an opportunity to potentially enhance their protective functions by modulating the expression of complement or lysosome-related genes. By understanding the pathways and biological processes that correlate with the degree of pigmentation, researchers can explore strategies to manipulate these pathways to improve the functionality of iPSC-RPE cells. For example, enhancing the expression of genes involved in lysosomal function could improve the cells' ability to phagocytose and degrade cellular debris, contributing to a healthier retinal environment. Similarly, modulating complement-related genes could enhance the cells' immune-like functions, providing better protection to the surrounding retinal tissue. Leveraging the dynamic nature of pigmentation in iPSC-RPE cells to fine-tune their functional characteristics could lead to improved outcomes in cell transplantation therapies for retinal degenerative diseases.