Heterozygous retinoblastoma gene mutation compromises in vitro osteogenesis of adipose mesenchymal stem cells - a temporal gene expression study

Monoallelic loss of RB1 enhances osteogenic differentiation and delays DNA repair without inducing tumorigenicity

The Retinoblastoma (RB1) gene plays a pivotal role in osteogenic differentiation. Our previous study, employing temporal gene expression analysis using quantitative reverse transcriptase polymerase chain reaction (qRT-PCR), revealed the deregulation of osteogenic differentiation in patient-derived heterozygous RB1 mutant orbital adipose-derived mesenchymal stem cells (OAMSCs). The study revealed increased Alizarin Red staining, suggesting heightened mineralization without a corresponding increase in osteogenic lineage-specific gene expression. In this study, we performed high-throughput RNA sequencing on RB1+/+ and RB1+/- patient-derived OAMSCs differentiated towards the osteogenic lineage to investigate the pathways and molecular mechanisms. The pathway analysis revealed significant differences in cell proliferation, DNA repair, osteoblast differentiation, and cancer-related pathways in RB1+/- OAMSC-derived osteocytes. These findings were subsequently validated through functional assays. The study revealed that osteogenic differentiation is increased in RB1+/- cells, along with enhanced proliferation of the osteocytes. There were delayed but persistent DNA repair mechanisms in RB1+/- osteocytes, which were sufficient to maintain genomic integrity, thereby preventing or delaying the onset of tumors. This contrasts with our earlier observation of increased mineralization without corresponding gene expression changes, emphasizing the importance of high-throughput analysis over preselected gene set analysis in comprehending functional assay results.

Heterozygous RB1 mutation enhanced ATP production in human iPSC-derived retinal organoids

BACKGROUND

Recent in vitro studies using RB1+/- fibroblasts and MSCs have shown molecular and functional disruptions without the need for biallelic loss of RB1. However, this was not reflected in the recent in vitro studies employing RB1+/- retinal organoids. To gain further insights into the molecular disruptions in the RB1+/- retinal organoids, we performed a high throughput RNA sequencing analysis.

METHODS AND RESULTS

iPSCs were generated from RB1+/+ and RB1+/- OAMSCs derived from retinoblastoma patients. RB1+/+ and RB1+/- iPSCs were subjected to a step-wise retinal differentiation protocol. Retinal differentiation was evaluated by Real-time PCR and flow cytometry analysis of the retinal markers. To gain further insights into the molecular differences in RB1+/- retinal organoids, a high throughput RNA sequencing followed by differential gene expression analysis and gene set enrichment analysis (GSEA) was performed. The analysis revealed a shift from the regular metabolic process of glycolysis to oxidative phosphorylation in the RB1+/- retinal organoids. To investigate further, we performed assays to determine the levels of pyruvate, lactate and ATP in the retinal organoids. The results revealed significant increase in ATP and pyruvate levels in RB1+/- retinal organoids of day 120 compared to that of the RB1+/+. The results thus revealed enhanced ATP production in the RB1+/- retinal organoids.

CONCLUSION

The study provides novel insights into the metabolic phenotype of heterozygous RB1 mutant suggesting dysregulation of energy metabolism and glycolytic pathways to be first step even before the changes in cellular proliferation or other phenotypic consequences ensue.

Retinoblastoma patient-derived stem cells-an in vivo model to study the role of RB1 in adipogenesis

Retinoblastoma (RB1) protein is a multifunctional protein that plays an important role in cell cycle regulation and cell differentiation, including adipogenesis. A detailed literature search to understand the role of RB1 in adipogenesis revealed that the nature of the RB1 inactivation (in vivo/in vitro) led to differences in adipogenesis. The majority of these studies were animal-based, and the only study in humans employed an in vitro mode of RB1 inactivation. To overcome these differences and lack of human studies, we sought to explore the role of RB1 in adipogenesis using orbital adipose mesenchymal stem cells (OAMSCs) from patients with retinoblastoma that innately carry a heterozygous RB1 mutation. We hypothesized that these patient-derived RB1 mutant OAMSCs can model in vivo RB1 inactivation in humans. Our study revealed increased adipogenesis with a bias toward brown adipogenesis in the RB1 mutant in addition to an increased number of adipocytes in the mitotic phase.