Variants in genes encoding ribosomal proteins have thus far been associated with Diamond-Blackfan anemia, a rare inherited bone marrow failure, and isolated congenital asplenia. Here, we report one de novo missense variant and three de novo splice variants in RPL13, which encodes ribosomal protein RPL13 (also called eL13), in four unrelated individuals with a rare bone dysplasia causing severe short stature. The three splice variants (c.477þ1G>T, c.477þ1G>A, and c.477þ2 T>C) result in partial intron retention, which leads to an 18-amino acid insertion. In contrast to observations from Diamond-Blackfan anemia, we detected no evidence of significant pre-rRNA processing disturbance in cells derived from two affected individuals. Consistently, we showed that the insertion-containing protein is stably expressed and incorporated into 60S subunits similar to the wild-type protein. Erythroid proliferation in culture and ribosome profile on sucrose gradient are modified, suggesting a change in translation dynamics. We also provide evidence that RPL13 is present at high levels in chondrocytes and osteoblasts in mouse growth plates. Taken together, we show that the identified RPL13 variants cause a human ribosomopathy defined by a rare skeletal dysplasia, and we highlight the role of this ribosomal protein in bone development.

Ribosomopathies are a group of rare diseases in which genetic mutations cause defects in either ribosome biogenesis or function, given specific phenotypes. Ribosomal proteins, and multiple other factors that are necessary for ribosome biogenesis (rRNA processing, assembly of subunits, export to cytoplasm), can be affected in ribosomopathies. Despite the need for ribosomes in all cell types, these diseases result mainly in tissue-specific impairments. Depending on the type of ribosomopathy and its pathogenicity, there are many potential therapeutic targets. The present manuscript will review our knowledge of ribosomopathies, discuss current treatments, and introduce the new therapeutic perspectives based on recent research. Diamond–Blackfan anemia, currently treated with blood transfusion prior to steroids, could be managed with a range of new compounds, acting mainly on anemia, such as L-leucine. Treacher Collins syndrome could be managed by various treatments, but it has recently been shown that proteasomal inhibition by MG132 or Bortezomib may improve cranial skeleton malformations. Developmental defects resulting from ribosomopathies could be also treated pharmacologically after birth. It might thus be possible to treat certain ribosomopathies without using multiple treatments such as surgery and transplants. Ribosomopathies remain an open field in the search for new therapeutic approaches based on our recent understanding of the role of ribosomes and progress in gene therapy for curing genetic disorders.

Variants in genes encoding ribosomal proteins (RPs) have thus far been associated with Diamond-Blackfan anemia, a rare inherited bone marrow failure, and isolated congenital asplenia. We reported recently one de novo missense variant and three de novo splice variants in the RPL13 gene, which encodes ribosomal protein RPL13/eL13, in four unrelated individuals with a rare bone dysplasia causing severe short stature. The three splice variants (c.477+1G>T, c.477+1G>A, and c.477+2 T>C) result in partial intron retention, which leads to an 18-amino acid insertion. These RPL13 variants define a human ribosomopathy leading to a rare skeletal dysplasia and highlight the role of this ribosomal protein in bone development. It has been shown that patients suffering from ribosomopathies have a highly predisposition to develop cancer compared to general population. Moreover, recent studies have also revealed that mutations in factors involved in ribosome synthesis appear to be drivers of tumorigenesis in sporadic cancers. In this study, we focused on the role of variants of the riboprotein RPL13 in the bone biology and in the development of osteosarcoma. Mesenchymal stem cells expressing variants of RPL13 or wild type RPL13 have been cultured for chondrogenic and osteoblastic differentiation. Our results show that RPL13 variants did not modified the capacity of cells to differentiate into osteoblasts. However, the chondrogenic differentiation was increased in cells expressing variants of RPL13. The expression of sox9 and collagen type X were investigated by immunochemistry on chondrocyte micromass and revealed an increase of expression of these markers in RPL13 variants cells. We next investigated the role of variants of RPL13 in osteosarcoma cell lines. Several cell lines were transduced by lentiviral vector to produce variants of RPL13. The variants induced an increase of cell proliferation and survival. The clonogenecity and the invasion have been also studied. Taken together, these data show that variants of a gene encoding for a riboprotein causing a ribosomopathy could have an effect on chondrogenic differentiation and on osteosarcoma development. Citation Format: Emilien Orgebin, Benjamin Ory, Francois Lamoureux, Marie-Francoise O'Donohue, Céline Charrier, Pierre-Emmanuel Gleizes, Bertrand Isidor, Marc Baud'huin. Riboprotein variant and their role in chondrogenic differentiation and osteosarcoma development [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3595.