Abstract
Ras homologous guanosine triphosphatases (RhoGTPases) control several cellular functions, including cytoskeletal actin remodeling and cell migration. Their activities are downregulated by GTPase-activating proteins (GAPs). Although RhoGTPases are implicated in bone remodeling and osteoclast and osteoblast function, their significance in human bone health and disease remains elusive. Here, we report defective RhoGTPase regulation as a cause of severe, early-onset, autosomal-dominant skeletal fragility in a three-generation Finnish family. Affected individuals (n = 13) presented with multiple low-energy peripheral and vertebral fractures despite normal bone mineral density (BMD). Bone histomorphometry suggested reduced bone volume, low surface area covered by osteoblasts and osteoclasts, and low bone turnover. Exome sequencing identified a novel heterozygous missense variant c.652G>A (p.G218R) in ARHGAP25, encoding a GAP for Rho-family GTPase Rac1. Variants in the ARHGAP25 5′ untranslated region (UTR) also associated with BMD and fracture risk in the general population, across multiple genomewide association study (GWAS) meta-analyses (lead variant rs10048745). ARHGAP25 messenger RNA (mRNA) was expressed in macrophage colony-stimulating factor (M-CSF)–stimulated human monocytes and mouse osteoblasts, indicating a possible role for ARHGAP25 in osteoclast and osteoblast differentiation and activity. Studies on subject-derived osteoclasts from peripheral blood mononuclear cells did not reveal robust defects in mature osteoclast formation or resorptive activity. However, analysis of osteosarcoma cells overexpressing the ARHGAP25 G218R-mutant, combined with structural modeling, confirmed that the mutant protein had decreased GAP-activity against Rac1, resulting in elevated Rac1 activity, increased cell spreading, and membrane ruffling. Our findings indicate that mutated ARHGAP25 causes aberrant Rac1 function and consequently abnormal bone metabolism, highlighting the importance of RhoGAP signaling in bone metabolism in familial forms of skeletal fragility and in the general population, and expanding our understanding of the molecular pathways underlying skeletal fragility.
| Original language | English |
|---|---|
| Article number | e10509 |
| Journal | JBMR Plus |
| Volume | 5 |
| Issue number | 7 |
| DOIs | |
| Publication status | Published - 6 May 2021 |
Bibliographical note
Funding Information:This study was supported by the Sigrid Jusélius Foundation, the Novo Nordisk Foundation, the Folkhälsan Research Foundation, the Academy of Finland, the Foundation for Pediatric Research, the Helsinki University Research Funds, Helsinki University and Helsinki University Hospital through the Doctoral Programme in Clinical Research, the Orion Research Foundation, the Finnish ORL–HNS Foundation, the Päivikki and Sakari Sohlberg Foundation, the Finnish–Norwegian Medical Foundation, the Jalmari and Rauha Ahokas Foundation, the Juhani Aho Foundation, the Swedish Research Council, the Swedish Childhood Cancer Foundation, Konung Gustaf V:s och Drottning Victorias Frimurarestiftelse, Stockholm County Council and Karolinska Institutet, The Netherlands Organization for Health Research and Development ZonMw, National Natural Science Foundation of China, Natural Science Foundation of Shanghai, “100 talents program” from the Chinese Academy of Sciences, Shanghai Talent Development Funding, and the Wellcome Trust Strategic Award. The funders had no role in design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review, or approval of the manuscript. We thank Mira Aronen and Laura Koljonen for help with laboratory work and Päivi Turunen for help with collecting subject data and samples. The computations and data handling were enabled by resources provided by the Swedish National Infrastructure for Computing (SNIC) at UPPMAX partially funded by the Swedish Research Council through grant agreement no. 2018‐05973.
Funding Information:
This study was supported by the Sigrid Jus?lius Foundation, the Novo Nordisk Foundation, the Folkh?lsan Research Foundation, the Academy of Finland, the Foundation for Pediatric Research, the Helsinki University Research Funds, Helsinki University and Helsinki University Hospital through the Doctoral Programme in Clinical Research, the Orion Research Foundation, the Finnish ORL?HNS Foundation, the P?ivikki and Sakari Sohlberg Foundation, the Finnish?Norwegian Medical Foundation, the Jalmari and Rauha Ahokas Foundation, the Juhani Aho Foundation, the Swedish Research Council, the Swedish Childhood Cancer Foundation, Konung Gustaf V:s och Drottning Victorias Frimurarestiftelse, Stockholm County Council and Karolinska Institutet, The Netherlands Organization for Health Research and Development ZonMw, National Natural Science Foundation of China, Natural Science Foundation of Shanghai, ?100 talents program? from the Chinese Academy of Sciences, Shanghai Talent Development Funding, and the Wellcome Trust Strategic Award. The funders had no role in design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review, or approval of the manuscript. We thank Mira Aronen and Laura Koljonen for help with laboratory work and P?ivi Turunen for help with collecting subject data and samples. The computations and data handling were enabled by resources provided by the Swedish National Infrastructure for Computing (SNIC) at UPPMAX partially funded by the Swedish Research Council through grant agreement no. 2018-05973.
Publisher Copyright:
© 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.
