Loss of coactosin-like F-actin binding protein 1 (Cotl1) decreases platelet-mediated osteoclastogenesis and causes osteopetrosis phenotypes in mouse
Authors: Park Eunkuk , Yun Seung-Hee , Jin Hyun-Seok , Lee Chang-Gun , Lee So-Hyun , Choi Seok-Yong , Woo Hyun Goo , Lim Ji Eun , Oh Bermseok , Jeong Seon-Yong 
Published: December 2023

ABSTRACTBACKGROUNDSOsteopetrosis, a rare skeletal disease, is characterized by an increased bone mass resulting from impaired bone remodeling process. Platelet is the major bone-healing blood component involved in the regulation of bone resorption, particularly in the removal of compromised bones. Several actin-associated proteins contribute to the orchestration of actin ring formation in osteoclasts closely related to bone resorption. However, the role of coactosin-like F-actin binding protein 1 (Cotl1) in actin ring formation and platelet-mediated bone resorption mechanisms remains unclear.METHODSWhole-mountin situRNA hybridization was performed to detect cotl1 expression pattern in zebrafish.cotl1gene knockdown zebrafish using morpholino oligonucleotides and platelet marker-expressing transgenic zebrafish were investigated for finding the phenotypic clues.Cotl1knockout (Cotl1-/-) mice were generated usingCre/loxPrecombination systems.In siliconetwork analysis of the differentially expressed genes between bone marrow samples of wild type andCotl1-/-mice was conducted. Primary-cultured monocytes fromCotl1-/-mice were examined for osteoclast differentiation and mRNA and protein expression patterns.Cotl1-/-mice underwent hematological examination and bone phenotype assessments including micro-CT, bone density, histology, immunohistochemistry, electron microscopy, and mechanical testing. Genetic association of SNPs in humanCOTL1gene with estimated bone mineral density was analyzed.RESULTSZebrafishcotl1mRNA was highly expressed in the caudal hematopoietic tissue region. Knockdown ofcotl1in zebrafish embryos decreased the expression ofc-myb, a marker of hematopoietic stem cells (HSCs). Notably, the platelet receptor CD41 was reduced in the HSCs ofcotl1-depleted zebrafish andCotl1-/-mice showed reduced platelet production with platelet surface markers of CD41 and CD61. Significantly reduced osteoclast differentiation and bone resorption pit, and impaired actin ring formation were observed in the primary myocytes fromCotl1-/-mice. Structural and histological analyses of the femur revealed sclerotic bone phenotypes inCotl1-/-mice. Mechanical assessment ofCotl1-/-mouse femoral bones revealed osteopetrotic phenotypes. Association analysis of genetic variants inCOTL1gene in subjects from the UK Biobank suggested thatCOTL1is susceptible to bone density in humans.CONCLUSIONSOur results provide insights into the role of Cotl1 in platelet-mediated osteoclastogenesis and the novel finding that the loss ofCotl1-/-mice causes osteopetrosis phenotypes.Clinical PerspectiveWhat Is New?Deficiency of Cotl1 decreased platelet production in zebrafish and mice.Absence of Cotl1 disrupted the actin ring formation which is crucial for osteoclast differentiation in bone remodeling process.Cotl1knockout mice displayed sclerotic bone phenotypes and increased bone density that are representative characteristics of osteopetrosis.Genetic variants inCOTL1gene in subjects from the UK Biobank are significantly associated with bone density.What Are the Clinical Implications?The current findings suggest that Cotl1 plays a fundamental role in platelet production-mediated osteoclastogenesis during bone remodeling, providing valuable insights into novel strategies for bone health maintenance.Cotl1 may be a promising target for novel therapeutic strategies for the treatment and/or prevention of impaired osteoclastogenesis-mediated bone diseases such as osteopetrosis and osteoporosis.