Zebrafish mutants reveal unexpected role of Lrp5 in osteoclast regulation

• Type of Material: Article
• Authors: Iryna Khrystoforova, Bar Ilan University; Chen Shochat-Carvalho, Bar Ilan University; Ram Harari, Bar Ilan University; Katrin Henke, Emory University; Katherine Woronowicz, Boston Children’s Hospital; Matthew PP Harris, Boston Children’s Hospital; David Karasik, Bar Ilan University
• Language: English
• Date: 2022-09-02
• Publisher: FRONTIERS MEDIA SA
• Publication Version: Final Published Version
• Copyright Statement: © 2022 Khrystoforova, Shochat-Carvalho, Harari, Henke, Woronowicz, Harris and Karasik
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.3389/fendo.2022.985304
• Title of Journal or Parent Work: FRONTIERS IN ENDOCRINOLOGY
• Volume: 13
• Start Page: 985304
• End Page: 985304
• Grant/Funding Information: The study was supported by a grant No. 2017204 from US-Israel BSF and grant No. 1121/19 from Israel Science Foundation.
• Keywords: OSTEOPETROSIS; OSTEOPOROSIS; FRACTURE RISK; osteoclast; osteoporosis; TELEOST FISH; DISEASE; CARTILAGE; MUTATIONS; MECHANISMS; Endocrinology & Metabolism; Science & Technology; zebrafish; GENE; lrp5; bone; Life Sciences & Biomedicine
• Research Categories: Health Sciences, Medicine and Surgery

Abstract

Low-density Lipoprotein Receptor-related Protein 5 (LRP5) functions as a co-receptor for Wnt ligands, controlling expression of genes involved in osteogenesis. In humans, loss-of-function mutations in LRP5 cause Osteoporosis-Pseudoglioma syndrome, a low bone mass disorder, while gain-of-function missense mutations have been observed in individuals with high bone mass. Zebrafish (Danio rerio) is a popular model for human disease research, as genetic determinants that control bone formation are generally conserved between zebrafish and mammals. We generated lrp5- knock-out zebrafish to study its role in skeletogenesis and homeostasis. Loss of lrp5 in zebrafish leads to craniofacial deformities and low bone mineral density (total body and head) at adult ages. To understand the mechanism and consequences of the observed phenotypes, we performed transcriptome analysis of the cranium of adult lrp5 mutants and siblings. Enrichment analysis revealed upregulation of genes significantly associated with hydrolase activity: mmp9, mmp13a, acp5a. acp5a encodes Tartrate-resistant acid phosphatase (TRAP) which is commonly used as an osteoclast marker, while Matrix metalloprotease 9, Mmp9, is known to be secreted by osteoclasts and stimulate bone resorption. These genes point to changes in osteoclast differentiation regulated by lrp5. To analyze these changes functionally, we assessed osteoclast dynamics in mutants and observed increased TRAP staining, significantly larger resorption areas, and developmental skeletal dysmorphologies in the mutant, suggesting higher resorptive activity in the absence of Lrp5 signaling. Our findings support a conserved role of Lrp5 in maintaining bone mineral density and revealed unexpected insights into the function of Lrp5 in bone homeostasis through moderation of osteoclast function.