Zebrafish mutants reveal unexpected role of Lrp5 in osteoclast regulation

• Published in: Frontiers in endocrinology (Lausanne) Vol. 13; p. 985304
• Main Authors: Khrystoforova, Iryna, Shochat-Carvalho, Chen, Harari, Ram, Henke, Katrin, Woronowicz, Katherine, Harris, Matthew P, Karasik, David
• Format: Journal Article
• Language: English
• Published: Switzerland Frontiers Media S.A 02.09.2022
• Subjects: Animals; bone; Endocrinology; Humans; Ligands; Low Density Lipoprotein Receptor-Related Protein-5 - genetics; lrp5; Mammals; Matrix Metalloproteinase 9; osteoclast; Osteoclasts; osteoporosis; Tartrate-Resistant Acid Phosphatase; zebrafish; Zebrafish - genetics; lrp5; bone; zebrafish; osteoclast; osteoporosis
• ISSN: 1664-2392; 1664-2392
• DOI: 10.3389/fendo.2022.985304

Low-density Lipoprotein Receptor-related Protein 5 ( ) functions as a co-receptor for Wnt ligands, controlling expression of genes involved in osteogenesis. In humans, loss-of-function mutations in 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 ( ) is a popular model for human disease research, as genetic determinants that control bone formation are generally conserved between zebrafish and mammals. We generated knock-out zebrafish to study its role in skeletogenesis and homeostasis. Loss of 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 mutants and siblings. Enrichment analysis revealed upregulation of significantly associated with hydrolase activity: . 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 . 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.