Mutation of the Galectin-3 Glycan Binding Domain ( Lgals3 -R200S) Enhances Cortical Bone Expansion in Male and Trabecular Bone Mass in Female Mice

The study of galectin-3 is complicated by its ability to function both intracellularly and extracellularly. While the mechanism of galectin-3 secretion is unclear, studies have shown that the mutation of a highly conserved arginine to a serine in human galectin-3 (-R186S) blocks glycan binding and secretion. To gain insight into the roles of extracellular and intracellular functions of galectin-3, we generated mice with the equivalent mutation (-R200S) using CRISPR/Cas9-directed homologous recombination. Consistent with a reduction in galectin-3 secretion, we observed significantly reduced galectin-3 protein levels in the plasma of heterozygous and homozygous mutant mice. We observed a similar increased bone mass phenotype in -R200S mutant mice at 36 weeks as we previously observed in -KO mice with slight variation. Like -KO mice, -R200S females, but not males, had significantly increased trabecular bone mass. However, only male -R200S mice showed increased cortical bone expansion, which we had previously observed in both male and female -KO mice and only in female mice using a separate null allele (). These results suggest that the trabecular bone phenotype of -KO mice was driven primarily by loss of extracellular galectin-3. However, the cortical bone phenotype of -KO mice may have also been influenced by loss of intracellular galectin-3. Future analyses of these mice will aid in identifying the cellular and molecular mechanisms that contribute to the -deficient bone phenotype as well as aid in distinguishing the extracellular vs. intracellular roles of galectin-3 in various signaling pathways.