Legumain Regulates Differentiation Fate of Human Bone Marrow Stromal Cells and Is Altered in Postmenopausal Osteoporosis

Abstract

SummarySecreted factors are a key component of stem cell niche and their dysregulation compromises stem cell function. Legumain is a secreted cysteine protease involved in diverse biological processes. Here, we demonstrate that legumain regulates lineage commitment of human bone marrow stromal cells and that its expression level and cellular localization are altered in postmenopausal osteoporotic patients. As shown by genetic and pharmacological manipulation, legumain inhibited osteoblast (OB) differentiation and in vivo bone formation through degradation of the bone matrix protein fibronectin. In addition, genetic ablation or pharmacological inhibition of legumain activity led to precocious OB differentiation and increased vertebral mineralization in zebrafish. Finally, we show that localized increased expression of legumain in bone marrow adipocytes was inversely correlated with adjacent trabecular bone mass in a cohort of patients with postmenopausal osteoporosis. Our data suggest that altered proteolytic activity of legumain in the bone microenvironment contributes to decreased bone mass in postmenopausal osteoporosis.

Lansoprazole inhibits the cysteine protease legumain by binding to the active site

“…Moreover, legumain is initially up‐regulated during osteoblast differentiation but subsequently down‐regulated after 7 days . Our recent observations show that legumain levels are inversely correlated with hBMSC commitment to the osteoblast lineage . MTS analysis of hBMSC‐TERT cells showed that cell viability was not affected by up to 21 days exposure of lansoprazole.…”

“…27 Recently, we reported that legumain regulates osteoblast differentiation through degradation of the bone matrix protein fibronectin. 28 Herein, we have investigated the effects of lansoprazole on legumain and cathepsin B. Our results show that lansoprazole directly inhibits legumain by binding to the active site of the protease and does not regulate the pH of the lysosomes.…”

“…In bone homeostasis, the C‐terminal fragment of legumain has been described as an osteoclast inhibitory factor (OIP‐2) in vitro and a possible inhibitor of bone resorption in vivo . Recently, we reported that legumain regulates osteoblast differentiation through degradation of the bone matrix protein fibronectin …”

Bone Marrow Adipose Tissue and Skeletal Health

“…For instance, preadipocytes secrete the Wnt inhibitor, secreted frizzled-related protein 1 (sFRP-1) that directs MSC fate decision toward the adipogenic lineage and inhibits osteogenesis in response to inhibition of Wnt/β-catenin signaling [28]. Legumain, a cysteine protease secreted in increasing amounts with MSC adipogenic differentiation, has been shown to suppress osteoblast commitment and maturation concomitant with inducing adipogenic differentiation of undifferentiated cells in a paracrine/autocrine fashion [30]. Mechanistically, the degradation of fibronectin by legumain prevents extracellular matrix deposition essential for osteogenesis and provides a microenvironment more amenable to bone marrow adipogenesis.…”

“…Mechanistically, the degradation of fibronectin by legumain prevents extracellular matrix deposition essential for osteogenesis and provides a microenvironment more amenable to bone marrow adipogenesis. The nuclear factor-kappa-light-chain-enhancer of activated B cells (NF-κB) binding regions in legumain promoter is thought to be activated to induce legumain expression during the progression of adipogenic differentiation [30]. Consequently, legumain expression was found to be markedly induced in MSCs isolated from osteoporotic individuals suggesting a potential target to treat the condition [30].…”