Endogenous heparan sulfate and heparin modulate bone morphogenetic protein-4 signaling and activity

Abstract

Bone morphogenetic proteins (BMPs) and their endogenous antagonists are important for brain and bone development and tumor initiation and progression. Heparan sulfate (HS) proteoglycans (HSPG) modulate the activities of BMPs and their antagonists. How glycosaminoglycans (GAGs) influence BMP activity in various malignancies and in inherited abnormalities of GAG metabolism, and the structural features of GAGs essential for modulation of BMP signaling, remain incompletely defined. We examined whether chemically modified soluble heparins, the endogenous HS in malignant cells and the HS accumulated in Hurler syndrome cells influence BMP-4 signaling and activity. We show that both exogenous (soluble) and endogenous GAGs modulate BMP-4 signaling and activity, and that this effect is dependent on specific sulfate residues of GAGs. Our studies suggest that endogenous sulfated GAGs promote the proliferation and impair differentiation of malignant human cells, providing the rationale for investigating whether pharmacological agents that inhibit GAG synthesis or function might reverse this effect. Our demonstration of impairment of BMP-4 signaling by GAGs in multipotent stem cells in human Hurler syndrome identifies a mechanism that might contribute to the progressive neurological and skeletal abnormalities in Hurler syndrome and related mucopolysaccharidoses. bone morphogenetic proteins; glycosaminoglycans; mucopolysaccharidosis I; osteosarcoma; stem cells DETERMINING HOW COMPONENTS of the extracellular matrix (ECM) such as proteoglycans influence cytokine-induced cell growth and differentiation in malignancies and other diseases is critical for understanding disease pathophysiology and for developing novel therapeutic strategies (42).Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-␤ (TGF-␤) superfamily of extracellular signaling molecules that regulate the growth, differentiation, and apoptosis of cells in the brain, bone, bone marrow, and diverse tissues (2, 3). The Ͼ15 known BMPs are grouped into subfamilies based on homology within the mature domains, and BMP signaling is initiated by binding to specific type I and type II transmembrane serine/threonine kinase receptors (25). Type I receptors activated by ligand-bound type II receptors phosphorylate R-Smads (Smad-1, Smad-5, and presumably, Smad-8) anchored to the cell membrane, which then complex with Co-Smads (Smad-4), translocate to the nucleus, and regulate gene expression in cooperation with other transcription factors. The activity of R-Smads is further influenced by inhibitory Smads (I-Smads-6 and -7) (25).It is increasingly recognized that ECM and cell surface heparan sulfate (HS) proteoglycans (HSPG) are critical determinants of the biological activity of BMPs and their endogenous antagonists in vivo and in vitro (6, 9, 11, 12, 27-29, 34, 37). As with other proteins, it is believed that specific sulfated residues in the glycosaminoglycan (GAG) side chains of HSPG bind to BMPs and their antagonists and thereby modulate receptor-...

Hematopoietic differentiation of induced pluripotent stem cells from patients with mucopolysaccharidosis type I (Hurler syndrome)

“…It is the signal amplification through these pathways that underlies the varied and tissue-specific pathology in MPS IH, 35 indicating that many of the consequences of IDUA deficiency are not cell autonomous. 36,37 Related to this, one of the main physiologic roles of the lysosome, which is engaged in autophagosomal and proteosomal processes as a functional component of the endosomal-lysosomal system, is recycling of degraded macromolecules, such as GAG and proteoglycans. Experimental evidence suggests that a deficiency of IDUA hydrolase activity, accompanied by GAG storage in MPS IH and other lysosomal storage disorders, results in a state of a "sick lysosome."…”

Exogenous heparin binds and inhibits bone morphogenetic protein 6 biological activity

“…It was revealed that BMPs are heparin/HS-binding molecules and their binding to specific HS GAG chains is necessary for their biological activity. GAGs have been found to have opposite effects on BMP activity in various in vivo and in vitro systems, enhancing it in some, while inhibiting their activity in others [10,13,30]. These effects may depend on multiple factors, such as different BMPs examined [10,13,30,50], the source, concentration and sulphation structure of specific GAGs, the availability or absence of cell surface GAGs, as well as BMP receptors and the assay used.…”

“…GAGs have been found to have opposite effects on BMP activity in various in vivo and in vitro systems, enhancing it in some, while inhibiting their activity in others [10,13,30]. These effects may depend on multiple factors, such as different BMPs examined [10,13,30,50], the source, concentration and sulphation structure of specific GAGs, the availability or absence of cell surface GAGs, as well as BMP receptors and the assay used. Similarly, variable effects on the BMP efficacy were also observed in osteogenic assays [15,30,50].…”

“…It has been reported that heparin and HS influence the activity of bone morphogenetic proteins (BMPs) [10,[13][14][15], which are members of the transforming growth factor-β (TGF-β) superfamily of proteins that regulate a variety of developmental processes including proliferation, differentiation, pattern formation and apoptosis [13,14,[16][17][18][19]. In addition, several BMPs have confirmed osteogenic activity in different animal models, with BMP2 and -7 already in clinical use [20,21].…”

“…In addition, several BMPs have confirmed osteogenic activity in different animal models, with BMP2 and -7 already in clinical use [20,21]. BMPs were originally purified using heparin affinity chromatography [22], and subsequently cell surface and ECM heparan sulphate proteoglycans were shown to be critical for the biological activity of BMPs and their antagonists [10,13,23]. BMP2 and BMP4 have a heparin-binding domain at their N-terminus and strongly bind to heparin and HS via clustered basic residues in that domain [14].…”