Link protein N-terminal peptide binds to bone morphogenetic protein (BMP) type II receptor and drives matrix protein expression in rabbit intervertebral disc cells.
Intervertebral disc (IVD) degeneration and associated spinal disorders are leading sources of morbidity, and they can be responsible for chronic low back pain. Treatments for degenerative disc diseases continue to be a challenge. Intensive research is now focusing on promoting regeneration of degenerated discs by stimulating production of the disc matrix. Link protein N-terminal peptide (LPP) is a proteolytic fragment of link protein, an important cross-linker and stabilizer of the major structural components of cartilage, aggrecan and hyaluronan. In this study we investigated LPP action in rabbit primary intervertebral disc cells cultured ex vivo in a three-dimensional alginate matrix. Our data reveal that LPP promotes disc matrix production, which was evidenced by increased expression of the chondrocyte-specific transcription factor SOX9 and the extracellular matrix macromolecules aggrecan and collagen II. Using colocalization and pulldown studies we further document a noggin-insensitive direct peptide-protein association between LPP and BMP-RII. This association mediated Smad signaling that converges on BMP genes leading to expression of BMP-4 and BMP-7. Furthermore, through a cell-autonomous loop BMP-4 and BMP-7 intensified Smad1/5 signaling though a feedforward circuit involving BMP-RI, ultimately promoting expression of SOX9 and downstream aggrecan and collagen II genes. Our data define a complex regulatory signaling cascade initiated by LPP and suggest that LPP may be a useful therapeutic substitute for direct BMP administration to treat IVD degeneration and to ameliorate IVD-associated chronic low back pain.
From the Atlanta Department of Veterans Affairs Medical Center, Decatur, Georgia 30033.
Zili
Z
Wang
M Neale
MN
Weitzmann
Sreedhara
S
Sangadala
William C
WC
Hutton
S Tim
ST
Yoon
D053674:Aggrecans / Q000378:metabolism; D000818:Animals; D052006:Bone Morphogenetic Protein Receptors, Type II / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D019902:Chondrocytes / Q000166:cytology; D024043:Collagen Type II / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D016326:Extracellular Matrix Proteins / Q000378:metabolism*; D007403:Intervertebral Disc / Q000166:cytology / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D011509:Proteoglycans / Q000378:metabolism*; D011817:Rabbits; D044968:Regenerative Medicine; D055758:SOX9 Transcription Factor / Q000378:metabolism; D015398:Signal Transduction; D000099249:Proteoglycan Link Protein; D000099176:Noggin Protein
D053674:Aggrecans; D052006:Bone Morphogenetic Protein Receptors, Type II; D002352:Carrier Proteins; D024043:Collagen Type II; D016326:Extracellular Matrix Proteins; D010446:Peptide Fragments; D011509:Proteoglycans; D055758:SOX9 Transcription Factor; D000099249:Proteoglycan Link Protein; D000099176:Noggin Protein
BMP-RI; BMP-RII; Cell Signaling; Degenerated Disc Disease; Gene Regulation; Intervertebral Disc; LPP; Peptide Interactions; Regenerative Medicine; Signal Transduction