Effects of GDF6 on active protein synthesis by cells of degenerated intervertebral disc

Intervertebral disc degeneration (IVD) is a leading cause of low back pain, a prevalent musculoskeletal condition. IVD degeneration is characterized by the degradation of nucleus pulposus (NP), annulus fibrosus (AF), and cartilage endplates (EP). Growth Differentiation Factor 6 (GDF6), part of the bone morphogenetic protein family, has demonstrated potential in maintaining disc integrity. However, its precise role in cellular protein synthesis during IVD degeneration remains unclear.

This study employed Stable Isotope Labeling by Amino Acids in Cell Culture (SILAC) to investigate the effects of GDF6 on protein synthesis in NP, AF, and EP cells isolated from degenerated human IVDs. Cells were cultured in SILAC media with and without GDF6 treatment. The proteomic profiles were analyzed via mass spectrometry, comparing newly synthesized "heavy" proteins with pre-existing "light" proteins.

GDF6 treatment altered protein synthesis in degenerated IVD cells. In NP cells, GDF6 reduced the synthesis of matrisome proteins, including collagens and proteoglycans, while promoting proteins associated with ECM stability, such as LOX, PCOLCE and HAPLN1/3. AF cells demonstrated an upregulation of ECM-stabilizing proteins like POSTN and FMOD. EP cells showed minimal changes, but GDF6 enhanced the synthesis of collagen type II, suggesting improved ECM integrity. Secretome analysis revealed that GDF6 modulated extracellular signalling by promoting ECM-stabilizing proteins and reducing inflammatory markers.

GDF6 exerts compartment-specific effects on protein synthesis in degenerated IVDs, promoting ECM stability, reducing fibrosis, and potentially preserving hydration. These findings support the potential of GDF6 as a therapeutic agent in treating IVD degeneration, particularly in NP-targeted therapies. Future studies should optimize GDF6 dosing and delivery to maximize its regenerative potential.