Transcriptomic Signature of PDGF-BB Control of Annulus Fibrosus Reveals Modulation of Inflammatory and Neurogenic Pathways.

Low back pain is closely associated with intervertebral disc (IVD) degeneration, in which inflammation and neovascularization within the annulus fibrosus (AF) contribute to pain generation. Platelet-derived growth factor (PDGF)-BB plays a crucial role in tissue repair and cellular homeostasis, but its role in AF cell biology remains poorly understood. To investigate the effects of PDGF-BB on human AF cells, healthy and degenerated AF cells were treated with PDGF-BB for 3 or 5 days, followed by bulk RNA sequencing. Functional enrichment of differentially expressed genes, transcription factor activity analysis, and protein-protein interaction network analysis was performed. Publicly available single-cell RNA-seq data were used to compare the transcriptomic profiles of native healthy and degenerated AF samples. In addition, TNF-α stimulation was conducted to validate the anti-inflammatory effects of PDGF-BB. Our findings suggest that PDGF-BB induced both common and context-dependent transcriptional responses in healthy and degenerated AF cells. In healthy AF cells, PDGF-BB consistently upregulated genes associated with cell cycle and developmental growth. In degenerated AF cells, PDGF-BB also induced these responses, while additionally it downregulated the genes related to extracellular matrix remodeling and collagen degradation. Meanwhile, PDGF-BB showed common effects in both healthy and degenerated cells by modulating the expression of genes within G protein-coupled receptor (GPCR) networks that are linked to complement, inflammation, and neurotransmitter signaling. In addition, PDGF-BB also suppressed the expression of genes involved in inflammatory-neurogenic signaling, including nerve growth factor (NGF), C-X-C motif chemokine ligand 12 (CXCL12), and apolipoprotein E (APOE). To relate these PDGF-BB induced responses to disc degeneration, we reanalyzed publicly available single-cell RNA-seq datasets from native human AF tissues and found that NGF-positive cells showed increased tumor necrosis factor (TNF)-α signaling activity. When AF cells were stimulated with TNF-α, PDGF-BB treatment significantly inhibited the expression of NGF, endothelin-1 (EDN1), and interleukin 6 (IL6) under both baseline and TNF-α-stimulated conditions. These results suggest that PDGF-BB modulates gene expression associated with inflammatory and neurogenic signaling as well as ECM remodeling in human AF cells, providing a transcriptomic insight into the PDGF-BB's function in AF biology.