Oral Presentation 51st International Society for the Study of the Lumbar Spine Annual Meeting 2025

Introduction: It has been shown that platelet-derived growth factor (PDGF) mitigated IVD degeneration through anti-apoptosis, anti-inflammation, and pro-anabolism^1,2. The purpose of this study is to determine the mechanisms underlying the beneficial effects of PDGF on intervertebral disc health. One of the evolving cellular mechanisms of age-related disc degeneration has been disc cell senescence. Below, we describe novel mechanisms via which PDGF-BB inhibits disc senescence.

Methods: Following informed consent in accordance with the institutional review board approval, human nucleus pulposus (NP) tissues and annulus fibrosus (AF) cells were isolated from IVD tissues. To examine the changes of transcriptome profiling induced by PDGF-BB, degenerated NP and AF cells (n=5~6) were treated with recombinant human PDGF-BB (20ng/ml) for 5 days. Total RNA was isolated and used for mRNA sequencing. To establish cellular senescence in healthy IVD cells, cells were exposed to single doses of X-ray irradiation for different timepoints (7 and 10 days). NP and AF cells (n=4) were treated with PDGF-BB immediately after irradiation for 10 days. Data were analyzed using Students’ t test or one-way ANOVA followed by Bonferroni (Graphpad Prism 9) with a statistical significance of p<0.05.   

Results: Our seq data revealed that degenerated NP and AF cells exhibited an overall comparable transcriptomic signature in response to PDGF-BB treatment, while each retained some unique differential gene expression profiles. In both NP and AF cells, GO analysis (Fig.1A) demonstrated that the treatment upregulated the expression of genes involved in cell cycle regulation and response to reduced oxygen levels while downregulating the expression of genes related to senescence associated phenotype, including oxidative stress and mitochondria dysfunction. GSEA analysis (Fig.1B) showed reduced oxidative phosphorylation, an indicator of alterations in mitochondrial function. Network analysis of all the DEGs revealed that upregulated PDGF receptor alpha (PDGFRA), along with senescence hallmarks such as MDM2 and IL6 were among the top treatment responsive hub genes in NP cells (Fig.1C). To establish the functionality of these transcriptomic observations, we induced senescence in healthy NP cells via irradiation and examines potential anti-senescence effects of PDGF (Fig.2). The irradiation-induced senescence, measured by SA-b-Gal staining (Fig.3A), cell cycle progression (Fig.3B), and induction of SASP and other senescence related regulators such as P21, P16, IL6, and NF-κB (Fig.3C&D), was strongly inhibited by PDGF treatment. Noteworthy was the repression of PDGFRA gene in irradiated cells by PDGF, which we postulate as a novel mechanism of PDGF-controlled IVD cell senescence.

Discussion: The current study has shown for the first time that PDGF treatment not only alleviated the senescent phenotype, but also suppressed the progression of cellular senescence in the IVD. This novel function of PDGF/PDGFRA signaling is likely linked to their ability to stimulate cell cycle progression while inhibiting NF-κB, P16, and P21 pathways in NP cells. The PDGF-BB treatment downregulated groups of genes related to neurogenesis and response to mechanical stimulus in AF cells while downregulated genes in the NP were more associated with metabolic pathways, providing evidence that the treatment enhanced IVD functionality in different aspects between the two compartments.