The Species-Specific Regenerative Effect of Notochordal Cell-conditioned Medium on Degenerated Human Nucleus Pulposus Cells

Abstract

IntroductionDuring human intervertebral disc (IVD) degeneration, the main cell type shifts from notochordal cells (NCs) to nucleus pulposus cells (NPCs). NCs secrete factors with regenerative potential, making them an interesting focus for regenerative strategies. Research into these strategies employs non-human donors due to easy availability of their NC-rich nucleus pulposus (NP) tissue. To determine the feasibility of translating these strategies toward clinical application, this study aimed to delineate whether NC-secreted factors of different species have a cross-species regenerative effect on degenerated human NPCs. Material and MethodsHealthy human, porcine and canine NC-rich NP tissues (derived from Thompson grade I IVDs) were compared by histology, collagen, DNA and glycosaminoglycan (GAG) content per mg wet tissue weight. NP tissue of each species was cultured for 4 days and NC-conditioned medium (NCCM) was collected. Human NPC micro-aggregates from degenerated IVDs (Thompson grade III) were cultured for 28 days in human, canine or porcine NCCM. GAG content (corrected for DNA) was determined, and Safranin O/Fast Green staining, collagen type I, II and X IHC and gene expression profiling were performed. ResultsCanine and porcine NPs were richer in NCs than human NPs. Human NPs contained the highest collagen content, whereas the DNA and GAG content of canine NPs was significantly higher than human or porcine NPs. NCCM from all species significantly increased the DNA and GAG content of the human NPC micro-aggregates. Porcine and canine NCCM were significantly more potent than human NCCM in inducing GAG deposition, whereas only human NCCM induced collagen type II production. ConclusionSecreted factors from human, canine and porcine NC-rich NPs exerted regenerative effects on human NPCs, indicating a cross-species effect. The species-specific NP properties appear to influence the regenerative capacity of NCCM on human NPCs. Bioactive compound(s) with treatment potential for human IVD degeneration are present in NCCM of different species, implying that strategies based on NC-technology employing canine or porcine models have potential for successful translation into humans. AcknowledgmentsThis work was supported by an AOSpine Research Network grant (SRN2011_11) and the Dutch Arthritis Foundation (LLP22).