Harnessing Platelet-derived factors to reactivate Nucleus Pulposus cells in Intervertebral Disc Regeneration

Degenerative disc disease (DDD) is a significant healthcare challenge, particularly in the elderly population. Current treatment options range from conservative approaches to invasive surgical interventions. In intervertebral disc (IVD) disease, the degeneration of the Nucleus Pulposus (NP) is a key factor in the initiation of the pathology. Several tissue engineering strategies have been explored to restore the NP cell and matrix components, using adult mesenchymal stem cells (MSCs) and, more recently, induced pluripotent stem cells. However, these approaches have not been fully successful due to the acidic environment of the NP, which is harmful to implanted heterologous cells.Recent studies have shown that platelet derivatives, particularly Platelet-Rich Plasma (PRP) and Platelet Lysate (PL), are effective in promoting connective tissue regeneration.

This study aimed to explore the potential of PL to stimulate NP cell proliferation and differentiation, either by directly activating resident NP cells or by expanding them in vitro for subsequent implantation, with the overarching goal of promoting IVD regeneration. IVD biopsies were processed using two methods to isolate NP cells: enzymatic digestion (NPd), which degrades the extracellular matrix to release the cells, and direct plating of biopsy fragments (NPwd), which isolates migrating cells from the tissue. Phenotypic characterization was performed using flow cytometry to assess mesenchymal marker expression and cell proliferation was quantified by cell doubling counts. Chondrogenic differentiation was evaluated in a 3D culture model, followed by immunohistochemical analysis.

Our results demonstrate that NP cells cultured with PL show a progenitor-like state, with the ability to form cartilaginous pellets upon chondrogenic stimulation. Moreover, PL directly induces the release of progenitors from biopsy fragments, exhibiting mesenchymal stem cell-like properties and chondrogenic differentiation potential.

In conclusion, PL supports the maintenance of a progenitor state in NP cells and may contribute to the regeneration of damaged IVD tissue by activating resident quiescent stem/progenitor cells within the disc.