Nucleus Pulposus Mesenchymal Stem Cells in Acidic Conditions Mimicking Degenerative Intervertebral Discs Give Better Performance than Adipose Tissue-Derived Mesenchymal Stem Cells

Abstract

The microenvironment of the intervertebral disc (IVD) is characterized by matrix acidity, hypoxia, hyperosmolarity and limited nutrition, which are major obstacles to stem cell-based regeneration. Our recent work showed that nucleus pulposus mesenchymal stem cells (NPMSCs) had advantages over traditional sources of cell therapy under IVD-like hypoxic and hyperosmotic conditions. Here, we examined the viability, proliferation and matrix metabolism of NPMSCs compared with adipose tissue-derived mesenchymal stem cells (ADMSCs) under IVD-like acidic conditions in vitro. ADMSCs and NPMSCs from Sprague-Dawley rats were cultured at four different pH levels representing the standard condition (pH 7.4) and the normal, mildly degenerated and severely degenerated IVD (pH 7.1, 6.8 and 6.5, respectively). Cell viability was examined by annexin-V-fluorescein isothiocyanate/propidium iodide staining. Cell proliferation was measured using a cell counting kit cell proliferation assay. The expression of aggrecan, collagen-I, collagen-II, matrix metalloproteinase-2 (MMP-2), a disintegrin and metalloproteinase with thrombospondin motifs-4 (ADAMTS4) and the tissue inhibitor of metalloproteinase-3 (TIMP-3) was measured at mRNA and protein levels by RT-PCR and Western blotting. In both cell types, acidic pH inhibited cell viability and proliferation, downregulated the expression of aggrecan, collagen-I, collagen-II and TIMP-3, and upregulated the expression of MMP-2 and ADAMTS4. Compared with ADMSCs, NPMSCs were significantly less inhibited in viability and proliferation; they expressed significantly higher levels of aggrecan and collagen-II, and lower levels of MMP-2 and ADAMTS4. Thus, an acidic environment is a major obstacle for IVD regeneration by ADMSCs or NPMSCs. NPMSCs appeared less sensitive to inhibition by acidic pH and might be promising candidates for cell-based IVD regeneration.

Comparison of biological characteristics of nucleus pulposus mesenchymal stem cells derived from non-degenerative and degenerative human nucleus pulposus

“…Certain studies have reported that these stem cells lack viability, proliferation and matrix biosynthesis under conditions resembling the IVD microenvironment, which negatively influences the biological and metabolic vitality of stem cells and impairs their repair potential (16,17). In recent years, increasing evidence supported the existence of nucleus pulposus MSCs (NPMSCs) in the nucleus pulposus (18)(19)(20)(21)(22)(23)(24). They possess a similar capacity of chondrogenic differentiation to that of BMSCs (18) and have better adaptability to the harsh IVD microenvironment than ADMSCs (24).…”

“…In recent years, increasing evidence supported the existence of nucleus pulposus MSCs (NPMSCs) in the nucleus pulposus (18)(19)(20)(21)(22)(23)(24). They possess a similar capacity of chondrogenic differentiation to that of BMSCs (18) and have better adaptability to the harsh IVD microenvironment than ADMSCs (24). This suggests that NPMSCs may be a good candidate cell for IVD regeneration by cell therapy.…”

“…This suggests that NPMSCs may be a good candidate cell for IVD regeneration by cell therapy. Previous studies have proved that NPMSCs can be isolated from normal and degenerative nucleus pulposus (18)(19)(20)(21)(22)(23)(24). However, the biological properties of stem cells are crucial for the regenerative effects of cell therapy.…”

The Influence of Hyperosmolarity in the Intervertebral Disc on the Proliferation and Chondrogenic Differentiation of Nucleus Pulposus-Derived Mesenchymal Stem Cells

“…Our previous studies [Li et al, 2013;Han et al, 2014] and many others [Blanco et al, 2010;Wu et al, 2017;Molinos et al, 2018] have demonstrated that the IVD itself contains MSCs. Blanco et al [2010] identified human NP-derived (NP)-MSCs from human degenerative discs, and found that these cells fulfilled nearly all the morphological, immunophenotypical, and differentiation criteria described by the International Society of Cell Therapy for MSCs.…”

Cell properties of nucleus pulposus progenitor cells declines with intervertebral disc degeneration

“…NPPCs, a newly discovered type of endogenous intervertebral disc (IVD) SCs, have been characterized in mouse, rabbit, porcine, canine, rhesus monkey and both healthy and degenerating human IVDs [6][7][8][9][10]. In clinical practice, spine surgery patients treated with a dynamic fixation system occasionally display regeneration phenomena in operated segments [11], while experimentally, NPPCs exhibit superior performance in surviving adverse environments [12][13][14]. However, recent reports have indicated that NPPCs gradually become exhausted with increased age and progressive degeneration in IDD [15][16][17].…”