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

Abstract

Nucleus pulposus-derived mesenchymal stem cells (NP-MSCs) are suitable cell candidates for intervertebral disc (IVD) regeneration. However, little work has been done to determine the proliferation and chondrogenic differentiation of NP-MSCs in the hyperosmotic microenvironment of IVD. This study aimed to investigate the influence of the hyperosmolarity of IVD on the proliferation and chondrogenic differ­entiation of NP-MSCs. NP-MSCs were cultured in media of 300, 400, 430, and 500 mOsm/L, mimicking the osmotic pressures of serious degenerative, moderately degenerative, and healthy IVD. Cell proliferation was measured by CCK-8 assay. The expression of aggrecan, collagen I, and collagen II were measured by gene and protein expression analysis. Alcian blue and dimethylmethylene blue assay were used to investigate the accumulation of sulfate glycosaminoglycan. The regulation role of extracellular signal-regulated kinase (ERK) pathway was also analyzed. The results showed that, compared to 300 mOsm/L, hyperosmolarity of healthy IVD (430 and 500 mOsm/L) inhibited the proliferation and chondrogenic differentiation of NP-MSCs. The relative hypoosmotic condition of moderately degenerative IVD (400 mOsm/L) led to great proliferation and chondrogenic differentiation capacity. The ERK pathway was activated by the hyperosmolarity; inhibition of the ERK pathway abolished the difference in cell proliferation between the 300 mOsm/L and the hyperosmotic conditions, and enhanced chondrogenic differentiation. In conclusion, hyperosmolarity of IVD had a significant impact on the proliferation and chondrogenic differentiation of NP-MSCs. The ERK pathway was involved in the inhibition of proliferation and chondrogenic differentiation of NP-MSCs by the hyperosmolarity of IVD. The relative hypo-osmotic condition prevailing in degenerative discs offers a more permissive microenvironment for NP-MSCs.

Interaction between Mesenchymal Stem Cells and Intervertebral Disc Microenvironment: From Cell Therapy to Tissue Engineering

“…In a recent 5 Stem Cells International study, Li et al showed that exposing NP-MSCs to osmotic pressures mimicking the healthy IVD environment (430-500 mOsm/L) resulted in a decrease of cell proliferation and chondrogenic differentiation via activation of the ERK pathway, while the relative hypoosmotic condition of mild IDD proved to increase NP-MSC proliferation and chondrogenic potential. Based on this study, a degenerative microenvironment, due to lower osmotic pressures, may be less hostile to NP-MSCs, providing an interesting insight for future regenerative strategies [104].…”

“…Hyperosmolarity has been demonstrated to induce progenitor cell differentiation towards a mature NP phenotype [104].…”

Pathomechanism of intervertebral disc degeneration

“…Thereafter, several researchers have reported the presence of cells compatible with MSCs from NP, AF, and CEP of normal or degenerated IVDs . Further, several microenvironments of IVDs, such as extracellular matrix stiffness, pH, and osmotic pressure, have been shown to affect the properties of these progenitors …”

“…[107][108][109][110][111][112][113] Further, several microenvironments of IVDs, such as extracellular matrix stiffness, pH, and osmotic pressure, have been shown to affect the properties of these progenitors. [114][115][116] Sakai et al identified NP progenitors with novel NP-specific cell markers, and demonstrated that these progenitors are exhausted with aging and degeneration. 117 Using colony-forming assay with methylcellulose semi-solid medium, they identified progenitors from human and mouse NPs that express tyrosine-protein kinase receptor (Tie2) and disialoganglioside 2 (GD2).…”

Heme Oxygenase-1-Mediated Autophagy Protects against Oxidative Damage in Rat Nucleus Pulposus-Derived Mesenchymal Stem Cells

“…Then, they migrate to degenerative IVD tissues to differentiate into IVD cells to replace the damaged resident cells and (or) protect the damaged cells by some mediators [13]. However, during the process of endogenous repair, IVD-derived MSCs are inevitably exposed to the hostile microenvironments in IVD, including oxidative stress [14], excessive compression [15], acidic pH [16], hypoxia [17], limited nutrition [18], and high osmolarity [19]. These adverse microenvironments can significantly hinder the endogenous repair process by inhibiting the biological behaviors of IVD-derived MSCs and decreasing the number of the cells, and then finally lead to the failure of endogenous repair [13,20].…”