Behavior of mesenchymal stem cells in the chemical microenvironment of the intervertebral disc

Study Design. Responses of mesenchymal stem cells (MSCs) from 2 age groups was analyzed under chemical conditions representative of the intervertebral disc (IVD) ( low glucose levels, acidic pH, high osmolarity, and combined conditions). Objective. To determine the microenvironmental conditions of the IVD that are critical for MSC-based tissue repair and to determine whether MSCs from different age groups respond differently. Summary of Background Data. MSCs offer promise for IVD repair, but their potential is limited by the harsh chemical microenvironment in which they must survive. Methods. MSCs were isolated from bone marrow from mature (4-5 month old) and young (1 month old) rats and cultured in monolayer under IVD-like glucose, osmolarity, and pH conditions as well as under a combination of these conditions and under standard media conditions for 2 weeks. The response of MSCs was examined by measuring gene expression (real-time RT-PCR), proliferation (MTT assay), and viability (fluorescence staining). Results. Culturing under IVD-like glucose conditions (1.0 mg/mL glucose) stimulated aggrecan and collagen-1 expression and caused a small increase in proliferation. In contrast, IVD-like osmolarity (485 mOsm) and pH (pH = 6.8) conditions strongly decreased proliferation and expression of matrix proteins, with more pronounced effects for osmolarity. Combining these 3 conditions also resulted in decreased proliferation, and gene expression of matrix proteins, demonstrating that osmolarity and pH dominated the effects of glucose. Both age groups showed a similar response pattern to the disc microenvironment. Conclusion. IVD repair using MSCs requires increased knowledge of MSC response to the chemical microenvironment. IVD-like low glucose enhanced matrix biosynthesis and maintained cell proliferation whereas IVD-like high osmolarity and low pH conditions were critical factors that reduced biosynthesis and proliferation of young and mature MSCs. Since osmolarity decreases and acidity increases during degeneration, we speculate that pH may be the major limitation for MSC-based IVD repair.