Homing of Mesenchymal Stem Cells in Induced Degenerative Intervertebral Discs in a Whole Organ Culture System

Study Design. Homing of human bone marrow-derived mesenchymal stem cells (BMSCs) was studied using ex vivo cultured bovine caudal intervertebral discs (IVDs). Objective. To investigate in a whole organ culture whether metabolic and mechanical challenges can induce BMSC recruitment into the IVD. Summary of Background Data. Cells from injured tissues release cytokines and mediators that enable the recruitment of progenitor cells. BMSCs have the ability to survive within the IVD. Methods. Bovine IVDs with or without endplates were cultured for 1 week under simulated physiological or degenerative conditions; disc cells were analyzed for cell viability and gene expression, whereas media was analyzed for nitric oxide production and chemotaxis. Homing of BMSCs was investigated by supplying PKH-labeled human BMSCs onto cultured IVDs (1 x 10(6) cells/disc on d 8, 10, and 12 of culture); on day 14, the number of homed BMSCs was microscopically assessed. Moreover, a comparative study was performed between transduced BMSCs (transduced with an adenovirus encoding for insulin-like growth factor 1 [IGF-1]) and nontransduced BMSCs. Disc proteoglycan synthesis rate was quantified via S-35 incorporation. The secretion of IGF-1 was evaluated by enzyme-linked immunosorbent assay on both simulated physiological and degenerative discs. Results. Discs cultured under degenerative conditions showed reduced cell viability, upregulation of matrix degrading enzymes, and increased nitric oxide production compared with simulated physiological discs. Greater homing occurred under degenerative compared with physiological conditions with or without endplate. Media of degenerative discs demonstrated a chemoattractive activity toward BMSCs. Finally, discs homed with IGF-1 transduced BMSCs showed increased IGF-1 secretion and significantly higher proteoglycan synthesis rate than discs supplied with nontransduced BMSCs. Conclusion. We have demonstrated for the first time that degenerative conditions induce the release of factors promoting BMSC recruitment in an ex vivo organ culture. Moreover, IGF-1 transduction of BMSCs strongly increases the rate of proteoglycan synthesis within degenerative discs. This finding offers a new delivery system for BMSCs and treatment strategy for IVD regeneration.