Co-culture of annulus fibrosus cells and bone marrow mesenchymal stem cells

CD146/MCAM distinguishes stem cell subpopulations with distinct migration and regenerative potential in degenerative intervertebral discs

OBJECTIVE

This study aimed to characterize the mesenchymal stem cell (MSC) subpopulation migrating towards a degenerated intervertebral disc (IVD) and to assess its regenerative potential.

DESIGN

Based on initial screening for migration towards C-C motif chemokine ligand 5 (CCL5), the migration potential of CD146+ and CD146- mesenchymal stem cells (MSCs) was evaluated in vitro and in a degenerated organ culture model (degeneration by high-frequency loading in a bioreactor). Discogenic differentiation potential of CD146+ and CD146- MSCs was investigated by in vitro pellet culture assay with supplementation of growth and differentiation factor-6 (GDF6). Furthermore, trypsin degenerated IVDs were treated by either homing or injection of CD146+ or CD146- MSCs and glycosaminoglycan synthesis was evaluated by Sulphur 35 incorporation after 35 days of culture.

RESULTS

Surface expression of CD146 led to a higher number of migrated MSCs both in vitro and in organ culture. CD146+ and CD146- pellets responded with a similar up-regulation of anabolic markers. A higher production of sulfated glycosaminoglycans (sGAG)/DNA was observed for CD146+ pellets, while in organ cultures, sGAG synthesis rate was higher for IVDs treated with CD146- MSCs by either homing or injection.

CONCLUSIONS

The CD146+ MSC subpopulation held greater migration potential towards degenerative IVDs, while the CD146- cells induced a stronger regenerative response in the resident IVD cells. These findings were independent of the application route (injection vs migration). From a translational point of view, our data suggests that CD146+ MSCs may be suitable for re-population, while CD146- MSCs may represent the primary choice for stimulation of endogenous IVD cells.

Intervertebral disc response to stem cell treatment is conditioned by disc state and cell carrier: An ex vivo study

In vitro and in vivo studies evidenced that mesenchymal stem cells (MSCs) contribute to intervertebral disc (IVD) regeneration by differentiation towards the disc phenotype and matrix synthesis and/or by paracrine signalling to endogenous cells, thereby promoting a healthier disc phenotype in degenerative discs. The aim of this study was to investigate IVD response to human MSC (hMSC) treatment based on the disc degenerative state and hMSC carrier. Bovine caudal IVDs with endplates were cultured in a bioreactor under simulated physiological (0.1 Hz load and sufficient glucose) or degenerative (10 Hz load and limited glucose) conditions for 7 days. Discs were partially nucleotomised, restored with hMSCs in either fibrin gel or saline solution and cultured under physiological conditions for 7 days. Controls included fibrin and saline without hMSCs. Cell viability, histology, disc height, and gene expression analyses were performed to evaluate regeneration. hMSCs in fibrin were viable and homogenously distributed following 7 days of culture under dynamic loading in partially nucleotomised discs. IVD response to hMSCs was conditioned by both disc degenerative state and hMSC carrier. The effect of the regenerative treatment was stronger on simulated-degenerative discs than on simulated-physiological discs. hMSCs in fibrin induced a superior anabolic response in degenerative IVDs compared with fibrin alone, thus suggesting an added value of the cellular therapy compared with an acellular solution. When comparing fibrin and saline as a hMSC carrier, a significantly higher anabolic response was observed in IVDs treated with hMSCs in fibrin. Moreover, it was found that the degenerative state of the disc influenced hMSC differentiation. Indeed, a significantly higher expression of specific discogenic markers (ACAN and CA12) was observed in hMSCs implanted into physiological discs than in those implanted into degenerative discs. In conclusion, host disc cells and donor hMSC response depend on the degenerative state of the host disc and carrier used for hMSC delivery, and these two aspects need to be considered for a successful translation of hMSC therapies for the treatment of IVD degeneration.

Strategies to Optimize Adult Stem Cell Therapy for Tissue Regeneration

Stem cell therapy aims to replace damaged or aged cells with healthy functioning cells in congenital defects, tissue injuries, autoimmune disorders, and neurogenic degenerative diseases. Among various types of stem cells, adult stem cells (i.e., tissue-specific stem cells) commit to becoming the functional cells from their tissue of origin. These cells are the most commonly used in cell-based therapy since they do not confer risk of teratomas, do not require fetal stem cell maneuvers and thus are free of ethical concerns, and they confer low immunogenicity (even if allogenous). The goal of this review is to summarize the current state of the art and advances in using stem cell therapy for tissue repair in solid organs. Here we address key factors in cell preparation, such as the source of adult stem cells, optimal cell types for implantation (universal mesenchymal stem cells vs. tissue-specific stem cells, or induced vs. non-induced stem cells), early or late passages of stem cells, stem cells with endogenous or exogenous growth factors, preconditioning of stem cells (hypoxia, growth factors, or conditioned medium), using various controlled release systems to deliver growth factors with hydrogels or microspheres to provide apposite interactions of stem cells and their niche. We also review several approaches of cell delivery that affect the outcomes of cell therapy, including the appropriate routes of cell administration (systemic, intravenous, or intraperitoneal vs. local administration), timing for cell therapy (immediate vs. a few days after injury), single injection of a large number of cells vs. multiple smaller injections, a single site for injection vs. multiple sites and use of rodents vs. larger animal models. Future directions of stem cell-based therapies are also discussed to guide potential clinical applications.