Culture media for the differentiation of mesenchymal stromal cells

Abstract

Mesenchymal stromal cells (MSCs) can be isolated from various tissues such as bone marrow aspirates, fat or umbilical cord blood. These cells have the ability to proliferate in vitro and differentiate into a series of mesoderm-type lineages, including osteoblasts, chondrocytes, adipocytes, myocytes and vascular cells. Due to this ability, MSCs provide an appealing source of progenitor cells which may be used in the field of tissue regeneration for both research and clinical purposes. The key factors for successful MSC proliferation and differentiation in vitro are the culture conditions. Hence, we here summarize the culture media and their compositions currently available for the differentiation of MSCs towards osteogenic, chondrogenic, adipogenic, endothelial and vascular smooth muscle phenotypes. However, optimal combination of growth factors, cytokines and serum supplements and their concentration within the media is essential for the in vitro culture and differentiation of MSCs and thereby for their application in advanced tissue engineering.

Introduction

Since Owen and Friedenstein’s work [1] it has been assumed that bone marrow contains special cells that can be expanded in vitro and differentiated into various mesoderm-type lineages, including bone, fat, cartilage, muscle, tendon, haematopoiesis-supporting stroma and vasculature [2], [3], [4], [5], [6]. We presently refer to these nonhematopoietic cells as mesenchymal stromal cell (MSC; Fig. 1) [7]. In addition, researchers have recently transdifferentiated MSCs into non-mesodermal cell types such as neuronal-like cells [8], [9], [10], [11] and pancreatic cell progenitors [12], [13], [14], [15].

To date, MSCs have been isolated not only from bone marrow but also from many other tissues and organs, including adipose tissue, umbilical cord blood, placental tissue, liver, spleen, testes, menstrual blood, amniotic fluid, pancreas and periosteum [16], [17], [18], [19], [20]. When cultured in vitro on polystyrene surfaces, MSCs reveal morphological heterogeneity. These cells can be narrow spindle-shaped, large polygonal or even cuboidal-shaped when growing into a confluent monolayer [21]. In adult human, MSCs lack the hematopoietic surface antigens, e.g. CD11, CD14, CD34 and CD45 [22]. Meanwhile numerous molecular markers have been found on MSC surface, but none of them is specific to MSCs. Despite this, molecules such as CD44, CD73, CD90, STRO-1 and CD105/SH2 [3], [23], [24], [25] are still currently used to identify MSCs.

MSCs are considered to be nonimmunogenic since these cells have been transplanted into allogeneic hosts even without using any immunosuppressive drugs [22], [26]. Furthermore, it has been reported that MSCs actually possess immunosuppressive properties by modulating the function of T-cells [27], [28], dendritic cells and B-cells [29], [30], [31], [32].

For the characterization of MSC plasticity, their ability to differentiate in vitro into osteoblasts, chondrocytes and adipocytes is currently treated as the gold standard. This, in combination with the advantages that MSCs have no immunogenicity and can be easily isolated from different tissues and expanded in vitro, enables MSCs to be a promising source of stem cells. Hence MSCs have been used in the therapy of diseases such as extended osseous defects [33], acute myocardial infarction [34], leukemia [35] and diabetes [36]. In addition, the homing capability endows MSCs with further potential applications. For example, MSCs may be used for supporting tissue regeneration [37], correcting congenital disorders (e.g. osteogenesis imperfecta [38]) and controlling chronic inflammatory diseases [39], [40], and have even employed as vehicles for the delivery of biological agents [22] and as probes in the biocompatibility test of new implant materials. A prerequisite for the therapeutic application of MSCs is to develop efficient and standardized protocols so that MSCs can be induced to differentiate along the way as required. Therefore, we here present an overview of the optimized protocols for MSC differentiation towards the osteogenic, chondrogenic, adipogenic, endothelial and vascular smooth muscle phenotypes.