Mesenchymal stem cells (MSCs) are fibroblastoid multipotent adult stem cells with a high capacity for selfrenewal and differentiation. These cells have been isolated from several human tissues, including bone marrow, adipose tissue, umbilical cord matrix, tendon, lung, and the periosteum.1 Recently it has been shown that MSC originate from the perivascular niche, a tight network present throughout the vasculature of the whole body. These perivascular cells lack endothelial and hematopoietic markers, e.g. CD31, CD34 and CD45, but express CD146, PDGFR beta, and alkaline phosphatase.2 According to the position paper published by the International Society for Cellular Therapy (ISCT), MSC express the surface markers CD73, CD90 and CD105 and stain negative for CD14 or CD11b, CD34, CD45, CD79α or CD19, and HLADR.3 In addition to surface marker analysis, the most common and reliable way to identify a population of MSC is to verify their multipotency. MSC can differentiate into adipocytes, osteoblasts, myocytes, and chondrocytes in vivo and in vitro.1,4 Transdifferentiation of MSC into cells of nonmesenchymal origin, such as hepatocytes, neurons and pancreatic islet cells, has also been observed in vitro when specific culture conditions and stimuli are applied.1 The directed differentiation of MSCs is carried out in vitro using appropriate differentiation media, such as the readytouse PromoCell MSC Differentiation Media (C-28016, C-28012, C-28014, C-28013, C-28015).
Figure 1. In vitro differentiation of human MSCs.Under appropriate culture conditions, multipotent human mesenchymal stem cells can differentiate into osteoblasts, adipocytes, chondrocytes, myocytes and neurons.
Figure 2. Alizarin Red S staining of extracellular calcium deposits in mineralized hMSCBM derived mature osteoblasts. MSC cells were cultured for 12 days in PromoCell MSC Growth Medium 2 for the negative control (upper panel) or MSC Osteogenic Differentiation Medium for the differentiation sample (lower panel). In contrast with the negative control, the mature osteoblasts differentiated from MSC show intense redorange staining of mineralized bone matrix. Note also the concentration of Alizarin Red S staining in some of the larger bone nodules.
Figure 3. Oil Red O staining of lipid droplets in hMSC-BM derived adipocytes.Lipid vesicle accumulation in adipocytes differentiated from hMSC-BM (human MSC derived from bone marrow) using the PromoCell MSC Adipogenic Differentiation Medium 2. The differentiated culture exhibits extensive intracellular lipid vacuole formation typical of mature adipocytes (left: 40x magnification; right: 100x magnification).
Figure 4. Alcian Blue staining of hMSC-BM derived chondrocytes.MSC spheroids after in vitro differentiation into cartilage using PromoCell MSC Chondrogenic Differentiation Medium. Spheroids cultured in the negative control medium stain light blue (upper row). In contrast, the induced spheroids exhibit an intensely blue color indicative of cartilage extracellular matrix (lower row).