Mesenchymal Stromal Cells and Tissue-Specific Progenitor Cells: Their Role in Tissue Homeostasis

Abstract

Multipotent mesenchymal stromal/stem cells (MSCs) reside in many human organs and comprise heterogeneous population of cells with self-renewal ability. These cells can be isolated from different tissues, and their morphology, immunophenotype, and differentiation potential are dependent on their tissue of origin. Each organ contains specific population of stromal cells which maintain regeneration process of the tissue where they reside, but some of them have much more wide plasticity and differentiate into multiple cells lineage. MSCs isolated from adult human tissues are ideal candidates for tissue regeneration and tissue engineering. However, MSCs do not only contribute to structurally tissue repair but also MSC possess strong immunomodulatory and anti-inflammatory properties and may influence in tissue repair by modulation of local environment. This paper is presenting an overview of the current knowledge of biology of tissue-resident mesenchymal stromal and progenitor cells (originated from bone marrow, liver, skeletal muscle, skin, heart, and lung) associated with tissue regeneration and tissue homeostasis.

Figure 1

Tissue distribution and the phenotype of tissue-resident stem cells characterized by immunocytochemistry for CD45, CD34, CD73, CD90, c-kit, and Pax7. Tissue samples were collected from skin, liver, heart, and skeletal muscle. Immunostaining for CD45 and CD34 (arrows) illustrated the presence of cells of hematopoietic origin in the tissues. Note CD34 positivity on the vessel endothelial cells. Common feature of tissue localized stem cells was expression of CD73, CD90, and c-kit. Skeletal muscle progenitor cells exclusively express transcriptional factor Pax7. CD73, CD90, and c-kit were expressed on single stem cells of examined tissues and were localized in specific tissue compartments: in the basal layer of epidermis, the epithelium of adnexal structure of the skin, the periportal area of the liver, between the basal lamina and sarcolemma of myofibers of the muscle, and were connected to myocytes and fibroblasts in the cardiac niches.