“Synapse-like” connections between adipocytes and stem cells: morphological and molecular features of human adipose tissue

Abstract

Adult mesenchymal stem cells are a heterogeneous population of stem cell that is not completely defined. The importance of increasing knowledge of this cell population will allow us to understand how to use them in multiple treatments for various diseases. Adipose tissue is a rich source from which to easily obtain a great amount of stem cells. We explore and study adipose stem cells (AdSCs) from human abdominal tissue by immunohistochemical analysis, transmission (TEM) and scanning (SEM) electron microscopy. The focus of this study is on the cell population that surrounds each adipocyte. In these populations of cells are included the adipose tissue stem cells (AdSCs) with different potentiality. We observe that the putative AdSCs have an intimate relationship involving close contact with adipocytes which we define here as “synapse-like.” We show “synapse-like” connections between adipocytes and small cells to be mediated by connexin43 (Cx43). Our data suggest AdSCs constitute a heterogeneous population both in size and expression of different stem cell markers. We found that some of the AdSC attached to adipocytes are positive for Sox2, Pax6 and Nestin by immunostaining methods. TEM and SEM analysis demonstrate that small cells and adipocytes are surrounded by a compact mesh of collagen fibers that maintain physical adhesion between these cells. TEM also shows structural characteristics of putative stem cells and a presence of vesicles in synapse-like contact. SEM images moreover exhibited a large variation and quantity of cell sizes coexisting with adipocytes. Direct cell-to-cell communication could serve at least two purposes: a) as a survival strategy to maintain cells as stem cells, and b) as a source of signaling for differentiation into a new cell type.