Search for the preadipocyte progenitor cell

Abstract

An increase in adipocyte number is a major contributor to the increase in adipose tissue mass that is characteristic of obesity. The identity and regulation of the adipocyte precursor cell (or preadipocyte) and the preadipocyte precursor cell (or progenitor cell) have been intensely studied for many years. In this issue of the JCI, Crossno et al. report that progenitor cells originating from outside the adipose tissue, in particular the bone marrow, can contribute to an increase in adipocyte number (see the related article beginning on page 3220). Their study in mice reveals that treatment with the thiazolidinedione rosiglitazone or exposure to a high-fat diet promotes the trafficking of circulating bone marrow-derived progenitor cells into adipose tissue, where they become multilocular adipocytes. This adds a new and unexpected dimension to this research arena.

Figure 1. Schematic representation of the basic features of adipose tissue expansion.

The major processes at work within adipose tissue are the proliferation of a progenitor cell population within the stromal vascular cell pool and the differentiation of these cells into adipose or vascular cells. These processes are regulated by stimulatory and inhibitory endocrine, neural, and paracrine/autocrine controls (17). Monoclonal antibodies raised against adipocyte surface proteins identify preadipocyte progenitors and closely associated developing blood vessels in developing adipose tissues (24). These observations were substantiated by examination of the preadipocyte progenitor cells and endothelial cells by electron microscopy and studies of the major extracellular components (25, 26). The study by Crossno et al. (7) in this issue of the JCI indicates that progenitor cells may also be delivered to adipose tissue by trafficking from extra-adipose sources, such as bone marrow, and that this trafficking my be upregulated by high-fat diet and TZD administration. TZDs also promote mobilization and homing of bone marrow–derived circulatory endothelial progenitor cells to various tissues in the process of endothelial regeneration (12, 13). The green cells in this figure represent cells originating from bone marrow that differentiate within adipose tissue to form clusters of multilocular adipocytes.