Utility of transplantation in studying adipocyte biogenesis and function

Abstract

Adipose tissue plays important roles in the regulation of energy homeostasis and metabolism. Two features distinguish adipose tissue from other organs--the ability to greatly expand its mass, via increases in cell size and/or number, and the wide anatomical distribution. While adipose tissue function is greatly affected by adipocyte size and anatomic location, regulations of adipocyte size, number, and body fat distribution are poorly understood. Transplantation of either mature adipose tissue or adipocyte progenitor cells has been used in studying adipocyte function and biogenesis. In this review, we will attempt to summarize methodological considerations for transplantation, including selections of donor material, transplantation site and the length of transplantation study, as well as effects of these factors and vascularization and innervation on the function of transplants. Specific studies are also reviewed to illustrate the utility of adipose tissue transplants in studying adipose tissue function and biogenesis. The focus is on studies in three areas: (1) use of transplants in demonstrating adipose tissue function, such as effects of adipose tissue transplants on metabolism and energy homeostasis of the recipient animals and depot-specific differences in adipose tissue function; (2) use of transplantation to dissect direct or cell-autonomous from indirect or non-cell-autonomous effects of leptin signaling and sex on adipocyte size; (3) use of transplantation in the identification of adipocyte progenitor cells and lineage analysis. Finally, future applications of transplantation in studying depot-specific adipocyte biogenesis, and genetic and hormonal effects of sex and age on adipocyte biogenesis and function are discussed.

Figure 1

A schematic illustration of the transplantation technique for studying adipocyte biogenesis and function. Transplantation can be used to assess effects of specific cellular elements of adipose tissue (or intact tissue) on the physiology of recipient mice, such as energy intake and expenditure and disease susceptibility; influences of recipient mice on the transplants; or cell-autonomous functions of transplants. Whole adipose tissue, preadipocytes, or stromal vascular cells of adipose tissue (SVCs) can be used as donor materials. Various anatomic locations in recipient mice - as indicated - can be used as transplantation sites. Factors that influence the function and morphology of transplants and the effects of the transplants on recipient mice include anatomic location of the donor tissue and transplants, and sex, age, and genetic makeup of donor and recipient mice. The degree of vascularization and innervation of the transplants also affect their survival and function.