PROJECT 3: Z. ELIZABETH FLOYD, Ph.D.
Assistant Professor | View Bio
Mentor: Randall L. Mynatt, Ph.D.

ABSTRACT

Characterization of ubiquitin and ubiquitin-like modification of PPAR_y in Human Adipose-Derived Adult Stem Cells

Z. Elizabeth Floyd, Ph.D.

Obesity is a major concern in the United States today because it is associated with long-term and costly health problems such as diabetes and hypertension. Obesity is due to an increase in the size or number of adipocytes, which are commonly referred to as fat cells. The formation of adipocytes depends on a protein called the peroxisome proliferator-activated receptor gamma (PPAR_y), which is considered to be the “master switch” in producing adipocytes. PPAR_y controls the production of a range of genes dedicated to importing, storing, and releasing lipids in adipocytes. PPAR_y itself is controlled by many factors including a cellular system called the ubiquitin-proteasome pathway, which is responsible for the carefully timed destruction of most proteins found in the cell. Recent studies show that modulation of PPAR_y levels affects insulin sensitivity and protects against insulin resistance associated with aging. Much of our current knowledge about PPAR_y regulation in adipocytes comes from studies carried out in mice or cells in culture that are derived from mice. Our previous studies using the mouse 3T3-L1 adipocyte model system indicate regulation of PPAR_y levels by the ubiquitin-proteasome system is linked to control of PPAR_y activity. In addition, we have learned that modification of PPAR_y by the ubiquitin-like protein, SUMO-1, affects PPAR_y stability and activity. These studies suggest that modulation of PPAR_y by ubiquitin and ubiquitin-like proteins may play an important role in forming adipocytes and the development of obesity. While these studies are invaluable, we are interested in exploring how the ubiquitin-proteasome pathway functions to regulate PPAR_y in adipocytes derived from human sources.
In this study, we are beginning to describe the relationship between PPAR_y activity and ubiquitin-proteasome-dependent degradation using adult stem cells isolated from human liposuction aspirates. These primary cell cultures, identified as Adipose Derived Adult Stem Cells (ASCs), are an abundant resource that reliably produces adipocytes in culture. This allows us to study the relationship between PPAR_y activity and ubiquitin-dependent destruction in a human-based, clinically relevant model system. We hypothesize that modification of PPAR_y by ubiquitin and ubiquitin-like proteins is an important regulator of PPAR_y activity in human adipocytes. We have collected samples from eight donors, both lean and obese, and have carried out initial experiments to determine PPAR_y protein levels as well as establish assays to measure PPAR_y activity. We are now focused on examining the relationship between PPAR_y activation and ubiquitin-proteasome dependent destruction in human adipocytes.