Figure 7. Partnership between Pcpe2 and SR-BI in HDL-C uptake.

The stromal vascular fraction contains progenitor cells that differentiate into adipocytes. During the fed-state, adipocytes store energy as lipids in two ways: (i) hyperplasic expansion where cells receive signals to differentiate and increase in number or (ii) hypertrophic expansion where existing cells take on more triglycerides. Hypertrophic adipocyte morphology is positively associated with insulin resistance, diabetes and cardiovascular disease. In Pcpe2 null mice, hypertrophic adipocytes were associated with decreased adipose mass, independent of body weight, and a reciprocal elevation in plasma lipoprotein triglyceride and cholesterol concentrations. Paradoxically, in the absence of Pcpe2, these hypertrophic adipocytes were also associated with improved glucose tolerance, less inflammation and increased SR-BI expression. Based on these cumulative observations, we hypothesize that Pcpe2 partners with SR-BI in the extracellular matrix surrounding adipocytes, thereby facilitating the uptake of lipoprotein lipids for storage.