Increased prevalence of obesity in the US population continues to drive greater risk for developing type 2
diabetes and cardiovascular disease (CVD). Excessive caloric intake stresses adipocytes into storing lipid in an
unhealthy manner, directing lipid into existing adipocytes, known as adipocyte hypertrophy. On the other hand,
healthy adipose tissue expansion and remodeling occurs when adipose tissue precursor cells (PC) in the stromal
vascular fraction (SVF) differentiate to create new pre-adipocytes which store lipid, called hyperplasia. Single
cell sequencing of visceral adipose tissue (VAT) has identified two main types of PCs in the SVF, one called
adipocyte precursor cells (APCs), while the other is a fibroinflammatory adipocyte progenitors (FAPs). As their
names implies APC are pre-adipocytes which given the proper signals, differentiate into mature adipocytes, while
FAPs, can secrete cytokines inhibiting APC differentiation and initiating inflammation. Also influencing APC and
FAP lineage in the SVF are the transforming growth factor beta (TGFb)-like signaling pathways which inhibit
adipogenesis, while bone morphogenetic protein (BMP)-like signaling promotes adipogenesis. Overall, little is
known about how signaling through these pathways alters the fate of APCs and FAPs especially during increased
lipoprotein flux resulting from a high fat diet (HFD). Recently we discovered that both VAT PCs, APCs and FAPs
express high levels of the extracellular matrix (ECM) protein, procollagen endopeptidase enhancer protein 2
(Pcpe2, gene Pcolce2) whose expression decreases as APCs become committed adipocytes. We found that
Pcpe2 is significantly upregulated (>2-fold by HFD feeding) suggesting that Pcpe2 may play a role in TGFb-like
signaling pathways in VAT PCs. Thus, the study of how Pcpe2 expression impacts TGFb /BMP-like signaling
pathways within VAT PCs represents a major knowledge gap in our understanding of how PCs respond during
HFD induced adipose tissue expansion and remodeling. Based on our preliminary data and previous Pcpe2
studies in mature adipocytes from global Pcpe2 knockout mice, we hypothesize that PC-Pcpe2
expression stimulates TGFb-like and/or suppressing BMP-like signaling pathways in VAT resulting in
fibroinflammatory, hypertrophic adipose tissue and thus, unhealthy adipose expansion. To test our
hypothesis, we will carry out two aims; Aim 1: Elucidate the mechanism by which Pcpe2’s regulates TGFb and
BMP-like signaling using PC-specific Pcpe2-hemagglutinin tagged (HA) over-expressor (ox) (PC-PcpeoxHA) and
PC cell-specific Pcpe2 knockout (KO) (PC-Pcpe2KO) mice lines. Preliminary studies show PC-Pcpe2KO mice
have reduced (~35-40%) body and VAT weight, while PC-PcpeoxHA mice showed an increase (~40-45%) in body
and VAT weight, characterized by hypertrophic adipocytes. Aim 2 Investigate Pcpce2’s structure-function
relationship based on its newly identified mucin-like O-linked glycoprotein linker domain and examine its ECM
localization and function in TGFb-like signaling. Successful completion of these integrated but independent aims
will reveal novel mechanistic insight into the dysfunctional fat storage, Pcpe2, lipoprotein metabolism and CVD.