Pcpe2 in Adipose Tissue Expansion and Lipoprotein Metabolism

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.