Plasma Fibronectin Regulates Adipocyte Differentiation and Lipid Droplet Size
Elahe Mirzarazi-Dahaghi1, Mahdokht Mahmoodi2 , Mari T. Kaartinen 1,2,3
1Department of Anatomy and Cell Biology, Faculty of Medicine and Health Sciences, 污污草莓视频 University, Montreal, QC, Canada, 2Faculty of Dental Medicine and Oral Health Sciences (Biomedical Sciences), 污污草莓视频 University, Montreal, QC, Canada, 3Department of Medicine (Division of Experimental Medicine), Faculty of Medicine and Health Sciences 污污草莓视频 University, Montreal, QC, Canada
Adipocytes are specialized connective tissue cell types capable of storing energy in the form of triglycerides in lipid droplets (LDs). LD biogenesis lies in the center of adipogenesis as the differentiation of preadipocytes to mature adipocytes is characterized by the accumulation of LDs within the cells. Extracellular matrix (ECM) plays a crucial role in regulating the differentiation of preadipocytes into mature adipocytes. Fibronectin (FN), a key ECM protein, exists as circulation plasma FN and cellular FN. FN matrix has been implicated in regulation of adipocyte morphology and in promoting preadipocyte and inhibiting adipocyte maturation in vitro. We have demonstrated that pFN assembly in vitro promotes preadipocyte proliferation and modulates insulin signaling, however, its full role in adipogenesis remains unknown as no in vivo models lacking FNs have not been investigated. Our novel work on plasma FN deficient mice (liver-specific Fn1 knockout) (pFN KO) shows dramatically smaller adipocytes in normal adipose tissue. Mice have also significantly increased adipose tissue insulin sensitivity. Here we hypothesized that pFN affects adipogenesis and LD accumulation and tested this in 3T3-L1 adipocyte cultures grown in the cell culture mediate with reduced pFN levels under adipogenic conditions. pFN was depleted from bovine serum with gelatin column which results in 65% reduction in pFN. At the endpoint of 12 days, LD accumulation was assessed via Bodipy and Oil red staining and differentiation via qPCR of adipocyte markers. Our data shows that pFN-reduced media results in no change in total lipid content but dramatically smaller LD size. qPCR analysis of adipocyte marker Cebpa showed no change, however, Pparg transcription factor was significantly reduced. This suggested that pFN reduction may block the terminal maturation of the cells and affect merging of LDs. Subcutaneous adipose tissue mRNA extracts from the pFN KO showed increased Pref1, preadipocyte marker, and interestingly increased Prdm16 and Ucp1, beige adipocyte and thermogenesis markers, respectively. No change in Cebpa levels and a slight increase in Pparg was seen. This demonstrates that pFN is a novel regulator of adipocyte differentiation in vitro and in vivo. Our observations shed light on the important function of ECM in regulating adipogenesis and provide insights for therapeutic interventions to sustain adipose tissue health where it is compromised like in lipodystrophies and obesity.