Both white and brown adipose tissues exhibit extensive vascularity. Increased angiogenesis in brown adipose tissue (BAT) is crucial for brown fat activation and thermogenesis in animals during cold acclimation. BAT can be similarly activated by food intake to generate heat through cellular respiration, in a process known as diet induced thermogenesis. Vascular endothelial growth factor (VEGF) is a potent angiogenic factor that regulates both pathological and physiological angiogenesis and can stimulate cell proliferation, migration, survival and vessel permeability. However, VEGF has also been shown to affect an increasing number of non-vascular cells such as skeletal muscle and kidney podocytes. The expression and function of VEGF in white and brown adipocytes are not fully understood. We have previously shown that the expression of VEGF is concomitantly regulated with skeletal muscle differentiation. Here we show that VEGF is expressed in BAT and all major white adipose depots in mice. VEGF expression was increased during white and brown adipocyte differentiation and was regulated in cultured brown adipocytes by the \(PPAR\gamma\) agonist troglitazone and by \(PGC1\alpha\) in BAT in vivo. Systemic VEGF neutralization led to brown adipocyte apoptosis in vivo, loss of mitochondrial cristae and increased mitophagy and was associated with increased inflammation and fibrosis. VEGFR2 was expressed in both brown preadipocytes and adipocytes. Blockade of VEGF signaling using anti-VEGFR2 antibody DC101 increased brown adipocyte apoptosis in vitro. VEGF also functioned as a mitogen and survival factor for brown preadipocytes. VEGF 164 and VEGF 188, isoforms that can bind heparan sulfate proteoglycans, comprise >98% of total VEGF in BAT, subcutaneous and perigonadal fat depots. Embryos that lacked VEGF 164 and 188 displayed abnormal BAT development with fewer brown adipocytes, lower levels of mitochondrial uncoupling protein 1 and Cox IV. These results indicate a direct role for VEGF signaling in brown adipocytes and preadipocytes and suggest the importance of heparan sulfate binding VEGF isoforms in BAT development. Elucidation of the role of VEGF signaling in adipocytes is vital to understanding adipose tissue expansion and activation and may reveal novel therapeutic targets for the activation of brown fat in humans.
| Identifer | oai:union.ndltd.org:harvard.edu/oai:dash.harvard.edu:1/10417574 |
| Date | 06 August 2013 |
| Creators | Bagchi, Mandrita |
| Contributors | D’Amore, Patricia, Kahn, C. Ronald |
| Publisher | Harvard University |
| Source Sets | Harvard University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis or Dissertation |
| Rights | open |
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