SREBP-regulated adipocyte lipogenesis is dependent on substrate availability and redox modulation of mTORC1

The synthesis of lipid and sterol species through de novo lipogenesis (DNL) is regulated by 2 functionally overlapping but distinct transcription factors: the SREBPs and carbohydrate response element–binding protein (ChREBP). ChREBP is considered to be the dominant regulator of DNL in adipose tissue (AT); however, the SREBPs are highly expressed and robustly regulated in adipocytes, suggesting that the model of AT DNL may be incomplete. Here, we describe what we believe to be a new mouse model of inducible, adipocyte-specific overexpression of the insulin-induced gene 1 (Insig1), a negative regulator of SREBP transcriptional activity. Contrary to convention, Insig1 overexpression did block AT lipogenic gene expression. However, this was immediately met with a compensatory mechanism triggered by redox activation of mTORC1 to restore SREBP1 DNL gene expression. Thus, we demonstrate that SREBP1 activity sustains adipocyte lipogenesis, a conclusion that has been elusive due to the constitutive nature of current mouse models.