Early enforcement of cell identity by a functional component of the terminally differentiated state

Abstract

How differentiating progenitor cells can attain a distinct differentiated cell-identity is a challenging problem given the promiscuous nature of critical transcription factors and the typically fluctuating signaling environment in which cells exist. Here we test the hypothesis that a unique and robust differentiated cell identity can result from a core component of the differentiated state doubling up such that it has key functions in the differentiated state and also works at low levels as a positive-feedback signaling mediator that drives progenitor cells to differentiate. Using live single-cell fluorescence imaging analysis in the adipocyte differentiation system, we show that FABP4, one of the most abundant core components that buffers lipids in differentiated adipocytes, regulates at low levels expression of PPARG, the master regulator of adipocyte differentiation. Adipocyte progenitor cells transition from a priming phase of differentiation to a second phase during which low levels of FABP4 and PPARG mutually reinforce each other's expression. In this way both proteins reach a threshold where cells irreversibly commit to the differentiated state. Before and after reaching this threshold, PPARG transcriptionally increases FABP4 expression while fatty-acid loaded FABP4 binds to and increases PPARG activity. Together, our study suggests a control principle for robust cell identity, whereby a core component of the differentiated state also promotes differentiation from its own progenitor state. HIGHLIGHTS• Only a small fraction (~10%) of the maximally reached FABP4 levels in cells is needed to commit cells to the differentiated state.• Mature adipocytes express levels of FABP4 ten times the minimal level needed to commit cells to the differentiated state, thus providing an explanation for why the mature adipocyte state is so stable.• Fatty-acid loaded FABP4 binds to and activates PPARG, thereby turning on PPARG positive feedback loops that increase PPARG expression.• FABP4 critically controls the second phase of adipogenesis between activation of the feedback loops and reaching the threshold to differentiate.

Bifidobacterium longum subsp. infantis YB0411 Inhibits Adipogenesis in 3T3-L1 Pre-adipocytes and Reduces High-Fat-Diet-Induced Obesity in Mice

“…These major factors, C/EBPα, PPARγ, and C/EBPβ, co-adjust each other’s expression during regulation of the whole adipogenesis process . Fatty-acid-binding protein 4, aP2, is another late-stage adipogenesis factor that has been found to increase with the expression of PPARγ . In addition, PPARγ co-activator sirtuin 1 (SIRT1) regulates glucose metabolism in adipogenesis, where acetyl-CoA carboxylase (ACC) induces lipogenesis, which is a key factor for adipocyte maturation. , The initiation of adipogenesis is widely known to be controlled by several kinases such as AMP-activated protein kinase (AMPK), mammalian target of rapamycin complex 1 (mTOR1), protein kinase A (PKA), p38 mitogen-activated protein kinase (p38 MAPK), and phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT). , Researchers have shown the relevance of AMPK to anti-adipogenesis and inhibition of lipid synthesis. , Furthermore, AMPK activation induces thermogenesis, including lipid metabolism and glucose transport via brown differentiation of white adipocytes .…”