Dynamic Regulation of Genes Involved in Mitochondrial DNA Replication and Transcription during Mouse Brown Fat Cell Differentiation and Recruitment

Abstract

BackgroundBrown adipocytes are specialised in dissipating energy through adaptive thermogenesis, whereas white adipocytes are specialised in energy storage. These essentially opposite functions are possible for two reasons relating to mitochondria, namely expression of uncoupling protein 1 (UCP1) and a remarkably higher mitochondrial abundance in brown adipocytes.Methodology/Principal FindingsHere we report a comprehensive characterisation of gene expression linked to mitochondrial DNA replication, transcription and function during white and brown fat cell differentiation in vitro as well as in white and brown fat, brown adipose tissue fractions and in selected adipose tissues during cold exposure. We find a massive induction of the majority of such genes during brown adipocyte differentiation and recruitment, e.g. of the mitochondrial transcription factors A (Tfam) and B2 (Tfb2m), whereas only a subset of the same genes were induced during white adipose conversion. In addition, PR domain containing 16 (PRDM16) was found to be expressed at substantially higher levels in brown compared to white pre-adipocytes and adipocytes. We demonstrate that forced expression of Tfam but not Tfb2m in brown adipocyte precursor cells promotes mitochondrial DNA replication, and that silencing of PRDM16 expression during brown fat cell differentiation blunts mitochondrial biogenesis and expression of brown fat cell markers.Conclusions/SignificanceUsing both in vitro and in vivo model systems of white and brown fat cell differentiation, we report a detailed characterisation of gene expression linked to mitochondrial biogenesis and function. We find significant differences in differentiating white and brown adipocytes, which might explain the notable increase in mitochondrial content observed during brown adipose conversion. In addition, our data support a key role of PRDM16 in triggering brown adipocyte differentiation, including mitochondrial biogenesis and expression of UCP1.

MCT1 and MCT4 Expression and Lactate Flux Activity Increase During White and Brown Adipogenesis and Impact Adipocyte Metabolism

“…Oil Red O staining and immunoblotting for hormone-sensitive lipase (HSL) confirmed the robust differentiation using the protocol employed (Supplementary Fig. 1), in congruence with our previous reports 29,30 . Based on the in vivo expression levels and cold-induced changes (Fig.…”

“…1, isolation of total RNA, reverse transcription and quantitative real-time PCR was performed as described 29 , except that the SensiFAST SYBR Lo-ROX Kit (Bioline) was used. For Fig.…”

NAT8L (N-Acetyltransferase 8-Like) Accelerates Lipid Turnover and Increases Energy Expenditure in Brown Adipocytes

“…Moreover, our studies using the enzymatically inactive protein support this concept because the D165A mutant does not increase lipogenesis. PPAR␣, its coactivator PGC1␣ (43,44), and PRDM16 (45) have been shown to be important for mitochondrial biogenesis. Elevated expression of all of these genes upon Nat8l overexpression could explain the increase in mitochondria in these cells.…”

Dynamic regulation of mitochondrial network and oxidative functions during 3T3-L1 fat cell differentiation

“…Brown adipocytes undergo profound differentiation program leading to increased mitochondrial mass with a specialized function of uncoupling the proton gradient from ATP synthesis in order to produce heat. Expression of genes involved in mitochondrial machinery during differentiation of white adipose cells has been shown to be limited to just a few genes compared to brown fat [23]. White adipose differentiation transforms "basic" fibroblastic preadipocyte metabolism into lipid storage structured in triglyceride droplets.…”