Loss of MyoD Promotes Fate Transdifferentiation of Myoblasts Into Brown Adipocytes

Abstract

Brown adipose tissue (BAT) represents a promising agent to ameliorate obesity and other metabolic disorders. However, the abundance of BAT decreases with age and BAT paucity is a common feature of obese subjects. As brown adipocytes and myoblasts share a common Myf5 lineage origin, elucidating the molecular mechanisms underlying the fate choices of brown adipocytes versus myoblasts may lead to novel approaches to expand BAT mass. Here we identify MyoD as a key negative regulator of brown adipocyte development. CRISPR/CAS9-mediated deletion of MyoD in C2C12 myoblasts facilitates their adipogenic transdifferentiation. MyoD knockout downregulates miR-133 and upregulates the miR-133 target Igf1r, leading to amplification of PI3K–Akt signaling. Accordingly, inhibition of PI3K or Akt abolishes the adipogenic gene expression of MyoD null myoblasts. Strikingly, loss of MyoD converts satellite cell-derived primary myoblasts to brown adipocytes through upregulation of Prdm16, a target of miR-133 and key determinant of brown adipocyte fate. Conversely, forced expression of MyoD in brown preadipocytes blocks brown adipogenesis and upregulates the expression of myogenic genes. Importantly, miR-133a knockout significantly blunts the inhibitory effect of MyoD on brown adipogenesis. Our results establish MyoD as a negative regulator of brown adipocyte development by upregulating miR-133 to suppress Akt signaling and Prdm16.

Protein kinase CK2 subunits exert specific and coordinated functions in skeletal muscle differentiation and fusogenic activity

“…As a consequence, CK2b deletion prevents also the appearance of the later muscle differentiation markers and the formation of myotubes ( Fig. 2A-C, E), similarly to the phenotype previously described in Myod1 2/2 cells (61,62,64). Notably, the CK2b effect on MyoD expression seems to be independent of the CK2 catalytic subunits and holoenzyme activity based on the following pieces of evidence: 1) changes in MyoD protein level parallel those of CK2b (Fig.…”

A Molecular Switch Regulating Cell Fate Choice between Muscle Progenitor Cells and Brown Adipocytes

“…Several recent reports demonstrated that Prdm16 could also be suppressed post-transcriptionally in both myoblasts and white preadipocytes by miR-133, a cardiac and skeletal muscle-enriched microRNA (i.e., MyomiR) (Liu et al, 2013b;Pasut et al, 2016;Trajkovski et al, 2012;Yin et al, 2013b). Interestingly, miR-133 was also shown to be a direct transcriptional target of MyoD in cultured myoblasts (Pasut et al, 2016;Rao et al, 2006;Wang et al, 2017). In freshly isolated MPCs, we confirmed that miR-133 was indeed transcriptionally regulated by both MyoD and Myf5 ( Figure S6A).…”

“…The critical role of MyoD/Myf5 in suppressing the BA fate is also supported by existing data in literature. In a most recent study, deletion of Myod in myoblasts was also found to promote the cell fate change to BA in culture (Wang et al, 2017). In addition, in Myod/Myf5 double-KO mouse embryos, excessive fat tissues were found in the muscle-forming regions at the expense of muscles (Kablar et al, 2003).…”

“…The existing data and our own work here show that they antagonize each other mainly by inhibiting each other's expression. Ectopic expression of Prdm16 in myoblasts converted them to BA by suppressing the expression of Myod, while that of Myod in primary brown preadipocytes converted them to myocytes via suppression of Prdm16 (Seale et al, 2008;Wang et al, 2017). The precise mechanism for Prdm16-mediated Myod suppression remains unclear.…”

The requirement of Mettl3-promoted MyoD mRNA maintenance in proliferative myoblasts for skeletal muscle differentiation

“…The identification of MyoD and the MyoD family of myogenic regulatory factors (MRFs) has revealed that the myogenic potential is determined by the expression of transcription factors that influence myogenic gene expression. Conversely, the loss of MyoD and/or MRFs in skeletal myoblasts, both in vitro in C2C12 cells [ 11 , 12 ] and in vivo , suppresses skeletal myogenesis [ 13 , 14 ]. During differentiation, together with Pbx homeodomain protein, MyoD binds to the regulatory regions of myogenic genes, including Myog , Mylpf , Myh3 , Tnni and Ryr1 [ 15 ], which triggers chromatin remodelling by recruiting the SWI/SNF chromatin remodelling factor Brg1 for myogenic gene transcription [ 16 , 17 ].…”