Alteration of NCoR Corepressor Splicing in Mice Causes Increased Body Weight and Hepatosteatosis without Glucose Intolerance

Abstract

Alternative mRNA splicing is an important means of diversifying function in higher eukaryotes. Notably, both NCoR and SMRT corepressors are subject to alternative mRNA splicing, yielding a series of distinct corepressor variants with highly divergent functions. Normal adipogenesis is associated with a switch in corepressor splicing from NCoR to NCoR␦, which appears to help regulate this differentiation process. We report here that mimicking this development switch in mice by a splice-specific whole-animal ablation of NCoR is very different from a whole-animal or tissue-specific total NCoR knockout and produces significantly enhanced weight gain on a high-fat diet. Surprisingly, NCoR ؊/؊ mice are protected against diet-induced glucose intolerance despite enhanced adiposity and the presence of multiple additional, prodiabetic phenotypic changes. Our results indicate that the change in NCoR splicing during normal development both helps drive normal adipocyte differentiation and plays a key role in determining a metabolically appropriate storage of excess calories. We also conclude that whole-gene "knockouts" fail to reveal how important gene products are customized, tailored, and adapted through alternative mRNA splicing and thus do not reveal all the functions of the protein products of that gene.

Regulation of corepressor alternative mRNA splicing by hormonal and metabolic signaling

“…Consistent with this observation, NCoRω is anti-adipogenic and NCoRδ is proadipogenic when overexpressed in 3T3-L1 cells (Goodson et al, 2011). In agreement with these conclusions based on ex vivo over expression, a whole mouse knockout of NCoRω increases adipose tissue size and weight gain, whereas the corresponding knockout of NCoRδ produces a lean phenotype (Goodson et al, 2014). The mouse knockout of NCoRω also produces a substantial increase in glucose sensitivity that renders the mice more resistant to obesity-induced diabetes.…”

“…The cDNAs derived from 25 ng RNA were amplified for 32 cycles using GoTaq DNA Polymerase (Promega, Madison, Wisconsin) and splice-specific primers (Supplemental Table 1). These splice-specific primer pairs flank each alternative splice-site and were used to yield multiple distinct-sized PCR products representing the individual corepressor isoforms generated from that particular alternative splicing location (Goodson et al, 2011, 2014). These PCR products were then loaded in individual lanes for each splice site, resolved by gel electrophoresis, detected by ethidium bromide staining, and quantified using an Alpha Innotech FluorChem 8900 and AlphaEase software (Version 3.1.2).…”

“…Conversely, NCoRδ incorporates a shorter version of this exon (37b−) that lacks this 3rd RID yet promotes adipose tissue formation (Goodson et al, 2011). Mice engineered to specifically ablate the NCoRω isoform also (somewhat paradoxically) exhibit a greatly improved glucose sensitivity that is refractory to diet induced diabetes (Goodson et al, 2014). Given that the different corepressor isoforms play distinct roles in energy metabolism (Goodson et al, 2011, 2014), targeting specific corepressor isoforms and understanding their regulation may serve as a particularly promising means for the treatment of metabolic disorders.…”

Role of co-regulators in metabolic and transcriptional actions of thyroid hormone

“…Consistent with the adipocyte-specific NCoR knockout phenotype, whole-body expression of the pro-adipogenic NCoRδ isoform results in protection from glucose intolerance despite increased weight gain and adiposity, as well as hepatic steatosis on a high-fat diet (Goodson et al 2014). These results indicate that adipocyte-specific change in NCoR splicing during development helps drive normal adipocyte differentiation, while the presence of the full-length NCoR splice variant prevents excessive fat accumulation in the liver.…”

“…To this end, mice bearing a conditional allele encoding for a mutant NCoR, termed NCoR∆ID, that is lacking the two N-terminal RID domains and is unable to interact with TR and liver X receptor (LXR) isoforms were generated (Astapova et al 2008). Recently, Goodson et al (2014) reported a mouse model (NCoRω −/− ) with a mutation introduced into a splicing site, which results in the inability to produce the full-length NCoRω isoform, and global expression of NCoRδ, containing only RID2 and RID1. In a similar approach, the Smrt mRID knock-in mouse model was created, where mutations were introduced into RID1 and RID2 domains, so that the resulting mutant Smrt mRID loses its ability to interact with RAR, TR, and PPAR isoforms (Nofsinger et al 2008).…”