Local modulation of glucocorticoid action in adipocytes regulates adiposity and systemic insulin sensitivity. However, the specific cofactors that mediate glucocorticoid receptor (GR) action in adipocytes remain unclear. Here we show that the silencing mediator of retinoid and thyroid hormone receptors (SMRT) is recruited to GR in adipocytes and regulates ligand-dependent GR function. Decreased SMRT expression in adipocytes in vivo increases expression of glucocorticoid-responsive genes. Moreover, adipocytes with decreased SMRT expression exhibit altered glucocorticoid regulation of lipolysis. We conclude that SMRT regulates the metabolic functions of GR in adipocytes in vivo. Modulation of GR-SMRT interactions in adipocytes represents a novel approach to control the local degree of glucocorticoid action and thus influence adipocyte metabolic function.

The Silencing Mediator of Retinoid and Thyroid Hormone Receptors (SMRT) is a nuclear corepressor, regulating the transcriptional activity of many transcription factors critical for metabolic processes. While the importance of the role of SMRT in the adipocyte has been well-established, our comprehensive understanding of its in vivo function in the context of homeostatic maintenance is limited due to contradictory phenotypes yielded by prior generalized knockout mouse models. Multiple such models agree that SMRT deficiency leads to increased adiposity, though the effects of SMRT loss on glucose tolerance and insulin sensitivity have been variable. We therefore generated an adipocyte-specific SMRT knockout (adSMRT-/-) mouse to more clearly define the metabolic contributions of SMRT. In doing so, we found that SMRT deletion in the adipocyte does not cause obesity – even when mice are challenged with a high-fat diet. This suggests that adiposity phenotypes of previously described models were due to effects of SMRT loss beyond the adipocyte. However, an adipocyte-specific SMRT deficiency still led to dramatic effects on systemic glucose tolerance and adipocyte insulin sensitivity, impairing both. This metabolically deleterious outcome was coupled with a surprising immune phenotype, wherein most genes differentially expressed in the adipose tissue of adSMRT-/- mice were upregulated in pro-inflammatory pathways. Flow cytometry and conditioned media experiments demonstrated that secreted factors from knockout adipose tissue strongly informed resident macrophages to develop a pro-inflammatory, MMe (metabolically activated) phenotype. Together, these studies suggest a novel role for SMRT as an integrator of metabolic and inflammatory signals to maintain physiological homeostasis.

Silencing Mediator of Retinoid and Thyroid Hormone Receptors (SMRT) is a nuclear corepressor, which regulates the transcriptional activity of metabolically essential transcription factors. While SMRT has been shown to modulate adipocyte function, in vivo experiments utilizing knock-out (KO) models have led to conflicting results. To more rigorously define the role of SMRT in the adipocyte, we generated adipocyte-specific SMRT KO (adSMRT KO) mice by crossing adiponectin-Cre mice with floxed SMRT mice on a C57/BL6 background. When adSMRT KO mice are challenged with a 45% high-fat diet, we observe 20% increase in glucose intolerance (p=0.006) compared to wild type (WT) counterparts. Additionally, RNA-Seq data of adipose tissue from these mice indicate a dramatic up-regulation of inflammatory gene expression. To further characterize the pro-inflammatory phenotype, we utilized flow cytometry to identify infiltration of specific populations of adipose tissue inflammatory cells. We found that overall macrophage infiltration in the adipose tissue of KO mice increased two-fold (p=0.026), with anti-inflammatory M2 macrophages infiltrating in significantly lower proportions (p=0.017), indicating a higher ratio of M1:M2 cells in the KO mice compared to WT. In contrast, body weight and total fat mass were not altered. These data suggest a role for SMRT in the cross-talk between adipocytes and pro-inflammatory macrophages for the regulation of systemic glucose tolerance, distinct from the development of obesity. SMRT therefore integrates metabolic and inflammatory signals to maintain physiological homeostasis. Disclosure J. Kahn: None. A.A. Goddi: None. R.N. Cohen: None.