MuRF2 regulates PPARγ1 activity to protect against diabetic cardiomyopathy and enhance weight gain induced by a high fat diet

Abstract

BackgroundIn diabetes mellitus the morbidity and mortality of cardiovascular disease is increased and represents an important independent mechanism by which heart disease is exacerbated. The pathogenesis of diabetic cardiomyopathy involves the enhanced activation of PPAR transcription factors, including PPARα, and to a lesser degree PPARβ and PPARγ1. How these transcription factors are regulated in the heart is largely unknown. Recent studies have described post-translational ubiquitination of PPARs as ways in which PPAR activity is inhibited in cancer. However, specific mechanisms in the heart have not previously been described. Recent studies have implicated the muscle-specific ubiquitin ligase muscle ring finger-2 (MuRF2) in inhibiting the nuclear transcription factor SRF. Initial studies of MuRF2−/− hearts revealed enhanced PPAR activity, leading to the hypothesis that MuRF2 regulates PPAR activity by post-translational ubiquitination.MethodsMuRF2−/− mice were challenged with a 26-week 60% fat diet designed to simulate obesity-mediated insulin resistance and diabetic cardiomyopathy. Mice were followed by conscious echocardiography, blood glucose, tissue triglyceride, glycogen levels, immunoblot analysis of intracellular signaling, heart and skeletal muscle morphometrics, and PPARα, PPARβ, and PPARγ1-regulated mRNA expression.ResultsMuRF2 protein levels increase ~20% during the development of diabetic cardiomyopathy induced by high fat diet. Compared to littermate wildtype hearts, MuRF2−/− hearts exhibit an exaggerated diabetic cardiomyopathy, characterized by an early onset systolic dysfunction, larger left ventricular mass, and higher heart weight. MuRF2−/− hearts had significantly increased PPARα- and PPARγ1-regulated gene expression by RT-qPCR, consistent with MuRF2’s regulation of these transcription factors in vivo. Mechanistically, MuRF2 mono-ubiquitinated PPARα and PPARγ1 in vitro, consistent with its non-degradatory role in diabetic cardiomyopathy. However, increasing MuRF2:PPARγ1 (>5:1) beyond physiological levels drove poly-ubiquitin-mediated degradation of PPARγ1 in vitro, indicating large MuRF2 increases may lead to PPAR degradation if found in other disease states.ConclusionsMutations in MuRF2 have been described to contribute to the severity of familial hypertrophic cardiomyopathy. The present study suggests that the lack of MuRF2, as found in these patients, can result in an exaggerated diabetic cardiomyopathy. These studies also identify MuRF2 as the first ubiquitin ligase to regulate cardiac PPARα and PPARγ1 activities in vivo via post-translational modification without degradation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12933-015-0252-x) contains supplementary material, which is available to authorized users.

The E3 ubiquitin ligase MuRF2 attenuates LPS‐induced macrophage activation by inhibiting production of inflammatory cytokines and migration

“…Lange et al [10] found that MuRF2 could translocate into nuclei and regulate the activity of the nuclear transcription factor SRF in myocytes. Coincidentally, another study performed by He et al [30] identified that MuRF2 could also regulate the nuclear transcription factor PPAR-c1 in cardiomyocytes. Our study found that MuRF2 translocated into nuclei in LPS-stimulated RAW264.7 cells compared with control groups.…”

“…Coincidentally, another study performed by He et al . identified that MuRF2 could also regulate the nuclear transcription factor PPAR‐γ1 in cardiomyocytes. Our study found that MuRF2 translocated into nuclei in LPS‐stimulated RAW264.7 cells compared with control groups.…”

MuRF1 mono-ubiquitinates TRα to inhibit T3-induced cardiac hypertrophy in vivo

“…5D, blue box). While the identification of a mono-ubiquitinated TRα was not achieved, we did identify the common dichotomy competing mono- and poly-ubiquitin for substrates, known to be dependent on the types of E2 present and ratios of E3 to substrates (He et al 2015, Kim et al 2007, Lai et al 2001). …”

“…By mono-ubiquitinating one to three lysines adjacent to a newly identified nuclear export sequence in PPARα, MuRF1 inhibited PPARα-regulated fatty acid oxidation both in vitro and in vivo (Rodriguez et al 2015). Complementary to these studies, the closely related muscle-specific ubiquitin ligase MuRF2 inhibited PPARγ 1 (He et al 2015), whereas MuRF3 inhibited PPARβ activity in vivo by mono-ubiquitination (Quintana et al 2015). In this study, we identify the cardiac ubiquitin ligase MuRF1 as an inhibitor of T3-induced physiological cardiac hypertrophy in vivo .…”

Cardiac ubiquitin ligases: Their role in cardiac metabolism, autophagy, cardioprotection and therapeutic potential

“…fatty acid metabolism) 146–148 . Complementary to this, cardiac MuRF2 and MuRF3 family members attenuate PPARβ/δ and/or PPARγ1 activities to protect against PPAR-ligand induced cardiomyopathy seen in high fat diet challenges in vivo 149,150 .…”