Ester Banayo

AMPK and PPARδ Agonists Are Exercise Mimetics

The benefits of endurance exercise on general health make it desirable to identify orally active agents that would mimic or potentiate the effects of exercise to treat metabolic diseases. Although certain natural compounds, such as reseveratrol, have endurance-enhancing activities, their exact metabolic targets remain elusive. We therefore tested the effect of pathway-specific drugs on endurance capacities of mice in a treadmill running test. We found that PPARbeta/delta agonist and exercise training synergistically increase oxidative myofibers and running endurance in adult mice. Because training activates AMPK and PGC1alpha, we then tested whether the orally active AMPK agonist AICAR might be sufficient to overcome the exercise requirement. Unexpectedly, even in sedentary mice, 4 weeks of AICAR treatment alone induced metabolic genes and enhanced running endurance by 44%. These results demonstrate that AMPK-PPARdelta pathway can be targeted by orally active drugs to enhance training adaptation or even to increase endurance without exercise.

Ataxin 1, a SCA1 neurodegenerative disorder protein, is functionally linked to the silencing mediator of retinoid and thyroid hormone receptors

Ataxin 1 (Atx1) is a foci-forming polyglutamine protein of unknown function, whose mutant form causes type 1 spinocerebellar ataxia in humans and exerts neurotoxicity in transgenic mouse and fly expressing mutant Atx1. In this study, we demonstrate that Atx1 interacts with the transcriptional corepressor SMRT (silencing mediator of retinoid and thyroid hormone receptors) and with histone deacetylase 3. Atx1 binds chromosomes and mediates transcriptional repression when tethered to DNA. Interaction with SMRT-related factors is a conserved feature of Atx1, because Atx1 also binds SMRTER, a Drosophila cognate of SMRT. Significantly, mutant Atx1 forms aggregates in Drosophila, and such mutant Atx1-mediated aggregates sequester SMRTER. Consistently, the neurodegenerative eye phenotype caused by mutant Atx1 is enhanced by a Smrter mutation and, conversely, is suppressed by a chromosomal duplication that contains the wild type Smrter gene. Together, our results suggest that Atx1 is a transcriptional factor whose mutant form exerts its deleterious effects in part by perturbing corepressor-dependent transcriptional pathways.

Exercise and PGC-1α-Independent Synchronization of Type I Muscle Metabolism and Vasculature by ERRγ

How type I skeletal muscle inherently maintains high oxidative and vascular capacity in the absence of exercise is unclear. We show that nuclear receptor ERRγ is highly expressed in type I muscle and, when transgenically expressed in anaerobic type II muscles (ERRGO mice), dually induces metabolic and vascular transformation in the absence of exercise. ERRGO mice show increased expression of genes promoting fat metabolism, mitochondrial respiration, and type I fiber specification. Muscles in ERRGO mice also display an activated angiogenic program marked by myofibrillar induction and secretion of proangiogenic factors, neovascularization, and a 100% increase in running endurance. Surprisingly, the induction of type I muscle properties by ERRγ does not involve PGC-1α. Instead, ERRγ genetically activates the energy sensor AMPK in mediating the metabovascular changes in ERRGO mice. Therefore, ERRγ represents a previously unrecognized determinant that specifies intrinsic vascular and oxidative metabolic features that distinguish type I from type II muscle.

Circadian Amplitude Regulation via FBXW7-Targeted REV-ERBα Degradation

Defects in circadian rhythm influence physiology and behavior with implications for the treatment of sleep disorders, metabolic disease, and cancer. Although core regulatory components of clock rhythmicity have been defined, insight into the mechanisms underpinning amplitude is limited. Here, we show that REV-ERBα, a core inhibitory component of clock transcription, is targeted for ubiquitination and subsequent degradation by the F-box protein FBXW7. By relieving REV-ERBα-dependent repression, FBXW7 provides an unrecognized mechanism for enhancing the amplitude of clock gene transcription. Cyclin-dependent kinase 1 (CDK1)-mediated phosphorylation of REV-ERBα is necessary for FBXW7 recognition. Moreover, targeted hepatic disruption of FBXW7 alters circadian expression of core clock genes and perturbs whole-body lipid and glucose levels. This CDK1-FBXW7 pathway controlling REV-ERBα repression defines an unexpected molecular mechanism for re-engaging the positive transcriptional arm of the clock, as well as a potential route to manipulate clock amplitude via small molecule CDK1 inhibition.

Abstract 5065: Harnessing epigenetic reprogramming by histone deacetylase inhibitor MS275 for pancreatic cancer therapy

Pancreatic ductal adenocarcinoma (PDAC) accounts for more than 85% of pancreatic cancer and is one of the most lethal malignancies with limited therapeutic options. Chromatin-modulating small molecules, or epigenetic drugs, have the ability to reprogram cell fate and alter disease phenotypes. The potential of these drugs for PDAC therapy remains to be fully investigated. Screening a panel of epigenetic drugs identified MS275 (MS, also called entinostat), a histone deacetylase inhibitor, as capable of suppressing PDAC cell proliferation and inhibiting stromal fibrosis. Genome-wide expression analysis revealed that MS extensively reprograms the transcriptomes of tumor cells and cancer-associated fibroblasts (CAFs). In tumor cells, MS downregulates genes important for cell cycle progression inducing cytostasis. In CAFs, MS specifically represses the profibrotic transcription program responsive to TGF-beta, effectively inhibiting the fibrotic response. Consistent with this, MS blocks the activation of pancreatic stellate cells, the primary source for CAFs in PDAC, to repress the fibroblast-like phenotypes in these cells. Using an orthotopic transplantation model, we confirmed that MS treatment reduces tumor cell proliferation and decreases intratumoral fibrotic content. Importantly, we showed that MS substantially enhances chemocytotoxicity, synergizing with gemcitabine to reduce tumor burden in PDAC mouse models. Our study establishes a novel therapeutic strategy for PDAC based on epigenetic reprogramming induced by HDAC inhibition. Citation Format: Gaoyang Liang, Ruth Yu, Christopher Liddle, Morgan Truitt, Corina Antal, Annette Atkins, Ester Banayo, Michael Downes, Ronald Evans. Harnessing epigenetic reprogramming by histone deacetylase inhibitor MS275 for pancreatic cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5065. doi:10.1158/1538-7445.AM2017-5065