Search

Significance Glucocorticoids are widely prescribed antiinflammatory drugs that suppress inflammatory gene expression through activation of the glucocorticoid receptor (GR); however, the mechanisms of GR-mediated repression are not fully understood. We show here that bromodomain containing 9 (BRD9), a component of the SWI/SNF chromatin remodeling complex, modulates GR activity in bone marrow-derived macrophages. Loss of BRD9 activity in macrophages attenuated the response to liposaccharides and interferon inflammatory stimuli. Notably, BRD9 inhibition synergized with the synthetic glucocorticoid dexamethasone to suppress the inflammatory response in macrophages. Our data support a model in which BRD9 restricts GR binding at a subset of inflammatory related genes, and suggests that BRD9 inhibitors may increase the efficacy of glucocorticoids., In macrophages, homeostatic and immune signals induce distinct sets of transcriptional responses, defining cellular identity and functional states. The activity of lineage-specific and signal-induced transcription factors are regulated by chromatin accessibility and other epigenetic modulators. Glucocorticoids are potent antiinflammatory drugs; however, the mechanisms by which they selectively attenuate inflammatory genes are not yet understood. Acting through the glucocorticoid receptor (GR), glucocorticoids directly repress inflammatory responses at transcriptional and epigenetic levels in macrophages. A major unanswered question relates to the sequence of events that result in the formation of repressive regions. In this study, we identify bromodomain containing 9 (BRD9), a component of SWI/SNF chromatin remodeling complex, as a modulator of glucocorticoid responses in macrophages. Inhibition, degradation, or genetic depletion of BRD9 in bone marrow-derived macrophages significantly attenuated their responses to both liposaccharides and interferon inflammatory stimuli. Notably, BRD9-regulated genes extensively overlap with those regulated by the synthetic glucocorticoid dexamethasone. Pharmacologic inhibition of BRD9 potentiated the antiinflammatory responses of dexamethasone, while the genetic deletion of BRD9 in macrophages reduced high-fat diet-induced adipose inflammation. Mechanistically, BRD9 colocalized at a subset of GR genomic binding sites, and depletion of BRD9 enhanced GR occupancy primarily at inflammatory-related genes to potentiate GR-induced repression. Collectively, these findings establish BRD9 as a genomic antagonist of GR at inflammatory-related genes in macrophages, and reveal a potential for BRD9 inhibitors to increase the therapeutic efficacies of glucocorticoids.

As an opportunistic predator, the Burmese python (Python molurus bivittatus) consumes large and infrequent meals, fasting for up to a year. Upon consuming a large meal, the Burmese python exhibits extreme metabolic responses. To define the pathways that regulate these postprandial metabolic responses, we performed a comprehensive profile of plasma metabolites throughout the digestive process. Following ingestion of a meal equivalent to 25% of its body mass, plasma lipoproteins and metabolites, such as chylomicra and bile acids, reach levels observed only in mammalian models of extreme dyslipidemia. Here, we provide evidence for an adaptive response to postprandial nutrient overload by the python liver, a critical site of metabolic homeostasis. The python liver undergoes a substantial increase in mass through proliferative processes, exhibits hepatic steatosis, hyperlipidemia-induced insulin resistance indicated by PEPCK activation and pAKT deactivation, and de novo fatty acid synthesis via FASN activation. This postprandial state is completely reversible. We posit that Burmese pythons evade the permanent hepatic damage associated with these metabolic states in mammals using evolved protective measures to inactivate these pathways. These include a transient activation of hepatic nuclear receptors induced by fatty acids and bile acids, including PPAR and FXR, respectively. The stress-induced p38 MAPK pathway is also transiently activated during the early stages of digestion. Taken together, these data identify a reversible metabolic response to hyperlipidemia by the python liver, only achieved in mammals by pharmacologic intervention. The factors involved in these processes may be relevant to or leveraged for remediating human hepatic pathology.

Summary ParagraphWe identify the prolyl-tRNA synthetase (PRS) inhibitor halofuginone1, a compound in clinical trials for anti-fibrotic and anti-inflammatory applications2, as a potent inhibitor of SARS-CoV-2 infection and replication. The interaction of SARS-CoV-2 spike protein with cell surface heparan sulfate (HS) promotes viral entry3. We find that halofuginone reduces HS biosynthesis, thereby reducing spike protein binding, SARS-CoV-2 pseudotyped virus, and authentic SARS-CoV-2 infection. Halofuginone also potently suppresses SARS-CoV-2 replication post-entry and is 1,000-fold more potent than Remdesivir4. Inhibition of HS biosynthesis and SARS-CoV-2 infection depends on specific inhibition of PRS, possibly due to translational suppression of proline-rich proteins. We find that pp1a and pp1ab polyproteins of SARS-CoV-2, as well as several HS proteoglycans, are proline-rich, which may make them particularly vulnerable to halofuginone’s translational suppression. Halofuginone is orally bioavailable, has been evaluated in a phase I clinical trial in humans and distributes to SARS-CoV-2 target organs, including the lung, making it a near-term clinical trial candidate for the treatment of COVID-19.

While 92 million Americans are currently estimated to have some form of cardiovascular disease (CVD), nearly one-half of adults in the United States are projected to develop CVD by 2030, annually eclipsing all other causes of death for the past century (1). Coronary heart disease, which confers a plurality of CVD etiologies resulting in death, is exceptional in its ties to insufficient cholesterol transfer from peripheral sites to the liver and subsequent disposal (1, 2). As a mediator of inflammation, a source of peripheral cholesterol, and a cell type integral to the deposition of vascular fatty lesions, the macrophage has been cast to play a leading role in atherosclerosis. Each of these contributors to atherogenesis are regulated by the liver X receptor (LXR) (3). In PNAS, Muse et al. (4) manipulate ligand-induced LXR activities to accentuate a transcriptional program that promotes cholesterol efflux gene expression specifically in the macrophage. The LXR family of nuclear receptors is implicated in a reciprocal coordination of gene products involved in lipid homeostasis and inflammation (3). While lipids bearing oxidative modifications not only underlie excessive neutral lipid accumulation and inflammatory gene expression, they also agonize LXR. Therefore, this nuclear receptor family is a uniquely suited drug target to mitigate vascular lesion development (5). LXR performs these functions by … [↵][1]1To whom correspondence should be addressed. Email: evans{at}salk.edu. [1]: #xref-corresp-1-1

Oxidized phospholipids (OxPLs), which arise due to oxidative stress, are pro-inflammatory and pro-atherogenic, but their roles in non-alcoholic steatohepatitis (NASH) are unknown. Here, we show that OxPLs accumulate in human and mouse NASH. Using a transgenic mouse that expresses a functional single chain variable fragment of E06, a natural antibody that neutralizes OxPLs, we demonstrate the casual role of OxPLs in NASH. Targeting OxPLs in hyperlipidemic Ldlr(−/−) mice improved multiple aspects of NASH, including steatosis, inflammation, fibrosis, hepatocyte death and progression to hepatocellular carcinoma. Mechanistically, we found that OxPLs promote ROS accumulation to induce mitochondrial dysfunction in hepatocytes. Neutralizing OxPLs in AMLN diet-fed Ldlr(−/−) mice reduced oxidative stress, improved hepatic and adipose tissue mitochondrial function and fatty acid oxidation. These results suggest targeting OxPLs may be an effective therapeutic strategy for NASH.

Intestinal epithelial cells (IEC) are known to produce monocyte chemoattractant protein-1 (MCP-1). However, MCP-1 production, as with many other cytokines, can be regulated by a network of cytokines present in the environment of the IEC. Both IEC and inflammatory cells have been shown to produce transforming growth factor-beta (TGF-beta), and the regulatory effect of this cytokine on MCP-1 secretion by IEC has not been determined. Using the IEC-18 cell line, we have found that TGF-beta1 alone induced the secretion of high levels of MCP-1. Treatment with TGF-beta1 also enhanced the levels of MCP-1 messenger ribonucleic acid. However, costimulation of the cells with TGF-beta1 and interleukin-1beta (IL-1beta) resulted in significant, but less than additive, increases in MCP-1 secretion. Finally, the enhancing effect of TGF-beta1 on MCP-1 secretion was not due to IL-6. These results suggest that TGF-beta1 from IEC or inflammatory cells may significantly enhance the secretion of MCP-1 by IEC and play an important role in inflamed mucosal tissues.

Objective— We studied the mechanistic links between fibrocalcific changes in the aortic valve and aortic valve function in mice homozygous for a hypomorphic epidermal growth factor receptor mutation (Wave mice). We also studied myocardial responses to aortic valve dysfunction in Wave mice. Approach and Results— At 1.5 months of age, before development of valve fibrosis and calcification, aortic regurgitation, but not aortic stenosis, was common in Wave mice. Aortic valve fibrosis, profibrotic signaling, calcification, osteogenic markers, lipid deposition, and apoptosis increased dramatically by 6 and 12 months of age in Wave mice. Aortic regurgitation remained prevalent, however, and aortic stenosis was rare, at all ages. Proteoglycan content was abnormally increased in aortic valves of Wave mice at all ages. Treatment with pioglitazone prevented abnormal valve calcification, but did not protect valve function. There was significant left ventricular volume overload, hypertrophy, and fetal gene expression, at all ages in Wave mice with aortic regurgitation. Left ventricular systolic function was normal until 6 months of age in Wave mice, but became impaired by 12 months of age. Myocardial transverse tubules were normal in the presence of left ventricular hypertrophy at 1.5 and 3 months of age, but became disrupted by 12 months of age. Conclusions— We present the first comprehensive phenotypic and molecular characterization of spontaneous aortic regurgitation and volume-overload cardiomyopathy in an experimental model. In Wave mice, fibrocalcific changes are not linked to valve dysfunction and are epiphenomena arising from structurally incompetent myxomatous valves.

Burmese pythons display a marked increase in heart mass after a large meal. We investigated the molecular mechanisms of this physiological heart growth with the goal of applying this knowledge to the mammalian heart. We found that heart growth in pythons is characterized by myocyte hypertrophy in the absence of cell proliferation and by activation of physiological signal transduction pathways. Despite high levels of circulating lipids, the postprandial python heart does not accumulate triglycerides or fatty acids. Instead, there is robust activation of pathways of fatty acid transport and oxidation combined with increased expression and activity of superoxide dismutase, a cardioprotective enzyme. We also identified a combination of fatty acids in python plasma that promotes physiological heart growth when injected into either pythons or mice.