Biology subjects

Ortlund, E. A.

Publications and source records attributed to Ortlund, E. A..

26 records · Page 2Linked to original sources

bioRxiv2020

Chemical Systems Biology Reveals Mechanisms of Dissociated Glucocorticoid Receptor Signaling

Glucocorticoids display remarkable anti-inflammatory activity, but their use is limited by on-target adverse effects including insulin resistance and skeletal muscle atrophy. We used a chemical systems biology approach, Ligand Class Analysis (LCA), to examine ligands designed to modulate glucocorticoid receptor activity through distinct structural mechanisms. These ligands displayed diverse activity profiles, providing the variance required to identify target genes and coregulator interactions that were highly predictive of their effects on myocyte glucose disposal and protein balance. Their anti-inflammatory effects were linked to glucose disposal but not muscle atrophy. This approach also predicted selective modulation in vivo, identifying compounds that were muscle sparing or anabolic for protein balance and mitochondrial potential. LCA defined the mechanistic links between the ligand-receptor interface and ligand-driven physiological outcomes, a general approach that can be applied to any ligand-regulated allosteric signaling system.

pharmacology and toxicology↗

bioRxiv2020

Development of a new class of liver receptor homolog-1 (LRH-1) agonists by photoredox conjugate addition

LRH-1 is a nuclear receptor that regulates lipid metabolism and homeostasis, making it an attractive target for the treatment of diabetes and non-alcoholic fatty liver disease. Building on recent structural information about ligand binding from our labs, we have designed a series of new LRH-1 agonists that further engage LRH-1 through added polar interactions. While the current synthetic approach to this scaffold has, in large part, allowed for decoration of the agonist core, significant variation of the bridgehead substituent is mechanistically precluded. We have developed a new synthetic approach to overcome this limitation, identified that bridgehead substitution is necessary for LRH-1 activation, and described an alternative class of bridgehead substituents for effective LRH-1 agonist development. We determined the crystal structure of LRH-1 bound to a bridgehead-modified compound, revealing a promising opportunity to target novel regions of the ligand-binding pocket to alter LRH-1 target gene expression.

biochemistry↗

bioRxiv2020

Alterations in the human plasma lipidome in response to Tularemia vaccination

Tularemia is a rare but highly contagious and potentially fatal disease caused by bacteria Francisella tularensis where as few as ten inhaled organisms can lead to an infection, making it one of the most infectious microorganisms known and a potential bioweapon. To better understand the response to a live, attenuated tularemia vaccine and the biological pathways altered post-vaccination, healthy adults were vaccinated by scarification and plasma was collected pre- and post-vaccination for longitudinal lipidomics studies. Using tandem mass spectrometry, we identified and quantified individual lipid molecular species within representative lipid classes in plasma to characterize alterations in the plasma lipidome during the vaccine response. Separately, we targeted oxylipins, a subset of lipid mediators involved in inflammatory pathways. We identified 14 differentially abundant lipid species from eight lipid classes. These included 5-Hydroxyeicosatetraenoic acid (5-HETE), an eicosanoid produced following arachidonic acid liberation and epoxygenation, which is indicative of lipoxygenase activity and, subsequently, inflammation. Results suggest that 5-HETE was metabolized to a dihydroxyeicosatrienoic acid (DHET) by Day 7 post-vaccination, shedding light on the kinetics of the 5-HETE-mediated inflammatory response. In addition to 5-HETE and DHET, we observed pronounced changes in 34:1 phosphatidylinositol, anandamide, oleamide, ceramides, 16:1 cholesteryl ester, and several glycerophospholipids, several of these changes in abundance were correlated with serum cytokines and T cell activation. These data provide new insights into alterations in plasma lipidome post tularemia vaccination, potentially identifying key mediators and pathways involved in vaccine response and efficacy.

biochemistry↗

bioRxiv2020

Thioesterase Superfamily Member 1 Undergoes Stimulus-coupled Reorganization to Regulate Metabolism

In brown adipose tissue, cold exposure promotes thermogenesis, in large part by increasing mitochondrial {beta}-oxidation of lipid droplet-derived fatty acids. This process is suppressed by thioesterase superfamily member 1 (Them1), a long chain fatty acyl-CoA thioesterase that is highly upregulated by cold ambient temperatures. Them1 reduces fatty acid availability for {beta}-oxidation in mitochondria and limits thermogenesis by cellular mechanisms that are not well defined. We show that Them1 regulates metabolism by undergoing marked intracellular conformational changes that occur in response to {beta}-adrenergic stimulation. Mechanistically, Them1 formed puncta that were localized near LD and mitochondria in an immortalized brown adipose cell line. In response to stimulation by norepinephrine, Them1 was phosphorylated by PKC{beta} at S15, which specifically inhibited puncta formation and resulted in a diffuse intracellular localization. This change in Them1 localization also occurred after stimulation in vivo. Puncta formation activated Them1 metabolic activity in vitro, as evidenced by suppression of oxygen consumption following {beta}-adrenergic stimulation. We show by correlative light and electron microscopy that puncta are biomolecular condensates (also known as membraneless organelles) that typically form by phase separation. Them1 contains one intrinsically disordered region at the N-terminus with multiple interacting motifs that is frequently observed in phase-separating proteins. Phosphorylation, which is known to disrupt phase separation and aggregation, results in a diffuse Them1 localization. Our data thus establish that Them1 forms intracellular biomolecular condensates that limit fatty acid oxidation and suppress thermogenesis. During a period of energy demand, the condensates are disrupted by phosphorylation to allow for maximal thermogenesis. The stimulus-coupled reorganization of Them1 thus provides fine-tuning of thermogenesis and energy expenditure.

cell biology↗

bioRxiv2020

Allosteric regulation of Thioesterase Superfamily Member 1 by free fatty acids and lysophosphatidylcholine

Non-shivering thermogenesis occurs in brown adipose tissue to generate heat in response to cold temperatures. Thioesterase superfamily member 1 (Them1) is transcriptionally upregulated in brown adipose tissue upon cold exposure and suppresses thermogenesis to conserve energy reserves. Them1 hydrolyzes long-chain fatty acyl-CoAs, preventing their use as fuel for thermogenesis. Them1 contains a C-terminal StAR-related lipid transfer domain (StarD) with unknown ligand or function. By complementary biophysical approaches, we show that StarD binds to long-chain fatty acids, products of Them1s enzymatic reaction, as well lysophosphatidylcholine (LPC), which activate thermogenesis in brown adipocytes. Certain fatty acids stabilize the StarD and allosterically enhance Them1 catalysis of acyl-CoA, whereas 18:1 LPC destabilizes and inhibits activity, which we verify in cell culture. Additionally, we demonstrate that the StarD functions to localize Them1 near lipid droplets. These findings define the role of the StarD as a lipid sensor that allosterically regulates Them1 activity and localization.

biochemistry↗

bioRxiv2020

A behavioral polymorphism caused by a single gene inside a supergene

Behavioral evolution relies on genetic changes, yet few social behaviors can be traced to specific genetic sequences in vertebrates. Here, we show experimental evidence that differentiation of a single gene has contributed to divergent behavioral phenotypes in the white-throated sparrow, a common North American songbird. In this species, one of two alleles of ESR1, encoding estrogen receptor (ER), has been captured inside a differentiating supergene that segregates with an aggressive phenotype, such that ESR1 expression predicts aggression. Here, we show that the aggressive phenotype associated with the supergene is prevented by ESR1 knockdown in a single brain region. Next, we show that in a free-living population, aggression is predicted by allelic imbalance favoring the supergene allele. Cis-regulatory variation between the two alleles affects transcription factor binding sites, DNA methylation, and rates of transcription. This work provides a rare illustration of how genotypic divergence has led to behavioral phenotypic divergence in a vertebrate.

neuroscience↗

bioRxiv2019

Development of the first low nanomolar Liver Receptor Homolog-1 agonist through structure-guided design

As a key regulator of metabolism and inflammation, the orphan nuclear hormone receptor, Liver Receptor Homolog-1 (LRH-1), has potential as a therapeutic target for diabetes, nonalcoholic fatty liver disease, and inflammatory bowel diseases. Discovery of LRH-1 modulators has been difficult, in part due to the tendency for synthetic compounds to bind unpredictably within the lipophilic binding pocket. Using a structure-guided approach, we exploited a newly-discovered polar interaction to lock agonists in a consistent orientation. This enabled the discovery of the first low nanomolar LRH-1 agonist, one hundred times more potent than the best previous modulator. We elucidate a novel mechanism of action that relies upon specific polar interactions deep in the LRH-1 binding pocket. In an organoid model of inflammatory bowel disease, the new agonist increases expression of LRH-1-conrolled steroidogenic genes and promotes anti-inflammatory gene expression changes. These studies constitute major progress in developing LRH-1 modulators with potential clinical utility.

pharmacology and toxicology↗

bioRxiv2018

Ligand modulation of allosteric networks in an ancestral steroid receptor

Understanding the evolution of binding specificity, a heavily studied area of research, is key for determining how protein sequence changes alter function. Ligand-activation in the steroid receptor subfamily of transcription factors operates via a common allosteric mechanism which permits extant receptors to respond specifically to their cognate hormones. Here, we combine atomistic simulations with graph theory-based modeling of the inter-residue interactions within protein complexes to gain insight into how allostery drove selectivity in an ancestral receptor. An inactive ligand complex displays weakened allosteric communication, as quantified by suboptimal paths linking two functional surfaces. When function-switching mutations are incorporated, responses in allosteric networks are consistent with ligand activation status. Further analysis reveals residues that modulate features distinguishing active and inactive complexes, identifying a key, conserved residue that is crucial for activation in steroid receptors. We have identified a computational method using dynamic network analysis to probe the allosteric mechanisms driving the evolution of ligand specificity in hormone receptors, determining how residue substitutions altered allosteric networks to permit gain or loss of ligand response. These results may have general utility in elucidating how modern steroid receptors are activated by endogenous and xenobiotic molecules.\n\nAuthor summaryProteins interact with a host of biological partners to mediate their function. These binding partners are able to alter structural properties of the protein to send signals dictating downstream biological activity. This mode of regulation is described as allostery. Here, we perform a computational investigation of allostery in steroid receptors, a family of proteins that regulate a host of important biological processes in response to binding and activation by a steroidal ligand. We leverage a defined evolutionary system where known historical amino acid substitutions within the receptor drive a switch in ligand preference and receptor activation. We show that activating ligands induce stronger allosteric signaling between the ligand and the functional surface on the receptor. In addition, we incorporate evolutionary mutations that are known to alter ligand preference and show that this effect may be explained by allostery. This work provides insight into how amino acid substitutions over evolution affect allostery in proteins, permitting the loss and gain of function.

biophysics↗