Using the tools of genetic epidemiology to understand sex differences in neuropsychiatric disorders

Many neuropsychiatric disorders exhibit differences in prevalence, age of onset, symptoms or course of illness between males and females. For the most part, the origins of these differences are not well understood. In this article, we provide an overview of sex differences in psychiatric disorders including autism spectrum disorder (ASD), attention deficit/hyperactivity disorder (ADHD), anxiety, depression, alcohol and substance abuse, schizophrenia, eating disorders and risk of suicide. We discuss both genetic and nongenetic mechanisms that have been hypothesized to underlie these differences, including ascertainment bias, environmental stressors, X‐ or Y‐linked risk loci, and differential liability thresholds in males and females. We then review the use of twin, family and genome‐wide association approaches to study potential genetic mechanisms of sex differences and the extent to which these designs have been employed in studies of psychiatric disorders. We describe the utility of genetic epidemiologic study designs, including classical twin and family studies, large‐scale studies of population registries, derived recurrence risks, and molecular genetic analyses of genome‐wide variation that may enhance our understanding sex differences in neuropsychiatric disorders.     

Diminished social interaction incentive contributes to social deficits in mouse models of autism spectrum disorder

One of the core symptoms of autism spectrum disorder (ASD) is impaired social interaction. Currently, no pharmacotherapies exist for this symptom due to complex biological underpinnings and distinct genetic models which fail to represent the broad disease spectrum. One convincing hypothesis explaining social deficits in human ASD patients is amotivation, however it is unknown whether mouse models of ASD represent this condition. Here we used two highly trusted ASD mouse models (male Shank3‐deficient [Shank3^+/ΔC] mice modeling the monogenic etiology of ASD, and inbred BTBR mice [both male and female] modeling the idiopathic and highly polygenic pathology for ASD) to evaluate the level of motivation to engage in a social interaction. In the behavioral paradigms utilized, a social stimulus was placed in the open arm of the elevated plus maze (EPM), or the light compartment of the light‐dark box (LDB). To engage in a social interaction, mice were thus required to endure innately aversive conditions (open areas, height, and/or light). In the modified EPM paradigm, both Shank3^+/ΔC and BTBR mice demonstrated decreased open‐arm engagement with a social stimulus but not a novel object, suggesting reduced incentive to engage in a social interaction in these models. However, these deficits were not expressed under the less severe aversive pressures of the LDB. Collectively, we show that ASD mouse models exhibit diminished social interaction incentive, and provide a new investigation strategy facilitating the study of the neurobiological mechanisms underlying social reward and motivation deficits in neuropsychiatric disorders.     

Tailoring microbes to upgrade lignin

Lignin depolymerization generates a mixture of numerous compounds that are difficult to separate cost-effectively. To address this heterogeneity issue, microbes have been employed to ‘biologically funnel’ a broad range of compounds present in depolymerized lignin into common central metabolites that can be converted into a single desirable product. Because the composition of depolymerized lignin varies significantly with the type of biomass and the depolymerization method, microbes should be selected and engineered by considering this compositional variation. An ideal microbe must efficiently metabolize all relevant lignin-derived compounds regardless of the compositional variation of feedstocks, but discovering or developing such a perfect microbe is very challenging. Instead, developing multiple tailored microbes to tolerate a given mixture of lignin-derived compounds and to convert most of these into a target product is more practical. This review summarizes recent progress toward the development of such microbes for lignin valorization and offers future directions.     

Methanol-free biosynthesis of fatty acid methyl ester (FAME) in Synechocystis sp. PCC 6803

To meet the increasing global demand of biodiesel over the next decades, alternative methods for producing one of the key constituents of biodiesel (e.g. fatty acid methyl esters (FAMEs)) are needed. Algal biodiesel has been a long-term target compromised by excessive costs for harvesting and processing. In this work, we engineered cyanobacteria to convert carbon dioxide into excreted FAME, without requiring methanol as a methyl donor. To produce FAME, acyl-ACP, a product of the fatty acid biosynthesis pathway, was first converted into free fatty acid (FFA) by a thioesterase, namely ’UcFatB1 from Umbellularia californica. Next, by employing a juvenile hormone acid O-methyltransferase (DmJHAMT) from Drosophila melanogaster and S-adenosylmethionine (SAM) as a methyl donor, FFAs were converted into corresponding FAMEs. The esters were naturally secreted extracellularly, allowing simple product separation by solvent overlay as opposed to conventional algae biodiesel production where the algae biomass must first be harvested and processed for transesterification of extracted triacylglycerols (TAGs). By optimizing both the promoter and RBS elements, up to 120 mg/L of FAMEs were produced in 10 days. Quantification of key proteins and metabolites, together with constructs over-expressing SAM synthetase (MetK), indicated that ’UcFatB1, MetK, and DmJHAMT were the main factors limiting pathway flux. In order to solve the latter limitation, two reconstructed ancestral sequences of DmJHAMT were also tried, resulting in strains showing a broader methyl ester chain-length profile in comparison to the native DmJHAMT. Altogether, this work demonstrates a promising pathway for direct sunlight-driven conversion of CO₂ into excreted FAME.     

Engineering Saccharomyces cerevisiae for high yield production of α-amyrin via synergistic remodeling of α-amyrin synthase and expanding the storage pool

α-Amyrin is a plant-originated high-valued triterpene that is highly effective against several pathological ailments. α-Amyrin production by engineered Saccharomyces cerevisiae has been achieved by introducing α-amyrin synthase (αAS). However, the low yield of α-amyrin highly limits its industrial application; the low catalytic activity of αAS and the toxic effect of α-amyrin have been considered key elements. In this study, the highest yield of α-amyrin was obtained in engineered S. cerevisiae by remodeling α-amyrin synthase MdOSC1 and expanding the storage pool. The yield of α-amyrin was increased to 11-fold higher than that of the control by the triple mutant MdOSC1^{N11T/P250H/P373A} obtained based on the modeling analysis. Furthermore, key genes of MVA pathway were overexpressed to provide sufficient precursors, and DGA1 (Diacylglycerol acyltransferase) was overexpressed to expand the intracellular storage capacity. Finally, the as-constructed aAM12 strain produced 213.7 ± 12.4 mg/L α-amyrin in the shake flask and 1107.9 ± 76.8 mg/L in fed-batch fermentation; the fermentation yield was 106-fold higher than that of the original aAM1 strain under the same conditions, representing the highest α-amyrin yield in yeast reported to date. Microbial production of α-amyrin with over 1 g/L will be suitable for commercialization and can accelerate the industrial production of α-amyrin in yeast.     

Crosstalk between Endo/Exocytosis and Autophagy in Health and Disease

Imbalance between the main intracellular degradative, trafficking and intercellular shuttling pathways has been implicated in disease pathogenesis. Autophagy controls degradation of cellular components, while vesicular trafficking permits transport of material in and out of the cell. Emerging evidence has uncovered the extensive interconnectivity between these pathways, which is crucial to maintain organismal homeostasis. Thus, therapeutic intervention and drug development strategies targeting these processes, particularly in neurodegeneration, should account for this broad crosstalk, to maximize effectiveness. Here, recent findings underlining the highly dynamic nature of the crosstalk between autophagy, endosomal transport, and secretion is reviewed. Synergy of autophagy and endosomes for degradation, as well as, competition of autophagy and secretion are discussed. Perturbation of this crosstalk triggers pathology especially neurodegeneration.     

Synthesis of 18F-labeled streptozotocin derivatives and an in-vivo kinetics study using positron emission tomography

Glucose transporter 2 (GLUT2) is involved in glucose uptake by hepatocytes, pancreatic beta cells, and absorptive cells in the intestine and proximal tubules in the kidney. Pancreatic GLUT2 also plays an important role in the mechanism of glucose-stimulated insulin secretion. In this study, novel Fluorine-18-labeled streptozotocin (STZ) derivatives were synthesized to serve as glycoside analogs for in-vivo GLUT2 imaging. Fluorine was introduced to hexyl groups at the 3′-positions of the compounds, and we aimed to synthesize compounds that were more stable than STZ. The nitroso derivatives exhibited relatively good stability during purification and purity analysis after radiosynthesis. We then evaluated the compounds in PET imaging and ex-vivo biodistribution studies. We observed high levels of radioactivity in the liver and kidney, which indicated accumulation in these organs within 5 min of administration. In contrast, the denitroso derivatives accumulated only in the kidney and bladder shortly after administration. Compounds with nitroso groups are thus expected to accumulate in GLUT2-expressing organs, and the presence of a nitroso group is essential for in-vivo GLUT2 imaging.     

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.     

Development of a potent and orally active activator of adenosine monophosphate-activated protein kinase (AMPK), ASP4132, as a clinical candidate for the treatment of human cancer

Adenosine monophosphate (AMP)-activated protein kinase (AMPK) plays a key role in maintaining cellular metabolism. AMP or adenosine diphosphate (ADP) levels rise during metabolic stress, such as during nutrient starvation, hypoxia and muscle contraction, and bind to AMPK to induce activity. Recently, activation of AMPK has been considered an attractive therapeutic strategy in the field of human oncology. Structural optimization of lead compound 2, a new type of AMPK activator with potent AMPK activation activity and attractive selective growth inhibition against human cancer cells, improved aqueous solubility, metabolic stability and animal pharmacokinetics (PK) and culminated in the identification of (5-{1-[(6-methoxypyridin-3-yl)methyl]piperidin-4-yl}-1H-benzimidazol-2-yl)(4-{[4-(trifluoromethyl)phenyl]methyl}piperazin-1-yl)methanone ditosylate, ASP4132 (28). Studies on ASP4132 had advanced to clinical trials for the treatment of cancer.