Biology subjects

Jang, C.

Publications and source records attributed to Jang, C..

30 records · Page 2Linked to original sources

bioRxiv2024

A PTER-dependent pathway of taurine metabolism linked to energy balance

Taurine is a conditionally essential micronutrient and one of the most abundant amino acids in humans1-3. In endogenous taurine metabolism, dedicated enzymes are involved in biosynthesis of taurine from cysteine as well as the downstream derivatization of taurine into secondary taurine metabolites4,5. One such taurine metabolite is N-acetyltaurine6. Levels of N-acetyltaurine are dynamically regulated by diverse physiologic perturbations that alter taurine and/or acetate flux, including endurance exercise7, nutritional taurine supplementation8, and alcohol consumption6,9. While taurine N-acetyltransferase activity has been previously detected in mammalian cells6,7, the molecular identity of this enzyme, and the physiologic relevance of N-acetyltaurine, have remained unknown. Here we show that the orphan body mass index-associated enzyme PTER (phosphotriesterase-related)10 is the principal mammalian taurine N-acetyltransferase/hydrolase. In vitro, recombinant PTER catalyzes bidirectional taurine N-acetylation with free acetate as well as the reverse N-acetyltaurine hydrolysis reaction. Genetic ablation of PTER in mice results in complete loss of tissue taurine N-acetyltransferase/hydrolysis activities and systemic elevation of N-acetyltaurine levels. Upon stimuli that increase taurine levels, PTER-KO mice exhibit lower body weight, reduced adiposity, and improved glucose homeostasis. These phenotypes are recapitulated by administration of N-acetyltaurine to wild-type mice. Lastly, the anorexigenic and anti-obesity effects of N-acetyltaurine require functional GFRAL receptors. Together, these data uncover enzymatic control of a previously enigmatic pathway of secondary taurine metabolism linked to energy balance.

biochemistry↗

bioRxiv2024

Off-target depletion of plasma tryptophan by allosteric inhibitors of BCKDK

The activation of branched chain amino acid (BCAA) catabolism has garnered interest as a potential therapeutic approach to improve insulin sensitivity, enhance recovery from heart failure, and blunt tumor growth. Evidence for this interest relies in part on BT2, a small molecule that promotes BCAA oxidation and is protective in mouse models of these pathologies. BT2 and other analogs allosterically inhibit branched chain ketoacid dehydrogenase kinase (BCKDK) to promote BCAA oxidation, which is presumed to underlie the salutary effects of BT2. Potential "off-target" effects of BT2 have not been considered, however. We therefore tested for metabolic off-target effects of BT2 in Bckdk-/- animals. As expected, BT2 failed to activate BCAA oxidation in these animals. Surprisingly, however, BT2 strongly reduced plasma tryptophan levels and promoted catabolism of tryptophan to kynurenine in both control and Bckdk-/- mice. Mechanistic studies revealed that none of the principal tryptophan catabolic or kynurenine-producing/consuming enzymes (TDO, IDO1, IDO2, or KATs) were required for BT2-mediated lowering of plasma tryptophan. Instead, using equilibrium dialysis assays and mice lacking albumin, we show that BT2 avidly binds plasma albumin and displaces tryptophan, releasing it for catabolism. These data confirm that BT2 activates BCAA oxidation via inhibition of BCKDK but also reveal a robust off-target effect on tryptophan metabolism via displacement from serum albumin. The data highlight a potential confounding effect for pharmaceutical compounds that compete for binding with albumin-bound tryptophan.

pharmacology and toxicology↗

bioRxiv2023

Aberrant splicing in Huntington's disease via disrupted TDP-43 activity accompanied by altered m6A RNA modification.

Huntingtons disease (HD) is a neurodegenerative disorder caused by a CAG repeat expansion in the first exon of the HTT gene encoding huntingtin. Prior reports have established a correlation between CAG expanded HTT and altered gene expression. However, the mechanisms leading to disruption of RNA processing in HD remain unclear. Here, our analysis of the reported HTT protein interactome identifies interactions with known RNA-binding proteins (RBPs). Total, long-read sequencing and targeted RASL-seq of RNAs from cortex and striatum of the HD mouse model R6/2 reveals increased exon skipping which is confirmed in Q150 and Q175 knock-in mice and in HD human brain. We identify the RBP TDP-43 and the N6-methyladenosine (m6A) writer protein methyltransferase 3 (METTL3) to be upstream regulators of exon skipping in HD. Along with this novel mechanistic insight, we observe decreased nuclear localization of TDP-43 and cytoplasmic accumulation of phosphorylated TDP-43 in HD mice and human brain. In addition, TDP-43 co-localizes with HTT in human HD brain forming novel nuclear aggregate-like bodies distinct from mutant HTT inclusions or previously observed TDP-43 pathologies. Binding of TDP-43 onto RNAs encoding HD-associated differentially expressed and aberrantly spliced genes is decreased. Finally, m6A RNA modification is reduced on RNAs abnormally expressed in striatum from HD R6/2 mouse brain, including at clustered sites adjacent to TDP-43 binding sites. Our evidence supports TDP-43 loss of function coupled with altered m6A modification as a novel mechanism underlying alternative splicing/unannotated exon usage in HD and highlights the critical nature of TDP-43 function across multiple neurodegenerative diseases.

neuroscience↗

bioRxiv2023

Serine synthesis pathway upregulated by E-cadherin is essential for the proliferation and metastasis of breast cancers

The loss of E-cadherin (E-cad), an epithelial cell adhesion molecule, has been implicated in the epithelial-mesenchymal transition (EMT), promoting invasion and migration of cancer cells and, consequently, metastasis. However, recent studies have demonstrated that E-cad supports the survival and proliferation of metastatic cancer cells, suggesting that our understanding of E-cad in metastasis is far from comprehensive. Here, we report that E-cad upregulates the de novo serine synthesis pathway (SSP) in breast cancer cells. The SSP provides metabolic precursors for biosynthesis and resistance to oxidative stress, critically beneficial for E-cad-positive breast cancer cells to achieve faster tumor growth and more metastases. Inhibition of PHGDH, a rate-limiting enzyme in the SSP, significantly and specifically hampered the proliferation of E-cad-positive breast cancer cells and rendered them vulnerable to oxidative stress, inhibiting their metastatic potential. Our findings reveal that E-cad adhesion molecule significantly reprograms cellular metabolism, promoting tumor growth and metastasis of breast cancers.

cancer biology↗

bioRxiv2023

Leveraging genetic correlation structure to target discrete signaling mechanisms across metabolic tissues

Abstract/IntroductionInter-organ communication is a vital process to maintain physiologic homeostasis, and its dysregulation contributes to many human diseases. Beginning with the discovery of insulin over a century ago, characterization of molecules responsible for signal between tissues has required careful and elegant experimentation where these observations have been integral to deciphering physiology and disease. Given that circulating bioactive factors are stable in serum, occur naturally, and are easily assayed from blood, they present obvious focal molecules for therapeutic intervention and biomarker development. For example, physiologic dissection of the actions of soluble proteins such as proprotein convertase subtilisin/kexin type 9 (PCSK9) and glucagon-like peptide 1 (GLP1) have yielded among the most promising therapeutics to treat cardiovascular disease and obesity, respectively1-4. A major obstacle in the characterization of such soluble factors is that defining their tissues and pathways of action requires extensive experimental testing in cells and animal models. Recently, studies have shown that secreted proteins mediating inter-tissue signaling could be identified by "brute-force" surveys of all genes within RNA-sequencing measures across tissues within a population5-9. Expanding on this intuition, we reasoned that parallel strategies could be used to understand how individual genes mediate signaling across metabolic tissues through correlative analyses of gene variation between individuals. Thus, comparison of quantitative levels of gene expression relationships between organs in a population could aid in understanding cross-organ signaling. Here, we surveyed gene-gene correlation structure across 18 metabolic tissues in 310 human individuals and 7 tissues in 103 diverse strains of mice fed a normal chow or HFHS diet. Variation of genes such as FGF21, ADIPOQ, GCG and IL6 showed enrichments which recapitulate experimental observations. Further, similar analyses were applied to explore both within-tissue signaling mechanisms (liver PCSK9) as well as genes encoding enzymes producing metabolites (adipose PNPLA2), where inter-individual correlation structure aligned with known roles for these critical metabolic pathways. Examination of sex hormone receptor correlations in mice highlighted the difference of tissue-specific variation in relationships with metabolic traits. We refer to this resource as Gene-Derived Correlations Across Tissues (GD-CAT) where all tools and data are built into a web portal enabling users to perform these analyses without a single line of code (gdcat.org). This resource enables querying of any gene in any tissue to find correlated patterns of genes, cell types, pathways and network architectures across metabolic organs.

physiology↗

bioRxiv2022

MAPK13 stabilization via m6A modification limits anti-cancer efficacy of rapamycin

N6-adenosine methylation (m6A) is the most abundant mRNA modification that controls gene expression through diverse mechanisms. m6A-dependent regulation of oncogenes and tumor suppressors indeed contribute to tumor development. However, the role of m6A-mediated gene regulation after drug treatment or resistance is poorly understood. Here, we report that m6A modification of mitogen-activated protein kinase 13 (MAPK13) determines the sensitivity of cancer cells to the mechanistic target of rapamycin complex 1 (mTORC1)- targeting chemotherapeutic agent rapamycin. mTORC1 induces m6A modification of MAPK13 mRNA at its 3 untranslated region (3UTR) through methyltransferase-like 3 (METTL3)-METTL14-Wilms tumor 1-associating protein (WTAP) methyltransferase complex, thereby stimulating its mRNA degradation via an m6A reader protein YTH domain family protein 2 (YTHDF2). Rapamycin blunts this process and stabilizes MAPK13. Unexpectedly, MAPK13 silencing suppresses cell growth and enhances rapamycins anti-cancer effects, suggesting that MAPK13 is an oncogenic gene activated by rapamycin via a feedback regulation. Together, our data indicate that rapamycin-mediated MAPK13 mRNA stabilization may confer drug resistance, and it can thus be a therapeutic target to sensitize cancer cells to rapamycin.

cancer biology↗

bioRxiv2022

ADOLESCENT EXPOSURE TO LOW-DOSE THC DISRUPTS ENERGY BALANCE AND ADIPOSE ORGAN HOMEOSTASIS IN ADULTHOOD

One of cannabis most iconic effects is the stimulation of hedonic high-calorie eating - the munchies - yet habitual cannabis users are on average leaner than non-users. We asked whether this unexpected phenotype might result from lasting changes in energy balance established during adolescence, when habitual use of the drug often begins. We found that daily low-dose administration of cannabis intoxicating constituent, {Delta}9-tetrahydrocannabinol (THC), to adolescent mice causes an adult metabolic phenotype characterized by reduced fat mass, increased lean mass and utilization of fat as fuel, partial resistance to diet-induced obesity and dyslipidemia, and enhanced thermogenesis. Multi-omics analyses revealed that this phenotype is associated with multiple molecular anomalies in the adipose organ, which include ectopic overexpression of muscle-associated proteins and heightened anabolic processing. Thus, adolescent exposure to THC may promote an enduring pseudo-lean state that superficially resembles healthy leanness but might in fact be rooted in adipose organ dysfunction.

pharmacology and toxicology↗

bioRxiv2022

Telomere dysfunction impairs intestinal differentiation andpredisposes to diet-induced colitis

Intestinal epithelium dysfunction causes barrier defects, malabsorption and dysbiosis, predicting local and systemic disease, morbidity and mortality in humans. However, the underlying causes are not well understood. Here we show that telomere shortening is a host intrinsic factor that impairs enterocyte differentiation. The presence of such undifferentiated enterocytes is associated with barrier disruption and malabsorption of nutrients, such as fructose. A fructose-rich diet causes increased fructose spillover to the colon and induces colitis in a microbiome-dependent manner. The microbiome uses fructose to synthesize essential metabolites, including NAD precursors, that complement the hosts low NAD pool in the inflamed colon. Thus, telomere shortening drives enterocyte dysfunction and predisposes to diet-induced colitis through barrier disruption, increased nutrient flux to the colon and modulation of the microbiome. This differerentiation defect expands the canonical stem cell failure-centered view of how telomere shortening impacts the intestine and predisposes to intestinal disease in conditions associated with short telomeres.

cell biology↗

bioRxiv2022

Interrogating Metabolic Interactions Between Skeletal Muscle and Liver Circadian Clocks In Vivo

Expressed throughout the body, the circadian clock system achieves daily metabolic homeostasis at every level of physiology, with clock disruption associated with metabolic disease (1, 2). Molecular clocks present in the brain, liver, adipose, pancreas and skeletal muscle each contribute to glucose homeostasis (3). However, it is unclear; 1) which organ clocks provide the most essential contributions, and 2) if these contributions depend on inter-organ communication. We recently showed that the liver clock alone is insufficient for most aspects of daily liver glucose handling and requires connections with other clocks (4). Considering the pathways that link glucose metabolism between liver and skeletal muscle, we sought to test whether a clock connection along this axis is important. Using our previous published methodology for tissue-specific rescue of Bmal1 in vivo (4, 5), we now show that in the absence of feeding-fasting cycles, liver and muscle clocks are not sufficient for systemic glucose metabolism, nor do they form a functional connection influencing local glucose handling or daily transcriptional rhythms in each tissue. However, the introduction of a daily feeding-fasting rhythm enables a synergistic state between liver and muscle clocks that leads to restoration of systemic glucose tolerance. These findings reveal limited autonomous capabilities of liver and muscle clocks and highlight the need for inter-organ clock communication for glucose homeostasis which involves at least two peripheral metabolic organs.

cell biology↗

bioRxiv2022

Gut bacterial nutrient preferences quantified in vivo

Great progress has been made in understanding gut microbiomes products and their effects on health and disease. Less attention, however, has been given to the inputs that gut bacteria consume. Here we quantitatively examine inputs and outputs of the mouse gut microbiome, using isotope tracing. The main input to microbial carbohydrate fermentation is dietary fiber, and to branched-chain fatty acids and aromatic metabolites is dietary protein. In addition, circulating host lactate, 3-hydroxybutyrate and urea (but not glucose or amino acids) feed the gut microbiome. To determine nutrient preferences across bacteria, we traced into genus-specific bacterial protein sequences. We find systematic differences in nutrient use: Most genera in the phylum Firmicutes prefer dietary protein, Bacteroides dietary fiber, and Akkermansia circulating host lactate. Such preferences correlate with microbiome composition changes in response to dietary modifications. Thus, diet shapes the microbiome by promoting the growth of bacteria that preferentially use the ingested nutrients.

molecular biology↗

bioRxiv2020

Photoperiod Sensitive Energy Sorghum Responses to Environmental and Nitrogen Variabilities

Recently introduced photoperiod-sensitive (PS) biomass sorghum (Sorghum bicolor L. Moench) needs to be investigated for their yield potentials under different cultivation environments with reasonable nitrogen (N) inputs. The objectives of this study were to 1) evaluate the biomass yield and feedstock quality of four sorghum hybrids with different levels of PS ranging from very PS (VPS) hybrids and to moderate PS (MPS) hybrids, and 2) determine the optimal N inputs (0~168 kg N ha-1) under four environments: combinations of both temperate (Urbana, IL) and subtropical (College Station, TX) regions during 2018 and 2019. Compared to TX, the PS sorghums in central IL showed higher yield potential and steady feedstock production with an extended daylength and with less precipitation variability, especially for the VPS hybrids. The mean dry matter (DM) yields of VPS hybrids were 20.5 Mg DM ha-1 and 17.7 Mg DM ha-1 in IL and TX, respectively. The highest N use efficiency occurred at a low N rate of 56 kg N ha-1 by improving approximately 33 kg DM ha-1 per 1.0 kg N ha-1 input. Approximately 70% of the PS sorghum biomass can be utilized for biofuel production, consisting of 58-65% of the cell wall components and 4-11% of the soluble sugar. This study demonstrated that the rainfed temperate area (e.g., IL) has a great potential for the sustainable cultivation of PS energy sorghum due their observed high yield potential, stable production, and low N requirements.

plant biology↗

bioRxiv2020

Quantitative fluxomics of circulating metabolites

Mammalian organs are nourished by nutrients carried by the blood circulation. These nutrients originate from diet and internal stores, and can undergo various interconversions before their eventual use as tissue fuel. Here we develop isotope tracing, mass spectrometry, and mathematical analysis methods to determine the direct sources of circulating nutrients, their interconversion rates, and eventual tissue-specific contributions to TCA cycle metabolism. Experiments with fifteen nutrient tracers enabled extensive accounting both for circulatory metabolic cycles and tissue TCA inputs, across fed and fasted mice on either high carbohydrate or ketogenic diet. We find that a majority of circulating carbon flux is carried by two major cycles: glucose-lactate and triglyceride-glycerol-fatty acid. Futile cycling through these pathways is prominent when dietary content of the associated nutrients is low, rendering internal metabolic activity robust to food choice. The presented in vivo flux quantification methods are broadly applicable to different physiological and disease states.

systems biology↗