Biology subjects

Luong, X. G.

Publications and source records attributed to Luong, X. G..

4 recordsLinked to original sources

bioRxiv2020

Regulation of gene transcription by thyroid hormone receptor β agonists in clinical development for the treatment of non-alcoholic steatohepatitis (NASH)

Thyroid hormones are important modulators of metabolic activity in mammals and alter cholesterol and fatty acid levels through activation of the nuclear thyroid hormone receptor (THR). Currently, there are several THR{beta} agonists in clinical trials for the treatment of non-alcoholic steatohepatitis (NASH) that have demonstrated the potential to reduce liver fat and restore liver function. In this study, we tested three THR{beta}-agonism-based NASH treatment candidates, GC-1 (sobetirome), MGL-3196 (resmetirom), and VK2809, and compared their selectivity for THR{beta} and their ability to modulate the expression of genes specific to cholesterol and fatty acid biosynthesis and metabolism in vitro using human hepatic cells and in vivo using a rat model. Treatment with GC-1 upregulated the transcription of CPT1A in the human hepatocyte-derived Huh-7 cell line with a dose-response comparable to that of the native THR ligand, triiodothyronine (T3). VK2809A (active parent of VK2809), MGL-3196, and VK2809 were approximately 30-fold, 1,000-fold, and 2,000-fold less potent than T3, respectively. Additionally, these relative potencies were confirmed by quantification of other direct gene targets of THR, namely, ANGPTL4 and DIO1. In primary human hepatocytes, potencies were conserved for every compound except for VK2809, which showed significantly increased potency that was comparable to that of its active counterpart, VK2809A. In high-fat diet fed rats, a single dose of T3 significantly reduced total cholesterol levels and concurrently increased liver Dio1 and Me1 RNA expression. MGL-3196 treatment resulted in concentration-dependent decreases in total and low-density lipoprotein cholesterol with corresponding increases in liver gene expression, but the compound was significantly less potent than T3. In conclusion, we have implemented a strategy to rank the efficacy of THR{beta} agonists by quantifying changes in the transcription of genes that lead to metabolic alterations, an effect that is directly downstream of THR binding and activation.

pharmacology and toxicology↗

bioRxiv2019

Genome-wide analysis reveals a switch in the translational program upon oocyte meiotic resumption

During oocyte maturation, changes in gene expression depend exclusively on translation and degradation of maternal mRNAs rather than transcription. Execution of this translation program is essential for assembling the molecular machinery required for meiotic progression, fertilization, and embryo development. With the present study, we used a RiboTag/RNA-Seq approach to explore the timing of maternal mRNA translation in quiescent oocytes as well as in oocytes progressing through the first meiotic division. This genome-wide analysis reveals a global switch in maternal mRNA translation coinciding with oocyte re-entry into the meiotic cell cycle. Messenger RNAs whose translation is highly active in quiescent oocytes invariably become repressed during meiotic re-entry, whereas transcripts repressed in quiescent oocytes become activated. Experimentally, we have defined the exact timing of the switch, the repressive function of CPE elements, and identified a novel role for CPEB1 in maintaining constitutive translation of a large group of maternal mRNAs during maturation.

developmental biology↗

bioRxiv2019

The RNA binding protein DAZL functions as repressor and activator of maternal mRNA translation during oocyte maturation

Deleted in azoospermia like (DAZL) is an RNA-binding protein playing critical function during gamete development. In fully-grown oocytes, DAZL protein is detected in prophase and levels increase four to five fold during reentry into the meiotic cell cycle. Here, we have investigated the functional significance of this DAZL accumulation in maturing oocytes. Oocyte depletion of DAZL prevents progression to MII. This maturation block is associated with widespread disruption in the pattern of maternal transcripts loading on ribosomes and their translation measured using a RiboTag IP/RNASeq or qPCR strategy. In addition to decreased ribosome loading of a subset of transcripts, we found that DAZL depletion causes also translational activation of distinct subset of mRNAs. DAZL binds to mRNAs whose translation is both repressed and activated during oocyte maturation. Unexpectedly, DAZL depletion also causes increased ribosome loading of a subset of mRNAs in quiescent GV-arrested oocytes. This dual role of repression and activation is recapitulated by using YFP reporters including the 3UTR of DAZL targets. Injection of recombinant DAZL protein in DAZL-depleted oocytes rescues the translation of these targets as well as maturation to MII. Mutagenesis of putative DAZL-binding sites in these candidate mRNAs mimics the effect of DAZL depletion. These findings demonstrate that DAZL regulates translation of maternal mRNAs in mature oocytes, functioning both as translational repressor and activator.

developmental biology↗

bioRxiv2018

Cyclin B2 is required for progression through meiosis in mouse oocytes

Cyclins associate with CDK1 to generate the M-phase-promoting factor (MPF) essential for progression through mitosis and meiosis. Previous studies concluded that CCNB2 is dispensable for cell cycle progression. Given our findings of high translation rates of CcnB2 mRNA in prophase-arrested oocytes, we have reevaluated its role during meiosis. CcnB2-/- oocytes undergo delayed germinal vesicle breakdown followed by a defective M-phase due to reduced pre-MPF activity. This disrupted maturation is associated with compromised CcnB1 and Mos mRNA translation and delayed spindle assembly. Given these defects, a significant population of oocytes fail to complete meiosis I because SAC remains activated and APC function is inhibited. In vivo, CCNB2 depletion leads to decreased oocyte developmental competence, compromised fecundity, and premature ovarian failure. These findings demonstrate that CCNB2 is required to assemble sufficient pre-MPF for timely meiosis reentry and progression. Although endogenous cyclins cannot compensate, overexpression of CCNB1 rescues the meiotic phenotypes, demonstrating similar molecular properties but divergent modes of regulation of these cyclins.

developmental biology↗