Biology subjects

Ong, S.-G.

Publications and source records attributed to Ong, S.-G..

8 recordsLinked to original sources

bioRxiv2024

Platelet Factor 4 (PF4) Regulates Hematopoietic Stem Cell Aging

Hematopoietic stem cells (HSCs) responsible for blood cell production and their bone marrow regulatory niches undergo age-related changes, impacting immune responses and predisposing individuals to hematologic malignancies. Here, we show that the age-related alterations of the megakaryocytic niche and associated downregulation of Platelet Factor 4 (PF4) are pivotal mechanisms driving HSC aging. PF4-deficient mice display several phenotypes reminiscent of accelerated HSC aging, including lymphopenia, increased myeloid output, and DNA damage, mimicking physiologically aged HSCs. Remarkably, recombinant PF4 administration restored old HSCs to youthful functional phenotypes characterized by improved cell polarity, reduced DNA damage, enhanced in vivo reconstitution capacity, and balanced lineage output. Mechanistically, we identified LDLR and CXCR3 as the HSC receptors transmitting the PF4 signal, with double knockout mice showing exacerbated HSC aging phenotypes similar to PF4-deficient mice. Furthermore, human HSCs across various age groups also respond to the youthful PF4 signaling, highlighting its potential for rejuvenating aged hematopoietic systems. These findings pave the way for targeted therapies aimed at reversing age-related HSC decline with potential implications in the prevention or improvement of the course of age-related hematopoietic diseases. Key PointsO_LIAge-related attrition of the megakaryocytic niche and associated PF4 downregulation is a central mechanism in HSC aging. C_LIO_LIPF4 supplementation, acting on LDLR and CXCR3 receptors, rejuvenates the function of aged HSCs. C_LI

cell biology↗

bioRxiv2024

Inhibition of β-catenin signaling by Amyloid-β in endothelial cells impairs vascular barrier integrity

Dysfunction of the blood-brain barrier (BBB) is emerging as a critical mediator of Alzheimers Disease (AD) progression and precedes the formation of large Amyloid-{beta} (A{beta}) plaques in AD patients. Maintenance of the blood brain barrier integrity by brain microvascular endothelial cells (BMECs) is essential for brain homeostasis and is in part maintained by WNT/{beta}-catenin signaling. We hypothesized that A{beta} induces blood-brain barrier dysfunction by inhibiting WNT/{beta}- catenin signaling in brain endothelial cells, leading to reduced expression of BBB-related genes and barrier function. In brain endothelial cells, we found that A{beta} directly decreased {beta}-catenin transcriptional activity, but also inhibited activation of {beta}-catenin by the WNT3A peptide. Additionally, A{beta} reduced barrier integrity of ECs, which was in part restored by exposure to exogenous WNT3A. We observed A{beta}-induced inhibition within 3 hours of exposure. A{beta}-induced inhibition of {beta}-catenin signaling was consistent across both immortalized brain ECs and ECs differentiated from human induced pluripotent stem cells(iPSCs). We next investigated human iPSCs with and without the N141I mutation in presenilin-2 (PSEN2), known to increase A{beta} buildup and familial AD risk. We found the AD ECs showed smaller cell size and expressed lower VE-cadherin at the protein level. RNA sequencing revealed that the presence of PSEN2 N141I did not significantly impact gene expression of genes coding for proteins canonically involved in barrier integrity but did show differences in the expression of transposable elements. These results indicate that BBB dysfunction early in AD may be the result of A{beta} in the brain impairing WNT/{beta}-catenin signaling which maintains the barrier integrity of brain endothelial cells.

neuroscience↗

bioRxiv2023

Estrogen prevents age-dependent beige adipogenesis failure through NAMPT-controlled ER stress pathway

Thermogenic beige adipocytes are recognized as potential therapeutic targets for combating metabolic diseases. However, the metabolic advantages they offer are compromised with aging. Here, we show that treating mice with estrogen (E2), a hormone that decreases with age, to mice can counteract the aging- related decline in beige adipocyte formation when subjected to cold, while concurrently enhancing energy expenditure and improving glucose tolerance. Mechanistically, we find that nicotinamide phosphoribosyltranferase (NAMPT) plays a pivotal role in facilitating the formation of E2-induced beige adipocytes, which subsequently suppresses the onset of age-related ER stress. Furthermore, we found that targeting NAMPT signaling, either genetically or pharmacologically, can restore the formation of beige adipocytes by increasing the number of perivascular adipocyte progenitor cells. Conversely, the absence of NAMPT signaling prevents this process. In conclusion, our findings shed light on the mechanisms governing the age-dependent impairment of beige adipocyte formation and underscore the E2-NAMPT controlled ER stress as a key regulator of this process. HighlightsO_LIEstrogen restores beige adipocyte failure along with improved energy metabolism in old mice. C_LIO_LIEstrogen enhances the thermogenic gene program by mitigating age-induced ER stress. C_LIO_LIEstrogen enhances the beige adipogenesis derived from SMA+ APCs. C_LIO_LIInhibiting the NAMPT signaling pathway abolishes estrogen-promoted beige adipogenesis. C_LI

physiology↗

bioRxiv2023

Myosin Light Chain Dephosphorylation by PPP1R12C Promotes Atrial Hypocontractility in Atrial Fibrillation

BackgroundAtrial fibrillation (AF), the most common sustained cardiac arrhythmia, increases thromboembolic stroke risk five-fold. Although atrial hypocontractility contributes to stroke risk in AF, the molecular mechanisms reducing myofilament contractile function remain unknown. We tested the hypothesis that increased expression of PPP1R12C, the PP1 regulatory subunit targeting atrial myosin light chain 2 (MLC2a), causes hypophosphorylation of MLC2a and results in atrial hypocontractility. MethodsRight atrial appendage tissues were isolated from human AF patients versus sinus rhythm (SR) controls. Western blots, co-immunoprecipitation, and phosphorylation studies were performed to examine how the PP1c-PPP1R12C interaction causes MLC2a de-phosphorylation. In vitro studies of pharmacologic MRCK inhibitor (BDP5290) in atrial HL-1 cells were performed to evaluate PP1 holoenzyme activity on MLC2a. Cardiac-specific lentiviral PPP1R12C overexpression was performed in mice to evaluate atrial remodeling with atrial cell shortening assays, echocardiography, and AF inducibility with EP studies. ResultsIn human patients with AF, PPP1R12C expression was increased two-fold versus SR controls (P=2.0x10-2, n=12,12 in each group) with > 40% reduction in MLC2a phosphorylation (P=1.4x10-6, n=12,12 in each group). PPP1R12C-PP1c binding and PPP1R12C-MLC2a binding were significantly increased in AF (P=2.9x10-2 and 6.7x10-3 respectively, n=8,8 in each group). In vitro studies utilizing drug BDP5290, which inhibits T560-PPP1R12C phosphorylation, demonstrated increased PPP1R12C binding with both PP1c and MLC2a, and dephosphorylation of MLC2a. Lenti-12C mice demonstrated a 150% increase in LA size versus controls (P=5.0x10-6, n=12,8,12), with reduced atrial strain and atrial ejection fraction. Pacing-induced AF in Lenti-12C mice was significantly higher than controls (P=1.8x10-2 and 4.1x10-2 respectively, n= 6,6,5). ConclusionsAF patients exhibit increased levels of PPP1R12C protein compared to controls. PPP1R12C overexpression in mice increases PP1c targeting to MLC2a and causes MLC2a dephosphorylation, which reduces atrial contractility and increases AF inducibility. These findings suggest that PP1 regulation of sarcomere function at MLC2a is a key determinant of atrial contractility in AF.

molecular biology↗

bioRxiv2022

Cdkn2a regulates beige fat maintenance through BECN1-mediated autophagy

A potential therapeutic target to curb the obesity and diabetes epidemic is thermogenic beige adipocytes. However, beige adipocytes quickly transition into white adipocytes upon removing stimuli. Here, we define the critical role of Cdkn2a as a molecular pedal for the beige-to-white transition. Beige adipocytes lacking Cdkn2a exhibit prolonged lifespan, and mice are more resistant to diet-induced obesity, along with enhanced energy expenditure and improved glucose tolerance. Mechanistic studies demonstrate that Cdkn2a promotes the expression and activity of BECN1 by directly binding to its mRNA and its negative regulator BCL2L1, activating autophagy and accelerating the beige-to-white transition. Notably, reactivating autophagy by pharmacological or genetic methods abolishes beige adipocyte maintenance induced by Cdkn2a-ablation. Furthermore, hyperactive BECN1 alone significantly accelerates the beige-to-white transition. Collectively, these findings show that Cdkn2a-mediated autophagy serves as a brake system for beige adipocyte maintenance and is a highly promising target for anti-obesity and anti-diabetes therapy. HighlightsO_LICdkn2a ablation promotes beige fat maintenance and ameliorates diet-induced obesity C_LIO_LILoss of Cdkn2a retains beige adipocytes by inhibiting BECN1-mediated autophagy C_LIO_LICdkn2a modulates BECN1 by binding to its mRNA and its inhibitor BCL2L1, respectively C_LIO_LIHyperactive BECN1 is sufficient to accelerate the beige-to-white transition C_LI

cell biology↗

bioRxiv2021

BEdeepoff: an in silico tool for off-target prediction of ABE and CBE base editors

Base editors, including adenine base editors (ABEs) and cytosine base editors (CBEs), are valuable tools for introducing point mutations, but they frequently induce unwanted off-target mutations. Here, we performed a high-throughput gRNA-target library screening to measure editing efficiencies at integrated genomic off-targets and obtained datasets of 48,632 and 52,429 off-targets for ABE and CBE, respectively. We used the datasets to train deep learning models, resulting in ABEdeepoff and CBEdeepoff which can predict editing efficiencies at off-targets. These tools are freely accessible via online web server http://www.deephf.com/#/bedeep.

bioinformatics↗

bioRxiv2021

BEdeepon: an in silico tool for prediction of base editor efficiencies and outcomes

Base editors enable direct conversion of one target base into another in a programmable manner, but conversion efficiencies vary dramatically among different targets. Here, we performed a high-throughput gRNA-target library screening to measure conversion efficiencies and outcome product frequencies at integrated genomic targets and obtained datasets of 60,615 and 73,303 targets for ABE and CBE, respectively. We used the datasets to train deep learning models, resulting in ABEdeepon and CBEdeepon which can predict on-target efficiencies and outcome sequence frequencies. The software is freely accessible via online web server http://www.deephf.com/#/bedeep/bedeepon.

bioinformatics↗

bioRxiv2020

Exosomes Facilitate Transmission of SARS-CoV-2 Genome into Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

ABSTRACTThe novel coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has evolved into a worldwide pandemic. Early data suggest that the prevalence and severity of COVID-19 appear to be higher among patients with underlying cardiovascular risk factors. Despite the expression of angiotensin-converting enzyme 2 (ACE2), a functional receptor for SARS-CoV-2 infection, in cardiomyocytes, there has been no conclusive evidence of direct viral infection although the presence of inflammation and viral genome within the hearts of COVID-19 patients have been reported. Here we transduced A549 lung epithelial cells with lentivirus overexpressing selected genes of the SARS-CoV-2. We then isolated extracellular vesicles (EVs) from the supernatant of A549 cells and detected the presence of viral RNA within the purified EVs. Importantly, we observed that human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) were able to actively uptake these EVs and viral genes were subsequently detected in the cardiomyocytes. Accordingly, uptake of EVs containing viral genes led to an upregulation of inflammation-related genes in hiPSC-CMs. Thus, our findings indicate that SARS-CoV-2 RNA-containing EVs represent an indirect route of viral RNA entry into cardiomyocytes.Competing Interest StatementThe authors have declared no competing interest.View Full Text

cell biology↗