Biology subjects

Nguyen, M. T.

Publications and source records attributed to Nguyen, M. T..

8 recordsLinked to original sources

bioRxiv2026

Sex differences in fear extinction are conditional, not categorical

Threat memories are dynamic, and their behavioral expression can change with subsequent experience and the passage of time. Extinction training can reduce conditioned fear responses, yet these responses may re-emerge over time through spontaneous recovery. Although biological sex has been implicated as modulatory factor in fear and extinction memory processes, studies have reported inconsistent findings. Here, we investigated how differences in extinction training and the timing of memory assessment influence extinction memory in male and female mice. Using contextual fear conditioning, we assessed fear acquisition and threat retention, characterized within-session and across-session extinction during repeated training, and compared shorter (3-minute) and longer (6-minute) daily extinction sessions. We subsequently evaluated extinction memory retention and spontaneous recovery at a later time point. Estrous-cycle stage in females was monitored daily throughout the experimental protocol to examine its potential association with fear and extinction behavior. We found that males and females demonstrated comparable fear acquisition and threat memory, as well as similar extinction progression across days. During longer extinction sessions, but not shorter, males showed greater within-session reductions in freezing, whereas females exhibited modestly higher overall freezing. We found no significant sex difference in the magnitude of spontaneous recovery. There was no significant association between estrous-cycle stage and freezing behavior. Together, our findings suggest that sex-dependent differences in contextual fear extinction are not uniformly expressed, but rather depend on the experimental conditions under which extinction is assessed

neuroscience↗

bioRxiv2026

Autophagic flux is increased in peripheral blood mononuclear cells in atherosclerotic vascular disease and associates inversely with adverse cardiovascular events

Background: Autophagy is a homeostatic pathway supporting stress adaptation and is dysregulated in atherosclerosis. Its potential as a biomarker or therapeutic target in atherosclerotic vascular disease (ASVD) remains incompletely defined. We measured autophagic flux in peripheral blood mononuclear cells (PBMCs) from patients with peripheral arterial disease (PAD) or carotid stenosis (CS), compared with healthy controls, and explored clinical outcome associations. Methods: Ninety-four patients with PAD or CS and 19 healthy controls were studied. Autophagic flux was quantified from fresh blood using a validated ex vivo chloroquine inhibition ELISA measuring LC3BII accumulation. Major adverse cardiovascular events (MACE) and major adverse limb events (MALE) were ascertained over a median follow up of 828 days. Results: The ASVD cohort comprised claudication (n = 16), chronic limb threatening ischemia (CLTI; n = 49), and CS (n = 29). Autophagic flux was higher in ASVD than controls (mean 281.4 vs. 182.3 ng LC3BII/mg protein/h; p < 0.0001) and remained independently associated after multivariable adjustment. Within CLTI, concurrent infection was associated with lower flux (p = 0.001), approaching control levels (p = 0.327). In CLTI, higher flux quartiles were associated with lower MACE risk, most strongly for quartile 3 (hazard ratio 0.07 vs. quartile 1, 95% CI 0.01 to 0.50; p = 0.009). Conclusion: Autophagic flux is elevated in PBMCs from ASVD patients, independent of age and sex. Attenuated flux in CLTI with concurrent infection may indicate autophagic exhaustion in advanced disease. The association between higher flux and lower MACE in CLTI suggests prognostic utility, warranting evaluation in larger prospective studies.

pathology↗

bioRxiv2026

Phospholipase D1 and Phosphatidic Acid are required for MVE Fusion and Exosome Secretion

Extracellular vesicles (EVs) mediate critical intercellular communication, yet the molecular mechanisms that govern multivesicular endosome (MVE) fusion with the plasma membrane and exosome release remain poorly understood. Phospholipase D1 (PLD1) produces phosphatidic acid (PA), a lipid involved in membrane remodeling, but when and how PLD1 and PA act during exosome secretion has not been defined. Here, we used immunofluorescence and total internal reflection fluorescence microscopy (TIRFM) to track individual CD63+ MVEs together with fluorescent PLD1 or a PA reporter (GFP-PASS) in A549 cells. PLD1 localized to CD63+ MVEs during visiting, docking, and fusion. Inhibition or knockdown of PLD1 significantly reduced MVE fusion frequency and decreased the number of secreted small EVs, while causing only a modest reduction in vesicle availability at the plasma membrane. PLD1 inhibition also increased the number of membrane-proximal lysosomes, suggesting that MVEs are diverted toward degradation when fusion is impaired. Meanwhile, PA dynamics were stage-specific: PA remained low on visiting vesicles, gradually accumulated during docking, and exhibited a sharp spike followed by loss during fusion. PA has been reported to stabilize negative curvature and potentially play a role during fusion. To test whether PA influences fusion pore behavior, we quantified CD63 decay duration (t1/2) for individual fusion events. K-means clustering revealed that vesicles with longer decay durations had higher PA levels, whereas short-decay events showed minimal PA. The PA intensity correlated positively with decay duration, while cytosolic GFP did not, indicating a specific relationship between PA and exosome release rates. Furthermore, pharmacological activation of PLD1 increased the proportion of long-decay events. Together, these findings demonstrate that PLD1-generated PA regulates MVE fate at two levels: it promotes the docking-to-fusion transition and prolongs exosome release. This identifies a lipid-based mechanism that controls both the efficiency and kinetics of exosome secretion. SIGNIFICANCE STATEMENTExosome release is essential for cell-cell communication in processes such as development, immunity, and cancer. However, the mechanism that determines whether a multivesicular endosome fuses with the plasma membrane to release exosome cargo remains unclear. We identified a lipid-based mechanism that regulates both fusion and the rate of content release. We show that phospholipase D1 (PLD1) and its product phosphatidic acid (PA) act at late stages of exosome secretion: PLD1 promotes the docking-to-fusion transition and PA levels quantitatively correlate with content release rate, suggesting that PA stabilizes the pore. These findings demonstrate that lipids can control secretion frequency and kinetics, providing a new framework for understanding and modulating exosome output.

biophysics↗

bioRxiv2026

Geographical gradients in leaky sex expression and reproductive effort in a dioecious plant are consistent with selection during range expansion

Range expansion involves repeated dispersal and the establishment of new populations through colonization. Natural selection is therefore expected to favour traits that enhance dispersal and enable uniparental reproduction when mates are scarce. It is known that range-edge populations may evolve increased dispersal and, in hermaphroditic species, an enhanced capacity for self-fertilization. Here, we report results from a large common-garden experiment showing that males and females of the dioecious annual herb Mercurialis annua are more likely to show leaky or inconstant sex expression towards the recently colonized edge of its geographical distribution in Europe than those from the eastern Mediterranean Basin, from where the species expanded its range. Range-edge populations also had greater reproductive effort (RE). Leaky sex expression allows otherwise unisexual individuals of M. annua to produce progeny by self-fertilization, a trait that may have been selected for reproductive assurance during the range expansion. High RE likely facilitated both colonization and subsequent population establishment. Our results show that selection during range expansions may modify reproductive traits towards range margins, extending this notion to the phenomenon of leaky sex expression in dioecious species. Previous work has shown that leaky sex expression in M. annua is strongly heritable; our results now further suggest that has been enhanced by selection for reproductive assurance towards range margins and confirm, in a natural setting, that the trait is not just an expression of developmental instability during floral development or a relic of an incomplete transition to dioecy.

evolutionary biology↗

bioRxiv2025

Genetic diversity shapes behavioral outcomes and reveals sex differences in mice exposed to early life stress

Understanding how genetic variability shapes responses to environmental and developmental factors is critical for advancing translational neuroscience. However, most preclinical studies rely on inbred mouse strains that do not capture the genetic complexity of human populations. One key area of translational research focuses on identifying the neural and behavioral consequences of early life trauma. Rodent models of childhood neglect, such as maternal separation with early weaning (MSEW), have been used in isogenic mouse strains like C57BL/6J (B6) to identify behavioral domains and neural loci of deficits stemming from exposure to MSEW. To understand how genetic diversity may contribute to the outcomes produced by MSEW, and thus inform future studies on the topic, we utilized the Jackson Laboratory Diversity Outbred (DO) line, a population derived from eight founder strains that exhibit broad genetic and phenotypic heterogeneity. We first compared MSEW effects on social behavior in DO mice versus B6 mice, because we have previously found social behavior deficits in B6 mice with a history of MSEW. Indeed, we established that MSEW incited social motivation deficits in DO mice, in a sex-specific manner. We then expanded our investigation of DO mice to test MSEW-related changes in anxiety-like behavior, fear learning and expression, and reward-seeking. Results revealed that MSEW produces distinct, sex-specific phenotypes: female DO mice displayed reduced social motivation and elevated anxiety-like behavior, while male DO mice showed attenuated CS-evoked fear expression and diminished reward-seeking behavior. Additionally, immunohistochemical analysis revealed increased Fos expression in the paraventricular nucleus of the hypothalamus (PVN) in MSEW-exposed DO mice, both at baseline and following acute stress. These findings highlight the importance of incorporating genetically diverse models to better capture the nuances of early life adversity-related outcomes relevant to human populations.

neuroscience↗

bioRxiv2024

Widespread male sterility and trioecy in androdioecious Mercurialis annua: an account of its distribution, its genetic basis, and estimates of its morph-specific fitness components

PremiseAngiosperms range from hermaphroditism through gynodioecy and androdioecy to dioecy. Trioecy, where females and males coexist with hermaphrodites, is rare. Recently, trioecy was documented in hexaploid populations of the wind-pollinated herb Mercurialis annua in Spain. MethodsWe surveyed the frequency of males, hermaphrodites and females in M. annua across its distribution in the Iberian Peninsula, tracked sex-ratio variation in several populations over consecutive generations, and assessed evidence for pollen limitation. In a common garden, we estimated male, female and hermaphrodite fitness. We used controlled crosses to infer the genetic basis of male sterility. Finally, we compared predictions of a deterministic model with the distribution of observed sex ratios in the field based on our fitness estimates and the inferred genetics of sex determination. Key resultsTrioecy is widespread in Spanish and Portuguese populations of M. annua. Males are determined by a dominant (Y-linked) allele, and female expression results from the interaction between cytoplasmic male sterility and multiple nuclear male sterility restorers partially linked to the male determiner. Male pollen production is approximately 12 times while female seed production is less than 1.12 times that of hermaphrodites. The distribution of sex ratios in natural populations conforms with predictions of our deterministic simulations. ConclusionsOur study documents and accounts for a clear case of trioecy in which sex is determined by both maternally and biparentally inherited genes.

plant biology↗

bioRxiv2023

Nature and nurture: comparing mouse behavior in classic versus revised anxiety-like and social behavioral assays in genetically or environmentally defined groups

Widely used rodent anxiety assays like the elevated plus maze (EPM) and the open field test (OFT) are often conflated with rodents natural preference for dark over light environments or protected over open spaces. The EPM and OFT have been used for many decades, yet have also been criticized by generations of behavioral scientists. Several years ago, two revised anxiety assays were designed to improve upon the "classic" tests by excluding the possibility to avoid or escape aversive areas of each maze. The 3-D radial arm maze (3DR) and the 3-D open field test (3Doft) each consist of an open space connected to ambiguous paths toward uncertain escape. This introduces continual motivational conflict, thereby increasing external validity as an anxiety model. But despite this improvement, the revised assays have not caught on. One issue may be that studies to date have not directly compared classic and revised assays in the same animals. To remedy this, we contrasted behavior in a battery of assays (EPM, OFT, 3DR, 3Doft, and a sociability test) in mice defined either genetically by isogenic strain, or environmentally by postnatal experience. Findings indicate that the optimal assay to assess anxiety-like behavior may depend upon grouping variable (e.g. genetic versus environment). We argue that the 3DR may be the most ecologically valid of the anxiety assays tested, while the OFT and 3Doft provided the least useful information. Finally, exposure to multiple assays significantly affected sociability measures, raising concerns for designing and interpreting batteries of behavioral tests in mice.

animal behavior and cognition↗

bioRxiv2022

Exosome secretion kinetics are controlled by temperature

When multivesicular endosomes (MVEs) fuse with the plasma membrane, exosomes are released into the extracellular space where they can affect other cells. Whether exosomes regulate cells nearby or further away depends on whether they remain attached to the secreting cell membrane. The regulation and kinetics of exosome secretion are not well characterized, but probes for directly imaging single MVE fusion events have allowed for visualization of the fusion and release process. In particular, the design of an exosome marker with a pH sensitive dye in the middle of the tetraspanin protein CD63 has facilitated studies of individual MVE fusion events. Using TIRF microscopy, single MVE fusion events were measured in A549 cells held at 23-37{degrees}C and events were identified using an automated detection algorithm. Stable docking precedes fusion almost all of the time and a decrease in temperature was accompanied by decrease in the rate of content loss and a decrease in the frequency of fusion events. The loss of CD63-pHluorin fluorescence was measured at fusion sites and fit with a single or double exponential decay, with approximately 50% of the events requiring two components and a plateau because the loss of fluorescence was typically incomplete. To interpret the kinetics, fusion events were simulated as a point source release of tethered/untethered exosomes coupled with the membrane diffusion of CD63. The experimentally observed decay required three components in the simulation: 1) free exosomes, 2) CD63 membrane diffusion from the endosomal membrane into the plasma membrane at a rate of 0.038 {micro}m2/s, as measured by FRAP, and 3) tethered exosomes. The final component of the decay arises from exosomes being secreted but tethered to the surface with one tether that has a lifetime of 8 seconds at 37{degrees}C and longer at lower temperatures. Simulating with fixed tethers or the absence of tethers fails to replicate the experimental data. This kinetic analysis increases our understanding of exosome secretion and how it is regulated by temperature. Our model suggests that exosome release from the fusion site is incomplete due to post-fusion, membrane attachment.

cell biology↗