Stress-induced Defects Research Articles

Sex-specific GABAergic microcircuits that switch vulnerability into resilience to stress and reverse the effects of chronic stress exposure.

Clinical and preclinical studies have identified somatostatin (SST)-positive interneurons as key elements that regulate the vulnerability to stress-related psychiatric disorders. Conversely, disinhibition of SST neurons in mice results in resilience to the behavioral effects of chronic stress. Here we established a low-dose chronic chemogenetic protocol to map these changes in positively and negatively motivated behaviors to specific brain regions. AAV-hM3Dq mediated chronic activation of SST neurons in the prelimbic cortex (PLC) had antidepressant drug-like effects on anxiety- and anhedonia-related motivated behaviors in male but not female mice. Analogous manipulation of the ventral hippocampus (vHPC) had such effects in female but not male mice. Moreover, activation of SST neurons in the PLC of male and the vHPC of female mice resulted in stress resilience. Activation of SST neurons in the PLC reversed prior chronic stress-induced defects in motivated behavior in males but was ineffective in females. Conversely, activation of SST neurons in the vHPC reversed chronic stress-induced behavioral alterations in females but not males. Quantitation of c-Fos+ and FosB+ neurons in chronic stress-exposed mice revealed that chronic activation of SST neurons leads to a paradoxical increase in pyramidal cell activity. Collectively, these data demonstrate that GABAergic microcircuits driven by dendrite targeting interneurons enable sex- and brain-region-specific neural plasticity that promotes stress resilience and reverses stress-induced anxiety- and anhedonia-like motivated behavior. Our studies provide a mechanistic rationale for antidepressant efficacy of dendrite-targeting, low-potency GABAA receptor agonists, independent of sex and despite striking sex differences in the relevant brain substrates.

Dynamic Modeling of Stress-Induced Defect Expansion in VCSELs

Dynamic Modeling of Stress-Induced Defect Expansion in VCSELs

Myocardial perfusion in patients with diabetes mellitus according to stress CMR with adenosine triphosphate

Aim. To evaluate the features of myocardial perfusion according to stress CMR with adenosine triphosphate (ATP) in patients with type 2 diabetes mellitus (DM) and obstructive and non-obstructive coronary arteries (CA).Materials and Methods. Stress СMR with ATP was provided in 55 patients with a suspected or known ischemic heart disease. 39 patients of them had DM type 2. All patients were provided with invasive coronary angiography or non-invasive CT angiogram to evaluate lesions of CA. Study protocol included providing myocardial perfusion in a rest and stress with ATP in dose 160 mkg/ kg/min during 3-6 min.Results. The detection of stress-induced perfusion defects was statistically significantly associated with the obstructive CA lesions of more than 50% (p<0,001). With non-obstructive CA lesions less than 50%, perfusion defects were found more often in patients with DM (36.4%) than in patients without DM (16.7%). Furthermore, the detection of stress-induced myocardial ischemia of patients with DM was not statistically significantly associated with obstructive CA (p=0,071) In case of positive result of stress CMR, patients with DM had a more widespread zone of stress-induced ischemia in the form of increase involved segments (6,45±3,78 (4,78-8,13) than patients without DM (3,17±1,60 (1,49-4,85), p=0,050).Conclusion. Patients with DM and non-obstructive CA are more likely to have a myocardial perfusion disorder than patients without DM due to coronary microvascular dysfunction.

Calebin A modulates inflammatory and autophagy signals for the prevention and treatment of osteoarthritis.

Osteoarthritis (OA) is associated with excessive cartilage degradation, inflammation, and decreased autophagy. Insufficient efficacy of conventional monotherapies and poor tissue regeneration due to side effects are just some of the unresolved issues. Our previous research has shown that Calebin A (CA), a component of turmeric (Curcuma longa), has pronounced anti-inflammatory and anti-oxidative effects by modulating various cell signaling pathways. Whether CA protects chondrocytes from degradation and apoptosis in the OA environment (EN), particularly via the autophagy signaling pathway, is however completely unclear. To study the anti-degradative and anti-apoptotic effects of CA in an inflamed joint, an in vitro model of OA-EN was created and treated with antisense oligonucleotides targeting NF-κB (ASO-NF-κB), and IκB kinase (IKK) inhibitor (BMS-345541) or the autophagy inhibitor 3-methyladenine (3-MA) and/or CA to affect chondrocyte proliferation, degradation, apoptosis, and autophagy. The mechanisms underlying the CA effects were investigated by MTT assays, immunofluorescence, transmission electron microscopy, and Western blot analysis in a 3D-OA high-density culture model. In contrast to OA-EN or TNF-α-EN, a treatment with CA protects chondrocytes from stress-induced defects by inhibiting apoptosis, matrix degradation, and signaling pathways associated with inflammation (NF-κB, MMP9) or autophagy-repression (mTOR/PI3K/Akt), while promoting the expression of matrix compounds (collagen II, cartilage specific proteoglycans), transcription factor Sox9, and autophagy-associated proteins (Beclin-1, LC3). However, the preventive properties of CA in OA-EN could be partially abrogated by the autophagy inhibitor 3-MA. The present results reveal for the first time that CA is able to ameliorate the progression of OA by modulating autophagy pathway, inhibiting inflammation and apoptosis in chondrocytes, suggesting that CA may be a novel therapeutic compound for OA.

Enhanced performance of fiber-based perovskite solar cell achieved by multi-functional high polymer doping strategy

Toward the realization of efficient, durable, and sustainable fiber-based perovskite solar cells (fb-PSCs), a comprehensive optimization strategy focused on enhancing electron transport layer (ETL), perovskite (PVK) photovoltaic layer, and hole transport layer (HTL) is presented. A champion PCE of 10.66 % with 37.9 % relative enhancement over control has been achieved in the optimized fb-PSC. A significantly improved mechanical resilience and storage durability are also recorded. Decorating the SnO2 ETL with methylammonium lead triiodide (MAPbI3) strengthened the ETL/PVK interfacial integrity, and doping the MAPbI3 layer with the multi-functional polymer of PJ71 remarkably enhanced the PVK layer’s crystallization quality, and effectively passivated the grain boundary defects. A CO2 pre-treatment of the spiro-OMeTAD HTL enhanced its hole conductivity. It is the synergetic combination of these methodologies that mutually contributed to the performance boost of the fb-PSC. The phenomenological model based on layer conductance shows that the PVK layer chiefly influences the device’s anti-bending ability, followed by the ETL, and HTL the least impact. To further enhance the PCE of fb-PSCs, optimizing the interface and minimizing the stress-induced defects are essential. These measures, coupled with increasing carrier diffusion length and reducing surface recombination, are key to advancing the fb-PSC performance. An encapsulation with polyolefin elastomer substantially reduced the potential lead leakage of the device, and facilitated its eco-friendly application.

Effect of Topical Programmed Death-Ligand1 on Corneal Epithelium in Dry Eye Mouse.

Dry eye disease (DED) is a growing health concern that impacts millions of individuals every year, and is associated with corneal injury, excessive oxidative stress and inflammation. Current therapeutic strategies, including artificial tears and anti-inflammatory agents, are unable to achieve a permanent clinical cure due to their temporary nature or adverse side effects. Therefore, here, we investigated the effectiveness of the topical administration of programmed death-ligand 1 (PD-L1) in the mouse model of DED. The model was generated in C57BL/6 mice by excising the extra orbital lacrimal gland and causing desiccation stress with scopolamine injections. Subsequently, either phosphate-buffered saline (3 µL/eye) or PD-L1 (0.5 µg/mL) was topically administered for 10 days. Tear volume was evaluated with phenol red thread, and corneal fluorescein staining was observed to quantify the corneal epithelial defect. Corneas were collected for histological analysis, and the expression levels of inflammatory signaling proteins such as CD4, CD3e, IL-17, IL-1β, pIkB-α, pNF-kB and pERK1/2 were assessed through immunofluorescence and Western blot techniques. Our results demonstrate that desiccating stress-induced corneal epithelial defect and tear secretion were significantly improved by topical PD-L1 and could reduce corneal CD4+ T cell infiltration, inflammation and apoptosis in a DED mouse model by downregulating IL-17 production and ERK1/2-NFkB pathways.

Technetium-99m Methoxyisobutyl Isonitrile Stress MPI in Suspected Coronary Artery Disease Patients: A Prospective Study to Evaluate Clinical Significance of Adenosine-induced ECG Changes.

The purpose of this study is to evaluate the adenosine pharmacological stress-induced electrocardiogram (ECG) changes and their association with stress-induced ischemic defects on myocardial perfusion scintigraphy (MPS) in the evaluation of coronary artery disease (CAD) and to evaluate event-free survival among patients with positive and negative ECG/MPS image findings. A total of 100 patients were examined using stress MPS from March 2020 to August 2021. Stress-induced ECG changes during adenosine infusion were evaluated. The summed stress score (SSS) was evaluated to identify ischemic defects in myocardium. Association of stress ECG changes and scintigraphic results was evaluated. Out of 100 patients, stress ECG changes during adenosine infusion were seen among 34 patients, whereas 66 patients had normal ECG findings. Positive stress MPS findings with SSS >3 were seen in 22 patients, whereas 78 patients had SSS ≤3. There was no agreement between stress ECG changes and MPS findings with Cohen's kappa coefficient (κ) = -0.023, whereas there was mild agreement between stress ECG changes and SSS >7 with κ = 0.105. Median follow-up of 11 months showed more events among patients with positive ECG changes than negative ECG changes. Adenosine, pharmacological stress is safe to use, but few patients might experience some minor and transient symptoms. Adenosine may induce ECG changes in patients with or without positive MPS findings. Patients with concordant positive findings need aggressive cardiac care, whereas patients with small or no defects on MPS need close monitoring.

Research on the microphysical mechanism of metal magnetic memory testing through 45 # steel under compressive stress

To explore the microphysical mechanism of metal magnetic memory testing (MMMT) technique, the effect of compressive stress on the domain structure in 45# steel specimen and the pinning effect of stress-induced defects on domain walls (DWs) were investigated by in-situ Lorentz Transmission Electron Microscopy (LTEM). The changes in domain structure and defects are observed simultaneously. And the deformation and magnetic moment distribution of the specimen under compressive stress were measured and analyzed. The results show that, the rotation of magnetic moment corresponding to the deformation of the specimen can greatly reduce the magnetoelastic energy according to the calculation of magnetoelastic energy. When stress is removed, the domain structures do not restore, and DWs’ pinning effect of defects could be clearly observed. The results provide a vigorous support for the memory effect of ferromagnetic material on historical stress.

Comparison of Stress-Rest and Stress-LGE Analysis Strategy in Patients Undergoing Stress Perfusion Cardiovascular Magnetic Resonance.

Stress perfusion cardiovascular magnetic resonance can be performed without rest perfusion for the quantification of ischemia burden. However, the optimal method of analysis is uncertain. We identified 666 patients from CE-MARC (Clinical Evaluation of Magnetic Resonance Imaging in Coronary Heart Disease) with complete stress perfusion, rest perfusion, late gadolinium enhancement (LGE), and quantitative coronary angiography data. For each segment of the 16-segment model, perfusion was visually graded during stress and rest imaging, with infarct transmurality assessed from LGE imaging. In the stress-LGE analysis, a segment was defined as ischemic if it had a subendocardial perfusion defect with no infarction. Rest perfusion was not used in this analysis. We compared the diagnostic accuracy of stress-LGE analysis against quantitative coronary angiography and the stress-rest method validated in the original CE-MARC analysis. The diagnostic accuracy of the stress-LGE method was evaluated with different thresholds of infarct transmurality used to define whether an infarcted segment had peri-infarct ischemia. The optimal stress-LGE analysis classified all segments with a stress perfusion defect as ischemic unless they had >75% infarct transmurality (area under the curve, 0.843; sensitivity, 75.6%; specificity, 93.1%; P<0.001). This analysis method has superior diagnostic accuracy to the stress-rest method (area under the curve, 0.834; sensitivity, 73.6%; specificity, 93.1%; P<0.001, P value for difference=0.02). Patients were followed-up for median 6.5 years for major adverse cardiovascular events, with the presence of inducible ischemia by either the stress-LGE or stress-rest analysis being similar and strongly predictive (hazard ratio, 2.65; P<0.001, for both). In this analysis of CE-MARC, the optimum definition of inducible ischemia was the presence of a stress-induced perfusion defect without transmural infarction. This definition improved the diagnostic accuracy compared with the stress-rest analysis validated in the original study. The absence of ischemia by either analysis strategy conferred a favorable long-term prognosis.

Numerical investigation of the mechano-electro-chemical effect of X100 buried pipelines with pre-existing corrosion defects

This study investigates the corrosion kinetics and crack propagation in buried transmission pipelines made of high-strength low alloy steel API X100. Despite its cost-effectiveness and ability to withstand high operating conditions without increasing pipe wall thickness, the corrosion kinetics in near-neutral pH environments for this steel grade is not fully understood. To address this gap, two numerical models were developed. The first model, using COMSOL Multiphysics v5.6, showed higher electrolyte potential at the corrosion defect center due to stress-induced defect growth, increasing corrosion susceptibility. The second model, employing the XFEM approach, evaluated crack initiation, propagation, and von Mises stress distribution along the crack path. This research contributes to a better understanding of corrosion and crack behavior in corroded pipelines, aiding in their performance improvement in near-neutral pH soil environments.

Residual Stress Characterization of an Additively Manufactured Titanium Alloy

Additive manufacturing (AM) has emerged as a revolutionary technology for producing complex and customized components, particularly in aerospace and medical industries, using materials like titanium alloys known for their exceptional strength-to-weight ratio. However, the inherent thermal gradients and rapid solidification processes during AM can introduce residual stresses in the manufactured parts, significantly affecting their mechanical properties and structural integrity. This study focuses on the comprehensive characterization of residual stresses in additively manufactured titanium alloy components, particularly on understanding the influence of various AM process parameters, post-processing techniques, and part geometries. We employ state-of-the-art semi-destructive techniques, incremental hole drilling and strain gauging to map and quantify the residual stress distribution within the fabricated parts. We elucidate the factors contributing to residual stress formation through carefully designed experiments and numerical simulations, including thermal history, cooling rates, and build orientation. The findings of this research not only advance our fundamental understanding of residual stress mechanisms in additively manufactured titanium alloys but also provide valuable insights for optimizing the AM process and post-processing steps to minimize residual stress-induced defects and enhance the reliability of components in critical applications. Ultimately, this work contributes to the broader goal of unlocking the full potential of additive manufacturing for high-performance engineering materials like titanium alloys.

Unveiling the Fatigue Behavior of 2D Hybrid Organic-Inorganic Perovskites: Insights for Long-Term Durability.

2D hybrid organic-inorganic perovskites (HOIPs) are commonly found under subcritical cyclic stresses and suffer from fatigue issues during device operation. However, their fatigue properties remain unknown. Here, the fatigue behavior of (C4 H9 -NH3 )2 (CH3 NH3 )2 Pb3 I10 , the archetype 2D HOIP, is systematically investigated by atomic force microscopy (AFM). It is found that 2D HOIPs are much more fatigue resilient than polymers and can survive over 1 billion cycles. 2D HOIPs tend to exhibit brittle failure at high mean stress levels, but behave as ductile materials at low mean stress levels. These results suggest the presence of a plastic deformation mechanism in these ionic 2D HOIPs at low mean stress levels, which may contribute to the long fatigue lifetime, but is inhibited at higher mean stresses. The stiffness and strength of 2D HOIPs are gradually weakened under subcritical loading, potentially as a result of stress-induced defect nucleation and accumulation. The cyclic loading component can further accelerate this process. The fatigue lifetime of 2D HOIPs can be extended by reducing the mean stress, stress amplitude, or increasing the thickness. These results can provide indispensable insights into designing and engineering 2D HOIPs and other hybrid organic-inorganic materials for long-term mechanical durability.

Optical power degradation mechanisms in 271 nm AlGaN-based deep ultraviolet light-emitting diodes.

The degradation of AlGaN-based UVC LEDs under constant temperature and constant current stress for up to 500 hrs was analyzed in this work. During each degradation stage, the two-dimensional (2D) thermal distributions, I-V curves, optical powers, combining with focused ion beam and scanning electron microscope (FIB/SEM), were thoroughly tested and analyzed the properties and failure mechanisms of UVC LEDs. The results show that: 1) the opto-electrical characteristics measured before/during stress indicate that the increased leakage current and the generation of stress-induced defects increase the non-radiative recombination in the early stress stage, resulting in a decrease in optical power; 2) the increase of temperature caused by the deterioration of the Cr/Al layer of p-metal after 48 hrs of stress aggravates the optical power in UVC LEDs. The 2D thermal distribution in conjunction with FIB/SEM provide a fast and visual way to precisely locate and analyze the failure mechanisms of UVC LEDs.

Influence of Several Heat Treatments on Residual Stress in Laser Powder Bed-Fused Maraging 18Ni-300 Steel

In laser powder bed fusion, process-inherited thermal residual stress is developed due to the thermal strain misfit between each layer. Detailed analysis and a prediction of the residual stress are needed because it can induce distortions of the components and, in some serious cases, stress-induced defects such as cracking. In this work, the effects of heat treatment conditions on residual stress in maraging 18Ni-300 steel, fabricated by laser powder bed fusion, were investigated. Cantilever-shaped specimens were used to experimentally analyze residual stress caused by the distortions of the specimens while cutting them from the supporters. The cantilever samples showed complex distortion behavior in the as-built state. They bent downward while cutting them from the supporter when the thickness was relatively thin, and the bending deformation became upward instead of downward with increasing thickness. Interpreting this behavior by finite element simulation showed that the downward bending was due to the compressive stress state at the top layer of the maraging steel. When the cantilever specimens were aging heat treated, the distortions were significantly reduced, implying that the process-inherited residual stress was diminished.

Association of Long Noncoding RNA Expression Signatures with Stress-Induced Myocardial Perfusion Defects.

Stress-induced myocardial perfusion defects found in dipyridamole-thallium-201 single-photon emission computed tomography imaging may indicate vascular perfusion abnormalities and risk of obstructive or nonobstructive coronary heart disease. Besides nuclear imaging and subsequent coronary angiography (CAG), no blood test can indicate whether dysregulated homeostasis is associated with stress-induced myocardial perfusion defects. This study investigated the expression signature of long noncoding RNAs (lncRNAs) and genes involved in vascular inflammation and stress response in the blood of patients with stress-induced myocardial perfusion abnormalities (n = 27). The results revealed an expression signature consisting of the upregulation of RMRP (p < 0.01) and downregulations of THRIL (p < 0.01) and HIF1A (p < 0.01) among patients with a positive thallium stress test and no significant coronary artery stenosis within 6 months after baseline treatment. We developed a scoring system based on the expression signatures of RMRP, MIAT, NTT, MALAT1, HSPA1A, and NLRP3 to predict the need for further CAG among patients with moderate-to-significant stress-induced myocardial perfusion defects (area under the receiver operating characteristic curve = 0.963). Therefore, we identified a dysregulated expression profile of lncRNA-based genes in the blood that could be valuable for the early detection of vascular homeostasis imbalance and personalized therapy.

Stress waves in laser-material interaction: From atomistic understanding to nanoscale characterization

During pulsed laser-assisted manufacturing, the extremely high-temperature gradient in space will lead to very high-stress waves that play a critical role in structuring. Both shear and normal stress waves emerge in space. This work provides a review and perspective based on our past work spanning theoretical analysis, 1D molecular dynamics (MD) modeling, 3D MD modeling, and experimental characterization. Discussions are given on the non-Fourier effect during ultrafast laser-material interaction, stress-induced structural defects in recrystallization, and ablation confinement by ambient gas and nanotip during nanotip-assisted near-field nanomanufacturing. The presence of stress waves in space could cause permanent and temporary damages, and these damages are more caused by the shear stresses than the normal ones where the compressive component usually is much stronger than the tensile part. Due to the fact of very fast stress waves propagation and slow cooling and solidification, it is very challenging to conduct MD modeling of the entire domain even using stage-of-the-art parallel computation. Hybrid modeling that combines MD and macroscale modelings provides a better choice to tackle this problem. Time-resolved ultrafast temperature and stress characterization are still highly needed to provide deep physics understanding of laser-material interaction toward process control and optimization.

Mechanical behavior and constitutive model of frozen soil subjected to cyclic impact loading

During the construction and service of projects in cold regions, frozen soil generally experiences strong dynamic loads, such as high-speed collisions and impact tunneling. Notably, during the mining of frozen soil in cold regions, the soil suffers from multiple impact loads owing to the drilling and blasting. To ensure project safety, the deformation and failure of frozen soil near the excavation face under load must be controlled using passive support technology. Thus, the cyclic dynamic response and constitutive model of frozen soil under a one-dimensional strain state must be studied for the safe implementation of projects in cold regions. Cyclic impact is the main driving force for defect development, which can induce multiple types of damage, such as sliding friction and instability propagation of microcracks, non-reversible plastic failure, ice phase transition, and weak interval of structure formation. Frequent impact loading is accompanied by the permeation and reflection of stress waves and the dissipation and propagation of energy, ultimately leading to a decline in the bearing performance of frozen soil, which exhibits dynamic fatigue characteristics. Based on the split Hopkinson pressure bar equipment, this study analyzed the strength deformation characteristics and toughness evolution law of frozen soil under cyclic impact loading and clarified the influence mechanism of damage, the coupling effect between defects, and the connection between wave impedance and the number of cycles. In the process of constructing the constitutive model, first, the slip friction of microcracks was considered based on the meso-mechanical theory. The macro-mesoscale transition and Drucker-Prager yield criteria were combined to construct a mesoscopic constitutive model of frozen soil under passive confining pressure. Subsequently, combined with the irreversible law of energy dissipation, the degradation behavior of frozen soil under cyclic impact loading was characterized by a specific energy absorption value. Furthermore, according to the boundary characteristics and loading conditions, the evolution mode and interaction mechanism of stress-induced defects at the mesoscale were analyzed, including crack propagation, plastic deformation, and progressive thermal damage. A coupling law of multistep damage was constructed based on the wing-shaped crack growth model, cavity collapse model, and relationship between temperature rise and phase transformation. Finally, a thermal–mechanical coupling cyclic mesoscopic model of frozen soil under a one-dimensional strain state was established. The rationality of the model was verified by predicting the strength and deformation behavior of frozen soil over a wide pressure range.

Improved Stability With Atomic-Layer-Deposited Encapsulation on Atomic-Layer In2O3 Transistors by Reliability Characterization

Ultrathin In2O3 and other recently explored low-thermal-budget ultrathin oxide semiconductors have shown great promise for back-end-of-line (BEOL)-compatible logic layers and monolithic 3-D (M3-D) integration. However, the long-term stability and reliability of these defect-rich atomically thin channels have not been intensively explored yet. Here, we present a study of the long-term reliability of transistors with 1.2-nm-thick atomic-layer-deposited (ALD)-grown In2O3 channels by room-temperature positive bias instability (PBI) and negative bias instability (NBI) experiments. The observed behavior can be largely explained by a trap neutrality level (TNL) model. A route to reduce the parameter drift has been developed using encapsulation in sequence with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{T}$ </tex-math></inline-formula> engineering by an O2 plasma treatment. After treatment, the magnitude of long-term <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{T}$ </tex-math></inline-formula> shift is reduced for both positive and negative gate bias stresses, and for negative bias stress, other transistor parameters are stabilized as well. In all cases, the subthreshold swing (SS) does not change over time, suggesting that stress-induced interface defects form far below the conduction band, if at all.

Endophytic extract Zhinengcong alleviates heat stress-induced reproductive defect in Solanum lycopersicum.

High temperature negatively affects reproductive process significantly, leading to tremendous losses in crop quality and yield. Zhinengcong (ZNC), a crude extract from the endophytic fungus Paecilomyces variotii, has been shown to improve plant growth and resistance to biotic and abiotic stresses. We show here that ZNC can also alleviate heat stress-induced reproductive defects in Solanum lycopersicum, such as short-term heat-induced inhibition on pollen viability, germination and tube growth, and long-term heat stress-induced pollen developmental defects. We further demonstrated that ZNC alleviates heat stress by downregulating the expressions of ROS production-related genes, RBOHs, and upregulating antioxidant related genes and the activities of the corresponding enzymes, thus preventing the over accumulation of heat-induced reactive oxygen species (ROS) in anther, pollen grain and pollen tube. Furthermore, spraying application of ZNC onto tomato plants under long-term heat stress promotes fruit and seed bearing in the field. In summary, plant endophytic fungus extract ZNC promotes the reproductive process and yield of tomato plants under heat stress and presents excellent potential in agricultural applications.

Nicotinamide mononucleotide supplementation improves the quality of porcine oocytes under heat stress

BackgroundElevated ambient temperature-caused heat stress is a major concern for livestock production due to its negative impact on animal feed intake, growth, reproduction, and health. Particularly, the germ cells are extremely sensitive to the heat stress. However, the effective approach and strategy regarding how to protect mammalian oocytes from heat stress-induced defects have not been determined.MethodsGerminal vesicle (GV) porcine oocytes were cultured at 41.5 °C for 24 h to induce heat stress, and then cultured at 38.5 °C to the specific developmental stage for subsequent analysis. Nicotinamide mononucleotide (NMN) was dissolved in water to 1 mol/L for a stock solution and further diluted with the maturation medium to the final concentrations of 10 μmol/L, 20 μmol/L, 50 μmol/L or 100 μmol/L, respectively, during heat stress. Immunostaining and fluorescence intensity quantification were applied to assess the effects of heat stress and NMN supplementation on the key processes during the oocyte meiotic maturation.ResultsHere, we report that NMN supplementation improves the quality of porcine oocytes under heat stress. Specifically, we found that heat stress resulted in oocyte maturation failure by disturbing the dynamics of meiotic organelles, including the cytoskeleton assembly, cortical granule distribution and mitochondrial function. In addition, heat stress induced the production of excessive reactive oxygen species (ROS) and DNA damage, leading to the occurrence of apoptosis in oocytes and subsequent embryonic development arrest. More importantly, we validated that supplementation of NMN during heat stress restored the meiotic defects during porcine oocyte maturation.ConclusionsTaken together, our study documents that NMN supplementation is an effective approach to improve the quality of oocytes under heat stress by promoting both nuclear and cytoplasmic maturation.