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Hypothalamic AMPK-ER Stress-JNK1 Axis Mediates the Central Actions of Thyroid Hormones on Energy Balance.
Thyroid hormones (THs) act in the brain to modulate energy balance. We show that central triiodothyronine (T3) regulates de novo lipogenesis in liver and lipid oxidation in brown adipose tissue (BAT) through the parasympathetic (PSNS) and sympathetic nervous system (SNS), respectively. Central T3 promotes hepatic lipogenesis with parallel stimulation of the thermogenic program in BAT. The action of T3 depends on AMP-activated protein kinase (AMPK)-induced regulation of two signaling pathways in the ventromedial nucleus of the hypothalamus (VMH): decreased ceramide-induced endoplasmic reticulum (ER) stress, which promotes BAT thermogenesis, and increased c-Jun N-terminal kinase (JNK) activation, which controls hepatic lipid metabolism. Of note, ablation of AMPKα1 in steroidogenic factor 1 (SF1) neurons of the VMH fully recapitulated the effect of central T3, pointing to this population in mediating the effect of central THs on metabolism. Overall, these findings uncover the underlying pathways through which central T3 modulates peripheral metabolism.
Estradiol regulates brown adipose tissue thermogenesis via hypothalamic AMPK.
Estrogens play a major role in the modulation of energy balance through central and peripheral actions. Here, we demonstrate that central action of estradiol (E2) inhibits AMP-activated protein kinase (AMPK) through estrogen receptor alpha (ERα) selectively in the ventromedial nucleus of the hypothalamus (VMH), leading to activation of thermogenesis in brown adipose tissue (BAT) through the sympathetic nervous system (SNS) in a feeding-independent manner. Genetic activation of AMPK in the VMH prevented E2-induced increase in BAT-mediated thermogenesis and weight loss. Notably, fluctuations in E2 levels during estrous cycle also modulate this integrated physiological network. Together, these findings demonstrate that E2 regulation of the VMH AMPK-SNS-BAT axis is an important determinant of energy balance and suggest that dysregulation in this axis may account for the common changes in energy homeostasis and obesity linked to dysfunction of the female gonadal axis.
3-Iodothyronamine Induces Tail Vasodilation Through Central Action in Male Mice.
3-Iodothyronamine (3-T1AM) is an endogenous thyroid hormone (TH)-derived metabolite that induces severe hypothermia in mice after systemic administration; however, the underlying mechanisms have remained enigmatic. We show here that the rapid 3-T1AM-induced loss in body temperature is a consequence of peripheral vasodilation and subsequent heat loss (e.g., over the tail surface). The condition is subsequently intensified by hypomotility and a lack of brown adipose tissue activation. Although the possible 3-T1AM targets trace amine-associated receptor 1 or α2a-adrenergic receptor were detected in tail artery and aorta respectively, myograph studies did not show any direct effect of 3-T1AM on vasodilation, suggesting that its actions are likely indirect. Intracerebroventricular application of 3-T1AM, however, replicated the phenotype of tail vasodilation and body temperature decline and led to neuronal activation in the hypothalamus, suggesting that the metabolite causes tail vasodilation through a hypothalamic signaling pathway. Consequently, the 3-T1AM response constitutes anapyrexia rather than hypothermia and closely resembles the heat-stress response mediated by hypothalamic temperature-sensitive neurons. Our results thus underline the well-known role of the hypothalamus as the body's thermostat and suggest an additional molecular link between TH signaling and the central control of body temperature.
Investigation of the Antiarrhythmic Mechanism of the Multi-herbal Medicine Xing Su Ning
Introduction. Xing Su Ning (XSN) is a multi-herbal Chinese medicine produced by Momentum Pharmaceutical Co. Ltd., which is sold in China since 2005 for treating cardiac ventricular arrhythmia, especially arrhythmias induced by cardiac ischemia and viral myocarditis. Aims. To discover the cellular electrophysiological mechanism of the actions of XSN in treating cardiac arrhythmia. Methods. Whole-cell patch-clamp techniques (1) were used to record action potentials and whole cell current in isolated adult rat ventricular myocytes. The myocytes were continuously perfused with physiological solution without or with XSN. Results. XSN at 2mg/ml significantly prolonged the action potential Duration (APD) as shown in the Figure: control was 45.4ms±4.9 and with XSN 2mg/ml was 52.2ms±4.5 (P<0.01, n=7). At this concentration XSN did not have significant effect on the resting potential or the amplitude of the action potential. The effect of XSN is reversible upon the washout of the medicine. Discussion. XSN Prolongs APD, an action that increases the effective refractory period which suppress tachyarrhythmias caused by reentry mechanisms. XSN displays the property of Class III antiarrhythmic drugs, such as amiodarone, without adverse reactions. Further studies on the effect of XSN at various concentrations on action potential and ionic channels, i.e. potassium channels, will be carried out. (1) Ma Y-L et al (2006) European Journal of Pharmacology. 545:87-92 2 4 6 8 10 46 48 50 52 54 b a&c a-Control b-XSN 2mg/ml c-Recovery 20mV 20ms XSN 2mg/ml Action Potential Duration (ms) Time (Min)
Ion Channel Targeted Mechanisms of Anti-arrhythmic Chinese Herbal Medicine Xin Su Ning.
Xin Su Ning (XSN) is a China patented and certified herbal medicine used to treat premature ventricular contractions (PVCs) since 2005. A recent completed clinical trial of 861 patients showed that XSN had similar PVC inhibition rate to the class I antiarrhythmic drug mexiletine, at 65.85% for XSN and 63.10% for mexiletine. We have previously reported that XSN prolongs action potential duration (APD) and suppresses action potential amplitude (APA) of the cardiac ventricular myocytes. In this report we aim to reveal the effect of XSN on the ionic channels that govern APD and APA, which would help to explain the cellular electrophysiological mechanism of XSN. Our main findings are: (1) On ECG recorded in isolated rat, in the presence of XSN the amplitude of R wave was significantly decreased and the amplitude of T wave was increased significantly; (2) XSN blocked hNaV1.5 channel stably transfected cell line in a dose-dependent manner with an IC50 of 0.18 ± 0.02 g/L; and (3) XSN suppresses hERG channels in a dose-dependent manner with an IC50 of 0.34 ± 0.01 g/L. In conclusion, the clinical antiarrhythmic efficacy of XSN is based on its class I and Class III antiarrhythmic properties by suppression hNaV1.5 channel and hERG channels, which are directly responsible for XSN's effect on APA suppression and APD prolongation.
Investigation on the cardio-protective effect of Xin Su Ning on ischemia-reperfusion induced injury in isolated heart.
Introduction: We previously reported that Xin Su Ning (XSN) prolongs action potential duration (APD) of isolated cardiac myocytes1,2. In this study we aimed to identify the cardio-protective effect of XSN in Ischemia-reperfusion (I/R) induced injury in isolated heart. Methods: CHL cell line stably transfected human NaV1.5 channel were used for electrophysiological assay using Axopatch 200B patch clamp system with external and internal solutions prepared as previously described3. For isolated hearts study, male Sprague-Dawley rats (280 ∼ 320g) were divided into control, I/R, XSN 0.05 g/L and 0.1 g/L groups. The hearts were isolated and perfused in retrograde mode at constant pressure of 60 mmHg at 37°C as previously reported3. The extracts of XSN in the form of frozen dried power were administrated by dissolving in the perfusing solution. The measurements used to evaluate XSN’s effects were: Left ventricular developed pressure (LVDP), the rate of pressure development and rate of relaxation (max/min dP/dt), and heart rate (HR). Rate pressure product (RPP) was calculated by multiplying LVDP by HR. The differences between control and other groups were tested using Student’s t-test. Results: XSN blocks human NaV1.5 channel in a dose dependent manner with an IC50 = 0.184±0.017 g/L. XSN at 0.1 g/L produced the significant recovery of LVDP during 60 min reperfusion as shown in Figure 1. Max dP/dt, min dP/dt and HR after 60 min perfusion with vehicle and difference concentrations of XSN were shown in Table 1. Fig. 1 (A) Dose response curve of XSN on human NaV1.5 channel (n=5); (B) Experimental protocol of contractile function of I/R perfused rat heart; (C) percent rate of LVDP of rat hearts with/without XSN treatment after reperfusion 0, 5, 10, 20, 30, 40, 60 min (n=5). The data were presented as mean±SEM. * p<0.05, ** p<0.01, ** p<0.001 vs. I/R group. Table 1 Myocardial contractile function measured ex vivo in a rat I/R heart (mean±SEM, n=5). %pre-ischemia LVDP max dP/dt min dP/dt HR RPP I/R 48.11±2.18 56.82±4.91 48.06±3.67 97.61±5.80 46.82±3.06 XSN 0.05 g/L 61.28±6.08 57.50±7.82 58.07±6.05* 79.15±4.34 48.85±6.43 XSN 0.1 g/L 87.36±4.34*** 93.39±4.53** 90.27±4.25*** 75.56±3.94* 70.57±5.38** * p<0.05, ** p<0.01, ** p<0.001 vs. I/R group. Conclusions: XSN blocked NaV1.5 channel dose dependently, and together with the APD prolongation which could be the cellular electrophysiological mechanisms of the anti-tachyarrhythmic effect of XSN. XSN improved cardiac systolic function on ischemia-reperfusion injured rat heart by increasing LVDP, RPP, max dP/dt and min dP/dt, the protective effect may contribute to the anti-arrhythmic effect of XSN on ischemic heart.
Assessing Oxidative Stress in Tumors by Measuring the Rate of Hyperpolarized [1-13C]Dehydroascorbic Acid Reduction Using 13C Magnetic Resonance Spectroscopy.
Rapid cancer cell proliferation promotes the production of reducing equivalents, which counteract the effects of relatively high levels of reactive oxygen species. Reactive oxygen species levels increase in response to chemotherapy and cell death, whereas an increase in antioxidant capacity can confer resistance to chemotherapy and is associated with an aggressive tumor phenotype. The pentose phosphate pathway is a major site of NADPH production in the cell, which is used to maintain the main intracellular antioxidant, glutathione, in its reduced state. Previous studies have shown that the rate of hyperpolarized [1-13C]dehydroascorbic acid (DHA) reduction, which can be measured in vivo using non-invasive 13C magnetic resonance spectroscopic imaging, is increased in tumors and that this is correlated with the levels of reduced glutathione. We show here that the rate of hyperpolarized [1-13C]DHA reduction is increased in tumors that have been oxidatively prestressed by depleting the glutathione pool by buthionine sulfoximine treatment. This increase was associated with a corresponding increase in pentose phosphate pathway flux, assessed using 13C-labeled glucose, and an increase in glutaredoxin activity, which catalyzes the glutathione-dependent reduction of DHA. These results show that the rate of DHA reduction depends not only on the level of reduced glutathione, but also on the rate of NADPH production, contradicting the conclusions of some previous studies. Hyperpolarized [1-13C]DHA can be used, therefore, to assess the capacity of tumor cells to resist oxidative stress in vivo However, DHA administration resulted in transient respiratory arrest and cardiac depression, which may prevent translation to the clinic.
Validation of structural brain connectivity networks: The impact of scanning parameters.
Evaluation of the structural connectivity (SC) of the brain based on tractography has mainly focused on the choice of diffusion model, tractography algorithm, and their respective parameter settings. Here, we systematically validate SC derived from a post mortem monkey brain, while varying key acquisition parameters such as the b-value, gradient angular resolution and image resolution. As gold standard we use the connectivity matrix obtained invasively with histological tracers by Markov et al. (2014). As performance metric, we use cross entropy as a measure that enables comparison of the relative tracer labeled neuron counts to the streamline counts from tractography. We find that high angular resolution and high signal-to-noise ratio are important to estimate SC, and that SC derived from low image resolution (1.03 mm3) are in better agreement with the tracer network, than those derived from high image resolution (0.53 mm3) or at an even lower image resolution (2.03 mm3). In contradiction, sensitivity and specificity analyses suggest that if the angular resolution is sufficient, the balanced compromise in which sensitivity and specificity are identical remains 60-64% regardless of the other scanning parameters. Interestingly, the tracer graph is assumed to be the gold standard but by thresholding, the balanced compromise increases to 70-75%. Hence, by using performance metrics based on binarized tracer graphs, one risks losing important information, changing the performance of SC graphs derived by tractography and their dependence of different scanning parameters.
Differences in Frontal Network Anatomy Across Primate Species.
The frontal lobe is central to distinctive aspects of human cognition and behavior. Some comparative studies link this to a larger frontal cortex and even larger frontal white matter in humans compared with other primates, yet others dispute these findings. The discrepancies between studies could be explained by limitations of the methods used to quantify volume differences across species, especially when applied to white matter connections. In this study, we used a novel tractography approach to demonstrate that frontal lobe networks, extending within and beyond the frontal lobes, occupy 66% of total brain white matter in humans and 48% in three monkey species: vervets (Chlorocebus aethiops), rhesus macaque (Macaca mulatta) and cynomolgus macaque (Macaca fascicularis), all male. The simian-human differences in proportional frontal tract volume were significant for projection, commissural, and both intralobar and interlobar association tracts. Among the long association tracts, the greatest difference was found for tracts involved in motor planning, auditory memory, top-down control of sensory information, and visuospatial attention, with no significant differences in frontal limbic tracts important for emotional processing and social behaviour. In addition, we found that a nonfrontal tract, the anterior commissure, had a smaller volume fraction in humans, suggesting that the disproportionally large volume of human frontal lobe connections is accompanied by a reduction in the proportion of some nonfrontal connections. These findings support a hypothesis of an overall rearrangement of brain connections during human evolution.SIGNIFICANCE STATEMENT Tractography is a unique tool to map white matter connections in the brains of different species, including humans. This study shows that humans have a greater proportion of frontal lobe connections compared with monkeys, when normalized by total brain white matter volume. In particular, tracts associated with language and higher cognitive functions are disproportionally larger in humans compared with monkeys, whereas other tracts associated with emotional processing are either the same or disproportionally smaller. This supports the hypothesis that the emergence of higher cognitive functions in humans is associated with increased extended frontal connectivity, allowing human brains more efficient cross talk between frontal and other high-order associative areas of the temporal, parietal, and occipital lobes.
Developmental trajectory of social influence integration into perceptual decisions in children.
The opinions of others have a profound influence on decision making in adults. The impact of social influence appears to change during childhood, but the underlying mechanisms and their development remain unclear. We tested 125 neurotypical children between the ages of 6 and 14 years on a perceptual decision task about 3D-motion figures under informational social influence. In these children, a systematic bias in favor of the response of another person emerged at around 12 years of age, regardless of whether the other person was an age-matched peer or an adult. Drift diffusion modeling indicated that this social influence effect in neurotypical children was due to changes in the integration of sensory information, rather than solely a change in decision behavior. When we tested a smaller cohort of 30 age- and IQ-matched autistic children on the same task, we found some early decision bias to social influence, but no evidence for the development of systematic integration of social influence into sensory processing for any age group. Our results suggest that by the early teens, typical neurodevelopment allows social influence to systematically bias perceptual processes in a visual task previously linked to the dorsal visual stream. That the same bias did not appear to emerge in autistic adolescents in this study may explain some of their difficulties in social interactions.
A simple educational programme substantially reduces unnecessary use of coagulation screening testing in an acute medical department.
A review suggested that coagulation screening tests (CST) were frequently performed unnecessarily in our Acute Medical Department. We reviewed the records of all patients for whom CST was ordered in one week (n141) before designing and delivering an e-mail, poster and presentation based educational programme to clinicians. We repeated the review of records three weeks after this programme (n79). The proportion of patients in whom CST was ordered was significantly lower (22% versus 32%, p0.0014) and proportion of CSTs sent with a valid indication was significantly higher (87% versus 49%, p 0.0001) in the second review period. This study demonstrates that a simple educational programme substantially reduces unnecessary use of CST in an acute medical department with significant potential efficiency savings.
An 18-kDa translocator protein (TSPO) polymorphism explains differences in binding affinity of the PET radioligand PBR28.
[(11)C]PBR28 binds the 18-kDa Translocator Protein (TSPO) and is used in positron emission tomography (PET) to detect microglial activation. However, quantitative interpretations of signal are confounded by large interindividual variability in binding affinity, which displays a trimodal distribution compatible with a codominant genetic trait. Here, we tested directly for an underlying genetic mechanism to explain this. Binding affinity of PBR28 was measured in platelets isolated from 41 human subjects and tested for association with polymorphisms in TSPO and genes encoding other proteins in the TSPO complex. Complete agreement was observed between the TSPO Ala147Thr genotype and PBR28 binding affinity phenotype (P value=3.1 × 10(-13)). The TSPO Ala147Thr polymorphism predicts PBR28 binding affinity in human platelets. As all second-generation TSPO PET radioligands tested hitherto display a trimodal distribution in binding affinity analogous to PBR28, testing for this polymorphism may allow quantitative interpretation of TSPO PET studies with these radioligands.
Myocardial perfusion and oxygenation are impaired during stress in severe aortic stenosis and correlate with impaired energetics and subclinical left ventricular dysfunction.
BACKGROUND: Left ventricular (LV) hypertrophy in aortic stenosis (AS) is characterized by reduced myocardial perfusion reserve due to coronary microvascular dysfunction. However, whether this hypoperfusion leads to tissue deoxygenation is unknown. We aimed to assess myocardial oxygenation in severe AS without obstructive coronary artery disease, and to investigate its association with myocardial energetics and function. METHODS: Twenty-eight patients with isolated severe AS and 15 controls underwent cardiovascular magnetic resonance (CMR) for assessment of perfusion (myocardial perfusion reserve index-MPRI) and oxygenation (blood-oxygen level dependent-BOLD signal intensity-SI change) during adenosine stress. LV circumferential strain and phosphocreatine/adenosine triphosphate (PCr/ATP) ratios were assessed using tagging CMR and 31P MR spectroscopy, respectively. RESULTS: AS patients had reduced MPRI (1.1 ± 0.3 vs. controls 1.7 ± 0.3, p < 0.001) and BOLD SI change during stress (5.1 ± 8.9% vs. controls 18.2 ± 10.1%, p = 0.001), as well as reduced PCr/ATP (1.45 ± 0.21 vs. 2.00 ± 0.25, p < 0.001) and LV strain (-16.4 ± 2.7% vs. controls -21.3 ± 1.9%, p < 0.001). Both perfusion reserve and oxygenation showed positive correlations with energetics and LV strain. Furthermore, impaired energetics correlated with reduced strain. Eight months post aortic valve replacement (AVR) (n = 14), perfusion (MPRI 1.6 ± 0.5), oxygenation (BOLD SI change 15.6 ± 7.0%), energetics (PCr/ATP 1.86 ± 0.48) and circumferential strain (-19.4 ± 2.5%) improved significantly. CONCLUSIONS: Severe AS is characterized by impaired perfusion reserve and oxygenation which are related to the degree of derangement in energetics and associated LV dysfunction. These changes are reversible on relief of pressure overload and hypertrophy regression. Strategies aimed at improving oxygen demand-supply balance to preserve myocardial energetics and LV function are promising future therapies.
Obese subjects show sex-specific differences in right ventricular hypertrophy.
BACKGROUND: As right ventricular (RV) remodeling in obesity remains underinvestigated, and the impact of left ventricular (LV) diastolic dysfunction on RV hypertrophy is unknown, we aimed to investigate whether (1) sex-specific patterns of RV remodeling exist in obesity and (2) LV diastolic dysfunction in obesity is related to RV hypertrophy. METHODS AND RESULTS: Seven hundred thirty-nine subjects (women, n=345; men, n=394) without identifiable cardiovascular risk factors (body mass index [BMI], 15.3-59.2 kg/m2) underwent cardiovascular magnetic resonance (1.5 T) to measure RV mass (g), RV end-diastolic volume (mL), RV mass/volume ratio, and LV diastolic peak filling rate (mL/s). All subjects were normotensive (average, 119±11/73±8 mm Hg), normoglycaemic (4.8±0.5 mmol/L), and normocholesterolaemic (4.8±0.9 mmol/L) at the time of scanning. Across both sexes, there was a moderately strong positive correlation between BMI and RV mass (men, +0.8 g per BMI point increase; women, +1.0 g per BMI point increase; both P<0.001). Whereas women exhibited RV cavity dilatation (RV end-diastolic volume, +1.0 mL per BMI point increase; P<0.001), BMI was not correlated with RV end-diastolic volume in men (R=0.04; P=0.51). Concentric RV remodeling was present in both sexes, with RV mass/volume ratio being positively correlated to BMI (men, R=0.41; women, R=0.51; both P<0.001). Irrespective of sex, the LV peak filling rate was negatively correlated with both RV mass (men, R=-0.43; women, R=-0.44; both P<0.001) and RV mass/volume ratio (men, R=-0.37; women, R=-0.35; both P<0.001). CONCLUSIONS: A sex difference in RV remodeling exists in obesity. Whereas men exhibit concentric RV remodeling, women exhibit a mixed pattern of eccentric and concentric remodeling. Regardless of sex, reduced LV diastolic function is associated with concentric RV remodeling.
CagA-ASPP2 complex mediates loss of cell polarity and favors H. pylori colonization of human gastric organoids.
The main risk factor for stomach cancer, the third most common cause of cancer death worldwide, is infection with Helicobacter pylori bacterial strains that inject cytotoxin-associated gene A (CagA). As the first described bacterial oncoprotein, CagA causes gastric epithelial cell transformation by promoting an epithelial-to-mesenchymal transition (EMT)-like phenotype that disrupts junctions and enhances motility and invasiveness of the infected cells. However, the mechanism by which CagA disrupts gastric epithelial cell polarity to achieve its oncogenicity is not fully understood. Here we found that the apoptosis-stimulating protein of p53 2 (ASPP2), a host tumor suppressor and an important CagA target, contributes to the survival of cagA-positive H. pylori in the lumen of infected gastric organoids. Mechanistically, the CagA-ASPP2 interaction is a key event that promotes remodeling of the partitioning-defective (PAR) polarity complex and leads to loss of cell polarity of infected cells. Blockade of cagA-positive H. pylori ASPP2 signaling by inhibitors of the EGFR (epidermal growth factor receptor) signaling pathway-identified by a high-content imaging screen-or by a CagA-binding ASPP2 peptide, prevents the loss of cell polarity and decreases the survival of H. pylori in infected organoids. These findings suggest that maintaining the host cell-polarity barrier would reduce the detrimental consequences of infection by pathogenic bacteria, such as H. pylori, that exploit the epithelial mucosal surface to colonize the host environment.
Cross-species cortical alignment identifies different types of anatomical reorganization in the primate temporal lobe.
Evolutionary adaptations of temporo-parietal cortex are considered to be a critical specialization of the human brain. Cortical adaptations, however, can affect different aspects of brain architecture, including local expansion of the cortical sheet or changes in connectivity between cortical areas. We distinguish different types of changes in brain architecture using a computational neuroanatomy approach. We investigate the extent to which between-species alignment, based on cortical myelin, can predict changes in connectivity patterns across macaque, chimpanzee, and human. We show that expansion and relocation of brain areas can predict terminations of several white matter tracts in temporo-parietal cortex, including the middle and superior longitudinal fasciculus, but not the arcuate fasciculus. This demonstrates that the arcuate fasciculus underwent additional evolutionary modifications affecting the temporal lobe connectivity pattern. This approach can flexibly be extended to include other features of cortical organization and other species, allowing direct tests of comparative hypotheses of brain organization.
Sensorimotor control
© 2017 Elsevier Inc. All rights reserved. Later in development many marine tunicates that start life as mobile larvae fix themselves onto a rock and never move thereafter; they then proceed to autolyze their own nervous systems because they no longer need to waste precious resources on servicing such an energy-hungry organ as the brain. This highlights that the main reason for having a brain at all is to control movement and to plan and execute appropriate actions in any given situation by representing in the brain, the whole panoply of current sensory inputs plus stored memories of previous sensory contexts, of the actions then selected and how successful they were, in order to predict which behavior will now best meet current requirements. Hence this sensorimotor section of the Reference Module in Neuroscience will include not only articles on muscle, proprioception, and spinal, subcortical, and cortical control of muscle contractions, but also articles on how decisions to embark on a particular course of action are made and how these movements are planned in relation to past experience and current predictions of their likely outcomes in order to optimize their adaptation to the needs of the moment.
Disruption of the kringle 1 domain of prothrombin leads to late onset mortality in zebrafish.
The ability to prevent blood loss in response to injury is a conserved function of all vertebrates. Complete deficiency of the central clotting enzyme prothrombin has never been observed in humans and is incompatible with postnatal life in mice, thus limiting the ability to study its role in vivo. Zebrafish are able to tolerate severe hemostatic deficiencies that are lethal in mammals. We have generated a targeted genetic deletion in the kringle 1 domain of zebrafish prothrombin. Homozygous mutant embryos develop normally into the mid-juvenile stage but demonstrate complete mortality by 2 months of age primarily due to internal hemorrhage. Mutants are unable to form occlusive venous and arterial thrombi in response to endothelial injury, a defect that was phenocopied using direct oral anticoagulants. Human prothrombin engineered with the equivalent mutation exhibits a severe reduction in secretion, thrombin generation, and fibrinogen cleavage. Together, these data demonstrate the conserved function of thrombin in zebrafish and provide insight into the role of kringle 1 in prothrombin maturation and activity. Understanding how zebrafish are able to develop normally and survive into early adulthood without thrombin activity will provide important insight into its pleiotropic functions as well as the management of patients with bleeding disorders.