The germline coordinates mitokine signaling.

The ability of mitochondria to coordinate stress responses across tissues is critical for health. In C. elegans, neurons experiencing mitochondrial stress elicit an inter-tissue signaling pathway through the release of mitokine signals, such as serotonin or the Wnt ligand EGL-20, which activate the mitochondrial unfolded protein response (UPRMT) in the periphery to promote organismal health and lifespan. We find that germline mitochondria play a surprising role in neuron-to-periphery UPRMT signaling. Specifically, we find that germline mitochondria signal downstream of neuronal mitokines, Wnt and serotonin, and upstream of lipid metabolic pathways in the periphery to regulate UPRMT activation. We also find that the germline tissue itself is essential for UPRMT signaling. We propose that the germline has a central signaling role in coordinating mitochondrial stress responses across tissues, and germline mitochondria play a defining role in this coordination because of their inherent roles in germline integrity and inter-tissue signaling.

The extracellular matrix integrates mitochondrial homeostasis.

Cellular homeostasis is intricately influenced by stimuli from the microenvironment, including signaling molecules, metabolites, and pathogens. Functioning as a signaling hub within the cell, mitochondria integrate information from various intracellular compartments to regulate cellular signaling and metabolism. Multiple studies have shown that mitochondria may respond to various extracellular signaling events. However, it is less clear how changes in the extracellular matrix (ECM) can impact mitochondrial homeostasis to regulate animal physiology. We find that ECM remodeling alters mitochondrial homeostasis in an evolutionarily conserved manner. Mechanistically, ECM remodeling triggers a TGF-ß response to induce mitochondrial fission and the unfolded protein response of the mitochondria (UPRMT). At the organismal level, ECM remodeling promotes defense of animals against pathogens through enhanced mitochondrial stress responses. We postulate that this ECM-mitochondria crosstalk represents an ancient immune pathway, which detects infection- or mechanical-stress-induced ECM damage, thereby initiating adaptive mitochondria-based immune and metabolic responses.

Lung endothelium, tau, and amyloids in health and disease.

Lung endothelia in the arteries, capillaries, and veins are heterogeneous in structure and function. Lung capillaries in particular represent a unique vascular niche, with a thin yet highly restrictive alveolar-capillary barrier that optimizes gas exchange. Capillary endothelium surveys the blood while simultaneously interpreting cues initiated within the alveolus and communicated via immediately adjacent type I and type II epithelial cells, fibroblasts, and pericytes. This cell-cell communication is necessary to coordinate the immune response to lower respiratory tract infection. Recent discoveries identify an important role for the microtubule-associated protein tau that is expressed in lung capillary endothelia in the host-pathogen interaction. This endothelial tau stabilizes microtubules necessary for barrier integrity, yet infection drives production of cytotoxic tau variants that are released into the airways and circulation, where they contribute to end-organ dysfunction. Similarly, beta-amyloid is produced during infection. Beta-amyloid has antimicrobial activity, but during infection it can acquire cytotoxic activity that is deleterious to the host. The production and function of these cytotoxic tau and amyloid variants are the subject of this review. Lung-derived cytotoxic tau and amyloid variants are a recently discovered mechanism of end-organ dysfunction, including neurocognitive dysfunction, during and in the aftermath of infection.

Surveillance of nuclear pore complex assembly by ESCRT-III/Vps4.

The maintenance of nuclear compartmentalization by the nuclear envelope and nuclear pore complexes (NPCs) is essential for cell function; loss of compartmentalization is associated with cancers, laminopathies, and aging. We uncovered a pathway that surveils NPC assembly intermediates to promote the formation of functional NPCs. Surveillance is mediated by Heh2, a member of the LEM (Lap2-emerin-MAN1) family of integral inner nuclear membrane proteins, which binds to an early NPC assembly intermediate, but not to mature NPCs. Heh2 recruits the endosomal sorting complex required for transport (ESCRT)-III subunit Snf7 and the AAA-ATPase Vps4 to destabilize and clear defective NPC assembly intermediates. When surveillance or clearance is compromised, malformed NPCs accumulate in a storage of improperly assembled nuclear pore complexes compartment, or SINC. The SINC is retained in old mothers to prevent loss of daughter lifespan, highlighting a continuum of mechanisms to ensure nuclear compartmentalization.

Long-term imaging of living adult zebrafish.

The zebrafish has become a widely used animal model due, in large part, to its accessibility to and usefulness for high-resolution optical imaging. Although zebrafish research has historically focused mostly on early development, in recent years the fish has increasingly been used to study regeneration, cancer metastasis, behavior and other processes taking place in juvenile and adult animals. However, imaging of live adult zebrafish is extremely challenging, with survival of adult fish limited to a few tens of minutes using standard imaging methods developed for zebrafish embryos and larvae. Here, we describe a new method for imaging intubated adult zebrafish using a specially designed 3D printed chamber for long-term imaging of adult zebrafish on inverted microscope systems. We demonstrate the utility of this new system by nearly day-long observation of neutrophil recruitment to a wound area in living double-transgenic adult casper zebrafish with fluorescently labeled neutrophils and lymphatic vessels, as well as intubating and imaging the same fish repeatedly. We also show that Mexican cavefish can be intubated and imaged in the same way, demonstrating this method can be used for long-term imaging of adult animals from diverse aquatic species.

Anatomy and development of the pectoral fin vascular network in the zebrafish.

The pectoral fins of teleost fish are analogous structures to human forelimbs, and the developmental mechanisms directing their initial growth and patterning are conserved between fish and tetrapods. The forelimb vasculature is crucial for limb function, and it appears to play important roles during development by promoting development of other limb structures, but the steps leading to its formation are poorly understood. In this study, we use high-resolution imaging to document the stepwise assembly of the zebrafish pectoral fin vasculature. We show that fin vascular network formation is a stereotyped, choreographed process that begins with the growth of an initial vascular loop around the pectoral fin. This loop connects to the dorsal aorta to initiate pectoral vascular circulation. Pectoral fin vascular development continues with concurrent formation of three elaborate vascular plexuses, one in the distal fin that develops into the fin-ray vasculature and two near the base of the fin in association with the developing fin musculature. Our findings detail a complex, yet highly choreographed, series of steps involved in the development of a complete, functional, organ-specific vascular network.

LSD1 promotes the egress of hematopoietic stem and progenitor cells into the bloodstream during the endothelial-to-hematopoietic transition.

During embryonic development, primitive and definitive waves of hematopoiesis take place to provide proper blood cells for each developmental stage, with the possible involvement of epigenetic factors. We previously found that lysine-specific demethylase 1 (LSD1/KDM1A) promotes primitive hematopoietic differentiation by shutting down the gene expression program of hemangioblasts in an Etv2/Etsrp-dependent manner. In the present study, we demonstrated that zebrafish LSD1 also plays important roles in definitive hematopoiesis in the development of hematopoietic stem and progenitor cells. A combination of genetic approaches and imaging analyses allowed us to show that LSD1 promotes the egress of hematopoietic stem and progenitor cells into the bloodstream during the endothelial-to-hematopoietic transition. Analysis of compound mutant lines with Etv2/Etsrp mutant zebrafish revealed that, unlike in primitive hematopoiesis, this function of LSD1 was independent of Etv2/Etsrp. The phenotype of LSD1 mutant zebrafish during the endothelial-to-hematopoietic transition was similar to that of previously reported compound knockout mice of Gfi1/Gfi1b, which forms a complex with LSD1 and represses endothelial genes. Moreover, co-knockdown of zebrafish Gfi1/Gfi1b genes inhibited the development of hematopoietic stem and progenitor cells. We therefore hypothesize that the shutdown of the Gfi1/Gfi1b-target genes during the endothelial-to-hematopoietic transition is one of the key evolutionarily conserved functions of LSD1 in definitive hematopoiesis.

Common factors regulating patterning of the nervous and vascular systems.

The vascular and the nervous systems of vertebrates share many features with similar and often overlapping anatomy. The parallels between these two systems extend to the molecular level, where recent work has identified ever-increasing similarities between the molecular mechanisms employed in the specification, differentiation, and patterning of both systems. This review discusses some of the most recent literature on this subject, with particular emphasis on the roles that the Ephrin, Semaphorin, Netrin, and Slit signaling pathways play in vascular development.

PFKFB3 Inhibits Fructose Metabolism in Pulmonary Microvascular Endothelial Cells.

Pulmonary microvascular endothelial cells contribute to the integrity of the lung gas exchange interface, and they are highly glycolytic. Although glucose and fructose represent discrete substrates available for glycolysis, pulmonary microvascular endothelial cells prefer glucose over fructose, and the mechanisms involved in this selection are unknown. 6-Phosphofructo-2-kinase/fructose-2, 6-bisphosphatase 3 (PFKFB3) is an important glycolytic enzyme that drives glycolytic flux against negative feedback and links glycolytic and fructolytic pathways. We hypothesized that PFKFB3 inhibits fructose metabolism in pulmonary microvascular endothelial cells. We found that PFKFB3 knockout cells survive better than wild-type cells in fructose-rich medium under hypoxia. Seahorse assays, lactate and glucose measurements, and stable isotope tracing showed that PFKFB3 inhibits fructose-hexokinase-mediated glycolysis and oxidative phosphorylation. Microarray analysis revealed that fructose upregulates PFKFB3, and PFKFB3 knockout cells increase fructose-specific GLUT5 (glucose transporter 5) expression. Using conditional endothelial-specific PFKFB3 knockout mice, we demonstrated that endothelial PFKFB3 knockout increases lung tissue lactate production after fructose gavage. Last, we showed that pneumonia increases fructose in BAL fluid in mechanically ventilated ICU patients. Thus, PFKFB3 knockout increases GLUT5 expression and the hexokinase-mediated fructose use in pulmonary microvascular endothelial cells that promotes their survival. Our findings indicate that PFKFB3 is a molecular switch that controls glucose versus fructose use in glycolysis and help better understand lung endothelial cell metabolism during respiratory failure.

Cytotoxic tau released from lung microvascular endothelial cells upon infection with Pseudomonas aeruginosa promotes neuronal tauopathy.

Patients who recover from nosocomial pneumonia oftentimes exhibit long-lasting cognitive impairment comparable with what is observed in Alzheimer's disease patients. We previously hypothesized that the lung endothelium contributes to infection-related neurocognitive dysfunction, because bacteria-exposed endothelial cells release a form(s) of cytotoxic tau that is sufficient to impair long-term potentiation in the hippocampus. However, the full-length lung and endothelial tau isoform(s) have yet to be resolved and it remains unclear whether the infection-induced endothelial cytotoxic tau triggers neuronal tau aggregation. Here, we demonstrate that lung endothelial cells express a big tau isoform and three additional tau isoforms that are similar to neuronal tau, each containing four microtubule-binding repeat domains, and that tau is expressed in lung capillaries in vivo. To test whether infection elicits endothelial tau capable of causing transmissible tau aggregation, the cells were infected with Pseudomonas aeruginosa. The infection-induced tau released from endothelium into the medium-induced neuronal tau aggregation in reporter cells, including reporter cells that express either the four microtubule-binding repeat domains or the full-length tau. Infection-induced release of pathological tau variant(s) from endothelium, and the ability of the endothelial-derived tau to cause neuronal tau aggregation, was abolished in tau knockout cells. After bacterial lung infection, brain homogenates from WT mice, but not from tau knockout mice, initiated tau aggregation. Thus, we conclude that bacterial pneumonia initiates the release of lung endothelial-derived cytotoxic tau, which is capable of propagating a neuronal tauopathy.

Live Imaging of Intracranial Lymphatics in the Zebrafish.

RATIONALE: The recent discovery of meningeal lymphatics in mammals is reshaping our understanding of fluid homeostasis and cellular waste management in the brain, but visualization and experimental analysis of these vessels is challenging in mammals. Although the optical clarity and experimental advantages of zebrafish have made this an essential model organism for studying lymphatic development, the existence of meningeal lymphatics has not yet been reported in this species. OBJECTIVE: Examine the intracranial space of larval, juvenile, and adult zebrafish to determine whether and where intracranial lymphatic vessels are present. METHODS AND RESULTS: Using high-resolution optical imaging of the meninges in living animals, we show that zebrafish possess a meningeal lymphatic network comparable to that found in mammals. We confirm that this network is separate from the blood vascular network and that it drains interstitial fluid from the brain. We document the developmental origins and growth of these vessels into a distinct network separated from the external lymphatics. Finally, we show that these vessels contain immune cells and perform live imaging of immune cell trafficking and transmigration in meningeal lymphatics. CONCLUSIONS: This discovery establishes the zebrafish as a important new model for experimental analysis of meningeal lymphatic development and opens up new avenues for probing meningeal lymphatic function in health and disease.

COVID-19 and Long-Term Outcomes: Lessons from Other Critical Care Illnesses and Potential Mechanisms.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel coronavirus that is currently causing a pandemic and has been termed coronavirus disease (COVID-19). The elderly or those with preexisting conditions like diabetes, hypertension, coronary heart disease, chronic obstructive pulmonary disease, cerebrovascular disease, or kidney dysfunction are more likely to develop severe cases when infected. Patients with COVID-19 admitted to the ICU have higher mortality than non-ICU patients. Critical illness has consistently posed a challenge not only in terms of mortality but also in regard to long-term outcomes of survivors. Patients who survive acute critical illness including, but not limited to, pulmonary and systemic insults associated with acute respiratory distress syndrome, pneumonia, systemic inflammation, and mechanical ventilation, will likely suffer from post-ICU syndrome, a phenomenon of cognitive, psychiatric, and/or physical disability after treatment in the ICU. Post-ICU morbidity and mortality continue to be a cause for concern when considering large-scale studies showing 12-month mortality risks of 11.8-21%. Previous studies have demonstrated that multiple mechanisms, including cytokine release, mitochondrial dysfunction, and even amyloids, may lead to end-organ dysfunction in patients. We hypothesize that COVID-19 infection will lead to post-ICU syndrome via potentially similar mechanisms as other chronic critical illnesses and cause long-term morbidity and mortality in patients. We consider a variety of mechanisms and questions that not only consider the short-term impact of the COVID-19 pandemic but its long-term effects that may not yet be imagined.

In vivo dissection of Rhoa function in vascular development using zebrafish.

The small monomeric GTPase RHOA acts as a master regulator of signal transduction cascades by activating effectors of cellular signaling, including the Rho-associated protein kinases ROCK1/2. Previous in vitro cell culture studies suggest that RHOA can regulate many critical aspects of vascular endothelial cell (EC) biology, including focal adhesion, stress fiber formation, and angiogenesis. However, the specific in vivo roles of RHOA during vascular development and homeostasis are still not well understood. In this study, we examine the in vivo functions of RHOA in regulating vascular development and integrity in zebrafish. We use zebrafish RHOA-ortholog (rhoaa) mutants, transgenic embryos expressing wild type, dominant negative, or constitutively active forms of rhoaa in ECs, pharmacological inhibitors of RHOA and ROCK1/2, and Rock1 and Rock2a/b dgRNP-injected zebrafish embryos to study the in vivo consequences of RHOA gain- and loss-of-function in the vascular endothelium. Our findings document roles for RHOA in vascular integrity, developmental angiogenesis, and vascular morphogenesis in vivo, showing that either too much or too little RHOA activity leads to vascular dysfunction.

Phosphodiesterase 4 mediates interleukin-8-induced heterologous desensitization of the ß2 -adrenergic receptor.

Acute respiratory distress syndrome (ARDS) is a life-threatening illness characterized by decreased alveolar-capillary barrier function, pulmonary edema consisting of proteinaceous fluid, and inhibition of net alveolar fluid transport responsible for resolution of pulmonary edema. There is currently no pharmacotherapy that has proven useful to prevent or treat ARDS, and two trials using beta-agonist therapy to treat ARDS demonstrated no effect. Prior studies indicated that IL-8-induced heterologous desensitization of the beta2-adrenergic receptor (ß2 -AR) led to decreased beta-agonist-induced mobilization of cyclic adenosine monophosphate (cAMP). Interestingly, phosphodiesterase (PDE) 4 inhibitors have been used in human airway diseases characterized by low intracellular cAMP levels and increases in specific cAMP hydrolyzing activity. Therefore, we hypothesized that PDE4 would mediate IL-8-induced heterologous internalization of the ß2 -AR and that PDE4 inhibition would restore beta-agonist-induced functions. We determined that CINC-1 (a functional IL-8 analog in rats) induces internalization of ß2 -AR from the cell surface, and arrestin-2, PDE4, and ß2 -AR form a complex during this process. Furthermore, we determined that cAMP associated with the plasma membrane was adversely affected by ß2 -AR heterologous desensitization. Additionally, we determined that rolipram, a PDE4 inhibitor, reversed CINC-1-induced derangements of cAMP and also caused ß2 -AR to successfully recycle back to the cell surface. Finally, we demonstrated that rolipram could reverse CINC-1-mediated inhibition of beta-agonist-induced alveolar fluid clearance in a murine model of trauma-shock. These results indicate that PDE4 plays a role in CINC-1-induced heterologous internalization of the ß2 -AR; PDE4 inhibition reverses these effects and may be a useful adjunct in particular ARDS patients.

Pneumonia initiates a tauopathy.

Pneumonia causes short- and long-term cognitive dysfunction in a high proportion of patients, although the mechanism(s) responsible for this effect are unknown. Here, we tested the hypothesis that pneumonia-elicited cytotoxic amyloid and tau variants: (1) are present in the circulation during infection; (2) lead to impairment of long-term potentiation; and, (3) inhibit long-term potentiation dependent upon tau. Cytotoxic amyloid and tau species were recovered from the blood and the hippocampus following pneumonia, and they were present in the extracorporeal membrane oxygenation oxygenators of patients with pneumonia, especially in those who died. Introduction of immunopurified blood-borne amyloid and tau into either the airways or the blood of uninfected animals acutely and chronically impaired hippocampal information processing. In contrast, the infection did not impair long-term potentiation in tau knockout mice and the amyloid- and tau-dependent disruption in hippocampal signaling was less severe in tau knockout mice. Moreover, the infection did not elicit cytotoxic amyloid and tau variants in tau knockout mice. Therefore, pneumonia initiates a tauopathy that contributes to cognitive dysfunction.

Carbonic Anhydrase IX and Hypoxia Promote Rat Pulmonary Endothelial Cell Survival during Infection.

Low tidal volume ventilation protects the lung in mechanically ventilated patients. The impact of the accompanying permissive hypoxemia and hypercapnia on endothelial cell recovery from injury is poorly understood. CA (carbonic anhydrase) IX is expressed in pulmonary microvascular endothelial cells (PMVECs), where it contributes to CO2 and pH homeostasis, bioenergetics, and angiogenesis. We hypothesized that CA IX is important for PMVEC survival and that CA IX expression and release from PMVECs are increased during infection. Although the plasma concentration of CA IX was unchanged in human and rat pneumonia, there was a trend toward increasing CA IX in the bronchoalveolar fluid of mechanically ventilated critically ill patients with pneumonia and a significant increase in CA IX in the lung tissue lysates of pneumonia rats. To investigate the functional implications of the lung CA IX increase, we generated PMVEC cell lines harboring domain-specific CA IX mutations. By using these cells, we found that infection promotes intracellular (IC) expression, release, and MMP (metalloproteinase)-mediated extracellular cleavage of CA IX in PMVECs. IC domain deletion uniquely impaired CA IX membrane localization. Loss of the CA IX IC domain promoted cell death after infection, suggesting that the IC domain has an important role in PMVEC survival. We also found that hypoxia improves survival, whereas hypercapnia reverses the protective effect of hypoxia, during infection. Thus, we report 1) that CA IX increases in the lungs of pneumonia rats and 2) that the CA IX IC domain and hypoxia promote PMVEC survival during infection.

To be or not to be: endothelial cell plasticity in development, repair, and disease.

Endothelial cells display an extraordinary plasticity both during development and throughout adult life. During early development, endothelial cells assume arterial, venous, or lymphatic identity, while selected endothelial cells undergo additional fate changes to become hematopoietic progenitor, cardiac valve, and other cell types. Adult endothelial cells are some of the longest-lived cells in the body and their participation as stable components of the vascular wall is critical for the proper function of both the circulatory and lymphatic systems, yet these cells also display a remarkable capacity to undergo changes in their differentiated identity during injury, disease, and even normal physiological changes in the vasculature. Here, we discuss how endothelial cells become specified during development as arterial, venous, or lymphatic endothelial cells or convert into hematopoietic stem and progenitor cells or cardiac valve cells. We compare findings from in vitro and in vivo studies with a focus on the zebrafish as a valuable model for exploring the signaling pathways and environmental cues that drive these transitions. We also discuss how endothelial plasticity can aid in revascularization and repair of tissue after damage- but may have detrimental consequences under disease conditions. By better understanding endothelial plasticity and the mechanisms underlying endothelial fate transitions, we can begin to explore new therapeutic avenues.

Neuronal Wiskott-Aldrich syndrome protein regulates Pseudomonas aeruginosa-induced lung vascular permeability through the modulation of actin cytoskeletal dynamics.

Pulmonary edema associated with increased vascular permeability is a severe complication of Pseudomonas (P.) aeruginosa-induced acute lung injury. The mechanisms underlying P aeruginosa-induced vascular permeability are not well understood. In the present study, we investigated the role of neuronal Wiskott Aldrich syndrome protein (N-WASP) in modulating P aeruginosa-induced vascular permeability. Using lung microvascular endothelial and alveolar epithelial cells, we demonstrated that N-WASP downregulation attenuated P aeruginosa-induced actin stress fiber formation and prevented paracellular permeability. P aeruginosa-induced dissociation between VE-cadherin and ß-catenin, but increased association between N-WASP and VE-cadherin, suggesting a role for N-WASP in promoting P aeruginosa-induced adherens junction rupture. P aeruginosa increased N-WASP-Y256 phosphorylation, which required the activation of Rho GTPase and focal adhesion kinase. Increased N-WASP-Y256 phosphorylation promotes N-WASP and integrin αVß6 association as well as TGF-ß-mediated permeability across alveolar epithelial cells. Inhibition of N-WASP-Y256 phosphorylation by N-WASP-Y256F overexpression blocked N-WASP effects in P aeruginosa-induced actin stress fiber formation and increased paracellular permeability. In vivo, N-WASP knockdown attenuated the development of pulmonary edema and improved survival in a mouse model of P aeruginosa pneumonia. Together, our data demonstrate that N-WASP plays an essential role in P aeruginosa-induced vascular permeability and pulmonary edema through the modulation of actin cytoskeleton dynamics.

Virulent Pseudomonas aeruginosa infection converts antimicrobial amyloids into cytotoxic prions.

Pseudomonas aeruginosa infection elicits the production of cytotoxic amyloids from lung endothelium, yet molecular mechanisms of host-pathogen interaction that underlie the amyloid production are not well understood. We examined the importance of type III secretion system (T3SS) effectors in the production of cytotoxic amyloids. P aeruginosa possessing a functional T3SS and effectors induced the production and release of cytotoxic amyloids from lung endothelium, including beta amyloid, and tau. T3SS effector intoxication was sufficient to generate cytotoxic amyloid release, yet intoxication with exoenzyme Y (ExoY) alone or together with exoenzymes S and T (ExoS/T/Y) generated the most virulent amyloids. Infection with lab and clinical strains engendered cytotoxic amyloids that were capable of being propagated in endothelial cell culture and passed to naïve cells, indicative of a prion strain. Conversely, T3SS-incompetent P aeruginosa infection produced non-cytotoxic amyloids with antimicrobial properties. These findings provide evidence that (1) endothelial intoxication with ExoY is sufficient to elicit self-propagating amyloid cytotoxins during infection, (2) pulmonary endothelium contributes to innate immunity by generating antimicrobial amyloids in response to bacterial infection, and (3) ExoY contributes to the virulence arsenal of P aeruginosa through the subversion of endothelial amyloid host-defense to promote a lung endothelial-derived cytotoxic proteinopathy.