Dual role of neutrophils in modulating liver injury and fibrosis during development and resolution of diet-induced murine steatohepatitis

Inflammatory changes in the liver represent a key feature of non-alcoholic steatohepatitis (NASH), the progressive form of non-alcoholic fatty liver disease (NAFLD). Innate immune activation including hepatic neutrophilic infiltration acts as an important inflammatory trigger as well as a potential mediator of inflammation resolution. In this study, we dissected the effects of neutrophil depletion via anti-lymphocyte antigen 6 complex locus G6D (Ly6G) antibodies administration during ongoing high fat-fructose-cholesterol (FFC) diet-induced murine NASH and during inflammation resolution by switching into a low-fat control diet. During NASH progression, protective effects were shown as HSC activation, cell infiltration and activation of pro-inflammatory macrophages were ameliorated. Furthermore, these changes were contrasted with the effects observed when neutrophil depletion was performed during the resolution phase. Impaired resolving mechanisms, such as a failure to balance the pro and anti-inflammatory cytokines ratio, deficient macrophage phenotypic switch into a pro-restorative profile, and defective repair and remodeling processes were observed when neutrophils were depleted in this scenario. This study described phase-dependent contrasting roles of neutrophils as triggers and pro-resolutive mediators of liver injury and fibrosis associated with diet-induced NASH in mice. These findings have important translational implications at the time of designing NASH therapeutic strategies.

B Lymphocyte-Deficiency in Mice Causes Vascular Dysfunction by Inducing Neutrophilia

B lymphocytes have been implicated in the development of insulin resistance, atherosclerosis and certain types of hypertension. In contrast to these studies, which were performed under pathological conditions, the present study provides evidence for the protective effect of B lymphocytes in maintaining vascular homeostasis under physiological conditions. In young mice not exposed to any known risk factors, the lack of B cells led to massive endothelial dysfunction. The vascular dysfunction in B cell-deficient mice was associated with an increased number of neutrophils in the circulating blood. Neutrophil depletion in B cell-deficient mice resulted in the complete normalization of vascular function, indicating a causal role of neutrophilia. Moreover, vascular function in B cell-deficient mice could be restored by adoptive transfer of naive B-1 cells isolated from wild-type mice. Interestingly, B-1 cell transfer also reduced the number of neutrophils in the recipient mice, further supporting the involvement of neutrophils in the vascular pathology caused by B cell-deficiency. In conclusion, we report in the present study the hitherto undescribed role of B lymphocytes in regulating vascular function. B cell dysregulation may represent a crucial mechanism in vascular pathology.

Angiotensin Receptor Type 1 Inhibition in Lymphopenia and in Neutropenia After Traumatic Brain Injury In Mice: a Randomized Controlled Study (ATLANTIS)

Background: Cerebral inflammation with invasion of neutrophils and lymphocytes is an important factor in the process of secondary brain damage expansion after traumatic brain injury (TBI). Depletion of neutrophils in mice has been shown to reduce neurologic impairment after TBI. The intrinsic cerebral renin-angiotensin system is an important mediator of cerebral inflammation, as inhibition of the angiotensin II receptor type 1 (AT1) with candesartan improves neurologic recovery, and reduces secondary brain damage and cerebral neutrophil invasion after TBI. The present study was therefore designed to determine the role of immune cells in AT1 inhibition-mediated neuroprotection after TBI. Methods: In study A we assessed the effect of neutrophil depletion in mice after TBI. In study B we investigated the impact of RAG1 deficiency (RAG1-/-; mice without mature B- and T-lymphocytes) after TBI. In study C we investigated the role of neutrophils in candesartan mediated protection after TBI in wild-type mice with and without neutrophil depletion. In study D we examined the role of lymphocytes in AT1 inhibition mediated neuroprotection after TBI in RAG1-/-.Results: Neutropenic and RAG1-/- mice showed reduced brain damage compared to control groups. In control antibody treated wild type mice AT1 inhibition reduced lesion volumes and inflammation compared to vehicle, while in neutropenic mice, candesartan had no effect. In RAG1-/- mice AT1 inhibition resulted in reduction of brain damage and neuroinflammation compared to vehicle group. Conclusion: The present results demonstrate, that reduction of neutrophils and of lymphocytes as well as AT1 inhibition in wild type and RAG1-/- mice reduce brain damage and inflammation after TBI. However, AT1 inhibition was neuroprotective in RAG1-/- mice, but not in neutropenic mice. Therefore, the results indicate that AT1 inhibition mediated neuroprotection may be exerted by anti-inflammatory effects on neutrophils, with a subsequent reduction of neutrophil invasion.

Peripheral NOD-like receptor deficient inflammatory macrophages trigger neutrophil infiltration disrupting daytime locomotion

Inflammation is known to disrupt normal behavior, yet the underlying neuroimmune interactions remain elusive. Here, we investigated whether inappropriate macrophage-evoked inflammation alters CNS control of daily-life animal locomotion using a set of zebrafish mutants selected for specific macrophage dysfunction and microglia deficiency. Large-scale genetic and computational analyses revealed that NOD-like receptor nlrc3l mutants are capable of normal motility and visuomotor response, but preferentially swim less in the daytime, suggesting low motivation rather than physical impairment. Examining their brain activities and structures implicate impaired dopaminergic descending circuits, where neutrophils abnormally infiltrate. Furthermore, neutrophil depletion recovered daytime locomotion. Restoring wild-type macrophages reversed behavioral and neutrophil aberrations, while three other microglia-lacking mutants failed to phenocopy nlrc3l mutants. Overall, we reveal how peripheral inflammatory macrophages with elevated pro-inflammatory cues (including il1b, tnfa, cxcl8a) in the absence of microglia co-opt neutrophils to infiltrate the brain, thereby enabling local modulation of neural circuits affecting spontaneous locomotion.

Abstract P365: Neutrophils Contribute To Doxorubicin-induced Cardiotoxicity

Doxorubicin is one for the most effective chemotherapy agents for the treatment of childhoodcancer. Unfortunately Dox treatment causes damage to the heart and childhood cancer survivorsare at higher risk of developing cardiovascular disease at an earlier age than community controls.Understanding the mechanisms by which Dox induces cardiotoxicity is crucial to identifyingpreventive interventions. Innate immune cells, in particular neutrophils, have been shown to playa role in other forms of cardiac disease such as atherosclerosis and myocardial infarction.However, the role of these immune cells in Dox-induced cardiotoxicity is poorly understood.We hypothesized that neutrophils contribute to the cardiac damage caused by Dox treatment andinvestigated this hypothesis using our juvenile mouse cardiotoxicity model. Mice were treated withDoxorubicin for 2 weeks. Echocardiograms were performed before and 24 hours after therapy.Hearts were then harvested, and the heart tissue evaluated for neutrophil infiltration using flowcytometry. There was a decrease in heart function as quantified by echocardiography (ejection fraction [EF] and fractional shortening [FS]) 24 hours after therapy which persisted for 12 weeks. There was also an elevation in neutrophils in heart tissue of Dox-treated mice as compared to controls. To determine whether neutrophils contributed to the functional decline seen in the Dox-treated mice, neutrophils were depleted using an anti-Ly6G antibody prior to Dox treatment. Neutrophil depletion was confirmed by flow cytometry in the blood and hearts of Dox-treated mice. Neutrophil depletion prevented the Dox-induced decrease in EF and FS seen at 24 hours and 12weeks after therapy. Additionally, we also analyzed heart sections for fibrosis and found that neutrophil depletion protected against excessive collagen deposition 12 weeks after therapy. Together these findings suggest that neutrophils contribute Dox-induced cardiotoxicity and that targeting neutrophils may be a potential strategy to prevent Dox-induced cardiotoxicity.

Myofiber injury induces capillary disruption and regeneration of disorganized microvascular networks

Myofibers regenerate following injury, however the microvasculature must also recover to restore skeletal muscle function. We aimed to define the nature of microvascular damage and repair during skeletal muscle injury and regeneration induced by BaCl2. To test the hypothesis that microvascular disruption occurred secondary to myofiber injury in mice, isolated microvessels were exposed to BaCl2 or the myotoxin was injected into the gluteus maximus (GM) muscle. In isolated microvessels, BaCl2 depolarized smooth muscle cells and endothelial cells while increasing [Ca2+]i, but did not elicit cell death. At 1 day post injury (dpi) of the GM, capillary fragmentation coincided with myofiber degeneration while arteriolar and venular networks remained intact; neutrophil depletion before injury did not prevent capillary damage. Perfused capillary networks reformed by 5 dpi in association with more terminal arterioles and were dilated through 10 dpi; with no change in microvascular area or branch point number in regenerating networks, fewer capillaries aligned with myofibers and capillary networks were no longer organized into microvascular units. By 21 dpi, capillary orientation and organization had nearly recovered to that in uninjured GM. We conclude that following their disruption secondary to myofiber damage, capillaries regenerate as disorganized networks that remodel while regenerated myofibers mature.

Maternal Neutrophil Depletion Fails to Avert Systemic Lipopolysaccharide-Induced Early Pregnancy Defects in Mice

Maternal infection-induced early pregnancy complications arise from perturbation of the immune environment at the uterine early blastocyst implantation site (EBIS), yet the underlying mechanisms remain unclear. Here, we demonstrated in a mouse model that the progression of normal pregnancy from days 4 to 6 induced steady migration of leukocytes away from the uterine decidual stromal zone (DSZ) that surrounds the implanted blastocyst. Uterine macrophages were found to be CD206+ M2-polarized. While monocytes were nearly absent in the DSZ, DSZ cells were found to express monocyte marker protein Ly6C. Systemic endotoxic lipopolysaccharide (LPS) exposure on day 5 of pregnancy led to: (1) rapid (at 2 h) induction of neutrophil chemoattractants that promoted huge neutrophil infiltrations at the EBISs by 24 h; (2) rapid (at 2 h) elevation of mRNA levels of MyD88, but not Trif, modulated cytokines at the EBISs; and (3) dose-dependent EBIS defects by day 7 of pregnancy. Yet, elimination of maternal neutrophils using anti-Ly6G antibody prior to LPS exposure failed to avert LPS-induced EBIS defects allowing us to suggest that activation of Tlr4-MyD88 dependent inflammatory pathway is involved in LPS-induced defects at EBISs. Thus, blocking the activation of the Tlr4-MyD88 signaling pathway may be an interesting approach to prevent infection-induced pathology at EBISs.

Tissue Accumulation of Neutrophil Extracellular Traps Mediates Muscle Hyperalgesia in a Mouse Model

Accumulation of uric acid (UA) during muscular trauma is a causative factor involved in the development of muscle hyperalgesia. Neutrophil extracellular traps (NETs), DNA-based reticular structures to capture UA, play a central role in the pain onset of gout attacks; however, the involvement of NETs via the elevation of local UA level in muscle hyperalgesia due to overuse injuries remains unknown. The triceps surae muscles (TSMs) in the unilateral hindlimb of mice were electrically stimulated to induce excessive muscle contraction. Mechanical withdrawal thresholds, tissue UA levels, neutrophil recruitment, protein amount of citrullinated histone 3 (citH3), a major marker of NETs, were investigated. Furthermore, whether neutrophil depletion, extracellular DNA cleavage, and administration of the urate-lowering agent febuxostat could improve muscle hyperalgesia due to NET formation was examined. CitH3 expression upon neutrophil recruitment significantly increased in the stimulated TSMs with an increase in tissue UA levels, whereas febuxostat administration improved muscle hyperalgesia with decreases in citH3 and tissue UA levels, as observed in neutrophil depletion and extracellular DNA digestion. The underlying mechanism of muscle hyperalgesia associated with locally recruited neutrophils forming NETs due to the increased tissue UA levels potentially plays a significant role in creating a vicious circle of muscle pain.

Modulation of HMGB1 Release in APAP-Induced Liver Injury: A Possible Strategy of Chikusetsusaponin V Targeting NETs Formation

Acetaminophen (APAP), one of the most common antipyretic analgesics, which is safe at therapeutic dose, cause acute liver injury and even death at overdose. However, the mechanism of APAP-induced inflammation in liver injury is still controversial. Therefore, effective drug intervention is urgently needed. The aim of this study was to explore the inflammatory exact mechanism of APAP, especially on neutrophils, and to study the intervention effect of Chikusetsusaponin V (CKV) derived from Panax japonicus. Establishment of hepatotoxicity model of APAP in vitro and in vivo. In vitro, HepG2 cells, AML12 cells, primary mouse hepatocytes and neutrophils were used to mimic APAP-affected hepatocytes and neutrophil. In vivo, C57BL/6 mice were administrated overdose of APAP with or without neutrophil depletion or abolishing neutrophil extracellular traps (NETs) formation. In this study, APAP stimulation increased the level of HMGB1, IL-1β and Caspase-1 in mouse liver, especially hepatocytes, which had a synergistic effect with LPS/ATP combination. NETs were formatted at early stage of APAP or HMGB1-stimulated neutrophils’ damage. Conditioned mediums from APAP-treated hepatocytes induced more significant NETs than direct APAP stimulation. Neutrophil depletion or abolishing NETs formation decreased HMGB1 level, eventually blocked hepatocytes necrosis. CKV pretreatment interfered Caspase-1 activation and HMGB1 release in APAP-damaged hepatocytes. CKV also prevented NETs formation. These results indicate that the production of HMGB1 may depend on the activation of Caspase-1 and play a key role in liver inflammation caused by APAP. The cross-dialogue between hepatocytes and neutrophils can be mediated by HMGB1. Therefore, CKV has a positive intervention effect on NETs-related inflammation in APAP-damaged liver, targeting Caspase-1-HMGB1.

Cordycepin confers long-term neuroprotection via inhibiting neutrophil infiltration and neuroinflammation after traumatic brain injury

Background The secondary injury caused by traumatic brain injury (TBI), especially white matter injury (WMI), is highly sensitive to neuroinflammation, which further leads to unfavored long-term outcomes. Although the cross-talk between the three active events, immune cell infiltration, BBB breakdown, and proinflammatory microglial/macrophage polarization, plays a role in the vicious cycle, its mechanisms are not fully understood. It has been reported that cordycepin, an extract from Cordyceps militaris, can inhibit TBI-induced neuroinflammation although the long-term effects of cordycepin remain unknown. Here, we report our investigation of cordycepin’s long-term neuroprotective function and its underlying immunological mechanism. Methods TBI mice model was established with a controlled cortical impact (CCI) method. Cordycepin was intraperitoneally administered twice daily for a week. Neurological outcomes were assessed by behavioral tests, including grid walking test, cylinder test, wire hang test, and rotarod test. Immunofluorescence staining, transmission electron microscopy, and electrophysiology recording were employed to assess histological and functional lesions. Quantitative-PCR and flow cytometry were used to detect neuroinflammation. The tracers of Sulfo-NHS-biotin and Evans blue were assessed for the blood-brain barrier (BBB) leakage. Western blot and gelatin zymography were used to analyze protein activity or expression. Neutrophil depletion in vivo was performed via using Ly6G antibody intraperitoneal injection. Results Cordycepin administration ameliorated long-term neurological deficits and reduced neuronal tissue loss in TBI mice. Meanwhile, the long-term integrity of white matter was also preserved, which was revealed in multiple dimensions, such as morphology, histology, ultrastructure, and electrical conductivity. Cordycepin administration inhibited microglia/macrophage pro-inflammatory polarization and promoted anti-inflammatory polarization after TBI. BBB breach was attenuated by cordycepin administration at 3 days after TBI. Cordycepin suppressed the activities of MMP-2 and MMP-9 and the neutrophil infiltration at 3 days after TBI. Moreover, neutrophil depletion provided a cordycepin-like effect, and cordycepin administration united with neutrophil depletion did not show a benefit of superposition. Conclusions The long-term neuroprotective function of cordycepin via suppressing neutrophil infiltration after TBI, thereby preserving BBB integrity and changing microglia/macrophage polarization. These findings provide significant clinical potentials to improve the quality of life for TBI patients.