Hypoxia inducible factor-1α mediates iron uptake which induces inflammatory response in amoeboid microglial cells in developing periventricular white matter through MAP kinase pathway

Hypoxia-inducible factor upregulation by roxadustat attenuates drug reward by altering brain iron homoeostasis

Substance use disorder remains a major challenge, with an enduring need to identify and evaluate new, translational targets for effective treatment. Here, we report the upregulation of Hypoxia-inducible factor-1α (HIF-1α) expression by roxadustat (Rox), a drug developed for renal anemia that inhibits HIF prolyl hydroxylase to prevent degradation of HIF-1α, administered either systemically or locally into selected brain regions, suppressed morphine (Mor)-induced conditioned place preference (CPP). A similar effect was observed with methamphetamine (METH). Moreover, Rox also inhibited the expression of both established and reinstated Mor-CPP and promoted the extinction of Mor-CPP. Additionally, the elevation of HIF-1α enhanced hepcidin/ferroportin 1 (FPN1)-mediated iron efflux and resulted in cellular iron deficiency, which led to the functional accumulation of the dopamine transporter (DAT) in plasma membranes due to iron deficiency-impaired ubiquitin degradation. Notably, iron-deficient mice generated via a low iron diet mimicked the effect of Rox on the prevention of Mor- or METH-CPP formation, without affecting other types of memory. These data reveal a novel mechanism for HIF-1α and iron involvement in substance use disorder, which may represent a potential novel therapeutic strategy for the treatment of drug abuse. The findings also repurpose Rox by suggesting a potential new indication for the treatment of substance use disorder.

Immunometabolic Signature during Respiratory Viral Infection: A Potential Target for Host-Directed Therapies

RNA viruses are known to induce a wide variety of respiratory tract illnesses, from simple colds to the latest coronavirus pandemic, causing effects on public health and the economy worldwide. Influenza virus (IV), parainfluenza virus (PIV), metapneumovirus (MPV), respiratory syncytial virus (RSV), rhinovirus (RhV), and coronavirus (CoV) are some of the most notable RNA viruses. Despite efforts, due to the high mutation rate, there are still no effective and scalable treatments that accompany the rapid emergence of new diseases associated with respiratory RNA viruses. Host-directed therapies have been applied to combat RNA virus infections by interfering with host cell factors that enhance the ability of immune cells to respond against those pathogens. The reprogramming of immune cell metabolism has recently emerged as a central mechanism in orchestrated immunity against respiratory viruses. Therefore, understanding the metabolic signature of immune cells during virus infection may be a promising tool for developing host-directed therapies. In this review, we revisit recent findings on the immunometabolic modulation in response to infection and discuss how these metabolic pathways may be used as targets for new therapies to combat illnesses caused by respiratory RNA viruses.

An ischemia-homing bioengineered nano-scavenger for specifically alleviating multiple pathogeneses in ischemic stroke

Background

Ischemic stroke is one of the most serious global public health problems. However, the performance of current therapeutic regimens is limited due to their poor target specificity, narrow therapeutic time window, and compromised therapeutic effect. To overcome these barriers, we designed an ischemia-homing bioengineered nano-scavenger by camouflaging a catalase (CAT)-loaded self-assembled tannic acid (TA) nanoparticle with a M2-type microglia membrane (TPC@M2 NPs) for ischemic stroke treatment.

Results

The TPC@M2 NPs can on-demand release TA molecules to chelate excessive Fe²⁺, while acid-responsively liberating CAT to synergistically scavenge multiple ROS (·OH, ·O₂⁻, and H₂O₂). Besides, the M2 microglia membrane not only can be served as bioinspired therapeutic agents to repolarize M1 microglia into M2 phenotype but also endows the nano-scavenger with ischemia-homing and BBB-crossing capabilities.

Conclusions

The nano-scavenger for specific clearance of multiple pathogenic elements to alleviate inflammation and protect neurons holds great promise for combating ischemic stroke and other inflammation-related diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01602-7.

A Novel Hypoxia-inducible Factor 1α Inhibitor KC7F2 Attenuates Oxygen-induced Retinal Neovascularization

Purpose

KC7F2 is a novel molecule compound that can inhibit the translation of hypoxia-inducible factor 1α (HIF1α). It has been reported to exhibit potential antiangiogenic effect. We hypothesized that KC7F2 could inhibit oxygen-induced retinal neovascularization (RNV). The purpose of this study was to investigate this assumption.

Methods

Oxygen-induced retinopathy (OIR) models in C57BL/6J mice and Sprague-Dawley rats were used for in vivo study. After intraperitoneal injections of KC7F2, RNV was detected by immunofluorescence and hematoxylin and eosin staining. Retinal inflammation was explored by immunofluorescence. EdU incorporation assay, cell counting kit-8 assay, scratch test, transwell assay, and Matrigel assay were used to evaluate the effect of KC7F2 on the proliferation, migration and tube formation of human umbilical vein endothelial cells (HUVEC) induced by vascular endothelial growth factor (VEGF) in vitro. Protein expression was examined by Western blot.

Results

KC7F2 treatment (10 mg/kg/d) in OIR mice significantly attenuated pathological neovascularization and decreased the number of preretinal neovascular cell nuclei, without changing the avascular area, which showed the same trends in OIR rats. Consistently, after the KC7F2 intervention (10 µM), cell proliferation was inhibited in VEGF-induced HUVEC, which was in agreement with the trend observed in the retinas of OIR mice. Meanwhile, KC7F2 suppressed VEGF-induced HUVEC migration and tube formation, and decreased the density of leukocytes and microglia colocalizing neovascular areas in the retinas. Moreover, the HIF1α–VEGF pathway activated in retinas of OIR mice and hypoxia-induced HUVEC, was suppressed by KC7F2 treatment.

Conclusions

The current study revealed that KC7F2 was able to inhibit RNV effectively via HIF1α–VEGF pathway, suggesting that it might be an effective drug for RNV treatment.

Role of endolysosome function in iron metabolism and brain carcinogenesis

Iron, the most abundant metal in human brain, is an essential microelement that regulates numerous cellular mechanisms. Some key physiological roles of iron include oxidative phosphorylation and ATP production, embryonic neuronal development, formation of iron-sulfur clusters, and the regulation of enzymes involved in DNA synthesis and repair. Because of its physiological and pathological importance, iron homeostasis must be tightly regulated by balancing its uptake, transport, and storage. Endosomes and lysosomes (endolysosomes) are acidic organelles known to contain readily releasable stores of various cations including iron and other metals. Increased levels of ferrous (Fe2+) iron can generate reactive oxygen species (ROS) via Fenton chemistry reactions and these increases can damage mitochondria and genomic DNA as well as promote carcinogenesis. Accumulation of iron in the brain has been linked with aging, diet, disease, and cerebral hemorrhage. Further, deregulation of brain iron metabolism has been implicated in carcinogenesis and may be a contributing factor to the increased incidence of brain tumors around the world. Here, we provide insight into mechanisms by which iron accumulation in endolysosomes is altered by pH and lysosome membrane permeabilization. Such events generate excess ROS resulting in mitochondrial DNA damage, fission, and dysfunction, as well as DNA oxidative damage in the nucleus; all of which promote carcinogenesis. A better understanding of the roles that endolysosome iron plays in carcinogenesis may help better inform the development of strategic therapeutic options for cancer treatment and prevention.

Iron homeostasis is altered in response to hypoxia and hypothermic preconditioning in brain glial cells

Background/aim

Altered iron metabolism is one of the pathophysiological mechanisms occurring during hypoxic injuries in the central nervous system. Proper homeostasis of cellular iron is regulated by iron import, storage, and export proteins that prevent excess iron overload or iron starvation in cells. Therapeutic hypothermia is an approved treatment for hypoxic ischemia in newborns, but the underlying molecular mechanism is still unknown. We studied the effects of hypoxia, preceded with preconditioning, on the iron homeostasis of glial cells, known as a major actor in the inflammatory process during perinatal brain injury.

Materials and methods

Primary microglia and astrocytes in culture were exposed to 12 h of hypoxia with or without mild hypothermic preconditioning. The mRNA expression was assessed using qPCR. Iron accumulation was visualized via modified Perl’s histochemistry. Cytokine levels in cell cultures were measured using ELISA.

Results

Hypothermic preconditioning enhanced microglial viability, which previously was decreased in both cell types due to hypoxia. Hypoxia increased iron accumulation in the mixed glial cells and in ferritin expression in both microglia and astrocytes. Hypotermic preconditioning decreased the elevated ferritin-light chain expression significantly in microglia. Iron importer proteins, DMT1 and TfR1, both increased their mRNA expression after hypoxia, and hypothermic preconditioning continued to support the elevation of DMT1 in both glial cell types. Ferroportin expression increased as a survival factor of the glial cell following hypoxia. Hypothermic preconditioning supported this increase in both cell types and was especially significant in astrocytes. IL-10 levels were prominently increased in cell culture after hypothermic preconditioning.

Conclusion

The data suggest that hypothermic preconditioning affects cellular iron homeostasis by regulating the storage and transfer proteins of iron. Regulation of the cellular iron traffic may prevent glial cells from experiencing the detrimental effects of hypoxia-related inflammation.

Heterogeneity of Microglia Phenotypes: Developmental, Functional and Some Therapeutic Considerations

BACKGROUND

Microglia play a pivotal role in maintaining homeostasis in complex brain environment. They first exist as amoeboid microglial cells (AMCs) in the developing brain, but with brain maturation, they transform into ramified microglial cells (RMCs). In pathological conditions, microglia are activated and have been classified into M1 and M2 phenotypes. The roles of AMCs, RMCs and M1/M2 microglia phenotypes especially in pathological conditions have been the focus of many recent studies.

METHODS

Here, we review the early development of the AMCs and RMCs and discuss their specific functions with reference to their anatomic locations, immunochemical coding etc. M1 and M2 microglia phenotypes in different neuropathological conditions are also reviewed.

RESULTS

Activated microglia are engaged in phagocytosis, production of proinflammatory mediators, trophic factors and synaptogenesis etc. Prolonged microglia activation, however, can cause damage to neurons and oligodendrocytes. The M1 and M2 phenotypes featured prominently in pathological conditions are discussed in depth. Experimental evidence suggests that microglia phenotype is being modulated by multiple factors including external and internal stimuli, local demands, epigenetic regulation, and herbal compounds.

CONCLUSION

Prevailing views converge that M2 polarization is neuroprotective. Thus, proper therapeutic designs including the use of anti-inflammatory drugs, herbal agents may be beneficial in suppression of microglial activation, especially M1 phenotype, for amelioration of neuroinflammation in different neuropathological conditions. Finally, recent development of radioligands targeting 18 kDa translocator protein (TSPO) in activated microglia may hold great promises clinically for early detection of brain lesion with the positron emission tomography.

Brain iron transport

Brain iron is a crucial participant and regulator of normal physiological activity. However, excess iron is involved in the formation of free radicals, and has been associated with oxidative damage to neuronal and other brain cells. Abnormally high brain iron levels have been observed in various neurodegenerative diseases, including neurodegeneration with brain iron accumulation, Alzheimer's disease, Parkinson's disease and Huntington's disease. However, the key question of why iron levels increase in the relevant regions of the brain remains to be answered. A full understanding of the homeostatic mechanisms involved in brain iron transport and metabolism is therefore critical not only for elucidating the pathophysiological mechanisms responsible for excess iron accumulation in the brain but also for developing pharmacological interventions to disrupt the chain of pathological events occurring in these neurodegenerative diseases. Numerous studies have been conducted, but to date no effort to synthesize these studies and ideas into a systematic and coherent summary has been made, especially concerning iron transport across the luminal (apical) membrane of the capillary endothelium and the membranes of different brain cell types. Herein, we review key findings on brain iron transport, highlighting the mechanisms involved in iron transport across the luminal (apical) as well as the abluminal (basal) membrane of the blood-brain barrier, the blood-cerebrospinal fluid barrier, and iron uptake and release in neurons, oligodendrocytes, astrocytes and microglia within the brain. We offer suggestions for addressing the many important gaps in our understanding of this important topic, and provide new insights into the potential causes of abnormally increased iron levels in regions of the brain in neurodegenerative disorders.

Biology of Microglia in the Developing Brain

Microglia exist in different morphological forms in the developing brain. They show a small cell body with scanty cytoplasm with many branching processes in the grey matter of the developing brain. However, in the white matter such as the corpus callosum where the unmyelinated axons are loosely organized, they appear in an amoeboid form having a round cell body endowed with copious cytoplasm rich in organelles. The amoeboid cells eventually transform into ramified microglia in the second postnatal week when the tissue becomes more compact with the onset of myelination. Microglia serve as immunocompetent macrophages that act as neuropathology sensors to detect and respond swiftly to subtle changes in the brain tissues in pathological conditions. Microglial functions are broadly considered as protective in the normal brain development as they phagocytose dead cells and sculpt neuronal connections by pruning excess axons and synapses. They also secrete a number of trophic factors such as insulin-like growth factor-1 and transforming growth factor-β among many others that are involved in neuronal and oligodendrocyte survival. On the other hand, microglial cells when activated produce a plethora of molecules such as proinflammatory cytokines, chemokines, reactive oxygen species, and nitric oxide that are implicated in the pathogenesis of many pathological conditions such as epilepsy, cerebral palsy, autism, and perinatal hypoxic-ischemic brain injury. Although many studies have investigated the origin and functions of the microglia in the developing brain, in-depth in vivo studies along with analysis of their transcriptome and epigenetic changes need to be undertaken to elucidate their full potential be it protective or neurotoxic. This would lead to a better understanding of their roles in the healthy and diseased developing brain and advancement of therapeutic strategies to target microglia-mediated neurotoxicity.

The Effects of Prenatal Iron Deficiency and Risperidone Treatment on the Rat Frontal Cortex: A Proteomic Analysis

Prenatal iron deficiency (pID) has been described to increase the risk for neurodevelopmental disorders such as autism and schizophrenia; however, the precise molecular mechanisms are still unknown. Here, we utilized high-throughput MS to examine the proteomic effects of pID in adulthood on the rat frontal cortex area (FCA). In addition, the FCA proteome was examined in adulthood following risperidone treatment in adolescence to see if these effects could be prevented. We identified 1501 proteins of which 100 were significantly differentially expressed in the FCA at postnatal day 90. Pathway analysis of proteins affected by pID revealed changes in metabolic processes, including the tricyclic acid cycle, mitochondrial dysfunction, and P13K/Akt signaling. Interestingly, most of these protein changes were not present in the adult pID offspring who received risperidone in adolescence. Considering the link between pID and several neurodevelopmental disorders such as autism and schizophrenia these presented results bring new perspectives to understand the role of iron in metabolic pathways and provide novel biomarkers for future studies of pID.

Cerebral microbleeds in a neonatal rat model

BACKGROUND

In adult humans, cerebral microbleeds play important roles in neurodegenerative diseases but in neonates, the consequences of cerebral microbleeds are unknown. In rats, a single pro-angiogenic stimulus in utero predisposes to cerebral microbleeds after birth at term, a time when late oligodendrocyte progenitors (pre-oligodendrocytes) dominate in the rat brain. We hypothesized that two independent pro-angiogenic stimuli in utero would be associated with a high likelihood of perinatal microbleeds that would be severely damaging to white matter.

METHODS

Pregnant Wistar rats were subjected to intrauterine ischemia (IUI) and low-dose maternal lipopolysaccharide (mLPS) at embryonic day (E) 19. Pups were born vaginally or abdominally at E21-22. Brains were evaluated for angiogenic markers, microhemorrhages, myelination and axonal development. Neurological function was assessed out to 6 weeks.

RESULTS

mRNA (Vegf, Cd31, Mmp2, Mmp9, Timp1, Timp2) and protein (CD31, MMP2, MMP9) for angiogenic markers, in situ proteolytic activity, and collagen IV immunoreactivity were altered, consistent with an angiogenic response. Vaginally delivered pups exposed to prenatal IUI+mLPS had spontaneous cerebral microbleeds, abnormal neurological function, and dysmorphic, hypomyelinated white matter and axonopathy. Pups exposed to the same pro-angiogenic stimuli in utero but delivered abdominally had minimal cerebral microbleeds, preserved myelination and axonal development, and neurological function similar to naïve controls.

CONCLUSIONS

In rats, pro-angiogenic stimuli in utero can predispose to vascular fragility and lead to cerebral microbleeds. The study of microbleeds in the neonatal rat brain at full gestation may give insights into the consequences of microbleeds in human preterm infants during critical periods of white matter development.

Prenatal Alcohol Exposure Alters Fetal Iron Distribution and Elevates Hepatic Hepcidin in a Rat Model of Fetal Alcohol Spectrum Disorders

BACKGROUND

Prenatal alcohol exposure (PAE) causes neurodevelopmental disabilities, and gestational iron deficiency (ID) selectively worsens learning and neuroanatomical and growth impairments in PAE. It is unknown why ID worsens outcomes in alcohol-exposed offspring.

OBJECTIVE

We hypothesized that PAE alters maternal-fetal iron distribution or its regulation.

METHODS

Nulliparous, 10-wk-old, Long-Evans rats were mated and then fed iron-sufficient (100 mg Fe/kg) or iron-deficient (≤4 mg Fe/kg) diets. On gestational days 13.5-19.5, dams received either 5.0 g ethanol/kg body weight (PAE) or isocaloric maltodextrin by oral gavage. On gestational day 20.5, maternal and fetal clinical blood counts, tissue mineral and iron transport protein concentrations, and hepatic hepcidin mRNA expression were determined.

RESULTS

In fetal brain and liver (P < 0.001) and in maternal liver (P < 0.005), ID decreased iron (total and nonheme) and ferritin content by nearly 200%. PAE reduced fetal bodyweight (P < 0.001) and interacted with ID (P < 0.001) to reduce it by an additional 20%. Independent of maternal iron status, PAE increased fetal liver iron (30-60%, P < 0.001) and decreased brain iron content (total and nonheme, 15-20%, P ≤ 0.050). ID-PAE brains had lower ferritin, transferrin, and transferrin receptor content (P ≤ 0.002) than ID-maltodextrin brains. PAE reduced fetal hematocrit, hemoglobin, and red blood cell numbers (P < 0.003) independently of iron status. Unexpectedly, and also independent of iron status, PAE increased maternal and fetal hepatic hepcidin mRNA expression >300% (P < 0.001).

CONCLUSIONS

PAE altered fetal iron distribution independent of maternal iron status in rats. The elevated iron content of fetal liver suggests that PAE may have limited iron availability for fetal erythropoiesis and brain development. Altered fetal iron distribution may partly explain why maternal ID substantially worsens growth and behavioral outcomes in PAE.

Effect of acetazolamide on cytokines in rats exposed to high altitude

Acute mountain sickness (AMS) is a dangerous hypoxic illness that can affect humans who rapidly reach a high altitude above 2500m. In the study, we investigated the changes of cytokines induced by plateau, and the acetazolamide (ACZ) influenced the cytokines in rats exposed to high altitude. Wistar rats were divided into low altitude (Control), high altitude (HA), and high altitude+ACZ (22.33mg/kg, Bid) (HA+ACZ) group. The rats were acute exposed to high altitude at 4300m for 3days. The HA+ACZ group were given ACZ by intragastric administration. The placebo was equal volume saline. The results showed that hypoxia caused the heart, liver and lung damage, compared with the control group. Supplementation with ACZ significantly alleviated hypoxia-caused damage to the main organs. Compared with the HA group, the biochemical and blood gas indicators of the HA+ACZ group showed no difference, while some cytokines have significantly changed, such as activin A, intercellular adhesion molecule-1 (ICAM-1, CD54), interleukin-1α,2 (IL-1α,2), l-selectin, monocyte chemotactic factor (MCP-1), CC chemokines (MIP-3α) and tissue inhibitor of matrix metalloproteinase 1 (TIMP-1). Then, the significant difference pro-inflammatory cytokines in protein array were chosen for further research. The protein and mRNA content of pro-inflammatory cytokines MCP-1, interleukin-1β (IL-1β), tumor necrosis factor (TNF-α), interferon-γ (IFN-γ) in rat lung were detected. The results demonstrated that the high altitude affected the body's physiological and biochemical parameters, but, ACZ did not change those parameters of the hypoxia rats. This study found that ACZ could decrease the content of pro-inflammatory cytokines, such as MCP-1, IL-1β, TNF-α and IFN-γ in rat lungs, and, the lung injury in the HA+ACZ group reduced. The mechanism that ACZ protected hypoxia rats might be related to changes in cytokine content. The reducing of the pro-inflammatory cytokines in rat lung might be other reason to explain ACZ against the acute mountain sickness.

Short communication: high cellular iron levels are associated with increased HIV infection and replication

HIV is a pandemic disease, and many cellular and systemic factors are known to alter its infectivity and replication. Earlier studies had suggested that anemia is common in HIV-infected patients; however, higher iron was also observed in AIDS patients prior to the introduction of antiretroviral therapy (ART). Therefore, the relationship between iron and viral infection is not well delineated. To address this issue, we altered the levels of cellular iron in primary CD4(+) T cells and showed that higher iron is associated with increased HIV infection and replication. In addition, HIV infection alone leads to increased cellular iron, and several ART drugs increase cellular iron independent of HIV infection. Finally, HIV infection is associated with increased serum iron in HIV-positive patients regardless of treatment with ART. These results establish a relationship between iron and HIV infection and suggest that iron homeostasis may be a viable therapeutic target for HIV.

Long-term vision and non-vision dominant behavioral deficits in the 2-VO rats are accompanied by time and regional glial activation in the white matter

The permanent occlusion of common carotid arteries (2-VO) in rats has been shown to induce progressive and long-lasting deficits in cognitive performance, however, whether these aberrant behaviors are attributed to visual dysfunction or cognitive impairment and what are the underlying mechanisms, remain controversial. In the present study, vision dominant (Morris water maze) and non-vision dominant (voice-cued fear conditioning) behavioral tests were assigned to comprehensively evaluate the influence of 2-VO lesion on cognitive behaviors. In the Morris water maze test, escape latencies of 2-VO rats were markedly increased in both hidden and unfixed visible platform tasks, which were accompanied by severe retinal damage. In the voice-cued fear conditioning test, significant reduction in the percentage of freezing behavior was observed at 60 days after 2-VO lesion. Chronic lesion by 2-VO failed to cause noticeable changes in the grey matter, as indicated by intact hippocampal and prefrontal cortical structures, sustained synaptic protein levels and glial cell numbers. In contrast, aberrant arrangement of myelinated axons was observed in the optic tract, but not in the corpus callosum and inner capsule of 2-VO rats. Concurrently, marked astrocyte proliferation and microglia activation in the optic tract occurred at 3 days after 2-VO lesion, and continued for up to 60 days. Differently, robust glial activation was observed in the corpus callosum at 3 days after 2-VO surgery, and then gradually returned to the baseline level at 14 and 60 days. Our study reported for the first time about the effect of 2-VO on the long-term cognitive impairment in the non-vision dominant fear conditioning test, which may be more applicable than the Morris water maze test for assessing 2-VO associated cognitive function. The time and region specific glial activation in the white matter may relate to retinal impairment, even behavioral deficits, in the setting of chronic cerebral hypoperfusion.

Iron chelation and multiple sclerosis

Histochemical and MRI studies have demonstrated that MS (multiple sclerosis) patients have abnormal deposition of iron in both gray and white matter structures. Data is emerging indicating that this iron could partake in pathogenesis by various mechanisms, e.g., promoting the production of reactive oxygen species and enhancing the production of proinflammatory cytokines. Iron chelation therapy could be a viable strategy to block iron-related pathological events or it can confer cellular protection by stabilizing hypoxia inducible factor 1α, a transcription factor that normally responds to hypoxic conditions. Iron chelation has been shown to protect against disease progression and/or limit iron accumulation in some neurological disorders or their experimental models. Data from studies that administered a chelator to animals with experimental autoimmune encephalomyelitis, a model of MS, support the rationale for examining this treatment approach in MS. Preliminary clinical studies have been performed in MS patients using deferoxamine. Although some side effects were observed, the large majority of patients were able to tolerate the arduous administration regimen, i.e., 6-8 h of subcutaneous infusion, and all side effects resolved upon discontinuation of treatment. Importantly, these preliminary studies did not identify a disqualifying event for this experimental approach. More recently developed chelators, deferasirox and deferiprone, are more desirable for possible use in MS given their oral administration, and importantly, deferiprone can cross the blood-brain barrier. However, experiences from other conditions indicate that the potential for adverse events during chelation therapy necessitates close patient monitoring and a carefully considered administration regimen.