Circulating myeloid-derived MMP8 in stress susceptibility and depression.

Psychosocial stress has profound effects on the body, including the immune system and the brain1,2. Although a large number of pre-clinical and clinical studies have linked peripheral immune system alterations to stress-related disorders such as major depressive disorder (MDD)3, the underlying mechanisms are not well understood. Here we show that expression of a circulating myeloid cell-specific proteinase, matrix metalloproteinase 8 (MMP8), is increased in the serum of humans with MDD as well as in stress-susceptible mice following chronic social defeat stress (CSDS). In mice, we show that this increase leads to alterations in extracellular space and neurophysiological changes in the nucleus accumbens (NAc), as well as altered social behaviour. Using a combination of mass cytometry and single-cell RNA sequencing, we performed high-dimensional phenotyping of immune cells in circulation and in the brain and demonstrate that peripheral monocytes are strongly affected by stress. In stress-susceptible mice, both circulating monocytes and monocytes that traffic to the brain showed increased Mmp8 expression following chronic social defeat stress. We further demonstrate that circulating MMP8 directly infiltrates the NAc parenchyma and controls the ultrastructure of the extracellular space. Depleting MMP8 prevented stress-induced social avoidance behaviour and alterations in NAc neurophysiology and extracellular space. Collectively, these data establish a mechanism by which peripheral immune factors can affect central nervous system function and behaviour in the context of stress. Targeting specific peripheral immune cell-derived matrix metalloproteinases could constitute novel therapeutic targets for stress-related neuropsychiatric disorders.

Peripheral immune-derived matrix metalloproteinase promotes stress susceptibility.

Psychosocial stress has profound effects on the body, including the peripheral immune system and the brain1,2. Although a large number of pre-clinical and clinical studies have linked peripheral immune system alterations to stress-related disorders such as major depressive disorder (MDD)3,4,5, the underlying mechanisms are not well understood. Here we show that a peripheral myeloid cell-specific proteinase, matrix metalloproteinase 8 (MMP8), is elevated in serum of subjects with MDD as well as in stress-susceptible (SUS) mice following chronic social defeat stress (CSDS). In mice, we show that this increase leads to alterations in extracellular space and neurophysiological changes in the nucleus accumbens (NAc), thereby altering social behaviour. Using a combination of mass cytometry and single-cell RNA-sequencing, we performed high-dimensional phenotyping of immune cells in circulation and brain and demonstrate that peripheral monocytes are strongly affected by stress. Both peripheral and brain-infiltrating monocytes of SUS mice showed increased Mmp8 expression following CSDS. We further demonstrate that peripheral MMP8 directly infiltrates the NAc parenchyma to control the ultrastructure of the extracellular space. Depleting MMP8 prevented stress-induced social avoidance behaviour and alterations in NAc neurophysiology and extracellular space. Collectively, these data establish a novel mechanism by which peripheral immune factors can affect central nervous system function and behaviour in the context of stress. Targeting specific peripheral immune cell-derived matrix metalloproteinases could constitute novel therapeutic targets for stress-related neuropsychiatric disorders.

A Case of Elsberg Syndrome in the Setting of Asymptomatic SARS-CoV-2 Infection.

ABSTRACT: Elsberg syndrome is a rare cause of lumbosacral radiculitis with concomitant thoracic and lumbosacral myelitis that can be seen after an acute or reactivated viral infection. After the initial coronavirus surge in New York City, a 68-year-old man developed progressive lower extremity weakness and a defined sensory level at the lower abdomen. He had highly elevated SARS-CoV-2 IgG antibodies despite an absence of preceding COVID-19 symptoms. Serial electrodiagnostic testing revealed absent lower extremity late responses, with otherwise normal distal sensorimotor conductions. Electromyography revealed active neurogenic changes and reduced motor unit recruitment in the L3-L4 myotomes. Treatment with methylprednisolone and intravenous immunoglobulin was followed by minimal clinical improvement but re-emergence of the lower extremity late responses on electrodiagnostic testing. We report here, to the best of our knowledge, the first case of suspected COVID-19-associated Elsberg syndrome, which expands the spectrum of neuromuscular manifestations associated with SARS-CoV-2 infection and sheds light on ways to approach diagnostic and treatment options for these patients.

The CNS and the Brain Tumor Microenvironment: Implications for Glioblastoma Immunotherapy.

Glioblastoma (GBM) is the most common and aggressive malignant primary brain tumor in adults. Its aggressive nature is attributed partly to its deeply invasive margins, its molecular and cellular heterogeneity, and uniquely tolerant site of origin-the brain. The immunosuppressive central nervous system (CNS) and GBM microenvironments are significant obstacles to generating an effective and long-lasting anti-tumoral response, as evidenced by this tumor's reduced rate of treatment response and high probability of recurrence. Immunotherapy has revolutionized patients' outcomes across many cancers and may open new avenues for patients with GBM. There is now a range of immunotherapeutic strategies being tested in patients with GBM that target both the innate and adaptive immune compartment. These strategies include antibodies that re-educate tumor macrophages, vaccines that introduce tumor-specific dendritic cells, checkpoint molecule inhibition, engineered T cells, and proteins that help T cells engage directly with tumor cells. Despite this, there is still much ground to be gained in improving the response rates of the various immunotherapies currently being trialed. Through historical and contemporary studies, we examine the fundamentals of CNS immunity that shape how to approach immune modulation in GBM, including the now revamped concept of CNS privilege. We also discuss the preclinical models used to study GBM progression and immunity. Lastly, we discuss the immunotherapeutic strategies currently being studied to help overcome the hurdles of the blood-brain barrier and the immunosuppressive tumor microenvironment.

CSF-1 controls cerebellar microglia and is required for motor function and social interaction.

Microglia, the brain resident macrophages, critically shape forebrain neuronal circuits. However, their precise function in the cerebellum is unknown. Here we show that human and mouse cerebellar microglia express a unique molecular program distinct from forebrain microglia. Cerebellar microglial identity was driven by the CSF-1R ligand CSF-1, independently of the alternate CSF-1R ligand, IL-34. Accordingly, CSF-1 depletion from Nestin+ cells led to severe depletion and transcriptional alterations of cerebellar microglia, while microglia in the forebrain remained intact. Strikingly, CSF-1 deficiency and alteration of cerebellar microglia were associated with reduced Purkinje cells, altered neuronal function, and defects in motor learning and social novelty interactions. These findings reveal a novel CSF-1-CSF-1R signaling-mediated mechanism that contributes to motor function and social behavior.

Role of Monocyte-Derived MicroRNA106b∼25 in Resilience to Social Stress.

BACKGROUND: Clinical studies suggest that heightened peripheral inflammation contributes to the pathogenesis of stress-related disorders, including major depressive disorder. However, the molecular mechanisms within peripheral immune cells that mediate enhanced stress vulnerability are not well known. Because microRNAs (miRs) are important regulators of immune response, we sought to examine their role in mediating inflammatory and behavioral responses to repeated social defeat stress (RSDS), a mouse model of stress vulnerability that produces susceptible and resilient phenotypes. METHODS: We isolated Ly6chigh monocytes via fluorescence-activated cell sorting in the blood of susceptible and resilient mice following RSDS and profiled miR expression via quantitative real-time polymerase chain reaction. Bone marrow chimeric mice were generated to confirm a causal role of the miR-106b∼25 cluster in bone marrow-derived leukocytes in mediating stress resilience versus susceptibility. RESULTS: We found that RSDS produces an increase in circulating Ly6chigh inflammatory monocytes in both susceptible and resilient mice. We next investigated whether intrinsic leukocyte posttranscriptional mechanisms contribute to individual differences in stress response and the resilient phenotype. Of the miRs profiled in our panel, eight were significantly regulated by RSDS within Ly6chigh monocytes, including miR-25-3p, a member of the miR-106b∼25 cluster. Selective knockout of the miR-106b∼25 cluster in peripheral leukocytes promoted behavioral resilience to RSDS. CONCLUSIONS: Our results identify the miR-106b∼25 cluster as a key regulator of stress-induced inflammation and depression that may represent a novel therapeutic target for drug development.

The cis-Regulatory Atlas of the Mouse Immune System.

A complete chart of cis-regulatory elements and their dynamic activity is necessary to understand the transcriptional basis of differentiation and function of an organ system. We generated matched epigenome and transcriptome measurements in 86 primary cell types that span the mouse immune system and its differentiation cascades. This breadth of data enable variance components analysis that suggests that genes fall into two distinct classes, controlled by either enhancer- or promoter-driven logic, and multiple regression that connects genes to the enhancers that regulate them. Relating transcription factor (TF) expression to the genome-wide accessibility of their binding motifs classifies them as predominantly openers or closers of local chromatin accessibility, pinpointing specific cis-regulatory elements where binding of given TFs is likely functionally relevant, validated by chromatin immunoprecipitation sequencing (ChIP-seq). Overall, this cis-regulatory atlas provides a trove of information on transcriptional regulation through immune differentiation and a foundational scaffold to define key regulatory events throughout the immunological genome.

Direct pro-inflammatory effects of prorenin on microglia.

Neuroinflammation has been implicated in hypertension, and microglia have been proposed to play an important role in the progression of this disease. Here, we have studied whether microglia are activated within cardiovascular regulatory area(s) of the brain during hypertension, especially in high blood pressure that is associated with chronic activation of the renin-angiotensin-system. In addition, we determined whether prorenin, an essential component of the renin-angiotensin-system, exerts direct pro-inflammatory effects on these microglia. Our data indicate that two rodent models which display neurogenic hypertension and over activation of the renin-angiotensin-system in the brain (sRA mice and spontaneously hypertensive rats) exhibit microglial activation, and increased levels of pro-inflammatory cytokines, in the paraventricular nucleus of the hypothalamus, an area crucial for regulation of sympathetic outflow. Further, the renin-angiotensin-system component prorenin elicits direct activation of hypothalamic microglia in culture and induction of pro-inflammatory mechanisms in these cells, effects that involve prorenin receptor-induced NFκB activation. In addition, the prorenin-elicited increases in cytokine expression were fully abolished by microglial inhibitor minocycline, and were potentiated by pre-treatment of cells with angiotensin II. Taken together with our previous data which indicate that pro-inflammatory processes in the paraventricular nucleus are involved in the hypertensive action of renin-angiotensin-system, the novel discovery that prorenin exerts direct stimulatory effects on microglial activation and pro-inflammatory cytokine production provides support for the idea that renin-angiotensin-system -induced neurogenic hypertension is not restricted to actions of angiotensin II alone.

Manual versus Automated Rodent Behavioral Assessment: Comparing Efficacy and Ease of Bederson and Garcia Neurological Deficit Scores to an Open Field Video-Tracking System.

Animal models of stroke have been crucial in advancing our understanding of the pathophysiology of cerebral ischemia. Currently, the standards for determining neurological deficit in rodents are the Bederson and Garcia scales, manual assessments scoring animals based on parameters ranked on a narrow scale of severity. Automated open field analysis of a live-video tracking system that analyzes animal behavior may provide a more sensitive test. Results obtained from the manual Bederson and Garcia scales did not show significant differences between pre- and post-stroke animals in a small cohort. When using the same cohort, however, post-stroke data obtained from automated open field analysis showed significant differences in several parameters. Furthermore, large cohort analysis also demonstrated increased sensitivity with automated open field analysis versus the Bederson and Garcia scales. These early data indicate use of automated open field analysis software may provide a more sensitive assessment when compared to traditional Bederson and Garcia scales.

The angiotensin type 2 receptor agonist Compound 21 elicits cerebroprotection in endothelin-1 induced ischemic stroke.

Evidence indicates that angiotensin II type 2 receptors (AT2R) exert cerebroprotective actions during stroke. A selective non-peptide AT2R agonist, Compound 21 (C21), has been shown to exert beneficial effects in models of cardiac and renal disease, as well as hemorrhagic stroke. Here, we hypothesize that C21 may exert beneficial effects against cerebral damage and neurological deficits produced by ischemic stroke. We determined the effects of central and peripheral administration of C21 on the cerebral damage and neurological deficits in rats elicited by endothelin-1 induced middle cerebral artery occlusion (MCAO), a model of cerebral ischemia. Rats infused centrally (intracerebroventricular) with C21 before endothelin-1 induced MCAO exhibited significant reductions in cerebral infarct size and the neurological deficits produced by cerebral ischemia. Similar cerebroprotection was obtained in rats injected systemically (intraperitoneal) with C21 either before or after endothelin-1 induced MCAO. The protective effects of C21 were reversed by central administration of an AT2R inhibitor, PD123319. While C21 did not alter cerebral blood flow at the doses used here, peripheral post-stroke administration of this agent significantly attenuated the MCAO-induced increases in inducible nitric oxide synthase, chemokine (C-C) motif ligand 2 and C-C chemokine receptor type 2 mRNAs in the cerebral cortex, indicating that the cerebroprotective action is associated with an anti-inflammatory effect. These results strengthen the view that AT2R agonists may have potential therapeutic value in ischemic stroke, and provide the first evidence of cerebroprotection induced by systemic post stroke administration of a selective AT2R agonist.

Centrally administered angiotensin-(1-7) increases the survival of stroke-prone spontaneously hypertensive rats.

NEW FINDINGS: What is the central question of this study? Activation of angiotensin-converting enzyme 2, resulting in production of angiotensin-(1-7) and stimulation of its receptor, Mas, exerts beneficial actions in a number cardiovascular diseases, including ischaemic stroke. A potential beneficial role for angiotensin-(1-7) in haemorrhagic stroke has not previously been reported. What is the main finding and its importance? Central administration of angiotensin-(1-7) into stroke-prone spontaneously hypertensive rats, a model of haemorrhagic stroke, increases lifespan and improves the neurological status of these rats, as well as decreasing microglial numbers in the striatum (implying attenuation of cerebral inflammation). These actions of angiotensin-(1-7) have not previously been reported and identify this peptide as a potential new therapeutic target in haemorrhagic stroke. Angiotensin-(1-7) [Ang-(1-7)] exerts cerebroprotective effects in ischaemic stroke, and this action is associated with a blunting of intracerebral inflammatory processes and microglial activation. Given that intracerebral inflammation and microglial activation play key roles in the mechanism of injury and brain damage in both ischaemic and haemorrhagic stroke, we have investigated the potential beneficial actions of Ang-(1-7) in stroke-prone spontaneously hypertensive rats (spSHRs), an established animal model of hypertension-induced haemorrhagic stroke. Angiotensin-(1-7) was administered by continuous infusion via the intracerebroventricular route for 6 weeks into spSHRs fed a high-sodium (4%) diet, starting at 49 days of age. This treatment resulted in a significant increase in survival of the spSHRs. Median survival was 108 days in control, artificial cerebrospinal fluid-infused spSHRs and 154 days in Ang-(1-7)-treated spSHRs. This effect was partly reversed by intracerebroventricular infusion of the Mas receptor blocker, A779. This Ang-(1-7) treatment also decreased the number of haemorrhages in the striatum, improved neurological status (reduced lethargy), decreased the number of microglia in the striatum and tended to increase neuron survival at the same site. Importantly, infusions of Ang-(1-7) had no effect on kidney pathology, heart pathology, body weight, serum corticosterone levels or blood pressure. This study is the first to demonstrate the cerebroprotective actions of Ang-(1-7), including increased survival time, in spSHRs. As such, these data reveal a potential therapeutic target for haemorrhagic stroke.

Anti-inflammatory effects of angiotensin-(1-7) in ischemic stroke.

Previously we demonstrated that central administration of angiotensin-(1-7) [Ang-(1-7)] into rats elicits significant cerebroprotection against ischemic stroke elicited by endothelin-1 induced middle cerebral artery occlusion. Ang-(1-7), acting via its receptor Mas, reduced cerebral infarct size, and rats exhibited improved performance on neurological exams. These beneficial actions of Ang-(1-7) were not due to inhibition of the effects of endothelin-1 on cerebral vasoconstriction or effects on cerebral blood flow, and so we considered other potential mechanisms. Here we investigated the possibility that the Ang-(1-7)-induced cerebroprotection involves an anti-inflammatory effect, since stroke-induced cerebral damage includes an excessive intracerebral inflammatory response. Our quantitative RT-PCR analyses revealed that central Ang-(1-7) treatment attenuates the increased expression of mRNAs for inducible nitric oxide synthase (iNOS), several pro-inflammatory cytokines and cluster of differentiation molecule 11b (microglial marker) within the cerebral cortex following endothelin-1 induced stroke. Western blotting confirmed similar changes in iNOS protein expression in the cerebral cortex. In support of these observations, immunostaining revealed the presence of immunoreactive Mas on activated microglia within the cerebral cortical infarct zone, and in vitro experiments demonstrated that lipopolysaccharide-induced increases in nitric oxide production in glial cultures are attenuated by Ang-(1-7) acting via Mas. Collectively these findings demonstrate an anti-inflammatory action of Ang-(1-7) in the brain, and suggest that the cerebroprotective action of this peptide in ischemic stroke may involve effects on nitric oxide generation by microglia.

Interleukin-10 inhibits angiotensin II-induced decrease in neuronal potassium current.

Previously we demonstrated that viral-mediated increased expression of the anti-inflammatory cytokine interleukin-10 within the paraventricular nucleus of the hypothalamus significantly reduces blood pressure in normal rats made hypertensive by infusion of angiotensin II. However, the exact cellular locus of this interleukin-10 action within the paraventricular nucleus is unknown. In the present study we tested whether interleukin-10 exerts direct effects at its receptors located on hypothalamic neurons to offset the neuronal excitatory actions of angiotensin II via its type 1 receptors. The results indicated the presence of immunoreactive interleukin-10 receptors on neurons in normal rat paraventricular nucleus and that receptors for this cytokine were also expressed in neurons cultured from the hypothalamus. Patch-clamp electrophysiological recordings from these cultures revealed that extracellular application of interleukin-10 alone did not exert any alterations in neuronal membrane delayed rectifier or transient potassium currents. However, angiotensin II elicited a significant decrease in delayed rectifier potassium current, an effect that was abolished by interleukin-10 application. Since decreases in delayed rectifier potassium current contribute to increased neuronal excitability, this result is consistent with a direct inhibitory action of interleukin-10 on angiotensin-induced excitation of hypothalamic neurons. As such, these data are the first indication of a neuronal locus of action of interleukin-10 to temper the actions of angiotensin II in the hypothalamus.

The NorR regulon is critical for Vibrio cholerae resistance to nitric oxide and sustained colonization of the intestines.

UNLABELLED: Vibrio cholerae, the cause of an often fatal infectious diarrhea, remains a large global public health threat. Little is known about the challenges V. cholerae encounters during colonization of the intestines, which genes are important for overcoming these challenges, and how these genes are regulated. In this study, we examined the V. cholerae response to nitric oxide (NO), an antibacterial molecule derived during infection from various sources, including host inducible NO synthase (iNOS). We demonstrate that the regulatory protein NorR regulates the expression of NO detoxification genes hmpA and nnrS, and that all three are critical for resisting low levels of NO stress under microaerobic conditions in vitro. We also show that prxA, a gene previously thought to be important for NO detoxification, plays no role in NO resistance under microaerobic conditions and is upregulated by H(2)O(2), not NO. Furthermore, in an adult mouse model of prolonged colonization, hmpA and norR were important for the resistance of both iNOS- and non-iNOS-derived stresses. Our data demonstrate that NO detoxification systems play a critical role in the survival of V. cholerae under microaerobic conditions resembling those of an infectious setting and during colonization of the intestines over time periods similar to that of an actual V. cholerae infection. IMPORTANCE: Little is known about what environmental stresses Vibrio cholerae, the etiologic agent of cholera, encounters during infection, and even less is known about how V. cholerae senses and counters these stresses. Most prior studies of V. cholerae infection relied on the 24-h infant mouse model, which does not allow the analysis of survival over time periods comparable to that of an actual V. cholerae infection. In this study, we used a sustained mouse colonization model to identify nitric oxide resistance as a function critical for the survival of V. cholerae in the intestines and further identified the genes responsible for sensing and detoxifying this stress.