A critical role for microglia in maintaining vascular integrity in the hypoxic spinal cord

Hypoxic preconditioning reduces disease severity in a mouse model of multiple sclerosis (MS), in part by enhancing the barrier properties of spinal cord blood vessels. Because other studies have shown that similar levels of hypoxia transiently increase permeability of central nervous system (CNS) blood vessels, the goal of this study was to define the impact of chronic mild hypoxia (CMH, 8% O2) on the integrity of spinal cord blood vessels and the responses of neighboring glial cells. Using extravascular fibrinogen as a marker of vascular disruption, we found that CMH triggered transient vascular leak in spinal cord blood vessels, particularly in white matter, which was associated with clustering and activation of Mac-1–positive microglia around disrupted vessels. Microglial depletion with the colony stimulating factor-1 receptor (CSF-1R) inhibitor PLX5622, while having no effect under normoxic conditions, profoundly increased vascular leak in both white and gray matter during CMH, and this was associated with disruption of astrocyte-vascular coupling and enhanced loss of tight junction proteins. Microglial repair of leaky blood vessels was blocked by a peptide that inhibits the interaction between fibrinogen and its Mac-1 integrin receptor. These findings highlight an important role for microglia in maintaining vascular integrity in the hypoxic spinal cord and suggest that a fibrinogen–Mac-1 interaction underpins this response. As relative hypoxia is experienced in many situations including high altitude, lung disease, obstructive sleep apnea, and age-related CNS ischemia/hypoxia, our findings have important implications regarding the critical role of microglia in maintaining vascular integrity in the CNS.

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Mild hypoxia triggers transient blood–brain barrier disruption: a fundamental protective role for microglia

Acta Neuropathologica Communications ◽

10.1186/s40478-020-01051-z ◽

2020 ◽

Vol 8 (1) ◽

Author(s):

Sebok K. Halder ◽

Richard Milner

Keyword(s):

Spinal Cord ◽

Blood Vessels ◽

Blood Brain Barrier ◽

Protective Role ◽

Neurological Dysfunction ◽

Brain Barrier ◽

Vascular Leak ◽

Vascular Integrity ◽

Blood Brain ◽

Mild Hypoxia

Abstract We recently demonstrated that when mice are exposed to chronic mild hypoxia (CMH, 8% O2), blood vessels in the spinal cord show transient vascular leak that is associated with clustering and activation of microglia around disrupted vessels. Importantly, microglial depletion profoundly increased hypoxia-induced vascular leak, implying that microglia play a critical role maintaining vascular integrity in the hypoxic spinal cord. The goal of the current study was to examine if microglia play a similar vasculo-protective function in the brain. Employing extravascular fibrinogen leak as an index of blood–brain barrier (BBB) disruption, we found that CMH provoked transient vascular leak in cerebral blood vessels that was associated with activation and aggregation of Mac-1-positive microglia around leaky vessels. Interestingly, CMH-induced vascular leak showed regional selectivity, being much more prevalent in the brainstem and olfactory bulb than the cerebral cortex and cerebellum. Pharmacological depletion of microglia with the colony stimulating factor-1 receptor inhibitor PLX5622, had no effect under normoxic conditions, but markedly increased hypoxia-induced cerebrovascular leak in all regions examined. As in the spinal cord, this was associated with endothelial induction of MECA-32, a marker of leaky CNS endothelium, and greater loss of endothelial tight junction proteins. Brain regions displaying the highest levels of hypoxic-induced vascular leak also showed the greatest levels of angiogenic remodeling, suggesting that transient BBB disruption may be an unwanted side-effect of hypoxic-induced angiogenic remodeling. As hypoxia is common to a multitude of human diseases including obstructive sleep apnea, lung disease, and age-related pulmonary, cardiac and cerebrovascular dysfunction, our findings have important translational implications. First, they point to a potential pathogenic role of chronic hypoxia in triggering BBB disruption and subsequent neurological dysfunction, and second, they demonstrate an important protective role for microglia in maintaining vascular integrity in the hypoxic brain.

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Spontaneous and Drug-induced Arteritis/Polyarteritis in the Göttingen Minipig—Review

Toxicologic Pathology ◽

10.1177/0192623318754791 ◽

2018 ◽

Vol 46 (2) ◽

pp. 121-130 ◽

Cited By ~ 2

Author(s):

Zuhal Dincer ◽

Virginie Piccicuto ◽

Ursula Junker Walker ◽

Andreas Mahl ◽

Sean McKeag

Keyword(s):

Spinal Cord ◽

Urinary Bladder ◽

Blood Vessels ◽

Polyarteritis Nodosa ◽

Pain Syndrome ◽

Vascular Changes ◽

Drug Induced ◽

Göttingen Minipig ◽

Age Related ◽

Immune Mediated

Arteritis/polyarteritis occurs spontaneously in many species used in preclinical toxicology studies. In Göttingen minipigs, arteritis/polyarteritis is an occasionally observed background change. In the minipig, this finding differs in frequency and nature from age-related polyarteritis nodosa in rats or monkeys, and Beagle pain syndrome in dogs. In minipigs, it can be present in a single small- or medium-sized artery of an organ or a few organs and is most commonly recorded in the cardiac and extracardiac blood vessels, vagina, oviduct, rectum, epididymis, spinal cord, pancreas, urinary bladder, kidneys, and stomach. The etiology is unknown although it has been considered in minipigs as well as in rats, dogs, and monkeys to be possibly immune mediated. This background change is important with respect to its nature and distribution in the minipig in order to distinguish it from drug-induced vascular changes, which might occur in similar locations and have similar morphologic features. This review summarizes the morphology, incidence, and predilection sites of arteritis as a spontaneously occurring background change and as a drug-induced vasculopathy in the minipig, and also describes the main aspects to consider when evaluating vascular changes in Göttingen minipig toxicity studies and their human relevance.

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The Age-Related Effects of Epidural Lidocaine, With and Without Epinephrine, on Spinal Cord Blood Flow in Anesthetized Rabbits

Anesthesia & Analgesia ◽

10.1097/00000539-199906000-00019 ◽

1999 ◽

Vol 88 (6) ◽

pp. 1302-1307 ◽

Cited By ~ 1

Author(s):

Herve Bouaziz ◽

Naomitsu Okubo ◽

Jean-Marc Malinovsky ◽

Dan Benhamou ◽

Kamran Samii ◽

...

Keyword(s):

Spinal Cord ◽

Blood Flow ◽

Cord Blood ◽

Spinal Cord Blood Flow ◽

Age Related

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Aminergic and cholinergic innervations of the spinal cord blood vessels of cats

Journal of Neurosurgery ◽

10.3171/jns.1983.58.6.0900 ◽

1983 ◽

Vol 58 (6) ◽

pp. 900-905 ◽

Cited By ~ 28

Author(s):

Toru Itakura

Keyword(s):

Spinal Cord ◽

Cord Blood ◽

Blood Vessels ◽

Nerve Fibers ◽

Anterior Spinal Artery ◽

Thoracic Spinal Cord ◽

Cholinergic Nerve ◽

Ischemic Change ◽

Thoracic Spinal ◽

Cholinergic Nerve Fibers

✓ The distribution patterns of aminergic and cholinergic nerve fibers in the feline spinal cord blood vessels were studied by means of amine histofluorescence and acetylcholinesterase (AChE) staining. These patterns were compared with those of the cerebral blood vessels. The anterior spinal artery had a dense network of aminergic and AChE-positive (probably cholinergic) nerve fibers. The posterior spinal vein, in contrast, exhibited only aminergic nerve fibers. Small intraparenchymal blood vessels in the spinal cord also had strongly fluorescent (probably peripheral) aminergic nerve fibers, as well as pial spinal blood vessels. This was a characteristic feature in the spinal cord. The distribution pattern and the density of these two sorts of nerve fibers in the anterior spinal artery varied widely with the individual segment of the spinal cord. The thoracic spinal cord had the lowest number of these nerve fibers of any part of the spinal cord. This fact may explain why the thoracic spinal cord is most susceptible to ischemic change.

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Age-related changes in the nervous apparatus of the blood vessels in the spinal cord

Bukovinian Medical Herald ◽

10.24061/2413-0737.xvii.3.67.2013.159 ◽

2013 ◽

Vol 17 (3 (67) p.1) ◽

pp. 122-124

Author(s):

Yu. I. Pigolkin ◽

G. V. Zolotenkova

Keyword(s):

Spinal Cord ◽

Blood Vessels ◽

Practical Work ◽

Biological Age ◽

Postnatal Ontogenesis ◽

Nervous Apparatus ◽

Age Related ◽

Brain And Spinal Cord ◽

The Brain ◽

Age Related Changes

This paper was designed to study changes in the nervous apparatus of the blood vessels in the spinal cord with a view to determining the biological age of man. The pial and intramedullary vascular systems of the brain and spinal cord were examined in different periods of postnatal ontogenesis (between the age of 1 to 90 years). The data obtained on the age-related rearrangement of the nervous apparatus of the spinocerebral arterial vessels can also be used for the solution of practical problems encountered in the practical work of forensic medical experts.

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The impact of chronic mild hypoxia on cerebrovascular remodelling; uncoupling of angiogenesis and vascular breakdown

Fluids and Barriers of the CNS ◽

10.1186/s12987-021-00284-x ◽

2021 ◽

Vol 18 (1) ◽

Author(s):

Sebok K. Halder ◽

Richard Milner

Keyword(s):

Blood Vessels ◽

Side Effect ◽

Vascular Perfusion ◽

Vascular Leak ◽

Unwanted Side Effect ◽

Endothelial Proliferation ◽

Junction Protein ◽

Temporary Closure ◽

The Impact ◽

Mild Hypoxia

Abstract Background Chronic mild hypoxia (CMH, 8% O2) stimulates robust vascular remodelling in the brain, but it also triggers transient vascular disruption. This raises the fundamental question: is the vascular leak an unwanted side-effect of angiogenic remodelling or is it a pathological response, unrelated to endothelial proliferation, in which declining oxygen levels trigger endothelial dysfunction? Methods To answer this question, mice were exposed to CMH (8% O2) for periods up to 14 days, after which, brain tissue was examined by immunofluorescence (IF) to determine which type of blood vessel (arteriole, capillary or venule) was most commonly associated with endothelial proliferation and vascular leak and how this correlated with tight junction protein expression. Vascular perfusion was examined using DiI. Data were analysed using one-way analysis of variance (ANOVA) followed by Tukey’s multiple comparison post-hoc test. Results The following was observed: (1) most endothelial proliferation and extravascular fibrinogen leak occurred in capillaries and to a lesser degree in venules, (2) much to our surprise, endothelial proliferation and extravascular fibrinogen leak never colocalized, (3) interestingly however, endothelial proliferation was strongly associated with an intravascular fibrinogen staining pattern not seen in stable blood vessels, (4) DiI perfusion studies revealed that angiogenic vessels were adequately perfused, suggesting that fibrinogen retention in angiogenic vessels is not due to temporary closure of the vessel, but more likely because fibrinogen is retained within the vessel wall, (5) bromodeoxyuridine (BrdU) labelling as a means to more permanently label proliferating endothelial cells, confirmed lack of any connection between endothelial proliferation and extravascular fibrinogen leak, while (6) in contrast, proliferating microglia were detected within extravascular leaks. Conclusions Taken together, our findings support the concept that in the short-term, hypoxia-induced endothelial proliferation triggers transient fibrinogen deposition within the walls of angiogenic blood vessels, but no overt vascular leak occurs in these vessels. Importantly, endothelial proliferation and extravascular fibrinogen leaks never co-localize, demonstrating that extravascular leak is not an unwanted side-effect of angiogenic endothelial proliferation, but rather a dysfunctional vascular response to hypoxia that occurs in a distinct group of non-angiogenic blood vessels.

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Kallikrein-related peptidase 6 exacerbates disease in an autoimmune model of multiple sclerosis

Biological Chemistry ◽

10.1515/hsz-2016-0239 ◽

2016 ◽

Vol 397 (12) ◽

pp. 1277-1286 ◽

Cited By ~ 4

Author(s):

Hyesook Yoon ◽

Isobel A. Scarisbrick

Keyword(s):

Multiple Sclerosis ◽

Spinal Cord ◽

Inflammatory Cytokines ◽

Immune Cells ◽

Inflammatory Responses ◽

Critical Role ◽

Systemic Administration ◽

Neurological Deficits ◽

Interleukin 17 ◽

The Impact

Abstract Kallikrein-related peptidase 6 (Klk6) is elevated in the serum of multiple sclerosis (MS) patients and is hypothesized to participate in inflammatory and neuropathogenic aspects of the disease. To test this hypothesis, we investigated the impact of systemic administration of recombinant Klk6 on the development and progression of MOG35-55-induced experimental autoimmune encephalomyelitis (EAE). First, we determined that Klk6 expression is elevated in the spinal cord of mice with EAE at the peak of clinical disease and in immune cells upon priming with the disease-initiating peptide in vitro. Systemic administration of recombinant Klk6 to mice during the priming phase of disease resulted in an exacerbation of clinical symptoms, including earlier onset of disease and higher levels of spinal cord inflammation and pathology. Treatment of MOG35-55-primed immune cells with Klk6 in culture enhanced expression of pro-inflammatory cytokines, interferon-γ, tumor necrosis factor, and interleukin-17, while reducing anti-inflammatory cytokines interleukin-4 and interleukin-5. Together these findings provide evidence that elevations in systemic Klk6 can bias the immune system towards pro-inflammatory responses capable of exacerbating the development of neuroinflammation and paralytic neurological deficits. We suggest that Klk6 represents an important target for conditions in which pro-inflammatory responses play a critical role in disease development, including MS.

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416 The impact of Obstructive Sleep Apnea severity on age-related comorbities: a population-based study

SLEEP ◽

10.1093/sleep/zsab072.415 ◽

2021 ◽

Vol 44 (Supplement_2) ◽

pp. A165-A165

Author(s):

Mayra Silva ◽

Dalva Poyares ◽

Luciana Oliveira ◽

Monica Andersen ◽

Sergio Tufik ◽

...

Keyword(s):

Older Adults ◽

Late Onset ◽

Clinical Manifestations ◽

Population Based ◽

Baseline Survey ◽

Older Individuals ◽

Blood Tests ◽

Age Related ◽

Obstructive Sleep ◽

The Impact

Abstract Introduction Although age per se has been considered a risk factor for OSA, evidence suggest OSA in older adults may be less severe and OSA diagnostic criteria might be adjusted for this age group. Concurrently, it is likely the late-onset OSA is a distinct phenotype having different pathophysiological mechanisms, as well as clinical manifestations and consequences. We sought to investigate the clinical consequences of OSA severity in older adults from a representative sample of the older population living in the São Paulo city. Methods From the baseline survey including 1042 participants in 2007, 715 were reassessed in 2016 completing full in-lab PSG, health-related questionnaires, blood tests, and blood pressure measurements. Individuals > 60 y.o. (n=199) of both genders were included in the analysis. Participants were stratified according to OSA presence and severity in 3 groups G1 (non and mild OSA n=83); G2 (moderate OSA n=56); G3 (severe OSA n=60). General Linear Model (GLM) tests and Chi-square were carried out. Results Participants mean age was 70.02±7.31 and mean body mass index (BMI) 28.61±5.39, 40.71% of men. The only comorbidity associated with OSA severity was arterial hypertension occurring in 61.7% of G3, 46.4% of G4 and 41% of G1 (p=0.04). Severe OSA participants were more likely to use a higher (>2/day) number of medications (p=0.03). Finally, out of all blood tests only cortisol was significantly higher in severe OSA group (p<0.001) Conclusion Severe OSA in older individuals of the general population is not associated with metabolic conditions, such as diabetes, but it was associated with hypertension. Severe OSA may be a stressful condition, since it was associated with higher cortisol in this population. Support (if any) Associaçao Fundo Incentivo a Pesquisa (AFIP)

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Age-related gene expression changes in lumbar spinal cord: Implications for neuropathic pain

Molecular Pain ◽

10.1177/1744806920971914 ◽

2020 ◽

Vol 16 ◽

pp. 174480692097191

Author(s):

Jack A Mayhew ◽

Mitchell J Cummins ◽

Ethan T Cresswell ◽

Robert J Callister ◽

Doug W Smith ◽

...

Keyword(s):

Gene Expression ◽

Spinal Cord ◽

Neuropathic Pain ◽

Dorsal Horn ◽

Dorsal Spinal Cord ◽

Age Related ◽

Pathological Pain ◽

The Impact ◽

Dorsal Spinal ◽

Young Mice

Clinically, pain has an uneven incidence throughout lifespan and impacts more on the elderly. In contrast, preclinical models of pathological pain have typically used juvenile or young adult animals to highlight the involvement of glial populations, proinflammatory cytokines, and chemokines in the onset and maintenance of pathological signalling in the spinal dorsal horn. The potential impact of this mismatch is also complicated by the growing appreciation that the aged central nervous system exists in a state of chronic inflammation because of enhanced proinflammatory cytokine/chemokine signalling and glial activation. To address this issue, we investigated the impact of aging on the expression of genes that have been associated with neuropathic pain, glial signalling, neurotransmission and neuroinflammation. We used qRT-PCR to quantify gene expression and focussed on the dorsal horn of the spinal cord as this is an important perturbation site in neuropathic pain. To control for global vs region-specific age-related changes in gene expression, the ventral half of the spinal cord was examined. Our results show that expression of proinflammatory chemokines, pattern recognition receptors, and neurotransmitter system components was significantly altered in aged (24–32 months) versus young mice (2–4 months). Notably, the magnitude and direction of these changes were spinal-cord region dependent. For example, expression of the chemokine, Cxcl13, increased 119-fold in dorsal spinal cord, but only 2-fold in the ventral spinal cord of old versus young mice. Therefore, we propose the dorsal spinal cord of old animals is subject to region-specific alterations that prime circuits for the development of pathological pain, potentially in the absence of the peripheral triggers normally associated with these conditions.

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