Pericyte Dysfunction Research Articles

Pericytes and Neurovascular Function in the Healthy and Diseased Brain.

Pericytes are multi-functional cells embedded within the walls of capillaries throughout the body, including the brain. Pericytes were first identified in the 1870s, but little attention was paid to them during the following century. More recently, numerous vascular functions of pericytes have been identified including regulation of cerebral blood flow, maintenance of the blood-brain barrier (BBB), and control of vascular development and angiogenesis. Pericytes can also facilitate neuroinflammatory processes and possess stem cell-like properties. Pericytes form part of the neurovascular unit (NVU), a collection of cells that control interactions between neurons and the cerebral vasculature to meet the energy demands of the brain. Pericyte structure, expression profile, and function in the brain differ depending on their location along the vascular bed. Until recently, it has been difficult to accurately define the sub-types of pericytes, or to specifically target pericytes with pharmaceutical agents, but emerging techniques both in vitro and in vivo will improve investigation of pericytes and allow for the identification of their possible roles in diseases. Pericyte dysfunction is increasingly recognized as a contributor to the progression of vascular diseases such as stroke and neurodegenerative diseases such as Alzheimer’s disease. The therapeutic potential of pericytes to repair cerebral blood vessels and promote angiogenesis due to their ability to behave like stem cells has recently been brought to light. Here, we review the history of pericyte research, the present techniques used to study pericytes in the brain, and current research advancements to characterize and therapeutically target pericytes in the future.

Bone marrow pericyte dysfunction in individuals with type 2 diabetes

Aims/hypothesisPrevious studies have shown that diabetes mellitus destabilises the integrity of the microvasculature in different organs by damaging the interaction between pericytes and endothelial cells. In bone marrow, pericytes exert trophic functions on endothelial cells and haematopoietic cells through paracrine mechanisms. However, whether bone marrow pericytes are a target of diabetes-induced damage remains unknown. Here, we investigated whether type 2 diabetes can affect the abundance and function of bone marrow pericytes.MethodsWe conducted an observational clinical study comparing the abundance and molecular/functional characteristics of CD146+ pericytes isolated from the bone marrow of 25 individuals without diabetes and 14 individuals with uncomplicated type 2 diabetes, referring to our Musculoskeletal Research Unit for hip reconstructive surgery.ResultsImmunohistochemistry revealed that diabetes causes capillary rarefaction and compression of arteriole size in bone marrow, without changing CD146+ pericyte counts. These data were confirmed by flow cytometry on freshly isolated bone marrow cells. We then performed an extensive functional and molecular characterisation of immunosorted CD146+ pericytes. Type 2 diabetes caused a reduction in pericyte proliferation, viability, migration and capacity to support in vitro angiogenesis, while inducing apoptosis. AKT is a key regulator of the above functions and its phosphorylation state is reportedly reduced in the bone marrow endothelium of individuals with diabetes. Surprisingly, we could not find a difference in AKT phosphorylation (at either Ser473 or Thr308) in bone marrow pericytes from individuals with and without diabetes. Nonetheless, the angiocrine signalling reportedly associated with AKT was found to be significantly downregulated, with lower levels of fibroblast growth factor-2 (FGF2) and C-X-C motif chemokine ligand 12 (CXCL12), and activation of the angiogenesis inhibitor angiopoietin 2 (ANGPT2). Transfection with the adenoviral vector carrying the coding sequence for constitutively active myristoylated AKT rescued functional defects and angiocrine signalling in bone marrow pericytes from diabetic individuals. Furthermore, an ANGPT2 blocking antibody restored the capacity of pericytes to promote endothelial networking.Conclusions/interpretationThis is the first demonstration of pericyte dysfunction in bone marrow of people with type 2 diabetes. An altered angiocrine signalling from pericytes may participate in bone marrow microvascular remodelling in individuals with diabetes.

Abstract 105: Obesity Induces Vascular Remodeling and Deteriorates Cognitive Function in Mice: Role of Pericytes

30 million Americans of the United States population have diabetes. Additional 90 million people in the pre-diabetic stage. Insulin resistance and obesity are the hallmarks of prediabetes. Understanding the effect of obesity on cerebrovasculature is crucial to identify novel therapies to prevent cerebrovascular complications of diabetes including vascular cognitive impairment and dementia. We hypothesize that pericyte dysfunction in prediabetes causes vascular remodeling and pathological neovascularization that leads to vascular cognitive impairment and dementia. Methods, male and female mice were fed regular or a high fat diet (HFD) for 12 weeks. Insulin resistance (IR) was confirmed with a glucose tolerance test. Neovascularization indices were measured (Vascular density, tortuosity, and branching density) to assess cerebral integrity. Pericyte count and basement membrane thickness (BMT) were determined in the cerebral cortex. Learning and memory functions were evaluated using Water maze, Y-maze and novel object recognition (NOR). Pericyte (PC) were grown in high glucose (HG) to mimic prediabetes. Pericytes MMP9 activity, TIMP1 and PDGFR beta internalization were measured. Results, male and female mice fed with HFD showed a significant increase in body weight and IR as indicated by impaired glucose tolerance. 3D reconstructed images of cerebral cortex vasculature showed that HFD significantly increases neovascularization indices (P<0.05, n=5). TEM studies showed an increase in cerebrovascular BMT in HFD mice that was associated with significantly decreased in PCs count and TIMP-1 expression in the cerebral cortex. HFD led to significant deterioration of cognitive memory function in Water maze, Y maze, and NOR. (P<0.05, n=5). MMP9 activity and internalization of PDGFR beta were increased in HG-treated PCs that were accompanied by a decrease in TIMP1 expression. (P<0.05, n=4). Conclusion, obesity-induced pericyte dysfunction is associated with pathological cerebral vessel remodeling and impaired cognitive function. These studies illustrate the crucial role of pericyte dysfunction in prediabetes and identify pericytes as a potential therapeutic target for the treatment of cognitive impairment in diabetes.

Pericytes in Type 2 Diabetes.

Pericytes are mural cells that are found ubiquitously throughoutthe microvasculature. Their main physiological roles are to support endothelial cells, regulate microvascular blood flow, and respond to perturbations in their microenvironment. Pericytes are sensitive to the metabolic abnormalities that are characteristic of type 2 diabetes mellitus, including dyslipidemia, hyperglycemia, and hyperinsulinemia. As a consequence of these abnormalities, advanced glycation end products, reactive oxygen species, polyol pathway activation, and protein kinase C isoform activation cause pericyte dysfunction and contribute to the pathogenesis of many common complications of type 2 diabetes. Pericyte dysfunction is known to be a contributing factor to the pathogenesis of retinopathy, nephropathy, neuropathy, beta cell dysfunction, and peripheral artery disease in people with type 2 diabetes. Therapies should target pericytes to treat these common diabetic complications.

Pericytes in Ischemic Stroke.

Recent stroke research has shifted the focus to the microvasculature from neuron-centric views. It is increasingly recognized that a successful neuroprotection is not feasible without microvascular protection. On the other hand, recent studies on pericytes, long-neglected cells on microvessels have provided insight into the regulation of microcirculation. Pericytes play an essential role in matching the metabolic demand of nervous tissue with the blood flow in addition to regulating the development and maintenance of the blood-brain barrier (BBB), leukocyte trafficking across the BBB and angiogenesis. Pericytes appears to be highly vulnerable to injury. Ischemic injury to pericytes on cerebral microvasculature unfavorably impacts the stroke-induced tissue damage and brain edema by disrupting microvascular blood flow and BBB integrity. Strongly supporting this, clinical imaging studies show that tissue reperfusion is not always obtained after recanalization. Therefore, prevention of pericyte dysfunction may improve the outcome of recanalization therapies by promoting microcirculatory reperfusion and preventing hemorrhage and edema. In the peri-infarct tissue, pericytes are detached from microvessels and promote angiogenesis and neurogenesis, and hence positively effect stroke outcome. Expectedly, we will learn more about the place of pericytes in CNS pathologies including stroke and devise approaches to treat them in the next decades.

Fli-1 Governs Pericyte Dysfunction in a Murine Model of Sepsis.

Pericytes are vascular mural cells and are embedded in the basement membrane of the microvasculature. Recent studies suggest a role for pericytes in lipopolysaccharide (LPS)-induced microvascular dysfunction and mortality, but the mechanisms of pericyte loss in sepsis are largely unknown. By using a cecal ligation and puncture (CLP)-induced murine model of sepsis, we observed that CLP led to lung and renal pericyte loss and reduced lung pericyte density and pericyte/endothelial cell (EC) coverage. Up-regulated Friend leukemia virus integration 1 (Fli-1) messenger ribonucleic acid (RNA) and protein levels were found in lung pericytes from CLP mice in vivo and in LPS-stimulated lung pericytes in vitro. Knockout of Fli-1 in Foxd1-derived pericytes prevented CLP-induced pericyte loss, vascular leak, and improved survival. Disrupted Fli-1 expression by small interfering RNA inhibited LPS-induced inflammatory cytokines and chemokines in cultured lung pericytes. Furthermore, CLP-induced pericyte pyroptosis was mitigated in pericyte Fli-1 knockout mice. Our findings suggest that Fli-1 is a potential therapeutic target in sepsis.

Pericyte Structural Remodeling in Cerebrovascular Health and Homeostasis.

The biology of brain microvascular pericytes is an active area of research and discovery, as their interaction with the endothelium is critical for multiple aspects of cerebrovascular function. There is growing evidence that pericyte loss or dysfunction is involved in the pathogenesis of Alzheimer’s disease, vascular dementia, ischemic stroke and brain injury. However, strategies to mitigate or compensate for this loss remain limited. In this review, we highlight a novel finding that pericytes in the adult brain are structurally dynamic in vivo, and actively compensate for loss of endothelial coverage by extending their far-reaching processes to maintain contact with regions of exposed endothelium. Structural remodeling of pericytes may present an opportunity to foster pericyte-endothelial communication in the adult brain and should be explored as a potential means to counteract pericyte loss in dementia and cerebrovascular disease. We discuss the pathophysiological consequences of pericyte loss on capillary function, and the biochemical pathways that may control pericyte remodeling. We also offer guidance for observing pericytes in vivo, such that pericyte structural remodeling can be more broadly studied in mouse models of cerebrovascular disease.

OCT-Angiography reveals reduced vessel density in the deep retinal plexus of CADASIL patients

Optical coherence tomography angiography (OCT-A) represents the most recent tool in ophthalmic imaging. It allows for a non-invasive, depth-selective and quantitative visualization of blood flow in central retinal vessels and it has an enormous diagnostic potential not only in ophthalmology but also with regards to neurologic and systemic diseases. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a hereditary vascular small-vessel disease caused by Notch3 mutations and represents the most common form of hereditary stroke disorder. In this study, CADASIL patients prospectively underwent OCT-A imaging to evaluate retinal and choriocapillaris blood flow as well as blood flow at the optic nerve head. The vessel density of the macular region and the size of the foveal avascular zone in the superficial and deep retinal plexus were determined as well as the vessel density at the optic nerve head and in the choriocapillaris. Additionally, cerebral magnetic resonance images were evaluated. The main finding was that vessel density of the deep retinal plexus was significantly decreased in CADASIL patients compared to healthy controls which may reflect pericyte dysfunction in retinal capillaries.

Disruption of Bmal1 Impairs Blood-Brain Barrier Integrity via Pericyte Dysfunction.

Circadian rhythm disturbances are well established in neurological diseases. However, how these disruptions cause homeostatic imbalances remains poorly understood. Brain and muscle aryl hydrocarbon receptor nuclear translocator-like protein 1 (Bmal1) is a major circadian clock transcriptional activator, and Bmal1 deficiency in male Bmal1nestin-/- mice induced marked astroglial activation without affecting the number of astrocytes in the brain and spinal cord. Bmal1 deletion caused blood-brain barrier (BBB) hyperpermeability with an age-dependent loss of pericyte coverage of blood vessels in the brain. Using Nestin-green fluorescent protein (GFP) transgenic mice, we determined that pericytes are Nestin-GFP+ in the adult brain. Bmal1 deletion caused Nestin-GFP+ pericyte dysfunction, including the downregulation of platelet-derived growth factor receptor β (PDGFRβ), a protein necessary for maintaining BBB integrity. Knockdown of Bmal1 downregulated PDGFRβ transcription in the brain pericyte cell line. Thus, the circadian clock component Bmal1 maintains BBB integrity via regulating pericytes.SIGNIFICANCE STATEMENT Circadian rhythm disturbances may play a role in neurodegenerative disorders, such as Alzheimer's disease. Our results revealed that one of the circadian clock components maintains the integrity of the blood-brain barrier (BBB) by regulating vascular-embedded pericytes. These cells were recently identified as a vital component for the control of BBB permeability and cerebral blood flow. Our present study demonstrates the involvement of circadian clock component Bmal1 in BBB homeostasis and highlights the role of Bmal1 dysfunction in multiple neurological diseases.

Palmitic acid dysregulates the Hippo–YAP pathway and inhibits angiogenesis by inducing mitochondrial damage and activating the cytosolic DNA sensor cGAS–STING–IRF3 signaling mechanism

Impaired angiogenesis and wound healing carry significant morbidity and mortality in diabetic patients. Metabolic stress from hyperglycemia and elevated free fatty acids have been shown to inhibit endothelial angiogenesis. However, the underlying mechanisms remain poorly understood. In this study, we show that dysregulation of the Hippo-Yes-associated protein (YAP) pathway, an important signaling mechanism in regulating tissue repair and regeneration, underlies palmitic acid (PA)-induced inhibition of endothelial angiogenesis. PA inhibited endothelial cell proliferation, migration, and tube formation, which were associated with increased expression of mammalian Ste20-like kinases 1 (MST1), YAP phosphorylation/inactivation, and nuclear exclusion. Overexpression of YAP or knockdown of MST1 prevented PA-induced inhibition of angiogenesis. When searching upstream signaling mechanisms, we found that PA dysregulated the Hippo-YAP pathway by inducing mitochondrial damage. PA treatment induced mitochondrial DNA (mtDNA) release to cytosol, and activated cytosolic DNA sensor cGAS-STING-IRF3 signaling. Activated IRF3 bound to the MST1 gene promoter and induced MST1 expression, leading to MST1 up-regulation, YAP inactivation, and angiogenesis inhibition. Thus, mitochondrial damage and cytosolic DNA sensor cGAS-STING-IRF3 signaling are critically involved in PA-induced Hippo-YAP dysregulation and angiogenesis suppression. This mechanism may have implication in impairment of angiogenesis and wound healing in diabetes.

Abstract 224: Angiogenic Imbalance Causes Cerebrovascular Pathological Neovascularization in Diabetes: Role of Pericytes.

Diabetes increases cerebrovascular complications such as stroke and cognitive impairment. We have previously showed that diabetes causes dysfunctional cerebral neovascularization. Pericytes have a pivotal role in modulating microvascular physiology and pathology, yet its role in diabetes dysfunctional cerebral neovascularization is unknown. In the present study we testedthe hypothesis that pericytes play a crucial role in diabetes-mediated dysfunctional pathological cerebral neovascularization via dysregulation of antiangiogenic Slit-2/ROBO4 and the proangiogenic EphrinB2/EphB4 signaling. Methods: Diabetes was induced in Wistar rats using low dose of streptozotocin and high fat diet (STZ/HFD). Immunohistochemistry and immunoblotting were used to assess ROBO4 and EphrinB2 expression in the brain and human brain microvascular pericytes (HBMVP). HBMVP was exposed to glucose (25 mM) /palmitate (200 uM) to mimic diabetic conditions. Scratch migration assay was used to assess the effect of high glucose/palmitate (HG/Pal) on pericytes migration. Adenovirus was used to overexpress ROBO4 in the brain in vivo. Results: STZ/HFD caused a significant increase in HbA1C (10.8*). Diabetic brains and HBMVP exposed to HG/Pal showed reduced ROBO4 expression (66%* and 48%*) and increased EphrinB2 expression (1.9* and 1.6* folds). HG/Pal increased pericyte migration by 2* fold. Pericyte migration was increased by 2.5* fold with silencing ROBO4 but significantly reduced with silencing EphrinB2 (35%*) or ROBO4 overexpression (47%*) under HG/Pal. In vivo ROBO4 overexpression decreased pathological neovascularization indices and increased pericyte coverage. (n= 3-5, *P<0.05). Conclusion: Our findings emphasize the importance of balanced anti- and proangiogenic signaling for proper pericyte function in diabetes. Our results suggest that pericytes are involved in proangiogenic and barrier functions of endothelial cells and pericyte dysfunction may contribute to pathological neovascularization in diabetes. Thus, pericyte ROBO4 and EphrinB2 signaling are promising therapeutic targets to improve cerebrovascular integrity in diabetes.

P75NTR and Its Ligand ProNGF Activate Paracrine Mechanisms Etiological to the Vascular, Inflammatory, and Neurodegenerative Pathologies of Diabetic Retinopathy.

In many diseases, expression and ligand-dependent activity of the p75(NTR) receptor can promote pericyte and vascular dysfunction, inflammation, glial activation, and neurodegeneration. Diabetic retinopathy (DR) is characterized by all of these pathological events. However, the mechanisms by which p75(NTR) may be implicated at each stage of DR pathology remain poorly understood. Using a streptozotocin mouse model of diabetic retinopathy, we report that p75(NTR) is upregulated very early in glia and in pericytes to mediate ligand-dependent induction of inflammatory cytokines, disruption of the neuro-glia-vascular unit, promotion of blood-retina barrier breakdown, edema, and neuronal death. In a mouse model of oxygen-induced retinopathy, mimicking proliferative DR, p75(NTR)-dependent inflammation leads to ischemia and pathological angiogenesis through Semaphorin 3A. The acute use of antagonists of p75(NTR) or antagonists of the ligand proNGF suppresses each distinct phase of pathology, ameliorate disease, and prevent disease progression. Thus, our study documents novel disease mechanisms and validates druggable targets for diabetic retinopathy. Diabetic retinopathy (DR) affects an estimated 250 million people and has no effective treatment. Stages of progression comprise pericyte/vascular dysfunction, inflammation, glial activation, and neurodegeneration. The pathophysiology of each stage remains unclear. We postulated that the activity of p75NTR may be implicated. We show that p75NTR in glia and in pericytes mediate ligand-dependent induction of inflammatory cytokines, disruption of the neuro-glia-vascular unit, promotion of blood-retina barrier breakdown, edema, and neuronal death. p75NTR-promoted inflammation leads to ischemia and angiogenesis through Semaphorin 3A. Antagonists of p75NTR or antagonists of proNGF suppress each distinct phase of pathology, ameliorate disease, and prevent disease progression. Our study documents novel mechanisms in a pervasive disease and validates druggable targets for treatment.

Combined deficiency of Notch1 and Notch3 causes pericyte dysfunction, models CADASIL, and results in arteriovenous malformations.

Pericytes regulate vessel stability and pericyte dysfunction contributes to retinopathies, stroke, and cancer. Here we define Notch as a key regulator of pericyte function during angiogenesis. In Notch1+/−; Notch3−/− mice, combined deficiency of Notch1 and Notch3 altered pericyte interaction with the endothelium and reduced pericyte coverage of the retinal vasculature. Notch1 and Notch3 were shown to cooperate to promote proper vascular basement membrane formation and contribute to endothelial cell quiescence. Accordingly, loss of pericyte function due to Notch deficiency exacerbates endothelial cell activation caused by Notch1 haploinsufficiency. Mice mutant for Notch1 and Notch3 develop arteriovenous malformations and display hallmarks of the ischemic stroke disease CADASIL. Thus, Notch deficiency compromises pericyte function and contributes to vascular pathologies.

Dysfunction of brain pericytes in chronic neuroinflammation

Brain pericytes are uniquely positioned within the neurovascular unit to provide support to blood brain barrier (BBB) maintenance. Neurologic conditions, such as HIV-1-associated neurocognitive disorder, are associated with BBB compromise due to chronic inflammation. Little is known about pericyte dysfunction during HIV-1 infection. We found decreased expression of pericyte markers in human brains from HIV-1-infected patients (even those on antiretroviral therapy). Using primary human brain pericytes, we assessed expression of pericyte markers (α1-integrin, α-smooth muscle actin, platelet-derived growth factor-B receptor β, CX-43) and found their downregulation after treatment with tumor necrosis factor-α (TNFα) or interleukin-1 β (IL-1β). Pericyte exposure to virus or cytokines resulted in decreased secretion of factors promoting BBB formation (angiopoietin-1, transforming growth factor-β1) and mRNA for basement membrane components. TNFα and IL-1β enhanced expression of adhesion molecules in pericytes paralleling increased monocyte adhesion to pericytes. Monocyte migration across BBB models composed of human brain endothelial cells and pericytes demonstrated a diminished rate in baseline migration compared to constructs composed only of brain endothelial cells. However, exposure to the relevant chemokine, CCL2, enhanced the magnitude of monocyte migration when compared to BBB models composed of brain endothelial cells only. These data suggest an important role of pericytes in BBB regulation in neuroinflammation.

A review of therapies for diabetic macular oedema and rationale for combination therapy.

Diabetic macular oedema (DMO) is responsible for significant visual impairment in diabetic patients. The primary cause of DMO is fluid leakage resulting from increased vascular permeability through contributory anatomical and biochemical changes. These include endothelial cell (EC) death or dysfunction, pericyte loss or dysfunction, thickened basement membrane, loss or dysfunction of glial cells, and loss/change of EC Glycocalyx. The molecular changes include increased reactive oxygen species, pro-inflammatory changes: advanced glycation end products, intracellular adhesion molecule-1, Complement 5-9 deposition and cytokines, which result in increased paracellular permeability, tight junction disruption, and increased transcellular permeability. Laser photocoagulation has been the mainstay of treatment until recently when pharmacological treatments were introduced. The current treatments for DMO target reducing vascular leak in the macula once it has occurred, they do not attempt to treat the underlying pathology. These pharmacological treatments are aimed at antagonising vascular endothelial growth factor (VEGF) or non-VEGF inflammatory pathways, and include intravitreal injections of anti-VEGFs (ranibizumab, aflibercept or bevacizumab) or steroids (fluocinolone, dexamethasone or triamcinolone) as single therapies. The available evidence suggests that each individual treatment modality in DMO does not result in a completely dry macula in most cases. The ideal treatment for DMO should improve vision and improve morphological changes in the macular (eg, reduce macular oedema) for a significant duration, reduced adverse events, reduced treatment burden and costs, and be well tolerated by patients. This review evaluates the individual treatments available as monotherapies, and discusses the rationale and potential for combination therapy in DMO. A comprehensive review of clinical trials related to DMO and their outcomes was completed. Where phase III randomised control trials were available, these were referenced, if not available, phase II trials have been included.

Neurovascular coupling during cortical spreading depolarization and -depression.

Cortical spreading depolarizations (CSDs) are self-propagating waves of transient loss of neuronal transmembrane ion gradients, followed by prolonged suppression of neuronal activity (spreading depression). CSDs emerge spontaneously in animal models of traumatic brain injury,1 subarachnoid hemorrhage,2 and in focal ischemia3 where they are associated with infarct growth.4 In humans, CSDs have been demonstrated in traumatic brain injury,5 subarachnoid hemorrhage,6,7 and malignant hemispheric stroke,8 and they are believed to be the brain mechanism underlying migraine aura.9 CSDs are associated with dramatic changes in cerebral blood flow (CBF). During the depolarization phase of CSDs induced in healthy and well-perfused brain tissue in animal models, an early hyperemic response is observed, typically followed by prolonged oligemia after the neuronal repolarization. Despite the initial CBF increase, tissue hypoxia may develop in more distant territories of capillary supply.10,11 Similar CBF changes have been observed in patients with migraine aura.12–14 In the injured brain, CSDs can be accompanied by severe initial CBF reduction instead of a CBF increase during the depolarization phase, termed spreading ischemia.15 When this inverse hemodynamic response is observed, the energy-dependent recovery from CSD is delayed in a characteristic fashion, indicating a severe mismatch between oxygen supply and demand2 and a high risk of tissue damage.16 In rat and cat models of focal ischemia, CSD-related CBF transients range from monophasic, positive CBF responses in peri-ischemic tissue, over biphasic transients in mildly ischemic tissue, to negative CBF transients in more severe ischemia.17–19 During CSD in animal models, capillary flow patterns become severely disturbed.10,20,21 The passage of a CSD causes erythrocytes in some capillaries to reduce their speed, whereas other capillaries reveal 4-fold increases in flow or higher. …

Pericyte dysfunction in blood brain barrier impairment caused by HIV infection (278.1)

Studies performed over the last decade indicated that functional alterations of brain endothelium is the main factor in blood brain barrier (BBB) injury during HIV infection. However, other cells constituting the BBB (like pericytes) received almost no attention. We propose that pericyte dysfunction present in HIV infection can contribute to BBB compromise and progression of HIV‐associated neurocognitive disorders (HAND). We used co‐cultures of primary human brain pericytes (BP) and human primary brain micsovascular endothelial cells (BMVEC) and human brain tissues of HIV infected patients to study alterations of pericyte function in chronic neuroinflammation driven by HIV infection. We found partial pericyte loss and down‐regulation of key receptors on these cells in brain tissue of HIV infected patients (even without detectable HIV in the brain) and in HIV infected ‘humanized’ mice that paralleled BBB compromise and neuroinflammation. BP treated with IL‐1β or TNFα demonstrated decreased secretion of angiopoetin 1 and transforming growth factor‐β1, diminished expression of platelet derived growth factor‐B receptor β1 and connexin 43 (critical for pericyte recruitment to BBB and gap junctions between BP and BMVEC). BP exposed to IL‐1β/TNFα showed enhanced expression of numerous pro‐inflammatory factors (relevant to HIV neuropathogenesis) and adhesion molecules paralleling increased adhesion of monocytes to pericyte monolayers. Using BBB models (composed of BMVEC‐BP), we showed increased monocyte migration across BBB constructs in response to the relevant chemokine, CCL2. IL‐1β/TNFα treatment of pericytes altered their ability to spread or migrate providing a potential mechanism for their decrease in brain tissue of HIV‐infected patients. These data point to a major decrease in barrier‐supporting function and enhanced inflammatory responses in brain pericytes after exposure to relevant cytokines and in brain tissues of HAND patients.Grant Funding Source: supported by NIH grants MH65151, AA015913

Stroke Literature Synopses: Basic Science

<i>Stroke</i> Literature Synopses: Basic Science

Circulation Editors’ Picks

<i>Circulation</i> Editors’ Picks

Brain pericytes from stress-susceptible pigs increase blood-brain barrier permeability in vitro

BackgroundThe function of pericytes remains questionable but with improved cultured technique and the use of genetically modified animals, it has become increasingly clear that pericytes are an integral part of blood–brain barrier (BBB) function, and the involvement of pericyte dysfunction in certain cerebrovascular diseases is now emerging. The porcine stress syndrome (PSS) is the only confirmed, homologous model of malignant hyperthermia (MH) in veterinary medicine. Affected animals can experience upon slaughter a range of symptoms, including skeletal muscle rigidity, metabolic acidosis, tachycardia and fever, similar to the human syndrome. Symptoms are due to an enhanced calcium release from intracellular stores. These conditions are associated with a point mutation in ryr1/hal gene, encoding the ryanodine receptor, a calcium channel. Important blood vessel wall muscle modifications have been described in PSS, but potential brain vessel changes have never been documented in this syndrome.MethodsIn the present work, histological and ultrastructural analyses of brain capillaries from wild type and ryr1 mutated pigs were conducted to investigate the potential impairment of pericytes, in this pathology. In addition, brain pericytes were isolated from the three porcine genotypes (wild-type NN pigs; Nn and nn pigs, bearing one or two (n) mutant ryr1/hal alleles, respectively), and tested in vitro for their influence on the permeability of BBB endothelial monolayers.ResultsEnlarged perivascular spaces were observed in ryr1-mutant samples, corresponding to a partial or total detachment of the astrocytic endfeet. These spaces were electron lucent and sometimes filled with lipid deposits and swollen astrocytic feet. At the ultrastructural level, brain pericytes did not seem to be affected because they showed regular morphology and characteristics, so we aimed to check their ability to maintain BBB properties in vitro. Our results indicated that pericytes from the three genotypes of pigs had differing influences on the BBB. Unlike pericytes from NN pigs, pericytes from Nn and nn pigs were not able to maintain low BBB permeability.ConclusionsElectron microscopy observations demonstrated brain capillary modifications in PSS condition, but no change in pericyte morphology. Results from in vitro experiments suggest that brain pericytes from ryr1 mutated pigs, even if they are not affected by this condition at the ultrastructural level, are not able to maintain BBB integrity in comparison with pericytes from wild-type animals.