Chronic hypoperfusion increases claudin-3 immunoreactivity in rat brain

The Impact of Paracoccidioides spp Infection on Central Nervous System Cell Junctional Complexes

Paracoccidioidomycosis (PCM), a systemic mycosis caused by the fungus Paracoccidioides spp. is the most prevalent fungal infection among immunocompetent patients in Latin America. The estimated frequency of central nervous system (CNS) involvement among the human immunodeficiency virus (HIV)/PCM-positive population is 2.5%. We aimed to address the impact of neuroparacoccidioidomycosis (NPCM) and HIV/NPCM co-infection on the tight junctions (TJ) and adherens junction (AJ) proteins of the CNS. Four CNS formalin-fixed paraffin-embedded (FFPE) tissue specimens were studied: NPCM, NPCM/HIV co-infection, HIV-positive without opportunistic CNS infection, and normal brain autopsy (negative control). Immunohistochemistry was used to analyze the endothelial cells and astrocytes expressions of TJ markers: claudins (CLDN)-1, -3, -5 and occludin; AJ markers: β-catenin and E-cadherin; and pericyte marker: alpha-smooth muscle actin. FFPE CNS tissue specimens were analyzed using the immunoperoxidase assay. CLDN-5 expression in the capillaries of the HIV/NPCM coinfected tissues (mixed clinical form of PCM) was lower than that in the capillaries of the HIV or NPCM monoinfected (chronic clinical form of PCM) tissues. A marked decrease in CLDN-5 expression and a compensatory increase in CLDN-1 expression in the NPCM/HIV co-infection tissue samples was observed. The authors suggest that Paracoccidioides spp. crosses the blood-brain barrier through paracellular pathway, owing to the alteration in the CLDN expression, or inside the macrophages (Trojan horse).

Resveratrol reduces inflammatory response and detrimental effects in chronic cerebral hypoperfusion by down-regulating stimulator of interferon genes/TANK-binding kinase 1/interferon regulatory factor 3 signaling

Inflammatory responses induced by chronic cerebral hypoperfusion (CCH) play a critical role in the progression of vascular dementia. Stimulator of interferon genes (STING) signaling function as a key mediator of inflammation and immunological responses in the central nervous system (CNS), and resveratrol (RES) exerts potent anti-inflammatory effects. However, the role of STING signaling and the relationship between RES and STING signaling in persistent hypoperfusion-induced cerebral inflammation remain unclear. In this study, Sprague–Dawley rats were subjected to either Sham or bilateral common carotid artery occlusion (2VO) surgery and received RES or vehicle daily by intraperitoneal injection for 4 or 8 weeks. Morris’s water maze was used for the analysis of cognitive function. The neuroinflammatory responses in white matter and hippocampus of the rat brain were assessed by Western blot, Immunofluorescence staining, and qRT-PCR analyses. Myelin integrity, neutrophil infiltration, and microglia proliferation were assessed by Immunohistochemistry and histologic analysis. We demonstrated that after CCH, neurons, microglia, and astrocyte under endoplasmic reticulum (ER) stress upregulated the expression of STING, TANK-binding kinase 1 (TBK1), and the transcription factor interferon regulatory factor 3 (IRF3), as well as translocation of IRF3 into the nucleus. These were accompanied by infiltration of neutrophils, activation of microglia, and overproduction of proinflammatory mediators. Improvements in cognitive deficits were related to reduced hippocampal neuronal cell death and increased myelin integrity in RES-treated rats. The neuroprotective effects of RES were associated with suppression of the expression of tumor necrosis factor-alpha (TNF-α), intercellular adhesion molecule 1 (ICAM-1), VCAM-1, interferon-β (IFN-β), and IL-1β, likely through mitigation of the STING/TBK1/IRF3 pathway. These inhibitory effects exerted by RES also inhibited the levels of myeloperoxidase, reduced excess expression of reactive astrocytes, and activated microglia. In conclusion, the STING/TBK1/IRF3 axis may be critical for proinflammatory responses in cerebral tissue with persistent hypoperfusion, and RES exerts its anti-inflammatory effects by suppressing STING/TBK1/IRF3 signaling.

Potential Applications of Remote Limb Ischemic Conditioning for Chronic Cerebral Circulation Insufficiency

Chronic cerebral circulation insufficiency (CCCI) refers to a chronic decrease in cerebral blood perfusion, which may lead to cognitive impairment, psychiatric disorders such as depression, and acute ischemic stroke. Remote limb ischemic conditioning (RLIC), in which the limbs are subjected to a series of transient ischemic attacks, can activate multiple endogenous protective mechanisms to attenuate fatal ischemic injury to distant organs due to acute ischemia, such as ischemic stroke. Recent studies have also reported that RLIC can alleviate dysfunction in distant organs caused by chronic, non-fatal reductions in blood supply (e.g., CCCI). Indeed, research has indicated that RLIC may exert neuroprotective effects against CCCI through a variety of potential mechanisms, including attenuated glutamate excitotoxicity, improved endothelial function, increased cerebral blood flow, regulation of autophagy and immune responses, suppression of apoptosis, the production of protective humoral factors, and attenuated accumulation of amyloid-β. Verification of these findings is necessary to improve prognosis and reduce the incidence of acute ischemic stroke/cognitive impairment in patients with CCCI.

Claudin-1-Dependent Destabilization of the Blood-Brain Barrier in Chronic Stroke

Recent evidence suggests that blood-brain barrier (BBB) recovery and reestablishment of BBB impermeability after stroke is incomplete. This could influence stroke recovery, increase the risk of repeat stroke, and be a solid substrate for developing vascular dementia. Although accumulating evidence has defined morphological alterations and underlying mechanisms of tight junction (TJ) changes during BBB breakdown in acute stroke, very little is known about the type of alterations and mechanisms in BBB "leakage" found subacutely or chronically. The current study examined BBB structural alterations during the "BBB leakage" associated with the chronic phase of stroke in male mice and both genders of humans. We found significant upregulation of claudin-1 mRNA and protein, a nonspecific claudin for blood vessels, and downregulation in claudin-5 expression. Morphological and biochemical as well as fluorescence resonance energy transfer and fluorescence recovery after photobleaching analysis of postischemic brain endothelial cells and cells overexpressing claudin-1 indicated that newly synthesized claudin-1 was present on the cell membrane (∼45%), was incorporated into the TJ complex with established interaction with zonula occludens-1 (ZO-1), and was building homophilic cis- and trans-interactions. The appearance of claudin-1 in the TJ complex reduced claudin-5 strands (homophilic claudin-5 cis- and trans-interactions) and claudin-5/ZO-1 interaction affecting claudin-5 incorporation into the TJ complex. Moreover, claudin-1 induction was associated with an endothelial proinflammatory phenotype. Targeting claudin-1 with a specific C1C2 peptide improved brain endothelial barrier permeability and functional recovery in chronic stroke condition. This study highlights a potential "defect" in postischemic barrier formation that may underlie prolonged vessel leakiness.SIGNIFICANCE STATEMENT Although rarely expressed at the normal blood-brain barrier (BBB), claudin-1 is expressed in pathological conditions. Analyzing poststroke human and mouse blood microvessels we have identified that claudin-1 is highly expressed in leaky brain microvessels. Our results reveal that claudin-1 is incorporated in BBB tight junction complex, impeding BBB recovery and causing BBB leakiness during poststroke recovery. Targeting claudin-1 with a claudin-1 peptide improves brain endothelial barrier permeability and consequently functional neurological recovery after stroke.

Advances in chronic cerebral circulation insufficiency

Chronic cerebral circulation insufficiency (CCCI) may not be an independent disease; rather, it is a pervasive state of long-term cerebral blood flow insufficiency caused by a variety of etiologies, and considered to be associated with either occurrence or recurrence of ischemic stroke, vascular cognitive impairment, and development of vascular dementia, resulting in disability and mortality worldwide. This review summarizes the features and recent progress of CCCI, mainly focusing on epidemiology, experimental research, pathophysiology, etiology, clinical manifestations, imaging presentation, diagnosis, and potential therapeutic regimens. Some research directions are briefly discussed as well.

Cilostazol reduces blood brain barrier dysfunction, white matter lesion formation and motor deficits following chronic cerebral hypoperfusion

Cerebral small vessel disease (CSVD) is a pathological process leading to lacunar infarcts, leukoaraiosis and cerebral microbleeds. Dysfunction of the blood brain barrier (BBB) has been proposed as a mechanism in the progression cerebral small vessel disease. A rodent model commonly used to study some aspects of CSVD is bilateral common carotid artery occlusion (BCCAO) in the rat. In the present study it was determined that gait impairment, as determined by a tapered beam test, and BBB permeability increased following BCCAO. Cilostazol, a type III phosphodiesterase inhibitor, has been shown to have anti-apoptotic effects and prevent white matter vacuolation and rarefaction induced by BCCAO in rats. In this study the protective effect of cilostazol administration on the increase BBB permeability following BCCAO was determined as well as the effect on plasma levels of circulating microparticles (MPs), cerebral white matter rarefaction, glial activation and gait disturbance. The effect of cilostazol on in vitro endothelial barriers was also evaluated. Cilostazol treatment improved BBB permeability and reduced gait disturbance, visual impairment and microglial activation in optic tract following BCCAO in vivo. It also reduced the degree of cell death and the reduction in trans-endothelial electrical resistance (TEER) in artificial endothelial barriers in vitro induced by MP treatment of in vitro barriers.

Ontogeny of tight junction protein expression in the ovine cerebral cortex during development

Tight junctions of the blood-brain barrier are composed of transmembrane and associated cytoplasmic proteins. The transmembrane claudin proteins form the primary seal between endothelial cells and junctional adhesion molecules (JAMs) regulate tight junction formation. We have previously shown that claudin-1, claudin-5, zonula occludens (ZO)-1, and ZO-2 exhibit differential developmental regulation from 60% of gestation up to maturity in adult sheep. The purpose of the current study was to examine developmental changes in claudin-3, -12, and JAM-A protein expression in cerebral cortices of fetuses at 60%, 80%, and 90% gestation, and in newborn and adult sheep. We also examined correlations between changes in endogenous cortisol levels and tight junction protein expression in cerebral cortices of the fetuses. Claudin-3, -12 and JAM-A expressions were determined by Western immunoblot. Claudin-3 and -12 were lower (P<0.01) at 60%, 80%, 90% and in newborns than in adults, and JAM-A was lower in adults than in fetuses at 80% and 90% gestation. Claudin-3 expression demonstrated a direct correlation with increasing plasma cortisol levels (r=0.60, n=15, P<0.02) in the fetuses. We conclude that: claudin-3, -12 and JAM-A are expressed as early as 60% of gestation in ovine cerebral cortices, exhibit differential developmental regulation, and that increasing endogenous glucocorticoids modulate claudin-3 expression in the fetus.

Total cerebral blood flow and mortality in old age: a 12-year follow-up study

OBJECTIVE

To examine the association of total cerebral blood flow (CBF) with all-cause, noncardiovascular, and cardiovascular mortality in older subjects at risk of cardiovascular disease.

METHODS

We included 411 subjects with a mean age of 74.5 years from the MRI substudy of the Prospective Study of Pravastatin in the Elderly at Risk. Total CBF was measured at baseline, and occurrence of death was recorded in an average follow-up period of 11.8 years. For each participant, total CBF was standardized for brain parenchymal volume. Cox regression models were used to estimate risk of all-cause, noncardiovascular, and cardiovascular mortality in relation to CBF.

RESULTS

Mortality rates among participants in low, middle, and high thirds of total CBF were 52.1, 41.5, and 28.7 per 1,000 person-years, respectively. Compared with participants in the high third of CBF, participants in the low third had 1.88-fold (95% confidence interval [CI]: 1.30-2.72) higher risk of all-cause mortality, 1.66-fold (95% CI: 1.06-2.59) higher risk of noncardiovascular mortality, and 2.50-fold (95% CI: 1.28-4.91) higher risk of cardiovascular mortality. Likewise, compared with participants in the high third of CBF, participants in the middle third had 1.44-fold (95% CI: 0.98-2.11) higher risk of all-cause mortality, 1.29-fold (95% CI: 0.82-2.04) higher risk of noncardiovascular mortality, and 1.86-fold (95% CI: 0.93-3.74) higher risk of cardiovascular mortality. These associations were independent of prevalent vascular status and risk factors.

CONCLUSIONS

Low total CBF is linked with higher risk of all-cause, noncardiovascular, and cardiovascular mortality in older people independent of clinical cardiovascular status.

Altered expression of claudin family proteins in Alzheimer's disease and vascular dementia brains

Claudins (Cls) are a multigene family of transmembrane proteins with different tissue distribution, which have an essential role in the formation and sealing capacity of tight junctions (TJs). At the level of the blood–brain barrier (BBB), TJs are the main molecular structures which separate the neuronal milieu from the circulatory space, by a restriction of the paracellular flow of water, ions and larger molecules into the brain. Different studies suggested recently significant BBB alterations in both vascular and degenerative dementia types. In a previous study we found in Alzheimer’s disease (AD) and vascular dementia (VaD) brains an altered expression of occludin, a molecular partner of Cls in the TJs structure. Therefore in this study, using an immunohistochemical approach, we investigated the expression of Cl family proteins (Cl-2, Cl-5 and Cl-11) in frontal cortex of aged control, AD and VaD brains. To estimate the number of Cl-expressing cells, we applied a random systematic sampling and the unbiased optical fractionator method. We found selected neurons, astrocytes, oligodendrocytes and endothelial cells expressing Cl-2, Cl-5 and Cl-11 at detectable levels in all cases studied. We report a significant increase in ratio of neurons expressing Cl-2, Cl-5 and Cl-11 in both AD and VaD as compared to aged controls. The ratio of astrocytes expressing Cl-2 and Cl-11 was significantly higher in AD and VaD as compared to aged controls. The ratio of oligodendrocytes expressing Cl-11 was significantly higher in AD and the ratio of oligodendrocytes expressing Cl-2 was significantly higher in VaD as compared to aged controls. Within the cerebral cortex, Cls were selectively expressed by pyramidal neurons, which are the ones responsible for cognitive processes and affected by AD pathology. Our findings suggest a new function of Cl family proteins which might be linked to response to cellular stress.