Systemic Listeria monocytogenes infection in aged mice induces long-term neuroinflammation: the role of miR-155.

BACKGROUND: Understanding mechanisms of pathologic neuroinflammation is essential for improving outcomes after central nervous system infections. Brain tissue-resident memory T cells (bTRM) are recruited during central nervous system infection and promote pathogen control as well as noxious inflammation. Our prior studies in young mice showed optimal recruitment of CD8+ bTRM during neuroinvasive Listeria monocytogenes (Lm) infection required miR-155, and was significantly inhibited by anti-miR-155 oligonucleotides. Since Lm is an important pathogen in the elderly, we hypothesized anti-miR-155 would also inhibit accumulation of CD8+ bTRM in aged mice infected with Lm. METHODS: Young (2 mo) and aged (> 18 mo) male C57BL/6 mice were infected intra-peritoneally with wild-type Lm, or avirulent Lm mutants lacking the genes required for intracellular motility (ΔactA) or phagosomal escape (Δhly), then were given antibiotics. Brain leukocytes and their intracellular cytokine production were quantified by flow cytometry >28d post-infection (p.i.). The role of miR-155 was tested by injecting mice with anti-miR-155 or control oligonucleotides along with antibiotics. RESULTS: Aged mice had significantly more homeostatic CD8+ bTRM than did young mice, which did not increase after infection with wild-type Lm despite 50% mortality, whereas young mice suffered no mortality after a larger inoculum. For direct comparison of post-infectious neuroinflammation after the same inoculum, young and aged mice were infected with 107 CFU ΔactA Lm. This mutant caused no mortality and significantly increased CD8+ bTRM 28d p.i. in both groups, whereas bone marrow-derived myeloid cells, particularly neutrophils, increased only in aged mice. Notably, anti-miR-155 reduced accumulation of brain myeloid cells in aged mice after infection, whereas CD8+ bTRM were unaffected. CONCLUSIONS: Systemic infection with Lm ΔactA is a novel model for studying infection-induced brain inflammation in aged mice without excessive mortality. CD8+ bTRM increase in both young and aged mice after infection, whereas only in aged mice bone marrow-derived myeloid cells increase long-term. In aged mice, anti-miR-155 inhibits brain accumulation of myeloid cells, but not CD8+ bTRM. These results suggest young and aged mice differ in manifestations and mechanisms of infection-induced neuroinflammation and give insight for developing therapies to ameliorate brain inflammation following severe infection in the elderly.

Interleukin 6 reduces allopregnanolone synthesis in the brain and contributes to age-related cognitive decline in mice.

Cognitive decline with age is a harmful process that can reduce quality of life. Multiple factors have been established to contribute to cognitive decline, but the overall etiology remains unknown. Here, we hypothesized that cognitive dysfunction is mediated, in part, by increased levels of inflammatory cytokines that alter allopregnanolone (AlloP) levels, an important neurosteroid in the brain. We assessed the levels and regulation of AlloP and the effects of AlloP supplementation on cognitive function in 4-month-old and 24-month-old male C57BL/6 mice. With age, the expression of enzymes involved in the AlloP synthetic pathway was decreased and corticosterone (CORT) synthesis increased. Supplementation of AlloP improved cognitive function. Interestingly, interleukin 6 (IL-6) infusion in young animals significantly reduced the production of AlloP compared with controls. It is notable that inhibition of IL-6 with its natural inhibitor, soluble membrane glycoprotein 130, significantly improved spatial memory in aged mice. These findings were supported by in vitro experiments in primary murine astrocyte cultures, indicating that IL-6 decreases production of AlloP and increases CORT levels. Our results indicate that age-related increases in IL-6 levels reduce progesterone substrate availability, resulting in a decline in AlloP levels and an increase in CORT. Furthermore, our results indicate that AlloP is a critical link between inflammatory cytokines and the age-related decline in cognitive function.

Neuroinvasive Listeria monocytogenes infection triggers accumulation of brain CD8+ tissue-resident memory T cells in a miR-155-dependent fashion.

BACKGROUND: Brain inflammation is a key cause of cognitive decline after central nervous system (CNS) infections. A thorough understanding of immune responses to CNS infection is essential for developing anti-inflammatory interventions that improve outcomes. Tissue-resident memory T cells (TRM) are non-recirculating memory T cells that provide surveillance of previously infected tissues. However, in addition to protecting the brain against reinfection, brain TRM can contribute to post-infectious neuroinflammation. We hypothesized that accumulation of CD8+ TRM in the brain could be reduced by inhibiting microRNA (miR)-155, a microRNA that influences development of cytotoxic CD8+ T lymphocytes during infection. METHODS: C57BL/6J mice were infected by intraperitoneal injection with a lethal inoculum of Listeria monocytogenes (Lm) then treated with antibiotics. Flow cytometry was used to quantify specific populations of brain leukocytes 28-29 days (d) post-infection (p.i.). To test the degree to which miR-155 altered leukocyte influxes into the brain, infected mice were injected with a miR-155 inhibitor or locked nucleic acid (LNA) scramble control 2d, 4d, 6d, and 8d p.i. along with antibiotic treatment. Bacterial loads in spleen and liver and body weights were measured up to 7d p.i. Brain leukocytes were analyzed 14d and 28d p.i. Confirmatory studies were performed in mutated mice lacking miR-155 (miR-155-/-) RESULTS: Lm infection significantly increased the numbers of brain CD3+CD8+ lymphocytes at 28d p.i. These cells were extravascular, and displayed markers characteristic of TRM, with the predominant phenotype of CD44+CD62L-CD69+CX3CR1-. Further analysis showed that > 75% of brain TRM also expressed CD49a, PD-1, Ly6C, CD103, and CD127. Mice injected with miR-155 inhibitor lost less weight through 7d p.i. than did control mice, whereas bacterial loads in brain, liver, and spleen were not different from controls. By 28d p.i., the numbers of brain CD8+ TRM cells were significantly decreased in mice treated with the inhibitor compared with controls. Similarly, miR-155-/- mice showed significantly reduced numbers of brain CD8+ TRM cells by 28d p.i. CONCLUSIONS: Brain CD8+ TRM populations are established during neuroinvasive Lm infection. Accumulation of brain CD8+ TRM cells is reduced by blocking miR-155 and in miR-155-/- mice, indicating that this molecule has a critical role in development of these specialized cells. Administering anti-miR-155 during infection could provide a novel avenue for reducing post-infectious neuroinflammation.

Regional changes in CNS and retinal glycerophospholipid profiles with age: a molecular blueprint.

We present here a quantitative molecular blueprint of the three major glycerophospholipid (GPL) classes, phosphatidylcholine (PC), phosphatidylserine (PS), and phosphatidylethanolamine (PE), in retina and six regions of the brain in C57Bl6 mice at 2, 10, and 26 months of age. We found an age-related increase in molecular species containing saturated and monoenoic FAs and an overall decrease in the longer-chain PUFA molecular species across brain regions, with loss of DHA-containing molecular species as the most consistent and dramatic finding. Although we found very-long-chain PUFAs (VLC-PUFAs) (C28) in PC in the retina, no detectable levels were found in any brain region at any of the ages examined. All brain regions (except hippocampus and retina) showed a significant increase with age in PE plasmalogens. All three retina GPLs had di-PUFA molecular species (predominantly 44:12), which were most abundant in PS (∼30%). In contrast, low levels of di-PUFA GPL (1-2%) were found in all regions of the brain. This study provides a regional and age-related assessment of the brain's lipidome with a level of detail, inclusion, and quantification that has not heretofore been published.

The Protein Tyrosine Phosphatase MEG2 Regulates the Transport and Signal Transduction of Tropomyosin Receptor Kinase A.

Protein tyrosine phosphatase MEG2 (PTP-MEG2) is a unique nonreceptor tyrosine phosphatase associated with transport vesicles, where it facilitates membrane trafficking by dephosphorylation of the N-ethylmaleimide-sensitive fusion factor. In this study, we identify the neurotrophin receptor TrkA as a novel cargo whose transport to the cell surface requires PTP-MEG2 activity. In addition, TrkA is also a novel substrate of PTP-MEG2, which dephosphorylates both Tyr-490 and Tyr-674/Tyr-675 of TrkA. As a result, overexpression of PTP-MEG2 down-regulates NGF/TrkA signaling and blocks neurite outgrowth and differentiation in PC12 cells and cortical neurons.

Sexually divergent induction of microglial-associated neuroinflammation with hippocampal aging.

BACKGROUND: The necessity of including both males and females in molecular neuroscience research is now well understood. However, there is relatively limited basic biological data on brain sex differences across the lifespan despite the differences in age-related neurological dysfunction and disease between males and females. METHODS: Whole genome gene expression of young (3 months), adult (12 months), and old (24 months) male and female C57BL6 mice hippocampus was analyzed. Subsequent bioinformatic analyses and confirmations of age-related changes and sex differences in hippocampal gene and protein expression were performed. RESULTS: Males and females demonstrate both common expression changes with aging and marked sex differences in the nature and magnitude of the aging responses. Age-related hippocampal induction of neuroinflammatory gene expression was sexually divergent and enriched for microglia-specific genes such as complement pathway components. Sexually divergent C1q protein expression was confirmed by immunoblotting and immunohistochemistry. Similar patterns of cortical sexually divergent gene expression were also evident. Additionally, inter-animal gene expression variability increased with aging in males, but not females. CONCLUSIONS: These findings demonstrate sexually divergent neuroinflammation with aging that may contribute to sex differences in age-related neurological diseases such as stroke and Alzheimer's, specifically in the complement system. The increased expression variability in males suggests a loss of fidelity in gene expression regulation with aging. These findings reveal a central role of sex in the transcriptomic response of the hippocampus to aging that warrants further, in depth, investigations.

Association between daily walking and antioxidant capacity in patients with symptomatic peripheral artery disease.

OBJECTIVE: The primary aim of the study was to assess whether both the amount and pace of daily walking were associated with circulating antioxidant capacity in symptomatic patients with peripheral artery disease (PAD). METHODS: Community-based walking was measured in 244 men and women who were limited by symptomatic PAD during a 1-week period in which they wore an ankle-mounted step activity monitor. Patients were further characterized by circulating antioxidant capacity with the OxiSelect (Cell Biolabs Inc, San Diego, Calif) hydroxyl radical antioxidant capacity (HORAC) activity assay. RESULTS: To assess the amount of walking, patients were grouped into low (≤2440 strides/d), middle (2441-3835 strides/d), and high (>3835 strides/d) stride tertiles. HORAC was higher in the middle (P = .03) and high (P = .01) stride tertiles than in the low tertile, but there was no difference between middle and high tertiles (P = .44). To assess the pace of walking, patients were grouped into slow (<25.0 strides/min), middle (25.0-31.6 strides/min), and fast (>31.6 strides/min) cadence tertiles. HORAC was higher in the high cadence tertile than in the low (P < .01) and middle (P < .01) tertiles, but there was no difference between low and middle tertiles (P = .48). Similar findings were obtained on group differences in HORAC after adjusting for age, sex, race, and ankle-brachial index for both the amount and pace of daily walking. CONCLUSIONS: Walking >2440 strides each day and walking at a cadence faster than 31.6 strides/min for 30 minutes each day are both associated with greater circulating antioxidant capacity in symptomatic patients with PAD. The clinical significance is that a home-based walking program may be one approach to increase endogenous antioxidant capacity.

Effects of age and insulin-like growth factor-1 on rat neurotrophin receptor expression after nerve injury.

INTRODUCTION: Neurotrophin receptors, such as p75(NTR) , direct neuronal response to injury. Insulin-like growth factor-1 receptor (IGF-1R) mediates the increase in p75(NTR) during aging. The aim of this study was to examine the effect of aging and insulin-like growth factor-1 (IGF-1) treatment on recovery after peripheral nerve injury. METHODS: Young and aged rats underwent tibial nerve transection with either local saline or IGF-1 treatment. Neurotrophin receptor mRNA and protein expression were quantified. RESULTS: Aged rats expressed elevated baseline IGF-1R (34% higher, P = 0.01) and p75(NTR) (68% higher, P < 0.01) compared with young rats. Post-injury, aged animals expressed significantly higher p75(NTR) levels (68.5% above baseline at 4 weeks). IGF-1 treatment suppressed p75(NTR) gene expression at 4 weeks (17.2% above baseline, P = 0.002) post-injury. CONCLUSIONS: Local IGF-1 treatment reverses age-related declines in recovery after peripheral nerve injuries by suppressing p75(NTR) upregulation and pro-apoptotic complexes. IGF-1 may be considered a viable adjuvant therapy to current treatment modalities. Muscle Nerve 54: 769-775, 2016.

Purinergic glio-endothelial coupling during neuronal activity: role of P2Y1 receptors and eNOS in functional hyperemia in the mouse somatosensory cortex.

Impairment of moment-to-moment adjustment of cerebral blood flow (CBF) via neurovascular coupling is thought to play a critical role in the genesis of cognitive impairment associated with aging and pathological conditions associated with accelerated cerebromicrovascular aging (e.g., hypertension, obesity). Although previous studies demonstrate that endothelial dysfunction plays a critical role in neurovascular uncoupling in these conditions, the role of endothelial NO mediation in neurovascular coupling responses is not well understood. To establish the link between endothelial function and functional hyperemia, neurovascular coupling responses were studied in mutant mice overexpressing or deficient in endothelial NO synthase (eNOS), and the role of P2Y1 receptors in purinergic glioendothelial coupling was assessed. We found that genetic depletion of eNOS (eNOS(-/-)) and pharmacological inhibition of NO synthesis significantly decreased the CBF responses in the somatosensory cortex evoked by whisker stimulation and by administration of ATP. Overexpression of eNOS enhanced NO mediation of functional hyperemia. In control mice, the selective and potent P2Y1 receptor antagonist MRS2179 attenuated both whisker stimulation-induced and ATP-mediated CBF responses, whereas, in eNOS(-/-) mice, the inhibitory effects of MRS2179 were blunted. Collectively, our findings provide additional evidence for purinergic glio-endothelial coupling during neuronal activity, highlighting the role of ATP-mediated activation of eNOS via P2Y1 receptors in functional hyperemia.

Gender and racial differences in endothelial oxidative stress and inflammation in patients with symptomatic peripheral artery disease.

BACKGROUND: We compared (1) cellular reactive oxygen species (ROS) production, inflammation, and apoptosis of cultured endothelial cells treated with sera and (2) circulating inflammatory measures, antioxidant capacity, vascular biomarkers, and calf muscle hemoglobin oxygen saturation (StO2) in men and women with peripheral artery disease (PAD). A secondary aim was to compare exercise performance and daily ambulatory activity between men and women. We hypothesized that women would have more impaired endothelial cellular ROS, inflammation, and apoptosis than men as well as worse systemic inflammation, antioxidant capacity, vascular biomarkers, calf muscle StO2, exercise performance, and daily ambulatory activity. METHODS: The 148 symptomatic men and women with PAD were characterized on the endothelial effects of circulating factors present in the sera by a cell culture-based bioassay on primary human arterial endothelial cells. Patients were further evaluated by circulating inflammatory and vascular biomarkers, physical examination and medical history, exercise performance, and calf muscle StO2 during exercise, and ambulatory activity was monitored during 1 week. RESULTS: Cellular ROS production was higher in African American women than in men (P = .021), but there was no gender difference in white individuals (P = .537). Men and women were not significantly different on endothelial cell apoptosis (P = .833) and nuclear factor κB activity (P = .465). For circulating factors, additional gender differences were found when comparisons were made within each race. In African Americans, women had higher intercellular adhesion molecule 1 (P = .022) and leptin (P < .001); whereas in white individuals, women had higher matrix metallopeptidase 9 (P = .047), higher vascular cell adhesion molecule 1 (P = .047), and lower hepatocyte growth factor (P = .046). Overall, women had higher apolipoprotein CIII (P = .035), lower pain-free distance (P = .048) and total distance (P < .001) during the 6-minute walk test, shorter time for calf muscle StO2 to reach the minimum value during exercise (P = .027), and slower average cadence (P = .004) during daily ambulation. CONCLUSIONS: African American women with symptomatic PAD have a heightened oxidative status, likely resulting in increased endothelial oxidative stress, compared with men. Furthermore, women exhibit a more pronounced proinflammatory profile of circulating biomarkers as well as more limited peripheral microcirculation, exercise performance, and ambulatory activity than men do. The clinical significance is that women with symptomatic PAD are in greater need than men of clinical intervention to improve oxidative stress, inflammation, and microcirculation, which may in turn have a favorable impact on their lower exercise performance and daily activity.

Resveratrol treatment rescues neurovascular coupling in aged mice: role of improved cerebromicrovascular endothelial function and downregulation of NADPH oxidase.

Moment-to-moment adjustment of cerebral blood flow (CBF) to neuronal activity via neurovascular coupling is essential for the maintenance of normal neuronal function. Increased oxidative stress that occurs with aging was shown to impair neurovascular coupling, which likely contributes to a significant age-related decline in higher cortical function, increasing the risk for vascular cognitive impairment. Resveratrol is a polyphenolic compound that exerts significant antiaging protective effects in large vessels, but its effects on the cerebromicrovasculature remain poorly defined. The present study was undertaken to investigate the capacity of resveratrol to improve neurovascular coupling in aging. In aged (24-mo-old) C57BL/6 mice N(ω)-nitro-l-arginine methyl ester-sensitive, nitric oxide-mediated CBF responses to whisker stimulation and to the endothelium-dependent dilator acethylcholine (ACh) were impaired compared with those in young (3-mo-old) mice. Treatment of aged mice with resveratrol rescued neurovascular coupling and ACh-induced responses, which was associated with downregulation of cortical expression of NADPH oxidase and decreased levels of biomarkers of oxidative/nitrative stress (3-nitrotyrosine, 8-isoprostanes). Resveratrol also attenuated age-related increases in reactive oxygen species (ROS) production in cultured cerebromicrovascular endothelial cells (DCF fluorescence, flow cytometry). In conclusion, treatment with resveratrol rescues cortical neurovascular coupling responses to increased neuronal activity in aged mice, likely by restoring cerebromicrovascular endothelial function via downregulation of NADPH oxidase-derived ROS production. Beneficial cerebromicrovascular effects of resveratrol may contribute to its protective effects on cognitive function in aging.

Systemic influences contribute to prolonged microvascular rarefaction after brain irradiation: a role for endothelial progenitor cells.

Whole brain radiation therapy (WBRT) induces profound cerebral microvascular rarefaction throughout the hippocampus. Despite the vascular loss and localized cerebral hypoxia, angiogenesis fails to occur, which subsequently induces long-term deficits in learning and memory. The mechanisms underlying the absence of vessel recovery after WBRT are unknown. We tested the hypotheses that vascular recovery fails to occur under control conditions as a result of loss of angiogenic drive in the circulation, chronic tissue inflammation, and/or impaired endothelial cell production/recruitment. We also tested whether systemic hypoxia, which is known to promote vascular recovery, reverses these chronic changes in inflammation and endothelial cell production/recruitment. Ten-week-old C57BL/6 mice were subjected to a clinical series of fractionated WBRT: 4.5-Gy fractions 2 times/wk for 4 wk. Plasma from radiated mice increased in vitro endothelial cell proliferation and adhesion compared with plasma from control mice, indicating that WBRT did not suppress the proangiogenic drive. Analysis of cytokine levels within the hippocampus revealed that IL-10 and IL-12(p40) were significantly increased 1 mo after WBRT; however, systemic hypoxia did not reduce these inflammatory markers. Enumeration of endothelial progenitor cells (EPCs) in the bone marrow and circulation indicated that WBRT reduced EPC production, which was restored with systemic hypoxia. Furthermore, using a bone marrow transplantation model, we determined that bone marrow-derived endothelial-like cells home to the hippocampus after systemic hypoxia. Thus, the loss of production and homing of EPCs have an important role in the prolonged vascular rarefaction after WBRT.

Caloric restriction confers persistent anti-oxidative, pro-angiogenic, and anti-inflammatory effects and promotes anti-aging miRNA expression profile in cerebromicrovascular endothelial cells of aged rats.

In rodents, moderate caloric restriction (CR) without malnutrition exerts significant cerebrovascular protective effects, improving cortical microvascular density and endothelium-dependent vasodilation, but the underlying cellular mechanisms remain elusive. To elucidate the persisting effects of CR on cerebromicrovascular endothelial cells (CMVECs), primary CMVECs were isolated from young (3 mo old) and aged (24 mo old) ad libitum-fed and aged CR F344xBN rats. We found an age-related increase in cellular and mitochondrial oxidative stress, which is prevented by CR. Expression and transcriptional activity of Nrf2 are both significantly reduced in aged CMVECs, whereas CR prevents age-related Nrf2 dysfunction. Expression of miR-144 was upregulated in aged CMVECs, and overexpression of miR-144 significantly decreased expression of Nrf2 in cells derived from both young animals and aged CR rats. Overexpression of a miR-144 antagomir in aged CMVECs significantly decreases expression of miR-144 and upregulates Nrf2. We found that CR prevents age-related impairment of angiogenic processes, including cell proliferation, adhesion to collagen, and formation of capillary-like structures and inhibits apoptosis in CMVECs. CR also exerts significant anti-inflammatory effects, preventing age-related increases in the transcriptional activity of NF-κB and age-associated pro-inflammatory shift in the endothelial secretome. Characterization of CR-induced changes in miRNA expression suggests that they likely affect several critical functions in endothelial cell homeostasis. The predicted regulatory effects of CR-related differentially expressed miRNAs in aged CMVECs are consistent with the anti-aging endothelial effects of CR observed in vivo. Collectively, we find that CR confers persisting anti-oxidative, pro-angiogenic, and anti-inflammatory cellular effects, preserving a youthful phenotype in rat cerebromicrovascular endothelial cells, suggesting that through these effects CR may improve cerebrovascular function and prevent vascular cognitive impairment.

Sex difference in brain functional connectivity of hippocampus in Alzheimer's disease.

Alzheimer's disease (AD), affecting nearly 6.5 million people, is the fifth leading cause of death in individuals 65 years or older in the USA. Prior research has shown that AD disproportionality affects females; females have a greater incidence rate, perform worse on a variety of neuropsychological tasks, and have greater total brain atrophy. Recent research has linked these sex differences to neuroimaging markers of brain pathology, such as hippocampal volumes. Specifically, research from our lab found that functional connectivity from the hippocampus to the precuneus cortex and brain stem was significantly stronger in males than in females with mild cognitive impairment. The aim of this study was to extend our understanding to individuals with AD and to determine if these potential sex-specific functional connectivity biomarkers extend through different disease stages. The resting state fMRI and T2 MRI of cognitively normal individuals (n = 32, female = 16) and individuals with AD (n = 32, female = 16) from the Alzheimer's Disease Neuroimaging Initiative (ADNI) were analyzed using the Functional Connectivity Toolbox (CONN). Our results demonstrate that males had a significantly stronger interhemispheric functional connectivity between the left and right hippocampus compared to females. These results improve our current understanding of the role of the hippocampus in sex differences in AD. Understanding the contribution of impaired functional connectivity sex differences may aid in the development of sex-specific precision medicine for improved AD treatment.

Impaired Neurovascular Coupling and Increased Functional Connectivity in the Frontal Cortex Predict Age-Related Cognitive Dysfunction.

Impaired cerebrovascular function contributes to the genesis of age-related cognitive decline. In this study, the hypothesis is tested that impairments in neurovascular coupling (NVC) responses and brain network function predict cognitive dysfunction in older adults. Cerebromicrovascular and working memory function of healthy young (n = 21, 33.2±7.0 years) and aged (n = 30, 75.9±6.9 years) participants are assessed. To determine NVC responses and functional connectivity (FC) during a working memory (n-back) paradigm, oxy- and deoxyhemoglobin concentration changes from the frontal cortex using functional near-infrared spectroscopy are recorded. NVC responses are significantly impaired during the 2-back task in aged participants, while the frontal networks are characterized by higher local and global connection strength, and dynamic FC (p < 0.05). Both impaired NVC and increased FC correlate with age-related decline in accuracy during the 2-back task. These findings suggest that task-related brain states in older adults require stronger functional connections to compensate for the attenuated NVC responses associated with working memory load.

Increased hippocampal NgR1 signaling machinery in aged rats with deficits of spatial cognition.

Myelin-associated inhibitor/NgR1 signaling has important roles in modulation of synaptic plasticity, with demonstrated effects on cognitive function. We have previously demonstrated that NgR1 and its ligands are upregulated in the hippocampus of aged rats with impaired spatial learning and memory, but it is unknown whether increased expression of these proteins indicates a potential increase in pathway signaling because NgR1 requires co-receptors for signal transduction through RhoA. Two co-receptor complexes have been identified to date, comprised of NgR1 and LINGO-1, and either p75 or TROY. In this study, we assessed the expression of LINGO-1, p75 and TROY, and the downstream effector RhoA in mature adult (12 months) and aged (26 months) male Fischer 344/Brown Norway hybrid rats classified as cognitively impaired or cognitively intact by Morris water maze testing. The hippocampal distribution of NgR1 and its co-receptors was assessed to determine whether receptor/co-receptor interaction, and therefore signaling through this pathway, is possible. Protein expression of LINGO-1, p75, TROY and RhoA was significantly elevated in cognitively impaired, but not intact, aged rats compared with mature adults, and expression levels correlated significantly with water maze performance. Co-localization of NgR1 with LINGO-1, p75 and TROY was observed in hippocampal neurons of aged, cognitively impaired rats. Further, expression profiles of NgR1 pathway components were demonstrated to classify rats as cognitively intact or cognitively impaired with high accuracy. Together, this suggests that hippocampal induction of this pathway is a conserved phenomenon in cognitive decline that may impair learning and memory by suppressing neuronal plasticity.

Synergistic effects of hypertension and aging on cognitive function and hippocampal expression of genes involved in ß-amyloid generation and Alzheimer's disease.

Strong epidemiological and experimental evidence indicate that hypertension in the elderly predisposes to the development of Alzheimer's disease (AD), but the underlying mechanisms remain elusive. The present study was designed to characterize the additive/synergistic effects of hypertension and aging on the expression of genes involved in ß-amyloid generation and AD in the hippocampus, an area of brain contributing to higher cognitive function, which is significantly affected by AD both in humans and in mouse models of the disease. To achieve that goal, we induced hypertension in young (3 mo) and aged (24 mo) C57BL/6 mice by chronic (4 wk) infusion of angiotensin II and assessed changes in hippocampal mRNA expression of genes involved in amyloid precursor protein (APP)-dependent signaling, APP cleavage, Aß processing and Aß-degradation, synaptic function, dysregulation of microtubule-associated τ protein, and apolipoprotein-E signaling. Aged hypertensive mice exhibited spatial memory impairments in the Y-maze and impaired performance in the novel object recognition assay. Surprisingly, hypertension in aging did not increase the expression of APP, ß- and γ-secretases, or genes involved in tauopathy. These genes are all involved in the early onset form of AD. Yet, hypertension in aging was associated with changes in hippocampal expression of APP binding proteins, e.g., [Mint3/amyloid ß A4 precursor protein-binding family A member 3 (APBA3), Fe65/amyloid ß A4 precursor protein-binding family B member 1 (APBB1)], amyloid ß (A4) precursor-like protein 1 (APLP1), muscarinic M1 receptor, and serum amyloid P component, all of which may have a role in the pathogenesis of late-onset AD. The hippocampal gene expression signature observed in aged hypertensive mice in the present study provides important clues for subsequent studies to elucidate the mechanisms by which hypertension may contribute to the pathogenesis and clinical manifestation of AD.

Role of 20-HETE, TRPC channels, and BKCa in dysregulation of pressure-induced Ca2+ signaling and myogenic constriction of cerebral arteries in aged hypertensive mice.

Hypertension in the elderly substantially increases the risk of stroke and vascular cognitive impairment in part due to an impaired functional adaptation of aged cerebral arteries to high blood pressure. To elucidate the mechanisms underlying impaired autoregulatory protection in aging, hypertension was induced in young (3 mo) and aged (24 mo) C57BL/6 mice by chronic infusion of angiotensin II and pressure-induced changes in smooth muscle cell (SMC) intracellular Ca(2+) concentration ([Ca(2+)]i) and myogenic constriction of middle cerebral arteries (MCA) were assessed. In MCAs from young hypertensive mice, pressure-induced increases in vascular SMC [Ca(2+)]i and myogenic tone were increased, and these adaptive responses were inhibited by the cytochrome P-450 ω-hydroxylase inhibitor HET0016 and the transient receptor potential (TRP) channel blocker SKF96365. Administration of 20- hydroxyeicosatetraenoic acid (HETE) increased SMC [Ca(2+)]i and constricted MCAs, and these responses were inhibited by SKF96365. MCAs from aged hypertensive mice did not show adaptive increases in pressure-induced calcium signal and myogenic tone and responses to HET0016 and SKF96365 were blunted. Inhibition of large-conductance Ca(2+)-activated K(+) (BK) channels by iberiotoxin enhanced SMC [Ca(2+)]i and myogenic constriction in MCAs of young normotensive animals, whereas it was without effect in MCAs of young hypertensive mice. Iberiotoxin did not restore myogenic adaptation in MCAs of aged hypertensive mice. Thus functional maladaptation of aged cerebral arteries to hypertension is due to the dysregulation of pressure-induced 20-HETE and TRP channel-mediated SMC calcium signaling, whereas overactivation of BK channels is unlikely to play a role in this phenomenon.

Whole brain radiation-induced vascular cognitive impairment: mechanisms and implications.

Mild cognitive impairment is a well-documented consequence of whole brain radiation therapy (WBRT) that affects 40-50% of long-term brain tumor survivors. The exact mechanisms for the decline in cognitive function after WBRT remain elusive and no treatment or preventative measures are available for use in the clinic. Here, we review recent findings indicating how changes in the neurovascular unit may contribute to the impairments in learning and memory. In addition to affecting neuronal development, WBRT induces profound capillary rarefaction within the hippocampus - a region of the brain important for learning and memory. Therapeutic strategies such as hypoxia, which restore the capillary density, result in the rescue of cognitive function. In addition to decreasing vascular density, WBRT impairs vasculogenesis and/or angiogenesis, which may also contribute to radiation-induced cognitive decline. Further studies aimed at uncovering the specific mechanisms underlying these WBRT-induced changes in the cerebrovasculature are essential for developing therapies to mitigate the deleterious effects of WBRT on cognitive function.

Expression of NgR1-antagonizing proteins decreases with aging and cognitive decline in rat hippocampus.

The myelin-associated inhibitor/Nogo-66 receptor 1 (NgR1) pathway directly functions in negative modulation of structural and electrophysiological synaptic plasticity. A previous study has established an important role of NgR1 pathway signaling in cognitive function, and we have demonstrated that multiple components of this pathway, including ligands, NgR1 co-receptors, and RhoA, are upregulated at the protein level specifically in cognitively impaired, but not age-matched cognitively intact aged rats. Recent studies have identified two novel endogenous NgR1 antagonists, LOTUS and LGI1, and an alternative co-receptor, ADAM22, which act to suppress NgR1 pathway signaling. To determine whether these endogenous NgR1-inhibiting proteins may play a compensatory role in age-related cognitive impairment by counteracting overexpression of NgR1 agonists and co-receptors, we quantified the expression of LOTUS, LGI1, and ADAM22 in hippocampal CA1, CA3 and DG subregions dissected from mature adult and aged rats cognitively phenotyped for spatial learning and memory by Morris water maze testing. We have found that endogenous inhibitors of NgR1 pathway action decrease significantly with aging and cognitive decline and that lower expression levels correlate with declining cognitive ability, particularly in CA1 and CA3. These data suggest that decreased expression of NgR1-antagonizing proteins may exert a combinatorial effect with increased NgR1 signaling pathway components to result in abnormally strong suppression of synaptic plasticity in age-related cognitive impairment.