Temporal course of cerebrospinal fluid dynamics and amyloid accumulation in the aging rat brain from three to thirty months

A Hidden Epithelial Barrier in the Brain with a Central Role in Regulating Brain Homeostasis. Implications for Aging

Despite increasing interest the last years, the choroid plexus still is a relatively understudied tissue in neuroscience. The choroid plexus contains fenestrated capillaries surrounded by tightly connected choroid plexus epithelial cells that form the blood-cerebrospinal fluid barrier. The choroid plexus is the main source of cerebrospinal fluid production, assures removal of toxic waste products, and acts as gatekeeper of the brain by the presence of resident inflammatory cells. Increasing evidence shows that choroid plexus' dysfunction, via altered secretory, transport, immune, and barrier function, plays a central role in a very diverse set of clinical conditions such as aging and the age-associated Alzheimer's disease. Indeed, age-related changes may weaken the barrier formed by the choroid plexus epithelial cells and/or impair the choroid plexus' ability to generate cerebrospinal fluid and to produce beneficial factors. Consequently, advanced knowledge of the choroid plexus-cerebrospinal fluid system in aging is essential to better understand age-associated neurological diseases and might open up new therapeutic strategies.

Aging alters mRNA expression of amyloid transporter genes at the blood-brain barrier

Decreased clearance of potentially toxic metabolites, due to aging changes, likely plays a significant role in the accumulation of amyloid-beta (Aβ) peptides and other macromolecules in the brain of the elderly and in the patients with Alzheimer's disease (AD). Aging is the single most important risk factor for AD development. Aβ transport receptor proteins expressed at the blood-brain barrier are significantly altered with age: the efflux transporters lipoprotein receptor-related protein 1 and P-glycoprotein are reduced, whereas the influx transporter receptor for advanced glycation end products is increased. These receptors play an important role in maintaining brain biochemical homeostasis. We now report that, in a rat model of aging, gene transcription is altered in aging, as measured by Aβ receptor gene messenger RNA (mRNA) at 3, 6, 9, 12, 15, 20, 30, and 36 months. Gene mRNA expression from isolated cerebral microvessels was measured by quantitative polymerase chain reaction. Lipoprotein receptor-related protein 1 and P-glycoprotein mRNA were significantly reduced in aging, and receptor for advanced glycation end products was increased, in parallel with the changes seen in receptor protein expression. Transcriptional changes appear to play a role in aging alterations in blood-brain barrier receptor expression and Aβ accumulation.

Inhibition of Bcl-xL prevents pro-death actions of ΔN-Bcl-xL at the mitochondrial inner membrane during glutamate excitotoxicity

ABT-737 is a pharmacological inhibitor of the anti-apoptotic activity of B-cell lymphoma-extra large (Bcl-xL) protein; it promotes apoptosis of cancer cells by occupying the BH3-binding pocket. We have shown previously that ABT-737 lowers cell metabolic efficiency by inhibiting ATP synthase activity. However, we also found that ABT-737 protects rodent brain from ischemic injury in vivo by inhibiting formation of the pro-apoptotic, cleaved form of Bcl-xL, ΔN-Bcl-xL. We now report that a high concentration of ABT-737 (1 μM), or a more selective Bcl-xL inhibitor WEHI-539 (5 μM) enhances glutamate-induced neurotoxicity while a low concentration of ABT-737 (10 nM) or WEHI-539 (10 nM) is neuroprotective. High ABT-737 markedly increased ΔN-Bcl-xL formation, aggravated glutamate-induced death and resulted in the loss of mitochondrial membrane potential and decline in ATP production. Although the usual cause of death by ABT-737 is thought to be related to activation of Bax at the outer mitochondrial membrane due to sequestration of Bcl-xL, we now find that low ABT-737 not only prevents Bax activation, but it also inhibits the decline in mitochondrial potential produced by glutamate toxicity or by direct application of ΔN-Bcl-xL to mitochondria. Loss of mitochondrial inner membrane potential is also prevented by cyclosporine A, implicating the mitochondrial permeability transition pore in death aggravated by ΔN-Bcl-xL. In keeping with this, we find that glutamate/ΔN-Bcl-xL-induced neuronal death is attenuated by depletion of the ATP synthase c-subunit. C-subunit depletion prevented depolarization of mitochondrial membranes in ΔN-Bcl-xL expressing cells and substantially prevented the morphological change in neurites associated with glutamate/ΔN-Bcl-xL insult. Our findings suggest that low ABT-737 or WEHI-539 promotes survival during glutamate toxicity by preventing the effect of ΔN-Bcl-xL on mitochondrial inner membrane depolarization, highlighting ΔN-Bcl-xL as an important therapeutic target in injured brain.

Promise, Progress, and Pitfalls in the Search for Central Nervous System Biomarkers in Neuroimmunological Diseases: A Role for Cerebrospinal Fluid Immunophenotyping

Biomarkers are central to the translational medicine strategic focus, though strict criteria need to be applied to their designation and utility. They are one of the most promising areas of medical research, but the "biomarker life-cycle" must be understood to avoid false-positive and false-negative results. Molecular biomarkers will revolutionize the treatment of neurological diseases, but the rate of progress depends on a bold, visionary stance by neurologists, as well as scientists, biotech and pharmaceutical industries, funding agencies, and regulators. One important tool in studying cell-specific biomarkers is multiparameter flow cytometry. Cerebrospinal fluid immunophenotyping, or immune phenotypic subsets, captures the biology of intrathecal inflammatory processes, and has the potential to guide personalized immunotherapeutic selection and monitor treatment efficacy. Though data exist for some disorders, they are surprisingly lacking in many others, identifying a serious deficit to be overcome. Flow cytometric immunophenotyping provides a valuable, available, and feasible "window" into both adaptive and innate components of neuroinflammation that is currently underutilized.

Insights into the human brain proteome: Disclosing the biological meaning of protein networks in cerebrospinal fluid

Cerebrospinal fluid (CSF) is an excellent source of biological information regarding the nervous system, once it is in close contact and accurately reflects alterations in this system. Several studies have analyzed differential protein profiles of CSF samples between healthy and diseased human subjects. However, the pathophysiological mechanisms and how CSF proteins relate to diseases are still poorly known. By applying bioinformatics tools, we attempted to provide new insights on the biological and functional meaning of proteomics data envisioning the identification of putative disease biomarkers. Bioinformatics analysis of data retrieved from 99 mass spectrometry (MS)-based studies on CSF profiling highlighted 1985 differentially expressed proteins across 49 diseases. A large percentage of the modulated proteins originate from exosome vesicles, and the majority are involved in either neuronal cell growth, development, maturation, migration, or neurotransmitter-mediated cellular communication. Nevertheless, some diseases present a unique CSF proteome profile, which were critically analyzed in the present study. For instance, 48 proteins were found exclusively upregulated in the CSF of patients with Alzheimer's disease and are mainly involved in steroid esterification and protein activation cascade processes. A higher number of exclusively upregulated proteins were found in the CSF of patients with multiple sclerosis (76 proteins) and with bacterial meningitis (70 proteins). Whereas in multiple sclerosis, these proteins are mostly involved in the regulation of RNA metabolism and apoptosis, in bacterial meningitis the exclusively upregulated proteins participate in inflammation and antibacterial humoral response, reflecting disease pathogenesis. The exploration of the contribution of exclusively upregulated proteins to disease pathogenesis will certainly help to envision potential biomarkers in the CSF for the clinical management of nervous system diseases.

The Glymphatic Pathway: Waste Removal from the CNS via Cerebrospinal Fluid Transport

The overall premise of this review is that cerebrospinal fluid (CSF) is transported within a dedicated peri-vascular network facilitating metabolic waste clearance from the central nervous system while we sleep. The anatomical profile of the network is complex and has been defined as a peri-arterial CSF influx pathway and peri-venous clearance routes, which are functionally coupled by interstitial bulk flow supported by astrocytic aquaporin 4 water channels. The role of the newly discovered system in the brain is equivalent to the lymphatic system present in other body organs and has been termed the "glymphatic pathway" or "(g)lymphatics" because of its dependence on glial cells. We will discuss and review the general anatomy and physiology of CSF from the perspective of the glymphatic pathway, a discovery which has greatly improved our understanding of key factors that control removal of metabolic waste products from the central nervous system in health and disease and identifies an additional purpose for sleep. A brief historical and factual description of CSF production and transport will precede the ensuing discussion of the glymphatic system along with a discussion of its clinical implications.

Direct, long-term intrathecal application of therapeutics to the rodent CNS

Systemic application of therapeutics to the CNS tissue often results in subtherapeutic drug levels, because of restricted and selective penetration through the blood-brain barrier (BBB). Here, we give a detailed description of a standardized technique for intrathecal drug delivery in rodents, analogous to the technique used in humans. The intrathecal drug delivery method bypasses the BBB and thereby offers key advantages over oral or intravenous administration, such as maximized local drug doses with minimal systemic side effects. We describe how to deliver antibodies or drugs over several days or weeks from a s.c. minipump and a fine catheter inserted into the subdural space over the spinal cord (20 min operative time) or into the cisterna magna (10 min operative time). Drug levels can be sampled by quick and minimally invasive cerebrospinal fluid (CSF) collection from the cisterna magna (5 min procedure time). These techniques enable targeted application of any compound to the CNS for therapeutic studies in a wide range of CNS disease rodent models. Basic surgery skills are helpful for carrying out the procedures described in this protocol.

Dynamic dual-isotope molecular imaging elucidates principles for optimizing intrathecal drug delivery

The intrathecal (IT) dosing route offers a seemingly obvious solution for delivering drugs directly to the central nervous system. However, gaps in understanding drug molecule behavior within the anatomically and kinetically unique environment of the mammalian IT space have impeded the establishment of pharmacokinetic principles for optimizing regional drug exposure along the neuraxis. Here, we have utilized high-resolution single-photon emission tomography with X-ray computed tomography to study the behavior of multiple molecular imaging tracers following an IT bolus injection, with supporting histology, autoradiography, block-face tomography, and MRI. Using simultaneous dual-isotope imaging, we demonstrate that the regional CNS tissue exposure of molecules with varying chemical properties is affected by IT space anatomy, cerebrospinal fluid (CSF) dynamics, CSF clearance routes, and the location and volume of the injected bolus. These imaging approaches can be used across species to optimize the safety and efficacy of IT drug therapy for neurological disorders.

Fast circulation of cerebrospinal fluid: an alternative perspective on the protective role of high intracranial pressure in ocular hypertension

As ocular hypertension refers to a condition in which the intraocular pressure is consistently elevated but without development of glaucoma, study of it may provide important clues to factors that may play a protective role in glaucoma. β-amyloid, one of the key histopathological findings in Alzheimer's disease, has been reported to increase by chronic elevation of intraocular pressure in animals with experimentally induced ocular hypertension and to cause retinal ganglion cell death, pointing to similarities in molecular cell death mechanisms between glaucoma and Alzheimer's disease. On the other hand, recent studies have reported that intracranial pressure is higher in patients with ocular hypertension compared with controls, giving rise to the idea that elevated intracranial pressure may provide a protective effect for the optic nerve by decreasing the trans-lamina cribrosa pressure difference. The speculation that the higher intracranial pressure reported in ocular hypertension patients may protect against glaucoma mainly through a lower trans-lamina cribrosa pressure difference remains at least questionable. Here, we present an alternative viewpoint, according to which the protective effect of higher intracranial pressure could be due, at least in part, to a pressure-independent mechanism, namely faster cerebrospinal fluid production leading to increased cerebrospinal fluid turnover with enhanced removal of potentially neurotoxic waste products that accumulate in the optic nerve. This suggests a new hypothesis for glaucoma, which, just like Alzheimer's disease, may be considered then as an imbalance between production and clearance of neurotoxins, including β-amyloid. If confirmed, then strategies to improve cerebrospinal fluid flow are reasonable and could provide a new therapeutic approach for stopping the neurotoxic β-amyloid pathway in glaucoma.

Epileptogenic effects of NMDAR antibodies in a passive transfer mouse model

Most patients with N-methyl D-aspartate-receptor antibody encephalitis develop seizures but the epileptogenicity of the antibodies has not been investigated in vivo. Wireless electroencephalogram transmitters were implanted into 23 C57BL/6 mice before left lateral ventricle injection of antibody-positive (test) or healthy (control) immunoglobulin G. Mice were challenged 48 h later with a subthreshold dose (40 mg/kg) of the chemo-convulsant pentylenetetrazol and events recorded over 1 h. Seizures were assessed by video observation of each animal and the electroencephalogram by an automated seizure detection programme. No spontaneous seizures were seen with the antibody injections. However, after the pro-convulsant, the test mice (n = 9) had increased numbers of observed convulsive seizures (P = 0.004), a higher total seizure score (P = 0.003), and a higher number of epileptic 'spike' events (P = 0.023) than the control mice (n = 6). At post-mortem, surprisingly, the total number of N-methyl D-aspartate receptors did not differ between test and control mice, but in test mice the levels of immunoglobulin G bound to the left hippocampus were higher (P < 0.0001) and the level of bound immunoglobulin G correlated with the seizure scores (R(2) = 0.8, P = 0.04, n = 5). Our findings demonstrate the epileptogenicity of N-methyl D-aspartate receptor antibodies in vivo, and suggest that binding of immunoglobulin G either reduced synaptic localization of N-methyl D-aspartate receptors, or had a direct effect on receptor function, which could be responsible for seizure susceptibility in this acute short-term model.

Uric Acid Produces an Inflammatory Response through Activation of NF-κB in the Hypothalamus: Implications for the Pathogenesis of Metabolic Disorders

Epidemiological studies have shown that an elevated uric acid (UA) level predicts the development of metabolic syndrome and diabetes; however, there is no direct evidence of this, and the underlying mechanism remains unclear. Here, we showed that a high-UA diet triggered the expression of pro-inflammatory cytokines, activated the NF-κB pathway, and increased gliosis in the hypothalamus. Intracerebroventricular injection of UA induced hypothalamic inflammation and reactive gliosis, whereas these effects were markedly ameliorated by the inhibition of NF-κB. Moreover, magnetic resonance imaging confirmed that hyperuricemia in rodents and humans was associated with gliosis in the mediobasal hypothalamus. Importantly, the rats administered UA exhibited dyslipidemia and glucose intolerance, which were probably mediated by hypothalamic inflammation and hypothalamic neuroendocrine alterations. These results suggest that UA can cause hypothalamic inflammation via NF-κB signaling. Our findings provide a potential therapeutic strategy for UA-induced metabolic disorders.

Choroid plexus dysfunction impairs beta-amyloid clearance in a triple transgenic mouse model of Alzheimer's disease

Compromised secretory function of choroid plexus (CP) and defective cerebrospinal fluid (CSF) production, along with accumulation of beta-amyloid (Aβ) peptides at the blood-CSF barrier (BCSFB), contribute to complications of Alzheimer’s disease (AD). The AD triple transgenic mouse model (3xTg-AD) at 16 month-old mimics critical hallmarks of the human disease: β-amyloid (Aβ) plaques and neurofibrillary tangles (NFT) with a temporal- and regional- specific profile. Currently, little is known about transport and metabolic responses by CP to the disrupted homeostasis of CNS Aβ in AD. This study analyzed the effects of highly-expressed AD-linked human transgenes (APP, PS1 and tau) on lateral ventricle CP function. Confocal imaging and immunohistochemistry revealed an increase only of Aβ42 isoform in epithelial cytosol and in stroma surrounding choroidal capillaries; this buildup may reflect insufficient clearance transport from CSF to blood. Still, there was increased expression, presumably compensatory, of the choroidal Aβ transporters: the low density lipoprotein receptor-related protein 1 (LRP1) and the receptor for advanced glycation end product (RAGE). A thickening of the epithelial basal membrane and greater collagen-IV deposition occurred around capillaries in CP, probably curtailing solute exchanges. Moreover, there was attenuated expression of epithelial aquaporin-1 and transthyretin (TTR) protein compared to Non-Tg mice. Collectively these findings indicate CP dysfunction hypothetically linked to increasing Aβ burden resulting in less efficient ion transport, concurrently with reduced production of CSF (less sink action on brain Aβ) and diminished secretion of TTR (less neuroprotection against cortical Aβ toxicity). The putative effects of a disabled CP-CSF system on CNS functions are discussed in the context of AD.

Kaolin-induced chronic hydrocephalus accelerates amyloid deposition and vascular disease in transgenic rats expressing high levels of human APP

BACKGROUND

Normal pressure hydrocephalus (NPH) is most common in the elderly and has a high co-morbidity with Alzheimer's disease (AD) and cerebrovascular disease (CVD). To understand the relationship between NPH, AD and CVD, we investigated how chronic hydrocephalus impacts brain amyloid-beta peptide (Aβ) accumulation and vascular pathology in an AD transgenic rodent model. Previously we showed that the altered CSF physiology produced by kaolin-hydrocephalus in older wild-type Sprague-Dawley rats increased Aβ and hyperphosphorylated Tau (Silverberg et. al. Brain Res. 2010, 1317:286-296). We postulated that hydrocephalus would similarly affect an AD rat model.

METHODS

Thirty-five transgenic rats (tgAPP21) that express high levels of human APP and naturally overproduce Aβ40 were used. Six- (n = 7) and twelve-month-old (n = 9) rats had hydrocephalus induced by cisternal kaolin injection. We analyzed Aβ burden (Aβ40, Aβ42 and oligomeric Aβ) and vascular integrity (Masson trichrome and Verhoeff-Van Gieson) by immunohistochemistry and chemical staining at 10 weeks (n = 8) and 6 months (n = 5) post hydrocephalus induction. We also analyzed whether the vascular pathology seen in tgAPP21 rats, which develop amyloid angiopathy, was accelerated by hydrocephalus. Age-matched naïve and sham-operated tgAPP21 rats served as controls (n = 19).

RESULTS

In hydrocephalic tgAPP21 rats, compared to naïve and sham-operated controls, there was increased Aβ 40 and oligomeric Aβ in hippocampal and cortical neurons at 10 weeks and 6 months post-hydrocephalus induction. No dense-core amyloid plaques were seen, but diffuse Aβ immunoreactivity was evident in neurons. Vascular pathology was accelerated by the induction of hydrocephalus compared to controls. In the six-month-old rats, subtle degenerative changes were noted in vessel walls at 10 weeks post-kaolin, whereas at six months post-kaolin and in the 12-month-old hydrocephalic rats more pronounced amyloid angiopathic changes were seen, with frequent large areas of infarction noted.

CONCLUSIONS

Kaolin-hydrocephalus can accelerate intraneuronal Aβ40 accumulation and vascular pathology in tgAPP21 rats. In addition, disrupted CSF production and reduced CSF turnover results in impaired Aβ clearance and accelerated vascular pathology in chronic hydrocephalus. The high co-morbidity seen in NPH, AD and CVD is likely not to be an age-related coincidence, but rather a convergence of pathologies related to diminished CSF clearance.

A novel method to study cerebrospinal fluid dynamics in rats

BACKGROUND

Cerebrospinal fluid (CSF) flow dynamics play critical roles in both the immature and adult brain, with implications for neurodevelopment and disease processes such as hydrocephalus and neurodegeneration. Remarkably, the only reported method to date for measuring CSF formation in laboratory rats is the indirect tracer dilution method (a.k.a., ventriculocisternal perfusion), which has limitations.

NEW METHOD

Anesthetized rats were mounted in a stereotaxic apparatus, both lateral ventricles were cannulated, and the Sylvian aqueduct was occluded. Fluid exited one ventricle at a rate equal to the rate of CSF formation plus the rate of infusion (if any) into the contralateral ventricle. Pharmacological agents infused at a constant known rate into the contralateral ventricle were tested for their effect on CSF formation in real-time.

RESULTS

The measured rate of CSF formation was increased by blockade of the Sylvian aqueduct but was not changed by increasing the outflow pressure (0-3cm of H2O). In male Wistar rats, CSF formation was age-dependent: 0.39±0.06, 0.74±0.05, 1.02±0.04 and 1.40±0.06μL/min at 8, 9, 10 and 12 weeks, respectively. CSF formation was reduced 57% by intraventricular infusion of the carbonic anhydrase inhibitor, acetazolamide.

COMPARISON WITH EXISTING METHODS

Tracer dilution methods do not permit ongoing real-time determination of the rate of CSF formation, are not readily amenable to pharmacological manipulations, and require critical assumptions. Direct measurement of CSF formation overcomes these limitations.

CONCLUSIONS

Direct measurement of CSF formation in rats is feasible. Our method should prove useful for studying CSF dynamics in normal physiology and disease models.

RF9 excitation of GnRH neurons is dependent upon Kiss1r in the adult male and female mouse

The neuropeptide FF receptor antagonist 1-adamantanecarbonyl-Arg-Phe-NH2 trifluoroacetate salt (RF9) has been found to be a remarkably potent activator of gonadotropin secretion in mammals. However, the mechanism of RF9 action on the reproductive axis is unknown. Using acute brain slice electrophysiology in genetically modified mouse models, we have investigated the possibility that RF9 may activate GnRH neurons. In transgenic GnRH-GFP male and female mice, RF9 was found to exert potent, dose-dependent, stimulatory effects on the firing rate of approximately 70% of GnRH neurons. These effects occurred directly on GnRH neurons and were independent of fast amino acid transmission. To assess RF9's action as an neuropeptide FF receptor antagonist at the GnRH neuron, its ability to antagonize the inhibitory effects of RFamide-related peptide-3 on GnRH neuron firing was examined. RF9 exhibited variable ability to prevent the inhibitory effects of RFamide-related peptide-3 on GnRH neurons. Whole-cell recordings from GnRH neurons showed that RF9 generated an inward current in GnRH neurons reminiscent of that evoked by kisspeptin. We therefore examined RF9 actions in kisspeptin receptor knockout mice. RF9 was found to have no effects at all on GnRH neurons in GnRH-GFP;Kiss1r-null mice, although these cells exhibited normal intrinsic electrical properties and remained responsive to GABA and glutamate. This study reveals that RF9 directly activates GnRH neurons in the mouse and that this is dependent upon Kiss1r expression.

Cerebrospinal fluid is drained primarily via the spinal canal and olfactory route in young and aged spontaneously hypertensive rats

BACKGROUND

Many aspects of CSF dynamics are poorly understood due to the difficulties involved in quantification and visualization. In particular, there is debate surrounding the route of CSF drainage. Our aim was to quantify CSF flow, volume, and drainage route dynamics in vivo in young and aged spontaneously hypertensive rats (SHR) using a novel contrast-enhanced computed tomography (CT) method.

METHODS

ICP was recorded in young (2-5 months) and aged (16 months) SHR. Contrast was administered into the lateral ventricles bilaterally and sequential CT imaging was used to visualize the entire intracranial CSF system and CSF drainage routes. A customized contrast decay software module was used to quantify CSF flow at multiple locations.

RESULTS

ICP was significantly higher in aged rats than in young rats (11.52 ± 2.36 mmHg, versus 7.04 ± 2.89 mmHg, p = 0.03). Contrast was observed throughout the entire intracranial CSF system and was seen to enter the spinal canal and cross the cribriform plate into the olfactory mucosa within 9.1 ± 6.1 and 22.2 ± 7.1 minutes, respectively. No contrast was observed adjacent to the sagittal sinus. There were no significant differences between young and aged rats in either contrast distribution times or CSF flow rates. Mean flow rates (combined young and aged) were 3.0 ± 1.5 μL/min at the cerebral aqueduct; 3.5 ± 1.4 μL/min at the 3rd ventricle; and 2.8 ± 0.9 μL/min at the 4th ventricle. Intracranial CSF volumes (and as percentage total brain volume) were 204 ± 97 μL (8.8 ± 4.3%) in the young and 275 ± 35 μL (10.8 ± 1.9%) in the aged animals (NS).

CONCLUSIONS

We have demonstrated a contrast-enhanced CT technique for measuring and visualising CSF dynamics in vivo. These results indicate substantial drainage of CSF via spinal and olfactory routes, but there was little evidence of drainage via sagittal sinus arachnoid granulations in either young or aged animals. The data suggests that spinal and olfactory routes are the primary routes of CSF drainage and that sagittal sinus arachnoid granulations play a minor role, even in aged rats with higher ICP.

Senescence-accelerated OXYS rats: a model of age-related cognitive decline with relevance to abnormalities in Alzheimer disease

Senescence-accelerated OXYS rats are an experimental model of accelerated aging that was established from Wistar stock via selection for susceptibility to cataractogenic effects of a galactose-rich diet and via subsequent inbreeding of highly susceptible rats. Currently, we have the 102nd generation of OXYS rats with spontaneously developing cataract and accelerated senescence syndrome, which means early development of a phenotype similar to human geriatric disorders, including accelerated brain aging. In recent years, our group found strong evidence that OXYS rats are a promising model for studies of the mechanisms of brain aging and neurodegenerative processes similar to those seen in Alzheimer disease (AD). The manifestation of behavioral alterations and learning and memory deficits develop since the fourth week of age, i.e., simultaneously with first signs of neurodegeneration detectable on magnetic resonance imaging and under a light microscope. In addition, impaired long-term potentiation has been demonstrated in OXYS rats by the age of 3 months. With age, neurodegenerative changes in the brain of OXYS rats become amplified. We have shown that this deterioration happens against the background of overproduction of amyloid precursor protein (AβPP), accumulation of β-amyloid (Aβ), and hyperphosphorylation of the tau protein in the hippocampus and cortex. The development of AMD-like retinopathy in OXYS rats is also accompanied by increased accumulation of Aβ in the retina. These published data suggest that the OXYS strain may serve as a spontaneous rat model of AD-like pathology and could help to decipher the pathogenesis of AD.

Mitochondrial dysfunction: cause and consequence of Alzheimer's disease

The etiology of common, nonfamiliar late-onset Alzheimer's disease (LOAD) is only partly understood and seems to be extremely complex including many genetic and environmental factors. The most important environmental risk factor to develop LOAD is aging itself. Aging and LOAD are considered to be strongly linked to mitochondrial dysfunction and enhanced oxidative stress. In this review, we focus on the interaction between mitochondrial dysfunction in aging especially on defects of the respiratory chain of the oxidative phosphorylation system resulting in enhanced oxidative stress and the interplay between aging-associated mitochondrial defects and LOAD-associated mitochondrial failure. The deleterious effects of the two hallmarks of LOAD, amyloid beta, and hyperphosphorylated tau, on mitochondrial function, movement, and morphology are described as well as the toxic effects of the most relevant genetic risk factor of LOAD, the apolipoprotein E4 allele. Finally, the review provides an overview about drugs and nutritional ingredients which improve mitochondrial function or/and act as antioxidants and discusses their potential role in the treatment of LOAD.

Rapamycin suppresses brain aging in senescence-accelerated OXYS rats

Cellular and organismal aging are driven in part by the MTOR (mechanistic target of rapamycin) pathway and rapamycin extends life span in C elegans, Drosophila and mice. Herein, we investigated effects of rapamycin on brain aging in OXYS rats. Previously we found, in OXYS rats, an early development of age-associated pathological phenotypes similar to several geriatric disorders in humans, including cerebral dysfunctions. Behavioral alterations as well as learning and memory deficits develop by 3 months. Here we show that rapamycin treatment (0.1 or 0.5 mg/kg as a food mixture daily from the age of 1.5 to 3.5 months) decreased anxiety and improved locomotor and exploratory behavior in OXYS rats. In untreated OXYS rats, MRI revealed an increase of the area of hippocampus, substantial hydrocephalus and 2-fold increased area of the lateral ventricles. Rapamycin treatment prevented these abnormalities, erasing the difference between OXYS and Wistar rats (used as control). All untreated OXYS rats showed signs of neurodegeneration, manifested by loci of demyelination. Rapamycin decreased the percentage of animals with demyelination and the number of loci. Levels of Tau and phospho-Tau (T181) were increased in OXYS rats (compared with Wistar). Rapamycin significantly decreased Tau and inhibited its phosphorylation in the hippocampus of OXYS and Wistar rats. Importantly, rapamycin treatment caused a compensatory increase in levels of S6 and correspondingly levels of phospo-S6 in the frontal cortex, indicating that some downstream events were compensatory preserved, explaining the lack of toxicity. We conclude that rapamycin in low chronic doses can suppress brain aging.

Blood-brain-barriers in aging and in Alzheimer's disease

The aging process correlates with a progressive failure in the normal cellular and organ functioning; these alterations are aggravated in Alzheimer's disease (AD). In both aging and AD there is a general decrease in the capacity of the body to eliminate toxic compounds and, simultaneously, to supply the brain with relevant growth and nutritional factors. The barriers of the brain are targets of this age related dysfunction; both the endothelial cells of the blood-brain barrier and the choroid plexus epithelial cells of the blood-cerebrospinal fluid barrier decrease their secretory capacity towards the brain and their ability to remove toxic compounds from the brain. Additionally, during normal aging and in AD, the permeability of the brain barriers increase. As such, a greater contact of the brain parenchyma with the blood content alters the highly controlled neural environment, which impacts on neural function. Of interest, the brain barriers are more than mere obstacles to the passage of molecules and cells, and therefore active players in brain homeostasis, which is still to be further recognized and investigated in the context of health and disease. Herein, we provide a review on how the brain barriers change during aging and in AD and how these processes impact on brain function.

Sustained choroid plexus function in human elderly and Alzheimer's disease patients

We and other investigators have postulated deterioration of essential choroid plexus (CP) functions in some elderly and especially Alzheimer’s disease patients based on apparent anatomical, histological and pathological changes in CP. We have termed this putative phenomenon CP failure. By focusing on four essential energy-requiring CP functions, specifically ascorbic acid (AA) and folate transport from blood into CSF, transthyretin synthesis and secretion into CSF, and electrolyte/acid–base balance in CSF, we were able to evaluate the hypothesis of CP failure by reviewing definitive human data. In both healthy elderly and Alzheimer’s disease patients, the CP functions normally to transport AA and folates actively from blood into CSF, synthesize and secrete transthyretin into CSF, and maintain CSF acid–base balance and ion concentrations. These human CSF compositional data provide no support for the notion of CP failure in elderly humans and Alzheimer’s disease patients.

VEGF, which is elevated in the CSF of patients with hydrocephalus, causes ventriculomegaly and ependymal changes in rats

Hydrocephalus is a condition characterized primarily by excessive accumulation of fluid in the ventricles of the brain for which there is currently no effective pharmacological treatment. Surgery, often accompanied by complications, is the only current treatment. Extensive research in our laboratory along with work from others has suggested a link between hydrocephalus and vascular function. We hypothesized that vascular endothelial growth factor (VEGF), the major angiogenic factor, could play a role in the pathogenesis of hydrocephalus. We tested this hypothesis by examining two predictions of such a link: first, that VEGF is present in many cases of clinical hydrocephalus; and second, that exogenous VEGF in an animal model could cause ventricular enlargement and tissue changes associated with hydrocephalus. Our results support the idea that VEGF elevation can potentiate hydrocephalus. The clinical relevance of this work is that anti-angiogenic drugs may be useful in patients with hydrocephalus, either alone or in combination with the currently available surgical treatments.