Environmental enrichment reduces Abeta levels and amyloid deposition in transgenic mice

Cerebral deposition of beta-amyloid (Abeta) peptides is an invariant pathological hallmark in brains of patients with Alzheimer's disease (AD) and transgenic mice coexpressing familial AD-linked APP and PS1 variants. We now report that exposure of transgenic mice to an "enriched environment" results in pronounced reductions in cerebral Abeta levels and amyloid deposits, compared to animals raised under "standard housing" conditions. The enzymatic activity of an Abeta-degrading endopeptidase, neprilysin, is elevated in the brains of "enriched" mice and inversely correlated with amyloid burden. Moreover, DNA microarray analysis revealed selective upregulation in levels of transcripts encoded by genes associated with learning and memory, vasculogenesis, neurogenesis, cell survival pathways, Abeta sequestration, and prostaglandin synthesis. These studies provide evidence that environmental enrichment leads to reductions in steady-state levels of cerebral Abeta peptides and amyloid deposition and selective upregulation in levels of specific transcripts in brains of transgenic mice.

Implantation of stimulated homologous macrophages results in partial recovery of paraplegic rats

Postinjury recovery in most tissues requires an effective dialog with macrophages; however, in the mammalian central nervous system, this dialog may be restricted (possibly due to its immune-privileged status), which probably contributes to its regeneration failure. We circumvented this by implanting macrophages, pre-exposed ex vivo to peripheral nerve segments, into transected rat spinal cord. This stimulated tissue repair and partial recovery of motor function, manifested behaviorally by movement of hind limbs, plantar placement of the paws and weight support, and electrophysiologically by cortically evoked hind-limb muscle response. We substantiated these findings immunohistochemically by demonstrating continuity of labeled nerve fibers across the transected site, and by tracing descending fibers distally to it by anterograde labeling. In recovered rats, retransection of the cord above the primary transection site led to loss of recovery, indicating the involvement of long descending spinal tracts. Injection of macrophages into the site of injury is relatively non-invasive and, as the cells are autologous, it may be developed into a clinical therapy.

Vascular dysfunction-The disregarded partner of Alzheimer's disease

Increasing evidence recognizes Alzheimer's disease (AD) as a multifactorial and heterogeneous disease with multiple contributors to its pathophysiology, including vascular dysfunction. The recently updated AD Research Framework put forth by the National Institute on Aging-Alzheimer's Association describes a biomarker-based pathologic definition of AD focused on amyloid, tau, and neuronal injury. In response to this article, here we first discussed evidence that vascular dysfunction is an important early event in AD pathophysiology. Next, we examined various imaging sequences that could be easily implemented to evaluate different types of vascular dysfunction associated with, and/or contributing to, AD pathophysiology, including changes in blood-brain barrier integrity and cerebral blood flow. Vascular imaging biomarkers of small vessel disease of the brain, which is responsible for >50% of dementia worldwide, including AD, are already established, well characterized, and easy to recognize. We suggest that these vascular biomarkers should be incorporated into the AD Research Framework to gain a better understanding of AD pathophysiology and aid in treatment efforts.

Human Hippocampal Neurogenesis Persists in Aged Adults and Alzheimer's Disease Patients

Whether hippocampal neurogenesis persists throughout life in the human brain is not fully resolved. Here, we demonstrate that hippocampal neurogenesis is persistent through the tenth decade of life and is detectable in patients with mild cognitive impairments and Alzheimer's disease. In a cohort of 18 participants with a mean age of 90.6 years, Nestin+Sox2+ neural progenitor cells (NPCs) and DCX+ neuroblasts and immature neurons were detected, but their numbers greatly varied between participants. Nestin+ cells localize in the anterior hippocampus, and NPCs, neuroblasts, and immature neurons are evenly distributed along the anterior to posterior axis. The number of DCX+PCNA+ cells is reduced in mild cognitive impairments, and higher numbers of neuroblasts are associated with better cognitive status. The number of DCX+PCNA+ cells correlates with functional interactions between presynaptic SNARE proteins. Our results suggest that hippocampal neurogenesis persists in the aged and diseased human brain and that it is possibly associated with cognition.

When neurogenesis encounters aging and disease

In this review, we consider the evidence that a reduction in neurogenesis underlies aging-related cognitive deficits and impairments in disorders such as Alzheimer's disease (AD). The molecular and cellular alterations associated with impaired neurogenesis in the aging brain are discussed. Dysfunction of presenilin-1, misprocessing of amyloid precursor protein and toxic effects of hyperphosphorylated tau and β-amyloid probably contribute to impaired neurogenesis in AD. Because factors such as exercise, environmental enrichment and dietary energy restriction enhance neurogenesis, and protect against age-related cognitive decline and AD, knowledge of the underlying neurogenic signaling pathways could lead to novel therapeutic strategies for preserving brain function. In addition, manipulation of endogenous neural stem cells and stem cell transplantation, as stand-alone or adjunct treatments, seems promising.

Neurogenesis and inflammation after ischemic stroke: what is known and where we go from here

This review covers the pathogenesis of ischemic stroke and future directions regarding therapeutic options after injury. Ischemic stroke is a devastating disease process affecting millions of people worldwide every year. The mechanisms underlying the pathophysiology of stroke are not fully understood but there is increasing evidence demonstrating the contribution of inflammation to the drastic changes after cerebral ischemia. This inflammation not only immediately affects the infarcted tissue but also causes long-term damage in the ischemic penumbra. Furthermore, the interaction between inflammation and subsequent neurogenesis is not well understood but the close relationship between these two processes has garnered significant interest in the last decade or so. Current approved therapy for stroke involving pharmacological thrombolysis is limited in its efficacy and new treatment strategies need to be investigated. Research aimed at new therapies is largely about transplantation of neural stem cells and using endogenous progenitor cells to promote brain repair. By understanding the interaction between inflammation and neurogenesis, new potential therapies could be developed to further establish brain repair mechanisms.

Neurogenesis and Alzheimer's disease: at the crossroads

While a massive and progressive neuronal loss in specific areas such as the hippocampus and cortex unequivocally underlies cognitive deterioration and memory loss in Alzheimer's disease, noteworthy alterations take place in the neurogenic microenvironments, namely, the subgranule layer of the dentate gyrus and the subventricular zone. Compromised neurogenesis presumably takes place earlier than onset of hallmark lesions or neuronal loss, and may play a role in the initiation and progression of neuropathology in Alzheimer's disease. Neurogenesis in the adult brain is thought to play a role in numerous forms and aspects of learning and memory and contribute to the plasticity of the hippocampus and olfactory system. Misregulated or impaired neurogenesis on the other hand, may compromise plasticity and neuronal function in these areas and exacerbate neuronal vulnerability. Interestingly, increasing evidence suggests that molecular players in Alzheimer's disease, including PS1, APP and its metabolites, play a role in adult neurogenesis. In addition, recent studies suggest that alterations in tau phosphorylation are pronounced in neurogenic areas, and may interfere with the potential central role of tau proteins in neuronal maturation and differentiation. On the other hand, numerous neurogenic players, such as Notch-1, ErbB4 and L1 are substrates of alpha- beta- and gamma- secretase that play a major role in Alzheimer's disease. This review will discuss current knowledge concerning alterations of neurogenesis in Alzheimer's disease with specific emphasis on the cross-talk between signaling molecules involved in both processes, and the ways by which familial Alzheimer's disease-linked dysfunction of these signaling molecules affect neurogenesis in the adult brain.

Impaired neurogenesis is an early event in the etiology of familial Alzheimer's disease in transgenic mice

Formation of new neurons in the adult brain takes place in the subventricular zone and in the subgranule layer of the dentate gyrus throughout life. Neurogenesis is thought to play a role in hippocampus- and olfaction-dependent learning and memory. However, whether impairments in neurogenesis take place in learning and memory disorders, such as Alzheimer's disease, is yet to be established. Importantly, it remains to be elucidated whether neurogenic impairments play a role in the course of the disease or are the result of extensive neuropathology. We now report that transgenic mice harboring familial Alzheimer's disease-linked mutant APPswe/PS1DeltaE9 exhibit severe impairments in neurogenesis that are evident as early as 2 months of age. These mice exhibit a significant reduction in the proliferation of neural progenitor cells and their neuronal differentiation. Interestingly, levels of hyperphosphorylated tau, the cytotoxic precursor of the Alzheimer's disease hallmark neurofibrillary tangles, are particularly high in the neurogenic niches. Isolation of neural progenitor cells in culture reveals that APPswe/PS1DeltaE9-expressing neurospheres exhibit impaired proliferation and tau hyperphosphorylation compared with wildtype neurospheres isolated from nontransgenic littermates. This study suggests that impaired neurogenesis is an early critical event in the course of Alzheimer's disease that may underlie memory impairments, at least in part, and exacerbate neuronal vulnerability in the hippocampal formation and olfaction circuits. Furthermore, impaired neurogenesis is the result of both intrinsic pathology in neural progenitor cells and extrinsic neuropathology in the neurogenic niches. Finally, hyperphosphorylation of the microtubule-associated protein tau, a critical player in cell proliferation, neuronal maturation, and axonal transport, is a major contributor to impaired neurogenesis in Alzheimer's disease.

Transplantation of activated macrophages overcomes central nervous system regrowth failure

Macrophages have long been known to play a key role in the healing processes of tissues that regenerate after injury; however, the nature of their involvement in healing of the injured central nervous system (CNS) is still a subject of controversy. Here we show that the absence of regrowth in transected rat optic nerve (which, like all other CNS nerves in mammals, cannot regenerate after injury) can be overcome by local transplantation of macrophages preincubated ex vivo with segments of a nerve (e.g., sciatic nerve) that can regenerate after injury. The observed effect of the transplanted macrophages was found to be an outcome of their stimulated activity, as indicated by phagocytosis. Thus, macrophage phagocytic activity was stimulated by their preincubation with sciatic nerve segments but inhibited by their preincubation with optic nerve segments. We conclude that the inability of nerves of the mammalian CNS to regenerate is related to the failure of their macrophages recruited after injury to acquire growth-supportive activity. We attribute this failure to the presence of a CNS resident macrophage inhibitory activity, which may be the biochemical basis underlying the immune privilege of the CNS. The transplantation of suitably activated macrophages into injured nerves may overcome multiple malfunctioning aspects of the CNS response to trauma, and thus may be developed into a novel, practical, and multipotent therapy for CNS injuries.

Evidence that synaptically released beta-amyloid accumulates as extracellular deposits in the hippocampus of transgenic mice

A neuropathological hallmark of Alzheimer's disease is the deposition of amyloid-beta (Abeta) peptides in senile plaques in the hippocampus and cerebral cortex. Abeta is derived from larger integral membrane proteins termed amyloid precursor proteins (APP). We demonstrated previously that APP, synthesized by neurons in the entorhinal cortex, is transported via the perforant pathway to presynaptic terminals in the dentate gyrus. We reported that, although full-length APP and membrane-tethered, C-terminal APP derivatives (APP-CTFs) accumulate at terminal fields, the production of Abeta peptides at these sites was indeterminate. To test the hypothesis that APP-CTFs, generated from axonally transported APP, are further metabolized to Abeta peptides that are subsequently released and deposited proximal to nerve terminals, we created unilateral knife lesions of the perforant pathway of transgenic mice that exhibit hippocampal amyloid deposits. We observed pronounced reductions in amyloid burden in the ipsilateral dentate gyrus, findings that lead us to conclude that axonally transported APP gives rise to Abeta peptides that are released from presynaptic sites in the dentate gyrus and deposited in extracellular plaques. Moreover, our findings are consistent with the view that Abeta deposits are dynamic structures and that the perforant path lesion alters the equilibrium between Abeta production-deposition toward clearance as a consequence of blocked axonal transport of APP from the entorhinal cortex to terminal fields in the hippocampus.

Hippocampal neurogenesis: Learning to remember

Alzheimer's disease, the most prevalent form of dementia in the elderly, is characterized by progressive memory loss and cognitive dysfunction. It has become increasingly clear that while neuronal cell loss in the entorhinal cortex and hippocampus occurs in Alzheimer's disease, it is preceded by a long period of deficits in the connectivity of the hippocampal formation that contributes to the vulnerability of these circuits. Hippocampal neurogenesis plays a role in the maintenance and function of the dentate gyrus and hippocampal circuitry. This review will examine the evidence suggesting that hippocampal neurogenesis plays a role in cognitive function that is affected in Alzheimer's disease, will discuss the cognitive assessments used for the detection of Alzheimer's disease in humans and rodent models of familial Alzheimer's disease, and their value for unraveling the mechanism underlying the development of cognitive impairments and dementia.

Axonal transport, amyloid precursor protein, kinesin-1, and the processing apparatus: revisited

The sequential enzymatic actions of beta-APP cleaving enzyme 1 (BACE1), presenilins (PS), and other proteins of the gamma-secretase complex liberate beta-amyloid (Abeta) peptides from larger integral membrane proteins, termed beta-amyloid precursor proteins (APPs). Relatively little is known about the normal function(s) of APP or the neuronal compartment(s) in which APP undergoes proteolytic processing. Recent studies have been interpreted as consistent with the idea that APP serves as a kinesin-1 cargo receptor and that PS and BACE1 are associated with the APP-resident membranous cargos that undergo rapid axonal transport. In this report, derived from a collaboration among several independent laboratories, we examined the potential associations of APP and kinesin-1 using glutathione S-transferase pull-down and coimmunoprecipitation assays. In addition, we assessed the trafficking of membrane proteins in the sciatic nerves of transgenic mice with heterozygous or homozygous deletions of APP. In contrast to previous reports, we were unable to find evidence for direct interactions between APP and kinesin-1. Furthermore, the transport of kinesin-1 and tyrosine kinase receptors, previously reported to require APP, was unchanged in axons of APP-deficient mice. Finally, we show that two components of the APP proteolytic machinery, i.e., PS1 and BACE1, are not cotransported with APP in the sciatic nerves of mice. These findings suggest that the hypothesis that APP serves as a kinesin-1 receptor and that the proteolytic processing machinery responsible for generating Abeta is transported in the same vesicular compartment in axons of peripheral nerves requires revision.

Axonal degeneration in Alzheimer's disease: when signaling abnormalities meet the axonal transport system

Alzheimer's disease (AD) is characterized by progressive, age-dependent degeneration of neurons in the central nervous system. A large body of evidence indicates that neurons affected in AD follow a dying-back pattern of degeneration, where abnormalities in synaptic function and axonal connectivity long precede somatic cell death. Mechanisms underlying dying-back degeneration of neurons in AD remain elusive but several have been proposed, including deficits in fast axonal transport (FAT). Accordingly, genetic evidence linked alterations in FAT to dying-back degeneration of neurons, and FAT defects have been widely documented in various AD models. In light of these findings, we discuss experimental evidence linking several AD-related pathogenic polypeptides to aberrant activation of signaling pathways involved in the phosphoregulation of microtubule-based motor proteins. While each pathway appears to affect FAT in a unique manner, in the context of AD, many of these pathways might work synergistically to compromise the delivery of molecular components critical for the maintenance and function of synapses and axons. Therapeutic approaches aimed at preventing FAT deficits by normalizing the activity of specific protein kinases may help prevent degeneration of vulnerable neurons in AD.

Non-cell-autonomous effects of presenilin 1 variants on enrichment-mediated hippocampal progenitor cell proliferation and differentiation

Presenilin 1 (PS1) regulates environmental enrichment (EE)-mediated neural progenitor cell (NPC) proliferation and neurogenesis in the adult hippocampus. We now report that transgenic mice that ubiquitously express human PS1 variants linked to early-onset familial Alzheimer's disease (FAD) neither exhibit EE-induced proliferation, nor neuronal lineage commitment of NPCs. Remarkably, the proliferation and differentiation of cultured NPCs from standard-housed mice expressing wild-type PS1 or PS1 variants are indistinguishable. On the other hand, wild-type NPCs cocultured with primary microglia from mice expressing PS1 variants exhibit impaired proliferation and neuronal lineage commitment, phenotypes that are recapitulated with mutant microglia conditioned media in which we detect altered levels of selected soluble signaling factors. These findings lead us to conclude that factors secreted from microglia play a central role in modulating hippocampal neurogenesis, and argue for non-cell-autonomous mechanisms that govern FAD-linked PS1-mediated impairments in adult hippocampal neurogenesis.

Complex environment experience rescues impaired neurogenesis, enhances synaptic plasticity, and attenuates neuropathology in familial Alzheimer's disease-linked APPswe/PS1DeltaE9 mice

Experience in complex environments induces numerous forms of brain plasticity, improving structure and function. It has been long debated whether brain plasticity can be induced under neuropathological conditions, such as Alzheimer's disease (AD), to an extent that would reduce neuropathology, rescue brain structure, and restore its function. Here we show that experience in a complex environment rescues a significant impairment of hippocampal neurogenesis in transgenic mice harboring familial AD-linked mutant APPswe/PS1DeltaE9. Proliferation of hippocampal cells is enhanced significantly after enrichment, and these proliferating cells mature to become new neurons and glia. Enhanced neurogenesis was accompanied by a significant reduction in levels of hyperphosphorylated tau and oligomeric Abeta, the precursors of AD hallmarks, in the hippocampus and cortex of enriched mice. Interestingly, enhanced expression of the neuronal anterograde motor kinesin-1 was observed, suggesting enhanced axonal transport in hippocampal and cortical neurons after enrichment. Examination of synaptic physiology revealed that environmental experience significantly enhanced hippocampal long-term potentiation, without notable alterations in basal synaptic transmission. This study suggests that environmental modulation can rescue the impaired phenotype of the Alzheimer's brain and that induction of brain plasticity may represent therapeutic and preventive avenues in AD.

Alzheimer's Disease and Hippocampal Adult Neurogenesis; Exploring Shared Mechanisms

New neurons incorporate into the granular cell layer of the dentate gyrus throughout life. Neurogenesis is modulated by behavior and plays a major role in hippocampal plasticity. Along with older mature neurons, new neurons structure the dentate gyrus, and determine its function. Recent data suggest that the level of hippocampal neurogenesis is substantial in the human brain, suggesting that neurogenesis may have important implications for human cognition. In support of that, impaired neurogenesis compromises hippocampal function and plays a role in cognitive deficits in Alzheimer's disease mouse models. We review current work suggesting that neuronal differentiation is defective in Alzheimer's disease, leading to dysfunction of the dentate gyrus. Additionally, alterations in critical signals regulating neurogenesis, such as presenilin-1, Notch 1, soluble amyloid precursor protein, CREB, and β-catenin underlie dysfunctional neurogenesis in Alzheimer's disease. Lastly, we discuss the detectability of neurogenesis in the live mouse and human brain, as well as the therapeutic implications of enhancing neurogenesis for the treatment of cognitive deficits and Alzheimer's disease.

Molecular mechanisms of environmental enrichment: impairments in Akt/GSK3β, neurotrophin-3 and CREB signaling

Experience of mice in a complex environment enhances neurogenesis and synaptic plasticity in the hippocampus of wild type and transgenic mice harboring familial Alzheimer's disease (FAD)-linked APPswe/PS1ΔE9. In FAD mice, this experience also reduces levels of tau hyperphosphorylation and oligomeric β-amyloid. Although environmental enrichment has significant effects on brain plasticity and neuropathology, the molecular mechanisms underlying these effects are unknown. Here we show that environmental enrichment upregulates the Akt pathway, leading to the downregulation of glycogen synthase kinase 3β (GSK3β), in wild type but not FAD mice. Several neurotrophic signaling pathways are activated in the hippocampus of both wild type and FAD mice, including brain derived neurotrophic factor (BDNF) and nerve growth factor (NGF), and this increase is accompanied by the upregulation of the BDNF receptor, tyrosine kinase B (TrkB). Interestingly, neurotrophin-3 (NT-3) is upregulated in the brains of wild type mice but not FAD mice, while insulin growth factor-1 (IGF-1) is upregulated exclusively in the brains of FAD mice. Upregulation of neurotrophins is accompanied by the increase of N-Methyl-D-aspartic acid (NMDA) receptors in the hippocampus following environmental enrichment. Most importantly, we observed a significant increase in levels of cAMP response element- binding (CREB) transcripts in the hippocampus of wild type and FAD mice following environmental enrichment. However, CREB phosphorylation, a critical step for the initiation of learning and memory-required gene transcription, takes place in the hippocampus of wild type but not of FAD mice. These results suggest that experience of wild type mice in a complex environmental upregulates critical signaling that play a major role in learning and memory in the hippocampus. However, in FAD mice, some of these pathways are impaired and cannot be rescued by environmental enrichment.

Impairments in fast axonal transport and motor neuron deficits in transgenic mice expressing familial Alzheimer's disease-linked mutant presenilin 1

Presenilins (PS) play a central role in gamma-secretase-mediated processing of beta-amyloid precursor protein (APP) and numerous type I transmembrane proteins. Expression of mutant PS1 variants causes familial forms of Alzheimer's disease (FAD). In cultured mammalian cells that express FAD-linked PS1 variants, the intracellular trafficking of several type 1 membrane proteins is altered. We now report that the anterograde fast axonal transport (FAT) of APP and Trk receptors is impaired in the sciatic nerves of transgenic mice expressing two independent FAD-linked PS1 variants. Furthermore, FAD-linked PS1 mice exhibit a significant increase in phosphorylation of the cytoskeletal proteins tau and neurofilaments in the spinal cord. Reductions in FAT and phosphorylation abnormalities correlated with motor neuron functional deficits. Together, our data suggests that defects in anterograde FAT may underlie FAD-linked PS1-mediated neurodegeneration through a mechanism involving impairments in neurotrophin signaling and synaptic dysfunction.

Depletion of adult neurogenesis exacerbates cognitive deficits in Alzheimer's disease by compromising hippocampal inhibition

BACKGROUND

The molecular mechanism underlying progressive memory loss in Alzheimer's disease is poorly understood. Neurogenesis in the adult hippocampus is a dynamic process that continuously changes the dentate gyrus and is important for hippocampal plasticity, learning and memory. However, whether impairments in neurogenesis affect the hippocampal circuitry in a way that leads to memory deficits characteristic of Alzheimer's disease is unknown. Controversial results in that regard were reported in transgenic mouse models of amyloidosis.

METHODS

Here, we conditionally ablated adult neurogenesis in APPswe/PS1ΔE9 mice by crossing these with mice expressing nestin-driven thymidine kinase (δ-HSV-TK).

RESULTS

These animals show impairment in performance in contextual conditioning and pattern separation tasks following depletion of neurogenesis. Importantly, these deficits were not observed in age-matched APPswe/PS1ΔE9 or δ-HSV-TK mice alone. Furthermore, we show that cognitive deficits were accompanied by the upregulation of hyperphosphorylated tau in the hippocampus and in immature neurons specifically. Interestingly, we observed upregulation of the immediate early gene Zif268 (Egr-1) in the dentate gyrus, CA1 and CA3 regions of the hippocampus following learning in the neurogenesis-depleted δ-HSV-TK mice. This may suggest overactivation of hippocampal neurons in these areas following depletion of neurogenesis.

CONCLUSIONS

These results imply that neurogenesis plays an important role in the regulation of inhibitory circuitry of the hippocampus. This study suggests that deficits in adult neurogenesis may contribute to cognitive impairments, tau hyperphosphorylation in new neurons and compromised hippocampal circuitry in Alzheimer's disease.

Peripheral nerve-stimulated macrophages simulate a peripheral nerve-like regenerative response in rat transected optic nerve

We have previously demonstrated that the failure of the mammalian central nervous system (CNS) to regenerate following axonal injury is related to its immunosuppressive nature, which restricts the ability of both recruited blood-borne monocytes and CNS-resident microglia to support a process of repair. In this study we show that transected optic nerve transplanted with macrophages stimulated by spontaneously regenerating nerve tissue, e.g., segments of peripheral nerve (sciatic nerve), exhibit axonal regrowth at least as far as the optic chiasma. Axonal regrowth was confirmed by double retrograde labeling of the injured optic axons, visualized in their cell bodies. Transplanted macrophages exposed to segments of CNS (optic) nerve were significantly less effective in inducing regrowth. Immunocytochemical analysis showed that the induced regrowth was correlated with a wide distribution of macrophages within the transplanted-transected nerves. It was also correlated with an enhanced clearance of myelin, known to be inhibitory for regrowth and poorly eliminated after injury in the CNS. These results suggest that healing of the injured mammalian CNS, like healing of any other injured tissue, requires the partnership of the immune system, which is normally restricted, but that the restriction can be circumvented by transplantation of peripheral nerve-stimulated macrophages.

Reduced pCREB in Alzheimer's disease prefrontal cortex is reflected in peripheral blood mononuclear cells

Cyclic-AMP response element-binding protein (CREB) signaling has a critical role in the formation of memories. CREB signaling is dysfunctional in the brains of mouse models of Alzheimer's disease (AD), and evidence suggests that CREB signaling may be disrupted in human AD brains as well. Here, we show that both CREB and its activated form pCREB-Ser(133) (pCREB) are reduced in the prefrontal cortex of AD patients. Similarly, the transcription cofactors CREB-binding protein (CBP) and p300 are reduced in the prefrontal cortex of AD patients, indicating additional dysfunction of CREB signaling in AD. Importantly, we show that pCREB expression is reduced in peripheral blood mononuclear cells (PBMC) of AD subjects. In addition, pCREB levels in PBMC positively correlated with pCREB expression in the postmortem brain of persons with AD. These results suggest that pCREB expression in PBMC may be indicative of its expression in the brain, and thus offers the intriguing possibility of pCREB as a biomarker of cognitive function and disease progression in AD.

S. Oliveira S, Zimnicka AM, Jiang Y, Sharma T, Chen S, Lazarov O, Bonini MG, Haus JM, Minshall RD. Reciprocal regulation of eNOS and caveolin-1 functions in endothelial cells

We hypothesized that the maintenance of vascular homeostasis is critically dependent on the expression and reciprocal regulation of caveolin-1 (Cav-1) and endothelial nitric oxide synthase (eNOS) in endothelial cells (ECs). Skeletal muscle biopsies from subjects with type 2 diabetes showed 50% less Cav-1 and eNOS than those from lean healthy controls. The Cav-1:eNOS expression ratio was 200:1 in primary culture human ECs. Cav-1 small interfering RNA (siRNA) reduced eNOS protein and gene expression in association with a twofold increase in eNOS phosphorylation and nitrate production per molecule of eNOS, which was reversed in cells overexpressing Adv-Cav-1-GFP. Upon addition of the Ca2+ ionophore A23187 to activate eNOS, we observed eNOS Ser1177 phosphorylation, its translocation to β-catenin-positive cell-cell junctions, and increased colocalization of eNOS and Cav-1 within 5 min. We also observed Cav-1 S-nitrosylation and destabilization of Cav-1 oligomers in cells treated with A23187 as well as insulin or albumin, and this could be blocked by L-NAME, PP2, or eNOS siRNA. Finally, caveola-mediated endocytosis of albumin or insulin was reduced by Cav-1 or eNOS siRNA, and the effect of Cav-1 siRNA was rescued by Adv-Cav-1-GFP. Thus, Cav-1 stabilizes eNOS expression and regulates its activity, whereas eNOS-derived NO promotes caveola-mediated endocytosis.

Soluble amyloid precursor protein: a novel proliferation factor of adult progenitor cells of ectodermal and mesodermal origin

INTRODUCTION

Soluble amyloid precursor protein α (sAPPα) is a proteolyte of APP cleavage by α-secretase. The significance of the cleavage and the physiological role of sAPPα are unknown. A crystal structure of a region of the amino terminal of sAPPα reveals a domain that is similar to cysteine-rich growth factors. While a previous study implicates sAPPα in the regulation of neural progenitor cell proliferation in the subventricular zone of adult mice, the ubiquitous expression of APP suggests that its role as a growth factor might be broader.

METHODS

sAPPα and α-secretase activities were determined in neural progenitor cells (NPCs), mesenchymal stem cells (MSC) and human decidua parietalis placenta stem cells (hdPSC). Inhibition of α-secretase was achieved by treatment with the matrixmetalloproteinase inhibitor GM6001, and proliferation was determined using clonogenic and immunocytochemical analysis of cell-lineage markers. Recovery of proliferation was achieved by supplementing GM6001-treated cells with recombinant soluble APPα. Expression of APP and its cellular localization in the subventricular zone was determined by Western blot and immunohistochemical analyses of APP wild type and knockout tissue. Alterations in pERK and pAKT expression as a function of soluble APPα production and activity in NPCs were determined by Western blot analysis.

RESULTS

Here we show that sAPPα is a proliferation factor of adult NPCs, MSCs and hdpPSC. Inhibition of α-secretase activity reduces proliferation of these stem cell populations in a dose-dependent manner. Stem cell proliferation can be recovered by the addition of sAPPα in a dose-dependent manner, but not of media depleted of sAPPα. Importantly, sAPPα operates independently of the prominent proliferation factors epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF), but in association with ERK signaling and MAP-kinase signaling pathways. Levels of sAPPα and putative α-secretase, ADAM10, are particularly high in the subventricular zone of adult mice, suggesting a role for sAPPα in regulation of NPCs in this microenvironment.

CONCLUSIONS

These results determine a physiological function for sAPPα and identify a new proliferation factor of progenitor cells of ectodermal and mesodermal origin. Further, our studies elucidate a potential pathway for sAPPα signaling through MAP kinase activation.

Nigrostriatal dysfunction in familial Alzheimer's disease-linked APPswe/PS1DeltaE9 transgenic mice

Alzheimer's disease (AD) is often accompanied by extrapyramidal signs attributed to nigrostriatal dysfunction. The association between amyloid deposition and nigrostriatal degeneration is essentially unknown. We showed previously that the striatum and the substantia nigra of transgenic mice harboring familial AD (FAD)-linked APPswe/PS1DeltaE9 mutants exhibit morphological alterations accompanied by amyloid-beta (Abeta) deposition (Perez et al., 2004). In the present study, we further investigated the interaction between Abeta deposition and dopaminergic nigrostriatal dysfunction, by correlating morphological and biochemical changes in the nigrostriatal pathway with amyloid deposition pathology in the brains of 3- to 17-month-old APPswe/PS1DeltaE9 transgenic mice and age-matched wild-type controls. We show that Abeta deposition is pronounced in the striatum of APPswe/PS1DeltaE9 mice at 6 months of age, and the extent of deposition increases in an age-dependent manner. Tyrosine hydroxylase (TH)-positive dystrophic neurites with rosette or grape-like cluster disposition are observed adjacent to Abeta plaques and display multilaminar, multivesicular, and dense-core bodies as well as mitochondria. In addition, an age-dependent increase of TH protein levels are shown in nigral cells in these mutant mice. Using HPLC analysis, we found a reduction in the dopamine metabolite DOPAC in the striatum of these mice. These findings show a close association between amyloid deposition and nigrostriatal pathology and suggest that altered FAD-linked amyloid metabolism impairs, at least in part, the function of dopaminergic neurons.

Differential effects of central and peripheral nerves on macrophages and microglia

The poor ability of injured central nervous system (CNS) axons to regenerate has been correlated, at least partially, with a limited and suppressed postinjury inflammatory response. A key cell type in the inflammatory process is the macrophage, which can respond in various ways, depending on the conditions of stimulation. The aim of this study is to compare the activities of macrophages or microglia when encountering CNS and peripheral nervous systems (PNS), on the assumption that nerve-related differences in the inflammatory response may have implications for tissue repair and thus for nerve regeneration. Phagocytic activity of macrophages or of isolated brain-derived microglia was enhanced upon their exposure to sciatic (PNS) nerve segments, but inhibited by exposure to optic (CNS) nerve segments. Similarly, nitric oxide production by macrophages or microglia was induced by sciatic nerve segments but not by optic nerve segments. The previously demonstrated presence of a resident inhibitory activity in CNS nerve, could account, at least in part, for the inhibited phagocytic activity of blood-borne macrophages in CNS nerve as well as of microglia resident in the brain. It seems that the CNS microglia are reversibly immunosuppressed by the CNS environment, at least with respect to the activities examined here. It also appears from this study that the weak induction of early healing-related activities of macrophages/microglia in the environment of CNS might explain the subsequent failure of this environment to acquire growth-supportive properties in temporal and spatial synchrony with the needs of regrowing axons.