Abstract 3164: Detection and CAR T-cell directed targeting of inflammation-responsive Wnt pathway receptors on multiple myeloma cancer stem-like cells

Multiple myeloma (MM) is the second most common hematological malignancy characterized by a malignant expansion of abnormal antibody-producing cells. Despite available treatments, relapsed disease is a common occurrence with patients receiving survival predictions of less than one year. Relapsed MM is often refractory to multiple lines of therapy and occurs due to the uncontrolled regeneration of a population of malignant cells displaying progenitor-cell-like phenotypes. Selectively targeting this cancer stem cell (CSC) population provides an effective way to limit incidence of relapsed disease, improving the prognosis for high-risk patients. In MM, the defining characteristics of CSCs remain poorly understood, though signaling pathways promoting ‘stemness’ that are often deregulated in CSCs, such as interleukin-6 (IL-6) signaling, as well as canonical and non-canonical Wnt signaling are also aberrantly activated in MM. In this context, the central objective of this project was to explore the functionality of two proteins which have been shown to be downstream targets of IL-6/JAK2/STAT3 signaling and potentiate Wnt signaling, the embryonic G-protein coupled receptor LGR4 and the fetal-oncogene tyrosine kinase like orphan receptor-1 (ROR1), as CSC biomarker candidates, and explore the feasibility of CSC targeting therapeutics for MM. Receptor expression was assessed by quantitative PCR and flow cytometry in primary plasma cell dyscrasia patient samples across the spectrum of disease, as well as in human myeloma cell lines (HMCLs). Whole transcriptome sequencing analyses were carried out in HMCLs induced to overexpress LGR4, which enriched genes associated with ion transport and embryonic development. Cell adhesion and extracellular matrix genes were downregulated, along with genes associated with metabolic and mitochondrial pathways. Results of ROR1 gene expression and flow cytometry studies suggest that a subset of MM patient samples harbor a low-frequency ROR1-positive cell population, and expression is enriched in an in vitro model of acquired drug resistance. Overexpression of interferon regulatory factor-4 (IRF4) - a myeloma cell-enriched transcription factor that we recently showed promotes myeloma regeneration - also contributed to increased human ROR1 protein levels. HMCLs with high endogenous ROR1 expression were sensitive to in vitro killing by anti-ROR1 CAR T-cell treatment, which employs an scFv generated from the fully humanized ROR1-specific monoclonal antibody cirmtuzumab, at effector:target cell ratios (ET) as low as 0.33:1. Together, these results suggest a central role for Wnt signaling in MM stem cell phenotypes and activation of embryonic transcriptional pathways, while also paving the way towards development of clinical therapies that target a CSC population in MM.

Citation Format: Lara C. Avsharian, Christopher S. Oh, Ashni A. Vora, Jayde Fernandez, Caitlin Shin, Navyaa Sinha, Charles Prussak, Leslie Crews. Detection and CAR T-cell directed targeting of inflammation-responsive Wnt pathway receptors on multiple myeloma cancer stem-like cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3164.

Inflammation-driven deaminase deregulation fuels human pre-leukemia stem cell evolution

Inflammation-dependent base deaminases promote therapeutic resistance in many malignancies. However, their roles in human pre-leukemia stem cell (pre-LSC) evolution to acute myeloid leukemia stem cells (LSCs) had not been elucidated. Comparative whole-genome and whole-transcriptome sequencing analyses of FACS-purified pre-LSCs from myeloproliferative neoplasm (MPN) patients reveal APOBEC3C upregulation, an increased C-to-T mutational burden, and hematopoietic stem and progenitor cell (HSPC) proliferation during progression, which can be recapitulated by lentiviral APOBEC3C overexpression. In pre-LSCs, inflammatory splice isoform overexpression coincides with APOBEC3C upregulation and ADAR1p150-induced A-to-I RNA hyper-editing. Pre-LSC evolution to LSCs is marked by STAT3 editing, STAT3β isoform switching, elevated phospho-STAT3, and increased ADAR1p150 expression, which can be prevented by JAK2/STAT3 inhibition with ruxolitinib or fedratinib or lentiviral ADAR1 shRNA knockdown. Conversely, lentiviral ADAR1p150 expression enhances pre-LSC replating and STAT3 splice isoform switching. Thus, pre-LSC evolution to LSCs is fueled by primate-specific APOBEC3C-induced pre-LSC proliferation and ADAR1-mediated splicing deregulation.

Abstract 5726: A-to-I RNA deaminase deregulation in pre-leukemia stem cell evolution

While inflammation induced ADAR1 RNA deaminases protect the human genome from retroviral integration, deregulation promotes therapeutic resistance in many malignancies. However, the combinatorial role of these deaminases in pre-leukemia stem cell (pre-LSC) evolution to therapy resistant LSC had not been elucidated. Thus, we performed whole genome sequencing (WGS) analysis of 43 CD34+pre-leukemic myeloproliferative neoplasm (MPN) samples compared with matched saliva and non-MPN controls andwhole transcriptome sequencing (RNA-seq) analysis of 113 FACS-purified hematopoietic stem cells (HSC) and hematopoietic progenitor cells (HPC) from MPN, acute myeloid leukemia (AML) and healthy young and aged samples. During MPN progression, inflammation-driven ADAR1 isoform p150 upregulation corresponded with increased Adenosine-to-Inosine (A-to-I) transitions in both MPN stem and progenitor populations. We identified unique A-to-I editing events in coding regions that are associated with either normal stem progenitors or with MPN progenitors. In addition, STAT3 transcript hyper-editing leads to STAT3beta splice isoform expression. Moreover, lentiviral ADAR1p150 overexpression enhanced replating as well as beta-catenin activation, which was reversed by lentiviral shRNA ADAR1 knockdown. In summary, innate immune deaminase deregulation fuels pre-LSC evolution to LSC and may represent a vital LSC therapeutic vulnerability.

Citation Format: Qingfei Jiang, Frida Holm, Jane Isquith, Adam Mark, Cayla Mason, Eduardo Reynoso, Isabella Morris, Wenxue Ma, Raymond Diep, Jessica Pham, Chanond Nasamran, Guorong Xu, Roman Sasik, Sara Brin Rosenthal, Amanda Birmingham, Leslie Crews, Gabriel Pineda, Thomas Whisenant, Kathleen Fisch, Catriona Jamieson. A-to-I RNA deaminase deregulation in pre-leukemia stem cell evolution [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5726.

Abstract LB-025: The role of NOTCH pathway in multiple myeloma associated drug resistance

The aim of this study was to investigate the role of Notch signaling in intrinsic and bone marrow stromal cells (BMSC)-mediated drug resistance in multiple myeloma (MM) and in MM-stem cell (SC) niche maintenance.

MM is an incurable hematological malignancy due to intrinsic or BMSC-mediated drug resistance; the hyperexpression of two Notch ligands, Jag1 and 2 in MM increases Notch signaling in MM cells and BMSCs resulting in malignant cells survival and proliferation. Notch pathway supports stem cell maintenance and drug resistance is an intrinsic feature of cancer stem cells; MM stem cells (MM-SCs) have been characterized as CD138- subpopulation. MM-SCs are resistant to common drugs used in therapy and responsible for disease relapse.

MM cell lines were cultured alone or co-cultured with NIH3T3 murine fibroblasts or HS5 human BMSC line. To detect apoptosis induced by Mitoxantrone, Bortezomib and Melphalan, AnnexinV+ cells were processed by flow cytometry (FC). Jag1 and Jag2 were transiently silenced in MM cells using specific siRNAs. The gene expression levels were analyzed by quantitative RT-PCR. Anti-apoptotic proteins were assessed by FC. Notch inhibition was obtained by γ-secretase inhibitor and the effect on MM cell stemness potential of was assessed by FC measure of CD138- MM cells or clonogenic serial replating in methylcellulose-based medium.

Our results demonstrate that Jag1 and 2 silencing reduces anti-apoptotic genes expression, i.e. SDF1α, CXCR4, Bcl-XL, Bcl2, Survivin and ABCC1 and increases sensitivity of MM cells to the used drugs. MM cells and BMSCs reciprocally activate Notch signaling resulting in increased drug resistance due to: i) an elevated expression of the anti-apoptotic genes in MM cells; ii) BMSCs release of soluble factors, i.e. SDF1α and VEGF, relevant for MM cell growth and survival. Interestingly, Jag1 and 2 silencing in MM cells co-cultured with BMSCs could reverse all gene and protein expression changes as well as BMSCs protective effect increasing the apoptotic rate of MM cells. In addition, we show in MM cell lines that DAPT-mediated Notch inhibition decreases MM-SCs and reduces the clonogenic ability in serial replating.

The evidence that Jag1 and 2 silencing affects the intrinsic and BMSC-induced drug resistance in MM cells also by affecting the MM-SC population supports the rationale for a Notch-tailored approach to overcome the unavoidable relapse pf MM patient.

Citation Format: Silvia Garavelli, Elisa Lazzari, Michela Colombo, Natalia Platonova, Maria Teresa Palano, Francesco Baccianti, Serena Galletti, Antonino Neri, Leslie Crews, Catriona Jamieson, Raffaella Chiaramonte. The role of NOTCH pathway in multiple myeloma associated drug resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-025. doi:10.1158/1538-7445.AM2017-LB-025

Abstract 3351: Aberrant RNA editing of GLI1 promotes malignant regeneration in multiple myeloma

Introduction: Despite novel therapies, most of multiple myeloma (MM) patients relapse as a result of clonal evolution in inflammatory microenvironments. Adenosine-to-inosine (A-to-I) RNA editing, driven by inflammatory cytokine-responsive adenosine deaminase acting on RNA1 (ADAR1), promotes cancer progression by enhancing survival and self-renewal of malignant progenitor cells. Amplifications of chromosome 1q21, containing IL-6R and ADAR1 loci, occur frequently in high-risk MM patients, who frequently develop secondary plasma cell leukemia (PCL) and have shorter survival. While increased IL-6 signaling has been linked to relapse and A-to-I editing contributes to therapeutic resistance in a broad array of malignancies, the role of ADAR1 in MM pathogenesis has not been elucidated. This study aimed to investigate whether pro-inflammatory cues in MM activate ADAR1 editing thereby promoting malignant regeneration.

Procedures: Publicly available primary patient datasets were analyzed and validated in a separate cohort of biobanked primary samples and human myeloma cell lines. Lentiviral vector-mediated activation or knockdown of ADAR1, or treatment with extrinsic pro-inflammatory stimuli, was utilized to probe the functional impact of RNA editing activity in MM models. Site-specific qPCR was used to quantify RNA editing in specific cancer stem cell-associated loci. Functional effects of ADAR1 activity were assessed in in vitro survival and self-renewal assays, and in novel in vivo PCL xenografts.

Results: Patients harboring 1q21 amplification showed significant and stage-dependent increases in ADAR1 expression. In a set of separate primary PCL samples, aberrant RNA editing in the coding region of the Hedgehog (Hh) pathway transcription factor GLI1 was observed in high ADAR1-expressing samples. Notably, increased GLI1 editing, previously reported to have increased capacity to activate its transcriptional targets, was detected in serially transplantable, patient-derived xenograft models. Furthermore, abolition of ADAR1 editase activity impaired GLI1 editing. Lastly, in vitro pro-inflammatory IL-6 stimulation, or continuous exposure to the immunomodulatory drug lenalidomide led to increased ADAR1 mRNA and protein levels, with a concomitant induction of RNA editing activity.

Conclusions: In MM, 1q21 amplification has been linked to progression. We provide new evidence linking expression and activity of ADAR1, located on 1q21, and disease stage. Because ADAR1 induces transcript recoding, A-to-I editing could contribute to the marked transcriptomic diversity typical of advanced MM. While the Hh pathway has been linked to cancer stem cell generation in human MM, here we identified a primate-specific mechanism of Hh pathway activation in MM through RNA editing-dependent stabilization of GLI1. Together, both genetic and microenvironmental factors modulate epitranscriptomic deregulation of cancer stem cell pathways in MM.

Citation Format: Elisa Lazzari, Nathaniel Delos Santos, Christina Wu, Heather Leu, Gabriel Pineda, Shawn Ali, Caitlin Costello, Mark Minden, Raffaella Chiaramonte, Leslie Crews, Catriona Jamieson. Aberrant RNA editing of GLI1 promotes malignant regeneration in multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3351. doi:10.1158/1538-7445.AM2017-3351

Mechanisms of HIV-1 Tat neurotoxicity via CDK5 translocation and hyper-activation: role in HIV-associated neurocognitive disorders

The advent of more effective antiretroviral therapies has reduced the frequency of HIV dementia, however the prevalence of milder HIV associated neurocognitive disorders [HAND] is actually rising. Neurodegenerative mechanisms in HAND might include toxicity by secreted HIV-1 proteins such as Tat, gp120 and Nef that could activate neuro-inflammatory pathways, block autophagy, promote excitotoxicity, oxidative stress, mitochondrial dysfunction and dysregulation of signaling pathways. Recent studies have shown that Tat could interfere with several signal transduction mechanisms involved in cytoskeletal regulation, cell survival and cell cycle re-entry. Among them, Tat has been shown to hyper-activate cyclin-dependent kinase [CDK] 5, a member of the Ser/Thr CDKs involved in cell migration, angiogenesis, neurogenesis and synaptic plasticity. CDK5 is activated by binding to its regulatory subunit, p35 or p39. For this manuscript we review evidence showing that Tat, via calcium dysregulation, promotes calpain-1 cleavage of p35 to p25, which in turn hyper-activates CDK5 resulting in abnormal phosphorylation of downstream targets such as Tau, collapsin response mediator protein-2 [CRMP2], doublecortin [DCX] and MEF2. We also present new data showing that Tat interferes with the trafficking of CDK5 between the nucleus and cytoplasm. This results in prolonged presence of CDK5 in the cytoplasm leading to accumulation of aberrantly phosphorylated cytoplasmic targets [e.g.: Tau, CRMP2, DCX] that impair neuronal function and eventually lead to cell death. Novel therapeutic approaches with compounds that block Tat mediated hyper-activation of CDK5 might be of value in the management of HAND.

α-Synuclein induces alterations in adult neurogenesis in Parkinson disease models via p53-mediated repression of Notch1

Parkinson disease is characterized by the loss of dopaminergic neurons mainly in the substantia nigra. Accumulation of α-synuclein and cell loss has been also reported in many other brain regions including the hippocampus, where it might impair adult neurogenesis, contributing to nonmotor symptoms. However, the molecular mechanisms of these alterations are still unknown. In this report we show that α-synuclein-accumulating adult rat hippocampus neural progenitors present aberrant neuronal differentiation, with reduction of Notch1 expression and downstream signaling targets. We characterized a Notch1 proximal promoter that contains p53 canonical response elements. In vivo binding of p53 represses the transcription of Notch1 in neurons. Moreover, we demonstrated that α-synuclein directly binds to the DNA at Notch1 promoter vicinity and also interacts with p53 protein, facilitating or increasing Notch1 signaling repression, which interferes with maturation and survival of neural progenitors cells. This study provides a molecular basis for α-synuclein-mediated disruption of adult neurogenesis in Parkinson disease.

Regional comparison of the neurogenic effects of CNTF-derived peptides and cerebrolysin in AβPP transgenic mice

Adult neurogenesis, the production of new neurons in certain brain regions, is known to decrease with age and the loss of neurogenic potential has been implicated in Alzheimer's disease (AD), a leading cause of dementia in the elderly. Cerebrolysin (CBL) has been shown to increase neurogenesis in models of stroke and AD. CBL is composed of small peptides with activity similar to neurotrophic factors including ciliary neurotrophic factor (CNTF), which may mediate its neurogenic effects. This study compares the effects of CBL and two peptides with corresponding to an active region of CNTF (Peptide 6 and 6A) across neurogenic brain regions in amyloid-β protein precursor (AβPP) transgenic (tg) mice. Both CBL and Peptides 6 and 6A were able to increase the numbers of neuroblasts (DCX+ cells) and BrdU+ cells in a regionally specific manner across the subventricular zone, olfactory bulb, and hippocampus. The increased generation of new cells and cell survival in animals treated with Peptides 6 and 6A was accompanied by an increase in PCNA+ cells. In contrast, AβPP tg mice treated with CBL displayed reduced levels of TUNEL staining, while levels of PCNA were unaltered. Collectively these results demonstrate that while CBL and Peptides 6 and 6A all potentiate neurogenesis in the AβPP tg mice, their relative modes of action may differ with CBL associated with reduced apoptosis and Peptides 6 and 6A working by augmenting cell proliferation. These results are consistent with a potential therapeutic relevance for Peptides 6 and 6A in AD and other disorders characterized by neurogenic deficits.

Role of α-synuclein penetration into the membrane in the mechanisms of oligomer pore formation

Parkinson's disease (PD) and dementia with Lewy bodies are common disorders of the aging population and characterized by the progressive accumulation of α-synuclein (α-syn) in the central nervous system. Aggregation of α-syn into oligomers with a ring-like appearance has been proposed to play a role in toxicity. However, the molecular mechanisms and the potential sequence of events involved in the formation of pore-like structures are unclear. We utilized computer modeling and cell-based studies to investigate the process of oligomerization of wild-type and A53T mutant α-syn in membranes. The studies suggest that α-syn penetrates the membrane rapidly, changing its conformation from α-helical towards a coiled structure. This penetration facilitates the incorporation of additional α-syn monomers in the complex, and the subsequent displacement of phospholipids and the formation of oligomers in the membrane. This process occurred more rapidly, and with a more favorable energy of interaction, for mutant A53T compared with wild-type α-syn. After 4 ns of simulation of the protein-membrane model, α-syn had penetrated through two-thirds of the membrane. By 9 ns, the penetration of the annular α-syn oligomers can result in the formation of pore-like structures that fully perforate the lipid bilayer. Experimental incubation of recombinant α-syn in synthetic membranes resulted in the formation of similar pore-like complexes. Moreover, mutant (A53T) α-syn had a greater tendency to accumulate in neuronal membrane fractions in cell cultures, resulting in greater neuronal permeability, as demonstrated with the calcein efflux assay. These studies provide a sequential molecular explanation for the process of α-syn oligomerization in the membrane, and support the role of formation of pore-like structures in the pathogenesis of the neurodegenerative process in PD.

Phosphorylation of collapsin response mediator protein-2 disrupts neuronal maturation in a model of adult neurogenesis: Implications for neurodegenerative disorders

BACKGROUND

Recent studies suggest that the pathogenic process in neurodegenerative disorders may disrupt mature neuronal circuitries and neurogenesis in the adult brain. Abnormal activation of CDK5 is associated with neurodegenerative disorders, and recently a critical role for CDK5 in adult neurogenesis has been identified. We have developed an in vitro model of abnormal CDK5 activation during adult hippocampal neurogenesis, and here we used this model to investigate aberrantly phosphorylated downstream targets of CDK5.

RESULTS

Abnormal CDK5 activation in an in vitro model of adult neurogenesis results in hyperphosphorylation of collapsin-response mediator protein-2 (CRMP2) and impaired neurite outgrowth. Inhibition of CDK5, or expression of a non-phosphorylatable (S522A) CRMP2 construct reduced CRMP2 hyperphosphorylation, and reversed neurite outgrowth deficits. CRMP2 plays a role in microtubule dynamics; therefore we examined the integrity of microtubules in this model using biochemical and electron microscopy techniques. We found that microtubule organization was disrupted under conditions of CDK5 activation. Finally, to study the relevance of these findings to neurogenesis in neurodegenerative conditions associated with HIV infection, we performed immunochemical analyses of the brains of patients with HIV and transgenic mice expressing HIV-gp120 protein. CDK5-mediated CRMP2 phosphorylation was significantly increased in the hippocampus of patients with HIV encephalitis and in gp120 transgenic mice, and this effect was rescued by genetic down-modulation of CDK5 in the mouse model.

CONCLUSIONS

These results reveal a functional mechanism involving microtubule destabilization through which abnormal CDK5 activation and CRMP2 hyperphosphorylation might contribute to defective neurogenesis in neurodegenerative disorders such as HIV encephalitis.

Neurotoxic effects of the HCV core protein are mediated by sustained activation of ERK via TLR2 signaling

Hepatitis C virus (HCV) infection is a serious problem among those co-infected with human immunodeficiency virus; however, its impact in the central nervous system (CNS) remains unclear. This study aimed to investigate the mechanisms underlying HCV core protein-mediated neurodegeneration. Analysis of human HCV seropositive cases demonstrated widespread damage to neuronal dendritic processes and sustained activation of extracellular signal-related kinase (ERK); analogous pathologies were observed in wild type injected with HCV core protein into the hippocampus. In vitro analysis in neuronal cells exposed to HCV core demonstrated retraction of the neuronal processes in an ERK/Signal Transducer and Activator of Transcription 3 (STAT3)-dependent manner dependent on toll-like receptor 2 (TLR2) signaling activation. These results indicate that HCV core protein neurotoxicity may be mediated by the sustained activation of ERK/STAT3 via TLR2-IRAK1 signaling pathway. These pathways provide novel targets for development of neuroprotective treatments for HCV involvement of the CNS.

Passive immunization reduces behavioral and neuropathological deficits in an alpha-synuclein transgenic model of Lewy body disease

Dementia with Lewy bodies (DLB) and Parkinson's Disease (PD) are common causes of motor and cognitive deficits and are associated with the abnormal accumulation of alpha-synuclein (α-syn). This study investigated whether passive immunization with a novel monoclonal α-syn antibody (9E4) against the C-terminus (CT) of α-syn was able to cross into the CNS and ameliorate the deficits associated with α-syn accumulation. In this study we demonstrate that 9E4 was effective at reducing behavioral deficits in the water maze, moreover, immunization with 9E4 reduced the accumulation of calpain-cleaved α-syn in axons and synapses and the associated neurodegenerative deficits. In vivo studies demonstrated that 9E4 traffics into the CNS, binds to cells that display α-syn accumulation and promotes α-syn clearance via the lysosomal pathway. These results suggest that passive immunization with monoclonal antibodies against the CT of α-syn may be of therapeutic relevance in patients with PD and DLB.

Increased CDK5 expression in HIV encephalitis contributes to neurodegeneration via tau phosphorylation and is reversed with Roscovitine

Recent treatments with highly active antiretroviral therapy (HAART) regimens have been shown to improve general clinical status in patients with human immunodeficiency virus (HIV) infection; however, the prevalence of cognitive alterations and neurodegeneration has remained the same or has increased. These deficits are more pronounced in the subset of HIV patients with the inflammatory condition known as HIV encephalitis (HIVE). Activation of signaling pathways such as GSK3β and CDK5 has been implicated in the mechanisms of HIV neurotoxicity; however, the downstream mediators of these effects are unclear. The present study investigated the involvement of CDK5 and tau phosphorylation in the mechanisms of neurodegeneration in HIVE. In the frontal cortex of patients with HIVE, increased levels of CDK5 and p35 expression were associated with abnormal tau phosphorylation. Similarly, transgenic mice engineered to express the HIV protein gp120 exhibited increased brain levels of CDK5 and p35, alterations in tau phosphorylation, and dendritic degeneration. In contrast, genetic knockdown of CDK5 or treatment with the CDK5 inhibitor roscovitine improved behavioral performance in the water maze test and reduced neurodegeneration, abnormal tau phosphorylation, and astrogliosis in gp120 transgenic mice. These findings indicate that abnormal CDK5 activation contributes to the neurodegenerative process in HIVE via abnormal tau phosphorylation; thus, reducing CDK5 might ameliorate the cognitive impairments associated with HIVE.

Modulation of aberrant CDK5 signaling rescues impaired neurogenesis in models of Alzheimer's disease

Recent studies show that in Alzheimer's disease (AD), alterations in neurogenesis contribute to the neurodegenerative process. Neurodegeneration in AD has been associated with aberrant signaling through the cyclin-dependent kinase-5 (CDK5) pathway via its activators p35/p25; however, the role of CDK5 in the mechanisms of defective adult neurogenesis in AD is unknown. First, to study AD-like abnormal activation of CDK5 signaling in an in vitro model of neurogenesis, neuronal progenitor cells (NPCs) were infected with a viral vector expressing p35, and exposed to amyloid-β protein (Aβ(1-42)). These conditions resulted in impaired maturation and neurite outgrowth in vitro, and these effects were reversed by pharmacological or genetic inhibition of CDK5. Similarly, neurogenesis was impaired in a transgenic mouse model of AD that expresses high levels of amyloid precursor protein (APP), and this effect was reversed in transgenic mice crossed with a CDK5 heterozygous-deficient mouse line. A similar rescue effect was observed in APP transgenic mice treated with Roscovitine, a pharmacological inhibitor of CDK5. Taken together, these data suggest that the CDK5 signaling pathway has a critical role in maintaining the integrity of NPCs and neuronal maturation in the adult hippocampus. Moreover, potential therapeutic approaches could focus on modulating the aberrant activity of CDK5 to target the neurogenic and neurodegenerative alterations in AD.

Progressive accumulation of amyloid-beta oligomers in Alzheimer's disease and in amyloid precursor protein transgenic mice is accompanied by selective alterations in synaptic scaffold proteins

The cognitive impairment in patients with Alzheimer's disease is closely associated with synaptic loss in the neocortex and limbic system. Although the neurotoxic effects of aggregated amyloid-beta oligomers in Alzheimer's disease have been studied extensively in experimental models, less is known about the characteristics of these aggregates across the spectrum of Alzheimer's disease. In this study, postmortem frontal cortex samples from controls and patients with Alzheimer's disease were fractionated and analyzed for levels of oligomers and synaptic proteins. We found that the levels of oligomers correlated with the severity of cognitive impairment (blessed information-memory-concentration score and mini-mental state examination) and with the loss of synaptic markers. Reduced levels of the synaptic vesicle protein, vesicle-associated membrane protein-2, and the postsynaptic protein, postsynaptic density-95, correlated with the levels of oligomers in the various fractions analyzed. The strongest associations were found with amyloid-beta dimers and pentamers. Co-immunoprecipitation and double-labeling experiments supported the possibility that amyloid-beta and postsynaptic density-95 interact at synaptic sites. Similarly, in transgenic mice expressing high levels of neuronal amyloid precursor protein, amyloid-beta co-immunoprecipitated with postsynaptic density-95. This was accompanied by a decrease in the levels of the postsynaptic proteins Shank1 and Shank3 in patients with Alzheimer's disease and in the brains of amyloid precursor protein transgenic mice. In conclusion, this study suggests that the presence of a subpopulation of amyloid-beta oligomers in the brains of patients with Alzheimer's disease might be related to alterations in selected synaptic proteins and cognitive impairment.

Molecular mechanisms of neurodegeneration in Alzheimer's disease

Alzheimer's disease (AD) is characterized by cognitive impairment, progressive neurodegeneration and formation of amyloid-beta (Abeta)-containing plaques and neurofibrillary tangles composed of hyperphosphorylated tau. The neurodegenerative process in AD is initially characterized by synaptic damage accompanied by neuronal loss. In addition, recent evidence suggests that alterations in adult neurogenesis in the hippocampus might play a role. Synaptic loss is one of the strongest correlates to the cognitive impairment in patients with AD. Several lines of investigation support the notion that the synaptic pathology and defective neurogenesis in AD are related to progressive accumulation of Abeta oligomers rather than fibrils. Abnormal accumulation of Abeta resulting in the formation of toxic oligomers is the result of an imbalance between the levels of Abeta production, aggregation and clearance. Abeta oligomers might lead to synaptic damage by forming pore-like structures with channel activity; alterations in glutamate receptors; circuitry hyper-excitability; mitochondrial dysfunction; lysosomal failure and alterations in signaling pathways related to synaptic plasticity, neuronal cell and neurogenesis. A number of signaling proteins, including fyn kinase; glycogen synthase kinase-3beta (GSK3beta) and cyclin-dependent kinase-5 (CDK5), are involved in the neurodegenerative progression of AD. Therapies for AD might require the development of anti-aggregation compounds, pro-clearance pathways and blockers of hyperactive signaling pathways.

Selective molecular alterations in the autophagy pathway in patients with Lewy body disease and in models of alpha-synucleinopathy

BACKGROUND

Lewy body disease is a heterogeneous group of neurodegenerative disorders characterized by alpha-synuclein accumulation that includes dementia with Lewy bodies (DLB) and Parkinson's Disease (PD). Recent evidence suggests that impairment of lysosomal pathways (i.e. autophagy) involved in alpha-synuclein clearance might play an important role. For this reason, we sought to examine the expression levels of members of the autophagy pathway in brains of patients with DLB and Alzheimer's Disease (AD) and in alpha-synuclein transgenic mice.

METHODOLOGY/PRINCIPAL FINDINGS

By immunoblot analysis, compared to controls and AD, in DLB cases levels of mTor were elevated and Atg7 were reduced. Levels of other components of the autophagy pathway such as Atg5, Atg10, Atg12 and Beclin-1 were not different in DLB compared to controls. In DLB brains, mTor was more abundant in neurons displaying alpha-synuclein accumulation. These neurons also showed abnormal expression of lysosomal markers such as LC3, and ultrastructural analysis revealed the presence of abundant and abnormal autophagosomes. Similar alterations were observed in the brains of alpha-synuclein transgenic mice. Intra-cerebral infusion of rapamycin, an inhibitor of mTor, or injection of a lentiviral vector expressing Atg7 resulted in reduced accumulation of alpha-synuclein in transgenic mice and amelioration of associated neurodegenerative alterations.

CONCLUSIONS/SIGNIFICANCE

This study supports the notion that defects in the autophagy pathway and more specifically in mTor and Atg7 are associated with neurodegeneration in DLB cases and alpha-synuclein transgenic models and supports the possibility that modulators of the autophagy pathway might have potential therapeutic effects.

APP transgenic modeling of Alzheimer's disease: mechanisms of neurodegeneration and aberrant neurogenesis

Neurodegenerative disorders of the aging population affect over 5 million people in the US and Europe alone. The common feature is the progressive accumulation of misfolded proteins with the formation of toxic oligomers. Alzheimer’s disease (AD) is characterized by cognitive impairment, progressive degeneration of neuronal populations in the neocortex and limbic system, and formation of amyloid plaques and neurofibrillary tangles. Amyloid-β (Aβ) is the product of proteolysis of amyloid precursor protein (APP) by β and γ-secretase enzymes. The neurodegenerative process in AD initiates with axonal and synaptic damage and is associated with progressive accumulation of toxic Aβ oligomers in the intracellular and extracellular space. In addition, neurodegeneration in AD is associated with alterations in neurogenesis. Aβ accumulation is the consequence of an altered balance between protein synthesis, aggregation rate, and clearance. Identification of genetic mutations in APP associated with familial forms of AD and gene polymorphisms associated with the more common sporadic variants of AD has led to the development of transgenic (tg) and knock out rodents as well as viral vector driven models of AD. While APP tg murine models with mutations in the N- and C-terminal flanking regions of Aβ are characterized by increased Aβ production with plaque formation, mutations in the mid-segment of Aβ result in increased formation of oligomers, and mutations toward the C-terminus (E22Q) segment results in amyloid angiopathy. Similar to AD, in APP tg models bearing familial mutations, formation of Aβ oligomers results in defective plasticity in the perforant pathway, selective neuronal degeneration, and alterations in neurogenesis. Promising results have been obtained utilizing APP tg models of AD to develop therapies including the use of β- and γ-secretase inhibitors, immunization, and stimulating neurogenesis.

Role of synucleins in Alzheimer's disease

Alzheimer's disease (AD) and Parkinson's disease (PD) are the most common causes of dementia and movement disorders in the elderly. While progressive accumulation of oligomeric amyloid-beta protein (Abeta) has been identified as one of the central toxic events in AD leading to synaptic dysfunction, accumulation of alpha-synuclein (alpha-syn) resulting in the formation of oligomers has been linked to PD. Most of the studies in AD have been focused on investigating the role of Abeta and Tau; however, recent studies suggest that alpha-syn might also play a role in the pathogenesis of AD. For example, fragments of alpha-syn can associate with amyloid plaques and Abeta promotes the aggregation of alpha-syn in vivo and worsens the deficits in alpha-syn tg mice. Moreover, alpha-syn has also been shown to accumulate in limbic regions in AD, Down's syndrome, and familial AD cases. Abeta and alpha-syn might directly interact under pathological conditions leading to the formation of toxic oligomers and nanopores that increase intracellular calcium. The interactions between Abeta and alpha-syn might also result in oxidative stress, lysosomal leakage, and mitochondrial dysfunction. Thus, better understanding the steps involved in the process of Abeta and alpha-syn aggregation is important in order to develop intervention strategies that might prevent or reverse the accumulation of toxic proteins in AD.

Neurofibrillary and neurodegenerative pathology in APP-transgenic mice injected with AAV2-mutant TAU: neuroprotective effects of Cerebrolysin

Alzheimer's disease (AD) continues to be the most common cause of cognitive and motor alterations in the aging population. Accumulation of amyloid beta (Abeta)-protein oligomers and the microtubule associated protein-TAU might be responsible for the neurological damage. We have previously shown that Cerebrolysin (CBL) reduces the synaptic and behavioral deficits in amyloid precursor protein (APP) transgenic (tg) mice by decreasing APP phosphorylation via modulation of glycogen synthase kinase-3beta (GSK3beta) and cyclin-dependent kinase-5 (CDK5) activity. These kinases also regulate TAU phosphorylation and are involved in promoting neurofibrillary pathology. In order to investigate the neuroprotective effects of CBL on TAU pathology, a new model for neurofibrillary alterations was developed using somatic gene transfer with adeno-associated virus (AAV2)-mutant (mut) TAU (P301L). The Thy1-APP tg mice (3 m/o) received bilateral injections of AAV2-mutTAU or AAV2-GFP, into the hippocampus. After 3 months, compared to non-tg controls, in APP tg mice intra-hippocampal injections with AAV2-mutTAU resulted in localized increased accumulation of phosphorylated TAU and neurodegeneration. Compared with vehicle controls, treatment with CBL in APP tg injected with AAV2-mutTAU resulted in a significant decrease in the levels of TAU phosphorylation at critical sites dependent on GSK3beta and CDK5 activity. This was accompanied by amelioration of the neurodegenerative alterations in the hippocampus. This study supports the concept that the neuroprotective effects of CBL may involve the reduction of TAU phosphorylation by regulating kinase activity.

Molecular pathology of neuro-AIDS (CNS-HIV)

The cognitive deficits in patients with HIV profoundly affect the quality of life of people living with this disease and have often been linked to the neuro-inflammatory condition known as HIV encephalitis (HIVE). With the advent of more effective anti-retroviral therapies, HIVE has shifted from a sub-acute to a chronic condition. The neurodegenerative process in patients with HIVE is characterized by synaptic and dendritic damage to pyramidal neurons, loss of calbindin-immunoreactive interneurons and myelin loss. The mechanisms leading to neurodegeneration in HIVE might involve a variety of pathways, and several lines of investigation have found that interference with signaling factors mediating neuroprotection might play an important role. These signaling pathways include, among others, the GSK3beta, CDK5, ERK, Pyk2, p38 and JNK cascades. Of these, GSK3beta has been a primary focus of many previous studies showing that in infected patients, HIV proteins and neurotoxins secreted by immune-activated cells in the brain abnormally activate this pathway, which is otherwise regulated by growth factors such as FGF. Interestingly, modulation of the GSK3beta signaling pathway by FGF1 or GSK3beta inhibitors (lithium, valproic acid) is protective against HIV neurotoxicity, and several pilot clinical trials have demonstrated cognitive improvements in HIV patients treated with GSK3beta inhibitors. In addition to the GSK3beta pathway, the CDK5 pathway has recently been implicated as a mediator of neurotoxicity in HIV, and HIV proteins might activate this pathway and subsequently disrupt the diverse processes that CDK5 regulates, including synapse formation and plasticity and neurogenesis. Taken together, the GSK3beta and CDK5 signaling pathways are important regulators of neurotoxicity in HIV, and modulation of these factors might have therapeutic potential in the treatment of patients suffering from HIVE. In this context, the subsequent sections will focus on reviewing the involvement of the GSK3beta and CDK5 pathways in neurodegeneration in HIV.

Mutant Pink1 induces mitochondrial dysfunction in a neuronal cell model of Parkinson's disease by disturbing calcium flux

Parkinson's disease (PD) is characterized by accumulation of alpha-synuclein (alpha-syn) and degeneration of neuronal populations in cortical and subcortical regions. Mitochondrial dysfunction has been considered a potential unifying factor in the pathogenesis of the disease. Mutations in genes linked to familial forms of PD, including SNCA encoding alpha-syn and Pten-induced putative kinase 1 (PINK1), have been shown to disrupt mitochondrial activity. We investigated the mechanisms through which mutant Pink1 might disrupt mitochondrial function in neuronal cells with alpha-syn accumulation. For this purpose, a neuronal cell model of PD was infected with virally-delivered Pink1, and was analyzed for cell survival, mitochondrial activity and calcium flux. Mitochondrial morphology was analyzed by confocal and electron microscopy. These studies showed that mutant (W437X) but not wildtype Pink1 exacerbated the alterations in mitochondrial function promoted by mutant (A53T) alpha-syn. This effect was associated with increased intracellular calcium levels. Co-expression of both mutant Pink1 and alpha-syn led to alterations in mitochondrial structure and neurite outgrowth that were partially ameliorated by treatment with cyclosporine A, and completely restored by treatment with the mitochondrial calcium influx blocker Ruthenium Red, but not with other cellular calcium flux blockers. Our data suggest a role for mitochondrial calcium influx in the mechanisms of mitochondrial and neuronal dysfunction in PD. Moreover, these studies support an important function for Pink1 in regulating mitochondrial activity under stress conditions.

Neuronal injury in simian immunodeficiency virus and other animal models of neuroAIDS

The success of antiretroviral therapy has reduced the incidence of severe neurological complication resulting from human immunodeficiency virus (HIV) infection. However, increased patient survival has been associated with an increased prevalence of protracted forms of HIV encephalitis leading to moderate cognitive impairment. NeuroAIDS remains a great challenge to patients, their families, and our society. Thus development of preclinical models that will be suitable for testing promising new compounds with neurotrophic and neuroprotective capabilities is of critical importance. The simian immunodeficiency virus (SIV)-infected macaque is the premiere model to study HIV neuropathogenesis. This model was central to the seminal work of Dr. Opendra "Bill" Narayan. Similar to patients with HIV encephalitis, in the SIV model there is injury to the synaptodendritic structure of excitatory pyramidal neurons and inhibitory calbindin-immunoreactive interneurons. This article, which is part of a special issue of the Journal of NeuroVirology in honor of Dr. Bill Narayan, discusses the most important neurodegenerative features in preclinical models of neuroAIDS and their potential for treatment development.

Long-term neprilysin gene transfer is associated with reduced levels of intracellular Abeta and behavioral improvement in APP transgenic mice

Background

Proteolytic degradation has emerged as a key pathway involved in controlling levels of the Alzheimer's disease (AD)-associated amyloid-β (Aβ) peptide in the brain. The endopeptidase, neprilysin, has been implicated as a major Aβ degrading enzyme in mice and humans. Previous short and intermediate term studies have shown the potential therapeutic application of neprilysin by delivering this enzyme into the brain of APP transgenic mice using gene transfer with viral vectors. However the effects of long-term neprilysin gene transfer on other aspects of Aβ associated pathology have not been explored yet in APP transgenic mice.

Results

We show that the sustained expression of neprilysin for up to 6 months lowered not only the amyloid plaque load but also reduced the levels of intracellular Aβ immunoreactivity. This was associated with improved behavioral performance in the water maze and ameliorated the dendritic and synaptic pathology in the APP transgenic mice.

Conclusion

These data support the possibility that long-term neprilysin gene therapy improves behavioral and neurodegenerative pathology by reducing intracellular Aβ.

Neurotrophic effects of Cerebrolysin in the Mecp2(308/Y) transgenic model of Rett syndrome

Rett syndrome is a childhood neurodevelopmental disorder caused by mutations in the gene encoding for methyl-CpG-binding protein (MeCP2). Neuropathological studies in patients with Rett syndrome and in MeCP2 mutant models have shown reduced dendritic arborization and abnormal neuronal packing. We have previously shown that Cerebrolysin (CBL), a neurotrophic peptide mixture, ameliorates the synaptic and dendritic pathology in models of aging and neurodegeneration. This study aimed to determine whether CBL was capable of reducing behavioral and neuronal alterations in Mecp2(308/Y) mutant mice. Two sets of experiments were performed, the first with 4-month-old male Mecp2(308/Y) mutant mice treated with CBL or vehicle for 3 months (Group A) and the second with 1-month-old mice treated for 6 months (Group B). Behavioral analysis showed improved motor performance with CBL in Group A and a trend toward improvement in Group B. Consistent with behavioral findings, neuropathological analysis of the basal ganglia showed amelioration of dendritic simplification in CBL-treated Mecp2(308/Y) mutant mice. CBL treatment also ameliorated dendritic pathology and neuronal loss in the hippocampus and neocortex in Mecp2(308/Y) mutant mice. In conclusion, this study demonstrates that CBL promotes recovery of dendritic and neuronal damage and behavioral improvements in young adult Mecp2(308/Y) mutant mice and suggests that CBL may have neurotrophic effects in this model. These findings support the possibility that CBL may have beneficial effects in the management of Rett syndrome.

Mechanisms of hybrid oligomer formation in the pathogenesis of combined Alzheimer's and Parkinson's diseases

Background

Misfolding and pathological aggregation of neuronal proteins has been proposed to play a critical role in the pathogenesis of neurodegenerative disorders. Alzheimer's disease (AD) and Parkinson's disease (PD) are frequent neurodegenerative diseases of the aging population. While progressive accumulation of amyloid β protein (Aβ) oligomers has been identified as one of the central toxic events in AD, accumulation of α-synuclein (α-syn) resulting in the formation of oligomers and protofibrils has been linked to PD and Lewy body Disease (LBD). We have recently shown that Aβ promotes α-syn aggregation and toxic conversion in vivo, suggesting that abnormal interactions between misfolded proteins might contribute to disease pathogenesis. However the molecular characteristics and consequences of these interactions are not completely clear.

Methodology/Principal Findings

In order to understand the molecular mechanisms involved in potential Aβ/α-syn interactions, immunoblot, molecular modeling, and in vitro studies with α-syn and Aβ were performed. We showed in vivo in the brains of patients with AD/PD and in transgenic mice, Aβ and α-synuclein co-immunoprecipitate and form complexes. Molecular modeling and simulations showed that Aβ binds α-syn monomers, homodimers, and trimers, forming hybrid ring-like pentamers. Interactions occurred between the N-terminus of Aβ and the N-terminus and C-terminus of α-syn. Interacting α-syn and Aβ dimers that dock on the membrane incorporated additional α-syn molecules, leading to the formation of more stable pentamers and hexamers that adopt a ring-like structure. Consistent with the simulations, under in vitro cell-free conditions, Aβ interacted with α-syn, forming hybrid pore-like oligomers. Moreover, cells expressing α-syn and treated with Aβ displayed increased current amplitudes and calcium influx consistent with the formation of cation channels.

Conclusion/Significance

These results support the contention that Aβ directly interacts with α-syn and stabilized the formation of hybrid nanopores that alter neuronal activity and might contribute to the mechanisms of neurodegeneration in AD and PD. The broader implications of such hybrid interactions might be important to the pathogenesis of other disorders of protein misfolding.

Climbing the scaffolds of Parkinson's disease pathogenesis

Several neurodegenerative disorders, including Parkinson's and Alzheimer's diseases, are characterized neuropathologically by accumulation of misfolded proteins such as alpha-synuclein that disrupts scaffold molecules in the caveolae. A new study by Ihara et al. in this issue of Neuron shows that a novel scaffold protein, Sept4, may be an important player in modulating the pathological alterations of alpha-synuclein in models of Parkinson's disease, suggesting that gene therapies targeting scaffold proteins might be effective in the treatment of neurodegenerative disorders.

Toll-like receptor pathway gene expression is associated with human immunodeficiency virus-associated neurodegeneration

The innate immune system is a significant component of the brain's defense against infection, especially as the blood-brain barrier restricts access of the members of the adaptive immune system, such as T and B cells. The innate immune system includes Toll-like receptors (TLRs) that recognize pathogen-associated molecular patterns. Within the central nervous system, they are expressed on glial cells and their expression can be modulated by pathological states. Although their function is to recognize foreign pathogens and stimulate a protective immune response through the production of cytokines and interferons, there is emerging evidence that activation of these receptors can result in neurodegeneration. In the current study, the authors assessed the expression of TLR-related genes, using a customized Superarray gene chip, and correlated the expression findings with indices of neurodegeneration. We found that, using a stringent threshold for statistical significance to overcome the potential problem of multiple statistical testing, there were significant correlations between the expression of nine TLR-related genes and reduction in dendritic and synaptic staining. Two of these genes, TLR4 and SIGIRR, were validated by quantitative real-time polymerase chain reaction. Additionally, the authors demonstrated in vitro at the protein level that human primary astrocytes exposed to the toxic human immunodeficiency virus (HIV) envelope protein gp120 had a significant increase in TLR4 protein expression. In conclusion, these findings indicate that TLR-related gene expression may contribute to the development of HIV-related neurodegeneration.

Statins reduce neuronal alpha-synuclein aggregation in in vitro models of Parkinson's disease

Aggregation of alpha-synuclein (alpha-syn) is believed to play a critical role in the pathogenesis of disorders such as dementia with Lewy bodies and Parkinson's disease. The function of alpha-syn remains unclear, although several lines of evidence suggest that alpha-syn is involved in synaptic vesicle trafficking probably via lipid binding. Moreover, interactions with cholesterol and lipids have been shown to be involved in alpha-syn aggregation. In this context, the main objective of this study was to determine if statins--cholesterol synthesis inhibitors--might interfere with alpha-syn accumulation in cellular models. For this purpose, we studied the effects of lovastatin, simvastatin, and pravastatin on the accumulation of alpha-syn in a stably transfected neuronal cell line and in primary human neurons. Statins reduced the levels of alpha-syn accumulation in the detergent insoluble fraction of the transfected cells. This was accompanied by a redistribution of alpha-syn in caveolar fractions, a reduction in oxidized alpha-syn, and enhanced neurite outgrowth. In contrast, supplementation of the media with cholesterol increased alpha-syn aggregation in detergent insoluble fractions of transfected cells and was accompanied by reduced neurite outgrowth. Taken together, these results suggest that regulation of cholesterol levels with cholesterol inhibitors might be a novel approach for the treatment of Parkinson's disease.

Novel strategies for Alzheimer's disease treatment

Considerable progress has been made in recent years towards better understanding the pathogenesis of Alzheimer's disease (AD), a dementing neurodegenerative disorder that affects > 10 million individuals in the US and Europe combined. Recent studies suggest that alterations in the processing of amyloid precursor protein (APP), resulting in the accumulation of amyloid-beta protein (Abeta) and the formation of oligomers leads to synaptic damage and neurodegeneration. Therefore, strategies for treatment development have been focused on reducing Abeta accumulation using, among other approaches, antiaggregation molecules, regulators of the APP proteolysis and processing, reducing APP production (e.g., small-interfering RNA), and increasing Abeta clearance with antibodies, apolipoprotein E and Abeta-degrading enzymes (e.g., neprilysin). The main focus of this review is on novel treatments for AD with a special emphasis on delivering neuroprotective and antiamyloidogenic molecules by gene therapy and by promoting neurogenesis.

Transgenic animal models of neurodegenerative diseases and their application to treatment development

Neurodegenerative disorders of the aging population affect over 5 million people in the US and Europe alone. The common feature is the progressive accumulation of misfolded proteins with the formation of toxic oligomers. Previous studies show that while in Alzheimer's disease (AD) misfolded amyloid-beta protein accumulates both in the intracellular and extracellular space, in Lewy body disease (LBD), Parkinson's disease (PD), Multiple System Atrophy (MSA), Fronto-Temporal dementia (FTD), prion diseases, amyotrophic lateral sclerosis (ALS) and trinucleotide repeat disorders (TNRD), the aggregated proteins accumulate in the plasma membrane and intracellularly. Protein misfolding and accumulation is the result of an altered balance between protein synthesis, aggregation rate and clearance. Based on these studies, considerable advances have been made in the past years in developing novel experimental models of neurodegenerative disorders. This has been in part driven by the identification of genetic mutations associated with familial forms of these conditions and gene polymorphisms associated with the more common sporadic variants of these diseases. Transgenic and knock out rodents and Drosophila as well as viral vector driven models of Alzheimer's disease (AD), PD, Huntington's disease (HD) and others have been developed, however the focus for this review will be on rodent models of AD, FTD, PD/LBD, and MSA. Promising therapeutic results have been obtained utilizing amyloid precursor protein (APP) transgenic (tg) models of AD to develop therapies including use of inhibitors of the APP-processing enzymes beta- and gamma-secretase as well as vaccine therapies.

Escalating dose-multiple binge methamphetamine exposure results in degeneration of the neocortex and limbic system in the rat

Abuse of stimulant drugs such as methamphetamine (METH) and cocaine has been associated with long-lasting persistent behavioral alterations. Although METH-induced changes in the striatal dopaminergic system might play a role in these effects, the potential underlying neuroanatomical substrate for the chronic cognitive dysfunction in METH users is unclear. To investigate the involvement of non-dopaminergic systems in the neurotoxic effects of METH, we treated rats with an escalating dose-multiple binge regimen, which we have suggested may more closely simulate human METH exposure profiles. Combined neuropathological and stereological analyses showed that 30 days after the last binge, there was shrinkage and degeneration in the pyramidal cell layers of the frontal cortex and in the hippocampal CA3 region. Further immunocytochemical analysis showed that METH exposure resulted in loss of calbindin interneurons in the neocortex and selective damage to pyramidal neurons in the CA3 region of the hippocampus and granular cells in the dentate gyrus that was accompanied by microglial activation. Taken together, these studies suggest that selective degeneration of pyramidal neurons and interneurons in the neocortex and limbic system might be involved in the cognitive alterations in METH users.

Dynamics of alpha-synuclein aggregation and inhibition of pore-like oligomer development by beta-synuclein

Accumulation of alpha-synuclein resulting in the formation of oligomers and protofibrils has been linked to Parkinson's disease and Lewy body dementia. In contrast, beta-synuclein (beta-syn), a close homologue, does not aggregate and reduces alpha-synuclein (alpha-syn)-related pathology. Although considerable information is available about the conformation of alpha-syn at the initial and end stages of fibrillation, less is known about the dynamic process of alpha-syn conversion to oligomers and how interactions with antiaggregation chaperones such as beta-synuclein might occur. Molecular modeling and molecular dynamics simulations based on the micelle-derived structure of alpha-syn showed that alpha-syn homodimers can adopt nonpropagating (head-to-tail) and propagating (head-to-head) conformations. Propagating alpha-syn dimers on the membrane incorporate additional alpha-syn molecules, leading to the formation of pentamers and hexamers forming a ring-like structure. In contrast, beta-syn dimers do not propagate and block the aggregation of alpha-syn into ring-like oligomers. Under in vitro cell-free conditions, alpha-syn aggregates formed ring-like structures that were disrupted by beta-syn. Similarly, cells expressing alpha-syn displayed increased ion current activity consistent with the formation of Zn(2+)-sensitive nonselective cation channels. These results support the contention that in Parkinson's disease and Lewy body dementia, alpha-syn oligomers on the membrane might form pore-like structures, and that the beneficial effects of beta-synuclein might be related to its ability to block the formation of pore-like structures.

Pathogenesis of hepatitis C virus coinfection in the brains of patients infected with HIV

Involvement of the nervous system by human immunodeficiency virus (HIV) continues to be a serious problem. Among individuals with HIV who have a history of illicit drug use, those coinfected with hepatitis C virus (HCV) are a fast-growing population. However, few studies have assessed the penetration of HCV into the central nervous system (CNS) and its clinical and neuropathological impacts on HIV-infected individuals. For this purpose, the distribution of HCV was investigated in the brains of patients infected with HIV. The presence of HCV RNA in the CNS as detected by nested polymerase chain reaction was associated with a history of methamphetamine use, considerable antemortem cognitive impairment and abundant astrogliosis, and less-severe HIV encephalitis. HCV antigens were detected by immunoblot analysis, using heparin-purified brain samples, and HCV immunoreactivity was detected in astrocytes and in macrophage-microglial cells. The results support the hypothesis that HCV traffics into the HIV-infected brain, where it might lead to a productive coinfection associated with cognitive impairment.

Effects of Cerebrolysin on neurogenesis in an APP transgenic model of Alzheimer's disease

Cerebrolysin (CBL) is a peptide mixture with neurotrophic effects that might reduce the neurodegenerative alterations in Alzheimer's disease (AD). We have previously shown that in the amyloid precursor protein (APP) transgenic (tg) mouse model of AD, CBL improves synaptic plasticity and behavioral performance. However, the mechanisms are not completely clear. The neuroprotective effects of CBL might be related to its ability to promote neurogenesis in the hippocampal subgranular zone (SGZ) of the dentate gyrus (DG). To study this possibility, tg mice expressing mutant APP under the Thy-1 promoter were injected with BrdU and treated with CBL for 1 and 3 months. Compared to non-tg controls, vehicle-treated APP tg mice showed decreased numbers of BrdU-positive (+) and doublecortin+ (DCX) neural progenitor cells (NPC) in the SGZ. In contrast, APP tg mice treated with CBL showed a significant increase in BrdU+ cells, DCX+ neuroblasts and a decrease in TUNEL+ and activated caspase-3 immunoreactive NPC. CBL did not change the number of proliferating cell nuclear antigen+ (PCNA) NPC or the ratio of BrdU+ cells converting to neurons and astroglia in the SGZ cells in the APP tg mice. Taken together, these studies suggest that CBL might rescue the alterations in neurogenesis in APP tg mice by protecting NPC and decreasing the rate of apoptosis. The improved neurogenesis in the hippocampus of CBL-treated APP tg mice might play an important role in enhancing synaptic formation and memory acquisition.

Neuroprotective effects of regulators of the glycogen synthase kinase-3beta signaling pathway in a transgenic model of Alzheimer's disease are associated with reduced amyloid precursor protein phosphorylation

The glycogen synthase kinase-3beta (GSK3beta) pathway plays an important role in mediating neuronal fate and synaptic plasticity. In Alzheimer's disease (AD), abnormal activation of this pathway might play an important role in neurodegeneration, and compounds such as lithium that modulate GSK3beta activity have been shown to reduce amyloid production and tau phosphorylation in amyloid precursor protein (APP) transgenic (tg) mice. However, it is unclear whether regulation of GSK3beta is neuroprotective in APP tg mice. In this context, the main objective of the present study was to determine whether pharmacological or genetic manipulations that block the GSK3beta pathway might ameliorate the neurodegenerative alterations in APP tg mice and to better understand the mechanisms involved. For this purpose, two sets of experiments were performed. First, tg mice expressing mutant human APP under the Thy1 promoter (hAPP tg) were treated with either lithium chloride or saline alone. Second, hAPP tg mice were crossed with GSK3beta tg mice, in which overexpression of this signaling molecule results in a dominant-negative (DN) effect with inhibition of activity. hAPP tg mice that were treated with lithium or that were crossed with DN-GSK3beta tg mice displayed improved performance in the water maze, preservation of the dendritic structure in the frontal cortex and hippocampus, and decreased tau phosphorylation. Moreover, reduced activation of GSK3beta was associated with decreased levels of APP phosphorylation that resulted in decreased amyloid-beta production. In conclusion, the present study showed that modulation of the GSK3beta signaling pathway might also have neuroprotective effects in tg mice by regulating APP maturation and processing and further supports the notion that GSK3beta might be a suitable target for the treatment of AD.

Deficiency in neuronal TGF-beta signaling promotes neurodegeneration and Alzheimer's pathology

Alzheimer's disease (AD) is characterized by progressive neurodegeneration and cerebral accumulation of the beta-amyloid peptide (Abeta), but it is unknown what makes neurons susceptible to degeneration. We report that the TGF-beta type II receptor (TbetaRII) is mainly expressed by neurons, and that TbetaRII levels are reduced in human AD brain and correlate with pathological hallmarks of the disease. Reducing neuronal TGF-beta signaling in mice resulted in age-dependent neurodegeneration and promoted Abeta accumulation and dendritic loss in a mouse model of AD. In cultured cells, reduced TGF-beta signaling caused neuronal degeneration and resulted in increased levels of secreted Abeta and beta-secretase-cleaved soluble amyloid precursor protein. These results show that reduced neuronal TGF-beta signaling increases age-dependent neurodegeneration and AD-like disease in vivo. Increasing neuronal TGF-beta signaling may thus reduce neurodegeneration and be beneficial in AD.

Cognitive deficits and degeneration of interneurons in HIV+ methamphetamine users

The cellular basis for cognitive deficits in HIV+ patients with and without a history of methamphetamine (METH) use is unclear. We found that HIV+ METH users had more severe loss of interneurons that was associated with cognitive impairment. Compared with other markers, loss of calbindin and parvalbumin interneurons in the frontal cortex was the most significant correlate to memory deficits, suggesting a role in neurobehavioral alterations of HIV+ METH users.

Synaptic remodeling during aging and in Alzheimer's disease

Cognitive functioning is dependent on synapse density in the brain. Factors modulating synapse density might include the balance between synaptic pruning and sprouting. Loss of synapses during aging might explain cognitive decline and while previous reports have suggested a 10-15% synapse loss occurs during the normal aging process, more recent studies have found that decline in synaptic density only occurs after 65 years of age. In this context, the main objective of this manuscript is to discuss the findings of our 1993 study in light of more recent studies in aging, synapses and Alzheimer's disease.

Cerebrolysin decreases amyloid-beta production by regulating amyloid protein precursor maturation in a transgenic model of Alzheimer's disease

Cerebrolysin is a peptide mixture with neurotrophic effects that might reduce the neurodegenerative pathology in Alzheimer's disease (AD). We have previously shown in an amyloid protein precursor (APP) transgenic (tg) mouse model of AD-like neuropathology that Cerebrolysin ameliorates behavioral deficits, is neuroprotective, and decreases amyloid burden; however, the mechanisms involved are not completely clear. Cerebrolysin might reduce amyloid deposition by regulating amyloid-beta (Abeta) degradation or by modulating APP expression, maturation, or processing. To investigate these possibilities, APP tg mice were treated for 6 months with Cerebrolysin and analyzed in the water maze, followed by RNA, immunoblot, and confocal microscopy analysis of full-length (FL) APP and its fragments, beta-secretase (BACE1), and Abeta-degrading enzymes [neprilysin (Nep) and insulin-degrading enzyme (IDE)]. Consistent with previous studies, Cerebrolysin ameliorated the performance deficits in the spatial learning portion of the water maze and reduced the synaptic pathology and amyloid burden in the brains of APP tg mice. These effects were associated with reduced levels of FL APP and APP C-terminal fragments, but levels of BACE1, Notch1, Nep, and IDE were unchanged. In contrast, levels of active cyclin-dependent kinase-5 (CDK5) and glycogen synthase kinase-3beta [GSK-3beta; but not stress-activated protein kinase-1 (SAPK1)], kinases that phosphorylate APP, were reduced. Furthermore, Cerebrolysin reduced the levels of phosphorylated APP and the accumulation of APP in the neuritic processes. Taken together, these results suggest that Cerebrolysin might reduce AD-like pathology in the APP tg mice by regulating APP maturation and transport to sites where Abeta protein is generated. This study clarifies the mechanisms through which Cerebrolysin might reduce Abeta production and deposition in AD and further supports the importance of this compound in the potential treatment of early AD.

Astroglial activation of extracellular-regulated kinase in early stages of Alzheimer disease

Characterization of the earliest neuropathologic features of Alzheimer disease (AD) indicates that synaptic degeneration accompanied by tau hyperphosphorylation and amyloid deposition might be an important feature. The mechanisms involved are unclear; however, dysregulation of signaling cascades such as the extracellular signal-regulated kinase (ERK) pathway might play a role. In this context, the main objective of this study was to determine whether ERK hyperactivation occurs in early stages of AD. We compared the patterns of total and phosphorylated ERK (pERK) expression in the midfrontal cortex of patients clinically and neuropathologically characterized with early, intermediate, or advanced AD. Immunocytochemical and Western blot analysis showed that in early AD, there was extensive activation of ERK in astroglial cells in the white matter accompanied by intense astrogliosis. In contrast, in patients with more advanced AD, pERK immunoreactivity was associated with neuronal cell bodies and dystrophic neurites around plaques. Levels of astroglial pERK immunoreactivity in the white matter were strongly correlated with scores of cognitive performance (Blessed, Mini-Mental Status Examination, and Clinical Dementia Rating) and with the severity of AD neuropathology (Braak stage). These findings suggest that astroglial ERK activation may be an important early response to the onset of AD pathology. Identification of cell signaling events unique to early AD may provide therapeutic targets for the prevention or delay of dementia.

Neurological and neurodegenerative alterations in a transgenic mouse model expressing human alpha-synuclein under oligodendrocyte promoter: implications for multiple system atrophy

Multiple system atrophy (MSA) is a progressive, neurodegenerative disease characterized by parkinsonism, ataxia, autonomic dysfunction, and accumulation of alpha-synuclein (alpha-syn) in oligodendrocytes. To better understand the mechanisms of neurodegeneration and the role of alpha-syn accumulation in oligodendrocytes in the pathogenesis of MSA, we generated transgenic mouse lines expressing human (h) alpha-syn under the control of the murine myelin basic protein promoter. Transgenic mice expressing high levels of halpha-syn displayed severe neurological alterations and died prematurely at 6 months of age. Furthermore, mice developed progressive accumulation of halpha-syn-immunoreactive inclusions in oligodendrocytes along the axonal tracts in the brainstem, basal ganglia, cerebellum, corpus callosum, and neocortex. The inclusions also reacted with antibodies against phospho-serine (129) halpha-syn and ubiquitin, and halpha-syn was found in the detergent-insoluble fraction. In high-expresser lines, the white matter tracts displayed intense astrogliosis, myelin pallor, and decreased neurofilament immunostaining. Accumulation of halpha-syn in oligodendrocytes also leads to prominent neurodegenerative changes in the neocortex with decreased dendritic density and to loss of dopaminergic fibers in the basal ganglia. The oligodendrocytic inclusions were composed of fibrils and accompanied by mitochondrial alterations and disruption of the myelin lamina in the axons. Together, these studies support the contention that accumulation of alpha-syn in oligodendrocytes promotes neurodegeneration and recapitulates several of the key functional and neuropathological features of MSA.

Abeta vaccination effects on plaque pathology in the absence of encephalitis in Alzheimer disease

The authors report a patient with Alzheimer disease (AD) without encephalitis who was immunized with AN-1792 (an adjuvanted formulation of Abeta-42). There were no amyloid plaques in the frontal cortex and abundant Abeta-immunoreactive macrophages, but tangles and amyloid angiopathy were present. The white matter appeared normal and minimal lymphocytic infiltration in the leptomeninges was observed. This case illustrates the effects of an Abeta-based immunization on AD pathogenesis in the absence of overt meningoencephalitis and leukoencephalopathy.