Recent evidence implicates exosomes in the aggregation of A␤ and spreading of tau in Alzheimer's disease. In neural cells, exosome formation can be blocked by inhibition or silencing of neutral sphingomyelinase-2 (nSMase2). We generated genetically nSMase2-deficient 5XFAD mice ( fro;5XFAD) to assess AD-related pathology in a mouse model with consistently reduced ceramide generation. We conducted in vitro assays to assess A␤ 42 aggregation and glial clearance with and without exosomes isolated by ultracentrifugation and determined exosome-induced amyloid aggregation by particle counting. We analyzed brain exosome content, amyloid plaque formation, neuronal degeneration, sphingolipid, A␤ 42 and phospho-tau levels, and memory-related behaviors in 5XFAD versus fro;5XFAD mice using contextual and cued fear conditioning. Astrocyte-derived exosomes accelerated aggregation of A␤ 42 and blocked glial clearance of A␤ 42 in vitro. A␤ 42 aggregates were colocalized with extracellular ceramide in vitro using a bifunctional ceramide analog preloaded into exosomes and in vivo using anticeramide IgG, implicating ceramide-enriched exosomes in plaque formation. Compared with 5XFAD mice, the fro;5XFAD mice had reduced brain exosomes, ceramide levels, serum anticeramide IgG, glial activation, total A␤ 42 and plaque burden, tau phosphorylation, and improved cognition in a fear-conditioned learning task. Ceramide-enriched exosomes appear to exacerbate AD-related brain pathology by promoting the aggregation of A␤. Reduction of exosome secretion by nSMase2 loss of function improves pathology and cognition in the 5XFAD mouse model.

Aberrant amyloid-β peptide (Aβ) accumulation along with altered expression and function of nicotinic acetylcholine receptors (nAChRs) stand prominently in the etiology of Alzheimer's disease (AD). Since the discovery that Aβ is bound to α7 nAChRs under many experimental settings, including post-mortem AD brain, much effort has been expended to understand the implications of this interaction in the disease milieu. This research update will review the current literature on the α7 nAChR-Aβ interaction in vitro and in vivo, the functional consequences of this interaction from sub-cellular to cognitive levels, and discuss the implications these relationships might have for AD therapies.

Early Alzheimer's disease (AD) is marked by cholinergic hypofunction, neuronal marker loss, and decreased nicotinic acetylcholine receptor (nAChR) density from the cortex and hippocampus. ␣7 nAChRs expressed on cholinergic projection neurons and target regions have been implicated in neuroprotection against ␤-amyloid (A␤) toxicity and maintenance of the septohippocampal phenotype. We tested the role that ␣7 nAChRs perform in the etiology of early AD by genetically deleting the ␣7 nAChR subunit from the Tg2576 mouse model for AD and assessing animals for cognitive function and septohippocampal integrity. Thus, Tg2576 mice transgenic for mutant human amyloid precursor protein (APP) were crossed with ␣7 nAChR knock-out mice (A7KO) to render an animal with elevated A␤ in the absence of ␣7 nAChRs (A7KO-APP). We found that learning and memory deficits seen in 5-month-old APP mice are more severe in the A7KO-APP animals. Analyses of animals in early-stage preplaque cognitive decline revealed signs of neurodegeneration in A7KO-APP hippocampus as well as loss of cholinergic functionality in the basal forebrain and hippocampus. These changes occurred concomitant with the appearance of a dodecameric oligomer of A␤ that was absent from all other genotypic groups, generating the hypothesis that increased soluble oligomeric A␤ may underlie additional impairment of A7KO-APP cognitive function. Thus, ␣7 nAChRs in a mouse model for early-stage AD appear to serve a neuroprotective role through maintenance of the septohippocampal cholinergic phenotype and preservation of hippocampal integrity possibly through influences on A␤ accumulation and oligomerization.

Transcription is a critical component for consolidation of long-term memory. However, relatively few transcriptional mechanisms have been identified for the regulation of gene expression in memory formation. In the current study, we investigated the activity of one specific member of the NF-B transcription factor family, c-Rel, during memory consolidation. We found that contextual fear conditioning elicited a time-dependent increase in nuclear c-Rel levels in area CA1 and DG of hippocampus. These results suggest that c-rel is active in regulating transcription during memory consolidation. To identify the functional role of c-Rel in memory formation, we characterized c-rel −/− mice in several behavioral tasks. c-rel −/− mice displayed significant deficits in freezing behavior 24 h after training for contextual fear conditioning but showed normal freezing behavior in cued fear conditioning and in short-term contextual fear conditioning. In a novel object recognition test, wild-type littermate mice exhibited a significant preference for a novel object, but c-rel −/− mice did not. These results indicate that c-rel −/− mice have impaired hippocampus-dependent memory formation. To investigate the role of c-Rel in long-term synaptic plasticity, baseline synaptic transmission and long-term potentiation (LTP) at Schaffer collateral synapses in c-rel −/− mice was assessed. c-rel −/− slices had normal baseline synaptic transmission but exhibited significantly less LTP than did wild-type littermate slices. Together, our results demonstrate that c-Rel is necessary for long-term synaptic potentiation in vitro and hippocampus-dependent memory formation in vivo.Memory is a process through which learned information is stored, and newly formed memories are susceptible to disruption and must be stabilized for long-term storage through a process referred to as memory consolidation (McGaugh 2000). Consolidation of explicit long-term memory requires a series of hippocampus-dependent molecular processes, including gene transcription. The necessity for gene transcription to sustain longterm memory has been demonstrated in several animal models using transcription inhibitors (Thut and Lindell 1974;Kandel 2001). However, the identity and role of transcriptional mediators in long-term memory formation has yet to be fully addressed. So far, a relatively few transcription factors such as CREB, C/EBP, c-fos, and Zif268/egr-1 have been implicated in the consolidation of long-term memory (Yin et al. 1995;Jones et al. 2001;Chen et al. 2003;Fleischmann et al. 2003). Therefore in a previous study, we identified a list of candidate transcription factors that are potentially involved in the process of long-term memory consolidation using expression array profiling and a bioinformatics approach (Levenson et al. 2004a). Through these studies, the c-Rel transcription factor was identified as the most probable candidate for contributing to memory consolidation from among this novel list of transcription factors, because its DNA-binding motif is highly ...

Microalbuminuria (MA) and proteinuria (P) are believed to be precursors of sickle cell nephropathy. We analyzed our longitudinal data on MA/P in children with sickle cell disease (SS) to define the age of onset, association with age, sex, and hemoglobin, and to explore the safety and efficacy of hydroxyurea and angiotensin converting enzyme inhibitor (ACEI) therapy. Data on 191 patients with SS (ages 3 to 20 y) with a mean follow up of 2.19 years+/-2.05 were available. Urine MA was measured yearly with follow-up testing if abnormal. Prevalence of MA/P was 19.4%. Increasing age and lower hemoglobin levels were related to MA/P but sex was not. Microalbumin excretion normalized in 44% of patients treated with hydroxyurea and 56% of patients treated with ACEI. Hyperkalemia developed in 4 ACEI patients resulting in discontinuation of treatment in 3 children. In summary, MA/P often develops in childhood and preventive and treatment strategies for sickle cell nephropathy should be a focus of pediatric programs. Our preliminary data suggest that although both hydroxyurea and ACEI therapy may be beneficial for MA/P, hyperkalemia may limit the utility of ACEI.