Lindsay C. Reese

Amyloid-β oligomers impair fear conditioned memory in a calcineurin-dependent fashion in mice

Soluble oligomeric aggregates of the amyloid‐β (Aβ) peptide are believed to be the most neurotoxic Aβ species affecting the brain in Alzheimer disease (AD), a terminal neurodegenerative disorder involving severe cognitive decline underscored by initial synaptic dysfunction and later extensive neuronal death in the CNS. Recent evidence indicates that Aβ oligomers are recruited at the synapse, oppose expression of long‐term potentiation (LTP), perturb intracellular calcium balance, disrupt dendritic spines, and induce memory deficits. However, the molecular mechanisms behind these outcomes are only partially understood; achieving such insight is necessary for the comprehension of Aβ‐mediated neuronal dysfunction. We have investigated the role of the phosphatase calcineurin (CaN) in these pathological processes of AD. CaN is especially abundant in the CNS, where it is involved in synaptic activity, LTP, and memory function. Here, we describe how oligomeric Aβ treatment causes memory deficits and depresses LTP expression in a CaN‐dependent fashion. Mice given a single intracerebroventricular injection of Aβ oligomers exhibited increased CaN activity and decreased pCREB, a transcription factor involved in proper synaptic function, accompanied by decreased memory in a fear conditioning task. These effects were reversed by treatment with the CaN inhibitor FK506. We further found that expression of hippocampal LTP in acutely cultured rodent brain slices was opposed by Aβ oligomers and that this effect was also reversed by FK506. Collectively, these results indicate that CaN activation may play a central role in mediating synaptic and memory disruption induced by acute oligomeric Aβ treatment in mice.

Selective induction of calcineurin activity and signaling by oligomeric amyloid beta

Alzheimers disease (AD) is a terminal age‐associated dementia characterized by early synaptic dysfunction and late neurodegeneration. Although the presence of plaques of fibrillar aggregates of the amyloid beta peptide (Aβ) is a signature of AD, evidence suggests that the preplaque small oligomeric Aβ promotes both synaptic dysfunction and neuronal death. We found that young Tg2576 transgenic mice, which accumulate Aβ and develop cognitive impairments prior to plaque deposition, have high central nervous system (CNS) activity of calcineurin (CaN), a phosphatase involved in negative regulation of memory function via inactivation of the transcription factor cAMP responsive element binding proteins (CREB), and display CaN‐dependent memory deficits. These results thus suggested the involvement of prefibrillary forms of Aβ. To investigate this issue, we compared the effect of monomeric, oligomeric, and fibrillar Aβ on CaN activity, CaN‐dependent pCREB and phosphorylated Bcl‐2 Associated death Protein (pBAD) levels, and cell death in SY5Y cells and in rat brain slices, and determined the role of CaN on CREB phosphorylation in the CNS of Tg2576 mice. Our results show that oligomeric Aβ specifically induces CaN activity and promotes CaN‐dependent CREB and Bcl‐2 Asociated death Protein (BAD) dephosphorylation and cell death. Furthermore, Tg2576 mice display Aβ oligomers and reduced pCREB in the CNS, which is normalized by CaN inhibition. These findings suggest a role for CaN in mediating effects of oligomeric Aβ on neural cells. Because elevated CaN levels have been reported in the CNS of cognitively impaired aged rodents, our results further suggest that abnormal CaN hyperactivity may be a common event exacerbating the cognitive and neurodegenerative impact of oligomeric Aβ in the aging CNS.

α-Synuclein oligomers oppose long-term potentiation and impair memory through a calcineurin-dependent mechanism: relevance to human synucleopathic diseases.

J. Neurochem. (2012) 120, 440–452.

A Role for Calcineurin in Alzheimer’s Disease

Alzheimer’s disease (AD) is an incurable age-related neurodegenerative disorder characterized by profound memory dysfunction. This bellwether symptom suggests involvement of the hippocampus -- a brain region responsible for memory formation -- and coincidentally an area heavily burdened by hyperphosphorylated tau and neuritic plaques of amyloid beta (Aβ). Recent evidence suggests that pre-fibrillar soluble Aβ underlies an early, progressive loss of synapses that is a hallmark of AD. One of the downstream effects of soluble Aβ aggregates is the activation of the phosphatase calcineurin (CaN). This review details the evidence of CaN hyperactivity in ‘normal’ aging, models of AD, and actual disease pathogenesis; elaborates on how this could manifest as memory impairment, neuroinflammation, hyperphosphorylated tau, and neuronal death.

Absence of amyloid β oligomers at the postsynapse and regulated synaptic Zn2+in cognitively intact aged individuals with Alzheimer's disease neuropathology

BackgroundEarly cognitive impairment in Alzheimer Disease (AD) is thought to result from the dysfunctional effect of amyloid beta (Aβ) oligomers targeting the synapses. Some individuals, however, escape cognitive decline despite the presence of the neuropathologic features of AD (Aβ plaques and neurofibrillary tangles). We term this group Non-Demented with AD Neuropathology or NDAN. The present study illustrates one putative resistance mechanism involved in NDAN cases which may suggest targets for the effective treatment of AD.ResultsHere we describe the localization of Aβ oligomers at the postsynapse in hippocampi from AD cases. Notably, however, we also found that while present in soluble fractions, Aβ oligomers are absent from hippocampal postsynapses in NDAN cases. In addition, levels of phosphorylated (active) CREB, a transcription factor important for synaptic plasticity, are normal in NDAN individuals, suggesting that their synapses are functionally intact. Analysis of Zn2+ showed that levels were increased in both soluble fractions and synaptic vesicles in AD hippocampi, paralleled by a decrease of expression of the synaptic vesicle Zn2+ transporter, ZnT3. Conversely, in NDAN individuals, levels of Zn2+ in soluble fractions were significantly lower than in AD, whereas in synaptic vesicles the levels of Zn2+ were similar to AD, but accompanied by preserved expression of the ZnT3.ConclusionsTaken together, these data illustrate that despite substantial AD neuropathology, Aβ oligomers, and increased synaptic vesicle Zn2+, susceptible brain tissue in these aged NDAN individuals features, as compared to symptomatic AD subjects, significantly lower total Zn2+ levels and no association of Aβ oligomers with the postsynapse, which collectively may promote the maintenance of intact cognitive function.

Neuropathologic basis of white matter hyperintensity accumulation

cohort ranging from cognitively-normal elderly (NC) to Alzheimer’s Disease dementia (AD), over 3 years. Methods: 174 participants were studied at entry from the Australian Imaging, Biomarkers and Lifestyle Study of Ageing (AIBL) with 3T SWI MRI and 11C-PiB PET. 120 (79 NC, 23 with Mild Cognitive Impairment (MCI) and 18 AD) returned for imaging at 18 months or 3 years. Images were inspected for microbleeds and infarction, blind to clinical and PiB findings. White matter hyperintensity (WMH) volume was quantified from FLAIR images using a semi-automated algorithm. PiB binding was treated as both a continuous variable (SUVR) and dichotomized as previously published (PiB+/-). All regression analyses were adjusted for age and gender. Results: LMB were present at baseline in 28% of NC, 34% of MCI and 44% of AD patients. The prevalence was 53% in PiB+ NC and 16% in PiBNC. The mean incidence rate of LMB was significantly different between NC (0.18 LMB/year), MCI (0.28) and AD (1.04 LMB/year). In NC, it was 0.38 for PiB+ and 0.09 for PiB(P<0.01). Baseline LMB were associated with age (OR 1.1, 95% C.I.1.01.2) and SUVR (OR 4.8, 95% C.I.1.5-14.8) in NC participants, and with SUVR (OR 3.6, 95% C.I.1.2-10.3), male gender (OR 7.9, 95% C.I.2.328.1) and WMH volume (OR 1.1, 95%C.I. 1.0-1.1) in MCI and AD. For NC, LMB incidence rate was associated with SUVR and the presence of baseline lacunes, while for AD and MCI patients, LMB incidence was associated with WMH volume and of baseline lacunes. Conclusions: Incidence of lobarmicrobleeds is associated with Ab-burden andmarkers of small vessel disease.

Amyloid-beta Oligomers are Excluded From the Post-synapses in the Hippocampus of Cognitively Intact Individuals with Severe Alzheimer's Disease Nuropathology

genotype, 34/34 or 33/33, differed between pairs. Adjacent sections from each pair were stained using two LCPs/LCOs: pentamer formyl thiophene acetic acid (pFTAA) and polythiophene acetic acid (PTAA). Fluorescence spectra from tissue sections were recorded with an LSM 510 META confocal laser scanning microscope, and spectral processing was achieved with an LSM Image browser. Results: Using PTAA, we observed that AD patients with 34/34 exhibited a different conformational spectrum for core and cerebrovascular amyloid whereas their respective matched 33/33 pair exhibited indistinguishable conformational spectra between the two amyloid structures. pFTAA, sensitive for different conformations for Ab and NFTs, revealed NFT densities in 34/34 AD patients that were apparently greater than those in 33/33 AD patients. Conclusions: The observation that PTAA core amyloid and cerebrovascular amyloid spectra distinguish the amyloid deposits of APOE 34/34 from APOE 33/33 AD patients supports the hypothesis that APOE genotype modulates amyloid structure. pFTAA holds promise as an especially sensitive reagent for visualizing NFTs. LCOs/LCPs show great potential as research tools for the study of proteinopathies, including the pathogenesis of sporadic AD and possibly the influence of APOE genotype.

Altered phosphorylation of calcium/calmodulin activated kinase II in Alzheimer hippocampi

each case being the summation of subregional scores. Results: PIN1-immunopositive granules were present in 62% of the total study population, including 100% of AD, 79% of PD and DLB, 67% of PSP and CBD, 15% of FTLD, and 18% of MND cases. The higher frequency of PIN1 in AD and lower frequency in FTLD and MND resulted in a significant frequency difference between groups (p < 0.001). Mean PIN1 overall severity scores (AD 1⁄4 9.2, PD/DLB 1⁄4 2.6, PSP/CBD 1⁄4 3.5, FTLD 1⁄4 0.5 and MND 1⁄4 0.8) were significantly different across all groups (P PD/DLB and PSP/CBD > FTLD/ MND. In addition, subregional hippocampal distribution of PIN1 differed hierarchically but in similar fashion in AD, PD/DLB and PSP/CBD indicating that the distribution of PIN1 pathology parallels that of AD in these disorders. There was, however, only a weak correlation between hippocampal NFTs and PIN1 in PD (rs 1⁄4 0.34, p 1⁄4 0.028). These might represent concurrent, though independent, pathological processes. PIN1 pathology did not relate to the pattern of TDP-43 ((TAR)-DNA-binding protein) pathology in PD cases bearing that additional pathological change. Conclusions: PIN1 plays a pivotal role in the pathology of AD, and in other neurodegenerative disorders where additional AD pathological changes are present.

Alpha-synuclein oligomers induce calcineurin-dependent neurotoxicity and memory deficits

Background: Parkinson Disease (PD) is a terminal neurodegenerative disorders characterized by motor, autonomic and cognitive deficits and second only to Alzheimer Disease (AD) for population incidence. Like the pathological significance of aggregation of amyloid beta (Ab) in AD, the misfolding and aggregation into amyloid fibrils of the protein alpha synuclein (aSyn) is a pathologic signature of the PD brain. While recent evidece suggests that, rather than fibrils, pre-fibrillar small oligomeric aSyn aggregates are the most toxic species, the mechanism of action of aSyn oligomers remains elusive. Our previous studies, however, showed that calcineurin (CaN), a protein phosphatase involved in neuronal death and memory function, mediates neurotoxicity of Ab oligomers, which are structurally similar to aSyn oligomers. On this basis, here we investigated the role of CaN in the neurodysfunctional effects elicited by aSyn oligomers. Methods: The effect of monomeric, oligomeric and fibrillar aSyn on neuronal death, long term potentiation (LTP) and memory function were determined in in vitro, ex vivo and in vivo experimental models as a function of CaN activity and CaN-dependent signaling. Results: We found that oligomeric aSyn, but not monomeric or fibrillar aSyn, induced CaN activity and CaN-dependent cell death in human neuroblastoma cells, increased CaN activity and thus suppressed expression of LTP in brain slices and promoted CaN-dependent memory deficits after acute icv injection in mice. Furthermore, we found that transgenic mice overexpressing mutant aSyn had increased CaN activity in their brain as compared to wt control. Conclusions: These results suggest that activation of CaN may be a central mechanism mediating the neurodysfunctional effects of aSyn oligomers. These results further suggest that pre-fibrillar oligomeric assemblies of Ab and aSyn may share a common neuropathological mechanism of action. Supported by grants from the NIH/ NINDS (NS053986) and from the UTMB Mitchell Center for Neurodegenerative Diseases to GT.