Multi-input synapses, but not LTP-strengthened synapses, correlate with hippocampal memory storage in aged mice

Long-lasting changes at synapses enable memory storage in the brain. Although aging is associated with impaired memory formation, it is not known whether the synaptic underpinnings of memory storage differ with age. Using a training schedule that results in the same behavioral memory formation in young and aged mice, we examined synapse ultrastructure and molecular signaling in hippocampus after contextual fear conditioning. Only in young, but not old mice contextual fear memory formation was associated with synaptic changes that characterize well-known long-term potentiation,a strengthening of existing synapses with one input. Instead old age memory was correlated with generation of multi-innervated dendritic spines (MIS), which are predominantly two-input synapses formed by the attraction of an additional excitatory, presynaptic terminal onto an existing synapse. Accordingly, a blocker used to inhibit MIS generation impaired contextual fear memory only in old mice. Our results reveal how the synaptic basis of hippocampal memory storage changes with age and they suggest that these distinct memory-storing mechanisms may explain impaired updating in old age

Disruption of endoplasmic reticulum-mitochondria tethering proteins in post-mortem Alzheimer's disease brain

Signaling between the endoplasmic reticulum (ER) and mitochondria regulates a number of key neuronal functions, many of which are perturbed in Alzheimer's disease. Moreover, damage to ER-mitochondria signaling is seen in cell and transgenic models of Alzheimer's disease. However, as yet there is little evidence that ER-mitochondria signaling is altered in human Alzheimer's disease brains. ER-mitochondria signaling is mediated by interactions between the integral ER protein VAPB and the outer mitochondrial membrane protein PTPIP51 which act to recruit and “tether” regions of ER to the mitochondrial surface. The VAPB-PTPIP51 tethers are now known to regulate a number of ER-mitochondria signaling functions including delivery of Ca2+from ER stores to mitochondria, mitochondrial ATP production, autophagy and synaptic activity. Here we investigate the VAPB-PTPIP51 tethers in post-mortem control and Alzheimer's disease brains. Quantification of ER-mitochondria signaling proteins by immunoblotting revealed loss of VAPB and PTPIP51 in cortex but not cerebellum at end-stage Alzheimer's disease. Proximity ligation assays were used to quantify the VAPB-PTPIP51 interaction in temporal cortex pyramidal neurons and cerebellar Purkinje cell neurons in control, Braak stage III-IV (early/mid-dementia) and Braak stage VI (severe dementia) cases. Pyramidal neurons degenerate in Alzheimer's disease whereas Purkinje cells are less affected. These studies revealed that the VAPB-PTPIP51 tethers are disrupted in Braak stage III-IV pyramidal but not Purkinje cell neurons. Thus, we identify a new pathogenic event in post-mortem Alzheimer's disease brains. The implications of our findings for Alzheimer's disease mechanisms are discussed

Region-specific blood-brain barrier transporter changes leads to increased sensitivity to amisulpride in Alzheimer’s disease

BACKGROUND: Research into amisulpride use in Alzheimer’s disease (AD) implicates blood–brain barrier (BBB) dysfunction in antipsychotic sensitivity. Research into BBB transporters has been mainly directed towards the ABC superfamily, however, solute carrier (SLC) function in AD has not been widely studied. This study tests the hypothesis that transporters for organic cations contribute to the BBB delivery of the antipsychotics (amisulpride and haloperidol) and is disrupted in AD. METHODS: The accumulation of [3H]amisulpride (3.7–7.7 nM) and [3H]haloperidol (10 nM) in human (hCMEC/D3) and mouse (bEnd.3) brain endothelial cell lines was explored. Computational approaches examined molecular level interactions of both drugs with the SLC transporters [organic cation transporter 1 (OCT1), plasma membrane monoamine transporter (PMAT) and multi-drug and toxic compound extrusion proteins (MATE1)] and amisulpride with the ABC transporter (P-glycoprotein). The distribution of [3H]amisulpride in wildtype and 3×transgenic AD mice was examined using in situ brain perfusion experiments. Western blots determined transporter expression in mouse and human brain capillaries . RESULTS: In vitro BBB and in silico transporter studies indicated that [3H]amisulpride and [3H]haloperidol were transported by the influx transporter, OCT1, and efflux transporters MATE1 and PMAT. Amisulpride did not have a strong interaction with OCTN1, OCTN2, P-gp, BCRP or MRP and could not be described as a substrate for these transporters. Amisulpride brain uptake was increased in AD mice compared to wildtype mice, but vascular space was unaffected. There were no measurable changes in the expression of MATE1, MATE2, PMAT OCT1, OCT2, OCT3, OCTN1, OCTN2 and P-gp in capillaries isolated from whole brain homogenates from the AD mice compared to wildtype mice. Although, PMAT and MATE1 expression was reduced in capillaries obtained from specific human brain regions (i.e. putamen and caudate) from AD cases (Braak stage V–VI) compared to age matched controls (Braak stage 0–II). CONCLUSIONS: Together our research indicates that the increased sensitivity of individuals with Alzheimer’s to amisulpride is related to previously unreported changes in function and expression of SLC transporters at the BBB (in particular PMAT and MATE1). Dose adjustments may be required for drugs that are substrates of these transporters when prescribing for individuals with AD

Cysteine string protein alpha accumulates with early pre-synaptic dysfunction in Alzheimer's disease.

In Alzheimer's disease, synapse loss causes memory and cognitive impairment. However, the mechanisms underlying synaptic degeneration in Alzheimer's disease are not well understood. In the hippocampus, alterations in the level of cysteine string protein alpha, a molecular co-chaperone at the pre-synaptic terminal, occur prior to reductions in synaptophysin, suggesting that it is a very sensitive marker of synapse degeneration in Alzheimer's. Here, we identify putative extracellular accumulations of cysteine string alpha protein, which are proximal to beta-amyloid deposits in post-mortem human Alzheimer's brain and in the brain of a transgenic mouse model of Alzheimer's disease. Cysteine string protein alpha, at least some of which is phosphorylated at serine 10, accumulates near the core of beta-amyloid deposits and does not co-localize with hyperphosphorylated tau, dystrophic neurites or glial cells. Using super-resolution microscopy and array tomography, cysteine string protein alpha was found to accumulate to a greater extent than other pre-synaptic proteins and at a comparatively great distance from the plaque core. This indicates that cysteine string protein alpha is most sensitive to being released from pre-synapses at low concentrations of beta-amyloid oligomers. Cysteine string protein alpha accumulations were also evident in other neurodegenerative diseases, including some fronto-temporal lobar dementias and Lewy body diseases, but only in the presence of amyloid plaques. Our findings are consistent with suggestions that pre-synapses are affected early in Alzheimer's disease, and they demonstrate that cysteine string protein alpha is a more sensitive marker for early pre-synaptic dysfunction than traditional synaptic markers. We suggest that cysteine string protein alpha should be used as a pathological marker for early synaptic disruption caused by beta-amyloid

Cysteine string protein alpha accumulates with early pre-synaptic dysfunction in Alzheimer’s disease

In Alzheimer’s disease, synapse loss causes memory and cognitive impairment. However, the mechanisms underlying synaptic degeneration in Alzheimer’s disease are not well understood. In the hippocampus, alterations in the level of cysteine string protein alpha, a molecular co-chaperone at the pre-synaptic terminal, occur prior to reductions in synaptophysin, suggesting that it is a very sensitive marker of synapse degeneration in Alzheimer’s. Here, we identify putative extracellular accumulations of cysteine string alpha protein, which are proximal to beta-amyloid deposits in post-mortem human Alzheimer’s brain and in the brain of a transgenic mouse model of Alzheimer’s disease. Cysteine string protein alpha, at least some of which is phosphorylated at serine 10, accumulates near the core of beta-amyloid deposits and does not co-localize with hyperphosphorylated tau, dystrophic neurites or glial cells. Using super-resolution microscopy and array tomography, cysteine string protein alpha was found to accumulate to a greater extent than other pre-synaptic proteins and at a comparatively great distance from the plaque core. This indicates that cysteine string protein alpha is most sensitive to being released from pre-synapses at low concentrations of beta-amyloid oligomers. Cysteine string protein alpha accumulations were also evident in other neurodegenerative diseases, including some fronto-temporal lobar dementias and Lewy body diseases, but only in the presence of amyloid plaques. Our findings are consistent with suggestions that pre-synapses are affected early in Alzheimer’s disease, and they demonstrate that cysteine string protein alpha is a more sensitive marker for early pre-synaptic dysfunction than traditional synaptic markers. We suggest that cysteine string protein alpha should be used as a pathological marker for early synaptic disruption caused by beta-amyloid