Amyloid-ß/Fyn-induced synaptic, network, and cognitive impairments depend on tau levels in multiple mouse models of Alzheimer's disease.

Alzheimer's disease (AD), the most common neurodegenerative disorder, is a growing public health problem and still lacks effective treatments. Recent evidence suggests that microtubule-associated protein tau may mediate amyloid-ß peptide (Aß) toxicity by modulating the tyrosine kinase Fyn. We showed previously that tau reduction prevents, and Fyn overexpression exacerbates, cognitive deficits in human amyloid precursor protein (hAPP) transgenic mice overexpressing Aß. However, the mechanisms by which Aß, tau, and Fyn cooperate in AD-related pathogenesis remain to be fully elucidated. Here we examined the synaptic and network effects of this pathogenic triad. Tau reduction prevented cognitive decline induced by synergistic effects of Aß and Fyn. Tau reduction also prevented synaptic transmission and plasticity deficits in hAPP mice. Using electroencephalography to examine network effects, we found that tau reduction prevented spontaneous epileptiform activity in multiple lines of hAPP mice. Tau reduction also reduced the severity of spontaneous and chemically induced seizures in mice overexpressing both Aß and Fyn. To better understand these protective effects, we recorded whole-cell currents in acute hippocampal slices from hAPP mice with and without tau. hAPP mice with tau had increased spontaneous and evoked excitatory currents, reduced inhibitory currents, and NMDA receptor dysfunction. Tau reduction increased inhibitory currents and normalized excitation/inhibition balance and NMDA receptor-mediated currents in hAPP mice. Our results indicate that Aß, tau, and Fyn jointly impair synaptic and network function and suggest that disrupting the copathogenic relationship between these factors could be of therapeutic benefit.

Aggressive amyloidosis in mice expressing human amyloid peptides with the Arctic mutation.

The Arctic mutation within the amyloid-beta (Abeta) peptide causes Alzheimer disease. In vitro, Arctic-mutant Abeta forms (proto)fibrils more effectively than wild-type Abeta. We generated transgenic mouse lines expressing Arctic-mutant human amyloid precursor proteins (hAPP). Amyloid plaques formed faster and were more extensive in Arctic mice than in hAPP mice expressing wild-type Abeta, even though Arctic mice had lower Abeta(1-42/1-40) ratios. Thus, the Arctic mutation is highly amyloidogenic in vivo.

Adult mouse astrocytes degrade amyloid-beta in vitro and in situ.

Alzheimer disease (AD) is a progressive neurodegenerative disorder characterized by excessive deposition of amyloid-beta (Abeta) peptides in the brain. One of the earliest neuropathological changes in AD is the accumulation of astrocytes at sites of Abeta deposition, but the cause or significance of this cellular response is unclear. Here we show that cultured adult mouse astrocytes migrate in response to monocyte chemoattractant protein-1 (MCP-1), a chemokine present in AD lesions, and cease migration upon interaction with immobilized Abeta(1-42). We also show that astrocytes bind and degrade Abeta(1-42). Astrocytes plated on Abeta-laden brain sections from a mouse model of AD associate with the Abeta deposits and reduce overall Abeta levels in these sections. Our results suggest a novel mechanism for the accumulation of astrocytes around Abeta deposits, indicate a direct role for astrocytes in degradation of Abeta and implicate deficits in astroglial clearance of Abeta in the pathogenesis of AD. Treatments that increase removal of Abeta by astrocytes may therefore be a critical mechanism to reduce the neurodegeneration associated with AD.

Trophic factors GDNF and BDNF improve function of retinal sheet transplants.

The aim of this study was to compare glial-derived neurotrophic factor (GDNF) treatment with brain-derived neurotrophic factor (BDNF) treatment of retinal transplants on restoration of visual responses in the superior colliculus (SC) of the S334ter line 3 rat model of rapid retinal degeneration (RD). RD rats (age 4-6 weeks) received subretinal transplants of intact sheets of fetal retina expressing the marker human placental alkaline phosphatase (hPAP). Experimental groups included: (1) untreated retinal sheet transplants, (2) GDNF-treated transplants, (3) BDNF-treated transplants, (4) none surgical, age-matched RD rats, (5) sham surgery RD controls, (6) progenitor cortex transplant RD controls, and (7) normal pigmented rat controls. At 2-8 months after transplantation, multi-unit visual responses were recorded from the SC using a 40 ms full-field stimulus (-5.9 to +1 log cd/m(2)) after overnight dark-adaptation. Responses were analyzed for light thresholds, spike counts, response latencies, and location within the SC. Transplants were grouped into laminated or rosetted (more disorganized) transplants based on histological analysis. Visual stimulation of control RD rats evoked no responses. In RD rats with retinal transplants, a small area of the SC corresponding to the position of the transplant in the host retina, responded to light stimulation between -4.5 and -0.08 log cd/m(2), whereas the light threshold of normal rats was at or below -5 log cd/m(2) all over the SC. Overall, responses in the SC in rats with laminated transplants had lower response thresholds and were distributed over a wider area than rats with rosetted transplants. BDNF treatment improved responses (spike counts, light thresholds and responsive areas) of rats with laminated transplants whereas GDNF treatment improved responses from rats with both laminated and rosetted (more disorganized) transplants. In conclusion, treatment of retinal transplants with GDNF and BDNF improved the restoration of visual responses in RD rats; and GDNF appears to exert greater overall restoration than BDNF.

Reduction in mitochondrial superoxide dismutase modulates Alzheimer's disease-like pathology and accelerates the onset of behavioral changes in human amyloid precursor protein transgenic mice.

Alzheimer's disease (AD) is associated with accumulations of amyloid-beta (Abeta) peptides, oxidative damage, mitochondrial dysfunction, neurodegeneration, and dementia. The mitochondrial antioxidant manganese superoxide dismutase-2 (Sod2) might protect against these alterations. To test this hypothesis, we inactivated one Sod2 allele (Sod2(+/-)) in human amyloid precursor protein (hAPP) transgenic mice, reducing Sod2 activity to approximately 50% of that in Sod2 wild-type (Sod2(+/+)) mice. A reduction in Sod2 activity did not obviously impair mice without hAPP/Abeta expression. In hAPP mice, however, it accelerated the onset of behavioral alterations and of deficits in prepulse inhibition of acoustic startle, a measure of sensorimotor gating. In these mice, it also worsened hAPP/Abeta-dependent depletion of microtubule-associated protein 2, a marker of neuronal dendrites. Sod2 reduction decreased amyloid plaques in the brain parenchyma but promoted the development of cerebrovascular amyloidosis, gliosis, and plaque-independent neuritic dystrophy. Sod2 reduction also increased the DNA binding activity of the transcription factor nuclear factor kappaB. These results suggest that Sod2 protects the aging brain against hAPP/Abeta-induced impairments. Whereas reductions in Sod2 would be expected to trigger or exacerbate neuronal and vascular pathology in AD, increasing Sod2 activity might be of therapeutic benefit.

Tumor-specific chromosome mis-segregation controls cancer plasticity by maintaining tumor heterogeneity.

Aneuploidy with chromosome instability is a cancer hallmark. We studied chromosome 7 (Chr7) copy number variation (CNV) in gliomas and in primary cultures derived from them. We found tumor heterogeneity with cells having Chr7-CNV commonly occurs in gliomas, with a higher percentage of cells in high-grade gliomas carrying more than 2 copies of Chr7, as compared to low-grade gliomas. Interestingly, all Chr7-aneuploid cell types in the parental culture of established glioma cell lines reappeared in single-cell-derived subcultures. We then characterized the biology of three syngeneic glioma cultures dominated by different Chr7-aneuploid cell types. We found phenotypic divergence for cells following Chr7 mis-segregation, which benefited overall tumor growth in vitro and in vivo. Mathematical modeling suggested the involvement of chromosome instability and interactions among cell subpopulations in restoring the optimal equilibrium of tumor cell types. Both our experimental data and mathematical modeling demonstrated that the complexity of tumor heterogeneity could be enhanced by the existence of chromosomes with structural abnormality, in addition to their mis-segregations. Overall, our findings show, for the first time, the involvement of chromosome instability in maintaining tumor heterogeneity, which underlies the enhanced growth, persistence and treatment resistance of cancers.

Three-dimensional early retinal progenitor 3D tissue constructs derived from human embryonic stem cells.

PURPOSE: To develop three-dimensional (3D) constructs of retinal pigment epithelium (RPE) and early retina progenitor cells from human embryonic stem cells (hESCs). METHODS: 3D tissue constructs were developed by culturing hESC-derived neural retinal progenitors in a matrix on top of hESC-derived RPE cells in a cell culture insert. An osmolarity gradient maintained the nutrition of the 3D cell constructs. Cross-sections through hESC-derived tissue constructs were characterized by immunohistochemistry for various transcription factors and cell markers. RESULTS: hESC-derived tissue constructs expressed transcription factors characteristic of retinal development, such as pax6, Otx2, Chx10, retinal RAX; Brn3b (necessary for differentiation of retinal ganglion cells); and crx and nrl (role in photoreceptor development). Many cells expressed neuronal markers including nestin, beta-tubulin and microtubule-associated proteins. CONCLUSIONS: This study shows for the first time that 3D early retinal progenitor tissue constructs can be derived from hESCs.

Three-dimensional optical coherence tomography imaging of retinal sheet implants in live rats.

PURPOSE: To obtain three-dimensional images from retinal transplants in live animals and evaluate the placement and structural quality of the transplants. METHODS: Donor retinal sheets were isolated from E19 fetuses of transgenic rats expressing human alkaline phosphatase (hPAP), and transplanted to the subretinal space of 19-56 days old S334ter-3 rat recipients with fast retinal degeneration (average age at surgery 32 days). A total of 143 rats were imaged 1 day to 2.8 months after surgery, using a Fourier-domain optical coherence tomography (FDOCT) system, with an axial resolution of 3.5 microm. The CCD A-line integration time was set at 200 micros for better visualization of degenerated retina. After targeting the transplant area, 139 or 199 consecutive slices were scanned. Projection images and movies of the retinal transplant area were computed and later compared with histology. RESULTS: OCT scans identified 137 of 141 transplants as a thickening of the degenerated retina. OCT indicated the laminar structure of the transplants and surgical defects, such as RPE/choroid damage with an accuracy rate between 83 and 99%. Three-dimensional projections showed the transplant position in the retina in relation to the optic disc. Histology of transplants by hPAP and hematoxylin-eosin staining was correlated with the OCT results. CONCLUSIONS: Optical coherence tomography is an excellent tool to image retinal layers in a live rat. This procedure helps to evaluate the placement and quality of the transplants in the living eye.

Reducing endogenous tau ameliorates amyloid beta-induced deficits in an Alzheimer's disease mouse model.

Many potential treatments for Alzheimer's disease target amyloid-beta peptides (Abeta), which are widely presumed to cause the disease. The microtubule-associated protein tau is also involved in the disease, but it is unclear whether treatments aimed at tau could block Abeta-induced cognitive impairments. Here, we found that reducing endogenous tau levels prevented behavioral deficits in transgenic mice expressing human amyloid precursor protein, without altering their high Abeta levels. Tau reduction also protected both transgenic and nontransgenic mice against excitotoxicity. Thus, tau reduction can block Abeta- and excitotoxin-induced neuronal dysfunction and may represent an effective strategy for treating Alzheimer's disease and related conditions.

Prominent neurodegeneration and increased plaque formation in complement-inhibited Alzheimer's mice.

Abnormal accumulation of beta-amyloid (Abeta) in Alzheimer's disease (AD) is associated with prominent brain inflammation. Whereas earlier studies concluded that this inflammation is detrimental, more recent animal data suggest that at least some inflammatory processes may be beneficial and promote Abeta clearance. Consistent with these observations, overproduction of transforming growth factor (TGF)-beta1 resulted in a vigorous microglial activation that was accompanied by at least a 50% reduction in Abeta accumulation in human amyloid precursor protein (hAPP) transgenic mice. In a search for inflammatory mediators associated with this reduced pathology, we found that brain levels of C3, the central component of complement and a key inflammatory protein activated in AD, were markedly higher in hAPP/TGF-beta1 mice than in hAPP mice. To assess the importance of complement in the pathogenesis of AD-like disease in mice, we inhibited C3 activation by expressing soluble complement receptor-related protein y (sCrry), a complement inhibitor, in the brains of hAPP mice. Abeta deposition was 2- to 3-fold higher in 1-year-old hAPP/sCrry mice than in age-matched hAPP mice and was accompanied by a prominent accumulation of degenerating neurons. These results indicate that complement activation products can protect against Abeta-induced neurotoxicity and may reduce the accumulation or promote the clearance of amyloid and degenerating neurons. These findings provide evidence for a role of complement and innate immune responses in AD-like disease in mice and support the concept that certain inflammatory defense mechanisms in the brain may be beneficial in neurodegenerative disease.