[F-18]FDDNP microPET imaging correlates with brain Aß burden in a transgenic rat model of Alzheimer disease: effects of aging, in vivo blockade, and anti-Aß antibody treatment.

In vivo detection of Alzheimer's disease (AD) neuropathology in living patients using positron emission tomography (PET) in conjunction with high affinity molecular imaging probes for ß-amyloid (Aß) and tau has the potential to assist with early diagnosis, evaluation of disease progression, and assessment of therapeutic interventions. Animal models of AD are valuable for exploring the in vivo binding of these probes, particularly their selectivity for specific neuropathologies, but prior PET experiments in transgenic mice have yielded conflicting results. In this work, we utilized microPET imaging in a transgenic rat model of brain Aß deposition to assess [F-18]FDDNP binding profiles in relation to age-associated accumulation of neuropathology. Cross-sectional and longitudinal imaging demonstrated that [F-18]FDDNP binding in the hippocampus and frontal cortex progressively increases from 9 to 18months of age and parallels age-associated Aß accumulation. Specificity of in vivo [F-18]FDDNP binding was assessed by naproxen pretreatment, which reversibly blocked [F-18]FDDNP binding to Aß aggregrates. Both [F-18]FDDNP microPET imaging and neuropathological analyses revealed decreased Aß burden after intracranial anti-Aß antibody administration. The combination of this non-invasive imaging method and robust animal model of brain Aß accumulation allows for future longitudinal in vivo assessments of potential therapeutics for AD that target Aß production, aggregation, and/or clearance. These results corroborate previous analyses of [F-18]FDDNP PET imaging in clinical populations.

A transgenic rat model of Alzheimer's disease with extracellular Abeta deposition.

Many transgenic mouse models of Alzheimer's disease (AD) that deposit amyloid (Abeta) have been produced, but development of an Abeta-depositing rat model has not been successful. Here, we describe a rat model with extracellular fibrillar Abeta deposition. Two lines of Sprague Dawley rats with transgenes expressing human amyloid precursor protein (APP) with the familial AD (FAD) mutations K670N/M671L and K670N/M671L/V717I were crossed. Abeta production in the double homozygous rats was sufficient for deposition by 17-18 months of age. The age of onset of Abeta deposition was reduced by crossing in a third rat line carrying a human presenilin-1 (PS-1) transgene with the FAD M146V mutation. The triple homozygous line had an onset of Abeta deposition by 7 months of age. Deposits appeared similar to those observed in the mouse models and displayed surrounding glial and phosphorylated tau reactivity. Abeta levels measured by ELISA were comparable to those reported in mouse models, suggesting that substantially greater amounts of soluble Abeta are not required in the rat to generate Abeta deposition.

Inhibition of mixed lineage kinase 3 attenuates MPP+-induced neurotoxicity in SH-SY5Y cells.

The neuropathology of Parkinson's Disease has been modeled in experimental animals following MPTP treatment and in dopaminergic cells in culture treated with the MPTP neurotoxic metabolite, MPP(+). MPTP through MPP(+) activates the stress-activated c-Jun N-terminal kinase (JNK) pathway in mice and SH-SY5Y neuroblastoma cells. Recently, it was demonstrated that CEP-1347/KT7515 attenuated MPTP-induced nigrostriatal dopaminergic neuron degeneration in mice, as well as MPTP-induced JNK phosphorylation. Presumably, CEP-1347 acts through inhibition of at least one upstream kinase within the mixed lineage kinase (MLK) family since it has been shown to inhibit MLK 1, 2 and 3 in vitro. Activation of the MLK family leads to JNK activation. In this study, the potential role of MLK and the JNK pathway was examined in MPP(+)-induced cell death of differentiated SH-SY5Y cells using CEP-1347 as a pharmacological probe and dominant negative adenoviral constructs to MLKs. CEP-1347 inhibited MPP(+)-induced cell death and the morphological features of apoptosis. CEP-1347 also prevented MPP(+)-induced JNK activation in SH-SY5Y cells. Endogenous MLK 3 expression was demonstrated in SH-SY5Y cells through protein levels and RT-PCR. Adenoviral infection of SH-SY5Y cells with a dominant negative MLK 3 construct attenuated the MPP(+)-mediated increase in activated JNK levels and inhibited neuronal death following MPP(+) addition compared to cultures infected with a control construct. Adenoviral dominant negative constructs of two other MLK family members (MLK 2 and DLK) did not protect against MPP(+)-induced cell death. These studies show that inhibition of the MLK 3/JNK pathway attenuates MPP(+)-mediated SH-SY5Y cell death in culture and supports the mechanism of action of CEP-1347 as an MLK family inhibitor.

FAD mutant PS-1 gene-targeted mice: increased A beta 42 and A beta deposition without APP overproduction.

To investigate the consequences of mutant presenilin-1 (PS-1) expression under the control of the normal PS-1 gene, a gene-targeted mouse bearing the FAD mutation P264L was made. Gene-targeted models are distinct from transgenic models because the mutant gene is expressed at normal levels, in the absence of the wild-type protein. PS-1(P264L/P264L) mice had normal expression of PS-1 mRNA, but levels of the N- and C-terminal protein fragments of PS-1 were reduced while levels of the holoprotein were increased. When crossed into Tg(HuAPP695.K670N/M671L)2576 mice, the PS-1(P264L) mutation accelerated the onset of amyloid (Abeta) deposition in a gene-dosage dependent manner. Tg2576/PS-1(P264L/P264L) mice also had Abeta deposition that was widely distributed throughout the brain and spinal cord. APP(NLh/NLh)/PS-1(P264L/P264L) double gene-targeted mice had elevated levels of Abeta42, sufficient to cause Abeta deposition beginning at 6 months of age. Abeta deposition increased linearly over time in APP(NLh/NLh)/PS-1(P264L/P264L) mice, whereas the increase in Tg2576 mice was exponential. The APP(NLh/NLh)/PS-1(P264L/P264L) double gene-targeted mouse represents an animal model that exhibits Abeta deposition without overexpression of APP.