Generation and characterization of two transgenic mouse lines expressing human ApoE2 in neurons and glial cells

Enhanced neuronal plasticity and elevated endogenous sAPPα levels in mice over-expressing MMP9

Evidence accumulating during the past few years points to a significant role of matrix metalloproteinase 9 (MMP9) enzymatic activity in synaptic plasticity and cognitive processes. We have previously demonstrated that MMP9 is involved in receptor-mediated α-secretase-like cleavage of APP in vitro, resulting in increased secretion of sAPPα, the soluble N-terminal product of the non-amyloidogenic pathway known to be involved in neuronal plasticity and memory formation. To study the in vivo role of MMP9, we have generated transgenic mice over-expressing MMP9 in the brain. Herein, we demonstrate that MMP9 transgenic animals display enhanced performance in the non-spatial novel object recognition and the spatial water-maze task and that their enhanced performance was accompanied by increased dendritic spine density in the hippocampus and cortex following behavioural testing. Consistent with the above observations, the electrophysiological analysis revealed prolonged maintenance of long-term synaptic potentiation in hippocampal slices from MMP9 transgenic mice. Moreover, elevated sAPPα levels in the hippocampus and cortex of MPP9 transgenic animals were also observed. Overall, our results extend previous findings on the physiological role of MMP9 in neuronal plasticity and furthermore reveal that, APP may be one of the physiological proteolytic targets of MMP9 in vivo.

Scavenger receptor class B type I (SR-BI) regulates perivascular macrophages and modifies amyloid pathology in an Alzheimer mouse model

Scavenger receptor class B type I (SR-BI) is a high-density lipoprotein receptor that regulates cholesterol efflux from the peripheral tissues to the liver. SR-BI has been identified on astrocytes and vascular smooth muscle cells in Alzheimer's disease brain and has been shown to mediate adhesion of microglia to fibrillar amyloid-β (Aβ). Here we report that SR-BI mediates perivascular macrophage response and regulates Aβ-related pathology and cerebral amyloid angiopathy in an Alzheimer's mouse model. Reduction or deletion of SR-BI gene in heterozygous or homozygous deficient mice (SR-BI(+/-), (-/-)) resulted in a significant increase in perivascular macrophages in the brain. SR-BI deletion had no effect on apolipoprotein E or apolipoprotein AI levels in the mouse brain. Our analysis revealed increased levels of SR-BI expression in the brains of human amyloid precursor protein (Swedish, Indiana) transgenic mice (J20 line). To evaluate the role of SR-BI in Alzheimer's disease pathogenesis, we inactivated one SR-BI allele in J20 transgenic mice. SR-BI reduction in J20/SR-BI(+/-) mice enhanced fibrillar amyloid deposition and cerebral amyloid angiopathy and also exacerbated learning and memory deficits compared with J20 littermates. Immunohistochemical analysis revealed localization of SR-BI on perivascular macrophages in tight association with Aβ deposits. Our data suggest that SR-BI reduction impairs the response of perivascular macrophages to Aβ and enhances the Aβ-related phenotype and cerebral amyloid angiopathy in J20 mice. These results reveal that SR-BI, a scavenger receptor primarily involved in high-density lipoprotein cholesterol transport, plays an essential role in Alzheimer's disease and cerebral amyloid angiopathy.

ApoE isoform affects LTP in human targeted replacement mice

Inheritance of the epsilon4 allele for apolipoprotein E (apoE) increases the risk of Alzheimer disease and memory impairment, whereas epsilon2 decreases these risks compared with the most common epsilon3 allele, but the mechanism for these effects is unknown. Long-term potentiation (LTP) is an experimentally induced increase in synaptic efficacy that models memory. Using hippocampal slices from wild type (WT), apoE knockout (apoE-KO), and targeted replacement mice expressing human apoE2, E3, or E4 (apoE-TR) we found that although all strains had comparable basal synaptic transmission, LTP was significantly greater in WT and apoE3-TR than in apoE-KO, apoE2-TR or apoE4-TR. This novel system may be used to investigate the mechanisms of apoE isoform dependent modulation of susceptibility to memory impairment.

CMV enhancer/human PDGF-beta promoter for neuron-specific transgene expression

Using cell-type-specific promoters to restrict expression of therapeutic genes to particular cells is an attractive approach for gene therapy, but often hindered by inefficient transcriptional activities of the promoters. Knowing the enhancer for the human cytomegalovirus (CMV) immediate-early gene improves activities of several cell-type- or tissue-type-specific promoters, we set out to investigate whether it improves neuronal transgene expression driven by a neuron-specific promoter, the platelet-derived growth factor B-chain (PDGF-beta) promoter. A hybrid promoter was constructed by appending a 380-bp fragment of the CMV enhancer 5' to the PDGF-beta promoter. The plasmid containing the promoter was complexed with polyethylenimine for in vitro and in vivo gene transfer. In cultured cells, the plasmid with the hybrid promoter significantly augmented expression of a luciferase reporter gene, providing expression levels 8- to 90-fold and 7- to 178-fold higher than those from two baseline constructs containing the PDGF-beta promoter alone and the CMV enhancer alone, respectively. In particular, the activities of the hybrid promoter in two neural cell lines were close to or higher than that of the CMV immediate-early gene enhancer/promoter, a transcriptional control element that has been considered to be the most robust one identified thus far. After stereotaxic injection into the hippocampus and striatum in rats, the hybrid promoter displayed a neuronal specificity, driving gene expression almost exclusively in neurons. Transgene expression in the brain driven by the hybrid promoter was detectable 24 h after injection, being 10-fold higher than that driven by the PDGF-beta promoter alone. The expression peaked around 5 days at 1.5 x 10(5) relative light units per brain and lasted for at least 4 weeks. This differed strikingly from the expression driven by the PDGF-beta promoter, which was no longer detectable on day 3. The new gene regulatory construct reported in this study will be useful to improve neuronal transgene expression required for gene therapy of neurological disorders and functional studies of the nervous system.