Peptides derived from proteolytic processing of the ␤-amyloid precursor protein (APP), including the amyloid-␤ peptide (A␤), play a critical role in the pathogenesis of Alzheimer's dementia. We report that transgenic mice overexpressing APP and A␤ have a profound attenuation in the increase in neocortical blood flow elicited by somatosensory activation. The impairment is highly correlated with brain A␤ concentration and is reproduced in normal mice by topical neocortical application of exogenous A␤1-40 but not A␤1-42. Overexpression of M146L mutant presenilin-1 in APP mice enhances the production of A␤1-42 severalfold, but it does not produce a commensurate attenuation of the hyperemic response. APP and A␤ overexpression do not diminish the intensity of neural activation, as reflected by the increase in somatosensory cortex glucose usage. Thus, A␤-induced alterations in functional hyperemia produce a potentially deleterious mismatch between substrate delivery and energy demands imposed by neural activity.Alzheimer's disease͞␤-amyloid͞cerebral blood flow͞functional activation T he amyloid precursor protein is closely linked to the pathogenesis of Alzheimer's dementia (AD; refs. 1 and 2). Mutations in all three early onset familial AD genes, the amyloid precursor protein (APP), presenilin-1 (PS1), and 2 (PS2), cause elevation of APP-derived A␤ peptides that accumulate in the brain parenchyma and blood vessels (3-5). These observations, collectively, have led to the hypothesis that A␤ peptides are intimately involved in the pathogenesis of AD. Furthermore, transgenic mice overexpressing APP have increased levels of A␤ in brain, and transgenic lines expressing high levels of mutant APP develop some of the pathological and behavioral hallmarks of AD (6).The mechanisms by which A␤ contributes to neuronal dysfunction and neurodegeneration in AD have not been elucidated. Although most studies have focused on the effects of A␤ on neurons, recent evidence suggests that A␤ has profound effects on cerebral blood vessels as well (7-10). Patients with AD have morphological alterations of the cerebral vasculature and reduced cerebral blood flow (CBF), and mice overexpressing APP have a marked impairment in the response of cerebral blood vessels to exogenous vasoactive agents (9-12). However, the impact that these cerebrovascular alterations have on the regulation of the cerebral circulation remains to be defined. Neural activity is one of the major factors regulating CBF (13). Thus, CBF is closely matched to the energy requirements of the brain (14-17). If a brain region is activated, blood flow to that region increases to facilitate local delivery of nutrients and to remove metabolic waste (13). Here we report that APP and A␤ overexpression impairs the increase in neocortical CBF produced by physiological activation of the somatosensory pathway and causes a potentially-deleterious mismatch between blood flow and cerebral energy consumption. MethodsTransgenic Mice. All transgenic lines used in these studies have been described...

Different prion Isolates, often referred to as "strains," present an enigma because considerable evidence argues that prions are devoid of nucleic acid. To investigate prion diversity, we inoculated three "strains" of prions into congenic and transgenic mice harboring variable numbers of two dierent alleles, designated a and b, of the prion protein (rP) structural gene, Prn-p. The length of the incubation time was inversely related to the number of Pm-p genes in mice inoculated with the Rocky Mountain Laboratory (RML) prion strain. Results with mice lacking this locus (Prnpe/) and ransgenic mice argue that long incubation times are not a dominant trait as thought for many years, but rather they are due to reduced levels of the substrate PrPC-A (cellular isoform of PrP, allotype A) in (Prn-p5 x Pvn-pb)Fi mice. In contrast, the Prn-pa gene extended incubation times in mice inoculated with the 87V and 22A prion strains, whereas the Prm-pb gene was permissive. Experiments with the 87V Isolate suggest that a genetic locus distinct from Prn-p controls deposition of the scraple isoform of PrP (Prs) and attendant neuropathology.Each prion isolate produced di hable patterns of PrPsc accumulation in brain; of note, the patterns in Prn-pa and Prn-pb congenic mice inculated with RML prions were more different than those in congenic Prn-9b mice with RML or 22A prions. Our results suggest that scrapie "strain-specific" incubation times can be explained by differences in the relative efficiency of allotypic interactions that lead to conversion of PrPC Into prPsc.

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A large genome-wide, recessive, N-ethyl-N-nitrosourea (ENU)-induced mutagenesis screen was performed on a mixed C57BL/6J and C3H.SW-H2/SnJ mouse background to identify genes regulating bone mass. Approximately 6500 male and female G 3 hybrid mice were phenotyped at 8 and 10 wk of age by DXA analysis for evidence of changes in unadjusted or body weight-adjusted BMD or BMC. Phenodeviant lines were identified based on statistical criteria that included a false discovery rate (FDR) <20% and Z-score >2.8. Genome-wide mapping scans were initiated on 22 lines, with evidence of high or low BMD or BMC that deviated by approximately 230% to +50% from the means. Several lines were discontinued as showing lack of heritability, but two heritable lines were identified with narrow chromosomal regions that allowed sequencing of potential mutant candidate genes. Novel mutations were identified in the Enpp1 (C397S) gene on chromosome 10 (line 4482) and the Ptpn6 (I482F) gene on chromosome 6 (line 4489) that were both associated with low bone mass. In addition, the phenotype of the Enpp1 mice showed a striking joint disease and calcification of blood vessels including the aorta, myocardium, and renal arteries and capillaries. These results support a role for the Enpp1 gene in the pathogenesis associated with mineralization of articular cartilage and vascular calcification. This work confirms the utility of the chemical mutagenesis approach for identification of potential disease genes and confirms the role of Enpp1 and Ptpn6 in regulating mineralization and skeletal bone mass.

Phenotypes produced by expression of human amyloid precursor protein (APP) transgenes vary depending on the genetic background of the mouse. FVB/N mice overexpressing human APP695 develop a central nervous system disorder and die prematurely, precluding development of Abeta peptide amyloid plaques. 129S6 mice are resistant to the lethal effects of APP overexpression, allowing sufficient levels of Abeta expression for the development of amyloid plaques and age-dependent memory deficits. To identify the genes that determine susceptibility or resistance to APP we analyzed crosses involving FVB/NCr and 129S6.Tg2576 mice that overexpress 'Swedish' mutant (K670N, M671L) APP695. APP transgene-positive FVB129S6F1 (F1) mice are resistant to the lethal effects of APP overexpression, so FVBxF1 backcross and F2 intercross offspring were produced. Analysis of age of death as a quantitative trait revealed significant linkage to loci on proximal chromosome 14 and on chromosome 9; 129S6 alleles protect against the lethal effects of APP. Within the chromosome 14 interval are segments homologous to regions on human chromosome 10 that have been linked to late onset Alzheimer's disease or to levels of Abeta peptide in plasma. However, analysis of plasma Abeta peptide concentrations at 6 weeks in backcross offspring produced no significant linkage. Similarly, elevation of human Abeta peptide concentrations by expression of mutant presenilin transgenes did not increase the proportion of mice dying prematurely, suggesting that early death reflects effects of APP or fragments other than Abeta.

Scrapie is a transmissible neurodegenerative disease caused by unusual pathogens called prions. The interval between inoculation and illness for experimental mouse scrapie is dramatically influenced by an incubation time gene (Prn-i) that is linked to Prn-p, the structural gene for prion protein (PrP). Although prion proteins from mouse strains with short and long scrapie incubation times differ by two amino acids, mice with discordant disease phenotype and Prn-p genotype occur in segregating crosses, suggesting recombination between Prn-p and a distinct incubation time locus. In addition, expression of Prn-pb transgenes from long incubation time mice shortened, rather than prolonged, incubation time. In this study, mice carrying chromosomes with meiotic crossovers near Prn-p were analyzed for scrapie incubation time phenotype. The results indicated that Prn-i (should it exist) must lie within an interval 0.67 cM proximal and 0.22 cM distal to Prn-p. The results also suggest that the cumulative effects of other genes, rather than meiotic recombination, were responsible for the putative recombinants of earlier studies. However, the effect of Prn-pb transgene expression in abbreviating scrapie incubation time was mitigated when the transgenes were transferred to mice with an endogenous long incubation time allele. Thus, Prn-pb transgenes and Prn-i may modulate scrapie pathogenesis by different mechanisms.

Mice homozygous for the gray tremor (gt) mutation have a pleiotropic phenotype that includes pigmentation defects, megacolon, whole body tremors, sporadic seizures, hypo- and dysmyelination of the CNS and PNS, vacuolation of the CNS, and early death. Vacuolation similar to that caused by prions was originally reported to be transmissible, but subsequent studies showed the inherited disease was not infectious. The gt mutation mapped to distal mouse chromosome 15, to the same region as Sox10, which encodes a transcription factor with essential roles in neural crest survival and differentiation. As dominant mutations in mouse or human SOX10 cause white spotting and intestinal aganglionosis, we screened the Sox10 coding region for mutations in gt/gt DNA. An adenosine to guanine transversion was identified in exon 2 that changes a highly conserved glutamic acid residue in the SOX10 DNA binding domain to glycine. This mutant allele was not seen in wildtype mice, including the related GT/Le strain, and failed to complement a Sox10 null allele. Gene expression analysis revealed significant down-regulation of genes involved in myelin lipid biosynthesis pathways in gt/gt brains. Knockout mice for some of these genes develop CNS vacuolation and/or myelination defects, suggesting that their down-regulation may contribute to these phenotypes in gt mutants and could underlie the neurological phenotypes associated with Peripheral demyelinating neuropathy-Central dysmyelinating leukodystrophy-Waardenburg syndrome-Hirschsprung (PCWH) disease, caused by mutations in human SOX10.