  alzheimer 's disease ( ad ) is a progressive neurodegenerative disorder involving memory dysfunction that is characterized by cerebral amyloid accumulation , which is observed as senile plaques consisting of amyloid -proteins ( a ) ending at the ala or val residues ( a42 and a40 , resp . ) .
although robust a deposition was observed in the postmortem brains of critical ad patients with hippocampal atrophy , the pathological relationship between memory impairment and amyloid pathologies remains unclear .
a is produced from -amyloid precursor protein ( app ) by two proteases , - and -secretases [ 2 , 3 ] .
mutations in the genes for app or two homologous genes , presenilin-1 and -2 ( ps1 and ps2 ) , which produce components of the -secretase complex are linked to familial alzheimer 's disease ( fad ) [ 4 , 5 ] .
fad represents a small percentage ( about 5% ) of ad cases , but the pathology of this disease arises at an unusually young age , as early as the third decade of life , and so is termed early - onset ad .    to understand the pathophysiological relationship between amyloidosis and memory impairment in ad in order to develop effective therapies and preventative measures ( reviews [ 6 , 7 ] ) , fad - linked mutations in app have been produced in mice to provide ad mouse models , such as pdapp , tg2576 , app23 , and tgcrnd8 mice .
these mice typically demonstrate diffuse deposition of amyloid plaques with dystrophic neurites , in addition to inflammatory responses in microgliosis and astroglioses , but no neurofibrillary tangle pathology . the tg2576 mouse line , which expresses the prion promoter - driven human app with the swedish mutation ( appswe , lysasn , and metleu ) has been utilized as a model for ad analyses .
tg2576 mice showed impaired spatial learning and memory in the morris water maze at 6 months of age , when amyloid deposition was not observed in their brain .
typical neuritic plaques appeared in tg2576 mice brain at 7 - 8 months of age .  
many fad pathologic mutations have been reported in the ps1 gene , and transgenic mouse models have been produced by crossbreeding with app mutant mice to clarify the pathological role of the ps1 mutation on app mutant mice , such as ps1tg2576 .
reported that the ps1 mutation accelerated ad - like pathologies with increased a42 production through enhanced -secretase activity in ps1 ( metleu ) and tg2576 double transgenic mice ( ps1tg2576 ) .
in contrast , the fad - linked mutations found in the ps2 gene have been well characterized , including asnile ( n141i , volga german kindred type )   and metval ( m239v , italian fad type ) .
these ps2 mutations also enhance -secretase activity , leading to increased a42 production .    in the present study , to clarify the pathophysiological role of the ps2 ( n141i ) mutation on amyloid formation and memory function in tg2576 mice , we generated double transgenic mice ( ps2tg2576 ) by crossbreeding a ps2 mutant with tg2576 mice .
we show the early onset of ad - like phenotypes in ps2tg2576 mice compared to tg2576 mice .
tg2576 mice ( tg(appswe)2576kha ) , which express human -amyloid precursor proteins ( happ ) containing the k670n and m671l mutations , which are known as the swedish type mutation ( appswe ) , coupled with hamster prion promoter on a 129s6.cg background were purchased from taconic laboratories .
ps2m1 mice , which express human presenilin-2 ( ps2 ) proteins containing the n141i mutation on a c57bl/6jjcl background , were also used .
the ps2 transgene is expressed under control of a ubiquitous caggs promoter consisting of cytomegalovirus early enhancer coupled with chicken -actin promoter .
we crossbred a tg2576 male mouse with ps2 female mice using in vitro fertilization and embryo transfer techniques to generate ps2tg2576 double transgenic mice born on the same day .   
tail tips were dissolved in 700  l of 0.05  n naoh for 45  min at 95c and then suspended in 60  l of 1  m tris - hcl , ph 8.0 .
the suspensions were centrifuged at 20 , 400    g for 10  min at 4c ( mx-100 , tomy ) the resultant supernatants were collected and used as dna templates .
the primers for ps2m1 ( 5-cgg ctc tag agc ctc tgc taa c-3 and 5-ctc tgt gta gaa gcg cac aga c-3 ) and tg2576 ( 5-ctg acc act cga cca ggt tct ggg t-3 and 5-gtg gat aac
ccc tcc ccc agc cta gac ca-3 ) were used to identify each transgenic allele .
pcr was performed using the following conditions : 1 cycle of 94c for 2  min ; 35 cycles of 98c for 10  sec , 60c for 30  sec , and 72c for 1  min ; and 1 cycle of 72c for 5  min .   
all analyses were performed using first generation ( 129b6f1 ) mice at 2 to 11 months of age , and there were four genotypes : wild type , ps2 , tg2576 , and ps2tg2576 .
the animals were housed under a 12-hour light / dark cycle and were allowed ad libitum access to food and water .
the mice were maintained and studied according to the protocols approved by the animal care committee of the tokyo metropolitan institute of gerontology .
mouse brains were collected at each time point ( 2 - 3 , 4 - 5 , 6 - 7 , and 10 - 11 months of age ) after anesthesia and perfusion .
the removed brains were split into two hemispheres , and then one was frozen in liquid nitrogen . the other hemisphere was fixed in 4% paraformaldehyde and embedded in paraffin for the immunohistochemical study . the resultant sections ( 5  m ) were deparaffinized , rehydrated , and washed in phosphate buffered saline ( pbs ) , before being treated briefly with formic acid for 5  min and washed in running water for 15  min in the case of a staining .
after incubation for 30  min in 0.1% hydrogen peroxide in methanol to prevent endogenous peroxidation , the sections were washed in pbs - t ( pbs containing 0.1% tween-20 ) and blocked with 10% normal goat serum in pbs , before being incubated with an anti - a antibody ( 0.5  g / ml 82e1 , a42 and a40 , resp . ,
then , the sections were incubated with biotinylated secondary antibody for 30  min at room temperature .
immunoreactivity was visualized using an abc elite kit according to the manufacturer 's protocol and the sections were then stained for 57  min with 0.2  mg / ml diaminobenzidine and 0.1% hydrogen peroxide in 10  mm tris - hcl ( ph 7.5 ) .
mouse brain tissue ( 0.1 - 0.2  g ) was homogenized in 3 volumes ( w / v ) of tbs ( 50  mm tris - hcl ( ph 7.6 ) containing 150  mm nacl supplemented with 0.7  mg / ml pepstatin a , 1  mm phenylmethylsulfonyl fluoride , and cocktails of protease and phosphatase inhibitors ( complete mini and phosstop , roche diagnostics ) .
the homogenates were centrifuged at 55,000    g for 60  min at 4c using an optima tl ultracentrifuge and a tla-55 rotor ( beckman coulter ) to give the supernatant ( s-55 ) and pellet ( p-55 ) fractions .
the s-55 fraction was centrifuged at 100,000    g for 30  min at 4c , and then the supernatant was collected as a tbs - soluble fraction .
the p-55 fraction was then dissolved by sonication in an equal volume ( v / v ) of 6  m guanidine - hcl ( sigma ) containing a mixture of protease inhibitors ( roche diagnostics ) , followed by centrifugation at 100,000    g for 30  min at 4c .
the supernatant was diluted in a 12-times volume ( v / v ) of tbs to generate a guanidine - soluble fraction .
the guanidine - soluble fraction was then centrifuged at 20,400    g for 10  min at 4c , and the supernatant was collected as a tbs - insoluble fraction .
the total protein concentration of the fractions was determined using the dc protein assay kit ( bio - rad ) , according to the manufacturer 's protocol .
the amounts of a42 and a40 in the tbs - soluble and tbs - insoluble fractions were determined using a sandwich eia kit ( no .
27712 for a42 and 27714 for a40 , ibl ) , according to the manufacturer 's instructions .
all behavior experiments were performed longitudinally . the water maze pool ( muromachi kikai ) , which had a diameter of 120  cm , contained opaque water ( 22  2c ) with a platform ( 10  cm in diameter ) that had been submerged 1.5  cm below the surface .
the hidden platform task took 4 days to perform ( 4 sessions per day , at least 1 hour apart ) .
the platform location remained constant , and the entry points were changed semirandomly between trials .
one day after day 4 of the hidden platform task , a 2-minute probe trial was carried out without the platform . the entry point for the probe trials was the quadrant opposite the target quadrant .
performance was monitored with the compact vas / dv video - tracking system ( muromachi kikai ) .
mouse brain tissue ( approximately 0.2  g ) was homogenized in 5 volumes ( w / v ) of ripa buffer ( 25  mm tris - hcl ( ph 7.5 ) containing 150  mm nacl , 1% np-40 , 1% sodium deoxycholate , and 0.1% sodium dodecyl sulfate ) supplemented with 0.7  mg / ml pepstatin a , 1  mm phenylmethylsulfonyl fluoride , and a mixture of protease and phosphatase inhibitors ( roche diagnostics ) .
the protein concentrations of the brain homogenates were determined using the dc protein assay kit , before they were diluted to 1  mg / ml with ezapply solution ( atto ) , according to the manufacturer 's instructions .    the proteins ( 10 or 20  g / well ) were subjected to a 10%20% gradient tris - tricine gel ( novex , invitrogen ) and transferred to a pvdf membrane ( 0.2  m pore size , immobilon - p , millipore ) .
then , the membranes were blocked in tbs - t ( tbs containing 0.01% tween-20 ) with 2% blocking regent ( ecl advance blocking agent , ge healthcare ) for 1 hour at room temperature .
the membranes were then incubated with anti - app c - termini antibody app(c ) ( 1  g / ml , ibl ) , anti - soluble -cleavage app fragment ( sapp , 5  g / ml , ibl ) , anti - soluble -cleavage appswe fragment ( sappsw , 5  g / ml , ibl ) , and anti - gapdh antibody ( 0.1  g / ml , abd serotec ) for 1 hour at room temperature , before being washed with tbs - t and treated with the secondary antibody ( 1 hour ) . the anti - sapp and sapp antibodies exclusively detect only human sapp and sappsw , respectively , but are not reactive to app full length .
development was performed with enhanced chemiluminescence reagent ( ecl plus , ge healthcare ) and detected using an las-3000 mini ( fujifilm ) .
the antibodies used were anti - a42 ; 1  :  2,000 ( ibl , no . 18582 ) , anti - a40 ; 1  :  2,000 ( ibl , no .
18580 ) , anti - a(n ) ; 1  :  2,000 ( ibl , no .
10323 , clone 82e1 ) , anti - app(c ) ; 1  :  100 ( ibl , no .
18961 ) , anti - sapp ; 1  :  20 ( ibl , no . 11088 , clone 2b3 ) , anti - sapp ; 1  :  20 ( ibl , no . 10321 , clone 6a1 ) and anti - gapdh ; 1  :  3,000 ( abd serotec , no .
the differences among the four groups were analyzed with one - way analysis of variance ( anova ) followed by bonferroni 's test , and p values of < .05 or < .01 on the unpaired t - test or welch 's test were considered statistically significant .
we crossbred a tg2576 mouse with ps2 ( n141i ) mutant mice to generate double transgenic mice .
the ps2tg2576 mutant mice were born at the expected mendelian ratio in males ( 23.0% ) and females ( 28.1% ) and grew without morphological abnormalities . of the male mice ,
three mutant mice showed a significantly low body weight compared to the wild - type mice ( supplementary figure1(a ) available online on doi : 10.1155/2011/617974 ) . in the female mice ,
the ps2tg2576 and tg2576 mice exhibited a significantly low body weight compared to the wild - type and ps2 mice ( supplementary figure1(b ) ) .
however , we failed to detect any differences in food intake ( supplementary figure2(a ) ) , drinking water ( supplementary figure2(b ) ) , or metabolic parameters ( supplementary figures2(c)and 2(d ) ) among the mutant mice .  
to investigate the pathological effect of the familial ps2 ( n141i ) mutation on tg2576 mice , amyloid plaques in the brain sections of the ps2tg2576 mice were immunostained with the 82e1 monoclonal antibody against the n - terminal of a. as shown in figure 1(a ) , amyloid depositions were positively detected in the ps2tg2576 mice at 2 - 3 months of age . at 4 - 5 months
, significant amyloid accumulations were observed in the hippocampus and the cerebral neocortex of the ps2tg2576 mice ( figure 1(b ) ) .
interestingly , the levels of typical senile plaques were dramatically increased in the ps2tg2576 mice at 6 - 7 months of age ( figure 1(c ) ) ; in contrast , no plaques were detected in the brains of the tg2576 mice at 6 - 7 months of age ( figure 1(d ) ) .
furthermore , the amyloid plaques also immunoreacted with antibodies against the c - terminus of a42 ( supplementary figure3 ) or a40 ( supplementary figure4 ) , producing the same staining pattern as seen with the 82e1 antibody .   next , to quantify the amyloid plaques in the neocortex and hippocampus
, we measured the number of plaques in the brain sections by densitometric analysis ( table 1 and figure 2(a ) ) .
the mean plaque number of the ps2tg2576 mice at 2 - 3 months of age was 17.7  2.9 , and it had markedly increased at 4 - 5 months ( 160.3  4.3 ) and 6 - 7 months of age ( 645.7  98.6 ) .
we failed to count any plaques until 6 - 7 months of age in the tg2576 , ps2 , and wild - type mice ( table 1 and figure 2(a ) ) .
in addition , the numbers of a42 and a40 positive - plaques were also increased in the ps2tg2576 mice with the same pattern ( data not shown ) .
these results indicated that ps2tg2576 mice showed significant deposition of robust senile plaques from a young age ( 2 - 3 months of age ) .   
to confirm the results of the immunohistochemical analyses , we measured the concentration of brain a in the tbs - insoluble fraction by specific elisa ( table 1 and figures 2(b ) and 2(c ) ) . in agreement with the plaque numbers ,
the concentrations of a42 and a40 in the ps2tg2576 mice at 2 - 3 months of age were significantly higher ( 4.2  0.4 and 2.9
 0.3  ng / mg protein , resp . ) than those in the tg2576 mice at the same age ( table 1 ) . at 4 - 5 months of age ,
the concentrations of a42 and a40 in the ps2tg2576 mice were dramatically enhanced to 75.2  3.9 and 51.5  4.0  ng / mg protein , respectively , ( table 1 ) . at 6 - 7 months of age , these concentrations in the ps2tg2576 mice were increased to 411.8  19.0 and 380.1  18.5  ng / mg protein , respectively ( table 1 ) . in contrast , the tg2576 mice did not show altered levels of insoluble a from 2 - 3 to 6 - 7 months of age .
these results indicated that the early accumulation of insoluble a occurs in ps2tg2576 mice and that the insoluble a burden was consistent with the results of the immunohistochemical analyses ( figure 2 and table 1 ) .    in the tbs - soluble fraction ,
no difference in the levels of a42 and a40 was detected in the ps2tg2576 mice at 2 - 3 months of age ( table 1 ) . at 4 - 5 months of age
, the concentration of a42 in the ps2tg2576 mice was detected to be 2.9  0.6  pg / mg protein ( table 1 ) . at 6 - 7 months of age ,
the concentrations of a42 and a40 in the ps2tg2576 mice were significantly higher ( 7.1  0.7 and 151.4  11.8 pg / mg protein , resp . ) than those in the tg2576 mice at the same age ( table 1 ) .  
we used the morris water maze   to examine whether the presence of a ps2 mutant transgene leads to the exacerbation of spatial learning and memory dysfunctions in tg2576 mice .
the mouse cohorts with approximately equal numbers of males and females were repeatedly tested at 4 - 5 and 6 - 7 months of age in a longitudinal study .
males and females separately had tendencies similar to the gender - mixed results in the behavioral tests ( data not shown ) . at 4 - 5 months of age ,
the latency in each group was approximately 30  sec at day 4 ( figure 3(a ) ) . in the probe trial , only the ps2tg2576 mice demonstrated a significantly low score with regard to the number of crossings over the removed - platform as a narrow range analysis ( unpaired t - test , p < .01 versus tg2576 mice and p < .05 versus wild - type mice , figures 3(b ) and 3(d ) ) and the percentage of time spent in the target quadrant as a broad range analysis ( unpaired t - test , p < .05 versus tg2576 mice and p < .01 versus wild - type mice , figures 3(c ) and 3(d ) ) .   at 6 - 7
months of age , only the ps2tg2576 mice showed a significant typical delay at day 3 and day 4 on the training task ( one - way anova and unpaired t - test versus wild - type mice , p < .01 , figure 4(a ) ) .
in contrast , the tg2576 , ps2 , and wild - type mice learned to locate the platform during training and quickly achieved the goal ( figure 4(a ) ) . in the probe trial ,
the ps2tg2576 mice showed significantly lower scores than the wild - type mice with regard to the number of crossings ( unpaired t - test , p < .05 , figures 4(b ) and 4(d ) ) and the time spent in the target quadrant ( unpaired t - test , p < .01 , figures 4(c ) and 4(d ) ) .
the tg2576 mice also showed significantly lower scores compared with the wild - type mice with regard to the time spent in the target quadrant ( unpaired t - test , p < .05 , figures 4(c ) and 4(d ) ) , indicating that memory impairment progressed in the tg2576 mice according to age as previously described elsewhere .
these results indicated that the ps2 ( n141i ) mutation significantly accelerates a-dependent spatial learning and memory dysfunction in tg2576 mice .   
next , we performed other behavioral tests under the placidity home cage , y maze , elevated plus maze , and open field protocols , because tg2576 mice showed abnormal activities and behaviors even before a deposition .
locomotive activity was monitored by infrared sensors in the home cage . at 6 - 7 months of age ,
the tg2576 and ps2tg2576 mice showed significantly higher activity in the dark phase compared to the ps2 and wild - type mice ( supplementary figure5 ) .
the same activities were observed in the tg2576 and ps2tg2576 mice at 2 - 3 and 4 - 5 months of age ( data not shown ) . to investigate cognitive function , we analyzed spontaneous alternation using the y maze .
our tg2576 and ps2tg2576 mice also made fewer alternations in course than the ps2 and wild - type mice from 2 - 3 months of age ( supplementaryfigure  6 ) .
the elevated plus maze test showed that the tg2576 and ps2tg2576 mice presented with significantly lower scores compared to the ps2 and wild - type mice with regard to the number of entries to open arms as well as the percentage of time spent in open arms ( supplementary figure  7 ) .
lastly , in the open field exploration , we observed no difference among any of the mice ( supplementary figure  8) . taken together , these results indicated that both ps2tg2576 and tg2576 mice showed abnormal behaviors in an a-independent manner from 2 - 3 months of age . to investigate whether the ps2 ( n141i ) mutation enhances the cleavage of app in tg2576 mice , we examined the levels of app processing by western blotting analyses using antibodies against the c - terminal ends of full - length app and soluble app fragments ( figure 5(a ) ) .
the low molecular weight bands for the app c - terminal fragments were consistent with the 13-kda -cleavage fragment ( -ctf ) and the 10-kda -cleavage fragment ( -ctf ) by their apparent molecular mass ( figure 5(b ) ) .
these bands were slightly increased in the brain extracts of ps2tg2576 compared with tg2576 mice . to confirm the enhancement of - and -cleavages of app in the ps2tg2576 mouse brains
, we next examined the levels of app n - terminus fragments ( sapp ) by a western blotting analysis using anti - sapp and sapp antibodies .
these antibodies specifically recognize the c - terminus of human sapp and sapp , respectively .
the bands corresponding to sapp and sapp were observed in the tg2576 and ps2tg2576 mice ( figures 5(c ) and 5(d ) ) .
both sapp bands in the ps2tg2576 mice were also upregulated compared with those in the tg2576 mice , indicating that the - and -cleavage activities against app were upregulated in the ps2tg2576 mice . in addition , the app full - length band was slightly enhanced by the ps2 mutation in tg2576 mice ( figure 5(a ) ) , suggesting that holo - app proteins were upregulated or stabilized in the ps2tg2576 mouse brain .
these results suggest that the hyperaccumulation of cerebral a in the ps2tg2576 mice was induced by the modulation of app processing in the brains of these mice .
survival plots for male and female mice of each genotype were produced using kaplan - meier survival curves , and statistical significance was calculated using the original method of the log - rank test ( figure 6 ) . in males ,
the ps2tg2576 and tg2576 mice gradually died from day 70 to day 294 , but this was not the case for the wild - type or ps2 mice , except for accidental deaths attributed to fighting . in females ,
the tg2576 and ps2tg2576 mice had significantly shortened life spans compared with the wild - type and ps2 mice ( p < .05 ) . at 132 days of age , the ps2tg2576 female mice showed a significant life span extension compared with the tg2576 mice ( p < .05 ) .
in the present study , we showed that a ps2 mutant accelerated ad - like phenotypes such as a deposition and memory impairment .
since the formation of a42 aggregates occurs faster than that of a40 in vitro and increased a42 production accelerates a accumulation in senile plaques , insoluble a42 hyperaccumulation in ps2tg2576 mice ( figure 2(b ) ) suggests that a42 hyperproduction induces plaque formation in the brain .
it has been reported that the ps2 ( n141i ) mutation upregulates the ratio of a42 to a40 by abnormal -secretase activity in cultured cells and transgenic mice [ 23 , 24 ] .
unexpectedly , the ps2tg2576 mice showed enhancement of both a42 and a40 including sapp as well as -ctf ( figures 2(b ) and 2(c ) , and table 1 ) , indicating the modification of app processing , such as - and -cleavage .
in addition , the ps2tg2576 mice showed increased holo - app protein expression ( figure 5(a ) ) , suggesting that the ps2 mutation upregulates or stabilizes app proteins , leading to enhancement of app processing with increased substrate availability .
interestingly , the ps2tg2576 mice also exhibited the modification of -cleavage of app , such as sapp and -ctf ( figures 5(b ) and 5(c ) ) , suggesting that increased substrate availability of app induced the upregulation of -cleavage .
further studies are needed to clarify the molecular mechanism underlying the - and -cleavage activation and app upregulation or stabilization induced by the ps2 mutation .  
next , we focused on whether early spatial learning and memory disorders were accelerated in ps2tg2576 mice .
although errors were generally seen in the water maze task in the tg2576 mice without amyloid plaques at 6 months of age , the ps2 mutation accelerated error - prone exploration by at least 2 months in the tg2576 mice ( figures 3 and 4 ) . since amyloid plaque hyper - deposition was observed at 4 - 5 months of age , we consider that insoluble a hyperaccumulation induced early memory impairment in the ps2tg2576 mice .   
recently , saura reported that leukocytes and inflammatory mediators were elevated in the sera of ps conditional double knockout mice on an ad model background , suggesting that genetic inactivation of ps conferred neuronal impairments caused by the inflammatory reaction .
de strooper also reported that fad - linked ps1 or ps2 mutations , including ps2 ( n141i ) , altered the app cleavage pattern , leading to an increase of a -ctf stubble while there was a decrease in the app intracellular domain ( aicd ) , notch intracellular domain ( nicd ) , and erbb4 intracellular domain ( eicd ) .
although we failed to detect the aicd band by an anti - app c - terminal antibody ( figure 5(b ) ) , the depletion of icds caused by the ps2 mutation might accelerate neuronal impairments due to the inflammatory response via intracellular signaling through aicd , notch , or erbb4 in tg2576 mice .   intriguingly , the ps2tg2576 mice also exhibited earlier onset of ad - like phenotypes compared to those of the ps1tg2576   or ps2app   double transgenic mice , which were other models of presenilin and app double transgenic mice .
furthermore , previous reports of ps1tg2576 and ps2app mice also suggest that the onset of plaque formation ( at 5 and 6 months of age , resp . ) was present before the task errors in the water maze occurred at 8 and 15 - 16 months of age , respectively , ( table 2 ) .
although we can not explain why the ps2tg2576 mice showed earlier onset of amyloid formation and memory impairment compared to ps1tg2576 and ps2app mice , some genetic modifiers might affect a metabolism and memory function in ps2tg2576 mice .   
interestingly , the levels of insoluble a42 and a40 in the brains of the ps2tg2576 mice at 4 - 5 months of age were consistent with the values observed in a human fad patient with the ps2 ( n141i ) mutation ( table 1 ) .
the values of these factors observed in an fad patient with the ps2 ( n141i ) mutation were 6.7 and 1.5  ng / mg wet weight , respectively , in a previous paper by maarouf et al . .
when the concentrations of a42 and a40 in the ps2tg2576 mice at 4 - 5 months of age were converted to ng per mg wet weight of mouse brain , they were found to have values of 1.9  0.1 and 1.3  0.1  ng / mg wet weight , respectively .
the insoluble a burden in the ps2tg2576 mouse brain was therefore consistent with that found in an fad case involving a ps2 ( n141i ) mutation .
this data suggests that the ad - like pathology of ps2tg2576 mice is similar to human fad pathology .
recently , noninvasive methods of visualizing amyloid depositions in human brains using positron emission tomography have been developed .
imaging agents against amyloid fibrils such as n - c methyl-2-(4-methylaminophenyl)-6-hydroxybenzothiazole ( c - pib ) can be detected in typical ad patients and model mice . by applying this in vivo imaging system to our ps2tg2576 mice
, we would be able to validate interventional protocols such as amyloid - lowering therapies .
in conclusion , we have demonstrated that ps2tg2576 mice consistently develop an early - onset and rapidly progressive ad - like cerebral -amyloidosis .
we have also shown that ps2 mutation induces early insoluble amyloid accumulation and memory impairment in tg2576 mice , a mouse model of ad . based on the phenotypic characteristics of the mouse line , we suggest that ps2tg2576 is a suitable mouse model for studying amyloid - lowering therapies and presumably also for validating new target candidates .
 in order to clarify the pathophysiological role of presenilin-2 ( ps2 ) carrying the volga german kindred mutation ( n141i ) in a conventional mouse model of alzheimer 's disease ( ad ) expressing amyloid precursor protein ( app ) with the swedish mutation ( tg2576 line ) , we generated a double transgenic mouse ( ps2tg2576 ) by crossbreeding the ps2 mutant with tg2576 mice . here , we demonstrate that the ps2 mutation induced the early deposition of amyloid -protein ( a ) at 2 - 3 months of age and progressive accumulation at 4 - 5 months of age in the brains of the mutant mice . 
 the ps2 mutation also accelerated learning and memory impairment associated with a accumulation at 4 - 5 months of age in tg2576 mice . 
 these results suggest that the ps2 mutation causes early cerebral amyloid accumulation and memory dysfunction . 
 ps2tg2576 mice are a suitable mouse model for studying amyloid - lowering therapies . 
1. Introduction
2. Materials and Methods
3. Results
4. Discussion
5. Conclusions