Retinoic Acid Attenuates β-Amyloid Deposition and Rescues Memory Deficits in an Alzheimer's Disease Transgenic Mouse Model

ATRA treatment significantly decreased APP processing, measured as production of APP C-terminal fragments (APP-CTFs), in APP/PS1 mice.

“This was accompanied by a significant decrease in the APP phosphorylation and processing.”

• Also stated in: § ATRA prevents APP processing and phosphorylation of both APP and tau, likely through inhibition of CDK5 expression · plain

  “As shown in Figure 2 A (row 1), a significant decrease in the production of APP-CTFs was observed in the ATRA-treated APP/PS1 mice compared with the vehicle-treated APP/PS1 mice.”

• Also stated in: § ATRA prevents APP processing and phosphorylation of both APP and tau, likely through inhibition of CDK5 expression · plain

  “Quantitative analysis showed an ϳ70% reduction in the frontal cortex and a 50% reduction in the hippocampus (Fig. 2 B).”

ATRA treatment significantly reduced the area occupied by Aβ plaques in the frontal cortex and hippocampus compared with vehicle-treated APP/PS1 mice.

“The plaque number, average volume of the plaques, and area occupied by the A␤ plaques were all reduced significantly in both the frontal cortex and hippocampus compared with the vehicle-treated APP/PS1 mice (Fig. 1C,D).”

ATRA-treated APP/PS1 mice showed decreased activation of microglia compared with vehicle-treated APP/PS1 mice.

“The ATRA-treated APP/PS1 mice showed decreased activation of microglia and astrocytes, attenuated neuronal degeneration, and improved spatial learning and memory compared with the vehicle-treated APP/ PS1 mice.”

• Also stated in: § Introduction · plain

  “ATRA treatment of the APP/PS1 mice significantly alleviated glial activation and neuronal loss in the brain and rescued the spatial learning and memory deficits.”

No significant difference in APP expression levels was observed between APP/PS1 mice treated with ATRA and vehicle.

“no significant difference in APP expression levels was observed between the APP/ PS1 mice treated with ATRA and vehicle (Fig. 2 A, row 1).”

Eight weeks of vehicle treatment had no significant effect on Aβ deposition in APP/PS1 mice compared with untreated age- and gender-matched APP/PS1 mice.

“Noticeably, 8 weeks of vehicle treatment had no significant effect on A␤ deposition in APP/PS1 mice compared with the untreated ageand gender-matched APP/PS1 mice (data not shown).”

No significant difference in BACE1 levels was observed between the groups.

“Similarly, we did not observe a significant difference in the levels of BACE1 between the groups (Fig. 2 A, row 2).”

ATRA treatment (20 mg/kg i.p. three times weekly for 8 weeks starting at 5 months) robustly decreased brain Aβ deposition in APP/PS1 transgenic mice in a blinded study.

“Here we report a robust decrease in brain A␤ deposition and tau phosphorylation in the blinded study of APP/PS1 transgenic mice treated intraperitoneally for 8 weeks with ATRA (20 mg/kg, three times weekly, initiated when the mice were 5 months old).”

• Also stated in: § ATRA treatment prevents A␤ plaque accumulation in APP/PS1 mice · boosted

  “The results demonstrated that ATRA treatment significantly attenuated A␤ levels in both the frontal cortex and hippocampus (Fig. 1 A, B).”

• Also stated in: § ATRA treatment prevents A␤ plaque accumulation in APP/PS1 mice · plain

  “Stereological analysis of multiple stained sections also revealed a significant decrease in A␤ deposition.”

ATRA-treated APP/PS1 mice showed attenuated neuronal degeneration compared with vehicle-treated APP/PS1 mice.

“The ATRA-treated APP/PS1 mice showed decreased activation of microglia and astrocytes, attenuated neuronal degeneration, and improved spatial learning and memory compared with the vehicle-treated APP/ PS1 mice.”

• Also stated in: § Introduction · plain

  “ATRA treatment of the APP/PS1 mice significantly alleviated glial activation and neuronal loss in the brain and rescued the spatial learning and memory deficits.”

ATRA treatment markedly downregulated cyclin-dependent kinase 5 (CDK5) activity.

“The activity of cyclin-dependent kinase 5, a major kinase involved in both APP and tau phosphorylation, was markedly downregulated by ATRA treatment.”

ATRA-treated APP/PS1 mice showed decreased activation of astrocytes compared with vehicle-treated APP/PS1 mice.

“The ATRA-treated APP/PS1 mice showed decreased activation of microglia and astrocytes, attenuated neuronal degeneration, and improved spatial learning and memory compared with the vehicle-treated APP/ PS1 mice.”

• Also stated in: § Introduction · plain

  “ATRA treatment of the APP/PS1 mice significantly alleviated glial activation and neuronal loss in the brain and rescued the spatial learning and memory deficits.”

ATRA treatment significantly reduced plaque number in the frontal cortex and hippocampus compared with vehicle-treated APP/PS1 mice.

“The plaque number, average volume of the plaques, and area occupied by the A␤ plaques were all reduced significantly in both the frontal cortex and hippocampus compared with the vehicle-treated APP/PS1 mice (Fig. 1C,D).”

Vehicle-treated APP/PS1 mice did not show a significant difference in production of APP-CTFs compared with untreated age- and gender-matched APP/PS1 mice.

“In contrast, the vehicle-treated APP/PS1 mice did not show a significant difference in the production of CTFs compared with the untreated age-and gender-matched APP/ PS1 mice (data not shown), suggesting a specific inhibitory effect of ATRA on APP processing.”

ATRA treatment (20 mg/kg i.p. three times weekly for 8 weeks starting at 5 months) robustly decreased tau phosphorylation in APP/PS1 transgenic mice in a blinded study.

“Here we report a robust decrease in brain A␤ deposition and tau phosphorylation in the blinded study of APP/PS1 transgenic mice treated intraperitoneally for 8 weeks with ATRA (20 mg/kg, three times weekly, initiated when the mice were 5 months old).”

• Also stated in: § Introduction · plain

  “ATRA effectively reduced A␤ accumulation and tau hyperphosphorylation.”

• Also stated in: § ATRA prevents APP processing and phosphorylation of both APP and tau, likely through inhibition of CDK5 expression · plain

  “except for a slight decrease in the phosphorylation at Ser396, a robust decrease in the tau phosphorylation at Ser235, Ser404, Ser519, and Thr205 was observed in the both the frontal cortex and hippocampus of the ATRA-treated APP/PS1 mice.”

ATRA treatment significantly reduced average plaque volume in the frontal cortex and hippocampus compared with vehicle-treated APP/PS1 mice.

“The plaque number, average volume of the plaques, and area occupied by the A␤ plaques were all reduced significantly in both the frontal cortex and hippocampus compared with the vehicle-treated APP/PS1 mice (Fig. 1C,D).”

ATRA treatment significantly reduced APP phosphorylation at Thr668 in APP/PS1 mice.

“This was accompanied by a significant decrease in the APP phosphorylation and processing.”

• Also stated in: § ATRA prevents APP processing and phosphorylation of both APP and tau, likely through inhibition of CDK5 expression · plain

  “In contrast, the APP phosphorylation was significantly reduced in the ATRA-treated APP/PS1 mice (Fig. 2 A, row 3).”

• Also stated in: § ATRA prevents APP processing and phosphorylation of both APP and tau, likely through inhibition of CDK5 expression · plain

  “Quantitative analysis shows an ϳ70% decrease in the frontal cortex and 60% decrease in the hippocampus in the ATRA-treated APP/PS1 mice compared with the vehicle-treated APP/PS1 mice (Fig. 2C).”

ATRA-treated APP/PS1 mice showed improved spatial learning and memory compared with vehicle-treated APP/PS1 mice.

“The ATRA-treated APP/PS1 mice showed decreased activation of microglia and astrocytes, attenuated neuronal degeneration, and improved spatial learning and memory compared with the vehicle-treated APP/ PS1 mice.”

• Also stated in: § Introduction · plain

  “ATRA treatment of the APP/PS1 mice significantly alleviated glial activation and neuronal loss in the brain and rescued the spatial learning and memory deficits.”

ATRA-treated APP/PS1 mice show a slight increase in tau-1 immunoreactivity.

“A slight increase in the tau-1 immunoreactivity was observed in the ATRA-treated APP/PS1 mice (Fig. 2 A, row 9).”

Elevated levels of p35 observed in vehicle-treated APP/PS1 mice were reversed by ATRA treatment.

“As expected, the elevated levels of p35 observed in the vehicle-treated APP/PS1 mice were reversed by the ATRA treatment (Fig. 2 A, row 12).”

A robust enhancement of CDK5 phosphorylation at Ser159 was observed in the brains of vehicle-treated APP/PS1 mice compared with wild-type controls.

“As shown in Figure 2 A (row 11), a robust enhancement of CDK5 phosphorylation at Ser159 was observed in the brains of the vehicle-treated APP/PS1 mice compared with the wild-type controls.”

No significant difference in GSK3β (Tyr216) phosphorylation was observed between ATRA- and vehicle-treated APP/PS1 mice.

“However, no significant difference in the GSK3␤ (Tyr216) phosphorylation was observed between the ATRA-and vehicle-treated APP/PS1 mice (Fig. 2 A, row 14).”

Vehicle-treated APP/PS1 mice show robust elevation of phosphorylated APP at Thr668.

“As shown in Figure 2 A (row 3), a robust elevation of phosphorylated APP was detected in the vehicle-treated APP/PS1 mice.”

No significant difference in GSK3α Tyr279 phosphorylation was observed between ATRA- and vehicle-treated APP/PS1 mice.

“no significant difference was observed between the ATRA-and vehicle-treated APP/PS1 mice (Fig. 2 A, row 14).”

A marked decrease in phosphorylation of GSK3β at Ser9 was observed in vehicle-treated APP/PS1 mice relative to wild-type controls.

“Interestingly, Western blot analysis with an antibody against the phosphorylated GSK3␤ (Ser9) showed a marked decrease in the phosphorylation of GSK3␤ at Ser9 in the vehicle-treated APP/PS1 mice relative to the wild-type controls (Fig. 2 A, row 15).”

No difference in total CDK5 levels was observed between the groups.

“We did not observe a difference in the total CDK5 levels between the groups (Fig. 2 A, row 13).”

No significant difference in total tau levels was revealed between the groups.

“No significant difference in the total tau levels was revealed between the groups (Fig. 2 A, row 10).”

Vehicle-treated APP/PS1 mice show robust enhancement of tau phosphorylation at Thr205, Ser235, Ser396, Ser404, and Ser519 in both the frontal cortex and hippocampus.

“As shown in Figure 2 A (rows 4 -8), a robust enhancement of tau phosphorylation at all these sites was observed in both the frontal cortex and hippocampus of the vehicle-treated APP/PS1 mice.”

A significant increase in phosphorylation of GSK3α at Tyr279 was observed in the brains of vehicle-treated APP/PS1 mice relative to wild-type controls.

“Similarly, although a significant increase in the phosphorylation of GSK3␣ at Tyr279 was observed in the brains of the vehicle-treated APP/PS1 mice relative to the wild-type controls”

The decreases in tau phosphorylation at Ser519 represented a return to wild-type levels.

“Both of these decreases represented a return to wild-type levels.”

ATRA-treated APP/PS1 mice showed a remarkable decrease in phosphorylation of CDK5 compared with vehicle-treated APP/PS1 mice.

“Strikingly, the ATRA-treated APP/PS1 mice showed a remarkable decrease in the phosphorylation of CDK5 (Fig. 2 A, row 11) compared with the vehicletreated APP/PS1 mice.”

Vehicle-treated APP/PS1 mice show a significant decrease in tau-1 immunoreactivity in brain tissues compared with wild-type controls.

“In addition, Western blotting with a tau-1 antibody, recognizing the nonphosphorylated tau at Ser198/Ser199/Ser202, showed a significant decrease in the tau-1 immunoreactivity in the brain tissues of the vehicle-treated APP/ PS1 mice compared with the wild-type controls (Fig. 2 A, row 9), consistent with a previous report (Zhou et al., 2008).”

Enhancement of GSK3β phosphorylation was observed in both the hippocampus and frontal cortex in vehicle-treated APP/PS1 mice compared with wild-type controls.

“Western blot analysis with an antibody against the phosphorylated GSK3␣,␤ (Tyr279/216) showed an enhancement of GSK3␤ phosphorylation in both the hippocampus and frontal cortex in the vehicle-treated APP/PS1 mice compared with the wild-type controls (Fig. 2 A, row 14).”

ATRA treatment significantly improved memory retention during the probe trial.

“Furthermore, we confirmed that ATRA treatment not only significantly promoted learning during the hidden-platform trials but also significantly improved memory retention during the probe trial (Fig. 7B).”

Double staining of Iba-I and Aβ plaques showed reactive microglia around Aβ plaques in the brains of vehicle-treated control APP/PS1 mice.

“Double staining of Iba-I and A␤ plaques showed reactive microglia around the A␤ plaques in the brains of vehicle-treated control APP/PS1 mice”

Vehicle-treated APP/PS1 mice had a dramatic decrease (50%) in MAP2 reactivity in the pyramidal neurons of the CA1 region of the hippocampus compared with vehicle-treated wild-type controls.

“our semiquantitative results showed that the vehicle-treated APP/PS1 mice had a dramatic decrease (50%) in MAP2 reactivity in the pyramidal neurons of the CA1 region of the hippocampus compared with the vehicle-treated wild-type controls (Fig. 6 A, B).”

No significant difference in the expression of APP or BACE1 was observed between the groups.

“However, we did not observe a significant difference in the expression of APP or BACE1 between the groups.”

Vehicle-treated APP/PS1 mice were impaired in learning to use the available visuospatial cues to locate the submerged escape platform, indicated by slower improvements in escape latency across consecutive trials.

“These mice were impaired in learning to use the available visuospatial cues to locate the submerged escape platform, as indicated by slower improvements in the escape latency across consecutive trials (Fig. 7A).”

Stereological analysis of GFAP immunoreactivity in the hippocampus showed an approximately 45% decrease in astrocytic volume in ATRA-treated APP/PS1 mice relative to vehicle-treated APP/PS1 mice.

“These results were confirmed by stereological analysis of GFAP immunoreactivity in the hippocampus, which showed an ϳ45% decrease in the astrocytic volume in the ATRA-treated APP/PS1 mice relative to the vehicle-treated APP/PS1 mice (Fig. 3C)”

Quantitative analysis showed a 50% decrease in GFAP expression in ATRA-treated APP/PS1 mice relative to control APP/PS1 mice.

“Quantitative analysis showed a 50% decrease in GFAP expression in the ATRA-treated APP/PS1 mice relative to that in the control APP/PS1 mice (Fig. 3F ).”

A significant decrease in the volume of neuronal bodies was observed in vehicle-treated APP/PS1 mice compared with vehicle-treated wild-type mice.

“but there was a significant decrease in the volume of neuronal bodies in the vehicle-treated APP/PS1 mice compared with that in the vehicletreated wild-type mice (Fig. 6 E).”

A significant improvement in the integrity of neuronal fibers surrounding the smaller Aβ plaques was observed in the frontal cortex of ATRA-treated APP/PS1 mice.

“In contrast, a significant improvement in the integrity of the neuronal fibers surrounding the smaller A␤ plaques was observed in the frontal cortex of the ATRA-treated APP/PS1 mice (Fig. 6C, right).”

Unbiased stereological quantification showed an approximately 50% reduction in the number of SIPBs in the hippocampus of vehicle-treated APP/PS1 mice compared with vehicle-treated wild-type controls.

“The unbiased stereological quantification showed an ϳ50% reduction in the number of SIPBs in the hippocampus of the vehicle-treated APP/PS1 mice compared with the vehicle-treated wild-type controls (Fig. 5D).”

A significant elevation of Iba-I immunoreactivity was observed in vehicle-treated APP/PS1 mice compared with vehicle-treated wild-type mice.

“As shown in Figure 4 A, a significant elevation of Iba-I immunoreactivity was observed in the vehicle-treated APP/ PS1 mice compared with the vehicle-treated wild-type mice.”

No significant difference in microglia number was observed between the groups.

“No significant difference in the microglia number was observed between the groups (Fig. 4 D)”

Fewer reactive microglia were observed around the smaller and less Aβ plaques in the brains of ATRA-treated APP/PS1 mice.

“whereas fewer reactive microglia were observed around the smaller and less A␤ plaques in the brains of ATRA-treated APP/PS1 mice (Fig. 4 B).”

The production of APP-CTFs, the direct precursor of Aβ, was attenuated by ATRA treatment.

“because the production of APP-CTFs, the direct precursor of A␤ (Evin et al., 2003), was attenuated by the ATRA treatment.”

• cites Evin et al., 2003Not checked yet

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ATRA-treated APP/PS1 mice showed a complete rescue of the loss of SIPBs in the hippocampus.

“Rather, the ATRA-treated APP/PS1 mice showed a complete rescue of the loss of SIPBs in the hippocampus (Fig. 5D).”

The size of Aβ plaques was decreased in the brains of ATRA-treated APP/PS1 mice.

“whereas both the size of A␤ plaques and astrocytic reactivity were decreased in the brains of ATRA-treated APP/PS1 mice (right panel).”

A marked elevation of GFAP expression was observed in the hippocampal tissues of control APP/PS1 mice.

“A marked elevation of GFAP expression was observed in the hippocampal tissues of the control APP/PS1 mice (Fig. 3E).”

Accumulation of reactive astrocytes surrounding Aβ plaques was evident in the brains of vehicle-treated control APP/PS1 mice.

“As shown in Figure 3B, accumulation of reactive astrocytes surrounding the A␤ plaques was evident in the brains of the vehicletreated control APP/PS1 mice (left panel)”

ATRA-treated APP/PS1 mice showed 80% more MAP2 immunoreactivity than vehicle-treated APP/PS1 mice.

“Intriguingly, the ATRA-treated APP/PS1 mice showed 80% more MAP2 immunoreactivity than the vehicle-treated APP/PS1 mice (Fig. 6 A, B).”

The reduced neuronal volume seen in vehicle-treated APP/PS1 mice was reversed in ATRA-treated APP/PS1 mice.

“The reduced neuronal volume seen in the vehicle-treated APP/PS1 mice was reversed in the ATRA-treated APP/PS1 mice (Fig. 6 E).”

A marked reversal of the decreased phosphorylation of GSK3β at Ser9 was observed in ATRA-treated APP/PS1 mice.

“In contrast, a marked reversal of the decreased phosphorylation of GSK3␤ at Ser9 was observed in the ATRA-treated APP/PS1 mice (Fig. 2 A, row 15).”

No significant difference in astrocyte number was observed between the groups.

“The hnRNP-U immunostaining indicated no significant difference in astrocyte number between the groups (Fig. 3A).”

• Also stated in: § ATRA treatment inhibits activation of microglia and astrocytes in APP/PS1 mice · plain

  “whereas no significance difference in the astrocyte number was observed between the groups (Fig. 3D).”

Double staining of SYN and Aβ plaques showed a robust decrease in the number of SIPBs surrounding Aβ plaques in the hippocampal dentate gyrus of vehicle-treated APP/PS1 mice.

“Double staining of SYN and A␤ plaques showed a robust decrease in the number of SIPBs surrounding the A␤ plaques in the hippocampal dentate gyrus of vehicle-treated APP/PS1 mice (Fig. 5C, left).”

ATRA treatment significantly promoted learning during the hidden-platform trials.

“Furthermore, we confirmed that ATRA treatment not only significantly promoted learning during the hidden-platform trials but also significantly improved memory retention during the probe trial (Fig. 7B).”

GFAP immunoreactivity was markedly decreased in ATRA-treated APP/PS1 mice.

“In contrast, the GFAP immunoreactivity was markedly decreased in the ATRA-treated APP/PS1 mice (Fig. 3A).”

The decreased density of SIPBs was completely reversed in ATRA-treated APP/PS1 mice compared with vehicle-treated APP/PS1 mice.

“The decreased density of SIPBs was completely reversed in the ATRA-treated APP/PS1 mice compared with the vehicle-treated APP/PS1 mice (Fig. 5 A, B).”

• Also stated in: § Discussion · plain

  “and a significant reversal of this decrease was observed in the ATRA-treated APP/PS1 mice.”

GFAP immunostaining demonstrated a marked increase of reactive astrocytes in the brains of vehicle-treated control APP/PS1 mice.

“Immunostaining against GFAP demonstrated a marked increase of reactive astrocytes in the brains of the vehicletreated control APP/PS1 mice (Fig. 3A).”

The density of SIPBs was markedly decreased in the CA3 subfield of the hippocampus in vehicle-treated APP/PS1 mice compared with vehicle-treated wild-type controls.

“The semiquantitative results indicated that the density of SIPBs was markedly decreased in the CA3 subfield of the hippocampus in the vehicle-treated APP/PS1 mice compared with the vehicle-treated wild-type controls (Fig. 5 A, B)”

• Also stated in: § Discussion · plain

  “In this study, a significant decrease in SYN immunoreactivity was observed in the stratum lucidum of the CA3 area in the brains of the vehicle-treated APP/PS1 mice compared with the vehicletreated wild-type mice”

Double staining of MAP2 and Aβ plaques showed significant degeneration of neurons, characterized by damage or loss of neuronal fibers surrounding plaques in the frontal cortex of vehicle-treated APP/PS1 mice.

“Double staining of MAP2 and A␤ plaques showed a significant degeneration of neurons, characterized by damage or loss of neuronal fibers surrounding the plaques in the frontal cortex of the vehicle-treated APP/PS1 mice (Fig. 6C, left).”

Stereological analysis of Iba-I immunostaining in the hippocampus showed an approximately 60% decrease in microglial volume in ATRA-treated APP/PS1 mice relative to vehicle-treated APP/PS1 mice.

“These results were confirmed by stereological analysis of Iba-I immunostaining in the hippocampus, which showed an ϳ60% decrease in the microglial volume in the ATRA-treated APP/PS1 mice relative to the vehicle-treated APP/PS1 mice (Fig. 4C).”

ATRA-treated APP/PS1 mice showed markedly reduced GFAP expression.

“In contrast, the ATRA-treated APP/PS1 mice showed a markedly reduced GFAP expression (Fig. 3E).”

Vehicle-treated APP/PS1 mice showed impaired acquisition of spatial learning as assessed by the Morris water maze test.

“Consistently, our study demonstrated that the vehicle-treated APP/PS1 mice showed impaired acquisition of spatial learning, as assessed by the Morris water maze test”

ATRA-treated APP/PS1 mice were able to locate the escape platform, demonstrated by significantly reduced escape latency across trials.

“In contrast, ATRA-treated APP/PS1 mice were able to locate the escape platform, as demonstrated by significantly reduced escape latency across trials (Fig. 7A).”

Significantly less Iba-I immunoreactivity was observed in ATRA-treated APP/PS1 mice relative to vehicle-treated APP/PS1 mice.

“Strikingly, a significantly less Iba-I immunoreactivity was observed in the ATRA-treated APP/PS1 mice relative to the vehicletreated APP/PS1 mice.”

Stereological quantification of MAP2 immunopositive neurons in the frontal cortex indicated no significant difference in neuronal number between the groups.

“Stereological quantification of the MAP2 immunopositive neurons in the frontal cortex indicated no significant difference in the neuronal number between the groups (Fig. 6 D)”

CDK5 phosphorylation sites were more susceptible to ATRA treatment than GSK3β sites on tau.

“Compatible with this result, we observed that CDK5 phosphorylation sites were more susceptible to the ATRA treatment than GSK3␤ sites on tau.”

ATRA treatment reversed the elevation of APP phosphorylation in APP/PS1 mice.

“Based on the observation that ATRA-treatment reversed the elevation of APP phosphorylation in APP/ PS1 mice”

ATRA treatment significantly inhibits tau hyperphosphorylation.

“Another interesting finding of the present study is the significant inhibition of tau hyperphosphorylation by the ATRA treatment.”

Among several phosphorylation sites tested, phosphorylation of tau at Ser396 was attenuated to a less extent by ATRA treatment than other phosphorylation sites.

“For instance, among the several phosphorylation sites tested, e.g., Ser235, Ser396, Ser404, Ser519, and Thr205, the phosphorylation of tau at Ser396, which is catalyzed by GSK3␤ rather than CDK5 (Li and Paudel, 2006;Wang et al., 2007), was attenuated to a less extent by the ATRA treatment than other phosphorylation sites.”

ATRA treatment reduced the levels of p35.

“Based on the observation that ATRA treatment reduced the levels of p35”

In ATRA-treated APP/PS1 mice, the extent of neuronal loss was much lower compared with vehicle-treated APP/PS1 mice.

“In the ATRA-treated APP/PS1 mice, A␤ deposits were significantly smaller, and, correspondingly, the extent of neuronal loss was much lower compared with the vehicle-treated APP/PS1 mice.”

ATRA treatment of APP/PS1 mice significantly attenuated impairment of neuronal integrity compared with vehicle treatment.

“We observed that ATRA treatment of the APP/PS1 mice significantly attenuated impairment of neuronal integrity compared with the vehicle treatment.”

Degenerative neurons surrounding Aβ plaques were observed in APP/PS1 mice treated with vehicle.

“Consistent with this result, we observed degenerative neurons surrounding the A␤ plaques in the APP/PS1 mice treated with vehicle.”

CDK5, rather than GSK3β, was predominantly inhibited by ATRA.

“our results demonstrated that CDK5, rather than GSK3␤, was predominantly inhibited by ATRA”

Chronic ATRA treatment of APP/PS1 mice results in attenuation of AD-type spatial memory deterioration.

“Chronic ATRA treatment of APP/PS1 mice results in attenuation of AD-type spatial memory deterioration.”

In the frontal cortex, ATRA-treated APP/PS1 mice show more significant integrity of neuronal fibers surrounding Aβ plaques than vehicle-treated control APP/PS1 mice.

“Double staining of MAP2 and A␤ plaques (Campbell-Switzer staining) showing more significant integrity of neuronal fibers surrounding the A␤ plaques in the frontal cortex of ATRA-treated APP/PS1 mice than in vehicle-treated control APP/PS1 mice.”

Learning deficits in vehicle-treated control APP/PS1 mice were ameliorated in ATRA-treated APP/PS1 mice.

“Learning deficits in the control vehicle (Veh)-treated control APP/PS1 mice were ameliorated in the ATRA-treated APP/PS1 mice.”

ATRA treatment prevents loss of presynaptic terminals in the brains of APP/PS1 mice.

“ATRA treatment prevents loss of presynaptic terminals in the brains of APP/PS1 mice.”

In the hippocampal CA3 region, ATRA-treated APP/PS1 mice have less activated microglia surrounding Aβ plaques than vehicle-treated control APP/PS1 mice.

“Double staining of Iba-I and A␤ plaques (Campbell-Switzer staining) showing less activated microglia surrounding the A␤ plaques in the hippocampal CA3 region of ATRA-treated (right) than the vehicle-treated (left) control APP/PS1 mice.”

In the Morris water maze probe trial, deficits in vehicle-treated APP/PS1 mice were improved in ATRA-treated APP/PS1 mice.

“Memory test in Morris water maze probe trial without platform.Note that the deficits in the vehicle-treated APP/PS1 mice were improved in the ATRA-treated APP/PS1 mice.”

ATRA treatment prevents loss of MAP2 immunoreactivity in the brains of APP/PS1 mice.

“ATRA treatment prevents loss of MAP2 immunoreactivity in the brains of APP/PS1 mice.”

ATRA treatment results in a decrease in microglial reactivity in the brains of APP/PS1 mice.

“ATRA treatment results in a decrease in microglial reactivity in the brains of APP/ PS1 mice.”

ATRA has a specific inhibitory effect on Aβ deposition.

“These data suggest a specific inhibitory effect of ATRA on A␤ deposition.”

ATRA has a specific inhibitory effect on APP processing.

“In contrast, the vehicle-treated APP/PS1 mice did not show a significant difference in the production of CTFs compared with the untreated age-and gender-matched APP/ PS1 mice (data not shown), suggesting a specific inhibitory effect of ATRA on APP processing.”

ATRA influences APP processing via a mechanism beyond modulating the expression of APP and BACE1.

“These findings suggest that ATRA influences APP processing via a mechanism beyond modulating the expression of APP and BACE1.”

CDK5 and GSK3β are key kinases responsible for APP phosphorylation.

“Moreover, CDK5 and GSK3␤ are the key kinases responsible for the APP phosphorylation (Aplin et al., 1996;Iijima et al., 2000).”

• cites Aplin et al., 1996 sourceNot checked yet

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• cites Iijima et al., 2000Not checked yet

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The impairment in spatial learning and memory and the depression of synaptic plasticity that occurs in vitamin A-deprived rodents also occur during aging in rodents.

“The impairment in spatial learning and memory and the depression of synaptic plasticity that occurs in vitamin A-deprived rodents also occur during aging in rodents (Etchamendy et al., 2001).”

• cites Etchamendy et al., 2001 sourceNot checked yet

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ATRA treatment downregulates CDK5 activity.

“These data suggest that ATRA treatment downregulates CDK5 activity.”

RA inhibits formation of fibrillar Aβ from fresh Aβ in vitro.

“RA has been shown to inhibit formation of fibrillar A␤ from fresh A␤ in vitro (Ono et al., 2004).”

• cites Ono et al., 2004Not checked yet

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Hyperphosphorylated tau appears in the APP/PS1 mouse brain after the onset of Aβ deposition.

“Hyperphosphorylated tau appears in the APP/PS1 mouse brain after the onset of A␤ deposition (Kurt et al., 2003).”

• cites Kurt et al., 2003Not checked yet

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ATRA treatment did not affect the swimming ability of APP/PS1 mice, as reflected by similar swimming speeds between the groups.

“In the present study, ATRA treatment did not affect the swimming ability of the APP/PS1 mice, as reflected by their similar swimming speeds between the groups (data not shown).”

ATRA may benefit spatial memory deficits in APP/PS1 mice selectively, through the attenuation of Aβ-associated neurodegeneration.

“These findings support the hypothesis that ATRA may benefit spatial memory deficits in APP/PS1 mice selectively, through the attenuation of A␤-associated neurodegeneration.”

In the brains of human AD patients and transgenic AD mouse models, infiltration of activated astrocytes and microglia is seen in the area of Aβ plaques.

“In the brains of human AD patients and transgenic AD mouse models, infiltration of activated astrocytes and microglia are seen in the area of A␤ plaques (Itagaki et al., 1989;Frautschy et al., 1998;Stalder et al., 1999;Bornemann et al., 2001;Matsuoka et al., 2001)”

• cites Itagaki et al., 1989Not checked yet

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• cites Frautschy et al., 1998 sourceNot checked yet

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• cites Stalder et al., 1999Not checked yet

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RA differentially influences APP expression under diverse conditions.

“This discrepancy suggests that RA differentially influences APP expression under diverse conditions.”

ATRA has a modest inhibitory effect on GSK3β activity.

“These results suggest that ATRA has a modest inhibitory effect on GSK3␤ activity.”

The inhibitory effect of ATRA on Aβ accumulation is likely attributable to its inhibition of APP processing.

“The inhibitory effect of ATRA on A␤ accumulation is likely attributable to its inhibition of APP processing”

There is a significant decrease in microglia activation in the brains of ATRA-treated APP/PS1 mice.

“suggesting a significant decrease in microglia activation in the brains of ATRA-treated APP/PS1 mice.”

The APP/PS1 AD mouse model is well known to develop Aβ-associated cognitive deterioration with increasing age.

“The APP/PS1 AD mouse model is well known to develop A␤associated cognitive deterioration with increasing age (Trinchese et al., 2004).”

• cites Trinchese et al., 2004Not checked yet

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Deficits in the acquisition phase of place learning and in the probe trial were not attributable to noncognitive factors because APP/PS1 and wild-type mice displayed identical swimming speeds and escape latencies on the visible platform trails.

“In the Morris water maze, observed deficits in the acquisition phase of place learning and in the probe trial were not attributable to noncognitive factors, because APP/PS1 mice and wild-type mice displayed identical swimming speeds and escape latencies on the visible platform trails.”

ATRA is involved in multiple steps of Aβ deposition.

“suggesting that ATRA is involved in multiple steps of A␤ deposition.”

ATRA decreases synaptic loss in APP/PS1 mice.

“These data suggest that ATRA decreases synaptic loss in the APP/ PS1 mice.”

ATRA treatment decreases the rate of neuronal degeneration in APP/PS1 mice.

“These data suggest that ATRA treatment decreases the rate of neuronal degeneration in APP/PS1 mice.”

Previous in vitro studies showed that RA inhibited the neurotoxic effect of activated microglia by suppressing the production of inflammatory cytokines and cytotoxic molecules.

“Based on previous in vitro studies showing that RA inhibited the neurotoxic effect of activated microglia by suppressing the production of inflammatory cytokines and cytotoxic molecules (Dheen et al., 2005)”

• cites Dheen et al., 2005Not checked yet

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APP reciprocally regulates CDK5 activity.

“Because APP has been shown to reciprocally regulate CDK5 activity (Han et al., 2005)”

• cites Han et al., 2005Not checked yet

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The cholinergic system is a potential target of retinoids, because RA increases the levels of choline acetyltransferase (ChAT).

“The cholinergic (ACh) system is a potential target of retinoids, because RA increases the levels of choline acetyltransferase (ChAT) (Berse and Blusztajn, 1995)”

• cites Berse and Blusztajn, 1995Not checked yet

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CDK5 is believed to be a key kinase responsible for APP phosphorylation in neuronal cells.

“CDK5 is believed to be a key kinase responsible for APP phosphorylation in neuronal cells (Iijima et al., 2000;Liu et al., 2003;Wen et al., 2008a)”

• cites Iijima et al., 2000Not checked yet

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• cites Liu et al., 2003Not checked yet

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• cites Wen et al., 2008aNot checked yet

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The anti-inflammatory effect of ATRA in the AD model mouse provides additional evidence for its therapeutic potential for AD.

“Nevertheless, because brain inflammation is a risk factor for neurodegenerative disease, the anti-inflammatory effect of ATRA in the AD model mouse provides additional evidence for its therapeutic potential for AD.”

• AssumptionRests on an assumption: Brain inflammation is a risk factor for neurodegenerative disease.

Excessive Aβ accumulation is associated with disturbed cognitive function in an AD mouse model.

“As reported, excessive A␤ accumulation is associated with disturbed cognitive function in an AD mouse model (Chen et al., 2000)”

• cites Chen et al., 2000Not checked yet

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ATRA attenuates tau phosphorylation primarily through the inhibition of CDK5.

“suggesting that ATRA attenuates tau phosphorylation primarily through the inhibition of CDK5.”

Loss of ChAT-expressing neurons is characteristic of AD.

“Because the loss of ChAT-expressing neurons is characteristic of AD (Whitehouse et al., 1982)”

• cites Whitehouse et al., 1982Not checked yet

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ATRA overcomes the reduction in ChAT induced by Aβ peptides.

“and because ATRA overcomes the reduction in ChAT induced by A␤ peptides (Sahin et al., 2005)”

• cites Sahin et al., 2005 sourceNot checked yet

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The beneficial effect of ATRA on cognitive improvement in APP/PS1 mice is likely attributable to the combined effects of decreased levels of toxic Aβ peptides, tau hyperphosphorylation, and neurodegeneration.

“The beneficial effect of ATRA on cognitive improvement in APP/PS1 mice is likely attributable to the combined effects of decreased levels of toxic A␤ peptides, tau hyperphosphorylation, and neurodegeneration.”

ATRA appears to possess an inherent anti-inflammatory function independent of Aβ.

“However, ATRA appears to possess an inherent anti-inflammatory function independent of A␤ (Mehta et al., 1994;Datta et al., 2001).”

• cites Mehta et al., 1994 sourceNot checked yet

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• cites Datta et al., 2001Not checked yet

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The significant decrease in activated microglia and astrocytes seen in ATRA-treated APP/PS1 mice can be attributed to its inhibition of Aβ accumulation.

“Given the central role of fibrillar A␤ in the activation of microglia and astrocytes seen in AD brain (Rozemuller et al., 2005) and in AD animal models (Frautschy et al., 1998;Apelt and Schliebs, 2001;Matsuoka et al., 2001), the significant decrease in activated microglia and astrocytes seen in the ATRA-treated APP/PS1 mice can be attributed to its inhibition of A␤ accumulation.”

• cites Rozemuller et al., 2005Not checked yet

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• cites Frautschy et al., 1998 sourceNot checked yet

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• cites Apelt and Schliebs, 2001Not checked yet

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ATRA-mediated prevention of synaptic loss in the stratum lucidum of the CA3 area may play a key role in rescuing deficits of learning and memory.

“ATRAmediated prevention of synaptic loss in the stratum lucidum of the CA3 area, in which the mossy fibers from the dentate gyrus synapse with the dendrites of the pyramidal neurons, may play a key role in rescuing deficits of learning and memory”

• cites Cremer et al., 1998Not checked yet

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• cites Ramirez-Amaya et al., 2001 sourceNot checked yet

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ATRA treatment of APP/PS1 transgenic mice reverses cognitive deficits.

“We demonstrate that ATRA treatment of APP/PS1 transgenic mice reverses cognitive deficits.”

ATRA may prevent APP processing by inhibiting its phosphorylation.

“we postulate that ATRA may prevent APP processing by inhibiting its phosphorylation.”

ATRA attenuates Aβ accumulation via regulating axonal transport of Aβ.

“we propose that ATRA attenuates A␤ accumulation via regulating axonal transport of A␤.”

The neuroprotective effect of ATRA seen in APP/PS1 mice is in line with a previous report showing protection against Aβ-induced injury of primary hippocampal neuronal cultures.

“The neuroprotective effect of ATRA seen in APP/PS1 mice is in line with a previous report showing protection against A␤-induced injury of primary hippocampal neuronal cultures (Sahin et al., 2005).”

• cites Sahin et al., 2005 sourceNot checked yet

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In the brains of APP/PS1 mice, a discrete neuronal loss is associated with Aβ plaques.

“In the brains of APP/PS1 mice, a discrete neuronal loss is associated with A␤ plaques (Calhoun et al., 1998).”

• cites Calhoun et al., 1998Not checked yet

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ATRA may inhibit CDK5 through stabilizing APP.

“In addition to a possible direct influence on CDK5 activation, ATRA may inhibit CDK5 through stabilizing APP.”

The present study provides evidence that ATRA is able to attenuate Aβ-associated neuropathology and memory deficits in an APP/PS1 transgenic AD mouse model.

“Together, the present study provides evidence that ATRA is able to attenuate A␤-associated neuropathology and memory deficits in a APP/PS1 transgenic AD mouse model.”