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Behavioral defects in chaperone-deficient Alzheimer's disease model mice.

Ojha J, Karmegam RV, Masilamoni JG, Terry AV, Cashikar AG - PLoS ONE (2011)

Bottom Line: Molecular chaperones protect cells from the deleterious effects of protein misfolding and aggregation.We observed that the overall content of αB-crystallin, a small heat shock protein molecular chaperone, decreased in AD model mice in an age-dependent manner.Our results highlight a synergistic effect of combining chaperone deficiency in a transgenic mouse model for AD underscoring an important role for chaperones in protein misfolding diseases.

View Article: PubMed Central - PubMed

Affiliation: Center for Molecular Chaperones and Radiobiology, Medical College of Georgia, Augusta, Georgia, United States of America.

ABSTRACT
Molecular chaperones protect cells from the deleterious effects of protein misfolding and aggregation. Neurotoxicity of amyloid-beta (Aβ) aggregates and their deposition in senile plaques are hallmarks of Alzheimer's disease (AD). We observed that the overall content of αB-crystallin, a small heat shock protein molecular chaperone, decreased in AD model mice in an age-dependent manner. We hypothesized that αB-crystallin protects cells against Aβ toxicity. To test this, we crossed αB-crystallin/HspB2 deficient (CRYAB⁻/⁻HSPB2⁻/⁻) mice with AD model transgenic mice expressing mutant human amyloid precursor protein. Transgenic and non-transgenic mice in chaperone-sufficient or deficient backgrounds were examined for representative behavioral paradigms for locomotion and memory network functions: (i) spatial orientation and locomotion was monitored by open field test; (ii) sequential organization and associative learning was monitored by fear conditioning; and (iii) evoked behavioral response was tested by hot plate method. Interestingly, αB-crystallin/HspB2 deficient transgenic mice were severely impaired in locomotion compared to each genetic model separately. Our results highlight a synergistic effect of combining chaperone deficiency in a transgenic mouse model for AD underscoring an important role for chaperones in protein misfolding diseases.

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Chaperone levels in AD model mice.(A) Immunoblots showing age-dependence of αB-crystallin expression in mice expressing mutant human APP transgene. Brain lysates were prepared from two individual non-transgenic (NTg1 & NTg2) or transgenic (Tg1 & Tg2) mice each at 3 months or 7 months of age. Samples were immunoblotted for αB-crystallin, Hsp70, Hsp27, Aβ and actin. 40 µg of total protein was analyzed. Similar levels of Hsp70, Hsp27 and actin in all samples show equal protein loading. (B) Densitometric analysis of band intensities in A. Intensities were compared by two-sample Student's t-test for statistical signifcance. APP expression in Tg mice were significantly greater than NTg mice as expected (p = 0.006 at 3 months, p = 0.017 at 7 months). αB-crystallin expression was significantly lower at 7-months compared to 3-months old transgenic mice brain (p = 0.044). αB-crystallin levels in 7-month old transgenic mice was also significantly lower than non-transgenic mice at similar age (p = 0.018). All other comparisons showed no significant differences.
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pone-0016550-g001: Chaperone levels in AD model mice.(A) Immunoblots showing age-dependence of αB-crystallin expression in mice expressing mutant human APP transgene. Brain lysates were prepared from two individual non-transgenic (NTg1 & NTg2) or transgenic (Tg1 & Tg2) mice each at 3 months or 7 months of age. Samples were immunoblotted for αB-crystallin, Hsp70, Hsp27, Aβ and actin. 40 µg of total protein was analyzed. Similar levels of Hsp70, Hsp27 and actin in all samples show equal protein loading. (B) Densitometric analysis of band intensities in A. Intensities were compared by two-sample Student's t-test for statistical signifcance. APP expression in Tg mice were significantly greater than NTg mice as expected (p = 0.006 at 3 months, p = 0.017 at 7 months). αB-crystallin expression was significantly lower at 7-months compared to 3-months old transgenic mice brain (p = 0.044). αB-crystallin levels in 7-month old transgenic mice was also significantly lower than non-transgenic mice at similar age (p = 0.018). All other comparisons showed no significant differences.

Mentions: As guardians against protein misfolding and aggregation, chaperones protect the cells from the deleterious effects of aggregation. Stressful conditions such as heat shock cause an acute increase in misfolded proteins resulting in an increase in demand for chaperones, which is normally met by the stress-inducible expression of chaperones. On the other hand, a steady increase in damaged proteins (oxidized and nitrosylated) takes place due to aging, leading to a chronic demand for chaperones and accumulation of damaged proteins. Such a reduction in chaperone availability is thought to play a central role in triggering the protein aggregation cascade of natively unstructured and amyloidogenic polypeptides associated with several neurodegenerative diseases. Because misfolding and aggregation of the amyloid-beta (Aβ) peptide is a major hallmark of AD, we premised that an age-dependent decrease in available chaperones might exacerbate the increased demand for proteostasis mechanisms. We investigated this possibility by examining the expression of Hsp70, Hsp27 and αB-crystallin in the brains of non-transgenic and transgenic mice at young (3 months) and older (7 months) ages by immunoblotting (Figure 1A) and densitometric analysis of the band intensities (Figure 1B). Due to the muscle-specific expression of HspB2 and the unavailability of appropriate antibodies recognizing mouse HspB2, we did not examine its expression in the mouse brain. The expression of the human APP transgene was examined using an antibody specific to human Aβ. As expected, only transgenic mice showed expression of APP and the band intensities were significantly above the intensities in the same molecular weight range in non-trangenic mice (p<0.05, two-sample t-test). The expression of Hsp70 and Hsp27 were unchanged at the ages tested irrespective of the transgene expression or age of mice. A marginal elevation in the expression of Hsp27 and Hsp70 observed in Figure 1B was not significantly different between the two ages or between the two genotypes (p>0.05, two-sample t-test). The equal expression levels of these proteins also serve as control for equal protein loading. Interestingly, the expression of αB-crystallin was significantly decreased in older transgenic mice but not in non-transgenic mice. Densitometric measurement of band intensities showed that αB-crystallin levels of 3-month old transgenic mice were comparable to that in non-transgenic mice. The levels of αB-crystallin in 7 month-old transgenic mice decreased significantly compared to 3-month old transgenic mice (p<0.05, two-sample t-test). This suggests that αB-crystallin may be an early indicator of protein misfolding defects in the brains of transgenic mice.


Behavioral defects in chaperone-deficient Alzheimer's disease model mice.

Ojha J, Karmegam RV, Masilamoni JG, Terry AV, Cashikar AG - PLoS ONE (2011)

Chaperone levels in AD model mice.(A) Immunoblots showing age-dependence of αB-crystallin expression in mice expressing mutant human APP transgene. Brain lysates were prepared from two individual non-transgenic (NTg1 & NTg2) or transgenic (Tg1 & Tg2) mice each at 3 months or 7 months of age. Samples were immunoblotted for αB-crystallin, Hsp70, Hsp27, Aβ and actin. 40 µg of total protein was analyzed. Similar levels of Hsp70, Hsp27 and actin in all samples show equal protein loading. (B) Densitometric analysis of band intensities in A. Intensities were compared by two-sample Student's t-test for statistical signifcance. APP expression in Tg mice were significantly greater than NTg mice as expected (p = 0.006 at 3 months, p = 0.017 at 7 months). αB-crystallin expression was significantly lower at 7-months compared to 3-months old transgenic mice brain (p = 0.044). αB-crystallin levels in 7-month old transgenic mice was also significantly lower than non-transgenic mice at similar age (p = 0.018). All other comparisons showed no significant differences.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3040748&req=5

pone-0016550-g001: Chaperone levels in AD model mice.(A) Immunoblots showing age-dependence of αB-crystallin expression in mice expressing mutant human APP transgene. Brain lysates were prepared from two individual non-transgenic (NTg1 & NTg2) or transgenic (Tg1 & Tg2) mice each at 3 months or 7 months of age. Samples were immunoblotted for αB-crystallin, Hsp70, Hsp27, Aβ and actin. 40 µg of total protein was analyzed. Similar levels of Hsp70, Hsp27 and actin in all samples show equal protein loading. (B) Densitometric analysis of band intensities in A. Intensities were compared by two-sample Student's t-test for statistical signifcance. APP expression in Tg mice were significantly greater than NTg mice as expected (p = 0.006 at 3 months, p = 0.017 at 7 months). αB-crystallin expression was significantly lower at 7-months compared to 3-months old transgenic mice brain (p = 0.044). αB-crystallin levels in 7-month old transgenic mice was also significantly lower than non-transgenic mice at similar age (p = 0.018). All other comparisons showed no significant differences.
Mentions: As guardians against protein misfolding and aggregation, chaperones protect the cells from the deleterious effects of aggregation. Stressful conditions such as heat shock cause an acute increase in misfolded proteins resulting in an increase in demand for chaperones, which is normally met by the stress-inducible expression of chaperones. On the other hand, a steady increase in damaged proteins (oxidized and nitrosylated) takes place due to aging, leading to a chronic demand for chaperones and accumulation of damaged proteins. Such a reduction in chaperone availability is thought to play a central role in triggering the protein aggregation cascade of natively unstructured and amyloidogenic polypeptides associated with several neurodegenerative diseases. Because misfolding and aggregation of the amyloid-beta (Aβ) peptide is a major hallmark of AD, we premised that an age-dependent decrease in available chaperones might exacerbate the increased demand for proteostasis mechanisms. We investigated this possibility by examining the expression of Hsp70, Hsp27 and αB-crystallin in the brains of non-transgenic and transgenic mice at young (3 months) and older (7 months) ages by immunoblotting (Figure 1A) and densitometric analysis of the band intensities (Figure 1B). Due to the muscle-specific expression of HspB2 and the unavailability of appropriate antibodies recognizing mouse HspB2, we did not examine its expression in the mouse brain. The expression of the human APP transgene was examined using an antibody specific to human Aβ. As expected, only transgenic mice showed expression of APP and the band intensities were significantly above the intensities in the same molecular weight range in non-trangenic mice (p<0.05, two-sample t-test). The expression of Hsp70 and Hsp27 were unchanged at the ages tested irrespective of the transgene expression or age of mice. A marginal elevation in the expression of Hsp27 and Hsp70 observed in Figure 1B was not significantly different between the two ages or between the two genotypes (p>0.05, two-sample t-test). The equal expression levels of these proteins also serve as control for equal protein loading. Interestingly, the expression of αB-crystallin was significantly decreased in older transgenic mice but not in non-transgenic mice. Densitometric measurement of band intensities showed that αB-crystallin levels of 3-month old transgenic mice were comparable to that in non-transgenic mice. The levels of αB-crystallin in 7 month-old transgenic mice decreased significantly compared to 3-month old transgenic mice (p<0.05, two-sample t-test). This suggests that αB-crystallin may be an early indicator of protein misfolding defects in the brains of transgenic mice.

Bottom Line: Molecular chaperones protect cells from the deleterious effects of protein misfolding and aggregation.We observed that the overall content of αB-crystallin, a small heat shock protein molecular chaperone, decreased in AD model mice in an age-dependent manner.Our results highlight a synergistic effect of combining chaperone deficiency in a transgenic mouse model for AD underscoring an important role for chaperones in protein misfolding diseases.

View Article: PubMed Central - PubMed

Affiliation: Center for Molecular Chaperones and Radiobiology, Medical College of Georgia, Augusta, Georgia, United States of America.

ABSTRACT
Molecular chaperones protect cells from the deleterious effects of protein misfolding and aggregation. Neurotoxicity of amyloid-beta (Aβ) aggregates and their deposition in senile plaques are hallmarks of Alzheimer's disease (AD). We observed that the overall content of αB-crystallin, a small heat shock protein molecular chaperone, decreased in AD model mice in an age-dependent manner. We hypothesized that αB-crystallin protects cells against Aβ toxicity. To test this, we crossed αB-crystallin/HspB2 deficient (CRYAB⁻/⁻HSPB2⁻/⁻) mice with AD model transgenic mice expressing mutant human amyloid precursor protein. Transgenic and non-transgenic mice in chaperone-sufficient or deficient backgrounds were examined for representative behavioral paradigms for locomotion and memory network functions: (i) spatial orientation and locomotion was monitored by open field test; (ii) sequential organization and associative learning was monitored by fear conditioning; and (iii) evoked behavioral response was tested by hot plate method. Interestingly, αB-crystallin/HspB2 deficient transgenic mice were severely impaired in locomotion compared to each genetic model separately. Our results highlight a synergistic effect of combining chaperone deficiency in a transgenic mouse model for AD underscoring an important role for chaperones in protein misfolding diseases.

Show MeSH
Related in: MedlinePlus