Remarkable reduction of MAP2 in the brains of scrapie-infected rodents and human prion disease possibly correlated with the increase of calpain

Abstract

Microtubule-associated protein 2 (MAP2) belongs to the family of heat stable MAPs, which takes part in neuronal morphogenesis, maintenance of cellular architecture and internal organization, cell division and cellular processes. To obtain insight into the possible alteration and the role of MAP2 in transmissible spongiform encephalopathies (TSEs), the MAP2 levels in the brain tissues of agent 263K-infected hamsters and human prion diseases were evaluated. Western blots and IHC revealed that at the terminal stages of the diseases, MAP2 levels in the brain tissues of scrapie infected hamsters, a patient with genetic Creutzfeldt-Jakob disease (G114V gCJD) and a patient with fatal familial insomnia (FFI) were almost undetectable. The decline of MAP2 was closely related with prolonged incubation time. Exposure of SK-N-SH neuroblastoma cell line to cytotoxic PrP106-126 peptide significantly down-regulated the cellular MAP2 level and remarkably disrupted the microtubule structure, but did not alter the level of tubulin. Moreover, the levels of calpain, which mediated the degradation of a broad of cytoskeletal proteins, were significantly increased in both PrP106-126 treated SK-N-SH cells and brain tissues of 263K prion-infected hamsters. Our data indicate that the decline of MAP2 is a common phenomenon in TSEs, which seems to occur at an early stage of incubation period. Markedly increased calpain level might contribute to the reduction of MAP2.

Figure 1. Comparative analyses of the levels of MAP2 in brain tissues of normal and 263K-infected hamsters.

A. Western blots. Same amounts of individual brain homogenate were loaded in 6% or 12% SDS-PAGE and various specific immunoblots were marked on the left side of the graphs. B. Quantitative analysis of each gray numerical value of MAP2a/2b, MAP2c, 2d, tubulin and total PrP vs that of individual β-actin. The average values were calculated from four individual infected hamsters or three individual normal hamsters and presented as mean ± SD. Statistical differences compared with controls were illustrated as P<0.05 or P<0.01. C. IHC assays of MAP2, total PrP and GFAP in cortex of normal and 263K-infected hamsters. The magnifications are ×20 in the left row and ×40 in the right row.

Figure 2. Dynamic analysis of MAP2 and PrP^Sc in the brain tissues of normal and 263K-infected hamsters during incubation period.

A. Western blots. Same amounts of individual brain homogenate were loaded in 6% or 12% SDS-PAGE. Various specific immunoblots were marked on the left and the time of post-inoculation are showed as days (d) at the bottom. B. Quantitative analysis of each gray numerical value of MAP2a/2b, MAP2c, 2d and PrP^Sc vs that of individual β-actin. The average relative gray value is calculated from three independent blots and presented as mean ± S.D.

Figure 3. Analyses of the levels of MAP2 in the brain tissues of human prion diseases.

A. Western blots of six brain regions of a gCJD patient (left panel) and a FFI patient (right panel). The immunoblots for MAP2, total PrP and β-actin are indicated on the left. Various brain regions are indicated at the top.

Figure 4. Analyses of the MAP2 levels in SK-N-SH cells exposed to PrP106–126.

A. SK-N-SH cells were treated with 200 µM of PrP106–126, scrambled peptide PrP106–126 (SCR) or DMSO for 6 h and 12 h. The treated cells were photographed with a light microscope (×20). B. Cell viability after exposed to different concentrations of PrP106–126 or SCR. The average data of each preparation was calculated based on three independent experiments and represented as mean ± S.D. C. Western blots of MAP2a/2b, MAP2c, 2d and β-actin in SK-N-SH cells after treated with 200 µM of PrP106–126, SCR or DMSO for 6 h and 12 h. D. Quantitative analyses of each gray numerical value of MAP2a/2b, MAP2c, 2d vs that of individual β-actin. The average relative gray value is calculated from three independent blots and presented as mean ± S.D. Statistical differences compared with controls are illustrated as P<0.05 and P<0.01.

Figure 5. Immunofluorescent assays of MAP2 on PrP106–126 treated SK-N-SH cells.

A. Immunofluorescence images of the cells were exposed to DMSO (upper), PrP106–126 (middle) or SCR (lower) for 6 h. The images of MAP2 (red), DAPI (blue) and merge are indicated above. B. Quantitative analysis of fluorescence intensity of MAP2 in the cells. MOD data each preparation is calculated from three independent images and presented as mean ± S.D. Statistical differences is illustrated as P<0.01.

Figure 6. Analyses of the tubulin levels and microtubule structure in cells exposed to DMSO, PrP106–126 or SCR.

A. Western blots with anti-α-tubulin mAb. B. Quantitative analyses of each gray numerical value of tubulin vs that of individual β-actin. The average relative gray value is calculated from three independent blots and presented as mean ± S.D. C. Immunofluorescence images of cellular microtubule structure.

Figure 7. Analyses of calpain levels in PrP106–126 treated SK-N-SH cells.

A. Western blots of calpain in cells exposed to DMSO, PrP106–126 or SCR. B. Quantitative analyses of the gray numerical values of calpain. The average relative gray value is calculated from three independent blots and presented as mean ± S.D. Statistical differences are illustrated as P<0.01. C. Western blots of MAP2 in the cells treated with PrP106–126 alone and PrP106–126 plus calpain inhibitor ALLN. D. Quantitative analyses of the gray numerical values of MAP2a/2b, MAP2d and MAP2c. The average relative gray value is calculated from three independent blots and presented as mean ± S.D. Statistical differences are illustrated as P<0.01.

Figure 8. Analyses of calpain levels in the brain tissues of 263K-infected hamsters.

A. Western blots of calpain in the infected and normal hamsters. B. Quantitative analyses of the gray numerical values of calpain. The average gray values were calculated from four infected hamsters or or four normal after normalized with that of individual β-actin and presented as mean ± SD. Statistical difference is illustrated as P<0.01. C. Western blots of calpain and tubulin in the brain tissues of 263K-infected hamsters on 0, 20, 40, 60 and 80 dpi. D. Quantitative analyses of the gray numerical values of calpain and tubulin vs that of individual β-actin. The average relative gray value is calculated from three independent blots and presented as mean ± S.D.

Figure 9. Inhibition of calpain activity reversed the PrP106–126-induced destruction on microtubule structures and cytotoxicity.

A. SK-N-SH cells were treated with 200 µM of PrP 106–126 with or without calpain inhibitor ALLN for 12 h. Immunofluorescence images of cellular microtubule structure (upper) and morphological analyses of cells (lower) were shown. B. Cell viability after exposed to PrP106–126 with or without ALLN. The average data of each preparation was calculated based on three independent experiments and represented as mean ± S.D. Statistical differences are illustrated as P<0.05.