Caspase-6 activation in familial alzheimer disease brains carrying amyloid precursor protein or presenilin i or presenilin II mutations

Abstract

We previously demonstrated the activation of caspase-6 (Casp-6) in the hippocampus and cortex in cases of mild, moderate, severe, and very severe Alzheimer disease (AD). To determine whether Casp-6 is also activated in familial AD, we performed an immunohistochemical analysis of active Casp-6 and Tau cleaved by Casp-6 in temporal cortex and hippocampal tissue sections from cases of familial AD. The cases included 5 carrying the amyloid precursor protein K670N and M671L Swedish mutation, 1 carrying the amyloid precursor protein E693G Arctic mutation, 2 each carrying the Presenilin I M146V, F105L, A431E, V261F, and Y115C mutations, and 1 with the Presenilin II N141I mutation. Active Casp-6 immunoreactivity was found in all cases. Caspase-6 immunoreactivity was observed in neuritic plaques or in some cases cotton-wool plaques, and in neuropil threads and neurofibrillary tangles. These results indicate that Casp-6 is activated in familial forms of AD, as previously observed in sporadic forms. Because sporadic and familial AD cases have similar pathological features, these results support a fundamental role of Casp-6 in the pathophysiology of both familial and sporadic AD.

Figure 1

Immunohistochemical staining with 1277 anti-active Casp6 antiserum, anti-TauΔCasp6 antiserum, and anti-active Casp6 antiserum + anti-PHF-1 antibodies in the superior temporal gyrus (STG) and hippocampus of a representative familial Alzheimer disease (AD) case. Micrographs were taken with the 2x objective and reduced by 50% after importing the image. Detection of anti-active Casp6 and TauΔCasp6 was with diaminobenzidine; PHF-1 immunoreactivity was detected with Fast Red. The squares represent areas shown in Figures 2 and 3. Scale bars = 1 mm.

Figure 2

Immunohistochemical staining with anti-active Casp6 antiserum. Micrographs of anti-Casp6 immunostained superior temporal gyrus or hippocampus in the areas indicated in Figure 1 from a sporadic Alzheimer disease (AD) case (A), a non-AD case (B), an AD with the Arctic mutation (C), a representative AD APP Swedish case (D), an AD with the PSEN II N141I AD case (E), and a representative AD case of each of the PSEN I mutants indicated (F–J). Micrographs were taken with the 40x objective and reduced to 35%. Scale bars = 50 µm.

Figure 2

Immunohistochemical staining with anti-active Casp6 antiserum. Micrographs of anti-Casp6 immunostained superior temporal gyrus or hippocampus in the areas indicated in Figure 1 from a sporadic Alzheimer disease (AD) case (A), a non-AD case (B), an AD with the Arctic mutation (C), a representative AD APP Swedish case (D), an AD with the PSEN II N141I AD case (E), and a representative AD case of each of the PSEN I mutants indicated (F–J). Micrographs were taken with the 40x objective and reduced to 35%. Scale bars = 50 µm.

Figure 3

Immunohistochemical staining with 10635 anti-TauΔCasp6 antisera. Micrographs of TauΔCasp6 immunostained superior temporal gyrus or hippocampus in the areas indicated in Figure 1 from a sporadic Alzheimer disease (AD) case (A), a non-AD case (B), an AD with the Arctic mutation (C), a representative AD APP Swedish case (D), an AD with the PSEN II N141I AD case (E), and a representative AD case of each of the PSEN I mutants indicated (F–J). Micrographs were taken with the 40x objective and reduced to 35%. Scale bars = 50 µm.

Figure 3

Immunohistochemical staining with 10635 anti-TauΔCasp6 antisera. Micrographs of TauΔCasp6 immunostained superior temporal gyrus or hippocampus in the areas indicated in Figure 1 from a sporadic Alzheimer disease (AD) case (A), a non-AD case (B), an AD with the Arctic mutation (C), a representative AD APP Swedish case (D), an AD with the PSEN II N141I AD case (E), and a representative AD case of each of the PSEN I mutants indicated (F–J). Micrographs were taken with the 40x objective and reduced to 35%. Scale bars = 50 µm.

Figure 4

Co-immunostaining of active Casp6 with PHF-1. Micrographs show colocalization of active Casp6 (brown) and PHF-1 (red) in (A) neurofibrillary tangles (black arrow), (B) neuropil threads (black arrowhead) and a structure resembling a tangle stained only with anti-active Casp6 (white arrow). Left panel is a lower magnification indicating the area where the picture was taken (black arrow). Scale bar = 1 mm. Right panel is a higher magnification. Scale bar = 50 µm. (C) Micrograph showing punctate cytoplasmic anti-active Casp6 immunoreactivity in the APP Arctic case. The right panel represents a magnified image of the anti-active Casp6 immunopositive neurons with more or less PHF-1 immunoreactivity.