Chromogranin B and Secretogranin II in transgenic mice overexpressing human APP751 with the London (V717I) and Swedish (K670M/N671L) mutations and in Alzheimer patients.

Chromogranin B and secretogranin II are major soluble constituents of large dense core vesicles of presynaptic structures and have been found in neuritic plaques of Alzheimer patients. We examined the distribution and expression of these peptides in both transgenic mice over expressing human amyloid-beta protein precursor APP751 with the London (V717I) and Swedish (K670M/N671L) mutations and in human post-mortem brain. In transgenic mice, the number of amyloid-beta plaques and chromogranin immunopositive plaques increased from 6 to 12 months. About 60% of amyloid-beta plaques were associated with chromogranin B and about 40% with secretogranin II. Chromogranin immunoreactivity appeared mainly as swollen dystrophic neurites. Neither synaptophysin- nor glial fibrillary acidic protein- immunoreactivity was expressed in chromogranin immunoreactive structures at any timepoint. Density of chromogranin peptides in hippocampal structures did not change in transgenic animals at any timepoint, even though animals had a poorer performance in the Morris water maze task. In conclusion, our findings in transgenic animals partly resembled findings in Alzheimer patients. Chromogranin peptides were associated with amyloid-beta plaques, but were not reduced in specific brain areas as previously reported by our group. Therefore specific changes of chromogranin peptides observed in Alzheimer patients can be related to amyloid-beta pathology only.