Co-localization of hyperphosphorylated tau and caspases in the brainstem of Alzheimer's disease patients

Hyperphosphorylation of microtubule associated protein tau had limited studies in Alzheimer’s disease (AD) brainstem. We compared the distribution and number of neurons with hyperphosphorylated tau in two age groups of AD brainstems with mean ages of 65.4 ± 5.7 and 91.1 ± 6.4 years. The degree of co-localization of hyperphosphorylated tau positive cells with either cleaved caspase-3 or cleaved caspase-6 was also quantified. Results showed hyperphosphorylated tau mainly occurred in hypoglossal, dorsal motor vagal, trigeminal sensory/motor nuclei as well as in dorsal raphe, locus coeruleus and substantia nigra. Older AD brainstem consistently had higher density of hyperphosphorylated tau cells. Up to 70% of tau positive cells also displayed either cleaved caspase-3 or caspase-6, and the number of co-localized tau cells in each caspase subfamily group was always higher in older aged group. Some hyperphosphorylated tau cells with cleaved caspases had TUNEL positive nuclei. These findings suggest that these latter cells went through the apoptotic process or DNA fragmentation.