PPARGC1A and Alzheimer disease: With the aim to investigate the involvement of the SIRT1/PGC1α/Nrf2 pathway in neuroprotection, the gene expression and the protein levels of the single molecules were evaluated in the frontal and occipital cortex samples of AD brains, which were classified based on the Braak staging system of neurofibrillary pathology [55] and indicated as Early AD (stages I to III, age at death from 71 to 86 years; six samples) or Late AD (stages IV to VI, age at death from 75 to 83 years; eight samples).