Cell proliferation markers, such as cyclin-dependent kinase inhibitor 1 (CDKN1/p21) and proliferating cell nuclear antigen (PCNA) expressions, were measured in AD: CDKN1/p21 activation and substantial PCNA reductions in the tubular system of AD mice were normalized by physical activity [49]. The gene discussed is CDKN1A; the disease is Alzheimer disease.