PIN1 and Alzheimer disease: Furthermore, cis pT231-tau, but not trans pT231-tau, strongly correlates with neurofibrillary degeneration, which is associated with decreased Pin1 levels in the AD hippocampus, in accord with the binding of Pin1 to PHFs leading to the depletion of soluble Pin1 (Lu et al., 1999a; Nakamura et al., 2012).