PPIA and Alzheimer disease: In multiple animal models, inhibition of CypA-MMP pathway improved BBB integrity, reduced loss of neurons and attenuated behavioral deficits.501 In AD patients, BBB damage is associated with loss of pericytes,503 while the decrease in pericytes is followed by an increase in activated microglia.504 The loss of pericytes is probably caused by increased expression of friend leukemia virus integration 1 (Fli-1) after being activated.503 Fli-1 is an important regulator of inflammation and was reported to enhance the proinflammatory cytokine secretion from lung pericytes.