Modulation of BDNF Cleavage by Plasminogen-activator Inhibitor-1 Contributes to Alzheimer's Neuropathology and Cognitive Deficits

Brain-derived neurotrophic factor (BDNF) plays pivotal roles in neuronal function. The cleaved - mature - form of BDNF (mBDNF), predominantly expressed in adult brains, critically determines its effects. However, insufficient proteolytic processing under pathology may lead to the precursor form of BDNF (proBDNF) and thereby increased neuronal apoptosis and synaptic weakening. Previous findings in our lab showed that cognitive stimulation (CS) delayed memory decline in Tg2576 mouse model of Alzheimer's disease (AD), an effect that was tightly associated with augmented levels of mBDNF. In view of this association, the present study explored whether altered cleavage of BDNF could be involved in AD-related traits triggered by excessive amyloid-β (Aβ) pathology and whether this process could be therapeutically targeted. Aβ pathology, both in AD patient samples and experimental models, triggered the upregulation of plasminogen-activator inhibitor-1 (PAI-1) via JNK/c-Jun. This led to inhibition of plasmin-regulated conversion of mBDNF. Pharmacological inhibition of PAI-1 with PAI-039 sufficiently reverted Aβ-induced tau hyperphosphorylation and neurotoxicity. Chronic treatment of 15 old-month Tg2576 mice with oral administration of PAI-039 resulted in improved BDNF maturation and cognitive function without inducing significant changes in amyloid burden. In conclusion, upregulation of PAI-1 may be a critical mechanism underlying insufficient neurotrophic support and increased neurodegeneration associated with AD. Thus, targeting BDNF maturation through pharmacological inhibition of PAI-1 might become a potential treatment for AD.