Pharmacological inhibiTion of PCSK9 in AlzheimeR’s disEAse: in viTro And in vivo stuDies(TREAT-AD)

The protease Proprotein Convertase Subtilisin-like Kexin type 9 (PCSK9), beyond its well-established function as a master regulator of plasma lipid levels, is expressed in the brain and seems to be involved in Alzheimer’s disease (AD) pathogenesis. Consistently with this hypothesis, we previously observed that: a) AD patients display higher levels of PCSK9 in cerebrospinal fluid (CSF) compared to controls; b) genetic deletion of PCSK9 improves cognitive performances, reduced beta amyloid (Aß) plaque deposition and microgliosis in AD mice models; c) exogenous PCSK9 enhances the Aß-induced neuroinflammatory response in human astrocytes; d) PCSK9 overexpression associates to worsened neurotoxicity in neuronal cells; e) PCSK9 overexpression reduced expression of LDL receptor (LDLR) and apoE receptor 2 (ApoER2) and consequently reduced cholesterol uptake from neuronal cells. Based on these observations, the general aim of this project will be to investigate the in vivo benefits of small molecules PCSK9 inhibitors in AD mice models. The project will provide the first in vivo evidence on the potential efficacy of an anti-PCSK9 small-molecule drug-candidate in AD. In detail, the specific aims of the project will be: 1) to prove PCSK9 inhibition as an effective strategy to treat AD. In 5XFAD mice subcutaneously injected with a commercially available PCSK9 antagonist (SBC-115076) it will be evaluated: a) pharmacokinetic profile and biodistribution; b) PCSK9 expression and activity on target receptors in liver and brain; c) cognitive functions; d) Aß plaques deposition and neuroinflammation; 2) to develop a new small molecule PCSK9 inhibitor. We recently discovered a new class of lipophilic small molecules inhibiting PCSK9 transcription. One of these demonstrated to reverse the PCSK9-mediated reduction of cholesterol uptake in neuronal cells. To this aim, more potent analogues will be synthetized and selected by a preliminary screening based on the inhibitory activity on PCSK9 and target receptors in human hepatic and cerebral cell models. The activity of the new molecules will be also evaluated for the efficacy on AD-related parameters, including neuroinflammation, Aß metabolism and neurotoxicity in human cerebral cell models. The best candidate will be tested, in parallel with SBC-115076, for its pharmacokinetic profile/biodistribution and efficacy on the above in vivo AD model, after subcutaneous administration. We believe that this project has a highly innovative potential because, for the first time, it seeks to demonstrate the effect of a PCSK9 pharmacological inhibition in a severe AD mouse model, that simultaneously express five AD-linked mutations and thus recapitulate many AD-related phenotypes. Whether the novel pharmacological approach based on PCSK9 pharmacological inhibition will be successful, it will open new perspectives for AD treatment, with a remarkable scientific impact.