Levosimendan prevents tau pathology by inhibiting disulfide-linked tau oligomerization posing as a promising anti-tau therapeutics

Abstract

Tau oligomers play critical roles in tau pathology, responsible for neuronal cell death and transmitting the disease in the brain. Accordingly, preventing tau oligomerization becomes an important therapeutic strategy to treat tauopathies including Alzheimer’s disease, however progress has been slow due to difficulties of detecting tau oligomers in cellular context. Toward tau-targeted drug discovery, our group have developed a tau-BiFC platform to monitor and quantify tau oligomerization. By using the tau-BiFC platform, we screened 1,018 compounds in FDA-approved & Passed Phase I drug library, and identified levosimendan as a potent anti-tau agent inhibiting tau oligomerization. 14C-isotope labeling of levosimendan identified that levosimendan covalently bound to tau cysteines, directly inhibiting disulfide-linked tau oligomerization. In addition, levosimendan was able to disassemble tau oligomers into monomers, and rescuing neurons from aggregation states. In comparison, the well-known anti-tau agents, methylene blue (MB) and LMTM, failed to protect neurons from tau-mediated toxicity, generating high-molecular weight tau oligomers. The administration of levosimendan also suppressed tau pathology in the brain, preventing cognitive declines in TauP301L-BiFC transgenic mice. Although careful validation is required, here we present the potential of levosimendan as a disease modifying therapy for tauopathies targeting tau oligomerization.

Recent advances in cellular biosensor technology to investigate tau oligomerization

“…(c) High‐throughput screening of 1018 FDA approved compounds using Venus‐based tau‐BiFC fluorescence turn‐on biosensor expressed in HEK293 cells. Tau‐BiFC OFF (+), Tau‐BiFC ON (green), FDA library (gray), methylene blue (MB, blue), LMTM (cyan), and levosimendan (hit compound, yellow) are indicated on the plot 111 . (d) Treatment of levosimendan at different timings along the aggregation cascade of K18‐P301L induced tau aggregation in tau‐BiFC cells.…”

“…(d) Treatment of levosimendan at different timings along the aggregation cascade of K18‐P301L induced tau aggregation in tau‐BiFC cells. Inhibitory effect of levosimendan is characterized by decreases in the tau‐BiFC responses 111 . Permissions obtained from References 58 and 111…”

“… 111 Levosimendan directly inhibits disulfide‐linked tau oligomerization by covalently binding to tau cysteines as characterized by 14 C‐isotope labeling of the small molecule. In addition, levosimendan prevents the formation of oligomers from monomers and is also capable of disassembling preformed tau oligomers or aggregates into monomers (Figure 7(d)), thus rescuing neurons from tau‐induced toxicity 111 . The study also made a comparison between levosimendan and the well‐known inhibitors of tau aggregation, methylene blue (MB) and LMTM, and they show that MB and LMTM disrupt fibrils but generate high‐molecular‐weight tau oligomers which are toxic to neurons.…”

“…A key strength of this study is that they tested levosimendan in vivo with the tauP301L‐BiFC transgenic mice. The administration of levosimendan reduces tau oligomerization as illustrated by a decrease in tau‐BiFC signals, suppresses tau pathology in the brain, and prevents cognitive declines in the mice 111 …”

“…Tau‐BiFC OFF (+), Tau‐BiFC ON (green), FDA library (gray), methylene blue (MB, blue), LMTM (cyan), and levosimendan (hit compound, yellow) are indicated on the plot. 111 (d) Treatment of levosimendan at different timings along the aggregation cascade of K18‐P301L induced tau aggregation in tau‐BiFC cells. Inhibitory effect of levosimendan is characterized by decreases in the tau‐BiFC responses.…”