The Potential of Indole/Indolylquinoline Compounds in Tau Misfolding Reduction by Enhancement of HSPB1

Background: Neurofibrillary tangles formed from tau misfolding have long been considered one of the pathological hallmarks of Alzheimer's disease (AD). The misfolding of tau in AD correlates with the clinical progression of AD and inhibition or reversal of tau misfolding may protect the affected neurons. Methods: We generated 293 and SH-SY5Y cells expressing DsRed-tagged pro-aggregation mutant of repeat domain of tau (ΔK280 tau_RD) to test indole/indolylquinoline derivatives for reducing tau misfolding and neuroprotection. Results: Four of the 10 derivatives tested displayed good misfolding-inhibitory effects on Tet-On 293 cells. Among them, NC009-1 and NC009-7 enhanced heat-shock 27 kDa protein 1 (HSPB1) expression to increase ∆K280 tau_RD-DsRed solubility and promoted neurite outgrowth in Tet-On SH-SY5Y cells. Knockdown of HSPB1 resulted in decreased ∆K280 tau_RD-DsRed solubility and reduced neurite outgrowth, which were rescued by addition of NC009-1/NC009-7. Treatment with indole/indolylquinoline derivatives also improved neuronal cell viability and neurite outgrowth in mouse hippocampal primary culture under tau cytotoxicity. Conclusion: Our results demonstrate how indole/indolylquinoline derivatives are likely to work in tau misfolding reduction, providing insight into the possible working mechanism of indole and indolylquinoline derivatives in AD treatment.