Crocetin promotes clearance of amyloid-ß by inducing autophagy via the STK11/LKB1-mediated AMPK pathway.

ABSTRACT

Alzheimer disease (AD) is usually accompanied by two prominent pathological features, cerebral accumulation of amyloid-ß (Aß) plaques and presence of MAPT/tau neurofibrillary tangles. Dysregulated clearance of Aß largely contributes to its accumulation and plaque formation in the brain. Macroautophagy/autophagy is a lysosomal degradative process, which plays an important role in the clearance of Aß. Failure of autophagic clearance of Aß is currently acknowledged as a contributing factor to increased accumulation of Aß in AD brains. In this study, we have identified crocetin, a pharmacologically active constituent from the flower stigmas of Crocus sativus, as a potential inducer of autophagy in AD. In the cellular model, crocetin induced autophagy in N9 microglial and primary neuron cells through STK11/LKB1 (serine/threonine kinase 11)-mediated AMP-activated protein kinase (AMPK) pathway activation. Autophagy induction by crocetin significantly increased Aß clearance in N9 cells. Moreover, crocetin crossed the blood-brain barrier and induced autophagy in the brains' hippocampi of wild-type male C57BL/6 mice. Further studies in transgenic male 5XFAD mice, as a model of AD, revealed that one-month treatment with crocetin significantly reduced Aß levels and neuroinflammation in the mice brains and improved memory function by inducing autophagy that was mediated by AMPK pathway activation. Our findings support further development of crocetin as a pharmacological inducer of autophagy to prevent, slow down progression, and/or treat AD.Abbreviations Aß amyloid-ß; ABCB1/P-gp/P-glycoprotein ATP-binding cassette, subfamily B (MDR/TAP), member 1; AD Alzheimer disease; AMPK/PRKAA AMP-activated protein kinase; APP amyloid beta (A4) precursor protein; ATG autophagy related; BBB blood-brain barrier; BECN1 beclin 1, autophagy related; CAMKK2/CaMKKß calcium/calmodulin-dependent protein kinase kinase 2, beta; CSE Crocus sativus extract; CTSB cathepsin B; EIF4EBP1 eukaryotic translation initiation factor 4E binding protein 1; GFAP glial fibrillary acidic protein; GSK3B/GSK3ß glycogen synthase kinase 3 beta; Kp brain partition coefficient; LRP1 low density lipoprotein receptor-related protein 1; MAP1LC3B/LC3B microtubule-associated protein 1 light chain 3 beta; MAP2 microtubule-associated protein 2; MAPK/ERK mitogen-activated protein kinase; MAPT/tau microtubule-associated protein tau; MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; MTOR mechanistic target of rapamycin kinase; MWM Morris water maze; NFKB/NF-κB nuclear factor of kappa light polypeptide gene enhancer in B cells; NMDA N-methyl-d-aspartic acid; RPTOR regulatory associated protein of MTOR; RPS6KB1/p70S6K ribosomal protein S6 kinase 1; SQSTM1 sequestosome 1; SRB sulforhodamine B; STK11/LKB1 serine/threonine kinase 11; TFEB transcription factor EB; TSC2 TSC complex subunit 2; ULK1 unc-51 like kinase 1.