Ramalin Ameliorates Alzheimer's Disease Pathology by Targeting BACE1, HDAC6, and MAPK Pathways.

Aberrant deposition of β-amyloid (Aβ) and hyperphosphorylated tau, along with neuroinflammation, are key drivers of Alzheimer's disease (AD) pathology. Here, we identify ramalin, a natural antioxidant, as a promising therapeutic agent that alleviates AD pathology by modulating β-site APP cleaving enzyme 1 (BACE1), histone deacetylase 6 (HDAC6), and the mitogen-activated protein kinases (MAPK) pathway. Ramalin reduced BACE1 protein levels, independently of its transcription, translation, or enzymatic activity, an effect mediated by inhibition of HDAC6. Consistently, HDAC6 knockout similarly decreased BACE1 levels, highlighting HDAC6 as a key regulator of BACE1. Ramalin further suppressed neuroinflammatory responses by downregulating inducible nitric oxide synthase (iNOS) and the NLR family pyrin domain containing 3 (NLRP3) inflammasome. In AD mouse models, ramalin treatment significantly attenuated neuroinflammation, Aβ plaque burden, and tau hyperphosphorylation, while improving cognitive performance. Notably, ramalin reversed Aβ oligomer-induced synaptic transmission impairment and restored synaptic vesicle recycling in hippocampal neurons. Transcriptomic analysis identified modulation of the MAPK pathway, with reduced phosphorylation of c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) implicated in tau pathology. These findings establish ramalin as a disease-modifying intervention that provides neuroprotection through concurrent regulation of BACE1, HDAC6, and MAPK signaling pathway. Collectively, our findings highlight ramalin as a compelling disease-modifying candidate with the potential to drive a breakthrough approach targeting AD pathology.