Pterosin sesquiterpenoids from Pteris laeta Wall. ex Ettingsh. protect cells from glutamate excitotoxicity by modulating mitochondrial signals.

ETHNOPHARMACOLOGICAL RELEVANCE: The genus Pteris (Pteridaceae) has been used as a traditional herb for a long time. In particular, Pteris laeta Wall. ex Ettingsh. has been widely used in traditional Chinese medicine to treat nervous system diseases and some pterosin sesquiterpenes from Pteris show neuroprotective activity, but their underlying molecular mechanisms remain elusive. Therefore, to investigate the neuroprotective activity and working mechanism of pterosin sesquiterpenes from P. laeta Wall. ex Ettingsh. will provide a better understanding and guidance in using P. laeta Wall. ex Ettingsh. as a traditional Chinese medicine. AIM OF THE STUDY: We aim to develop effective treatments for neurodegenerative diseases from pterosin sesquiterpenes by evaluating their neuroprotective activity and investigating their working mechanisms. MATERIALS AND METHODS: Primary screening on the glutamate-induced excitotoxicity cell model was assessed by 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) assay. Fluorescent-activated cell sorting (FACS) was used to analyze the activation level of glutamate receptors and mitochondria membrane potential after treatment. Transcriptomics and proteomics analysis was performed to identify possible targets of pterosin B. The key pathways were enriched by the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis through the Database for Annotation, Visualization, and Integrated Discovery (DAVID). The core targets were visualized by a protein-protein interaction network using STRING. The mRNA and protein expressions were evaluated using real-time quantitative polymerase chain reaction (Q-PCR) and western blot, respectively. Immunocytochemistry was performed to monitor mitochondrial and apoptotic proteins. Cellular reactive oxygen species (ROS) were measured by ROS assay, and Ca2+ was stained with Fluo-4 AM to quantify intracellular Ca2+ levels. RESULTS: We found pterosin B from Pteris laeta Wall. ex Ettingsh. showed significant neuroprotective activity against glutamate excitotoxicity, enhancing cell viability from 43.8% to 105% (p-value: <0.0001). We demonstrated that pterosin B worked on the downstream signaling pathways of glutamate excitotoxicity rather than directly blocking the activation of glutamate receptors. Pterosin B restored mitochondria membrane potentials, alleviated intracellular calcium overload from 107.4% to 95.47% (p-value: 0.0006), eliminated cellular ROS by 36.55% (p-value: 0.0143), and partially secured cells from LPS-induced inflammation by increasing cell survival from 46.75% to 58.5% (p-value: 0.0114). Notably, pterosin B enhanced the expression of nuclear factor-erythroid factor 2-related factor 2 (NRF2) and heme oxygenase-1 (HO-1) by 2.86-fold (p-value: 0.0006) and 4.24-fold (p-value: 0.0012), and down-regulated Kelch-like ECH-associated protein 1 (KEAP1) expression by 2.5-fold (p-value: 0.0107), indicating that it possibly promotes mitochondrial biogenesis and mitophagy to maintain mitochondria quality control and homeostasis, and ultimately inhibits apoptotic cell death. CONCLUSIONS: Our work revealed that pterosin B protected cells from glutamate excitotoxicity by targeting the downstream mitochondrial signals, making it a valuable candidate for developing potential therapeutic agents in treating neurodegenerative diseases.

Selective C9orf72 G-Quadruplex-Binding Small Molecules Ameliorate Pathological Signatures of ALS/FTD Models.

The G-quadruplex (G4) forming C9orf72 GGGGCC (G4C2) expanded hexanucleotide repeat (EHR) is the predominant genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Developing selective G4-binding ligands is challenging due to the conformational polymorphism and similarity of G4 structures. We identified three first-in-class marine natural products, chrexanthomycin A (cA), chrexanthomycin B (cB), and chrexanthomycin C (cC), with remarkable bioactivities. Thereinto, cA shows the highest permeability and lowest cytotoxicity to live cells. NMR titration experiments and in silico analysis demonstrate that cA, cB, and cC selectively bind to DNA and RNA G4C2 G4s. Notably, cA and cC dramatically reduce G4C2 EHR-caused cell death, diminish G4C2 RNA foci in (G4C2)29-expressing Neuro2a cells, and significantly eliminate ROS in HT22 cells. In (G4C2)29-expressing Drosophila, cA and cC significantly rescue eye degeneration and improve locomotor deficits. Overall, our findings reveal that cA and cC are potential therapeutic agents deserving further clinical study.

Griseocazines: Neuroprotective Multiprenylated Cyclodipeptides Identified through Targeted Genome Mining.

Prenylation can impart pharmacological advantages to bioactive compounds. Global genome mining for prenylated cyclodipeptides identified a gczABC BGC from Streptomyces griseocarneus 132 containing a cyclodipeptide synthase and two prenyltransferase genes. Subsequent heterologous expression allowed isolation and characterization of griseocazines, which displayed potent neuroprotective activity. Further biotransformation analyses revealed that prenyltransferases GczB and GczC catalyzed the stereospecific prenylation of cWW and attached geranyl and farnesyl groups to a cyclodipeptide scaffold, respectively.