L-Proline Prevents Endoplasmic Reticulum Stress in Microglial Cells Exposed to L-azetidine-2-carboxylic Acid

Abstract

L-Azetidine-2-carboxylic acid (AZE) is a non-protein amino acid that shares structural similarities with its proteogenic L-proline amino acid counterpart. For this reason, AZE can be misincorporated in place of L-proline, contributing to AZE toxicity. In previous work, we have shown that AZE induces both polarization and apoptosis in BV2 microglial cells. However, it is still unknown if these detrimental effects involve endoplasmic reticulum (ER) stress and whether L-proline co-administration prevents AZE-induced damage to microglia. Here, we investigated the gene expression of ER stress markers in BV2 microglial cells treated with AZE alone (1000 µM), or co-treated with L-proline (50 µM), for 6 or 24 h. AZE reduced cell viability, nitric oxide (NO) secretion and caused a robust activation of the unfolded protein response (UPR) genes (ATF4, ATF6, ERN1, PERK, XBP1, DDIT3, GADD34). These results were confirmed by immunofluorescence in BV2 and primary microglial cultures. AZE also altered the expression of microglial M1 phenotypic markers (increased IL-6, decreased CD206 and TREM2 expression). These effects were almost completely prevented upon L-proline co-administration. Finally, triple/quadrupole mass spectrometry demonstrated a robust increase in AZE-bound proteins after AZE treatment, which was reduced by 84% upon L-proline co-supplementation. This study identified ER stress as a pathogenic mechanism for AZE-induced microglial activation and death, which is reversed by co-administration of L-proline.

Metabolites of intestinal fora can be used as diagnostic and progressive markers for mild cognitive impairment

“…NF-light is a family of filament proteins, which mainly exist in the axons of nerve cells and participate in the formation and maintenance of the cytoskeleton, and the level of neurofilament light chain in the cerebrospinal fluid can be used as a biomarker for neurodegenerative diseases (Lin et al, 2023). L-Proline reverses endoplasmic reticulum stress, which is a pathogenic mechanism of Azetidine-2-carboxylic Acid (AZE)induced microglia activation and death (Piper et al, 2023), and Indoleacetaldehyde in intestinal host cells and the production of KYN metabolites can activate hydrocarbon receptors, proteins found in humans and animals that can bind to many chemicals and regulate gene expression (Salminen, 2023). However, the mechanism of their relationship with NF-light remains unclear.…”

Mechanical Properties and Temperature and Pressure Effects on the Crystal Structure of (2S,3S,4R)-2,3,4-(Trinitratomethyl)-1-nitroazetidine (TMNA) by Single-Crystal X-ray Diffractometry and Density Functional Theory

“…Azetidine [(CH 2 ) 3 NH], a saturated four-membered, heterocyclic molecule, and its derivatives have sparked significant interest in recent years because of their potential use as pharmacological products, agriculture compounds, and energetic ingredients. − The versatile azetidine scaffold presents great opportunities for building a variety of azetidine derivatives. Its versatility stems from its structural rigidity as well as from its electronegative nitrogen atom, which provides the ring nucleophilic activity, and its three carbon atoms, which offer the addition of a variety of functional groups.…”