Mitochondrial translation is a unique relic of the symbiotic origin of the organelle. Alterations of its components cause a number of severe human diseases. Hereby we report a study of mice devoid of Mettl15 mitochondrial 12S rRNA methyltransferase, responsible for the formation of m⁴C839 residue (human numbering). Homozygous Mettl15^−/− mice appeared to be viable in contrast to other mitochondrial rRNA methyltransferase knockouts reported earlier. The phenotype of Mettl15^−/− mice is much milder than that of other mutants of mitochondrial translation apparatus. In agreement with the results obtained earlier for cell cultures with an inactivated Mettl15 gene, we observed accumulation of the RbfA factor, normally associated with the precursor of the 28S subunit, in the 55S mitochondrial ribosome fraction of knockout mice. A lack of Mettl15 leads to a lower blood glucose level after physical exercise relative to that of the wild-type mice. Mettl15^−/− mice demonstrated suboptimal muscle performance and lower levels of Cox3 protein synthesized by mitoribosomes in the oxidative soleus muscles. Additionally, we detected decreased learning capabilities in the Mettl15^−/− knockout mice in the tests with both positive and negative reinforcement. Such properties make Mettl15^−/− knockout mice a suitable model for mild mitochondriopathies.

Background/Objectives: Autophagy is an important cellular self-cleansing process whose normal functioning is essential for preventing many age-related diseases. The search for and study of new autophagy activators allows the proposal of novel therapeutic approaches for the treatment of age-related diseases. Medical plants are a rich source of bioactive compounds with variable functions. In this study, we propose an HR-LCMS/MS-based technique for identifying the principal autophagy activators in plant extracts. Methods: We performed a Western blot analysis of the autophagy-inducing activity of plant extract HPLC fractions on a model of SH-SY5Y cells. The composition of the fractions showing autophagy-activating potential was determined via HR-LCMS/MS. Results: We analyzed five plants known to produce autophagy activators and proved the ability of the method to detect the main bioactive compounds. Additional screening demonstrated for the first time that Astragalus dasyanthus is a producer of the autophagy-inducer glabrol. Conclusions: The described HR-LCMS/MS-based method for identifying autophagy activators in multicomponent plant extracts is effective and could be used for further high-throughput screening.

Autophagy is a conserved lysosome-dependent process essential for cellular homeostasis, and pharmacological activation of autophagy has emerged as a promising therapeutic strategy for age-related, neurodegenerative, metabolic, and malignant diseases. Despite the growing interest in natural autophagy modulators, lichens remain largely unexplored as a source of autophagy-inducing compounds. Here, we tested ethanolic extracts from four commercially available lichens using LC3-II accumulation as a primary readout. Usnea sp. was identified as the most active species. Activity-guided fractionation followed by HRMS and NMR analyses identified salazinic acid as the active metabolite. Salazinic acid increased LC3-II accumulation, enhanced autophagic flux in the presence of bafilomycin A1, and promoted autophagosome formation as confirmed by transmission electron microscopy. The compound exhibited low cytotoxicity in human cell lines at concentrations exceeding those required for autophagy induction. Mechanistically, salazinic acid activated the phosphorylation of AMPK, ULK1, and AKT; however, it retained its ability to stimulate autophagic flux in AMPK- and ULK1-deficient cells, indicating that its activity is not strictly dependent on the canonical AMPK–ULK1 signaling pathway. Collectively, our findings identify salazinic acid as a previously unrecognized inducer of productive autophagic flux and demonstrate that lichen secondary metabolites represent a promising and largely untapped source of novel autophagy-modulating compounds.

Methyltransferases that modify spliceosomal small nuclear RNAs (snRNAs) play a crucial role in the cell by ensuring proper maturation of snRNAs, which is essential for optimal function of spliceosome. In this study, we investigated the enzyme METTL4, which catalyzes N6-methylation of 2′-O-methyladenosine at position 30 of U2 snRNA. Function of both the protein and the modification in splicing remains unclear. We demonstrated that inactivation of the METTL4 gene in HeLa S3 cells leads to significant changes in alternative splicing, general slowdown in spliceosome activity, and intron accumulation. In the cells lacking METTL4, expression of the set of genes associated with ribosomal RNA maturation is reduced, and the number of coilin-positive structures, most likely Cajal bodies, is decreased in the nuclei of these cells.