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Mitochondrial gene expression relies on mitoribosomes to translate mitochondrial mRNAs. The biogenesis of mitoribosomes is an intricate process involving multiple assembly factors. Among these factors, GTP-binding proteins (GTPBPs) play important roles. In bacterial systems, numerous GTPBPs are required for ribosome subunit maturation, with EngB being a GTPBP involved in the ribosomal large subunit assembly. In this study, we focus on exploring the function of GTPBP8, the human homolog of EngB. We find that ablation of GTPBP8 leads to the inhibition of mitochondrial translation, resulting in significant impairment of oxidative phosphorylation. Structural analysis of mitoribosomes from GTPBP8 knock-out cells shows the accumulation of mitoribosomal large subunit assembly intermediates that are incapable of forming functional monosomes. Furthermore, fPAR-CLIP analysis reveals that GTPBP8 is an RNA-binding protein that interacts specifically with the mitochondrial ribosome large subunit 16 S rRNA. Our study highlights the role of GTPBP8 as a component of the mitochondrial gene expression machinery involved in mitochondrial large subunit maturation., (© 2024. The Author(s).)

Background: Unhealthy lifestyles represent a key element fueling Non-alcoholic fatty liver disease (NAFLD) onset and worsening. We aimed to evaluate the effects of forced acute lifestyle changes on NAFLD evolution., Methods: 187 NAFLD patients were followed two years pre- and two years during the lockdown social restrictions in three Italian medical centers. For each patient, biochemical, clinical, non-invasive liver fibrosis, nutritional, and body composition data were collected., Results: An increase in fats and carbohydrate intake associated with impaired weekly physical activity during the lockdown was demonstrated as well as an increase in body mass index and waist-hip-ratio (p < 0.0001 for all). Total cholesterol, low-density lipoprotein, high-density lipoprotein, triglycerides, glucose, insulin, homeostatic model assessment for insulin resistance, and transaminases worsened during the lockdown (glucose: p = 0.0007; p < 0.0001 for the others). Moreover, NAFLD fibrosis score, liver stiffness, and controlled attenuation parameter were also impaired during the same period (p < 0.0001 for all). The bioelectrical impedance analysis (BIA) evidenced an increase of fat mass (FM), and a reduction of free fat mass (FFM) and body cell mass (BCM) (p < 0.0001 for all). The lockdown overall hepatocellular carcinoma (HCC) and Milan-out HCC occurrence revealed Hazard Ratio (HR): 2.398, 95% Confidence Interval (CI):1.16-5, p = 0.02, and HR:5.931, CI:2-17.6, p = 0.008 respectively. A liver disease stage and comorbidities independent association between both the assessed outcomes and body composition analysis in terms of mean values and variation (T1-T2 Δ) was demonstrated., Conclusions: The acute lifestyle changes impacted NAFLD evolution via body composition modifications negatively influencing the HCC occurrence., (© 2024. The Author(s).)

Mitochondrial ribosomes (mitoribosomes) synthesize a critical set of proteins essential for oxidative phosphorylation. Therefore, mitoribosomal function is vital to the cellular energy supply. Mitoribosome biogenesis follows distinct molecular pathways that remain poorly understood. Here, we determine the cryo-EM structures of mitoribosomes isolated from human cell lines with either depleted or overexpressed mitoribosome assembly factor GTPBP5, allowing us to capture consecutive steps during mitoribosomal large subunit (mt-LSU) biogenesis. Our structures provide essential insights into the last steps of 16S rRNA folding, methylation and peptidyl transferase centre (PTC) completion, which require the coordinated action of nine assembly factors. We show that mammalian-specific MTERF4 contributes to the folding of 16S rRNA, allowing 16 S rRNA methylation by MRM2, while GTPBP5 and NSUN4 promote fine-tuning rRNA rearrangements leading to PTC formation. Moreover, our data reveal an unexpected involvement of the elongation factor mtEF-Tu in mt-LSU assembly, where mtEF-Tu interacts with GTPBP5, similar to its interaction with tRNA during translational elongation.