Biology subjects

Filipovska, A.

Publications and source records attributed to Filipovska, A..

4 recordsLinked to original sources

bioRxiv2024

Skeletal Muscle Specific PolG Dysfunction Activates the Integrated Stress Response and Promotes a Cachexia like Phenotype

During mitochondrial damage, information is relayed between the mitochondria and nucleus to coordinate precise responses to preserve cellular health. One such pathway is the mitochondrial integrated stress response (mtISR), which is specifically activated by mitochondrial DNA (mtDNA) damage. However, the causal molecular signals responsible for this activation remain elusive. A gene often associated with mtDNA mutations/deletions is Polg1, which encodes the mitochondrial DNA Polymerase {gamma} (PolG). Here, we describe what is to our knowledge the first conditional muscle specific model of PolG mutation, and demonstrate a rapid development of mitochondrial dysfunction and cachexia in these animals from [~]5 months of age. Detailed molecular profiling of muscles demonstrated robust activation of the mtISR, likely mediated upstream by the HRI/DELE1 stress pathway. This was accompanied by striking alterations to the mitochondrial folate cycle and its metabolites, strongly implying imbalanced folate intermediates as a previously unrecognised pathology driving the mtISR in mitochondrial disease.

physiology↗

bioRxiv2024

Increased mitochondrial transcription initiation does not promote oxidative phosphorylation

POLRMT is the sole RNA polymerase in human mitochondria where it generates primers for mitochondrial DNA (mtDNA) replication and transcribes the mitochondrial genome to express genes encoding essential components of the oxidative phosphorylation (OXPHOS) system. Elevated POLRMT levels are found in several cancers and in mouse models with severe mitochondrial dysfunction. Here, we generated and characterized mice over-expressing Polrmt to investigate the physiological and molecular consequences of elevated POLRMT levels. Increasing POLRMT did not result in any pathological phenotype but instead positively affected exercise capacity under stress conditions. POLRMT overexpression increased in organello transcription initiation, resulting in higher steady-state levels of the promoter-proximal L-strand transcript 7S RNA and higher mtDNA levels. Surprisingly, the abundance of mature mitochondrial RNAs was not affected by the elevated POLRMT levels. Furthermore, ubiquitous simultaneous overexpression of POLRMT and LRPPRC, which stabilizes mitochondrial messenger RNAs, did not increase steady-state levels of mitochondrial transcripts in the mouse. Our data show that POLRMT levels regulate transcription initiation, but additional regulatory steps downstream of transcription initiation and transcript stability limit OXPHOS biogenesis.

molecular biology↗

bioRxiv2022

Temporal landscape of mitochondrial proteostasis governed by the UPRmt

Breakdown of mitochondrial proteostasis activates quality control pathways including the mitochondrial unfolded protein response (UPRmt) and PINK1/Parkin mitophagy. However, beyond the upregulation of chaperones and proteases, we have a limited understanding of how the UPRmt remodels and restores damaged mito-proteomes. Here, we have developed a functional proteomics framework, termed MitoPQ (Mitochondrial Proteostasis Quantification), to dissect the UPRmts role in maintaining proteostasis during stress. We discover essential roles for the UPRmt in both protecting and repairing proteostasis, with oxidative phosphorylation metabolism being a central target of the UPRmt. Transcriptome analyses together with MitoPQ reveal that UPRmt transcription factors drive independent signaling arms that act in concert to maintain proteostasis. Unidirectional interplay between the UPRmt and PINK1/Parkin mitophagy was found to promote oxidative phosphorylation recovery when the UPRmt failed. Collectively, this study defines the network of proteostasis mediated by the UPRmt and highlights the value of functional proteomics in decoding stressed proteomes.

cell biology↗

bioRxiv2021

Stepwise maturation of the peptidyl transferase region of human mitoribosomes

Mitochondrial ribosomes are specialized for the synthesis of membrane proteins responsible for oxidative phosphorylation. Mammalian mitoribosomes diverged considerably from the ancestral bacterial ribosomes and feature dramatically reduced ribosomal RNAs. Structural basis of the mammalian mitochondrial ribosome assembly is currently not understood. Here we present eight distinct assembly intermediates of the human large mitoribosomal subunit involving 7 assembly factors. We discover that NSUN4-MTERF4 dimer plays a critical role in the process by stabilizing the 16S rRNA in a conformation that exposes the functionally important regions of rRNA for modification by MRM2 methyltransferase and quality control interactions with a conserved mitochondrial GTPase MTG2 that contacts the sarcin ricin loop and the immature active site. The successive action of these factors leads to the formation of the peptidyl transferase active site of the mitoribosome and the folding of the surrounding rRNA regions responsible for interactions with tRNAs and the small ribosomal subunit.

biochemistry↗