Biology subjects

Olahova, M.

Publications and source records attributed to Olahova, M..

4 recordsLinked to original sources

bioRxiv2026

Pathogenic DRP1 variants reveal a role for biomolecular condensation in mitochondrial fission

Fission is essential for proper mitochondrial function and for cellular homeostasis. Dysfunction in mitochondrial fission is associated with several neurological disorders, including the rare and lethal encephalopathy EMPF1, which is caused by de novo heterozygous DNM1L variants. DNM1L encodes the mitochondrial fission mechanoenzyme DRP1, which can intrinsically self-assemble and induce membrane scission. Wild-type DRP1 puncta that appear throughout the cytoplasm are thought to be pre-scission complexes of well-ordered oligomeric assemblies. Immunofluorescence imaging of patient-derived EMPF1 fibroblasts carrying assembly-deficient DNM1L variants reveals elongated mitochondrial networks consistent with impaired fission. Despite this loss-of-function phenotype, these cells retain essentially wild-type numbers of DRP1 puncta. We confirmed the previously reported inability of purified pathogenic DRP1 variants p.Gly363Asp and p.Gly401Ser to assemble under conditions in which WT DRP1 forms helical polymers. Under macromolecular crowding conditions, however, both wild-type and mutant DRP1 access condensed states whose formation depends on protein concentration and solution conditions. Acute treatment of EMPF1 fibroblasts with 1,6-hexanediol preferentially alters DRP1 puncta fluorescence intensity and distribution in mutant cells relative to wild type, indicating genotype-dependent differences in puncta material properties. Together, these findings support a model in which DRP1 puncta occupy a continuum of condensed states, only a subset of which mature into fission-competent assemblies, revealing biomolecular condensation as a previously unrecognized layer of DRP1 regulation. Biasing DRP1 along this continuum may provide a mechanistic basis for impaired fission in EMPF1 and suggest opportunities to restore productive assembly in select pathogenic contexts. Significance StatementDRP1 puncta associated with mitochondrial fission are thought to be well-ordered oligomeric assemblies that precede membrane scission. Yet their dynamic behavior within cells has remained difficult to reconcile as well-ordered assembly. Under prevailing models, cells bearing pathogenic DNM1L variants impaired in assembly would be expected to lack puncta, but we show these cells retain wild-type puncta levels. We demonstrate that both wild-type and pathogenic mutant DRP1 populate multiple condensed states in vitro, and that disease variants are biased toward more fluid, chemically sensitive assemblies. These findings identify biomolecular condensation as a regulatory layer of DRP1 organization and suggest that shifting DRP1 along this assembly continuum may restore productive fission in select pathogenic contexts.

biophysics↗

bioRxiv2026

Pathogenic PTCD1 variants cause mitochondrial protein aggregation and cardiomyopathy

Disorders of mitochondrial oxidative phosphorylation affecting multiple respiratory chain complexes are among the most common causes of mitochondrial disease in humans. However, impaired energy metabolism alone does not fully account for tissue-specific vulnerability and disease progression, suggesting that additional molecular mechanisms contribute to disease pathology. We previously identified PTCD1 variants in a child with infantile cardiomyopathy associated with a combined respiratory chain deficiency. Here, we establish the pathogenicity of three PTCD1 (NM_015545.4) variants in which p.(Arg113Trp) and p.(Gly184Arg) segregate in cis whereas p.(Arg130*) is present in trans, demonstrating that disrupted mitochondrial proteostasis contributes to tissue damage in PTCD1 deficiency. PTCD1 patient cardiac tissue characterisation revealed impaired mitoribosome biogenesis, alongside increased aggregation of selective mitochondrial matrix proteins. Cell models expressing individual and combined PTCD1 missense variants, coupled with proteomics, recapitulated the protein aggregation, with the cis p.(Arg113Trp);p.(Gly184Arg) combination showing the most severe effect. Protein aggregation was accompanied by altered OPA1 processing and mitochondrial network remodelling. Our findings establish accumulating proteotoxic stress arising from impaired mitoribosome assembly as a pathogenic mechanism in post-mitotic tissues, driving PTCD1 cardiomyopathy.

cell biology↗

bioRxiv2024

RTN4IP1 is essential for the final stages of mitochondrial complex I assembly and coenzyme Q biosynthesis

A biochemical deficiency of mitochondrial complex I (CI) underlies [~]30% of cases of primary mitochondrial disease, yet the inventory of molecular machinery required for CI assembly remains incomplete. We previously characterised patients with isolated CI deficiency caused by segregating variants in RTN4IP1, encoding a mitochondrial NAD(P)H oxidoreductase. Here, we demonstrate that RTN4IP1 deficiency causes a CI assembly defect in both patient fibroblasts and knockout cells, and report that RTN4IP1 is a bona fide CI assembly factor. Complexome profiling revealed accumulation of unincorporated ND5-module and impaired N-module production. RTN4IP1 patient fibroblasts also exhibited defective coenzyme Q biosynthesis, substantiating this emerging function of RTN4IP1. Thus, our data reveal RTN4IP1 plays an essential role in both the terminal stages of CI assembly and in coenzyme Q metabolism, and that pathogenic RTN4IP1 variants impair both functions in patients with mitochondrial disease.

cell biology↗

bioRxiv2021

Detection of pathogenic splicing events from RNA-sequencing data using dasper

Although next-generation sequencing technologies have accelerated the discovery of novel gene-to-disease associations, many patients with suspected Mendelian diseases still leave the clinic without a genetic diagnosis. An estimated one third of these patients will have disorders caused by mutations impacting splicing. RNA-sequencing has been shown to be a promising diagnostic tool, however few methods have been developed to integrate RNA-sequencing data into the diagnostic pipeline. Here, we introduce dasper, an R/Bioconductor package that improves upon existing tools for detecting aberrant splicing by using machine learning to incorporate disruptions in exon-exon junction counts as well as coverage. dasper is designed for diagnostics, providing a rank-based report of how aberrant each splicing event looks, as well as including visualization functionality to facilitate interpretation. We validate dasper using 16 patient-derived fibroblast cell lines harbouring pathogenic variants known to impact splicing. We find that dasper is able to detect pathogenic splicing events with greater accuracy than existing LeafCutterMD or z-score approaches. Furthermore, by only applying a broad OMIM gene filter (without any variant-level filters), dasper is able to detect pathogenic splicing events within the top 10 most aberrant identified for each patient. Since using publicly available control data minimises costs associated with incorporating RNA-sequencing into diagnostic pipelines, we also investigate the use of 504 GTEx fibroblast samples as controls. We find that dasper leverages publicly available data effectively, ranking pathogenic splicing events in the top 25. Thus, we believe dasper can increase diagnostic yield for a pathogenic splicing variants and enable the efficient implementation of RNA-sequencing for diagnostics in clinical laboratories.

bioinformatics↗