Biology subjects

Viscomi, C.

Publications and source records attributed to Viscomi, C..

9 recordsLinked to original sources

bioRxiv2024

COA8 is a COX10-binding protein involved in the early biogenesis of cytochrome c oxidase

Human cytochrome c oxidase (COX) is composed of fourteen subunits, only two of which are catalytic. The functions of a myriad of accessory factors are needed to put together the structural subunits, as well as for the formation of the active centers. The molecular roles of most of these factors are still unknown, even if they are essential for COX function since their defects cause severe mitochondrial disease. COA8 is exclusively found in metazoa and loss-of-function genetic variants cause mitochondrial encephalopathy and COX deficiency in humans. In this work, we have resolved the function of COA8, as a factor that specifically binds to COX10, the heme O synthase. This interaction is necessary not only for the stabilization of human COX10, but also to guarantee its catalytic activity as the first step for the synthesis of the heme A cofactor, which is a crucial component of the COX catalytic center.

biochemistry↗

bioRxiv2024

Mitochondrial reverse electron transport in myeloid cells perpetuates neuroinflammation

Sustained smouldering, or low grade, activation of myeloid cells is a common hallmark of several chronic neurological diseases, including multiple sclerosis (MS)1. Distinct metabolic and mitochondrial features guide the activation and the diverse functional states of myeloid cells2. However, how these metabolic features act to perpetuate neuroinflammation is currently unknown. Using a multiomics approach, we identified a new molecular signature that perpetuates the activation of myeloid cells through mitochondrial complex II (CII) and I (CI) activity driving reverse electron transport (RET) and the production of reactive oxygen species (ROS). Blocking RET in pro-inflammatory myeloid cells protected the central nervous system (CNS) against neurotoxic damage and improved functional outcomes in animal disease models in vivo. Our data show that RET in myeloid cells is a potential new therapeutic target to foster neuroprotection in smouldering inflammatory CNS disorders3.

neuroscience↗

bioRxiv2023

Structural rather than catalytic role for mitochondrial respiratory chain supercomplexes

Mammalian mitochondrial respiratory chain (MRC) complexes are able to associate into quaternary structures named supercomplexes (SCs), which normally coexist with non bound individual complexes. The functional significance of SCs has not been fully clarified and the debate has been centered on whether or not they confer catalytic advantages to the non-bound individual complexes. Mitochondrial respiratory chain organization does not seem to be conserved in all organisms. In fact, and differently from mammalian species, mitochondria from Drosophila melanogaster tissues are characterized by low amounts of SCs, despite the high metabolic demands and MRC activity shown by these mitochondria. Here, we show that attenuating the biogenesis of individual respiratory chain complexes was accompanied by increased formation of stable SCs, which are missing in Drosophila melanogaster in physiological conditions. This phenomenon was not accompanied by an increase in mitochondrial respiratory activity. Therefore, we conclude that SC formation is necessary to stabilize the complexes in suboptimal biogenetic conditions, but not for the enhancement of respiratory chain catalysis.

biochemistry↗

bioRxiv2021

Tissue specific requirements for ECSIT in mitochondrial complex I assembly

Here we describe a mutation in the mitochondrial complex I assembly factor (Evolutionarily conserved signalling intermediate in Toll pathway) ECSIT which reveals tissue specific requirements for this factor in complex I assembly. Mitochondrial complex I assembly is a multi-step process dependant on assembly factors that organise and arrange the individual subunits, allowing for their incorporation into the complete enzyme complex. We have identified an ENU induced mutation in ECSIT (N209I) that exhibits a profound effect on complex I assembly only in heart tissue resulting in hypertrophic cardiomyopathy in the absence of other phenotypes. Mitochondrial function was reduced by 98% in mitochondria isolated from cardiac tissue but mitochondria from other tissues such as skeletal muscle, brain, liver, and kidney were unaffected. This data suggests the mechanisms underlying complex I assembly are tissue specific and has implications in understanding the pathogenesis of cardiomyopathy.

cell biology↗

bioRxiv2020

In vivo and in vitro mechanistic characterization of a clinically relevant PolγA mutation

Mutations in POLG, encoding POL{gamma}A, the catalytic subunit of the mitochondrial DNA polymerase, cause a spectrum of disorders characterized by mtDNA instability. However, the molecular pathogenesis of POLG-related diseases is poorly understood and efficient treatments are missing. Here, we generated a POLGA449T/A449T mouse model, which reproduces the most common human recessive mutation of POLG, encoding the A467T change, and dissected the mechanisms underlying pathogenicity. We show that the A449T mutation impairs DNA binding and mtDNA synthesis activities of POL{gamma} in vivo and in vitro. Interestingly, the A467T mutation also strongly impairs interactions with POL{gamma}B, the homodimeric accessory subunit of holo-POL{gamma}. This allows the free POL{gamma}A to become a substrate for LONP1 protease degradation, leading to dramatically reduced levels of POL{gamma}A, which in turn exacerbates the molecular phenotypes of PolgA449T/A449T mice. Importantly, we validated this mechanism for other mutations affecting the interaction between the two POL{gamma} subunits. We suggest that LONP1 dependent degradation of POL{gamma}A can be exploited as a target for the development of future therapies.

genetics↗

bioRxiv2020

Opa1 overexpression protects from early onset Mpv17-/--related mouse kidney disease

Moderate overexpression of Opa1, encoding a master regulator of mitochondrial cristae morphology, has been shown to improve significantly mitochondrial damage induced by drugs, surgical denervation, or genetically determined OXPHOS defects. However, this approach has been so far demonstrated in a limited number of genetically defective OXPHOS models characterized by specific impairment of a single mitochondrial respiratory chain complex. Here, we investigated the effectiveness of moderate Opa1 overexpression in the Mpv17-/- mouse, characterized by profound, multisystem mtDNA depletion. In naive Mpv17-/- individuals, whose genetic background was crossed with individuals belonging to the Opa1tg strain, we found a surprising anticipation of severe, progressive focal segmental glomerulosclerosis, previously described in Mpv17-/- animals as a late-onset clinical feature (after 12-18 months of life). In contrast, kidney failure led Mpv17-/- individuals from this new "mixed" strain leading to death 8-9 weeks after birth. However, Mpv17-/-::Opa1tg mice lived much longer than Mpv17-/- littermates, and developed much later severe proteinuria associated with focal segmental glomerulosclerosis. MtDNA content and OXPHOS activities were significantly higher in Mpv17-/-::Opa1tg than in Mpv17-/- kidneys, and similar to WT littermates. Mitochondrial network and cristae ultrastructure were largely preserved in Mpv17-/-::Opa1tg vs. Mpv17-/- kidney and isolated podocytes. Mechanistically, the protective effect of Opa1 overexpression in this model was mediated by a block in apoptosis due to the stabilization of the mitochondrial cristae, consequently increasing the levels of mitochondrial morphology proteins like MFN2 and MIC19 as well as stabilizing ATP synthase oligomers. These results demonstrate that strategies aiming at increasing Opa1 expression or activity can be an effective aid against mtDNA depletion syndromes.

pathology↗

bioRxiv2020

Neural stem cells traffic functional mitochondria via extracellular vesicles to correct mitochondrial dysfunction in target cells

Neural stem cell (NSC) transplantation induces recovery in animal models of central nervous system (CNS) diseases. Although the replacement of lost endogenous cells was originally proposed as the primary healing mechanism of NSC grafts, it is now clear that transplanted NSCs operate via multiple mechanisms, including the horizontal exchange of therapeutic cargoes to host cells via extracellular vesicles (EVs). EVs are membrane particles trafficking nucleic acids, proteins, metabolites and metabolic enzymes, lipids and entire organelles. However, the function and the contribution of these cargoes to the broad therapeutic effects of NSCs is yet to be fully understood. Mitochondrial dysfunction is an established feature of several inflammatory and degenerative CNS disorders, most of which are potentially treatable with exogenous stem cell therapeutics. Herein we investigated the hypothesis that NSCs release and traffic functional mitochondria via EVs to restore mitochondrial function in target cells. Untargeted proteomics revealed a significant enrichment of mitochondrial proteins spontaneously released by NSCs in EVs. Morphological and functional analyses confirmed the presence of ultrastructurally intact mitochondria within EVs (Mito-EVs) with conserved membrane potential and respiration. We found that the transfer of Mito-EVs to mtDNA-deficient L929 Rho0 cells rescued mitochondrial function and increased Rho0 cell survival. Furthermore, the incorporation of Mito-EVs into inflammatory professional phagocytes restored normal mitochondrial dynamics and cellular metabolism and reduced the expression of pro-inflammatory markers in target cells. When transplanted in an animal model of multiple sclerosis, exogenous NSCs actively transferred mitochondria to mononuclear phagocytes and induced a significant amelioration of clinical deficits. Our data provide the first evidence that NSCs deliver functional mitochondria to target cells via Mito-EVs, paving the way for the development of novel (a)cellular approaches aimed at restoring mitochondrial dysfunction not only in multiple sclerosis, but also in degenerative neurological diseases.

neuroscience↗

bioRxiv2020

Loss of function of the mitochondrial peptidase PITRM1 induces proteotoxic stress and Alzheimer's disease-like pathology in human cerebral organoids

Mutations in pitrilysin metallopeptidase 1 (PITRM1), a mitochondrial protease involved in mitochondrial precursor processing and degradation, result in a slow-progressive syndrome, characterized by cerebellar ataxia, psychotic episodes and obsessive behavior as well as cognitive decline. To investigate the pathogenetic mechanisms of mitochondrial presequence processing, we employed cortical neurons and cerebral organoids generated from PITRM1 knockout human induced pluripotent stem cells (iPSCs). PITRM1 deficiency strongly induced mitochondrial unfolded protein response (UPRmt) and enhanced mitochondrial clearance in iPSC-derived neurons. Furthermore, we observed increased levels of amyloid precursor protein and amyloid {beta} in PITRM1 knockout neurons. However, neither cell death nor protein aggregates were observed in 2D iPSC-derived cortical neuronal cultures. On the contrary, cerebral organoids generated from PITRM1 knockout iPSCs spontaneously developed over time pathological features of Alzheimers disease (AD), including accumulation of protein aggregates, tau pathology, and neuronal cell death. Importantly, we provide evidence for a protective role of UPRmt and mitochondrial clearance against impaired mitochondrial presequence processing and proteotoxic stress. In summary, we propose a novel concept of PITRM1-linked neurological syndrome whereby defects of mitochondrial presequence processing induce an early activation of UPRmt that, in turn, modulates cytosolic quality control pathways. Thus our work supports a mechanistic link between mitochondrial function and common neurodegenerative proteinopathies.

neuroscience↗

bioRxiv2019

Interpreting, forecasting, and controlling feeding behaviour using high-resolution data

Better understanding of feeding behaviour will be vital in reducing obesity and metabolic syndrome, but we lack a standard model that captures the complexity of feeding behaviour. We construct an accurate stochastic model of rodent feeding at the bout level in order to perform quantitative behavioural analysis. Analysing the different effects on feeding behaviour of PYY3-36, lithium chloride, GLP-1 and leptin shows the precise behavioural changes caused by each anorectic agent. Our analysis demonstrates that the changes in feeding behaviour evoked by the anorectic agents investigated not mimic satiety. In the ad libitum fed state during the light period, meal initiation is governed by complete stomach emptying, whereas in all other conditions there is a graduated response. We show how robust homeostatic control of feeding thwarts attempts to reduce food intake, and how this might be overcome. In silico experiments suggest that introducing a minimum intermeal interval or modulating gastric emptying can be as effective as anorectic drug administration.

animal behavior and cognition↗