Biology subjects

Misic, J.

Publications and source records attributed to Misic, J..

3 recordsLinked to original sources

bioRxiv2023

Inhibition of mammalian mtDNA transcription paradoxically activates liver fatty acid oxidation to reverse diet-induced hepatosteatosis and obesity

The oxidative phosphorylation (OXPHOS) system in mammalian mitochondria plays a key role in harvesting energy from ingested nutrients1, 2. Mitochondrial metabolism is very dynamic and can be reprogrammed to support both catabolic and anabolic reactions, depending on physiological demands or disease states3, 4. Rewiring of mitochondrial metabolism is intricately linked to metabolic diseases5, 6 and is also necessary to promote tumour growth7-11. Here, we demonstrate that per oral treatment with an inhibitor of mitochondrial transcription (IMT)11 shifts whole animal metabolism towards fatty acid oxidation, which, in turn, leads to rapid normalization of body weight, reversal of hepatosteatosis and restoration of glucose tolerance in mice on high-fat diet. Paradoxically, the IMT treatment causes a severe reduction of OXPHOS capacity concomitant with a marked upregulation of fatty acid oxidation in the liver, as determined by proteomics and non-targeted metabolomics analyses. The IMT treatment leads to a marked reduction of complex I, the main dehydrogenase that feeds electrons into the ubiquinone (Q) pool, whereas the levels of electron transfer flavoprotein dehydrogenase (ETF-DH) and other dehydrogenases connected to the Q pool are increased. This rewiring of metabolism caused by reduced mtDNA expression in the liver provides a novel principle for drug treatment of obesity and obesity-related pathology.

physiology↗

bioRxiv2023

Preserved respiratory chain capacity and physiology in mice with profoundly reduced levels of mitochondrial respirasomes

The mammalian respiratory chain complexes I, III2 and IV (CI, CIII2 and CIV) are critical for cellular bioenergetics and form a stable assembly, the respirasome (CI- CIII2-CIV), that is biochemically and structurally well documented. The role of the respirasome in bioenergetics and regulation of metabolism is subject to intense debate and is difficult to study because the individual respiratory chain complexes coexist together with high levels of respirasomes. To critically investigate the in vivo role of the respirasome, we generated homozygous knock-in mice that have normal levels of respiratory chain complexes but profoundly decreased levels of respirasomes. Surprisingly, the mutant mice are healthy, with preserved respiratory chain capacity and normal exercise performance. Our findings show that high levels of respirasomes are dispensable for maintaining bioenergetics and physiology in the mouse, but raises questions about their alternate functions, such as relating to regulation of protein stability and prevention of age-associated protein aggregation.

molecular biology↗

bioRxiv2022

MRPS36 provides a missing link in the eukaryotic 2-oxoglutarate dehydrogenase complex for recruitment of E3 to the E2 core

The tricarboxylic acid (TCA) cycle, or Krebs cycle, is the central pathway of energy production in eukaryotic cells and plays a key part in aerobic respiration throughout all kingdoms of life. The enzymes involved in this cycle generate the reducing equivalents NADH and FADH2 by a series of enzymatic reactions, which are utilized by the electron transport chain to produce ATP. One of the pivotal enzymes in this cycle is 2-oxoglutarate dehydrogenase complex (OGDHC), which generates NADH by oxidative decarboxylation of 2-oxoglutarate to succinyl-CoA. OGDHC is a megadalton protein complex originally thought to be assembled just from three catalytically active subunits (E1o, E2o, E3). In fungi and animals, however, the protein MRPS36 has more recently been proposed as a putative additional component. Based on extensive XL-MS data obtained from measurements in mice and bovine heart mitochondria, supported by phylogenetic analyses, we provide evidence that MRPS36 is an essential member of OGDHC, albeit only in eukaryotes. Comparative sequence analysis and computational structure predictions reveal that in eukaryotic OGDHC, E2o does not contain the peripheral subunit-binding domain (PSBD), present in bacterial and archaeal E2os. We propose that in eukaryotes MRPS36 evolved as an E3 adaptor protein, functionally replacing the PSBD. We further provide a refined structural model of the complete eukaryotic OGDHC containing 16 E1o, 12 E3, and 6 subunits of MRPS36 accommodated around the OGDHC core composed of 24 E2o subunits (3.45 MDa). The model provides new insights into the OGDH complex topology and stipulates putative mechanistic implications.

biochemistry↗