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

This review reflects comments and contributions from Marina Schernthanner, Shaunak Deota and Pablo Ranea-Robles. Review synthesized by Jonny Coates.

In this preprint, the authors investigate the rewiring of mitochondrial metabolism using an oral treatment with an inhibitor of mitochondrial transcription. The authors demonstrate that this treatment shifts whole animal metabolism to fatty acid oxidation. This led to normalisation of body weight and restoration of glucose tolerance in high-fat diet mice. The authors argue that this study provides evidence for drug treatment of obesity and obesity-related pathology. Overall, we only had minor comments.

Minor comments:

• What was the rationale for the IMT (LDC4857, 30 mg/kg) dosage?

• The lower RER in IMT may also indicate reduced/slower metabolic switching from fatty-acid oxidation in the fasting phase to glucose utilization during the refeeding phase. The authors should confirm higher fatty acid utilization using oral gavage of labeled fatty acids.

• Interestingly, after the refeeding experiment, HFD-IMT mice have lower RER (fig-1e) but the GTT shows improved glucose clearance (fig-2c, d). Does this mean that glucose uptake is better but it is not preferentially utilized? The authors should check for liver and muscle glycogen levels upon refeeding.

• Were isolated islets still treated with IMT in vitro? Perhaps sustained IMT treatment would be necessary to observe a decrease in insulin levels?

• Did the authors look at the concentration of IMT in the gastrointestinal tract as well? Where orally delivered drugs should be taken up preferentially in the proximal small intestine?

• Have the authors looked at transcriptional levels of fatty acid transporters in the mitochondrial membrane (if those are affected by IMT)? As I understand it the authors propose that increased FAO is due to metabolic rewiring in OXPHOS, but have they completely ruled out the possibility of increased FAO via increased FA uptake through f.e. an upregulation of FA transporters?

• The authors should mention the time of day (ZT) at which the IMT is administered.

Comments on reporting:

• Fig 5C is a very nice visual presentation of proteomics/metabolomics data - easy-to-understand but detailed

Suggestions for future studies:

• Although the authors measure IMT concentrations 24 hr after the last dose in plasma and tissues, they should identify the half-life of the drug, the major tissue which detoxifies the drug (liver, kidney, gut) and excretion (urine, feces). This information is critical to understand the results from fig-4c. If the drug has a smaller life, it is possible that the levels may be different 3-5 hr after dosing but might have reached equilibrium after 24 hr. Additionally, if the half-life is smaller, the time of day (ZT) at which the drug is administered is important because of daily rhythms in metabolism.

Competing interests

The author declares that they have no competing interests.