bims-resufa 2022-03-20 papers

Issue of 2022–03–20
two papers selected by
Vera Strogolova, Strong Microbials, Inc

Comp Biochem Physiol A Mol Integr Physiol. 2022 Mar 09. pii: S1095-6433(22)00043-5. [Epub ahead of print]268 111185

Acute pH alterations do not impact cardiac mitochondrial respiration in naked mole-rats or mice.

Kenny W Huynh, Soulene Sabir, Hang Cheng, Matthew E Pamenter.

Energetically demanding conditions such as hypoxia and exercise favour anaerobic metabolism (glycolysis), which leads to acidification of the cellular milieu from ATP hydrolysis and accumulation of the anaerobic end-product, lactate. Cellular acidification may damage mitochondrial proteins and/or alter the H+ gradient across the mitochondrial inner membrane, which may in turn impact mitochondrial respiration and thus aerobic ATP production. Naked mole-rats are among the most hypoxia-tolerant mammals, and putatively experience intermittent environmental and systemic hypoxia while resting and exercising in their underground burrows. Previous studies in naked mole-rat brain, heart, and skeletal muscle mitochondria have demonstrated adaptations that favour improved efficiency in hypoxic conditions; however, the impact of cellular acidification on mitochondrial function has not been explored. We hypothesized that, relative to hypoxia-intolerant mice, naked mole-rat cardiac mitochondrial respiration is less sensitive to cellular pH changes. To test this, we used high-resolution respirometry to measure mitochondrial respiration by permeabilized cardiac muscle fibres from naked mole-rats and mice exposed in vitro to a pH range from 6.6 to 7.6. Surprisingly, we found that acute pH changes do not impact cardiac mitochondrial respiration or compromise mitochondrial integrity in either species. Our results suggest that acute alterations of cellular pH have minimal impact on cardiac mitochondrial respiration.

Keywords: Acidity; Electron transport system; Mitochondrial integrity; alkaline; heart; oxidative phosphorylation

DOI: https://doi.org/10.1016/j.cbpa.2022.111185

Front Cell Dev Biol. 2022 ;10 786268

Applying Sodium Carbonate Extraction Mass Spectrometry to Investigate Defects in the Mitochondrial Respiratory Chain.

David R L Robinson, Daniella H Hock, Linden Muellner-Wong, Roopasingam Kugapreethan, Boris Reljic, Elliot E Surgenor, Carlos H M Rodrigues, Nikeisha J Caruana, David A Stroud.

Mitochondria are complex organelles containing 13 proteins encoded by mitochondrial DNA and over 1,000 proteins encoded on nuclear DNA. Many mitochondrial proteins are associated with the inner or outer mitochondrial membranes, either peripherally or as integral membrane proteins, while others reside in either of the two soluble mitochondrial compartments, the mitochondrial matrix and the intermembrane space. The biogenesis of the five complexes of the oxidative phosphorylation system are exemplars of this complexity. These large multi-subunit complexes are comprised of more than 80 proteins with both membrane integral and peripheral associations and require soluble, membrane integral and peripherally associated assembly factor proteins for their biogenesis. Mutations causing human mitochondrial disease can lead to defective complex assembly due to the loss or altered function of the affected protein and subsequent destabilization of its interactors. Here we couple sodium carbonate extraction with quantitative mass spectrometry (SCE-MS) to track changes in the membrane association of the mitochondrial proteome across multiple human knockout cell lines. In addition to identifying the membrane association status of over 840 human mitochondrial proteins, we show how SCE-MS can be used to understand the impacts of defective complex assembly on protein solubility, giving insights into how specific subunits and sub-complexes become destabilized.

Keywords: OXPHOS (oxidative phosphorylation); carbonate extraction; membrane protein; mitochondria; proteomic analyses; respiratory chain assembly

DOI: https://doi.org/10.3389/fcell.2022.786268