bims-mimbat Biomed News
on Mitochondrial metabolism in brown adipose tissue
Issue of 2024‒03‒10
seven papers selected by
José Carlos de Lima-Júnior, Washington University

  1. Cell Metab. 2024 Mar 05. pii: S1550-4131(24)00016-0. [Epub ahead of print]36(3): 459-460
      It is generally believed that the contributions of the UCP1-independent thermogenic pathways are secondary to UCP1-mediated thermogenesis in BAT. Now, Rahbani et al. demonstrate in vivo that adaptive thermogenesis in brown adipose tissue is regulated by UCP1 and CKB in parallel.
  2. Proc Natl Acad Sci U S A. 2024 Mar 12. 121(11): e2314199121
      Proton-powered c-ring rotation in mitochondrial ATP synthase is crucial to convert the transmembrane protonmotive force into torque to drive the synthesis of adenosine triphosphate (ATP). Capitalizing on recent cryo-EM structures, we aim at a structural and energetic understanding of how functional directional rotation is achieved. We performed multi-microsecond atomistic simulations to determine the free energy profiles along the c-ring rotation angle before and after the arrival of a new proton. Our results reveal that rotation proceeds by dynamic sliding of the ring over the a-subunit surface, during which interactions with conserved polar residues stabilize distinct intermediates. Ordered water chains line up for a Grotthuss-type proton transfer in one of these intermediates. After proton transfer, a high barrier prevents backward rotation and an overall drop in free energy favors forward rotation, ensuring the directionality of c-ring rotation required for the thermodynamically disfavored ATP synthesis. The essential arginine of the a-subunit stabilizes the rotated configuration through a salt bridge with the c-ring. Overall, we describe a complete mechanism for the rotation step of the ATP synthase rotor, thereby illuminating a process critical to all life at atomic resolution.
    Keywords:  ATP synthase; bioenergetics; c-ring; molecular dynamics simulations; rotary motor
  3. Nat Metab. 2024 Mar 08.
      In the healthy state, the fat stored in our body isn't just inert. Rather, it is dynamically mobilized to maintain an adequate concentration of fatty acids (FAs) in our bloodstream. Our body tends to produce excess FAs to ensure that the FA availability is not limiting. The surplus FAs are actively re-esterified into glycerides, initiating a cycle of breakdown and resynthesis of glycerides. This cycle consumes energy without generating a new product and is commonly referred to as the 'futile lipid cycle' or the glyceride/FA cycle. Contrary to the notion that it's a wasteful process, it turns out this cycle is crucial for systemic metabolic homeostasis. It acts as a control point in intra-adipocyte and inter-organ cross-talk, a metabolic rheostat, an energy sensor and a lipid diversifying mechanism. In this Review, we discuss the metabolic regulation and physiological implications of the glyceride/FA cycle and its mechanistic underpinnings.
  4. Mol Metab. 2024 Mar 06. pii: S2212-8778(24)00044-9. [Epub ahead of print] 101913
      Adipose tissue mass is maintained by a balance between lipolysis and lipid storage. The contribution of adipose lipogenesis to fat mass, especially in the setting of high-fat feeding, is considered minor. Here, we report that adipose-specific knockout of the peroxisomal lipid synthetic protein PexRAP promotes diet-induced obesity and insulin resistance through activation of de novo lipogenesis. PexRAP inactivation inhibits the flux of carbons to ethanolamine plasmalogens. This increases nuclear PC/PE ratio and promotes cholesterol mislocalization, resulting in the activation of liver X receptor (LXR), a nuclear receptor known to be activated by increased intracellular cholesterol. LXR activation leads to increased expression of the phospholipid remodeling enzyme LPCAT3 and induces fatty acid synthase-mediated lipogenesis, which promotes diet-induced obesity and insulin resistance. Treatment of PexRAP-deficient adipocytes with alkylglycerol, a plasmalogen precursor that enters the synthetic pathway downstream of PexRAP, rescues nuclear cholesterol mislocalization and LXR activation. These studies reveal an unexpected role for peroxisome-derived lipids in regulating LXR-dependent lipogenesis and suggest that activation of lipogenesis, combined with dietary lipid overload, exacerbates obesity and metabolic dysregulation.
  5. Biophys J. 2024 Mar 06. pii: S0006-3495(24)00176-0. [Epub ahead of print]
      The scientific literature on mitochondria has increased significantly over the years, due to findings that these organelles have widespread roles in the onset and progression of pathological conditions such as metabolic disorders, neurodegenerative and cardiovascular diseases, inflammation, and cancer. Researchers have extensively explored how mitochondrial properties and functions are modified in different models, often using fluorescent inner mitochondrial membrane potential (ΔΨm) probes to assess functional mitochondrial aspects such as protonmotive force and oxidative phosphorylation. This review provides an overview of existing techniques to measure ΔpH and ΔΨm, highlighting their advantages, limitations, and applications. It discusses drawbacks of ΔΨm probes, especially when used without calibration, and conditions where alternative methods should replace ΔΨm measurements for the benefit of the specific scientific objectives entailed. Studies investigating mitochondria and their vast biological roles would be significantly advanced by the understanding of the correct applications as well as limitations of protonmotive force measurements and use of fluorescent ΔΨm probes, adopting more precise, artifact-free, sensitive, and quantitative measurements of mitochondrial functionality.
  6. Nat Chem Biol. 2024 Mar 06.
      Metabolic efficiency profoundly influences organismal fitness. Nonphotosynthetic organisms, from yeast to mammals, derive usable energy primarily through glycolysis and respiration. Although respiration is more energy efficient, some cells favor glycolysis even when oxygen is available (aerobic glycolysis, Warburg effect). A leading explanation is that glycolysis is more efficient in terms of ATP production per unit mass of protein (that is, faster). Through quantitative flux analysis and proteomics, we find, however, that mitochondrial respiration is actually more proteome efficient than aerobic glycolysis. This is shown across yeast strains, T cells, cancer cells, and tissues and tumors in vivo. Instead of aerobic glycolysis being valuable for fast ATP production, it correlates with high glycolytic protein expression, which promotes hypoxic growth. Aerobic glycolytic yeasts do not excel at aerobic growth but outgrow respiratory cells during oxygen limitation. We accordingly propose that aerobic glycolysis emerges from cells maintaining a proteome conducive to both aerobic and hypoxic growth.