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During the electron transport chain, electrons from NADH and FADH2 are first transferred to complexes I and II, respectively. These two complexes then transfer the electrons to ubiquinol, which carries them further to complex III. Complex III passes the electrons across the intermembrane space to Cyt c, which carries them further to complex IV. Complex IV donates electrons to oxygen and reduces it to water. As electrons pass through complexes I, III, and IV, the energy released aids the pumping...
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Author Spotlight: Unveiling Mitochondrial Function and Cellular Metabolic Adaptation in Metabolic Diseases
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STX4 Is Indispensable for Mitochondrial Homeostasis in Skeletal Muscle.

Joseph M Hoolachan1, Rekha Balakrishnan1, Erika M McCown1

  • 1Department of Molecular and Cellular Endocrinology, Arthur Riggs Diabetes and Metabolism Research Institute, City of Hope Beckman Research Institute, Duarte, California, USA.

Journal of Cachexia, Sarcopenia and Muscle
|November 11, 2025
PubMed
Summary

Syntaxin 4 (STX4) is crucial for maintaining skeletal muscle mitochondrial health. Depleting STX4 impairs mitochondrial function, biogenesis, and mitophagy, highlighting its role in mitochondrial homeostasis.

Keywords:
STX4mitochondriamusclequality control

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Area of Science:

  • Mitochondrial Biology
  • Skeletal Muscle Physiology
  • Cellular Homeostasis

Background:

  • Mitochondrial homeostasis is essential for skeletal muscle function, regulated by processes like mitochondrial biogenesis, dynamics, and mitophagy.
  • Syntaxin 4 (STX4), previously known for glucose uptake, is also found at the outer mitochondrial membrane.
  • STX4's role in modulating mitochondrial homeostasis via MQC mechanisms remained unclear.

Purpose of the Study:

  • To investigate the role of Syntaxin 4 (STX4) in skeletal muscle mitochondrial structure, function, and quality control (MQC) processes.
  • To determine STX4's involvement in mitochondrial biogenesis and mitophagy in skeletal muscle.

Main Methods:

  • Utilized inducible skeletal muscle-specific STX4-knockout (skmSTX4-iKO) mice.
  • Employed siRNA-mediated STX4 depletion in immortalized L6.GLUT4myc myotubes (siSTX4).
  • Assessed mitochondrial morphology, oxygen consumption, electron transport chain (ETC) abundance, and MQC markers.

Main Results:

  • STX4 ablation in mice led to insulin resistance, reduced energy expenditure, and impaired mitochondrial oxygen consumption.
  • Mitochondrial damage, including fragmentation or swelling and decreased ETC abundance, was observed in STX4-depleted muscles and myotubes.
  • STX4 depletion reduced mitochondrial DNA levels and suppressed key mitochondrial biogenesis genes (PGC1-α, Tfam, NRF1).
  • Mitophagy was impaired, evidenced by reduced mitochondrial turnover, decreased mitochondria-lysosome colocalization, and lower levels of mitophagy markers (PINK1, PARKIN).

Conclusions:

  • Syntaxin 4 (STX4) is a critical regulator of mitochondrial homeostasis in skeletal muscle.
  • STX4 deficiency disrupts mitochondrial structure, function, biogenesis, and mitophagy, contributing to skeletal muscle dysfunction.