Mitochondria are physiologically maintained at close to 50 °C.

Area of Science:

• Cell Biology
• Bioenergetics
• Physiology

Background:

• Endothermic species rely on metabolic heat for stable internal temperatures.
• Mitochondria are key players in thermogenesis, releasing substantial heat during respiration.
• Understanding mitochondrial heat production is crucial for cellular energy balance.

Purpose of the Study:

• To measure mitochondrial temperature in situ under various physiological conditions.
• To investigate the role of the respiratory chain in mitochondrial heat generation.
• To explore the impact of thermogenic enzymes on mitochondrial temperature.

Main Methods:

• Utilized a temperature-sensitive fluorescent probe targeted to mitochondria for in situ measurements.
• Assessed mitochondrial temperature in human embryonic kidney (HEK) 293 cells and primary skin fibroblasts.
• Manipulated mitochondrial function by depleting mitochondrial DNA, using respiratory inhibitors, and expressing thermogenic enzymes.

Main Results:

• Mitochondria were over 10°C warmer than the external environment (38°C) when the respiratory chain was fully functional.
• This temperature differential was abolished by mitochondrial DNA depletion or respiratory inhibitors.
• The differential was preserved or enhanced by expressing thermogenic enzymes like alternative oxidase or uncoupling protein 1.
• Respiratory chain enzyme activity peaked around 50°C.

Conclusions:

• Mitochondria generate significant heat, contributing substantially to cellular thermogenesis.
• The respiratory chain is a major source of mitochondrial heat production.
• Further validation using independent methods is warranted to explore the implications of these findings on mitochondrial function and literature.