Re-Evaluating Hot Mitochondria: Too Slow to Cool.

Area of Science:

• Cellular biology
• Biophysics
• Mitochondrial function

Background:

• Mito Thermo Yellow (MTY) is a fluorescent probe designed to measure temperature within mitochondria.
• The 'hot mitochondria' concept proposes significant temperature differences between mitochondria and their environment.
• Published studies using MTY suggest large apparent temperature gradients (ΔT_app) exist.

Purpose of the Study:

• To re-evaluate MTY fluorescence data used to support the 'hot mitochondria' concept.
• To assess whether MTY accurately reports intramitochondrial temperature or other cellular phenomena.
• To determine if substantial mitochondrial temperature gradients are supported by MTY data.

Main Methods:

• Analysis of MTY fluorescence kinetics under various conditions.
• Examination of MTY responses to mitochondrial inhibitors.
• Thermodynamic modeling of heat production and diffusion within mitochondria.
• Assessment of cellular stress responses at high temperatures.

Main Results:

• MTY fluorescence kinetics are inconsistent with expected mitochondrial heat dynamics.
• MTY responses to inhibitors do not align with predicted heat production.
• The data suggests MTY signals may not exclusively represent intramitochondrial temperature.
• Temperatures inferred from MTY (> 48°C) are biologically improbable due to protein denaturation and stress responses.

Conclusions:

• MTY fluorescence intensity changes are unlikely to solely report intramitochondrial temperature.
• Published evidence for large mitochondrial temperature gradients (ΔT_app > 10°C) using MTY is questionable.
• MTY and similar probes require re-evaluation for accurately measuring local temperature.
• Current MTY data is insufficient to demonstrate the existence of 'hot mitochondria'.