Patterns of mitochondrial membrane remodeling parallel functional adaptations to thermal stress

Area of Science:

• Mitochondrial physiology
• Ectotherm adaptation
• Membrane biophysics

Background:

• Temperature significantly impacts mitochondrial performance, partly via effects on mitochondrial membranes.
• While changes in inner-mitochondrial membrane (IMM) amount are known, the capacity for modulating mitochondrial membrane composition remains understudied.
• Atlantic killifish subspecies exhibit local adaptation to different thermal environments.

Purpose of the Study:

• To investigate how thermal acclimation affects liver mitochondrial respiratory capacity and IMM composition in northern and southern Atlantic killifish.
• To determine if Atlantic killifish can modulate mitochondrial membrane composition in response to temperature changes.
• To explore the role of phospholipid and fatty acid remodeling in mitochondrial adaptation to temperature.

Main Methods:

• Acclimation of northern and southern *Fundulus heteroclitus* subspecies to 5°C and 33°C.
• Assessment of liver mitochondrial respiratory capacity using respirometry.
• Analysis of mitochondrial phospholipid headgroups and headgroup-specific fatty acid remodeling.
• Quantification of inner-mitochondrial membrane (IMM) amount.

Main Results:

• Thermal acclimation altered mitochondrial respiratory capacity in both subspecies.
• Northern *F. heteroclitus* showed higher mitochondrial respiratory capacity across temperatures.
• Mitochondrial phospholipids were remodeled upon thermal acclimation, with changes largely consistent between subspecies.
• Differences in membrane composition between subspecies were primarily driven by phospholipid classes.
• Changes in respiratory capacity were largely, but not entirely, explained by alterations in IMM amount.

Conclusions:

• Changes in liver mitochondrial function play a role in the ectothermic response to thermal stress.
• Lipid remodeling of mitochondrial membranes is implicated as a mechanism for thermal acclimation and adaptation.
• Mitochondrial membrane composition and IMM amount are critical factors in ectotherm thermal tolerance.