Simple method of thawing cryo-stored samples preserves ultrastructural features in electron microscopy.

Area of Science:

• Cell Biology
• Microscopy
• Histology

Background:

• Preserving ultrastructural details in biological samples for electron microscopy (EM) is crucial but challenging.
• Standard methods like chemical fixation or automated freeze substitution (AFS) require specialized equipment and are unsuitable for cryo-stored clinical or preclinical samples.
• Cryo-storage of bulk biopsies or whole tissues in liquid nitrogen often leads to insufficient ultrastructural preservation.

Purpose of the Study:

• To evaluate the efficacy of AFS for cryo-stored samples.
• To develop a simple, rapid, and effective thawing and fixation protocol for cryo-stored bulk tissue samples.
• To enable accurate ultrastructural and morphometric analysis of cryo-stored tissues without specialized instrumentation.

Main Methods:

• Developed a novel protocol involving dry ice-cooled pre-trimming of frozen tissue followed by aldehyde fixation at 37°C.
• Investigated human placentae, clinical lung samples, and various mouse tissues (adipose, cardiac, skeletal muscle, liver).
• Compared electron micrographs from cryo-stored samples prepared with the new method against fresh tissue samples fixed conventionally.

Main Results:

• The new protocol successfully preserved ultrastructural features and tissue-specific details in cryo-stored samples.
• The quality of ultrastructure achieved closely matched that of fresh tissue samples prepared with standard chemical fixation.
• Morphometric analysis of lipid droplets and mitochondria in mouse liver samples yielded statistically valid quantifications.

Conclusions:

• The developed method provides a simple and effective means to analyze cryo-stored bulk tissue samples at the ultrastructural level.
• This protocol significantly improves the preservation of ultrastructural integrity in samples not initially prepared for EM.
• It enables accurate morphometric analyses, expanding the utility of biobanked and cryo-stored tissue collections for research.