Human mesenchymal stromal cells release functional mitochondria in extracellular vesicles

Area of Science:

• Orthopedics
• Cell Biology
• Regenerative Medicine

Background:

• Skeletal soft tissues like cartilage have poor healing capacity due to limited vascularity and low metabolism.
• Current treatments for joint injury and osteoarthritis (OA) show limited efficacy in preventing chronic disease.
• Mesenchymal stromal cells (MSCs) show therapeutic potential but face challenges like variable outcomes and low engraftment.

Purpose of the Study:

• To investigate if MSCs package functional mitochondria into extracellular vesicles (EVs).
• To characterize these mitochondria-containing EVs (mitoEVs) and their cargo.
• To determine if chondrocytes can internalize MSC-derived mitoEVs.

Main Methods:

• Isolation of exosome, microvesicle, and vesicle-free fractions from MSC-conditioned media.
• Characterization of EV size and mitochondrial content using nanoparticle tracking, immunoblotting, and flow cytometry.
• Assessment of mitochondrial function and chondrocyte uptake of mitoEVs via fluorescent imaging and flow cytometry.

Main Results:

• MSC-derived EVs encompass various sizes, with abundant mitochondrial cargoes, particularly in larger vesicles (mitoEVs).
• A subset of these mitoEVs contains functional mitochondria.
• Chondrocytes successfully uptake mitoEVs, even when experiencing mitochondrial dysfunction.

Conclusions:

• MSCs export intact, functional mitochondria via EVs (mitoEVs).
• Intercellular transfer of mitoEVs to chondrocytes is feasible without direct cell contact.
• This suggests a novel acellular therapeutic strategy for enhancing mitochondrial function in damaged skeletal tissues.