Tenocytes form a 3-D network and are connected via nanotubes

Area of Science:

• Cell Biology
• Connective Tissue Research
• Biophysics

Background:

• Cell adhesion and communication structures are vital for tissue development, integrity, and repair.
• Cellular nanotubes (NTs) are a recently discovered mechanism for intercellular information exchange, primarily studied in vitro.
• In vivo evidence and the relevance of NTs in native tissues remain largely unexplored.

Purpose of the Study:

• To investigate the presence and characteristics of cellular nanotubes (NTs) in rat tendons in vivo.
• To explore the potential role of NTs in tenocyte communication and tendon structure.
• To examine the association of NTs with gap junction protein Connexin43 (Cx43) in tendons.

Main Methods:

• Examination of rat tail tendon fascicles and Achilles, flexor, extensor, and patellar tendons from various age groups.
• Staining with plasma membrane and nuclear dyes, and immunolabeling for Connexin43 (Cx43).
• Utilizing 3-D reconstruction from serial semithin sections and transmission electron microscopy (TEM) to verify NTs.

Main Results:

• Demonstrated the existence of NTs as straight, thin longitudinal processes (100-500 nm diameter, up to several hundred μm long) in all investigated tendon types.
• Observed NTs connecting tenocytes within and between rows, forming a complex 3-D cellular scaffold.
• Found Cx43-positive foci at tenocyte cell body contacts but rare Cx43 signals along NTs, suggesting limited gap junction involvement in NTs.

Conclusions:

• Cellular nanotubes (NTs) are present in rat tendons, forming a complex 3-D cellular network.
• NTs likely serve dual roles in long-distance intercellular communication and mechanical stabilization of tendons.
• The presence of NTs necessitates a re-evaluation of traditional models of cell-to-cell communication in mechanically loaded tissues.