Human scleral elastic system: an immunoelectron microscopic study

Area of Science:

• Ophthalmology
• Connective Tissue Biology
• Biochemistry

Background:

• The sclera, a key ocular tissue, contains a complex elastic system crucial for maintaining eye shape and integrity.
• Elastic tissue in the sclera comprises distinct fibre types: elastic, elaunin, and oxytalan fibres.
• Understanding the molecular composition of these fibres is essential for comprehending scleral biomechanics and age-related changes.

Purpose of the Study:

• To investigate the distribution and codistribution of specific extracellular matrix proteins within the three fibre types of the aged human sclera.
• To characterize the biochemical differences between elastic, elaunin, and oxytalan fibres using immunocytochemical methods.

Main Methods:

• Immunogold transmission electron microscopy was employed to study the distribution of elastin, amyloid P component, laminin, fibronectin, gp 115, and vitronectin.
• Double immunolabelling was utilized to examine the codistribution of amyloid P component and laminin.
• Conventional electron microscopy was used to identify the distinct fibre types.

Main Results:

• Elastic fibres contained elastin, while both elastic and elaunin fibres showed elastin presence.
• Microfibrillar sheaths of elastic fibres labelled for amyloid P component.
• Elaunin fibres labelled for both amyloid P component and laminin, whereas oxytalan fibres labelled for laminin only.
• No labelling was detected for fibronectin, gp 115, and vitronectin.

Conclusions:

• The three scleral fibre types (elastic, elaunin, oxytalan) exhibit distinct biochemical profiles based on their protein composition.
• Differences in serum amyloid P component binding affinity and association with laminin contribute to the heterogeneity of the elastic system in the aged human sclera.
• These findings provide novel insights into the molecular organization of the scleral extracellular matrix.