Tropoelastin is an important, soluble protein that serves as the building block for elastin. It’s like individual Lego bricks, flexible and ready to connect to form a larger, elastic structure. This precursor molecule is the initial form that undergoes processing to become mature, functional elastin throughout the body.
The Assembly of Elastin
Cells synthesize tropoelastin molecules from the elastin (ELN) gene. These molecules are then transported out of the cell into the extracellular space. Once outside, soluble tropoelastin molecules begin to self-assemble, forming aggregates on the cell surface.
This aggregation is followed by cross-linking. An enzyme, lysyl oxidase (LOX), which requires copper, plays a role in this transformation. Lysyl oxidase oxidizes specific lysine residues within tropoelastin, creating reactive aldehydes. These aldehydes then react with other lysine or allysine residues on adjacent tropoelastin molecules, forming stable covalent bonds. This cross-linking process locks individual tropoelastin monomers together, converting them into durable, insoluble, and functional elastin fibers. Microfibrils, such as fibrillin, act as a scaffold, guiding the organization of these cross-linked molecules into mature elastic fibers.
The Role of Elasticity in Tissues
The assembled elastin fiber provides tissues with stretch and recoil capabilities, similar to a rubber band. This property is important in organs and structures that undergo constant movement or changes in shape. For instance, in the skin, elastin allows it to stretch and return to its original position, contributing to firmness and preventing sagging.
In the lungs, elastin facilitates expansion during inhalation and passive recoil during exhalation, necessary for efficient breathing. Large blood vessels, like the aorta, use elastin; its elastic walls expand to accommodate blood surges and then snap back, helping to maintain consistent blood pressure and flow. Ligaments, which connect bones, also contain elastin, providing flexibility for joint movement while maintaining structural integrity.
Impact on Health and Aging
The body’s ability to produce new tropoelastin decreases after adolescence, meaning elastin fibers formed during development remain for a lifetime. Over time, these existing elastin fibers can degrade. Chronic sun exposure (photoaging) is a contributor, as ultraviolet (UV) radiation damages elastin and collagen fibers, leading to wrinkles, fine lines, and reduced skin resilience. Other environmental stressors, such as pollution and smoking, also promote oxidative stress, further breaking down these fibers.
Beyond natural aging, genetic disorders can affect tropoelastin and elastin integrity. Mutations in the ELN gene, which provides instructions for making tropoelastin, can lead to conditions like Cutis Laxa and Williams-Beuren syndrome. Cutis Laxa is characterized by loose, sagging skin and can also involve cardiovascular issues like aortic aneurysms and lung conditions such as emphysema. Williams-Beuren syndrome, resulting from a deletion that includes the ELN gene, causes cardiovascular problems like supravalvular aortic stenosis, a narrowing of the aorta just above the heart.
Applications in Medicine and Skincare
Tropoelastin has found applications in biomedical tissue engineering due to its elasticity and biocompatibility. Researchers use recombinant human tropoelastin as a building block to create elastic biomaterials, such as hydrogels and electrospun fibers. These materials are being developed for repairing or replacing damaged tissues like skin, cartilage, and blood vessels, aiming to mimic their natural mechanical properties. For example, methacrylated tropoelastin (MeTro) can be photocrosslinked to form stable hydrogels with tunable mechanical properties for tissue engineering.
In the cosmetics industry, tropoelastin is included in some skincare products, aiming to improve skin elasticity. However, directly supplementing elastin through topical application faces a challenge because tropoelastin’s large molecular size can limit its ability to penetrate the skin barrier effectively. While research continues into methods for better delivery and absorption, the primary benefit of such products often lies in hydration and surface improvements rather than direct replenishment of the skin’s deeper elastin network.