Using Silk to Grow Salivary Glands in the Laboratory

Colloquially, we use the word “spit” to describe saliva, which is secreted by our salivary glands. Saliva is a complex combination of water, salts, proteins, small molecules, and other components that lubricate our throats and mouths to facilitate swallowing, coat our gums and teeth to maintain good gum health and keep tooth decay at bay, and keep our breath fresh. Insufficient salivation production increases tooth decay rates, causes chronic halitosis (bad breath), and can swallowing difficult. Additionally, there are no treatments for poorly-functioning salivary glands, and these glands have poor regenerative capabilities.

Patients who suffer from head/neck cancers and have been treated with radiation suffer from “xerostoma” or dry mouth. Certain medications can also cause dry mouth as can old age. 50% of older Americans suffer from xerostoma.

If that isn’t bad enough, salivary glands are notoriously hard to grow in the laboratory.  So they slow down when we grow old, do not regenerate and grow poorly, in at all, in the laboratory.  Is there any good news about salivary glands?

Make that a yes!  A research team from the University of Texas Health Science Center, led by Chih-Ko Yeh has discovered a process that may lead to the growth of salivary glands in cell culture.  Yeh and his team used purified silk fibers that had many of their contaminants removed to grow salivary stem cells from rat salivary glands.  These cells grew in the laboratory and after several weeks in culture, generated a three-dimensional matrix that covered the silk scaffolds and shared many characteristics with the salivary glands that grow in the mouth.

Yeh underscored the importance of this discovery: “Salivary gland stem cells are some of the most difficult cells to grow in culture and retain their function.”  This work in Yeh’s laboratory have is the first time that salivary gland stem cells have been grown in cell culture while retaining their salivary gland properties.

Yeh continued, “The unique culture system has great potential for future salivary gland research and for the development of new cell-based therapeutics.”

Silk, contrary to what you might think, is an excellent choice for stem cell scaffolding because it is natural, biodegradable, flexible, porous material that provides cells easy access to oxygen and nutrition.  Silk also does not cause inflammation, which is a problem with other types of stem cell scaffolds.

Since there are so few salivary gland stem cells in the human mouth, Yeh and his group plan to continue using the rat model to refine their techniques.  Eventually, Yeh and others would like to use stem cells derived from bone marrow or umbilical cord blood to regenerate salivary glands in human patients.

In fact, Yeh and his coworkers have pioneered protocols for harvesting large numbers of bone marrow stem cells from bone marrow and human umbilical cord blood and growing them in culture.  These stem cells are abundant and can be differentiated into different cell types by means of tissue engineering technologies.

Yeh hopes that by the next decade, human salivary stem cells or tissue engineered artificial salivary gland will be used to initiate salivary gland regeneration in human patients.

This research was published in Tissue Engineering part A 2015; 21(9-10).