Restoring Saliva Flow May Improve Oral Health in Down Syndrome

Each year, thousands of babies born across the world have Down syndrome, which is caused by having three copies of chromosome 21.¹ Because of this, people with Down syndrome experience a number of health problems. These include risk of heart disease in cases of congenital heart defects, early-onset Alzheimer’s disease, and neurodevelopmental delays.

Among these health challenges, individuals with Down syndrome also experience oral health issues, such as dry mouth or hyposalivation and periodontal disease, which significantly affect their quality of life.^2,3 “A few years ago, oral surgeons of the United States noted that there was one unmet need in Down syndrome research, which focused on trying to address oral deficiencies in this population,” said Rodrigo Lacruz, a molecular pathobiology researcher at the New York University.

Recently, using preclinical Down syndrome models, Lacruz and his team identified that defects in calcium signaling likely contribute to low saliva production and gum disease observed in the condition. Their findings, published in Cell Reports, suggest potential therapeutic approaches to restore salivation which could benefit the oral health of people with Down syndrome.⁴

“In the dry mouth field…we don't often see studies looking at Down syndrome,” said Guy Carpenter, an oral biology researcher who studies salivation and salivary glands at King’s College London and who was not involved in the study. “So, I thought that was quite good because [this paper] does highlight something interesting there.”

Calcium Signaling and Saliva Secretion

Lacruz and his team turned to a Down syndrome mouse model to investigate oral health and hyposalivation in this condition. These mice, called Dp16, are genetically edited to carry a duplication of genes on chromosome 16 corresponding to those on human chromosome 21.

To measure saliva secretion, the researchers anesthetized the mice and injected a saliva-stimulating drug. Compared to wild type (WT) mice, Dp16 mice produced significantly less saliva.

One of the major factors controlling saliva production is calcium ions (Ca²⁺). Neurotransmitters trigger salivary gland cells to release Ca²⁺, which in turn leads to influx of Ca²⁺ into the cell through store-operated Ca²⁺ entry (SOCE) to replenish Ca²⁺. This helps maintain saliva production and secretion.⁵

To assess whether dysfunction in SOCE contributed to hyposalivation in Dp16 mice, Lacruz and his team isolated salivary gland cells from mice. Depleting the cell’s internal Ca²⁺ stores and exposing them to external Ca²⁺ revealed that compared to WT mice, Ca²⁺ influx through SOCE was significantly reduced in Dp16 mice. They observed similarly reduced SOCE in induced pluripotent stem cells (iPSCs) derived from an individual with Down syndrome, indicating that dysregulated Ca²⁺ signaling underlies Down syndrome-associated hyposalivation.

“[The] combination of a mouse model together with some work in a human-derived cell is a strength of the paper,” said David Yule, a pharmacology and physiology researcher at the University of Rochester. While Yule was not involved in the present study, he has collaborated with Lacruz previously. Given the importance of calcium signaling in saliva secretion, “this would have been the first place I would have looked as well,” he added.

Hyposalivation and Gum Disease in Down syndrome

After establishing calcium signaling as a potential driver of hyposalivation, Lacruz and his team dug deeper to study the salivary glands of the mice. Transcriptomic analyses indicated increased inflammation and decreased mitochondrial function in the salivary glands of Dp16 mice compared to WT.

Next, the researchers investigated how these observations might be tied to periodontal disease. “Often low saliva production can affect periodontal disease,” said Lacruz. So, they isolated the gum tissue from mice and carried out quantitative real-time PCR on periodontitis markers. This revealed heightened levels of genes encoding pro-inflammatory markers linked with periodontal disease in Dp16 mice compared to WT mice.

Treating Dp16 mice with pilocarpine, a drug used to treat dry mouth, increased saliva secretion. The treatment also reduced the expression of pro-inflammatory markers in the gums, suggesting that such drugs could potentially be used to improve oral health status in people with Down syndrome.

Continue reading below...

Product

The VAULT100 PRO: Inside the most advanced Stirling Ultracold ULT freezer ever built.

The Stirling Ultracold VAULT100™ PRO redefines ultra-low temperature storage with reliable -100°C performance, faster recovery, lower operating costs and sustainable operation. Learn how you can protect critical samples without compromise.

Read More

Since saliva flow rate could affect the oral microbiome, Lacruz and his team next isolated DNA from buccal swabs of mice and subjected it to metagenomics. WT and Dp16 mice showed significantly different oral microbiome compositions. Consistent with this, fecal samples revealed significant gut microbiome shifts in Dp16 mice compared to WT animals. This change in the gut microbiome was “striking,” said Lacruz, who was not expecting to see this degree of a microbiome shift.

Calcium Signaling, Hyposalivation, and Gum Disease: Connecting the Dots

Overall, Lacruz said that their findings indicate that the root of periodontal inflammation in Down syndrome could be calcium dysregulation. “That drives hyposalivation that changes the oral microbiome, [which] affects periodontal inflammation,” he explained.

However, Carpenter was not entirely convinced that hyposalivation drives periodontitis. “I don't think there's much evidence for that in…literature about human studies,” he said. Instead, he said that inflammation—which is present in Dp16 salivary glands—could cause hyposalivation. “There's lots of literature that shows that inflammatory cells can affect salivary secretion,” he noted.

According to Yule, next steps could include looking at whether dysregulated calcium signaling—which is linked with several other diseases—also underlies other Down syndrome-related complications like Alzheimer’s disease. While drugs targeting calcium signaling could potentially help, there is a complexity to it, he noted. “Knowing what the target is [is] good, but the fact that the target is almost universal in cells, then that makes you think about whether it's something that could be targeted,” explained Yule.

Lacruz agreed that disrupted calcium signaling occurs in other tissues as well. “Understanding why calcium is dysregulated is an important part of what we need to do [next],” he said. More work needs to be done to translate the findings to the clinic, “but we see that as a way forward to potentially impacting the lives of individuals with Down syndrome,” said Lacruz.