This organoid model allowed the researchers to observe cellular interactions in real-time and manipulate specific variables with high precision. One of the study’s most significant breakthroughs involved identifying a specific subpopulation of HBCs. These cells are distinguished by their production of a protein known as KRT5 (Keratin 5).
The researchers observed that these KRT5-producing HBCs were not merely sitting by; they were actively facilitating the generation of new olfactory neurons. To test the importance of these cells, the team performed a depletion experiment, selectively removing the KRT5-positive HBCs from the organoid cultures. The results were stark: without these specific stem cells, the generation of new neurons was significantly impaired. This finding provides strong evidence that HBCs are essential players in the regenerative process, even under conditions that were not previously considered "catastrophic" enough to trigger them.
Understanding the Impact of Aging and Disease
The development of this model comes at a critical time. The COVID-19 pandemic brought the issue of anosmia—the loss of smell—into the global spotlight, as millions of patients experienced sensory disruptions as a primary symptom of the virus. Beyond viral infections, the sense of smell is also known to decline with age and is often one of the earliest clinical signs of neurodegenerative diseases like Parkinson’s and Alzheimer’s.
By utilizing their model to compare cells from mice of different ages, the Tufts team began to uncover why these declines occur. "We found a decline in the ability of the older mice cells to generate new neurons," Lin said. "We think this is due to a decrease in the GBC population as we age, but we need to do more work to test this hypothesis and if so, develop ways to rejuvenate them."
The ability to pinpoint whether a regenerative failure is due to a lack of "worker" cells (GBCs) or a failure in the "support" system (HBCs) is vital. If the GBC population is indeed the bottleneck in aging, future therapies might focus on stimulating their proliferation or finding ways to "reset" their biological clock.
An Easy-To-Use Model
One of the most remarkable aspects of this research is not just the biological discovery itself, but the philosophy behind the model’s creation. The study’s lead author, Juliana Gutschow Gameiro, a former Ph.D. student who visited the Graduate School of Biomedical Sciences from the State University of Londrina in Brazil, was determined to create a tool that was accessible to the wider scientific community.
Research into olfactory stem cells has historically been a niche field, but the link between smell loss and major health conditions has spurred a surge of interest. "Because loss of smell is associated with COVID-19, as well as with Parkinson’s disease and other conditions, a much larger number of researchers from a variety of different fields have begun researching olfactory epithelial cells in the last few years," Lin noted.
