Could the lingering loss of smell associated with Long COVID be triggered by senescent cells? An impaired sense of smell is a well-documented symptom of Long COVID, and researchers have previously explored several possible causes, including an overactive sympathetic nervous system and viral persistence. Now, a fresh study authored by Tsuji et al. investigates a novel underlying factor, focusing on senescent cells present in the olfactory mucosa.

To grasp this concept, it helps to understand what senescence means. Cells can sometimes shift into this specific condition, which is frequently compared to being in a zombie-like state. In this phase, they are not completely dead, yet they no longer function properly. Instead of multiplying as healthy cells do, they cease division altogether. Additionally, these cells can release inflammatory materials that hinder the normal function of neighboring cells and disrupt the chemical messaging pathways of the body.

While this behavior seems highly problematic, cellular senescence is likely a natural defense mechanism designed to prevent future illnesses, such as cancer. When a specific cell suffers damage, halting its ability to divide and create new cells is actually beneficial. Consequently, entering a senescent state serves as a biological safeguard to restrict the negative consequences of diseased or aging cells.

During their investigation, Tsuji et al. observed this phenomenon in mice. They determined that exposure to SARS-CoV-2 prompted senescence among fibroblasts located within the olfactory mucosa of the animals. Remarkably, the virus caused this reaction despite the fact that those specific fibroblasts were not actually infected.

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