Do you like eating your dead neighbors? Well, if you do, you are one step closer to being like a hair follicle stem cell.

Billions of cells in our bodies die each day, making way for fresh replacements to maintain our healthy tissues. But how do our bodies handle this flood of cellular corpses without causing chaos? Surprisingly, the stem cells in your hair follicle take matters into their own hands by consuming their dying neighbors.

Recent research on hair follicles, which undergo regular cycles of growth and regression, reveals a remarkable mechanism involving stem cells acting as temporary “garbage collectors.” Hair follicle stem cells (HFSCs) are usually known as specialized cells capable of renewing themselves and generating various cell types needed for tissue growth and repair. However, these same cells also play an essential cleanup role during the hair follicle’s regression (or catagen) phase. During this phase, a substantial portion of the follicle cells undergo programmed death in a process known as apoptosis. As this happens, stem cells ingest the dying cells, swiftly clearing cellular debris and preventing undesired inflammatory and autoimmune responses.

To know when to “eat” their neighbors, these stem cells use a dual-sensor system. Researchers found that HFSCs utilize two molecular receptors, one that detects lipids released by dying cells as a sort of cellular distress signal, and another that senses retinoic acid emitted by healthy neighboring cells. Both signals must be present simultaneously for the stem cells to start the phagocytic cleanup. Once the dying cells are cleared and lipid signals fade, the remaining retinoic acid will signal to the healthy cells to shut the system down gracefully. This fine-tuned balance essentially ensures that stem cells only consume their neighboring cells when absolutely necessary, avoiding accidentally ingesting healthy tissue.

But all this begs the question. Why not leave it up to the experts? After all, phagocytes, which are immune cells specialized for engulfing foreign material or dead cells, are perfectly capable of clearing cellular debris. In the case of HFSCs though, the benefits of "self-clearance" are found to extend beyond mere debris removal. Stem cells appear to gain nutritional and energetic advantages from consuming their neighbors, which helps to sustain their vital regenerative functions. However, this process must be tightly regulated, as excessive phagocytic activity can distract stem cells from their primary role of maintaining tissue integrity and regeneration. Furthermore, this stem cell-driven cleanup provides an initial rapid response to cellular death that occurs well before traditional immune system phagocytes, such as macrophages, arrive on the scene. Following this line of logic, researchers found that when stem cells fail to clear apoptotic cells promptly, tissue damage and inflammation can occur even with phagocytes present.

As research progresses, scientists are learning more about how stem cells play a role in your body’s self-maintenance and healing. Hopefully, one day, understanding the myriad of functions stem cells may possess could open up avenues for new therapies, allowing both regeneration and repair to go hand in hand.

Disclaimer: stem cell cannibalism is performed by trained professionals. Please do not try this at home.