by: Claudia Casal

People Editor

A group of scientists from the University of Virginia School of Medicine has discovered a new organelle called hemifusomes in human and other mammalian cells. This discovery has already impacted how doctors understand and treat several genetic diseases.

Similar to organs in the human body, organelles carry out essential and specialized functions within cells. The common hemifusome has remained unknown for so long, as it is invisible to regular microscopes. Dr. Seham Ebrahim and her team used cryo-electron tomography to obtain their images of hemifusomes. Cryo-electron tomography technology functions by rapidly freezing four lab-grown cells, preserving the cells and allowing for 3D images that show very native states of the cell. In their paper, Ebrahim wrote that the harsh processing usually required to image cells may have prevented the hemifusomes from being observed earlier.

This organelle is about half the size of a small mitochondrion – an organelle that acts as the powerhouses of cells – at about 100 nanometers in diameter. While much about this organelle is a mystery, Ebrahim’s team found that the hemifusome is made up of vesicles, organelles that transport substances. The hemifusome is formed by two vesicles that are partially fused, in a structure reminiscent of a snowman. Hemifusomes are essential to organizing, removing, and recycling proteins. As she puts it, “The hemifusome is like a loading dock where they connect and transfer cargo. It’s a step in the process we didn’t know existed.” With their current knowledge, Ebrahim and other scientists have yet to fully understand the function and role that hemifusomes have within human cells.

Amidst uncertainty, hemifusomes offer a new possibility for the cause of many complex inherited neurodegenerative diseases, like Alzheimer’s and Parkinson’s. Ebrahim commented that, “We’re just beginning to understand how this new organelle fits into the bigger picture of cell health and disease.” Alzheimer’s, for example, is caused by a buildup of proteins that tangle and form a plaque, degenerating both the patient’s mind and memory. Another condition specifically pointed out in the study is Hermansky-Pudlak syndrome, a rare genetic disorder that often causes lung disease, issues with blood clotting, albinism, and vision problems. Malfunctions in how cells take care of excess proteins and other waste have been associated with Hermansky-Pudlak syndrome, along with many similar disorders.

While hemifusomes are a relative mystery, Ebrahim and other scientists are eager to explore all aspects of this organelle and its possibilities in treating diseases. Ebrahim details her next steps, “Now that we know hemifusomes exist, we can start asking how they behave in healthy cells and what happens when things go wrong.”

(Sources: Live Science, Nature, Sci News, UVA Health)