Mitochondria, the powerhouses of our cells, are vital for energy production and cell survival. A delicate balance of calcium within these organelles is crucial for their function. Too much calcium can disrupt energy metabolism and even trigger cell death. To maintain this balance, cells rely on a protein called the mitochondrial sodium-calcium exchanger, or NCLX. Now, groundbreaking research from the Lewis Katz School of Medicine at Temple University has identified a novel regulator of NCLX activity: a protein called TMEM65. This exciting discovery, published in Nature Metabolism, marks the first time scientists have characterized the interaction between TMEM65 and NCLX within mitochondria. According to Dr. John W. Elrod, senior investigator on the study, TMEM65 is the first protein identified as a direct interactor and regulator of NCLX. This finding could pave the way for new therapeutic strategies to combat calcium overload in mitochondria, a common factor in diseases like heart failure and Alzheimer's disease. Mitochondrial calcium exchange plays a critical role in regulating cell survival and energy signaling. When mitochondria accumulate excessive calcium, energy metabolism is compromised, leading to cell death. This is particularly evident in the heart, where calcium overload contributes to the irreversible loss of heart muscle cells during heart attacks and in heart failure. Similarly, in Alzheimer's disease and other neurodegenerative conditions, excessive calcium can lead to the demise of brain cells. Previously, Dr. Elrod and his team identified NCLX as a key player in removing calcium from mitochondria in the heart and brain. Research has also demonstrated that boosting NCLX activity can slow the progression of heart failure, Alzheimer's disease, and even cancer. However, despite these promising findings, the mechanisms governing NCLX regulation have remained poorly understood. The complex structure of NCLX has hindered research into its regulation and slowed the development of potential therapies. To overcome these challenges, the researchers adopted a novel approach using biotin tagging to trace NCLX's interactions with other proteins within intact cells. Postdoctoral fellow Dr. Joanne F. Garbincius led the effort to create a fusion protein of NCLX and a biotinylation protein. This fusion protein was then introduced back into cells, allowing researchers to biochemically label and isolate proteins in close proximity to NCLX. Using mass spectrometry, they identified TMEM65 as a prime candidate for regulating NCLX. TMEM65 was particularly intriguing because it is a mitochondrial protein with previously unknown function. Adding to the intrigue, a case report described a young girl with a loss-of-function mutation in TMEM65 who experienced severe muscle weakness, microcephaly, and neurological dysfunction. Subsequent experiments revealed that removing TMEM65 from cells led to a buildup of calcium within mitochondria, confirming its essential role in NCLX activity. This was further validated in a mouse model, where reduced TMEM65 levels resulted in progressive loss of neuromuscular function. These groundbreaking methods used to identify TMEM65 and elucidate NCLX regulation have been recognized in the field of cardiovascular science. Dr. Garbincius received the American Heart Association's Louis N. and Arnold M. Katz Basic Science Research Prize for Early Career Investigators in 2024 for her contributions to this research. The team is now focused on exploring the possibility of modulating TMEM65 activity as a therapeutic strategy. According to Dr. Elrod, TMEM65 holds significant promise as a therapeutic target, and manipulating its interaction with NCLX could offer a valuable treatment option for patients suffering from diseases involving excessive calcium accumulation in mitochondria. Dr. Amy J. Goldberg, Dean of the Lewis Katz School of Medicine, emphasized the transformative nature of this research, highlighting its potential to pave the way for innovative treatments for heart failure, Alzheimer's disease, and other related conditions.
