Unraveling the Effects of Mitochondrial Dysfunction

Based on News Release by Ellen Goldbaum

Mitochondria provide the lion’s share of energy that cells need to function normally, so genetic defects in mitochondria can cause severe diseases that can be devastating.

But exactly how those mitochondrial defects lead to disease and aging has not been well understood.

A paper published Aug. 22 in Aging Cell reveals for the first time the connection between mitochondrial defects and key signals in the aging process. In a separate Nature Communications paper, the researchers describe how a new technique they developed based on optogenetics can help restore normal function to abnormal mitochondrial interactions.

The Aging Cell paper links, for the first time, mitochondrial dysfunction to the shortening of telomeres, a key biomarker of premature aging.

“Telomeres are specialized DNA sequences that act as caps that stabilize the ends of chromosomes,” explains Taosheng Huang, MD, PhD, professor of pediatrics and chief of the department’s Division of Genetics.

“The shortening of telomeres is generally regarded as an important biomarker of aging, but for a long time, no one knew the mechanism. Now we are able to link mitochondrial dysfunction directly to the shortening of telomeres,” says Huang, the paper’s senior author.

The experiments were done with a type of mouse model called the Polg “mutator” in which the mice carry a specific genetic defect that accelerates the rate of mitochondrial DNA mutations.

“We also were able to show in humans how a single nucleotide change in mitochondrial DNA that’s specifically associated with poor function of mitochondria and causing pediatric mitochondrial disorders can accelerate aging,” Huang says. “We found that reactive oxygen species due to poor function of mitochondria leads to increased DNA damage over time.”

The paper is the first to show that the mitochondrial DNA mutations in this model produce more rapid aging as demonstrated by the DNA clock, which estimates an individual’s biological age according to particular chemical markers in the DNA.

Huang notes the research is the result of successful collaboration among all the authors, including Steve Horvath, PhD, professor of human genetics and biostatistics at UCLA, who developed the DNA clock; as well as Patricia Opresko, PhD, associate professor at the University of Pittsburgh; and Sabine Mai, PhD, of the University of Manitoba; both experts in telomeres and telomere damage.

Jesse Slone, PhD, a former postdoctoral associate in Huang’s lab at Cincinnati Children’s Hospital Medical Center and now a research assistant professor in the Department of Pediatrics at the Jacobs School, is co-first author.

Additional co-authors are from Cincinnati Children’s Hospital Medical Center and a student from Nanchang University. The research was funded by the National Institute of Environmental and Occupational Health and the National Institute on Aging, both of the National Institutes of Health.

Published July 25, the Nature Communications paper reveals how optogenetics, which uses light to manipulate cellular activity, can be employed as a tool not only to study, but also to orchestrate cellular organelle interactions in real time.

The paper focuses on mitochondrial dynamics, the processes that these organelles are constantly undergoing to maintain a healthy balance in the cell. They engage in fission, where one mitochondrion divides into two, and fusion, where two mitochondria fuse together to become one. An imbalance in a cell between the two types of processes can lead to mitochondrial disease.

“In the Nature Communications paper, we describe a technology that we developed that allows us for the first time to directly manipulate the interactions between mitochondria and other organelles in the cell,” Huang says.

“By utilizing optogenetics to force a physical interaction between mitochondria and another cellular component, the lysosome, we were able to restore the mitochondria to a more normal size while also improving their energy production functions,” he explains. “We believe that this new finding could be used as the basis for future diagnosis and treatments for this group of diseases.”

The work was made possible by the use of a powerful imaging technology called structural illumination microscopy, which allows for extremely high resolution real-time imgaing in living cells. This technology was available through a collaboration with Jiajie Diao, PhD, at the University of Cincinnati, where Huang began this research before taking his current position at UB. 

Recruited to UB and to the John R. Oishei Children’s Hospital in 2020 from Cincinnati Children’s Hospital Medical Center, Huang is an expert in the genetics of mitochondrial diseases and has pioneered groundbreaking innovations in detecting and treating genetic diseases.

Huang is also medical director, Genetics and Metabolism in Oishei Children’s Hospital, and chief of human genetics at UBMD Pediatrics.

Co-authors on the Nature Communications paper are from the University of Cincinnati College of Medicine, the Cincinnati Children’s Hospital Medical Center and the University of Illinois at Urbana-Champaign. The research was funded by the National Institutes of Health.