Hidden genetic mutations in stem cells could undermine therapeutic benefit

April 14, 2016, Oregon Health & Science University
A confocal microscopy image of human fibroblasts derived from SCNT-ESCs. Blue color: nuclei; red color: mitochondria; green color: microtubules. (X100) Credit: Mitalipov lab, OHSU.

For the first time, scientists have confirmed the long-standing hypothesis that as people age, they accumulate gene mutations in their mitochondria—cells' energy source.

A team led by Shoukhrat Mitalipov, Ph.D., director of the Center for Embryonic Cell and Gene Therapy at Oregon Health & Science University, has discovered that induced pluripotent stem, or iPS, , a type of stem cell derived from patients' skin or blood cells contain faulty mitochondrial DNA. The study was published today in the journal Cell Stem Cell.

"Pathogenic mutations in our mitochondrial DNA have long been thought to be a driving force in aging and age-onset diseases, though clear evidence was missing. Now with that evidence at hand, we know that we must screen for mutations or collect them at younger age to ensure their mitochondrial genes are healthy," said Mitalipov. "This foundational knowledge of how cells are damaged in the natural process of aging may help to illuminate the role of mutated mitochondria in degenerative disease."

Mitochondrial genes reside outside of the nucleus and have been known to be prone to damage. Mutations in mitochondrial DNA, which arise randomly within individual cells as we age, can limit cells' ability to create energy, produce signals and function properly.

Human iPS cell colony (X40). Credit: Mitalipov lab, OHSU

Potential therapies using stem cells hold tremendous promise for treating human disease. However, defects in the mitochondria could undermine the iPS cells' ability to repair damaged tissue or organs. To avoid impairing IPS cells' therapeutic value, Mitalipov and colleagues recommend screening the cells for mitochondrial DNA mutations.

"If you want to use iPS cells in a human, you must check for mutations in the mitochondrial genome," said Taosheng Huang, M.D., Ph.D., a medical geneticist and director of the Mitochondrial Disorders Program at Cincinnati Children's Hospital Medical Center. "Every single cell can be different. Two cells next to each other could have different mutations or different percentages of mutations."

"This collaborative multi-disciplinary effort identifies 'mitochondrial genome integrity' as a vital readout in assessing the proficiency of patient-derived regenerative products destined for clinical applications", adds study co-author Andre Terzic, M.D., Ph.D., Director, Mayo Clinic Center for Regenerative Medicine.

Every individual has trillions of cells and thousands of copies of mitochondria in each cell. As cells age, thousands of different mutations in each mitochondrial genome are possible. Because each cell has its own unique mutation, when researchers examine a pinch of skin or drop of blood containing millions of cells, most mitochondrial mutations are hidden. The mutation would only be visible if every cell has the same mutation.

However, these mutations become detectable in iPS cells. In the process of making iPS cell lines, researchers expand clones from each individual patient skin or blood cell. As a result, every cell in the iPS cell line will contain the same mitochondrial DNA mutations as that initial adult cell.

This visual abstract depicts Mitalipov and colleagues findings that human iPSCs derived from older adults carry more mitochondrial DNA mutations than those derived from younger individuals. Defects in metabolic function caused by mtDNA mutations suggest careful screening of hiPSC clones for mutational load before clinical application. Credit: Mitalipov et al./Cell Stem Cell 2016

In this study, rather than studying one iPS cell line, the researchers derived and sequenced 10 iPS cell clones from each patient tissue sample to get a better understanding of mitochondrial DNA mutation rates.

They took samples of blood and skin from healthy people and people with degenerative diseases, ranging in age from 24 to 72. When they tested the pooled skin or blood cells for mitochondrial DNA mutations, the levels of mutations appeared low.

Then they profiled 20 iPS cell lines per patient - 10 from their blood cells and 10 from their skin cells. When they sequenced the iPS cell lines, they found higher numbers of mitochondrial DNA mutations, particularly in cells from patients older than 60. They analyzed 130 iPS and discovered 80 percent showed mutations. They also found higher percentages of mitochondria containing within a cell. The higher the load of mutated mitochondrial DNA in a cell, the greater the cell's function is compromised.

The authors recommend producing and screening multiple lines per patient and then choose the least damaged line.

In May 2013, Mitalipov was the first scientist in the world to demonstrate the successful use of somatic cell nuclear transfer, or SCNT, to produce human embryonic stem cells from an individual's skin cell. That breakthrough was one of a six-year chain of discoveries that included his 2007 work demonstrating the nuclear transfer method to create embryonic stem cells from a nonhuman primate. OHSU scientists have also demonstrated that SCNT allows replacement of mutated mitochondrial genes with healthy donor egg mitochondria while retaining the patient cell's nucleus.

Explore further: Test run finds no cancer risk from stem cell therapy

More information: "Age-Related Accumulation of Mitochondrial DNA mutations in Adult-Derived Human iPSCs," Cell Stem Cell, 2016. dx.doi.org/10.1016/j.stem.2016.02.005

Related Stories

Test run finds no cancer risk from stem cell therapy

April 7, 2016
Therapeutic stem cells can be made without introducing genetic changes that could later lead to cancer, a study in PLOS Genetics has found.

Repairing fatal mutations behind mitochondrial disease

July 24, 2015
A multidisciplinary team of researchers has eliminated fatal mitochondrial DNA mutations in stem cells from patients with mitochondrial diseases. The study is published in a recent online issue of Nature as a collaboration ...

Researchers unlock first step toward gene therapy treatment of mitochondrial disease

July 15, 2015
A study led by Shoukhrat Mitalipov, Ph.D., and Hong Ma, M.D., Ph.D., at the Center for Embryonic Cell and Gene Therapy at Oregon Health & Science University and the Oregon National Primate Research Center has revealed the ...

Mitochondrial genome mutates when reprogrammed

July 28, 2011
Induced pluripotent stem cells (iPS cells) are truly talented multi-taskers. They can reproduce almost all cell types and thus offer great hope in the fight against diseases like Alzheimer's and Parkinson's. However, it would ...

Team reports a new mouse model to study how the EWS-FLI1 gene causes bone cancer

March 17, 2016
There exist several oncogenes that drive cancer. In many cases, however, the oncogenes themselves are not sufficient and must be complemented with other mutations before cancer develops. Researchers at the Center for iPS ...

Recommended for you

Shared genetics may shape treatment options for certain brain disorders

June 20, 2018
Symptoms of schizophrenia and bipolar disorder, including psychosis, depression and manic behavior, have both shared and distinguishing genetic factors, an international consortium led by researchers from Vanderbilt University ...

Targeting the engine room of the cancer cell

June 18, 2018
Researchers at Columbia University Irving Medical Center (CUIMC) have developed a highly innovative computational framework that can support personalized cancer treatment by matching individual tumors with the drugs or drug ...

Scientists learn more about how gene linked to autism affects brain

June 18, 2018
New preclinical research shows a gene already linked to a subset of people with autism spectrum disorder is critical to healthy neuronal connections in the developing brain, and its loss can harm those connections to help ...

161 genetic factors for myopia identified

June 15, 2018
The international Consortium for Refractive Error and Myopia (CREAM) recently published the largest-ever genetic study of myopia in Nature Genetics. Researchers from the Gutenberg Health Study at the Medical Center of Johannes ...

Genetic disorder identified in children

June 15, 2018
A genetic defect affecting normal development in children has been identified by a study involving University of Queensland researcher and alumnus Professor David Coman.

Scientists discover biomarker for flu susceptibility

June 13, 2018
Researchers at the Stanford University School of Medicine have found a way to predict whether someone exposed to the flu virus is likely to become ill.

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

winthrom
not rated yet Apr 14, 2016
If CRISPR mods can be made to IPC mitochondrial DNA by using a "majority selected correction" template from DNA maps of many mitochondrial DNA maps, each containing some random mutations, a healthy mitochondrial DNA can be used for older people, who need this help the most.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.