Mitochondria are essential to life: they produce energy, synthesize
building blocks critical to cell function and help regulate cellular activity,
including programmed cell death. Mitochondrial diseases can cause severe
metabolic disorders in children and dysfunctional mitochondria are thought to
play a role in cancer, diabetes, heart attack, stroke, Parkinson’s disease and
A new research tool offers an unprecedented glimpse at the
workings of these tiny, dynamic organelles, and could aid in the study of
For decades, cardiac researcher James McCully, PhD, has been spellbound by the idea of using mitochondria, the “batteries” of the body’s cells, as a therapy to boost heart function. Finally, a clinical trial at Boston Children’s Hospital is bringing his vision — a therapy called mitochondrial transplantation — to life.
Mitochondria, small structures inside all of our cells, synthesize the essential energy that our cells need to function. In the field of cardiac surgery, a well-known condition called ischemia often damages mitochondria and its mitochondrial DNA inside the heart’s muscle cells, causing the heart to weaken and pump blood less efficiently. Ischemia, a condition of reduced or restricted blood flow, can be caused by congenital heart defects, coronary artery disease and cardiac arrest.
For the smallest and most vulnerable patients who are born with severe heart defects, a heart-lung bypass machine called extracorporeal membrane oxygenation (ECMO) can help restore blood flow and oxygenation to the heart. But even after blood flow has returned, the mitochondria and their DNA remain damaged.
“In the very young and the very old, especially, their hearts are not able to bounce back,” says McCully.
Ischemia can be fatal for the tiniest patients
After cardiac arrest, for instance, a child’s mortality rate jumps to above 40 percent because of ischemia’s effects on mitochondria. If a child’s heart is too weak to function without the support of ECMO, his or her risk of dying increases each additional day spent connected to the machine.
But what if healthy mitochondria could come to the rescue and replace the damaged ones? …
Like all cells, the neurons of our nervous system depend on mitochondria to generate energy. Mitochondria need constant rejuvenation and turnover, and that’s especially true in neurons because of their high energy needs for signaling and “firing.” Mitochondria are especially abundant at presynaptic sites — the tips of axons that form synapses or junctions with other neurons and release neurotransmitters.
But the process of maintaining mitochondrial number and quality, known as mitostasis, also poses particular challenges in neurons. Increasingly, mitostasis is providing a helpful lens for understanding neurodegenerative disorders. Problems with mitostasis are implicated in Parkinson’s disease, Alzheimer’s disease, ALS, autism, stroke, multiple sclerosis, hypoxia and more. …
Placed near the heart, the device can potentially predict life-threatening cardiac arrest in critically ill heart patients, according to tests in animal models. The technology was developed through a collaboration between Boston Children’s Hospital and device maker Pendar Technologies (Cambridge, Mass.).
“With current technologies, we cannot predict when a patient’s heart will stop,” says John Kheir, MD, of Boston Children’s Heart Center, who co-led the study. “We can examine heart function on the echocardiogram and measure blood pressure, but until the last second, the heart can compensate quite well for low oxygen conditions. Once cardiac arrest occurs, its consequences can be life-long, even when patients recover.”
In critically ill patients with compromised circulation or breathing, oxygen delivery is often impaired. The new device measures, in real time, whether enough oxygen is reaching the mitochondria, the organelles that provide cells with energy. …
A study of tuberous sclerosis, a syndrome associated with autism, suggests a new treatment approach that could extend to other forms of autism.
The genetic disorder tuberous sclerosis complex (TSC) causes autism in about half of the children affected. Because its genetics are well defined, TSC offers a window into the cellular and network-level perturbations in the brain that lead to autism. A study published today by Cell Reports cracks the window open further, in an intriguing new way. It documents a defect in a basic housekeeping system cells use to recycle and renew their mitochondria.
Mitochondria are the organelles responsible for energy production and metabolism in cells. As they age or get damaged, cells digest them through a process known as autophagy (“self-eating”), clearing the way for healthy replacements. (Just this month, research on autophagy earned the Nobel Prize in Physiology or Medicine.)
Mustafa Sahin, MD, PhD, Darius Ebrahimi-Fakhari, MD, PhD, and Afshin Saffari, in Boston Children’s Hospital’s F.M. Kirby Neurobiology Center now report that autophagy goes awry in brain cells affected by TSC. But they also found that two existing medications restored autophagy: the epilepsy drug carbamazepine and drugs known as mTOR inhibitors. The findings may hold relevance not just for TSC but possibly for other forms of autism and some other neurologic disorders. …
She’s small for a 6-month-old, but otherwise Avery Gagnon looks perfectly healthy. She smiles, kicks, laughs and grabs her toys and pacifiers. What you’d never know is that Avery has complex congenital heart disease and might not be alive today if it weren’t for an innovative procedure that used mitochondria from her own cells to boost her heart’s energy.
The procedure is the brainchild of James McCully, PhD, a cardiovascular research scientist at the Heart Center at Boston Children’s Hospital, who spent most of his career working to solve a common complication of heart surgery: damage to heart muscle cells. …
Mitochondria, as you may know, are the engines that power cells. They’re always in motion, supplying energy wherever it’s needed. In brain cells, mitochondria especially have to hoof it around, traveling out into the axons and dendrites to fuel the energy-intensive task of communicating with other cells.
But in at least one form of Parkinson’s disease, that movement becomes a problem: the genetic mutations causing the disease leave neurons unable to make the fidgety organelles hold still. Without this ability, the dopamine-producing neurons in the brain’s substantia nigra can’t safely dispose of mitochondria when they go bad, and the neurons die or become impaired.
“When damaged, mitochondria produce reactive oxygen species that are highly destructive, and can fuse with healthy mitochondria and contaminate them, too,” explains Tom Schwarz, of the F.M. Kirby Neurobiology Center at Children’s Hospital Boston, senior investigator on a study published in Cell today. “It’s the equivalent of an environmental disaster in the cell.” …