Summary: Restoring mitochondrial homeostasis in diseased neurons can protect the optic nerve from being damaged and potentially reverse symptoms of glaucoma.
Source: Indiana University
Indiana University School of Medicine researchers have identified a new therapeutic target that could lead to more effective treatment of glaucoma.
Glaucoma is a neurodegenerative disease that causes vision loss and blindness due to a damaged optic nerve. More than 200,000 people are affected by glaucoma in the United States each year. Unfortunately, there is currently no treatment.
In a newly published paper in Communications Biology, researchers found neurons use mitochondria for a steady source of energy, and restoring mitochondrial homeostasis in the diseased neurons can protect the optic nerve cells from being damaged.
“Age-related neurodegenerative disease, which includes glaucoma, Parkinson’s disease, and amyotrophic lateral sclerosis (ALS), is the biggest global health problem,” said Arupratan Das, Ph.D., assistant professor of ophthalmology and principal investigator of the study.
“The fundamental mechanisms that we discovered can be used to protect neurons in glaucoma and be tested for the other diseases. We have identified a critical step of complex mitochondrial homeostasis process, which rejuvenates the dying neuron, similar to giving a lifeline to a dying person.”
The research team, led by Michelle Surma and Kavitha Anbarasu from the Department of Ophthalmology, used induced pluripotent stem cells (iPSCs) from patients with and without glaucoma as well as clustered regularly interspaced short palindromic repeats (CRISPR) engineered human embryonic stem cells with glaucoma mutation.
Using stem cell differentiated retinal ganglion cells (hRGCs) of the optic nerve, electron microscopy and metabolic analysis, researchers identified glaucomatous retinal ganglion cells suffer mitochondrial deficiency with more metabolic burden on each mitochondrion. This leads to mitochondrial damage and degeneration. Mitochondria are the tube like structures in cells which produce adenosine triphosphate, cell’s energy source.
However, the process could be reversed by enhancing mitochondrial biogenesis by a pharmacological agent. The team showed retinal ganglion cells are highly efficient in degrading bad mitochondria, but at the same time producing more to maintain homeostasis.
“Finding that retinal ganglion cells with glaucoma produce more adenosine triphosphate even with less mitochondria was astonishing,” Das said.
“However, when triggered to produce more mitochondria, the adenosine triphosphate production load was distributed among more mitochondrion which restored the organelle physiology. It is similar to a situation where a heavy stone is carried by fewer people versus a greater number of people—each person will have less pain and injury, just like each mitochondrion will have less difficulty and damage.”
In the future, Das would like to test if these mechanisms protect the optic nerve in animal models under injury before testing in humans to hopefully lead to new clinical interventions.
Enhanced mitochondrial biogenesis promotes neuroprotection in human pluripotent stem cell derived retinal ganglion cells
Mitochondrial dysfunctions are widely afflicted in central nervous system (CNS) disorders with minimal understanding on how to improve mitochondrial homeostasis to promote neuroprotection.
Here we have used human stem cell differentiated retinal ganglion cells (hRGCs) of the CNS, which are highly sensitive towards mitochondrial dysfunctions due to their unique structure and function, to identify mechanisms for improving mitochondrial quality control (MQC).
We show that hRGCs are efficient in maintaining mitochondrial homeostasis through rapid degradation and biogenesis of mitochondria under acute damage.
Using a glaucomatous Optineurin mutant (E50K) stem cell line, we show that at basal level mutant hRGCs possess less mitochondrial mass and suffer mitochondrial swelling due to excess ATP production load.
Activation of mitochondrial biogenesis through pharmacological inhibition of the Tank binding kinase 1 (TBK1) restores energy homeostasis, mitigates mitochondrial swelling with neuroprotection against acute mitochondrial damage for glaucomatous E50K hRGCs, revealing a novel neuroprotection mechanism.