Scientists at Scripps Research have developed a new screening platform that has allowed them to identify a new set of compounds that appear to have a potent protective effect on the mitochondria of brain cells, helping these cells to defend against the kinds of stresses encountered during Alzheimer’s disease and other neurodegenerative conditions.
Improved screening for neuroprotective molecules
The details of this new screening platform are described in detail in a new paper published in Science Advances . Essentially, the system allows for the rapid screening of thousands of molecules in order to identify possible candidates for the protection of neural mitochondria.
The mitochondria are well known as being the power stations of the cells, as they supply our cells with most of the energy they need to function. Unfortunately, as we age, our mitochondria because increasingly damaged and dysfunctional, and this mitochondrial dysfunction is a proposed reason we age. The role that dysfunctional mitochondria play in neurodegenerative diseases, such as Alzheimer’s, Parkinson’s, and ALS, has taken on increasing importance in the last few years.
During the study, the researchers showcased the capabilities of their platform, rapidly screening a library of 2,400 compounds. They discovered multiple compounds that increased the health of neural mitochondria and that also appeared to enhance their resilience to the stresses of neurodegenerative diseases.
Using cultured neurons taken from mouse brains, the researchers then marked the cells with fluorescent tags so that they could record mitochondrial numbers, shapes, behavior, and general health both before and after being treated with the compounds.
Intriguingly, prior to this, the researchers had tested some previously known compounds that appear to protect mitochondria in other types of cells to see if they would work the same way in neurons. They discovered that these compounds had absolutely no visible effect on the mitochondria residing in neurons, which highlights that there are often significant differences between the cells in the body, and what works in one type does not always do so in others.
Using their new screening platform and the 2,400 compounds in the library, the researchers initially found a total of 149 that were potentially beneficial for neuronal mitochondria. Following further refining, those initial 149 compounds were whittled down to several that robustly protected the neuronal mitochondria.
They introduced the cells to three forms of stress known to damage mitochondria during the progression of Alzheimer’s disease: small clusters of the harmful amyloid beta protein; the neurotransmitter glutamate, which is capable of exciting neurons to death; and peroxide, an extremely reactive molecule that is produced by damaged mitochondria and can harm nearby healthy mitochondria.
The various chosen compounds were found to effect the mitochondria in different ways, working via more than one biological pathway to convey protection. They found that dyclonine, a compound found in some sore-throat lozenges, was effective against glutamate and peroxide damage. It also appeared to improve the energy output of the mitochondria as well as increase the activity of the neurons themselves at their synapses, which are the connection points to other nearby neurons.
The researchers even tested the efficacy of dyclonine further by adding it to the drinking water of mice, and it appeared to improve the health of their mitochondria as well. The next step will be to test the most promising of the screened compounds in animal studies, and the results from dyclonine give them hope that the beneficial effects seen in cell studies could translate to the mice. The hope of the researchers is to test the compounds using animal models of specific neurodegenerative diseases and, ultimately, develop new drugs from them.
Impaired mitochondrial dynamics and function are hallmarks of many neurological and psychiatric disorders, but direct screens for mitotherapeutics using neurons have not been reported. We developed a multiplexed and high-content screening assay using primary neurons and identified 67 small-molecule modulators of neuronal mitostasis (MnMs). Most MnMs that increased mitochondrial content, length, and/or health also increased mitochondrial function without altering neurite outgrowth. A subset of MnMs protected mitochondria in primary neurons from Aβ(1–42) toxicity, glutamate toxicity, and increased oxidative stress. Some MnMs were shown to directly target mitochondria. The top MnM also increased the synaptic activity of hippocampal neurons and proved to be potent in vivo, increasing the respiration rate of brain mitochondria after administering the compound to mice. Our results offer a platform that directly queries mitostasis processes in neurons, a collection of small-molecule modulators of mitochondrial dynamics and function, and candidate molecules for mitotherapeutics.
Screening methods for drug discovery continue to become more and more refined and efficient, which is a good thing because it means reduced costs for new drug research, which could potentially be passed on to the patient. Lower development costs are also good news for pharmaceutical companies, which are facing ever-increasing costs for new drug development.
On a broader front, it is nice to see more interest in the role of mitochondrial dysfunction entering the research world. Perhaps, eventually, the majority of medical researchers will accept that in order to deal with age-related diseases comprehensively, the root causes of aging must be the target of therapies. Targeting mitochondrial dysfunction is a step in the right direction.
 Varkuti, B. H., Kepiro, M., Liu, Z., Vick, K., Avchalumov, Y., Pacifico, R., … & Davis, R. L. (2020). Neuron-based high-content assay and screen for CNS active mitotherapeutics. Science Advances, 6(2), eaaw8702.