Amyotrophic lateral sclerosis, or ALS, has been a tough nut to crack. Over the decades, investigators at Feinberg and across the globe have identified rare genes that cause ALS to run in families, leading to the creation of disease models that faithfully recapitulate aspects of the human disease in mice and other experimental platforms. But a disease-modifying treatment has remained elusive.
Still, all of this work has generated an explosion of information about how mutated proteins injure nerve cells and hint at unifying theories to explain the underlying cause of ALS. And it holds the promise of developing new and powerful treatments, according to Robert Kalb, MD, Les Turner Professor and director of the Les Turner ALS Center. (Listen to an interview with Kalb in our podcast series here.)
Kalb believes that the road to a transformative therapy is paved with incremental discoveries, a philosophy that guides investigation in his own laboratory and others under the Les Turner banner.
“Ultimately, it’s going to come down to better understanding of basic physiology and how the disease-causing proteins corrupt the normal operation of nerve cells,” said Kalb. He believes the mechanisms of cellular waste disposal may be one root cause of dysfunction in ALS.
“Cells are constantly making misfolded proteins, and they’re very effective at recognizing that garbage and getting rid of it,” said Kalb, who’s also a professor of Neurology in the Division of Neuromuscular Disease. “It turns out that several of the genetic mutations that cause familial ALS are in that protein degradation pathway — there are many reasons to think that the most effective treatments on the near horizon will be targeting cellular trash disposal pathways.”
To turn ideas into discoveries, and eventually treatments, investigators in the Les Turner ALS Center are working to uncover the genetic causes of ALS and define the mechanisms of degeneration in a variety of neurons.
“The laboratories and methods they use all have distinct advantages, so they fit together like pieces of a puzzle,” Kalb said. “You need people that are devoted to basic science, and I think we have that here.”
Decoding the Disease
Teepu Siddique, MD, the Les Turner ALS Foundation/Herbert C. Wenske Foundation Professor, has been at the forefront of ALS research for 30 years. In fact, Siddique and his collaborators discovered the first cause of ALS, linking mutations in the SOD1 gene to the disease, and they developed the first animal model for ALS, now used by investigators all over the world.
Since then, the Siddique team has discovered mutations in the genes , P62, ALS2, ALS5, CHCHD10 and others in familial cases of ALS. They found damaging ubiquilin2 and p62 protein aggregations in motor neurons. It was the first time a cause for ALS could be directly linked to the mechanism of disease as defects in protein recycling of damaged proteins, but the impact of ubiquilin2 and p62 goes further, according to Siddique.
“When we looked at a large number of autopsy cases of all forms of ALS and ALS dementia patients, we found that virtually all of them had protein aggregations in motor neurons decorated with ubiquilin2 and p62, irrespective of cause or family history. This tells you that these proteins have relevance to sporadic disease, not just familial disease — it’s also a universal pathology of ALS and ALS /dementia,” said Siddique, also a professor of Cell and Molecular Biology.
He further showed that p62 and other genetic causes of ALS can cause dementia, muscle, bone and eye diseases.
“This helped break the paradigm that ALS is only a motor neuron degeneration,” Siddique said. “We know now that ALS-causing mechanisms contribute to a wider spectrum of disease, affecting several organ systems.”
Another laboratory in the Les Turner ALS Center, led by Pembe Hande Ozdinler, PhD, associate professor of Neurology in Neuromuscular Disease, focuses on neuronal degeneration itself.
Ozdinler specializes in the degeneration of corticospinal motor neurons, also known as upper motor neurons. Previously, little was known about these neurons, as they proved difficult to identify, isolate and study. Ozdinler’s laboratory pioneered in their labeling, isolation and cellular investigation, and subsequently discovered that upper motor neurons are among the first neurons to show evidence of degeneration in ALS — a canary in a coal mine.
“These neurons become vulnerable up to six months before you see any symptoms in patients, so we developed ways to make them visible, to make them stand out,” she said. “We’ve now developed and characterized five different models in which upper motor neurons degenerate.”
Further investigation has revealed endoplasmic reticulum stress is a major factor for degeneration, and now Ozdinler is developing novel biomarkers that can detect that degeneration.
“We are lucky because certain proteins are secreted and can be detected in the blood,” she said. “Those are potential early detection biomarkers, or even biomarkers that could tell us what stage the disease is at before symptoms appear.”
In addition, Ozdinler advocates considering the health of corticospinal motor neurons in clinical trials of ALS drugs and is developing a novel drug discovery platform which includes the neurons’ survival as a read-out. This is important as current trials often just look at the health of the spinal motor neurons, she said.
“When corticospinal motor neurons die, the whole circuitry is affected,” Ozdinler said. “If we want to build effective and long-term solutions, we need to consider the health of brain motor neurons as well.”
While other laboratories in the Les Turner ALS Center use mouse models, Evangelos Kiskinis, PhD, assistant professor of Neurology in Neuromuscular Disease, uses a unique patient-derived stem cell model, allowing for direct study and manipulation of motor neurons with disease.
For example, Kiskinis and his team can produce motor neurons from patients and compare them with ones generated from healthy control individuals, looking for disease-related phenotypes or screen for potential therapeutic compounds. In cases where a disease-causing mutation is present, they can use CRISPR-Cas9 gene editing to reverse it, creating a stem cell line identical to the patient’s cells, but without the mutation — an isogenic control line.
“This allows us to test whether a phenotype or defect in a motor neuron is caused by that particular mutation,” Kiskinis said. He can also use these stem cells in other ways, such as combining them with a new technique called optopatch to measure electricity in cells en masse.
Kiskinis created patient-derived spinal cord motor neurons with ALS and measured the electrical patterns of hundreds of cells at once, finding the ALS neurons were hyper-excitable under normal conditions, but became under-excited when prompted to fire rapidly.
“The excitability changes observed in these patient neurons most likely represent the early steps in the disease process,” he said. “The fact that these changes are detectable in stem cell-derived neurons offers the hope that interventions that affect excitability could affect disease progression before symptoms begin.”
The fight against ALS is a marathon, not a sprint. The goal of a disease-modifying treatment is still out of reach, but a deep commitment to basic science is the approach that can move the needle in a concrete way, according to Kalb.
“You have to understand the underlying basic biology,” Kalb said. “That’s where the answers will come from.”
Listen to an interview with Kalb in our podcast series.