Kir2.1

Mice that received a chemical to inhibit KCNJ2 expression before sustaining a brain injury had lower levels of dysfunctional TDP-43 protein in their brains than those untreated. Traumatic brain injuries (TBIs) are not only one of the most common causes of disability in the U.S. but are also a major risk factor for neurodegenerative diseases like dementia, Alzheimer’s and amyotrophic lateral sclerosis (ALS). Some analyses suggest that as many as 15% of all dementia cases can be linked back to TBIs.  Researchers have wondered whether there might be a way to curb the risk of post-TBI neurodegeneration. Now, they’re closer to finding out: New organoid and mouse data from scientists at the University of Southern California (USC) suggest that inhibiting a gene called KCNJ2 can protect brain cells from changes caused by a TBI. The finding has the potential to inform new therapies that could prevent long-term damage after a head injury or even before.   “Targeting KCNJ2 may reduce the death of nerve cells after TBI,” Justin Ichida, Ph.D., co-corresponding author of the study, said in a press release. “This could have potential as either a post-injury treatment or as a prophylactic for athletes and others at high risk for TBI,” added Ichida, who is also the co-founder of AcuraStem and Modulo Bio and an employee of BioMarin, although none of these companies were involved in the new study. TBIs are called “traumatic” for a reason: They can break the skull, rupture cerebral blood vessels and shred or tear neurons in the white matter, a condition called a “diffuse axonal injury” that may also flood the brain with damage-perpetuating chemicals. But while the link between these mechanisms and acute damage is well established, it’s less clear how they lead to long-term consequences like neurodegeneration.  To try to illuminate this, the USC team designed a tool that blasts brain organoids with high-intensity ultrasound waves and injures them in a way that’s similar to a TBI. By using organoids grown from stem cells taken from patients with neurodegenerative disease, they could systematically analyze the chemical signatures of pathologies that emerge over time to figure out what might be contributing to the disease’s etiology.  In addition to seeing already-known changes involving the protein tau—a hallmark (PDF) of Alzheimer’s disease—the researchers also found that the dysfunction of another protein, TDP-43, kills off neurons soon after the injury. Organoids grown from the cells of patients with ALS or frontotemporal dementia had greater levels of TDP-43 dysfunction than those derived from healthy controls, suggesting the protein is a key player in the mechanisms that lead to long-term damage.  The researchers then looked at how gene expression changed during injury to see whether they could find a potential therapeutic target. A CRISPR-based genomewide screening technique revealed the KCNJ2 gene regulates processes that lead to cell death after a TBI. When the researchers knocked down the gene in brain organoids grown from the cells of people with and without ALS then injured them using a high-intensity ultrasound, they found that the cells were protected from TDP-43 dysfunction and were more likely to survive.  The team’s cell findings bore out in mouse models. Mice that received a chemical to inhibit KCNJ2 expression before sustaining a brain injury had lower levels of dysfunctional TDP-43 protein in their brains than did those that weren’t treated. They also had better recovery of motor function following injury, though this did not reach statistical significance in all dimensions.  Still, “collectively, these data suggest that inhibition of KCNJ2 can effectively reduce the acute TDP-43 injury and degenerative responses following TBI in vitro and in vivo,” the researchers wrote in the paper.  Going forward, the team plans to conduct future studies looking at the safety and tolerability of KCNJ2 suppression, Ichida told Fierce Biotech Research via email. They will also illuminate the mechanism that explains how inhibiting the gene prevents pathology related to TDP-43 and look into whether the findings apply to “milder repetitive type injuries,” he said.

A traumatic brain injury (TBI) can quadruple your risk for developing dementia and increase your chances of developing neurodegenerative diseases such as ALS. In a new study scientists use lab-grown human brain structures known as organoids to offer insights into why this is the case and how to mitigate the risk. A traumatic brain injury (TBI) can quadruple your risk for developing dementia and increase your chances of developing neurodegenerative diseases such as ALS. In a new study published in Cell Stem Cell, USC scientists use lab-grown human brain structures known as organoids to offer insights into why this is the case and how to mitigate the risk. In the study, former postdoc Jesse Lai and PhD student Joshua Berlind from the USC Stem Cell laboratory of Justin Ichida used human patient-derived stem cells to grow rudimentary brain structures known as organoids in the lab. They then injured these organoids with high-intensity ultrasound waves. The injured organoids showed some of the same features seen in TBI patients, including nerve cell death and pathological changes in tau proteins, as well as in a protein called TDP-43. The scientists found that the pathological changes in TDP-43 were more prevalent in organoids derived from patients with ALS or frontotemporal dementia, making their nerve cells more suspectable to dysfunction and death following injury. This suggests that TBI might increase the risk of developing these diseases even more for patients with a genetic predisposition. The worst injuries were sustained by nerve cells that share information -- called excitatory neurons -- located in the deep layers of the organoids. In their search for ways to protect these neurons against the effects of TBI, the scientists identified a gene called KCNJ2, which contains instructions for making channels that selectively allow potassium to pass through the cell membrane, helping to enable muscle contraction and relaxation. Inhibiting this gene had a protective effect on organoids derived from patients with and without ALS, as well as on mice, following a TBI. "Targeting KCNJ2 may reduce the death of nerve cells after TBI," said Ichida, who is the John Douglas French Alzheimer's Foundation Associate Professor of Stem Cell Biology and Regenerative Medicine at USC, and a principal investigator at the Eli and Edythe Broad Center for Regenerative Medicine and Stem Cell Research at USC. "This could have potential as either a post-injury treatment or as a prophylactic for athletes and others at high risk for TBI." About the authors and the study Co-corresponding author Ichida is also a co-founder of AcuraStem and Modulo Bio, a Scientific Advisory Board (SAB) member at Spinogenix and Vesalius Therapeutics, and an employee in the Research and Early Development group at BioMarin Pharmaceutical. Co-corresponding author Lai and co-author Violeta Yu were both employees of Amgen during the study, and currently work at Dewpoint Therapeutics. Named companies were not involved in this research project. First author Berlind is a PhD student in the Ichida Lab. Additional co-authors are Gabriella Fricklas, Cecilia Lie, Jean-Paul Urenda, Kelsey Lam, Naomi Sta Maria, Russell Jacobs, and Zhen Zhao from USC. Fifty percent of the work was supported by federal funding from the National Institute of Neurological Disorders and Stroke (NINDS) and the National Institute on Aging (grant F31NS117075), NINDS (grant R01 1R01NS097850-01), and the Department of Defense (grant 12907280). The project was also privately funded by an Amgen postdoctoral fellowship, the New York Stem Cell Foundation, the Tau Consortium, the Harrington Discovery Institute, the Alzheimer's Drug Discovery Foundation, the Association for Frontotemporal Dementia, and the John Douglas French Alzheimer's Foundation.

Ion channels play a crucial role in many cellular processes, including neuronal communication, muscle contraction or cell proliferation. Most multi subunit ion channels exist in two functional states, either closed or open. During gating, one should expect that all subunits undergo conformational changes. The absence of intermediate conduction levels is surprising and asks for an explanation. A team of researchers has created a smart model system to answer this important question. Ion channels play a crucial role in many cellular processes, including neuronal communication, muscle contraction or cell proliferation. Most multi subunit ion channels exist in two functional states, either closed or open. During gating, one should expect that all subunits undergo conformational changes. The absence of intermediate conduction levels is surprising and asks for an explanation. A team of researchers from the University of Vienna and the Washington University in St. Louis created a smart model system to answer this important question. The study is currently published in Nature Communications. Ion channels are membrane proteins that regulate the electrical activity of cells. In this study the scientific team investigated the inwardly rectifying potassium channel Kir2. This channel is crucial for maintaining a negative membrane potential in many cells. These channels are promising drug targets for treatment of cardiovascular diseases. To foster drug development, a detailed understanding of the gating mechanism is important. Intelligent model system & innovative methods "We designed a model system that allowed us to visualize the gating of individual subunits and track conductance changes," explains Grigory Maksaev from the Washington University in St. Louis. As a model system, the inwardly rectifying potassium channel Kir2 was used. This channel is crucial for maintaining a negative membrane potential in many cells. "We introduced an acidic residue near the channel gate. This led to novel states, so-called sub-conductance states" explains Eva Plessl from the Department of Pharmaceutical Sciences, University of Vienna. The life times of these sub-states were long enough to resolve them experimentally. Each of the observed sub-states represents a distinct subunit conformation. Interestingly, the sub-state occupancy is titratable by pH. "This suggests that protonation or deprotonation of individual acidic residues causes this phenomenon," explains Sun-Joo Lee from the Washington University in St. Louis. Sour is…less conductive "Molecular dynamics simulations with different protonation states of the acidic residue support this finding," explains Anna Weinzinger from the Department of Pharmaceutical Sciences, University of Vienna. The study reveals that each subunit gating transition leads to conductance level changes. This suggests that for a fully open channel, all subunits must move together. "By designing a smart model system, wehave answered a long-standing question about ion channel gating," explains Colin Nichols from the Washington University in St. Louis.