SPARC1 projects are mapping the innervation of organs and tissues, identifying new targets for future neuromodulation therapies
What if you could burn extra calories without breaking a sweat? It may sound counterintuitive, but a specific type of fat – called brown fat – has the potential to do just that. Brown fat is abundant in infants, where it helps regulate body temperature by converting energy stored in fat and sugar into heat. For decades scientists thought that brown fat didn’t have an active role later in life, but that view has changed in recent years with the discovery of brown fat deposits in adults that are activated by drops in temperature. When faced with cold temperatures, the nervous system sends electrical signals that tell brown fat cells to burn more calories, which helps raise the body’s core temperature to a more comfortable level. If scientists could figure out a way to regulate the intricate network of nerves that send these signals in order to harness brown fat’s calorie-burning potential this knowledge could be applied in a variety of ways – from treatments for health conditions related to energy regulation, such as diabetes, to enhancing the healthy effects of exercise.
To do this, we would need to know more about the locations of the nerves by finding a way to see through brown fat to map the neurons that innervate it. A team at SPARC awardee institution Louisiana State University, led by Dr. Heike Münzberg, used a combination of mouse genetics and fluorescent tracers to light up the neurons. They then made them visible using a recently developed chemical process for “clearing” the intact tissue containing the nerves. This process enables high-resolution imaging and 3D reconstruction of the specific neurons that innervate brown fat, without disturbing their location in the tissue. Improved understanding of brown fat innervation patterns could lead to neuromodulation strategies to precisely control the metabolic activity of brown fat by regulating the nerves’ electrical signals. These new tissue-clearing and circuit-tracing methods are being used to visualize and map innervation of other organs and tissues, bringing us closer to identifying precise targets for neuromodulation therapies that could be used to treat a variety of diseases and conditions.
Sympathetic innervation of the interscapular brown adipose tissue in mouse. François M, Torres H, Huesing C, Zhang R1, Saurage C, Lee N, Qualls-Creekmore E, Yu S, Morrison CD, Burk D, Berthoud HR, Münzberg H. Ann N Y Acad Sci. 2019 Jun 11.
Does your heart race when you are exercising and slow down when you are sleeping? Hopefully, it does because precise control of heart rate changes like these can influence medical outcomes, making the neural connections between your brain and heart important targets for devices that modulate the neural pathways running throughout your body (the autonomic nervous system). Historically, the variability in clinical trial results hampered being able to prove the therapeutic efficacy of neuromodulation devices for patients at risk of heart failure. One possible reason is that identifying specific neural connections can be difficult—like finding which wire amongst thousands of wires connects your TV to the cable box. If we improve upon current tools, adding cell-type specificity to existing maps of neural structures and electrical signaling, then we can empower clinicians and device developers to design more specific neuromodulation strategies and decrease treatment variability.
To this end, SPARC awardee Kalyanam Shivkumar and his collaborators are clearing a way for other researchers — literally. Dr. Shivkumar’s team made mouse hearts transparent, a critical step in an innovative multi-stage approach that ultimately allowed them to create 3D visualizations of the neural connections that impact heart rate. After using structure-preserving clearing methods to make mouse hearts easy to see through, they used genetically engineered viruses to “tag” and fluorescently trace specific neurons as a way to build 3D visualizations of the intricate circuits that receive input from nerve structures like the spinal cord and the vagus nerve (image from publication shown). They also showed that similar genetic techniques could be used to make only certain neuron types responsive to light, which could enable more specifically targeted neuromodulation in the future. This is crucial to improving the efficacy of neuromodulation devices because better targets mean new ways to treat heart disease!
Rajendran, P.S., Challis, R.C., Fowlkes, C.C., Hanna, P., Tompkins, J.D., Jordan, M.C., Hiyari, S., Gabris-Weber, B.A., Greenbaum, A., Chan, K.Y., Deverman, B.E., Münzberg H., Ardell J.L., Salama G., Gradinaru V., and Shivkumar K. Nature communications (2019) 565(7739), 361.
Computational modeling, using computers to simulate the behavior of complex systems through mathematics, physics and/or computer science, is increasingly important to therapeutic development. It allows for the exploration of possibilities in a shorter period of time than studies focused on humans or animals or even isolated cells. Several SPARC awardees are making strides in this area; here we highlight two that are working to improve the understanding of how current and future therapies interact with the heart.
Dr. Colleen E. Clancy’s team used computational modeling to look for structural nooks and crannies where novel heart medications and anesthetic drugs might interact with the heart’s tiny electrical “gates”, or channels. These channels control how and which charged particles enter heart cells and can be sites of action, or “targets” for therapeutics. The model shows how drug molecules might interact in 4D with the structures of the heart’s channels (see video simulations in movie 1 & movie 2). This innovative approach essentially ‘digitally screened’ the drugs, revealing it requires two drug molecules to properly bind to the channel as well as identifying additional three-dimensional pathways that drug molecules can take to get to their binding sites. This has important implications for the design of drugs for heart conditions and could help push the field toward smarter designs for new drug therapies before they are tested in animals or humans.
In another SPARC-supported computational modeling effort, Dr. Elenora Grandi’s team studied the importance of a different type of electrical channel in heart function. Working from a recent finding that this channel could be involved in heart disease, they simulated the effects of reducing its activity. In the simulation, this resulted in an increase in the duration of electrophysiological patterns that are associated with potentially dangerous abnormal heart rhythms such as atrial fibrillation. This is additional evidence that the balance of specific electrical activities is critical to healthy heart function. New approaches for managing abnormal heart rhythms could involve maintaining this balance with drugs or devices.
To improve neuromodulation therapies targeting the heart, we will need to understand the specific effects of nerve or spinal cord stimulation on the channel proteins studied by Clancy, Grandi, and others. Each of these studies is impactful in its own right; however, the SPARC program seeks to amplify the impact of this type of research by addressing data and model interoperability. As an example, these two studies both involve heart channels; yet without a shared vocabulary or common framework, the output of one study cannot be used as an input to another without manual curation and reformatting. Such gaps are routine across biomedical science and create delays in making findings useful and translational. Through its Data and Resource Center, the SPARC program is supporting the development of such a common framework, allowing maps and simulations to integrate diverse anatomical and physiological results from many different groups. The resulting resources, whose development you can track at http://sparc.science and MAP-core (a SPARC resource, building interactive visualizations of nerve-organ anatomy and function; see figure), will allow for the generation of new therapeutic hypotheses that leverage a broader multidisciplinary range of biomedical research than in the past.
Nguyen, P. T., DeMarco, K. R., Vorobyov, I., Clancy, C. E., & & Yarov-Yarovoy, V. . Proceedings of the National Academy of Sciences (2019) 116(8), 2945-2954.
Ni, H., Zhang, H., Grandi, E., Narayan, S. M., & & Giles, W. R. American Journal of Physiology-Heart and Circulatory Physiology (2018) 316(3), H527-H542.
K+ Channel Isoforms Regulate Human Atrial Arrhythmogenesis. Haibo Ni, Henggui Zhang, Elenora Grandi, Sanjiv M. Narayan, and Wayne R. Giles. AJP-Heart and Circulatory Podcasts.
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Overactive bladder is a condition that affects millions of people and causes a frequent need to urinate, incontinence, and an increase in bladder voiding. A common treatment uses low levels of electricity to stimulate nerves controlling the bladder. Unfortunately, it’s not precise and can lead to off-target effects and pain.awardee Dr. Aaron Mickle developed an innovative approach to this problem by creating a miniature implanted device that can sense and control bladder function in rats. This self-adjusting coordination of devices, that manipulate nerves to control organs, is called a closed-loop system.
Instead of activating nerves using electricity, Dr. Mickle and his team used a technique called optogenetics where genetically modified rat nerve cells could be activated using light. In rats, Mickle’s team inserted a stretch sensor that measured changes in bladder expansion over time. The sensor was connected to LEDs. Both were connected by wires to a flexible base-station device implanted in the abdomen. The bladder-stretch sensor communicated data to the base station, which wirelessly transmitted this information to an external device that recorded and monitored bladder function. Rats received the molecule cyclophosamide, which leads to frequent bladder emptying. When the external device detected this abnormal bladder function (i.e. signs of overactive bladder), it transmitted a wireless signal causing light-driven inhibition of nerves affecting bladder emptying—preventing abnormal frequency of urination.
Although the animal model of overactive bladder shows promise for this technology, questions remain about whether this approach could be used in humans or to treat other diseases. Additionally, the body’s long-term response to the stretchable sensor is unknown and there are other concerns about possible tissue damage or unintended adhesion to the tissue that affect the device’s function. However, if it ultimately proves fruitful, this work could correct organ dysfunction and manage pain.
. Mickle, A. D., Won, S. M., Noh, K. N., Yoon, J., Meacham, K. W., Xue, Y., Mcllvried, A. L., Copits, B. A., Samineni, V. K., Crawford, K. E., Kim, D. H., Srivastava, P., Kim, B. H., Min, S., Shiuan, Y., Yun, Y., Payne, M. A., Zhang, J., Jang, H., Li, Y., Lai, H. H., Huang, Y., Park, S., Gereau IV, R. W., & Rogers, J. A. Nature (2019) 565(7739), 361.
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The gut, or gastrointestinal tract, is an organ system responsible for the digestion of food. Several human diseases and conditions, including gastroparesis, obesity, and reflux disease, are associated with impaired regulation of gut function. Along with pharmaceutical, surgical, and dietary interventions, which are not always successful in treating these disorders, researchers have begun to explore electrical stimulation of the vagus nerve to precisely control gastrointestinal function. For this treatment strategy to work, scientists must understand the function of vagal nerve signals carried between the central nervous system and the gut.
A-funded research team at Purdue University is studying the effect of vagus nerve stimulation on emptying the stomach as food moves into the small intestine (gastric emptying) in rats. They observe the process of gastric emptying using a technique called Magnetic Resonance Imaging (MRI). They found that selective electrical stimulation of the vagus nerve significantly increased gastric emptying through relaxation of the pyloric sphincter, a valve-like band of muscle that separates the stomach from the small intestine, which allows movement of food out of the stomach. These findings suggest that electrical stimulation of the vagus nerve could be used to improve gut function to treat gastric emptying disorders like gastroparesis. In addition, their MRI protocol describes a new non-invasive method to assess the effectiveness of many different types of therapies on gastrointestinal function.
. Lu KH, Cao J, Oleson S, Ward MP, Phillips RJ, Powley TL, and Liu Z. October 2018. Wiley Publishers: Neurogastroenterology & Motility. e13380.
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MRI tool watches how electrical stimulation could cure digestive disorders, Purdue University News
Understanding the causes of inflammatory bowel disease is difficult because the associated abdominal pain can occur without any obvious changes to the structure of the colon or signs of inflammation. Because pain sensations can be carried by sensory neurons, one factor in the generation of abdominal pain could be abnormal sensory neuron activity, which can be influenced by secretions from cells called “epithelial cells” that line the interior of the colon. Understanding interactions between colon epithelial cells and sensory neurons could help us understand and treat abdominal pain. To study the interactions between the types of cells, a SPARC-funded team led by investigators Dr. Brian Davis and Dr. Kathryn Albers used genetically modified mice that contain blue light-activated colon epithelial cells to examine signaling between colon epithelial cells and neurons. These mouse colon epithelial cells could be specifically stimulated by blue light without any physical or chemical stimulation, allowing the study of their effects apart from other factors. Stimulating the epithelial cells caused activity in the pain-sensing neurons and behavioral responses similar to those that result from pain-inducing physical stimulation of the colon. Further study found that firing of neurons was likely triggered by release of a molecule called ATP from the colon epithelial cells. The results indicate that the activity of the colon epithelial cells alone, without any physical or chemical stimulation, could lead to abdominal pain through activation of the pain-sensing neurons. This study advances the understanding of how colon sensory neuron activity is regulated and could aid in development of new treatment strategies for inflammatory bowel disease.
Reference:. Makadia, PA, Naijar, SA, Saloman, JL, Adelman, P, Feng, B, Margiotta, J, Albers, KM, Davis, BM. June 2018. J Neurosci. 38(25): 5788-5798.
The Fat in Our Bones
You probably think of your bones as providing structure and support to your body and protecting your organs, but they have many other functions as well. The soft spongy area inside most bones, called the bone marrow, produces blood cells and stores energy in the form of fat and therefore plays an important role in bone health. The fat cells found in the bone marrow (bone marrow adipocytes) are very different from fat cells found in other parts of the body. Bone marrow adipocytes are also more difficult to study because they are found in small compartments inside of bones.program awardee Dr. Erica Scheller and her research team published a study in the journal Bone with some of the most detailed images ever acquired of bone marrow adipocytes. The images show that the bone marrow adipocytes interact with other components of their environment such as blood- and bone-forming cells and blood vessels. Of special interest to the SPARC program, a subset of the adipocytes were found to contact nerve cells. The results indicate that bone marrow adipocytes could send signaling molecules to nearby blood- and bone-forming cells and that nerves may coordinate the interactions between bone marrow adipocytes and these cells. This indicates that it could someday be possible to control or modulate bone formation and other bone processes by electrical stimulation of specific nerves. This could potentially lead to new treatments for conditions such as bone fragility, which occur more frequently in groups like the elderly and those with diabetes.
Reference:. Robles, H, Park, S, Joens, MS, Fitzpatrick, JAJ, Craft, CS, and Scheller, E. Jan 2018. Bone. Doi: 10.1016/j.bone.2018.01.020.
Click on the image to view a video of bone marrow innervation in Bone:
Getting the Gut Moving
The enteric nervous system (ENS) regulates stretching and contraction of muscles in the gastrointestinal tract (gut motility), which is critical for digestion. Gastrointestinal disorders resulting from irregular gut motility affect more than a quarter of the world’s population. One method of treating irregular organ function is neurostimulation, in which targeted electrical current is used to stimulate the ENS. However, this method has seen limited success for gastrointestinal disorders, because we don’t understand how electrical stimulation affects the ENS and gut motility. Current computational models that simulate the effects of electrical stimulation of the ENS are incomplete, which makes predicting the effects of different ENS stimulation patterns difficult in living organisms.
In a study funded by the NIH Common Fund SPARC Program, investigators Warren Grill and Xiling Shen developed a computational model of the ENS and used this model to assess neurostimulation strategies for regulating gut motility. The neuromechanical model included a network of parts involved in gut motility - enteric neurons, smooth muscle fibers, and interstitial cells of Cajal (ICCs, cells that act as electrical pacemakers and promote smooth muscle contraction during digestion). The team simulated intestinal tract motility by passing a virtual pellet that stimulates sensory neurons and responds to smooth muscle contractions through the ENS computer model. They found that simulated current pulses at a frequency of 0.5 Hz were more effective at regulating the pacemaker frequency of ICCs, and accelerating gut motility, than higher pulse frequencies that are more commonly used. They validated this model in experiments with rats, in which bead propulsion through the gut was measured during electrical stimulation of the colon and found to behave as predicted from the simulation. The results of this study have implications for the neurostimulation treatment of gastrointestinal disorders resulting from reduced gut motility.
Reference: Electrical stimulation of gut motility guided by an in silico model. Barth, BB, Henriquez, CS, Grill, WM, and Shen, X. Dec 2017. J. Neural Eng. 14(6): 066010.
Viruses Engineered for Good
One method of treating genetic diseases is to transfer new genes to cells affected by the disease. One tool scientists use to transfer genes is viruses, which interact with cells through an external covering, and then inject their DNA into the cells. Scientists take advantage of this ability by replacing virus DNA with DNA that encodes the genes they wish to deliver. In addition to treating diseases, this technique can be used to label cells with fluorescent colors in order to visualize them and identify their connections in the body. Using viruses to transfer genes to cells of the nervous system is difficult because neurons (nerve cells) are widely spread throughout the body, and reaching some neurons requires passage of the virus through the blood brain barrier, a selective layer that blocks the passage of many substances from reaching the brain and spinal cord tissue.
In a study led by NIH Common Fund SPARC program-funded investigator Viviana Gradinaru, a research team engineered viruses to efficiently deliver genes to neurons throughout the body of a mouse after injection into the bloodstream. They modified the external covering of existing viruses for more efficient gene delivery to neurons. They engineered one virus to pass the blood brain barrier and transfer genes to neurons in the brain and spinal cord (the central nervous system), and another virus to reach and transfer genes to neurons spread throughout the body (in the peripheral nervous system). The engineered viruses are highly efficient at gene delivery at low doses, can be designed for their delivered genes to be turned on only in certain cell types, and are able to precisely label cells with fluorescent colors for visualization. The viruses can be further customized and potentially used for future non-invasive treatments of neurological disorders, as well as for multi-color labeling of neurons for generation of neuron circuit maps. Neuron maps showing connections between neurons and organs could aid in development of treatments for a variety of human diseases by altering the activity of specific neurons through a process called neuromodulation.
Engineered AAVs for efficient noninvasive gene delivery to the central and peripheral nervous systems. Chan, KY, Jang, MJ, Yoo, BB, Greenbaum, A, Ravi, N, Wu, WL, Sanchez-Guardado, L, Lois, C, Manmanian, SK, Deverman, BE, and Gradinaru, V. June 2017. Nat Neurosci. 20(8): 1172-1179.
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Gene Therapy Vectors Come to Grips with Nervous System, Root and Branch, Genetic Engineering and Biotechnology News
This page last reviewed on July 1, 2019