Posted on by Dr. Francis Collins
More than 30 years ago, I co-led the Michigan-Toronto team that discovered that cystic fibrosis (CF) is caused by an inherited misspelling in the cystic fibrosis transmembrane conductance regulator (CFTR) gene . The CFTR protein’s normal function on the surface of epithelial cells is to serve as a gated channel for chloride ions to pass in and out of the cell. But this function is lost in individuals for whom both copies of CFTR are misspelled. As a consequence, water and salt get out of balance, leading to the production of the thick mucus that leaves people with CF prone to life-threatening lung infections.
It took three decades, but that CFTR gene discovery has now led to the development of a precise triple drug therapy that activates the dysfunctional CFTR protein and provides major benefit to most children and adults with CF. But about 10 percent of individuals with CF have mutations that result in the production of virtually no CFTR protein, which means there is nothing for current triple therapy to correct or activate.
That’s why more basic research is needed to tease out other factors that contribute to CF and, if treatable, could help even more people control the condition and live longer lives with less chronic illness. A recent NIH-supported study, published in the journal Nature Medicine , offers an interesting basic clue, and it’s visible in the image above.
The healthy lung tissue (left) shows a well-defined and orderly layer of ciliated cells (green), which use hair-like extensions to clear away mucus and debris. Running closely alongside it is a layer of basal cells (outlined in red), which includes stem cells that are essential for repairing and regenerating upper airway tissue. (DNA indicating the position of cell is stained in blue).
In the CF-affected airways (right), those same cell types are present. However, compared to the healthy lung tissue, they appear to be in a state of disarray. Upon closer inspection, there’s something else that’s unusual if you look carefully: large numbers of a third, transitional cell subtype (outlined in red with green in the nucleus) that combines properties of both basal stem cells and ciliated cells, which is suggestive of cells in transition. The image below more clearly shows these cells (yellow arrows).
The increased number of cells with transitional characteristics suggests an unsuccessful attempt by the lungs to produce more cells capable of clearing the mucus buildup that occurs in airways of people with CF. The data offer an important foundation and reference for continued study.
These findings come from a team led by Kathrin Plath and Brigitte Gomperts, University of California, Los Angeles; John Mahoney, Cystic Fibrosis Foundation, Lexington, MA; and Barry Stripp, Cedars-Sinai, Los Angeles. Together with their lab members, they’re part of a larger research team assembled through the Cystic Fibrosis Foundation’s Epithelial Stem Cell Consortium, which seeks to learn how the disease changes the lung’s cellular makeup and use that new knowledge to make treatment advances.
In this study, researchers analyzed the lungs of 19 people with CF and another 19 individuals with no evidence of lung disease. Those with CF had donated their lungs for research in the process of receiving a lung transplant. Those with healthy lungs were organ donors who died of other causes.
The researchers analyzed, one by one, many thousands of cells from the airway and classified them into subtypes based on their distinctive RNA patterns. Those patterns indicate which genes are switched on or off in each cell, as well as the degree to which they are activated. Using a sophisticated computer-based approach to sift through and compare data, the team created a comprehensive catalog of cell types and subtypes present in healthy airways and in those affected by CF.
The new catalogs also revealed that the airways of people with CF had alterations in the types and proportions of basal cells. Those differences included a relative overabundance of cells that appeared to be transitioning from basal stem cells into the specialized ciliated cells, which are so essential for clearing mucus from the lungs.
We are not yet at our journey’s end when it comes to realizing the full dream of defeating CF. For the 10 percent of CF patients who don’t benefit from the triple-drug therapy, the continuing work to find other treatment strategies should be encouraging news. Keep daring to dream of breathing free. Through continued research, we can make the story of CF into history!
 Identification of the cystic fibrosis gene: chromosome walking and jumping. Rommens JM, Iannuzzi MC, Kerem B, Drumm ML, Melmer G, Dean M, Rozmahel R, Cole JL, Kennedy D, Hidaka N, et al. Science.1989 Sep 8;245(4922):1059-65.
 Transcriptional analysis of cystic fibrosis airways at single-cell resolution reveals altered epithelial cell states and composition. Carraro G, Langerman J, Sabri S, Lorenzana Z, Purkayastha A, Zhang G, Konda B, Aros CJ, Calvert BA, Szymaniak A, Wilson E, Mulligan M, Bhatt P, Lu J, Vijayaraj P, Yao C, Shia DW, Lund AJ, Israely E, Rickabaugh TM, Ernst J, Mense M, Randell SH, Vladar EK, Ryan AL, Plath K, Mahoney JE, Stripp BR, Gomperts BN. Nat Med. 2021 May;27(5):806-814.
Cystic Fibrosis (National Heart, Lung, and Blood Institute/NIH)
Kathrin Plath (University of California, Los Angeles)
Brigitte Gomperts (UCLA)
Stripp Lab (Cedars-Sinai, Los Angeles)
Cystic Fibrosis Foundation (Lexington, MA)
Epithelial Stem Cell Consortium (Cystic Fibrosis Foundation, Lexington, MA)
NIH Support: National Heart, Lung, and Blood Institute; National Institute of Diabetes and Digestive and Kidney Diseases; National Institute of General Medical Sciences; National Cancer Institute; National Center for Advancing Translational Sciences
Posted on by Dr. Francis Collins
The spinal cord, as a key part of our body’s central nervous system, contains millions of neurons that actively convey sensory and motor (movement) information to and from the brain. Scientists have long sorted these spinal neurons into what they call “cardinal” classes, a classification system based primarily on the developmental origin of each nerve cell. Now, by taking advantage of the power of single-cell genetic analysis, they’re finding that spinal neurons are more diverse than once thought.
This image helps to visualize the story. Each dot represents the nucleus of a spinal neuron in a mouse; humans have a very similar arrangement. Most of these neurons are involved in the regulation of motor control, but they also differ in important ways. Some are involved in local connections (green), such as those that signal outward to a limb and prompt us to pull away reflexively when we touch painful stimuli, such as a hot frying pan. Others are involved in long-range connections (magenta), relaying commands across spinal segments and even upward to the brain. These enable us, for example, to swing our arms while running to help maintain balance.
It turns out that these two types of spinal neurons also have distinctive genetic signatures. That’s why researchers could label them here in different colors and tell them apart. Being able to distinguish more precisely among spinal neurons will prove useful in identifying precisely which ones are affected by a spinal cord injury or neurodegenerative disease, key information in learning to engineer new tissue to heal the damage.
This image comes from a study, published recently in the journal Science, conducted by an NIH-supported team led by Samuel Pfaff, Salk Institute for Biological Studies, La Jolla, CA. Pfaff and his colleagues, including Peter Osseward and Marito Hayashi, realized that the various classes and subtypes of neurons in our spines arose over the course of evolutionary time. They reasoned that the most-primitive original neurons would have gradually evolved subtypes with more specialized and diverse capabilities. They thought they could infer this evolutionary history by looking for conserved and then distinct, specialized gene-expression signatures in the different neural subtypes.
The researchers turned to single-cell RNA sequencing technologies to look for important similarities and differences in the genes expressed in nearly 7,000 mouse spinal neurons. They then used this vast collection of genomic data to group the neurons into closely related clusters, in much the same way that scientists might group related organisms into an evolutionary family tree based on careful study of their DNA.
The first major gene expression pattern they saw divided the spinal neurons into two types: sensory-related and motor-related. This suggested to them that one of the first steps in spinal cord evolution may have been a division of labor of spinal neurons into those two fundamentally important roles.
Further analyses divided the sensory-related neurons into excitatory neurons, which make neurons more likely to fire; and inhibitory neurons, which dampen neural firing. Then, the researchers zoomed in on motor-related neurons and found something unexpected. They discovered the cells fell into two distinct molecular groups based on whether they had long-range or short-range connections in the body. Researches were even more surprised when further study showed that those distinct connectivity signatures were shared across cardinal classes.
All of this means that, while previously scientists had to use many different genetic tags to narrow in on a particular type of neuron, they can now do it with just two: a previously known tag for cardinal class and the newly discovered genetic tag for long-range vs. short-range connections.
Not only is this newfound ability a great boon to basic neuroscientists, it also could prove useful for translational and clinical researchers trying to determine which specific neurons are affected by a spinal injury or disease. Eventually, it may even point the way to strategies for regrowing just the right set of neurons to repair serious neurologic problems. It’s a vivid reminder that fundamental discoveries, such as this one, often can lead to unexpected and important breakthroughs with potential to make a real difference in people’s lives.
 Conserved genetic signatures parcellate cardinal spinal neuron classes into local and projection subsets. Osseward PJ 2nd, Amin ND, Moore JD, Temple BA, Barriga BK, Bachmann LC, Beltran F Jr, Gullo M, Clark RC, Driscoll SP, Pfaff SL, Hayashi M. Science. 2021 Apr 23;372(6540):385-393.
What Are the Parts of the Nervous System? (Eunice Kennedy Shriver National Institute of Child Health and Human Development/NIH)
Spinal Cord Injury (National Institute of Neurological Disorders and Stroke/NIH)
Samuel Pfaff (Salk Institute, La Jolla, CA)
NIH Support: National Institute of Mental Health; National Institute of Neurological Disorders and Stroke; Eunice Kennedy Shriver National Institute of Child Health and Human Development
Posted on by Dr. Francis Collins
Most of our immune cells circulate throughout the bloodstream to serve as a roving security force against infection. But some immune cells don’t travel much at all and instead safeguard a specific organ or tissue. That’s what you are seeing in this electron micrograph of a type of scavenging macrophage, called a Kupffer cell (green), which resides exclusively in the liver (brown).
Normally, Kupffer cells appear in the liver during the early stages of mammalian development and stay put throughout life to protect liver cells, clean up old red blood cells, and regulate iron levels. But in their experimental system, Christopher Glass and his colleagues from University of California, San Diego, removed all original Kupffer cells from a young mouse to see if this would allow signals from the liver that encourage the development of new Kupffer cells.
The NIH-funded researchers succeeded in setting up the right conditions to spur a heavy influx of circulating precursor immune cells, called monocytes, into the liver, and then prompted those monocytes to turn into the replacement Kupffer cells. In a recent study in the journal Immunity, the team details the specific genomic changes required for the monocytes to differentiate into Kupffer cells . This information will help advance the study of Kupffer cells and their role in many liver diseases, including nonalcoholic steatohepatitis (NASH), which affects an estimated 3 to 12 percent of U.S. adults .
The new work also has broad implications for immunology research because it provides additional evidence that circulating monocytes contain genomic instructions that, when activated in the right way by nearby cells or other factors, can prompt the monocytes to develop into various, specialized types of scavenging macrophages. For example, in the mouse system, Glass’s team found that the endothelial cells lining the liver’s blood vessels, which is where Kupffer cells hang out, emit biochemical distress signals when their immune neighbors disappear.
While more details need to be worked out, this study is another excellent example of how basic research, including the ability to query single cells about their gene expression programs, is generating fundamental knowledge about the nature and behavior of living systems. Such knowledge is opening new possibilities to more precise ways of treating and preventing diseases all throughout the body, including those involving Kupffer cells and the liver.
 Liver-Derived Signals Sequentially Reprogram Myeloid Enhancers to Initiate and Maintain Kupffer Cell Identity. Sakai M, Troutman TD, Seidman JS, Ouyang Z, Spann NJ, Abe Y, Ego KM, Bruni CM, Deng Z, Schlachetzki JCM, Nott A, Bennett H, Chang J, Vu BT, Pasillas MP, Link VM, Texari L, Heinz S, Thompson BM, McDonald JG, Geissmann F3, Glass CK. Immunity. 2019 Oct 15;51(4):655-670.
 Recommendations for diagnosis, referral for liver biopsy, and treatment of nonalcoholic fatty liver disease and nonalcoholic steatohepatitis. Spengler EK, Loomba R. Mayo Clinic Proceedings. 2015;90(9):1233–1246.
Liver Disease (National Institute of Diabetes and Digestive and Kidney Diseases/NIH)
Glass Laboratory (University of California, San Diego)
NIH Support: National Institute of Diabetes and Digestive and Kidney Diseases; National Heart, Lung, and Blood Institute; National Institute of General Medical Sciences; National Cancer Institute