Announcer: From the Eunice Kennedy Shriver National Institute of Child Health and Human Development, part of the National Institutes of Health, welcome to another installment of NICHD Research Perspectives. Your host is the Director of the NICHD, Dr. Alan Guttmacher.
Dr. Alan Guttmacher: Hello, I’m Alan Guttmacher. Thanks for joining us for another in our monthly series of podcasts from the Eunice Kennedy Shriver National Institute of Child Health and Human Development at the National Institutes of Health.
Our guests today are Dr. Tracey Rouault and Dr. Stephen Kaler. We will be talking with them about research they conduct in the Molecular Medicine Program here at NICHD. In their work, they try to understand the biochemical systems that control the transport of certain trace minerals and the role that disturbances in these systems play in health and disease.Trace minerals are minerals that the body needs in very small amounts. Like other essential elements and nutrients, too much or too little of them can cause serious health problems. Our guests today will discuss their efforts to better understand the role of two important minerals in human health: iron and copper.
Our first guest, Dr. Rouault, investigates how iron metabolism is regulated. Principally, iron is used to make hemoglobin, the molecule in red blood cells that transports oxygen to our organs and tissues. Tracey identified two proteins, known as iron regulatory proteins 1 and 2, or Irp1 and Irp2. She and her colleagues have determined that these proteins play an important role not only in maintaining iron levels adequate for the body’s needs, but also in preventing an excessive accumulation of iron, which can actually cause harm. Irp1, for example, detects iron levels and directs either the utilization or storage of iron, depending on other conditions in the body.
Tracey, can you explain for us how you identified these proteins and how they actually function?
Dr. Tracey Rouault: Yes, I can try. Thank you very much for giving me the opportunity to talk about our work. The iron regulatory proteins, known as Irps, enable cells to optimize intracellular iron levels by binding to specific regions of messenger RNA molecules of some genes. These Irps bind only when they recognize iron deficiency in the cells. As many people know, messenger RNA carries information from genes in the nucleus to the portion of the cell that makes new proteins, and it dictates the nature of the protein that will be made. When cells are iron-deficient, Irps binds to RNAs that contain a particular sequence and they block manufacture of new protein from that RNA, or they can prevent the mRNA from being quickly degraded. We suspected that these regulatory proteins existed in cells, but we were not able to prove that they existed until we devised a way to trap them when they were bound to the messenger RNA for a very abundant iron storage protein known as ferritin. We purified a complex of ferritin mRNA together with a bound protein obtaining the amino sequence for that bound protein, and used that information to identify the nuclear gene for Irp1, and in that process we also found Irp2.
Dr. Guttmacher: Tracey, you recently published findings on what happens when the body lacks Irp1. As I understand it, in this study your research team reared mice lacking the gene that makes Irp1 and divided the animals into two groups, feeding one group a normal diet and the other group a diet low in iron. Findings from this research showed that, regardless of the diet, mice lacking Irp1 develop pulmonary hypertension, a form of high blood pressure that affects the lungs directly, and polycythemia, a relatively rare disorder in which the body produces excess red blood cells. However, a low-iron diet exacerbated this polycythemia. Typically, low iron levels in humans are associated with anemia, a deficiency of red blood cells; yet, in your study, iron deficiency led to a surplus of red blood cells. Also, iron regulation hadn’t been associated with pulmonary hypertension before. Can you explain to us what’s happening in these animals?
Dr. Rouault: I think I can explain what happens to cause the abnormally high red blood cell counts in animals that lack Irp1. As many people know erythropoietin; which is also known as EPO, which has been much in the news lately—is a potent hormone that enhances red cell production. Normal EPO production occurs in the kidneys were specialized cells determine how much EPO they should make. When those cells are iron-deficient, they shut off EPO production by repressing manufacture of a factor known as hypoxia-inducible factor 2 using the Irp regulatory system. Hypoxia-inducible factor 2-alpha or HIF2 alpha normally drives the production of EPO. When Irp1 is absent, synthesis of HIF2 alpha cannot be repressed, and therefore high HIF2 alpha and high EPO levels develop, even though cells may be iron-deficient. These high EPO levels drive red cell production, and iron deficiency worsens throughout the remainder of the body as more iron is poured into red cell production at the expense of other tissues. Thus, Irp1 determines whether red cells should be made, and its normal activity accounts for the fact that anemia is usually the first manifestation of iron deficiency. We were surprised to discover that animals that lack Irp1 develop pulmonary hypertension; which is a poorly understood disease. In the blood vessels of the lungs, high HIF2 alpha production drives production of a potent vasoconstrictor known as endothelin. The heart has to work extra hard to push blood through the constricted vascular bed of the lungs, and it fails. On the low-iron diet, animals develop extremely high red cell counts and they die from blood clots and bleeds. More Irp1 would normally repress these very high red cell counts and protect the patients from this development.
Dr. Guttmacher: Thanks, Tracy, for that explanation; as always with these podcasts, I’ve really learned something in listening to your answers. I know that promising leads from animal studies don’t always pan out in human beings. With that significant caveat, can you tell us if your finding has any implications for human health?
Dr. Rouault: We think it does. We have discovered a previously unknown key to controlling EPO production. We now understand that in patients with the polycythemia, when we remove the red cells in order to protect them from having too many red cells, we must also supplement them with iron so that we won’t worsen the condition. Also in pulmonary hypertension, we believe that our work contributes to a new paradigm in which HIF2 alpha activity is responsible for the development of early disease. That area has been an area of great mystery. Our work may explain high-altitude pulmonary hypertension, pulmonary hypertension caused by chronic hypoxia, and idiopathic pulmonary hypertension; which is a rare but very serious disease. We can use drugs to prevent the synthesis of HIF2 alpha, and in fact we are now treating animals in the laboratory with one compound to try to prevent pulmonary hypertension in a related mouse model.
Dr. Guttmacher: Thanks very much, Tracy. Our next guest, Dr. Stephen Kaler, studies disorders involving the body’s ability to regulate copper, an important trace mineral that supports nerve function and helps the body use iron. When functioning properly, the body naturally works to ensure a constant supply of available copper, while eliminating any excess amounts of the mineral. However, for people with a condition known as Menkes disease, changes in a gene, called ATP7A, result in difficulty transporting copper inside individual cells and deliver it to particular organs in the body such as the brain. Without enough copper in the brain, cells and other tissues can’t make myelin, the insulation material needed by certain kinds of brain cells. The symptoms of Menkes disease usually do not develop until 2 or 3 months of age, but unfortunately by that time, copper deficiency can already have caused significant brain damage, which treatment thus far has not been able to reverse.
The ATP7A gene is on the X chromosome. Because females have two X chromosomes, they would need two malfunctioning copies of the gene to develop Menkes disease. So the odds of their developing the disease are extremely low. But males only have one X chromosome and need only one mutated copy to develop the illness. Estimates suggest that Menkes disease occurs about once in every 100,000 newborn males.
Steve, your research team devised a test to diagnose Menkes disease early on, when the chances for successful treatment are greater than waiting until it’s clinically apparent. Could you tell us more about this test and the possibility of developing a test that can be used routinely for Menkes disease?
Dr. Stephen Kaler: Yes, thank you, Dr. Guttmacher, and you’ve summarized Menkes disease very well and the associated problem with copper metabolism. The test we used to diagnose this fatal condition in newborn infants is based on low activity of one of the enzymes in our bodies that needs plenty of copper to work properly. Without the ATP7A copper transporter, copper cannot be built into some of these enzymes that really need it, one consequence is much higher than normal levels of certain neurochemicals. These abnormal levels appear soon after birth, even before there are any clinical symptoms of Menkes disease. So a test to measure these neurochemicals became a valuable screening test to distinguish infants who had the disease from those who did not. And we used this test to identify affected patients and enroll them in a clinical trial of copper injection treatments, which we hoped would prevent death and lessen brain damage.
Dr. Guttmacher: Steve, as part of that same research study, I know that you examined the effectiveness of copper injections beginning shortly after birth in Menkes disease patients and that some of the patients had wonderful outcomes in response to early intervention, but others didn’t. Can you explain the differences in these treatment responses?
Dr. Kaler: Yes, Alan. We’ve found that instituting copper injections at an early age, ideally within 10 days after birth, could in fact, completely avert brain damage in some of the patients. Those were infants who had what we call treatment responsive mutations in the ATP7A gene, which did not completely block the proper transport of copper. A favorable ATP7A mutation plus starting copper treatment from an early age was a very successful combination. Unfortunately, however, in patients in whom more severe ATP7A gene defects were present, such as large missing pieces of the gene, the response to copper was not good. Some patients died, despite very early institution of copper treatment. This means that we need a supplemental treatment approach for many Menkes disease patients—in addition to copper injections—and we are presently working toward that goal.
Dr. Guttmacher: I know that you elected to stop giving the copper injections, even in the patients in which it seemed to be working well because long-term exposure to copper can damage the kidneys in patients with Menkes. Can you tell us how these children fared in the long term?
Dr. Kaler: Right. In all our patients with Menkes disease, we limit copper treatment to a total of 3 years. This is because the risk-to-benefit ratio appears to shift after 3 years in terms of an undesirable effect of copper on the kidneys. Fortunately, we found that any injury that does occur in the kidneys during treatment is reversible and does not persist after the copper is withdrawn. Important as well, of course, is the fact that none of our patients have regressed neurologically after stopping copper treatment.
Dr. Guttmacher: Steve, I know that your laboratory is constantly looking for even more effective approaches to Menkes disease and that you’ve tested a potential gene therapy treatment for Menkes in mice. Could you explain how that treatment works as well as what might be ahead in the future?
Dr. Kaler: Yes, I alluded to this prospect earlier, in terms of developing a supplemental treatment that would offer more hope for patients who do not respond to copper alone. We recently used viral gene therapy to rescue a lethal mouse model of Menkes disease, and we’re developing a path forward to use this treatment in human subjects. Gene therapy is a way to add correct versions of the ATP7A copper transporter to the cells of the body of Menkes disease patients. It seems that this promising approach, in combination with early copper injections, will be helpful for preventing brain damage in a larger percentage of patients with this illness. However, early diagnosis will remain important, and we hope that advances in newborn screening using DNA sequencing will eventually enable this.
Dr. Guttmacher: Thanks, Steve. I’d like to add that, through your efforts, the NICHD has developed a Menkes Disease and Occipital Horn Syndrome International Registry to gather information about these conditions and to enhance efforts and diagnosis and treatment. Occipital horn syndrome, of course, is a milder form of Menkes disease. Information about the registry is available on the NICHD website at menkesohs.nichd.nih.gov. Well, that brings us to the end of our podcast for this month. I’d like to thank both Dr. Tracey Rouault and Dr. Stephen Kaler for joining us today and for sharing with us some of their research on trace minerals and human health. I’d also like to thank our podcast listeners for joining us and for your interest in our work here at NICHD.
For more information on any of today’s topics and many related topics, visit www.nichd.nih.gov. That’s www.nichd.nih.gov. I’m Alan Guttmacher, and I hope you will join us for more NICHD podcasts as we post them on our website each month.
Announcer: This has been NICHD Research Perspectives, a monthly podcast series hosted by Dr. Alan Guttmacher. To listen to previous installments, visit nichd.nih.gov/researchperspectives. If you have any questions or comments, please email NICHDInformationResourceCenter@mail.nih.gov.
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