- Scientists discover new process shaping red blood cell development
- RNA-based process regulates red blood cell development
- A deeper understanding of development and disease
- Genetic code of red blood cells discovered
- Researchers discover mechanism controlling zinc
- Emerging drug class may enhance red blood cell production in anemic patients
Scientists discover new process shaping red blood cell development
A collaboration among Drs. Daniel Kuppers, Andrew Hsieh, Beverly Torok-Storb and Patrick Paddison revealed a new process governing red blood cell development. Composite image by Robert Hood / Fred Hutch News Service
Red blood cells make possible many lifesaving medical procedures that rely on blood transfusions. But they come directly from people; we haven’t yet figured out how to manufacture a replacement product in a pharmaceutical factory.
“Part of the reason is we don't understand the [red blood cell developmental] process well enough,” Paddison said. “A more detailed understanding of this process would allow us to actually think about clinical applications.”
One major reason red blood cell development is under-researched is that they’re difficult to grow in a laboratory. Kuppers developed a lab dish–based proxy for progenitor cells that enabled him to look for genes important in red blood cell development.
RNA-based process regulates red blood cell development
Kuppers systematically screened for genes that are required for cells to signal their commitment to turning into red blood cells. The screen flagged a group of genes that encode components of a molecular machine that adds a type of molecule, or “mark,” to RNA.
The molecular mark is called N6-methyladenosine, or m6A for short. RNA marks, including m6A, help our cells tweak how RNAs are processed and interpreted by our protein-producing factories, thereby influencing how proteins are made. Though the m6A mark was discovered more than 40 years ago, it wasn’t until recently that technological advances made studying it in detail finally possible.
At this point, Hsieh brought his expertise in protein production, or translation, to the team. “My hunch was that m6A controlled mRNA translation,” he said.
Hsieh’s instinct was borne out by Kupper’s experiments. Kupper knocked out genes coding for parts of this machine, preventing it from adding m6A marks to RNA. When he did that, he saw a drop in the translation levels of 300 mRNAs involved in red blood cell development — even though the RNA levels stayed the same.
This showed that the key targets for the m6A-adding machine were RNAs coding for proteins important to red blood cell development, Paddison explained. The targets “included a lot of key genes involved in erythroid [red blood cell] disease: leukemias and myelodysplastic syndromes and anemia,” he said.
The genes for the m6A-adding machinery are critical for red blood cell development. Kupper removed them in blood stem cells donated by patients undergoing bone marrow biopsies. When he did so, the stem cells could no longer turn into red blood cells.
But loss of m6A didn’t prevent these stem cells from turning into at least two other types of blood cell.
Unexpectedly, the team also found that m6A played an essential role in turning on a suite of other red blood cell–specific genes, including genes involved in synthesis of hemoglobin, our cells’ oxygen-carrying molecule, as well as genes linked to a type of congenital anemia.
A deeper understanding of development and disease
It’s often the case that diseases cannot be traced back to an obvious gene mutation. This is true for many cases of anemia. The revelation that m6A influences production of several anemia-linked proteins could be a breakthrough in understanding the causes of anemias — and may have revealed a new treatment target, Hsieh said.
He and Paddison are working to chase down potential connections between m6A and diseases related to red blood cell development, including anemia and cancer.
There are still a host of unanswered questions about m6A and what it’s doing on RNA, Paddison said. Scientists don’t know much about how cells determine which RNAs get these marks. And in any given cell type, including red blood cell progenitors, 30% to 40% of all RNAs have m6A marks.
“What is special about those RNAs that are regulated [by m6A] versus those that are not?” Hsieh said.
The forces shaping cellular development are complex, and m6A is just one player. Understanding the role it plays will also help scientists understand the bigger picture.
“There’s a symphony of gene regulation that happens during [an organism’s] development. Understanding its makeup and the players involved really helps you understand how an organism is put together and can provide important clues as to what can go wrong in disease,” Paddison said.
This work was funded by the National Heart, Lung, and Blood Institute, the National Institute of Diabetes and Digestive and Kidney Diseases, the American Association for Cancer Research, the V Foundation, the U.S. Department of Defense and the Burroughs Wellcome Fund.
Genetic code of red blood cells discovered
Eight days. That's how long it takes for skin cells to reprogram into red blood cells. Researchers at Lund University in Sweden, together with colleagues at Center of Regenerative Medicine in Barcelona, have successfully identified the four genetic keys that unlock the genetic code of skin cells and reprogram them to start producing red blood cells instead.
“We have performed this experiment on mice, and the preliminary results indicate that it is also possible to reprogram skin cells from humans into red blood cells.
One possible application for this technique is to make personalised red blood cells for blood transfusions, but this is still far from becoming a clinical reality,” says Johan Flygare, manager of the research group and in charge of the study.
Every individual has a unique genetic code, which is a complete instruction manual describing exactly how all the cells in the body are formed. This instruction manual is stored in the form of a specific DNA sequence in the cell nucleus. All human cells — brain, muscle, fat, bone and skin cells — have the exact same code.
The thing that distinguishes the cells is which chapter of the manual the cells are able to read. The research group in Lund wanted to find out how the cells open the chapter that contains instructions on how to produce red blood cells.
The skin cells on which the study was based had access to the instruction manual, but how were the researchers able to get them to open the chapter describing red blood cells?
With the help of a retrovirus, they introduced different combinations of over 60 genes into the skin cells' genome, until one day they had successfully converted the skin cells into red blood cells. The study is published in the scientific journal Cell Reports.
“This is the first time anyone has ever succeeded in transforming skin cells into red blood cells, which is incredibly exciting,” says Sandra Capellera, doctoral student and lead author of the study.
The study shows that 20,000 genes, only four are necessary to reprogram skin cells to start producing red blood cells. Also, all four are necessary in order for it to work.
“It's a bit a treasure chest where you have to turn four separate keys simultaneously in order for the chest to open,” explains Sandra.
The discovery is significant from several aspects.
Partly from a biological point of view — understanding how red blood cells are produced and which genetic instructions they require — but also from a therapeutic point of view, as it creates an opportunity to produce red blood cells from the skin cells of a patient. There is currently a lack of blood donors for, for instance, patients with anemic diseases. Johan Flygare explains:
“An aging population means more blood transfusions in the future. There will also be an increasing amount of people coming from other countries with rare blood types, which means that we will not always have blood to offer them.”
Red blood cells are the most common cells in the human body, and are necessary in order to transport oxygen and carbon dioxide. Millions of people worldwide suffer from anemia — a condition in which the patient has an insufficient amount of red blood cells. Patients with chronic anemia are among the most problematic cases.
They receive regular blood transfusions from different donors, which can eventually lead to the patient developing a reaction to the new blood. They simply become allergic to the donor's blood. Finding a feasible way to make blood from an individual's own skin cells would bring relief to this group of patients.
However, further studies on how the generated blood performs in living organisms are needed.
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Materials provided by Lund University. Note: Content may be edited for style and length.
- Johan Flygare et al. Defining the Minimal Factors Required for Erythropoiesis through Direct Lineage Conversion. Cell Reports, June 2016 DOI: 10.1016/j.celrep.2016.05.027
Researchers discover mechanism controlling zinc
Researchers have uncovered how a trace metal controls the generation of red blood cells, which are critical for life.
Scientists at the University of Wisconsin School of Medicine and Public Health demonstrated that two genes regulate the intake and expulsion of zinc from precursors to red blood cells. This process controls whether the cells survive and differentiate into red blood cells, according to Emery Bresnick, PhD, professor of cell and regenerative biology, director of the University of Wisconsin Blood Research Program, and lead author of the research.
“Zinc-deficiency anemia is a public-health problem world-wide, but we never really understood whether zinc directly or indirectly influences the generation and function of red blood cells,” he said.
Bresnick and his colleagues focused their attention on the relationship between GATA-1, a protein responsible for regulating genetic information in cells that become red blood cells, and the iron-containing compound heme, an essential component of hemoglobin protein in red blood cells.
The latter mediates the transport of oxygen to tissues in the body and is therefore essential for life.
In this relationship, heme regulates the ability of GATA-1 to control genes in red blood cell precursors.
By determining how GATA-1 and heme control genes that produce cellular messenger RNAs and corresponding proteins, Bresnick’s team identified a dynamic gene regulatory process that initially elevates intracellular zinc, allowing the red cell precursor to survive, and subsequently decreases zinc, enabling the final steps in the cellular remodeling in which the precursor cell expels its nucleus to generate a functional red blood cell.
The therapeutic implications of this discovery relate to the need to develop treatments for blood diseases called ineffective erythropoiesis disorders, which include myelodysplastic syndrome disorders and an assortment of anemias with unexplained causes.
In these disorders, roadblocks prevent red blood cell generation, and this defective process is often resistant to the common therapeutic agent that stimulates red blood cell production, erythropoietin.
“The discovery of a new mechanism that helps precursor cells survive and controls the ‘terminal’ differentiation step constitutes a new paradigm that can be investigated further in the context of these pathologies,” Bresnick said.
“From a fundamental perspective, this study illustrates a new way in which a cellular cofactor (heme) triggers a transcriptional regulator (GATA-1) to orchestrate the levels of an intracellular trace metal to control cellular differentiation.”
The findings recently appeared in the journal Developmental Cell.
The project was a multi-disciplinary collaboration including Nobuyuki Tanimura, postdoctoral fellow in the Bresnick laboratory who led the experimental effort; Joshua Coon, professor of biomolecular chemistry; Judith Burstyn, professor of chemistry; and Jian Xu, an assistant professor and genome scientist from University of Texas Southwestern Medical Center.
Emerging drug class may enhance red blood cell production in anemic patients
December 22, 2010
Lodish LabGenetics + Genomics
CAMBRIDGE, Mass. – By determining how corticosteroids act to promote red blood cell progenitor formation, Whitehead Institute researchers have identified a class of drugs that may be beneficial in anemias, including those resulting from trauma, sepsis, malaria, kidney dialysis, and chemotherapy.
Anemia occurs due to a breakdown in erythropoiesis, the multi-step process that creates red blood cells. Some common anemias can be treated with a recombinant form of the hormone erythropoietin (EPO), which normally stimulates red blood-cell production at a fairly early stage of erythropoiesis.
However, certain anemias fail to respond to EPO, creating a large unmet medical need. In the case of Diamond Blackfan anemia (DBA), patients lack a sufficient number of EPO-responsive cells. Instead, corticosteroids such as prednisone or prednisolone are used to treat DBA, although it has been unclear exactly how these agents affect erythropoiesis.
To see how corticosteroids are able to increase red blood cell counts, Johan Flygare, a postdoctoral researcher in the lab of Whitehead Institute Founding Member Harvey Lodish, purified two progenitors of red blood cells, called burst forming unit-erythroids (BFU-Es) and colony forming unit-erythroids (CFU-Es), from mouse fetal liver cells. During erythropoiesis, BFU-Es produce CFU-Es, which are then stimulated by EPO to generate the pro-erythroblasts that eventually become red blood cells. By dividing numerous times before maturing, both BFU-Es and CFU-Es have a limited ability to self-renew. When Flygare exposed BFU-Es and CFU-Es in vitro to a corticosteroid, only the BFU-Es responded–dividing 13 times instead of the usual 9 times before maturing into CFU-Es. These additional cell divisions ultimately led to a 13-fold increase in red blood-cell production.
Flygare identified 83 genes in BFU-Es that are stimulated by the corticosteroid, and he examined the promoters that facilitate those genes’ transcription.
The promoters appeared to have binding sites for a transcription factor, called hypoxia-induced factor 1-alpha (HIF1-alpha), that is activated when an organism is deprived of oxygen.
To prolong the 83 genes’ promotion by HIF1-alpha, Flygare used a class of drugs known as prolyl hydroxylase inhibitors (PHIs), which extends HIF1-alpha’s effectiveness. PHIs have also been used in early-stage clinical trials to increase EPO production.
When Flygare added both a corticosteroid and a PHI to BFU-Es in culture, the cells produced 300 times more red blood cells than did cells without exposure to the drugs. Flygare repeated the experiment with adult human BFU-Es, and found that a corticosteroid plus a PHI generated 10 times more red blood cells than BFU-Es exposed to a corticosteroid alone.
Flygare hopes this research eventually leads to improved treatment for DBA patients who currently suffer from a host of corticosteroid-induced side effects, including decreased bone density, immunosuppression, stunted growth, and cataracts.
“If you could lower the dose of steroids so DBA patients would get just a little bit, and then add on this kind of drug, a PHI, that would boost the effect, maybe you could get around the steroids’ side effects,” says Flygare. “That would be good.”
This new approach to increasing erythropoiesis by extending the self-renewal of BFU-Es—resulting in creation of more EPO-responsive cells—could lead to novel therapies for other anemias.
“There are a number of anemias that are much more prevalent than DBA and that cannot be treated with EPO, either, such as anemias from trauma, sepsis, malaria, and anemia in kidney dialysis patients,” says Lodish, who is also a professor of biology and bioengineering at MIT. “Whether these treatments will work in those conditions remains to be seen.”
This research was supported by the Diamond Blackfan Anemia Foundation, the Swedish Research Council, Maja och Hjalmar Leanders Stiftelse, The Sweden-America Foundation, and the National Institutes of Health (NIH).
Written by Nicole Giese Rura
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Harvey Lodish’s primary affiliation is with Whitehead Institute for Biomedical Research, where his laboratory is located and all his research is conducted. He is also a professor of biology and a professor of bioengineering at Massachusetts Institute of Technology.
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“HIF1alpha synergizes with glucocorticoids to promote BFU-E progenitor self-renewal”
Blood, online on December 21, 2010.
Johan Flygare (1), Violeta Rayon Estrada (1), Chanseok Shin (1,2), Sumeet Gupta (1), and Harvey F. Lodish (1,3).
1. Whitehead Institute for Biomedical Research, Cambridge, MA;
2. Department of Agricultural Biotechnology, Seoul National University, Seoul, Republic of Korea; and
3. Departments of Biology and Bioengineering, Massachusetts Institute of Technology, Cambridge, MA