Stories about: hemoglobin

Zeroing in on the fetal-to-adult hemoglobin switch and a new way to combat sickle cell disease

Normal red blood cell vs. sickle-shaped blood cell, which is found in sickle cell disease
Normal red blood cell vs. sickle-shaped blood cell.

It’s been known for more than 40 years that in rare individuals, lingering production of the fetal form of hemoglobin — the oxygen-transporting protein found in red blood cells — can reduce the severity of certain inherited blood disorders, most notably sickle cell disease and thalassemia. Typically, however, a protein called BCL11A switches off fetal hemoglobin production past infancy, but exactly how this happens has not been well understood until now.

In a new paper in Cell, researchers at Dana-Farber/Boston Children’s Cancer and Blood Disorders Center have revealed how BCL11A controls the switch in the body’s production of fetal hemoglobin to adult hemoglobin. It does so by binding to a DNA sequence — made up of the bases T-G-A-C-C-A — that lies just in front of the fetal hemoglobin genes.

Another approach to curing sickle cell disease is already being evaluated in a new clinical trial at Dana-Farber/Boston Children’s. The novel gene therapy restores fetal hemoglobin production by genetically suppressing BCL11A, which prevents it from blocking fetal hemoglobin production. Learn more.

“Genetically modifying this TGACCA segment could be another possible strategy to cure sickle cell disease by blocking BCL11A’s ability to bind to this DNA site and switch off fetal hemoglobin production,” says Stuart Orkin, MD, senior author on the study.

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A breakthrough in our understanding of how red blood cells develop

Artist's rendering of red blood cells
Red blood cells.

By taking a deep dive into the molecular underpinnings of Diamond-Blackfan anemia, scientists have made a new discovery about what drives the development of mature red blood cells from the earliest form of blood cells, called hematopoietic (blood-forming) stem cells.

For the first time, cellular machines called ribosomes — which create proteins in every cell of the body — have been linked to blood stem cell differentiation. The findings, published today in Cell, have revealed a potential new therapeutic pathway to treat Diamond-Blackfan anemia. They also cap off a research effort at Boston Children’s Hospital spanning nearly 80 years and several generations of scientists.

Diamond-Blackfan anemia — a severe, rare, congenital blood disorder — was first described in 1938 by Louis Diamond, MD, and Kenneth Blackfan, MD, of Boston Children’s. The disorder impairs red blood cell production, impacting delivery of oxygen throughout the body and causing anemia. Forty years ago, David Nathan, MD, of Boston Children’s determined that the disorder specifically affects the way blood stem cells become mature red blood cells.

Then, nearly 30 years ago, Stuart Orkin, MD, also of Boston Children’s, identified a protein called GATA1 as being a key factor in the production of hemoglobin, the essential protein in red blood cells that is responsible for transporting oxygen. Interestingly, in more recent years, genetic analysis has revealed that some patients with Diamond-Blackfan have mutations that block normal GATA1 production.

Now, the final pieces of the puzzle — what causes Diamond-Blackfan anemia on a molecular level and how exactly ribosomes and GATA1 are involved — have finally been solved by another member of the Boston Children’s scientific community, Vijay Sankaran, MD, PhD, senior author of the new Cell paper.

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Sickle cell gene therapy to boost fetal hemoglobin: A 70-year timeline of discovery

sickled cells occluding a blood vessel
Sickled cells occluding a blood vessel. (Image: Elena Hartley)

Boston Children’s Hospital is now enrolling patients age 3 to 35 in a clinical trial of gene therapy for sickle cell disease. Based on technology developed in its own labs, it differs from other gene therapy approaches by having a two-pronged action. It represses production of the mutated beta hemoglobin that causes red blood cells to form the stiff “sickle” shapes that block up blood vessels. It also increases production of the fetal form of hemoglobin, which people normally stop making after birth.

Fetal hemoglobin doesn’t sickle and works fine for oxygen transport. The gene therapy being tested now restores fetal hemoglobin production by turning “off” a silencing gene called BCH11A.

BCL11A represses fetal hemoglobin and also activates beta hemoglobin, which is affected by the sickle-cell mutation,” David Williams, MD, the trial’s principal investigator, told Vector last year. Williams is also president of the Dana-Farber/Boston Children’s Cancer and Blood Disorders Center. “So when you knock BCL11A down, you simultaneously increase fetal hemoglobin and repress sickling hemoglobin, which is why we think this is the best approach to gene therapy in this disease.”

The therapy is the product of multiple discoveries, the first dating back 70 years. Click selected images below to enlarge.

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“Vampires” may have been real people with this blood disorder

Mural of Vlad the Impaler, who was accused of being a vampire. Perhaps, instead, he suffered from a blood disorder called porphyria.Porphyrias, a group of eight known blood disorders, affect the body’s molecular machinery for making heme, which is a component of the oxygen-transporting protein, hemoglobin. When heme binds with iron, it gives blood its hallmark red color.

The different genetic variations that affect heme production give rise to different clinical presentations of porphyria — including one form that may be responsible for vampire folklore.

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Sickle cell disease and the thalassemias: The advantages of staying forever young

Flipping a single molecular switch could turn off the mutation that causes sickle cell diseae. Stuart Orkin has already done it in mice. (CDC PHIL)

What if we really could turn our bodies’ clocks back? In some cases, that could be a really good thing. Take sickle cell disease. A scourge of tens of thousands worldwide, it stems from a genetic defect in hemoglobin, the oxygen-carrying protein in red blood cells.

Normally, our bodies can produce two forms of hemoglobin: adult hemoglobin, the form susceptible to the sickle cell mutation; and fetal hemoglobin, which is largely produced during development and for a short time after birth. Our bodies finish making the switch from fetal to adult hemoglobin production by about four to six months old – the same time frame when children with the sickle cell mutation first start to show symptoms of the disease.

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