KLF1 Gene

Regulation and Control
of Haemoglobin Switching

Haemoglobin (Hb) carries oxygen throughout our bodies. It is the respiratory pigment of man and many other mammals. The molecule captures oxygen in the lungs and transports it within the red blood cells for release in the tissues.

Haemogloblin is a fascinating molecule. Although deceptively simple in structure, it is intriguingly complex in physiology and genetics. The fully functional molecule is one of the smaller proteins known. It is assembled from four subunits; all proteins and known as globins. Each globin resembles the structure of the simpler oxygen storage molecule, myoglobin, mostly found in muscle. There are 280 million molecules of haemoglobin in every red blood cell, and there are 30 trillion red blood cells in the body of a normal and healthy person. The genetic control of haemoglobin production i.e. globin biosynthesis, before and after birth is as complex and demanding as is the physiology of the molecule. Both matters have challenged some of the most leading luminaries in haematology, protein chemistry, physiology and genetics for the large part of the previous century. The molecular details of physiological function and the developmental control of globin gene expression remain fundamental inquiries even in contemporary human biology and medicine. The implications for health and disease are huge.

The haemoglobin content of a healthy individual is around 14g/dL. Many conditions decrease this concentration, such as iron deficiency anaemia, or heavy blood loss due to accidents. When haemoglobin decreases, the body goes into stress, and tries to bring levels back to normal. Anaemia occus when haemoglobin is very low, with sufferes complaining of fatigue amongst other symptoms. Nowadays such conditions or situations are easily cured or remedied by treatment within a few weeks.

The same cannot be said for other genetic conditions that are inherited. Conditions such as sickle cell disease and thalassaemia, involve either an abnormal haemoglobin protein or a complete absence of the normal protein. In turn, this will lead to unsuccessful or inefficient oxygen-carrying capacity in our human body, leading to chronic (lifelong) anaemia. The only possible treatment is by blood transfusion every 4 to 6 weeks coupled with iron chelating therapy that removes excess iron from the body. This has two drawbacks.

One 280 million molecules of haemoglobin in every red blood cell, and 30 trillion red blood cells in a person 7 is purely personal and patient-related. Having blood transfusions every month is not very ideal for a normal lifestyle, not to mention all the complications that can accompany it. The second drawback would be on the society itself, since such blood transfusions will deplete the stores that may be otherwise used for other emergency situations and haematological malignancies.

The composition of the haemoglobin protein changes during the early stages of life. There is a switch from embryonic to foetal and eventually from foetal to adult. In most cases of thalassaemia the adult haemoglobin is defective, which has a direct effect since it is usually the predominant form. Foetal haemoglobin (HbF) is expressed in very high levels in the foetus, and starts to decline steadily round the time of birth. The switch is complete around 6 to 9 months after birth. At this stage the adult form of haemoglobin would have become the predominant one. Since the adult haemoglobin is defective in beta thalassaemia patients, having higher levels of foetal haemoglobin in vivo, will generally lead to a better quality of life, reduced symptoms and possibly render them free from transfusions.

Scientific studies have tried for years, to induce high levels of foetal haemoglobin in adults suffering from haemoglobin disorders. Many studies focused on drugs and compounds that act on DNA sequences and other protein molecules. To be able to switch on foetal haemoglobin efficiently, the switching mechanism must be well understood.

One large study that has made an international impact originated from the University of Malta (Borg et al., 2010). A Maltese family was studied that exhibited abnormally high levels of foetal haemoglobin in their blood (lowest ranging from 3.3% and highest up to 19.5%). “Why did these people carry high levels of foetal haemoglobin?” Knowing the answer may help develop drugs or compounds to treat patients with beta thalassaemia.

280

million molecules

of haemoglobin in every red blood cell,
and 30 trillion red blood cells in a person

The research study identified a new DNA mutation in a gene called Erythroid Krupple-Like Factor 1 (KLF1) on chromosome 19. The participating Maltese patients donated 30mL of blood that were used to culture red blood cells. The patients had abnormal expression levels resulting in high foetal haemoglobin that was very different from individuals with normal levels of foetal haemoglobin. KLF1 is a transcription factor and its main role is to bind and initiate transcription (switch on) of the adult beta globin gene. The KLF1 protein in the Maltese family members was compromised due to the presence of the mutation, meaning that only one copy of KLF1 was functioning correctly. Since KLF1 is important to express the adult beta globin gene, this gene was compromised, reducing beta globin gene production. To compensate for low adult globin levels, foetal haemoglobin was switched on. Moreover, KLF1 appears to bind and regulate a foetal haemoglobin repressor – BCL11A. Hence, less BCL11A, resulted in even more foetal haemoglobin production.

The KLF1 protein in the Maltese family members with high
foetal haemoglobin was compromised due to the presence of the
mutation, meaning that only one copy of KLF1 was functional

Currently, the Malta group is analyzing additional DNA sequences that may regulate and control foetal haemoglobin in vivo. The results can yield potential targets for therapeutic intervention allowing the switch to high-level expression of foetal haemoglobin and possibly curing syndromes such as beta thalassaemia.

The Malta group is led by Professor Alexander E. Felice with active participation and leading roles by of Dr. Joseph Borg and Dr. Godfrey Grech on cell manipulation and culture studies. Ms Ruth Galdies and Ms Wilma Cassar on haematological testing using analytical lab techniques, and Professor Christian A. Scerri as a genetic counselor at the Thalassaemia and Molecular Genetics Clinic, located at the Mater Dei Hospital.

The Malta Group is also supported by undergraduate students as well as graduate (M.Sc studies) and post-graduate (PhD studies) who take active parts on haemoglobin and related research.

This research team has repeatedly made international headlines, hinting at the importance of these blood disorders that affect millions world wide. Finally, the decades long search for a beta thalassemia cure seems elusively near, since this team has uncovered an important underlying mechanism to genetically switch on foetal haemoglobin. The futue for curing thalassemia has become much brighter.