Introduction:
Aging is a natural process that causes many changes in the body. Hence, people during old age suffer from many medical issues associated with the heart, bones, muscles, and so on, which pose many challenges to the medical field. As part of aging, the hematopoietic system, which gives rise to blood cells, also gets affected. Inflammation and hematopoiesis get altered during the aging process. Research indicates that genetic instability and reduced communications between the cells could be the possible reason for age-related changes in hematopoiesis. It is important to understand the aging of hematopoietic stem cells to improve the quality of life during old age.
What Is Hematopoiesis?
The process of formation of blood cells and their components from the stem cells is known as hematopoiesis. The word hematopoiesis is derived from ‘haima’, meaning blood, and ‘poiesis’, meaning to produce something. It starts during embryonic development and continues throughout the lifetime to replenish the blood system. The blood cells are divided into three main categories: red blood cells (RBC), white blood cells (WBC), and platelets. RBCs transport oxygen, WBCs provide immunity or fight infection, and platelets help in blood clotting.
What Is the Process of Hematopoiesis?
The process of hematopoiesis occurs in the bone marrow, liver, and spleen. Hematopoiesis that occurs in bone marrow is known as medullary hematopoiesis, and the one which occurs in the spleen and liver is known as extramedullary hematopoiesis. During embryonic development, hematopoiesis occurs in the yolk sac, which surrounds the embryo. At the end of the first trimester, it starts occurring in the spleen, thymus, and liver. From the mid-trimester, most of the blood cells are produced in the bone marrow. After birth and throughout life, bone marrow continues to produce more blood cells. However, some white blood cells are produced in the thymus as well.
Hematopoiesis begins in the hematopoietic stem cells, giving rise to a precursor or progenitor cells. These progenitor cells are of two types:
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Myeloid Progenitor Cells: Megakaryocytes (produces platelets), eosinophils, basophils, erythrocytes (RBC), monocytes, and neutrophils arise from myeloid progenitor cells.
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Lymphoid Progenitor Cells: Immunity-providing T cells, B cells, and natural killer (NK) cells arise from lymphoid progenitor cells.
The factors that regulate hematopoiesis are:
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Stem cell factors.
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Thrombopoietin.
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Granulocyte-macrophage colony-stimulating factor.
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Thrombopoietin.
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Interleukin-3.
What Are the Disorders That Affect Hematopoiesis?
Several blood disorders and certain medications can interfere with blood cell formation.
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Myeloma: When the plasma cells become cancerous, they multiply exponentially, resulting in myeloma or multiple myeloma. These cancerous cells can take up the space of other normal cells that give rise to red blood cells, platelets, and other white blood cells. Bone pain, fever, and loss of appetite are some of the symptoms. Hence, myeloma can affect hematopoiesis.
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Leukemia: Leukemia refers to the group of blood cancers that affect the bone marrow and lymphatic system. The impairment of hematopoietic stem cells occurs in leukemia which affects the function of the immune system and the process of inflammation. In leukemia, abnormal white blood cells are produced that replace normal cells.
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Splenomegaly: The enlargement of the spleen that occurs due to infections, hypertension, cancer, cirrhosis, etc. is known as splenomegaly. As the spleen is one of the sites of extramedullary hematopoiesis, splenomegaly can interfere with the formation of blood cells.
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Thrombocytopenia: It is a condition where the number of thrombocytes or platelets gets reduced. The main causes of thrombocytopenia are leukemia, dysfunction of the immune system, or certain medications. People with thrombocytopenia experience frequent bruising and slow blood clotting, which results in an increased risk of bleeding.
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Neutropenia: In neutropenia, the number of neutrophils is reduced. Neutrophils belong to white blood cells. Hepatitis, HIV (Human immunodeficiency virus), leukemia, lymphoma, Lyme disease, etc. are some of the causes of neutropenia. In congenital neutropenia, hematopoiesis is significantly higher.
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Infections: Viral infections such as HIV, hepatitis, Ebstein-Barr virus, cytomegalovirus, etc. can affect the bone marrow and sometimes may impair hematopoiesis as well.
What Are the Hematopoietic Changes Associated With Aging?
A lot of factors contribute to age-related changes in hematopoiesis. The signaling pathways involved in DNA (Deoxyribonucleic acid) repair, mitochondrial function, mutations, and cell division can induce aging in hematopoietic stem cells. The number and cell dividing potency of the stem cells also decrease during late adulthood.
The main features of aged hematopoietic stem cells are:
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Low Repopulation Capacity- The capacity of hematopoietic stem cells to produce more blood cells or repopulate diminishes with age.
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Low Homing Ability- Homing is the rapid process of active migrations of hematopoietic stem cells to the bone marrow and other organs after being injected or administered into the bloodstream. Homing ability is low in aged hematopoietic stem cells.
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Myeloid Skewing- Skewing is the balance of myeloid and lymphoid progenitor cells which induces immunity. In aged hematopoietic stem cells, the number of myeloid progenitor cells is significantly increased as compared to the lymphoid progenitors. Myeloid stem cells give rise to the progenitors that produce red blood cells, platelets, and certain white blood cells such as eosinophils, basophils, and monocytes. Even though the myeloid progenitor cells are high in older people, they are not found to be as effective as their younger counterparts.
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High Reactive Oxygen Species- Increased reactive oxygen species can affect cell function and even may result in its damage. Reactive oxygen species can also progress inflammatory disorders.
How to Improve Hematopoiesis During Old Age?
The role of diet and lifestyle in hematopoiesis is still being discussed. However, certain vitamins and nutrients are effective in hematopoiesis to replenish blood. Carbohydrates, proteins, and fats can improve hematopoiesis. Therefore, eating a moderate amount of foods rich in these nutrients can improve hematopoiesis. Vitamin B12, vitamin C, and folic acid can prevent megaloblastic anemia by improving the DNA synthesis in the erythroid nucleus. Other vitamins such as vitamins A, D, and K also have a role in hematopoietic functions. Studies revealed that a diet rich in fish oil can improve hematopoiesis in the spleen.
Conclusion:
The changes in the hematopoietic system that occur with age can affect the health and lifespan of an individual. When the function of the hematopoietic stem cell gets affected, all major processes, such as inflammation, immunity, clotting, etc, get disrupted, which may result in anemia, infections, uncontrolled bleeding, and so on. However, age-related changes in hematopoiesis can be reduced to a certain extent by consuming a diet rich in vitamins, minerals, nutrients, and fish oils.
