The MYH11 gene provides instructions for a protein involved in cellular movement and material transport. Understanding MYH11 helps explain how certain tissues, especially those with involuntary muscle contractions, maintain strength and stability.
What is MYH11?
The MYH11 gene, or Myosin Heavy Chain 11, codes for the smooth muscle myosin heavy chain 11 protein. This protein belongs to the myosin family, often called “motor proteins” due to their role in cellular movement.
The smooth muscle myosin heavy chain 11 protein is part of the cytoskeleton, a cell’s internal scaffolding that maintains its shape and organizes contents. It forms thick filaments that work with thin actin filaments. These filaments are essential for muscle fibers and enable contraction. Each myosin complex has two heavy chains and two pairs of light chains for regulation. The heavy chains feature a head region that interacts with actin and binds ATP, plus a long tail region for forming thick filaments.
MYH11’s Role in Body Function
The MYH11 protein is primarily found in smooth muscle tissues throughout the body. Smooth muscles are involuntary, meaning their contractions are not consciously controlled. These muscles line the walls of many internal organs and structures.
Examples include the walls of blood vessels, the digestive tract, the bladder, and airways. In these locations, the MYH11 protein contributes to various bodily functions. For instance, in blood vessels, its contraction and relaxation help regulate blood pressure and blood flow.
In the digestive system, smooth muscle contractions, known as peristalsis, move food through the intestines. The protein also controls functions in the bladder and airways. The MYH11 protein regulates the ability of smooth muscle cells to contract and relax.
Health Conditions Associated with MYH11
Mutations in the MYH11 gene are linked to specific health conditions, notably Thoracic Aortic Aneurysm and Dissection (TAAD) and Patent Ductus Arteriosus (PDA). Familial TAAD is a hereditary cardiovascular disorder causing weakness, enlargement, and tears in artery walls. Individuals often experience issues with the thoracic aorta, the upper part of the large blood vessel carrying blood from the heart.
The aorta’s walls can weaken and stretch, leading to dilation and aneurysm formation (a bulge). A more severe event, aortic dissection, involves a sudden tearing of the aorta’s inner layers. These aortic conditions can be life-threatening.
Patent Ductus Arteriosus (PDA) is another condition associated with MYH11 mutations. This involves a blood vessel, the ductus arteriosus, which is present during fetal development and normally closes shortly after birth. When it fails to close, it can lead to complications. Rearrangements involving MYH11 are also connected to a form of blood cancer called acute myeloid leukemia (AML). These rearrangements, such as an inversion or translocation on chromosome 16, lead to the fusion of the MYH11 gene with another gene called CBFB, affecting blood cell development.
How MYH11 Mutations Cause Disease
Mutations in the MYH11 gene can disrupt the normal function of the MYH11 protein. When the MYH11 protein is faulty or non-functional, it compromises the structural integrity and contractility of smooth muscle cells. This cellular dysfunction leads to larger-scale problems within the body.
For Thoracic Aortic Aneurysm and Dissection (TAAD), impaired smooth muscle function in the aorta weakens vessel walls. This weakening makes the aorta susceptible to dilation, aneurysm formation, and ultimately increases the risk of dissection, a tear that can lead to severe bleeding. For Patent Ductus Arteriosus (PDA), a dysfunctional MYH11 protein can hinder the proper development or function of smooth muscle in the ductus arteriosus, preventing this fetal blood vessel from closing after birth.