Gene Editing Techniques in Treating Genetic Lung Disorder

Introduction

Although there is a thorough grasp of the genetics and pathology of congenital lung diseases, there is a need for more effective treatment options. Targeted delivery of technologies to correct genes to the respiratory system (through the intratracheal or intranasal routes) is an appealing alternative to therapy. This is mainly because the lung is a barrier organ in direct communication with the external environment. The organs that act as the first line of defense against the germs that enter the body are called barrier organs. They act as a physical barrier.

What Is Gene Therapy?

A medical approach that treats or helps to prevent diseases by correcting the genetic problem that causes it is called gene therapy. The patient’s genetic makeup is altered instead of using a drug or surgical procedure. Gene transfer or gene addition was one of the earliest attempts in gene therapy. In this process, a set of genes is either added or an altered gene copy replaces the faulty genes. Later, after much research, a new process called gene editing was introduced. It uses a different approach to correct the faulty genes. Instead of changing the genes, the process alters the genetic makeup by using molecular tools that can change the existing DNA (deoxyribonucleic acid).

What Are the Benefits of Gene Editing?

The benefits of genetic editing can include:

• Fix a genetic alteration that causes a disease so that it can function properly.

• Help a gene to fight a disease by turning it on or activating it.

• A gene that does not function properly can be deactivated.

• Remove a piece of DNA that is impaired and cause disease.

What Is the Need for an Alternate Therapy for Genetic Lung Diseases?

The cost of treating genetic lung disorders is a significant burden in healthcare, and they can be fatal sometimes. Definitive treatment options are limited, though there is an extensive understanding of the genetics. Many genetic lung diseases are monogenic (controlled by a single gene). Hence, they represent promising targets for therapies that use gene editing. Moreover, because the lung is a barrier organ and frequently comes in contact with the outer environment, pulmonary genetic diseases are particularly receptive to targeted gene editing therapies.

What Are the Genetic Causes of Monogenic Lung Diseases?

1. Surfactant Protein Deficiency: Mutations in many genes cause an inherited surfactant protein deficiency. Surfactant proteins are collagen-containing lectins (carbohydrates that bind to proteins) that reduce the surface tension at the interface between the air and liquid, thereby preventing the collapse of the alveoli in the lungs. There are four types of surface proteins: SP A, SP B, SP C, and SP D. ABCA3 is a transporter protein that helps transport lipids. The most prevalent cause of SP deficiency ABCA3, has been found to contain over seventy mutations that cause loss of functions.

2. Cystic Fibrosis: Cystic fibrosis (CF) is an autosomal recessive (a genetic disorder that requires two copies of the gene to be expressed) disorder. A defect in the cystic fibrosis transmembrane conductance regulator (CFTR) gene causes CF. CFTR is found on chromosome seven. It causes an abnormal transport of chloride ions in the ciliated epithelial cells in the airway. As a result, an accumulation of an excess thickened mucous occurs, and an impaired mucociliary clearance (a self-clearing mechanism found in the respiratory system). It increases the risk of recurrent infections, respiratory failure, and early death.

3. AAT: AAT (alpha 1 anti-trypsin) is a serine protease inhibitor. It is secreted in the liver and inhibits neutrophil elastase (an enzyme that helps in the breakdown of elastin), proteases (an enzyme that helps in the breakdown of protein), and defensins (a protein that helps in inhibiting bacteria) in the lung. It results in emphysema (a condition of the lung that destroys the alveoli) and reduces life expectancy.

What Is CRISPR?

CRISPR (clustered regularly interspaced short palindromic repeats) is a group of DNA sequences found in the genetic makeup of prokaryotes like bacteria. It is an improvement of the bacteria’s defense mechanism against foreign DNA. The locus of bacterial CRISPR consists of short palindromic repeats within the bacterial genome. The foreign DNA is incorporated into this as many small pieces. The CRISPR locus is converted into small RNAs on exposure to the foreign DNA. These small RNAs guide the Cas9 endonuclease (CRISPR-associated protein 9) to a specific site in the foreign DNA. As a result, a double-stranded break (DSB) is created. This protects the host bacteria from other foreign DNA complexes.

How Is CRISPR Applied in Monogenic Lung Diseases?

1. SP Deficiency: The reagents capable of performing gene editing are given intra-tracheally or intra-nasally to rectify the SP mutations in the lung. A relatively short donor DNA template might suffice for genetic repair. This is mainly because single-base substitutions mainly cause SP deficiency.

2. CF: Studies show intestinal organoids (a miniature version of an organ) taken from pediatric patients from CFTR cannot respond to forskolin stimulation (a potent vasodilator) by swelling. Genetically modified organoids were able to produce a normal response to forskolin stimulation. If a proper transplant test was created, a similar organoid system could be used to correct CF. A variety of mutations brings about CF. Hence, patients would benefit from a customized treatment plan if the patient-specific cells were employed to create tailored lung models. Screening programs in newborns facilitate the early diagnosis of the condition. Basal airway cells are harvested during early childhood for gene editing. This could be more useful for the therapy.

3. AAT: The current strategies for gene therapy target skeletal myocytes to augment AAT synthesis. The growth of hepatocytes is prevented due to continuous liver damage caused by the accumulation of abnormal AAT. This limitation can be overcome by genetic editing by CRISPR. Genetic editing enables the production of normal AT, thereby treating both the lungs and the liver.

Conclusion

Genetic editing is a good strategy for treating genetic lung diseases. There are multiple delivery options as the lungs are a barrier organ, having direct contact with the external environment. This also provides easy access to patient-specific progenitor cells for genetic editing. However, engrafting of the corrected cells remains a challenge.