The elevated level of LDL Cholesterol in individuals is a global concern, potentially caused by various factors including poor diet, obesity, lack of physical exercise, smoking, age, or genetics. No doubt with the help of Cholesterol-lowering drugs/intermittent injections one can lower their levels in the blood, but what if we don’t have to consume the pills daily, what if a one-time medication can last a lifetime? Sounds Amazing? Let’s dive into the generation and execution of this concept in the laboratory of Verve Therapeutics, a Boston-based biotechnology company.
Before jumping to details let me just brush up on your knowledge of molecular concepts behind this technology…
Our body is made up of 37.2 trillion cells, each cell has a nucleus where the genetic material (DNA) is packaged into a thread-like structure called a Chromosome. DNA contains the instructions necessary for our cells to function properly. It is made up of four chemical bases- Adenine, Guanine, Cytosine, and Thymine. Similar to how letters of the alphabet appear in a certain order to form words, the specific order or sequences of these bases encode our genes. Any disruption in the sequence of bases (mutations) can produce genes that are dysfunctional or missing altogether. Mutations can cause inherited diseases like the genetic disorder: “Heterozygous Familial hypercholesterolemia” which cranks up the “bad cholesterol” in the blood. LDL Cholesterol is infamous for clogging arteries. The patient’s disorder can lead to severe heart disease at an early age which can be fatal.
To overcome this genetic disorder, the Verve Therapeutics team came up with the idea of using CRISPR 2.0 (Base editing) Technology to lower the level of LDL Cholesterol permanently without worrying about the symptoms throughout their lifespan.
The origin story behind the creation of CRISPR/Cas9 system
In a document, if we suspect we have misspelled a word, we can use the find function to highlight the error and correct it or delete it. Within our DNA that function is taken on by a system called CRISPR/Cas9.
CRISPR is short for Clustered Regularly Interspaced Short Palindromic Repeats, a mouthful term which in simple words means that it is a short (20-30 nucleotides) palindromic repeating sequence of DNA that is interrupted by so-called spacer elements or spacers – sequences of genetic code, derived from the genomes of previously encountered bacterial pathogens.
The CRISPR technology came about through a basic research project being performed in Emmanuelle’s lab in Germany that was aimed at discovering how bacteria fight viral infections. Bacteria have to deal with viruses in their environment all the time and we can compare a viral infection to a ticking time bomb, a bacterium has only a few minutes to defuse the bomb before it gets destroyed.
So basically, Emmanuelle Charpentier and Jennifer Doudna collaborated on this project in 2011 and eventually, they were awarded the 2020 Nobel Prize in Chemistry for their work on CRISPR-Cas9- a method to edit DNA.
The emergence of CRISPR 2.0 (Base editing)
Base editing is also a gene-editing technology created to target single-point mutations where a single nucleotide base is changed, deleted, or inserted, it’s like a spell check for genes. It is different from the CRISPR/Cas9 approach wherein a combination of the Cas9 enzyme and a guide RNA (CRISPR RNA+ tracr RNA), cuts DNA, and the natural DNA repair process takes over. However, they can lead to unwanted effects such as insertions, deletions (Indels), or other DNA rearrangements at the site of the break which raises the risk of side effects.
Therefore, CRISPR/Cas9 acts like scissors whereas Base editing acts like an eraser. The therapy developed by Verve can erase and rewrite one letter of the genome at a time.
To use CRISPR 2.0, scientists first identify the sequence of the human genome that causes a health problem. In this case, that sequence is inside the PCSK9 gene in the liver which encodes instructions for manufacturing a protein that raises blood cholesterol level. Just one edit in a precise location shuts PCSK9 down.
The team created a genetic medicine called VERVE-101TM designed to turn off a Cholesterol-raising gene (PCSK9).
The structure and function of Verve-101TM
Verve-101 relies on a DNA-modifying protein called an adenine base editor. Base editors consist of two components joined together: a CRISPR-Cas9 protein bound to a guide RNA which identifies features of a target DNA sequence and a base-converting enzyme which carries out the desired edit to the target base.
Firstly, the RNA Cas9 combination searches for a docking sequence that unwinds the adjacent DNA, and searches for a perfect match between the guide RNA sequence and the target DNA sequence. If there is both a docking sequence and a matching sequence, then the Cas9 produces a single-strand DNA nick, and the base-converting enzyme makes a base change, in this case, a single A-to-G change in the DNA genetic sequence of PCSK9. Further, the cells repair the base change which leads to a permanent DNA change called a Base edit, with corrected DNA instructions the cell can now function normally.
The concept of this gene editing technology entails a “once-in-a-lifetime” approach, which could prove intriguing for future applications. However, alongside many benefits of genome editing, there are also some ethical and societal concerns to consider.
References:
- synthego.com
- sciencenews.org
- businesswire.com
- Challenges of Gene Editing Therapies for Genodermatoses by Imogen R. Brooks, Adam Sheriff, Declan Moran, Jingbo Wang, and Joanna Jacków
- crisprmedicinenews.com
Aanchal Bhatia
B. Tech Biotechnology from Punjab, Agricultural University (PAU)
About the author: I have a deep understanding of biotechnology and am passionate about science communication. I have a strong interest in the field of biological sciences and intend to pursue my master’s degree in the same field.
