Mental health plays a crucial role in our overall well-being, impacting our ability to function, work, and maintain healthy relationships with others. Anxiety disorders, encompassing conditions like generalized anxiety disorder, panic disorder, and social anxiety disorder, involve excessive fear and worry that can severely distress individuals and impair their daily lives.
According to the World Health Organization (WHO), in 2019, approximately 301 million people worldwide were affected by anxiety disorders, including 58 million children and adolescents. Furthermore, the prevalence of anxiety has increased by 25% due to the onset of the COVID-19 pandemic. While anxiety is commonly treated with medication, some individuals experience side effects or find that their symptoms persist despite treatment.
Researchers have now developed an innovative technique that enables noninvasive delivery of CRISPR/Cas9 gene editing technology to the brain. The primary objective was to target and deactivate a gene responsible for anxiety and depression in mice. This achievement represents the first successful demonstration of noninvasive delivery of the CRISPR/Cas9 system, which can effectively cross the blood-brain barrier and facilitate genetic modifications.
The blood-brain barrier (BBB), as its name suggests, acts as a protective barrier, preventing harmful substances like bacteria and viruses from entering the brain while allowing essential nutrients to pass through. While this serves as a vital defense mechanism for maintaining brain health, it poses a challenge for therapeutic agents attempting to access the brain.
CRISPR/Cas9 gene editing has shown immense potential for treating various diseases, such as muscular dystrophy, HIV, and lung cancer. The CRISPR system employs an enzyme called Cas9, guided by RNA, to precisely remove specific sections of DNA. This technology can eliminate problematic genes responsible for causing diseases. However, like other therapeutic agents, CRISPR encounters difficulties due to the presence of the blood-brain barrier.
In their study, the researchers focused on intranasal delivery of the CRISPR/Cas9 system to determine its ability to cross the blood-brain barrier successfully and deactivate the serotonin receptor gene (HTR2A). This gene modulates serotonin availability, a neurotransmitter that regulates mood. Insufficient serotonin levels have been associated with anxiety and depression, leading to the prescription of selective serotonin reuptake inhibitors (SSRIs) to increase serotonin levels in the brain.
Intranasal delivery of therapeutic agents involves administering them through the nasal cavity, allowing them to reach the central nervous system via nerve pathways. This delivery method is both practical and noninvasive.
The researchers introduced an inactivated adeno-associated virus (AAV) as a viral vector into the mice’s noses to deliver the RNA to the brain’s neurons. This RNA binds to the target HTR2A gene, which Cas9 subsequently removes. AAVs are commonly used as vectors for delivering CRISPR/Cas9 cargo due to their safety and low likelihood of eliciting an immune response. The researchers employed the AAV9 subtype, known for its high efficiency in delivering cargo to neurons throughout the central nervous system.
After five weeks of administering the gene-editing package, the mice’s anxiety levels were assessed using a light-dark behavioral test and a marble-burying test. The light-dark test involves giving mice a choice between exploring a brightly lit chamber or a dark chamber. Anxious mice tend to spend more time in the dark chamber. In the marble-burying test, glass marbles are placed in a sawdust-filled grid pattern, and anxious mice tend to bury more marbles.
The results showed an 8.47-fold decrease in HTR2A expression in the treated mice. In the marble-burying test, these mice exhibited a 14.8% decrease in marbles buried compared to the control group. Moreover, in the light-dark test, the treated mice spent significantly more time in the lit box (a 35.7% increase) and made more entries into the lit box (a 27.5% increase).
These outcomes were comparable to the effects of diazepam, a benzodiazepine drug used to treat anxiety, with the treated mice spending 40% more time in the lit box. Consequently, the researchers concluded that their therapy targeting the HTR2A gene performed on par with the drug.
“Our results suggest that even with a low percentage of neuronal gene editing, significant anxiolytic [anxiety-reducing] effects are observed,” the researchers stated.
Moreover, they highlighted the accomplishment of delivering therapeutic agents within the central nervous system through a noninvasive intranasal delivery platform that bypasses the blood-brain barrier, a significant obstacle for large cargos like CRISPR/Cas9.
The researchers believe that their proof-of-concept study demonstrates the long-term potential for modifying specific traits, which holds significant implications for developing new anxiety and depression medications, particularly for individuals resistant to existing treatments.
The study documenting these findings was published in the journal PNAS Nexus.
Source: Oxford Academic