MicroRNAs (miRNAs) are tiny molecules present in our cells that naturally regulate gene activity. They function as “dimmer switches” for genes, influencing which proteins a cell produces by controlling the messenger RNA (mRNA) blueprints. Scientists have developed synthetic miRNAs, which are human-made versions of these natural molecules, engineered for precise tasks in research and as potential medical treatments. These engineered RNA strands represent a new frontier in understanding and influencing biological processes.
Designing and Creating Synthetic miRNA
The creation of synthetic miRNA begins with a careful design process, tailored to achieve a specific effect within cells. Two main types of synthetic miRNAs exist, each with a distinct purpose. MicroRNA mimics, also known as agonists or agomirs, are designed to replicate the function of a naturally occurring miRNA that is deficient in disease. These mimics aim to restore normal gene-regulating activity.
Conversely, antimiRs, or antagomirs, are antagonists engineered to block the activity of a natural miRNA that is overactive in disease. These molecules are typically single-stranded, chemically modified RNAs that bind to and inactivate problematic natural miRNAs. Both types require precise sequence design to ensure they interact with their intended targets effectively.
Once designed, synthetic miRNAs are typically created through chemical synthesis, often using a method called solid-phase phosphoramidite chemistry. This process allows scientists to build the RNA strand nucleotide by nucleotide with high precision. Chemical modifications, such as adding 2′-O-methyl or phosphorothioate linkages, are frequently incorporated during synthesis. These modifications enhance the synthetic miRNA’s stability, protecting it from degradation by enzymes in the body, and can also improve its effectiveness and cellular uptake compared to unmodified RNA.
How Synthetic miRNA Functions
Once introduced into a cell, synthetic miRNAs interact with the cell’s internal machinery to regulate gene expression. A miRNA mimic, for example, is loaded into a cellular assembly called the RNA-induced silencing complex (RISC). This complex functions like a molecular foreman, guiding the synthetic miRNA to locate specific messenger RNA (mRNA) molecules.
When the RISC complex, guided by the mimic, binds to a target mRNA, it can block the cellular machinery from reading that blueprint, thereby preventing the production of the corresponding protein. This action is known as gene silencing.
In contrast, an antimiR operates by directly binding to the natural miRNA it intends to neutralize. This binding sequesters the problematic natural miRNA, making it unavailable to the RISC complex and preventing it from performing its own gene-silencing actions. By doing so, antimiRs allow genes that were previously suppressed by the overactive natural miRNA to be expressed normally, effectively “turning on” genes that were inappropriately silenced.
Key Applications in Medicine and Research
Synthetic miRNAs are promising across various fields, particularly in medicine and fundamental biological research. Their ability to precisely modulate gene expression makes them versatile tools for biological problems.
Therapeutic Potential
In medicine, synthetic miRNAs are being explored for their ability to treat a range of diseases by correcting aberrant gene activity. In cancer therapy, for example, synthetic miRNA mimics are being investigated to suppress tumor growth by targeting multiple genes involved in cancer cell proliferation and survival. Clinical trials have also explored mimics to target specific tumor cells in lung cancers.
Beyond cancer, synthetic miRNAs are being studied for viral infections by aiming at the virus’s genetic material. They also show potential in treating cardiovascular diseases, promoting cardiac cell proliferation after heart injury. Additionally, antimiRs are in preclinical development for metabolic conditions like type 2 diabetes. While many of these applications are still in early research or clinical trial phases, they represent a significant advancement in targeted therapies.
Fundamental Research Tools
Beyond their therapeutic applications, synthetic miRNAs are important tools for scientists. Researchers utilize these molecules to temporarily reduce or “turn off” the expression of specific genes in cell cultures or animal models. This controlled gene silencing allows scientists to study the function of individual genes and understand their roles in various biological processes, from normal development to disease progression. This understanding forms the groundwork for identifying new drug targets and developing innovative treatments.
Delivery and Stability Challenges
Bringing synthetic miRNAs to clinical use involves overcoming several technical hurdles, primarily related to their delivery and stability within the body. Naked synthetic RNA molecules are fragile and easily broken down by enzymes. This rapid degradation limits their lifespan and effectiveness before they can reach their intended targets.
Another challenge involves getting these negatively charged molecules past the cell membrane, which naturally repels them, and then directing them specifically to diseased cells or tissues without affecting healthy ones. To address these issues, scientists are developing advanced delivery systems.
One common approach involves encapsulating synthetic miRNAs within protective “bubbles” made of lipids, known as lipid nanoparticles (LNPs). These nanoparticles shield the RNA from degradation and facilitate its entry into cells. Researchers are also exploring ways to attach targeting molecules to the surface of these nanoparticles. These attachments act like molecular zip codes, directing the synthetic miRNAs specifically to the desired cells or organs, improving targeting and minimizing unintended effects.
Ensuring the synthetic miRNA remains stable within the cell and acts only on its intended target is equally important. The chemical modifications introduced during synthesis help prevent the synthetic RNA from degrading too quickly once inside the cell. However, a persistent challenge is avoiding “off-target effects,” where the synthetic miRNA might accidentally bind to and silence genes other than the one it was designed for. Designing highly specific sequences and optimizing chemical modifications are ongoing areas of research to enhance both the stability and precision of synthetic miRNA therapies.