RDEB is a severe, inherited skin disorder caused by loss-of-function mutations in the COL7A1 gene, which encodes type VII collagen, a structural protein that forms anchoring fibrils at the dermal–epidermal junction. These fibrils are essential for skin integrity. In RDEB, defective or absent type VII collagen results in extreme skin fragility, blistering, and chronic wounds, often starting at birth. The disease is recessive, meaning both alleles of COL7A1 are typically mutated.
Because the pathology is caused by a specific genetic defect, RDEB is a candidate for genetic or RNA-targeted therapies, including gene replacement, gene editing, and antisense-mediated exon skipping.
Exon Skipping Therapy
Exon skipping is a strategy that uses antisense oligonucleotides (AONs) to modulate pre-mRNA splicing. The idea is to “skip” over a defective exon containing a mutation so that the resulting mRNA can still be translated into a partially functional protein rather than producing a truncated, nonfunctional one.
In RDEB, certain mutations in COL7A1 disrupt the reading frame or introduce premature stop codons.
Exon skipping can restore the reading frame, producing type VII collagen that retains some functionality, even if it’s missing the amino acids encoded by the skipped exon.
This approach is particularly attractive because it works on the patient’s own gene and avoids introducing foreign DNA.
Tricyclo-DNA (tcDNA) Antisense Oligonucleotides
Tricyclo-DNA (tcDNA) is a chemically modified DNA analogue designed for high stability, strong binding to RNA, and enhanced uptake into cells. tcDNA has several advantages:
Resistance to nucleases, meaning it is not easily degraded in vivo.
High affinity for target RNA, increasing exon-skipping efficiency.
Tissue penetration, allowing systemic delivery to difficult-to-reach tissues like skin.
Palmitoyl Conjugation
Adding a palmitoyl group (a fatty acid) to tcDNA AONs enhances their delivery and uptake by cells in vivo:
Fatty acid conjugation increases lipophilicity, allowing the oligonucleotide to interact more efficiently with cell membranes.
This improves tissue distribution and bioavailability, particularly for systemic therapy targeting skin and mucosal tissues.
Restoration of Protein Expression In Vivo
When these palmitoyl-tcDNA AONs are administered in vivo (in animal models or potentially humans), they:
Bind to COL7A1 pre-mRNA at specific sites flanking the mutated exon.
Induce skipping of the exon during splicing.
Produce corrected mRNA that can be translated into partially functional type VII collagen.
Restore anchoring fibril formation in the dermal–epidermal junction, improving skin integrity.
Studies in animal models of RDEB have shown that this approach can partially restore type VII collagen expression, reduce skin fragility, and promote wound healing. The degree of functional restoration depends on which exon is skipped, the efficiency of AON uptake, and the stability of the modified protein.
Significance
This strategy represents a promising precision medicine approach for RDEB because it:
Targets the root genetic cause of the disease.
Avoids introducing viral vectors or permanent genome modifications.
Can potentially be systemically delivered to reach widespread skin and mucosal surfaces.
Offers personalized therapy, as AON sequences can be designed for specific mutations or exons in individual patients.
Challenges and Considerations
While promising, several challenges remain:
Efficiency: Not all cells may uptake sufficient AONs, leading to variable protein restoration.
Durability: Repeated dosing may be required, as antisense oligonucleotides are not permanently incorporated.
Safety: Long-term effects, off-target splicing, or immune reactions to the oligonucleotide need careful evaluation.
Mutation specificity: Each exon-skipping therapy is often tailored to specific mutations, limiting universal applicability.
Palmitoyl-conjugated tricyclo-DNA antisense oligonucleotides for exon skipping are an advanced RNA-based therapy for recessive dystrophic epidermolysis bullosa. By inducing skipping of specific mutant exons in COL7A1 pre-mRNA, they restore partial type VII collagen expression in vivo, strengthening skin structure and offering a targeted approach to treating a previously untreatable genetic disease.
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