Development of PE7, which precisely corrects the Alzheimer's genetic risk factor APOE4 to APOE3 using prime editing
Background
Sporadic Alzheimer's disease (AD) is a major health concern in aging societies. The apolipoprotein E4 (APOE4) allele is a strong genetic risk factor for the disease. Individuals carrying APOE4 exhibit increased accumulation of amyloid beta (Aβ) protein in the brain and are more likely to experience abnormal phosphorylation of tau protein and synaptic dysfunction compared to individuals without the allele. Existing therapeutic approaches have primarily focused on antibody-based therapies that target and remove accumulated proteins. However, these approaches have limitations in reversing damage to already affected neurons and addressing the underlying cause of the disease.
Consequently, gene editing research targeting genetic risk factors has gained attention. In particular, allele-specific correction, which converts the APOE4 gene into the safer APOE3 allele, has emerged as a potential alternative. The first-generation CRISPR-Cas9 gene editing system carries the risk of causing unintended mutations by cleaving double-stranded DNA. Therefore, there is a need for the introduction of next-generation gene editing technologies that can precisely correct single base pairs with high safety.
Key Findings
The researchers developed a new solution by optimizing the prime editing technology, which precisely rewrites genetic information without cleaving the double-stranded genome. They optimized an APOE4-targeting prime editing guide RNA (pegRNA) to develop an allele-specific system called 'PE7'. PE7 directly targets the Alzheimer's risk allele APOE4 and converts it into the lower-risk APOE3 variant without off-target side effects.
The researchers confirmed the efficacy of PE7 in an APP/APOE4 knock-in (KI) mouse model. After treatment, the levels of ApoE4 protein in the mouse brain decreased, and the accumulation of Aβ42 and the phosphorylation of tau protein were reduced. The activation of the ERK1/2 (Extracellular signal-regulated kinase 1/2) pathway, which is directly related to Alzheimer's pathology, was also inhibited. The researchers confirmed that these changes were associated with improved neuronal survival and enhanced cognitive function.
The therapeutic efficacy was also consistently observed in human cells. PE7 was applied to human induced neurons derived from skin fibroblasts of APOE3/4 heterozygous Alzheimer's patients. As a result, the allele was successfully corrected, and amyloid and tau pathologies were controlled, demonstrating that the system can effectively function in the treatment setting of actual patients.
Significance and Prospects
This research demonstrates the potential of a therapeutic strategy that targets and corrects APOE4, the major genetic factor for Alzheimer's disease. The absence of off-target side effects, which is essential for ensuring safety in brain cell therapy, is encouraging. The mechanism proposed by the researchers provides a new milestone for the prevention and treatment of Alzheimer's disease.
However, there are challenges that need to be overcome before clinical application. It is necessary to verify whether the high correction efficiency and safety observed in animal and in vitro cell models are consistently maintained in actual human brain tissue. Furthermore, the development of a drug delivery system (DDS) to deliver the drug to the target site is also essential. The development of a precise delivery system that can cross the blood-brain barrier (BBB) and deliver the prime editor to specific neurons will be the key to future commercialization.
The apolipoprotein E4 (APOE4) allele is the strongest genetic risk factor for sporadic Alzheimer's disease (AD), driving Aβ accumulation, tau pathology, and synaptic dysfunction. Allele-specific correction of APOE4 represents a promising therapeutic strategy to mitigate disease progression. In this study, we developed an APOE4-specific prime editing strategy based on an optimized APOE4-targeting pegRNA, enabling precise and efficient conversion of the APOE4 allele to the lower-risk APOE3 variant. We found that PE7 targeting the APOE4 allele achieved robust and specific editing without detectable off-target effects. This correction reduced ApoE4 protein levels and attenuated key AD-related pathologies, including Aβ42 accumulation, tau phosphorylation, and activation of the ERK1/2 pathway in APP/APOE4 knock-in (KI) mice. Notably, PE7 treatment enhanced neuronal survival and improved cognitive performance in these mice. Furthermore, in human induced neurons derived from APOE3/4 heterozygous AD patient fibroblasts, PE7 consistently corrected the APOE4 allele and suppressed both amyloid- and tau-associated pathologies. These findings establish PE7-mediated APOE4 correction as a precise and efficient therapeutic genome-editing strategy with translational potential for sporadic AD.
The gene editing technology presented in this study can be specifically utilized in future early preventive treatment scenarios for Alzheimer's disease. This involves administering PE7 as a one-time gene therapy to high-risk individuals identified through genetic testing as carrying the APOE4 allele before the onset of symptoms. By converting the APOE4 gene in brain cells to APOE3, it may be possible to design a scenario that prevents the onset of Alzheimer's disease. In clinical practice, it is also considered a new alternative that can overcome the frequent administration schedule and high cost associated with existing antibody therapies. Gene editing-based fundamental genetic modification can induce long-term brain function protection with a single or minimal number of treatments. Industrially, it is expected to significantly increase the speed of development of new pipelines in the Alzheimer's disease therapeutic market by linking the prime editing system with effective drug delivery platforms.