The role of CELF2 and its genetic variants in Alzheimer's disease

Age is the most important risk factor for Alzheimer's disease (AD), but the occurrence of this disease is also affected by environmental factors, individual experience and genetic pre-deposition. Genetic factors are well established to play an important role in risk of AD. CELF2, an RNA binding protein that regulates alternative splicing and RNA stability, has been recently identified as a risk factor associated with AD. Polymorphisms in CELF2 are significantly associated with high-risk alleles of APOE, and the “A” allele of SNP rs2242451 is associated with reduced AD risk. CELF2 is highly expressed in the nervous system, and enhanced neuronal CELF2 expression levels have been found in various neurodegeneration models and human patients. We generated a conditional knockout mouse Celf2 allele. Our preliminary data suggest that deleting Celf2 in adult brain has beneficial effects, including improved learning and memory. We identified mRNA targets of mouse CELF2 (using CLIP-seq; cross-linking immunoprecipitation high-throughput sequencing) and found that CELF2 binds to introns around the alternatively spliced exons of a set of AD- regulated genes, including APP, MAPT (Tau), PSEN1, PSEN2, and BIN1, suggesting a key role of CELF2 in regulating alternative splicing of AD-related genes. Alternative splicing of these AD-related genes is known to regulate AD pathogenesis. For example, alternative splicing of exon 10 of the tau mRNA gives rise to protein isoforms with three (3R) or four (4R) microtubule binding repeats. Imbalances in 4R: 3R ratio alone have been reported sufficient to induce the pathogenesis of AD in a human-Tau mouse model. Taken together with the genetic association between CELF2 SNP and reduced AD risk in humans, we hypothesize that CELF2 expression is up-regulated in AD brains and loss of CELF2 in adult brains is sufficient to rescue AD-related phenotypes. In Specific Aim 1, we will test whether loss of CELF2 can suppress AD-related phenotypes in C. elegans AD models. In Specific Aim 2, we will test whether loss of CELF2 in the adult brain is protective through regulating alternative splicing using AD mouse models. In Specific Aim 3, we will test whether CELF2 expression is increased in AD brains using postmortem human samples and ask if the AD risk-reducing SNP down regulates CELF2 expression or inhibits its function using human iPSC-derived neurons. We have obtained postmortem brain samples and established a strong research team with expertise in genetics, genomics, postmortem AD brains and iPSC. Data from the proposed work will provide important mechanistic insights that go well beyond published human genetic analyses and ultimately yield new therapeutic targets for the treatment of AD.