👤 Yusuke Sotomaru

APOE polymorphisms are major genetic risk factors of Alzheimer's disease (AD). Compared with APOE3/E3, the APOE4/E4 genotype is associated with a > 14-fold increased risk. Therefore, we hypothesized that conversion of APOE4 to APOE3 would ameliorate AD-related pathologies. Accordingly, we generated a knock-in mouse model harboring an APOE4-FLEx (Flip-Excision) 4-to-3 construct enabling postnatal Cre-mediated APOE4-to-APOE3 switching. This construct comprised an APOE3 exon inserted in a reverse orientation downstream of the APOE4 exon, flanked by alternating loxP and mutant loxP sites, allowing Cre-mediated FLEx switching from APOE4-to-APOE3. For in vitro validation, HEK293T cells were transfected with APOE4-FLEx 4-to-3 plasmid, followed by AAV8-mediated iCre delivery. For in vivo studies, endogenous Apoe was replaced with the APOE4-FLEx 4-to-3 construct to generate APOE4-FLEx 4-to-3 knock-in mice, which were crossed with tamoxifen-inducible Rosa26-CreERT2 mice to yield Cre: APOE4-FLEx 4-to-3 double-knock-in mice. Tamoxifen was administered to induce APOE switching. Cre expression successfully induced APOE4-to-APOE3 switching in vitro. Tamoxifen administration in Cre: APOE4-FLEx 4-to-3 mice triggered APOE4-to-APOE3 switching in the liver, demonstrating the feasibility of postnatal isoform switching. However, brain APOE protein levels were below the detection limit. Investigation of the underlying cause involving transcript analysis revealed aberrant retention of intron 3 (APOE-I3). This abnormal splicing probably contributed to the decreased expression of fully spliced, translation-competent (mature) APOE mRNA, driving the subsequent protein reduction. Although APOE expression across organs in APOE4-FLEx 4-to-3 mice requires further optimization, our findings demonstrate that Cre-mediated FLEx switching can serve as a potential strategy to induce APOE genotype switching in vivo. Show less

Neuroblastoma (NB), a common childhood solid tumor, is the leading cause of childhood cancer deaths. Transgelin (TAGLN) is an actin-binding protein of the calponin family, and it is involved in cell motility and migration. The TAGLN gene expression was induced in NB cell lines, such as GOTO, SK-N-SH, and TGW, by gene overexpression using a retroviral Tet-On inducible expression system, and was repressed by RNA interference (RNAi) treatment. TAGLN overexpression repressed cell growth and migration and induced cell arrest and differentiation. On the other hand, RNAi-mediated TAGLN repression activated cell growth. Cells overexpressing TAGLN showed decreased levels of undifferentiated cell markers, such as SOX2, OCT4, KLF4, and ID2. Single-cell analysis after TAGLN overexpression revealed a distinguishable cluster characterized by expression of POSTM, APOE, PDGFRA, IGFBP3, SMAD5, and IGFBP7. In TH-MYCN mice, which have a high frequency of NB development, Tagln overexpression by induction of the murine Tagln gene significantly reduced tumor formation and prolonged survival. In conclusion, these in vitro and in vivo analyses suggest that TAGLN is a candidate tumor suppressor gene in NB. Show less