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 t Show more
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
The central nervous system is involved in regulation of defaecation. It is generally considered that supraspinal regions control the spinal defaecation centre. However, signal transmission from supras Show more
The central nervous system is involved in regulation of defaecation. It is generally considered that supraspinal regions control the spinal defaecation centre. However, signal transmission from supraspinal regions to the spinal defaecation centre is still unclear. In this study, we investigated the regulatory role of an anorexigenic neuropeptide, α-MSH, in the spinal defaecation centre in rats. Intrathecal administration of α-MSH to the L6-S1 spinal cord enhanced colorectal motility. The prokinetic effect of α-MSH was abolished by severing the pelvic nerves. In contrast, severing the colonic nerves or thoracic cord transection at the T4 level had no impact on the effect of α-MSH. RT-PCR analysis revealed MC1R mRNA and MC4R mRNA expression in the L6-S1 spinal cord. Intrathecally administered MC1R agonists, BMS470539 and SHU9119, mimicked the α-MSH effect, but a MC4R agonist, THIQ, had no effect. These results demonstrate that α-MSH binds to MC1R in the spinal defaecation centre and activates pelvic nerves, leading to enhancement of colorectal motility. This is, to our knowledge, the first report showing the functional role of α-MSH in the spinal cord. In conclusion, our findings suggest that α-MSH is a candidate for a neurotransmitter from supraspinal regions to the spinal defaecation centre. Show less