Synj 1 modulates functional recovery after motor-incomplete spinal cord injury in male mice carriers of human ApoE4.. Synj 1 modulates functional recovery after motor-incomplete spinal cord injury in male mice carriers of human ApoE4.

Apolipoprotein E epsilon 4 (ApoE4) is the second most common variant of ApoE, being present in ~14% of population. Clinical reports identify ApoE4 as a genetic risk factor for poor outcomes after traumatic SCI and the spinal cord disease (SCD) cervical myelopathy. To date, there are no interventions to mitigate the potent effects of ApoE4 to reduce recovery of function after SCI/D. Studies in human and mouse brain link ApoE4 to elevated levels of synaptojanin 1 (synj1), a lipid phosphatase that dephosphorylates phosphoinositol 4,5-bisphosphate (PIP2) to inositol 4-monophosphate (PIP1). Synj1 regulates rearrangements of the cytoskeleton and the endocytosis and trafficking of synaptic vesicles. We report here that, as compared to ApoE3 mice, levels of synj1 mRNA and protein were elevated in spinal cords from healthy ApoE4 mice associated with lower PIP2 levels. Using a moderate severity model of contusion SCI in mice, we found that genetic reduction of syn1 improved locomotor function recovery at 14 days after SCI in ApoE4 mice without altering spared white matter. Genetic reduction of synj1 did not alter locomotor recover of ApoE3 mice after SCI. Bulk RNA-sequencing revealed that at 14 days after SCI in ApoE4 mice, genetic reduction of synj1 upregulated genes involved in glutaminergic synaptic transmission just above and below the lesion. Overall, our findings provide evidence for a link between synj1 to poor outcomes after SCI in ApoE4 mice through mechanisms that remain speculative but may include greater function of excitatory glutaminergic synapses. Overall design: At 4 months of age, male mice expressing human ApoE3 or ApoE4 variants, that either had one inactive synj1 allele (synj1+/-) or two normal synj1 alleles (synj1+/+), were subjected to a motor-incomplete spinal cord contusion or a laminectomy (sham) at level of thoracic vertebrae T9. At 14 days post-surgery, spinal cord tissues from three animals per group were collected immediately rostral or caudal from the lesion epicenter, and were used for total RNA extraction and later bulk RNA seq studies.

载脂蛋白Eε4（Apolipoprotein E epsilon 4, ApoE4）是载脂蛋白E（Apolipoprotein E, ApoE）的第二常见变异体，在人群中的携带率约为14%。临床研究证实，ApoE4是创伤性脊髓损伤（spinal cord injury, SCI）及脊髓疾病（spinal cord disease, SCD）性颈椎脊髓病（cervical myelopathy）预后不良的遗传风险因子。截至目前，尚无有效干预手段可削弱ApoE4对脊髓损伤/疾病（SCI/D）后功能恢复的不利影响。针对人类与小鼠大脑的相关研究表明，ApoE4会升高突触多磷酸肌醇磷酸酶1（synaptojanin 1, synj1）的表达水平——该酶属于脂质磷酸酶家族，可将磷脂酰肌醇4,5-二磷酸（phosphoinositol 4,5-bisphosphate, PIP2）去磷酸化为肌醇4-单磷酸（inositol 4-monophosphate, PIP1）。Synj1可调控细胞骨架重排、突触囊泡的内吞与转运过程。本研究发现，与表达ApoE3的小鼠相比，健康ApoE4小鼠的脊髓组织中synj1 mRNA与蛋白水平显著升高，同时伴随PIP2水平降低。利用小鼠中度挫伤型脊髓损伤模型，我们观察到：在ApoE4小鼠中，敲除一个synj1等位基因（synj1+/-）可改善脊髓损伤后14天的运动功能恢复，且未改变残存白质的含量；而敲除synj1并不会对ApoE3小鼠脊髓损伤后的运动功能恢复产生影响。批量RNA测序（bulk RNA-sequencing）结果显示，在ApoE4小鼠脊髓损伤后14天，敲除synj1可上调损伤灶头侧与尾侧紧邻区域中参与谷氨酸能突触传递的基因。综上，本研究结果证实，在ApoE4小鼠中，synj1与脊髓损伤后的不良预后存在关联，其具体机制尚待阐明，但可能涉及兴奋性谷氨酸能突触功能的增强。实验总体设计：选取4月龄的雄性小鼠，其分别表达人源ApoE3或ApoE4变异体，且要么携带一个失活的synj1等位基因（synj1+/-），要么携带两个正常的synj1等位基因（synj1+/+）；对所有小鼠在胸椎T9节段实施运动功能不全性脊髓挫伤手术，或仅进行椎板切除术作为假手术对照。术后14天，采集每组3只动物的脊髓组织，分别取自损伤中心的紧邻头侧与尾侧区域，提取总RNA后开展批量RNA测序分析。