Hyperbilirubinemia and phototherapy differentially alter hippocampal transcriptomic patterns in a Gunn rat model of neonatal hyperbilirubinemia.

Neonatal hyperbilirubinemia (jaundice) is common in infants, with extremely preterm infants (EPT, <28 weeks gestational age) being at high risk for bilirubin-induced neurotoxicity, resulting in neurodevelopmental impairment. Hyperbilirubinemia is treated using phototherapy to lower unconjugated bilirubin levels. However, the benefits and risks of phototherapy in EPTs have not been well studied, and bilirubin at low levels may be protective as an antioxidant. Phototherapy is associated with markers of oxidative stress in the plasma, but the effects of phototherapy on the hippocampus (HPC) are not known. Bilirubin and insults associated with EPTs impair hippocampal development, a brain structure critical for cognitive function, but their underlying mechanisms remain unknown. The effects of hyperbilirubinemia and phototherapy on the HPC were studied using a Gunn rat model. Jaundiced (jj) and non-jaundiced (Nj) pups were subjected to phototherapy from postnatal day 4 (P4) through P6. The HPC was harvested and processed for RNA sequencing. Serum bilirubin levels were elevated in jj compared to Nj control rats. Phototherapy significantly lowered serum bilirubin levels in jj rats. Compared to Nj rats, 1294 genes were differentially expressed in the jj hippocampal transcriptome and mapped onto the nervous system development, inflammation, and ferroptosis signaling pathways. Phototherapy induces 3297 differentially-expressed genes (DEGs) in rat hippocampal transcriptome compared to untreated rats. These DEGs were annotated to pathways regulating synaptogenesis, long-term potentiation, and neurogenesis. Both hyperbilirubinemia and phototherapy altered expression of 407 genes, which mapped onto hippocampal plasticity functions, including neuritogenesis and long-term potentiation. Our study demonstrates a model for investigating molecular effects of hyperbilirubemia and phototherapy in an EPT-equivalent Gunn rat pup. Our data revealed the effects of hyperbilirubinemia and phototherapy on signaling pathways critical for hippocampal development and plasticity.新生儿高胆红素血症（Neonatal hyperbilirubinemia，即黄疸）在婴幼儿中较为常见，其中极早早产儿（EPT，胎龄<28周）面临极高的胆红素诱导神经毒性风险，进而引发神经发育损害。高胆红素血症的常规治疗手段为光疗，以降低未结合胆红素水平。然而，针对极早早产儿的光疗获益与风险尚未得到充分研究，且低浓度胆红素可作为抗氧化剂发挥保护作用。光疗会与血浆中的氧化应激标志物相关联，但光疗对海马体（Hippocampus, HPC）的影响尚不明确。胆红素及极早早产儿相关的损伤因素会损害海马体发育——这一脑结构对认知功能至关重要，但其潜在分子机制仍未阐明。本研究通过古恩大鼠（Gunn rat）模型，探究了高胆红素血症与光疗对海马体的影响：将黄疸型（jj）与非黄疸型（Nj）幼鼠从出生后第4天（P4）至第6天（P6）进行光疗处理，随后获取海马体组织并开展RNA测序（RNA sequencing）。结果显示，与非黄疸型对照大鼠相比，黄疸型大鼠的血清胆红素水平显著升高，而光疗可显著降低黄疸型大鼠的血清胆红素水平。与非黄疸型大鼠相比，黄疸型大鼠的海马转录组中共存在1294个差异表达基因，这些基因富集于神经系统发育、炎症及铁死亡（ferroptosis）信号通路。与未接受光疗的大鼠相比，光疗可诱导大鼠海马转录组中3297个差异表达基因（differentially-expressed genes, DEGs），这些差异表达基因被注释到调控突触发生、长时程增强及神经发生的信号通路中。高胆红素血症与光疗共同调控了407个基因的表达，这些基因富集于海马可塑性相关功能通路，包括神经突生长与长时程增强。本研究构建了可用于探究模拟极早早产儿状态下高胆红素血症与光疗分子效应的古恩幼鼠模型，研究数据揭示了高胆红素血症与光疗对海马发育及可塑性相关关键信号通路的调控作用。