Suppression of 6-pyruvoyl-tetrahydropterin synthase promotes remyelination in multiple sclerosis

Background: Multiple sclerosis (MS) is a CNS autoimmune disease that is characterized by demyelination, neuroinflammation, and neuronal loss. Although current chemotherapies and immunotherapies for MS efficiently mitigate disease activity and relief clinical symptoms, neuroprotection targeting axon/neurons remains therapeutically challenging. Accumulating evidence has suggested that poor oligodendrocyte precursor cell (OPC) proliferation and subsequent migration/differentiation significantly impedes remyelination during MS. However, the molecular mechanisms underlying OPCs dysfunction during MS remain elusive. Methods: Re-analysis of single cell sequencing data from human and mouse oligodendrocyte lineage cells (OLCs), along with staining results from brain sections of MS patients, was conducted to investigate the role of 6-pyruvoyl-tetrahydropterin synthase (PTS) in determining oligodendrocyte fate. To assess PTS function in MS, conditional knockout mice targeting OLCs were employed. Transcriptomic analyses further illuminated the molecular mechanisms through which PTS influences the disease process. Results: PTS in OPCs is a suppressor of OPC proliferation that contributes to demyelination in MS. We found that PTS expression in OPCs was aberrantly increased in patients with MS. Mice lacking Pts specifically in OPCs displayed ameliorated experimental autoimmune encephalitis (EAE) severity, a mouse model of MS, which were accompanied by attenuated demyelination. Moreover, selective suppression of Pts in OPCs facilitated OPC proliferation and remyelination during EAE. Mechanistically, the knockdown of Pts activated the cholesterol biosynthesis pathway leading to enhanced OPC proliferation. Conclusions: Our findings suggest that PTS is a negative regulator of OPC proliferation, and its disinhibition could offer a potential therapeutic target for MS. To investigate the underlying mechanism of PTS-mediated inhibition of OPC proliferation during EAE, we performed RNA sequencing (RNA-seq) analysis on the spinal cord tissue on day 17 following EAE induction.

研究背景：多发性硬化（multiple sclerosis, MS）是一种中枢神经系统（central nervous system, CNS）自身免疫性疾病，以脱髓鞘、神经炎症及神经元丢失为核心病理特征。尽管当前针对MS的化疗与免疫疗法可有效缓解疾病活动度并改善临床症状，但靶向轴突/神经元的神经保护治疗仍存在极大的治疗挑战。越来越多的研究证据表明，少突胶质前体细胞（oligodendrocyte precursor cell, OPC）增殖不足以及后续迁移、分化障碍，会显著阻碍MS进程中的髓鞘再生。然而，MS发生过程中OPC功能异常的分子机制仍未明确。
研究方法：本研究通过重新分析人类与小鼠少突胶质细胞系（oligodendrocyte lineage cells, OLCs）的单细胞测序数据，并结合多发性硬化患者脑组织切片的染色结果，探究6-丙酮酰四氢蝶呤合酶（6-pyruvoyl-tetrahydropterin synthase, PTS）在调控少突胶质细胞命运中的作用。为评估PTS在MS中的功能，本研究构建了靶向OLCs的条件性基因敲除小鼠。转录组学分析进一步阐明了PTS影响疾病进程的分子机制。
研究结果：OPC内的PTS是OPC增殖的抑制因子，会加剧MS中的脱髓鞘病变。我们发现，MS患者的OPC中PTS表达出现异常升高。在特异性敲除OPC中Pts基因的小鼠中，作为MS小鼠模型的实验性自身免疫性脑脊髓炎（experimental autoimmune encephalitis, EAE）的病情严重程度得到显著缓解，同时脱髓鞘病变也有所减轻。此外，在EAE进程中，特异性抑制OPC内的Pts表达可促进OPC增殖与髓鞘再生。从分子机制来看，敲低Pts可激活胆固醇生物合成通路，进而增强OPC的增殖能力。
研究结论：本研究结果表明，PTS是OPC增殖的负向调控因子，解除其对OPC的抑制作用有望成为治疗MS的潜在治疗靶点。为进一步探究EAE进程中PTS介导的OPC增殖抑制的潜在分子机制，我们在EAE诱导后第17天采集脊髓组织进行了RNA测序（RNA-seq）分析。