VSX2

Scientists have achieved a significant research milestone in the field of spinal cord injuries -- mapping out the cellular and molecular dynamics of paralysis in unprecedented detail with their open-source project 'Tabulae Paralytica'. Gr goire Courtine and his team have integrated cutting-edge cell and molecular mapping technologies with artificial intelligence to chart the complex molecular processes that unfold in each cell after spinal cord injuries (SCI). This seminal work not only identifies a specific set of neurons and genes that plays a key role for recovery but also proposes a successful gene therapy derived from its discoveries. Scientists at EPFL have achieved a significant research milestone in the field of spinal cord injuries -- mapping out the cellular and molecular dynamics of paralysis in unprecedented detail with their open-source project 'Tabulae Paralytica'. Grégoire Courtine and his team have integrated cutting-edge cell and molecular mapping technologies with artificial intelligence to chart the complex molecular processes that unfold in each cell after spinal cord injuries (SCI). Published in Nature, this seminal work not only identifies a specific set of neurons and genes that plays a key role for recovery but also proposes a successful gene therapy derived from its discoveries. Understanding why spinal cord injuries are nearly impossible to heal sheds light on the significance of this breakthrough. The human spinal cord is one of the most complex biological systems known to science -- it is a mechanical, chemical, and electrical arrangement of different types of cells working in harmony to produce and regulate a multitude of neurological functions, including a natural, elegant gait. This cellular complexity amplifies the challenges to effectively treating paralysis caused by injury to the spinal cord. Until now, traditional imaging and mapping methods have offered a generalized view of the cellular mechanisms of SCI. But this lack of specificity blurs the distinct roles and reactions of individual cell types and has hindered the development of targeted treatments, as therapies could not be finely tuned to address specific cellular dynamics. "In this study, we aimed for nothing less than a revolution in the biological understanding of spinal cord injury," says Courtine. "By offering an exceptionally detailed view of the cellular and molecular dynamics of spinal cord injury in mice across space and time, the four cell atlases comprising the Tabulae Paralytica close a historic knowledge gap, paving the way for targeted treatments and enhanced recovery." The first treatment to come from this new understanding of the intricate cellular dynamics of paralysis is a targeted gene therapy. Developed in collaboration with fellow EPFL Neuro X professor Bernard Schneider, the therapy leverages a crucial finding: the researchers found that a specific type of support cell called an astrocyte loses its ability to respond to injury in aged animals. "For much of the last hundred years, it was believed that astrocytes were detrimental to neural repair. Our data further supports overturning this notion and suggests an essential protective role for these cells that can be exploited to repair spinal cord injuries," says EPFL's Mark Anderson, senior author of the study. Another key result of the study is the identification of a specific subset of neurons, known as Vsx2 neurons, that are inherently equipped to promote recovery. "Our previous studies have pointed in their direction, but with this new, fine-tuned understanding, we can now say for certain that Vsx2 neurons are largely responsible for neural circuit reorganization, meaning that they are by far the most interesting population of neurons for repairing spinal cord injury," asserts Jordan Squair, another senior author of the study from EPFL. To create the first-ever comprehensive cellular map of spinal cord injuries in rodent models, the researchers employed two innovative technologies. The first, single cell sequencing, examines the genetic makeup of each cell. While it has been employed for over a decade, recent advances allowed the scientists to scale up the process like never before, generating detailed accounts of millions of spinal cord cells. Secondly, spatial transcriptomics -- a cutting-edge technology that shows us where these cellular activities occur -- expanded the map across the entire spinal cord, preserving the spatial context and relationships between different cell types. The new data is so vast that new machine learning techniques needed to be developed specifically to harness its intricacy. This computational approach leverages artificial intelligence to not only chart the immediate genetic responses of individual cells but also situate these responses within the physical and temporal landscape of the spinal cord. "We now have a detailed map that not only shows us which cells are involved but also how they interact and change over the course of the injury and recovery process," explains Squair. "This comprehensive understanding is crucial for developing treatments that are precisely tailored to specific cells and unique requirements for repair of varying injuries, paving the way for more effective and personalized therapies." The 'Tabulae Paralytica' is a significant milestone in SCI research. It combines scientific insight with technological innovation to open new horizons in the understanding and treatment of SCI. Although this study has been conducted using rodent models, the insights gained are expected to translate into clinical applications, where Courtine and his team have been making significant advances for over a decade.

A group of nerve cells in the brain has the remarkable ability to completely stop all forms of movement, a new mouse study shows. The discovery provides valuable insight into how the nervous system can control our movements. When a hunting dog picks up the scent of a deer, it sometimes freezes. On the spot. The same thing can happen to people who need to concentrate on a challenging task. Now researchers have made a discovery that adds to our knowledge of what happens in the brain when we suddenly stop moving. "We have found a group of nerve cells in the midbrain which, when stimulated, stop all movement. Not just walking; all forms of motor activity. They even make the mice stop breathing or breathe more slowly, and the heart rate slow down," explains Professor Ole Kiehn, who is co-author on the study. "There are various ways to stop movement. What is so special about these nerve cells is that once activated they cause the the movement to be paused or freeze. Just like setting a film on pause. The actors movement suddenly stop on the spot," says Ole Kiehn. When the researchers ended activating the nerve cells, the mice would start the movement exactly where it stopped. Just like when pressing "play" again. "This 'pause-and-play pattern' is very unique; it is unlike anything we have seen before. It does not resemble other forms of movement or motor arrest we or other researchers have studied. There, the movement does not necessarily start where it stopped, but may start over with a new pattern," says PhD Haizea Goñi-Erro, who is first author of the study. The nerve cells stimulated by the researchers are found in the midbrain in an area called the pedunculopontine nucleus (PPN), and they differ from other nerve cells there by expressing a specific molecular marker called Chx10. The PPN is common to all vertebrates including humans. So even though the study was performed in mice, the researchers expect the phenomenon to apply to humans too. Not related to fear Some might suggest that the nerve cells are activated by fear. Most people are familiar with the phenomenon of "freezing" caused by extreme fear. But that is not the case. "We have compared this type of motor arrest to motor arrest or freezing caused by fear, and they are not identical. We are very sure that the movement arrest observe here is not related to fear. Instead, we believe it has something to do with attention or alertness, which is seen in certain situations," says Assistant Professor Roberto Leiras, who is co-author of the study. The researchers believe it is an expression of a focused attention. However, they stress that the study has not revealed if this is indeed the case. It is something that requires more research to demonstrate. May be able to explain some Parkinson's symptoms The new study may be able to help us understand some of the mechanisms of Parkinson's disease. "Motor arrest or slow movement is one of the cardinal symptoms of Parkinson's disease. We speculate that these special nerve cells in PPN are over-activated in Parkinson's disease. That would inhibit movement. Therefore, the study, which primarily has focused on the fundamental mechanisms that control movement in the nervous system, may eventually help us to understand the cause of some of the motor symptoms in Parkinson's disease," Ole Kiehn concludes. The study is funded by the Novo Nordisk Foundation, the Lundbeck Foundation and the Swedish Research Council.

瘫痪，一个沉重的字眼，给患者自身及其家庭带来的创伤是巨大的。造成瘫痪最常见的原因是脊髓损伤，其导致大脑和脑干投射到脊髓的通路被中断，从而导致瘫痪，这种自上而下通路的损伤基本是不可逆的。 瘫痪，一个沉重的字眼，给患者自身及其家庭带来的创伤是巨大的。造成瘫痪最常见的原因是脊髓损伤，其导致大脑和脑干投射到脊髓的通路被中断，从而导致瘫痪，这种自上而下通路的损伤基本是不可逆的。 科学家们想了很多办法试图使瘫痪患者能够重新站起来，比如干细胞治疗[1]和外骨骼机器人[2]等，但要使完全瘫痪患者实现独立行走还是十分困难的。 2018年，来自瑞士洛桑联邦理工学院的神经学家Grégoire Courtine及其团队报道通过硬膜外电刺激（EES）与康复训练相结合，使得三名严重运动障碍或完全瘫痪的脊髓损伤患者（下肢有部分感觉）能够拄拐甚至独立行走[3]，但这项技术对连感觉也完全丧失的脊髓损伤患者是否有效并不明确。同时，EES起效的内在机制也未得到深入分析。 近日，Grégoire Courtine团队联合同单位的Jordan W. Squair和Jocelyne Bloch团队再次在《自然》杂志发文，报道了EES技术的最近进展[4]。研究表明，EES技术对于下肢失去所有感觉的瘫痪患者同样有效，试验纳入的9位患者中3位完全瘫痪且腿部无任何感觉，在EES开启后，患者的行走功能可立刻获得改善或恢复。 在进行EES治疗联合康复训练5个月后，9位患者在EES开启和稳定装置辅助下可抵抗自身重力行走，且有4位在EES关闭情况下也恢复了行走能力。研究人员还找到了对重获行走能力起到关键作用的特定神经元亚群。 《自然》杂志同期对该研究的评论表示，该项技术将为脊髓损伤瘫痪患者带来巨大的希望[5]。 论文首页截图 该研究首先在9位脊髓损伤造成的瘫痪患者中再次验证了EES治疗联合康复训练（EES+康复训练）恢复行走功能的安全性和可行性（NCT02936453）。在这9位患者中，有6位患者表现出严重或完全的运动功能障碍，但保留了一定程度的腿部感觉，剩下的3位患者表现出完全的感觉运动障碍。 在将神经刺激器植入到患者脊髓背根神经处并开启EES后，9位患者均能够在机器人辅助下改善或恢复行走能力，并可在EES开启时按照自己的抑制控制步幅的幅度。 EES装置示意图及EES开启时患者部分恢复行走能力 在为期5个月的EES+康复训练治疗期间（包括每周4到5次开启EES进行站立、行走和各种锻炼），随着时间的推移，患者承重行走能力明显提高，有4位患者在EES关闭的情况下也能恢复行走。这些均表明EES+康复训练治疗可有效恢复瘫痪患者的行走功能，无论其感觉功能是否完全丧失。 行走功能的恢复必然涉及到脊髓功能的重塑，因此，为了检测EES+康复训练前后脊髓神经元活动的改变，研究人员使用了18F-氟脱氧葡萄糖摄取正电子发射断层扫描（18FDG-PET）来量化 EES+康复训练前后脊髓代谢活动的改变。出乎意料的是，EES+康复训练导致在行走时腰髓神经元活动减少。 EES+康复训练导致在行走时脊髓神经元活动减少 这种腰髓神经元活动的减少表明EES+康复训练重塑了脊髓神经元对于行走的响应，引导负责瘫痪后恢复行走功能的特定神经元亚群的选择性激活。 为了找到这一特定的神经元亚群，研究人员构建了相应的小鼠模型，以复制人类中EES+康复训练的关键技术和治疗特征。 小鼠在受到中段胸髓的损伤后，皮质脊髓束中断，同时损伤平面以下的谷氨酸能脊髓网状纤维也受到严重影响，导致永久性瘫痪。为了模拟EES+康复训练治疗，研究人员设计了小鼠专用的脊髓刺激装置和康复辅助机器人。 小鼠脊髓损伤模型及小鼠专用的脊髓刺激装置和康复辅助机器人 和在人类中观察到的现象一致，EES开启后，在机器人辅助下，小鼠立即恢复行走能力。而在进行EES+康复训练治疗后，所有小鼠的行走能力均有提升，且在EES关闭时，行走功能的恢复仍然存在。同时，在EES+康复训练治疗后，小鼠脊髓在行走时激活的神经元数量同样明显减少。 这些结果均表明该小鼠模型可复刻在人类中实现EES+康复训练的关键技术和治疗特征，为识别负责瘫痪后恢复行走功能的特定神经元亚群创造了条件。 研究人员通过对小鼠不同康复状态下的脊髓进行单核RNA测序和空间转录组分析，并借助机器学习算法，找到了对重获行走能力起到关键作用的两个特定神经元亚群，分别以表达Vsx2和Hoxa10为特征（Vsx2::Hoxa10 SC）。 通过单核RNA测序和空间转录组分析找到对重获行走能力起到关键作用的特定神经元亚群 通过跨突触追踪技术，研究人员发现Vsx2::Hoxa10 SC神经元接受背根神经节神经元和脊髓网状纤维神经元的直接突触投射，而这两者对行走功能至关重要，而EES+康复训练治疗后这两处的神经元到Vsx2::Hoxa10 SC神经元的突触投射密度大大增加。 紧接着，为了验证Vsx2::Hoxa10 SC神经元是EES+康复训练治疗后瘫痪患者行走功能恢复的关键，研究人员分别通过光遗传学和化学遗传学抑制了Vsx2::Hoxa10 SC神经元的活动，在该类神经元被抑制后，开启EES导致的行走功能恢复也被抑制。相反，Vsx2::Hoxa10 SC神经元的激活可模拟出小鼠行走功能恢复的表现，无论EES是开启还是关闭。 通过光遗传学和化学遗传学验证Vsx2::Hoxa10 SC神经元是EES+康复训练治疗后瘫痪患者行走功能恢复的关键 总的来说，本研究再次证实了EES可恢复瘫痪患者行走功能，并首次阐明了其内在机制，该技术对脊髓损伤患者来说无疑是“夜空中一颗明亮的星辰”。通过与干细胞疗法结合，增强关键神经元亚群Vsx2::Hoxa10 SC神经元的功能，或可增强EES的疗效。 此外，除了步行功能，膀胱控制、排泄控制和性功能的丧失同样对脊髓损伤患者的生活质量产生巨大的影响，这些功能是否也可通过EES来进行改善呢？这些都需要进一步的研究。 参考文献 1.Curtis E, Martin JR, Gabel B, Sidhu N, Rzesiewicz TK, Mandeville R, Van Gorp S, Leerink M, Tadokoro T, Marsala S et al: A First-in-Human, Phase I Study of Neural Stem Cell Transplantation for Chronic Spinal Cord Injury. Cell Stem Cell 2018, 22(6):941-950 e946. 2.Burton A: Expecting exoskeletons for more than spinal cord injury. Lancet Neurol 2018, 17(4):302-303. 3.Wagner FB, Mignardot JB, Le Goff-Mignardot CG, Demesmaeker R, Komi S, Capogrosso M, Rowald A, Seanez I, Caban M, Pirondini E et al: Targeted neurotechnology restores walking in humans with spinal cord injury. Nature 2018, 563(7729):65-71. 4.Kathe C, Skinnider MA, Hutson TH, Regazzi N, Gautier M, Demesmaeker R, Komi S, Ceto S, James ND, Cho N et al: The neurons that restore walking after paralysis. Nature 2022, 611(7936):540-547. 5.https://doi.org/10.1038/d41586-022-03605-8