Highly dynamic dural sinuses support meningeal immunity

The central nervous system (CNS) is surrounded by three interconnected membranes referred to as the meninges, which host a diverse immune network1-3. Situated within the skull-interfacing dura mater are venous sinuses, which are large veins thought to serve predominantly as passive blood drains for the brain and skull4,5. However, these structures also represent an important neuroimmune interface6-8. Here, we sought mechanistic insights into this interface using intravital microscopy, revealing that the dural sinuses and associated endothelial cells are a highly dynamic surface that constantly restructures to modulate blood flow, fluid movement, and immune surveillance. Specifically, we demonstrate that sinuses are not passive drains but instead constrict and dilate under RAMP1-dependent smooth muscle control similar to arteries. In addition, the murine superior sagittal sinus is bifurcated into an upper and lower chamber, both comprised of specialized, highly fenestrated endothelial cells that allow the movement of fluids, macromolecules, and microbes between the sinus lumen and leukocyte-rich perisinus space. To protect this permeable interface, sinus endothelial cells (SECs) continually open and close their boundaries in a RAMP2-dependent manner. Transcranial RAMP2 antagonism impeded SEC boundary dynamics and immune cell movement along the sinus wall during steady state and after systemic viral infection. Interference with SEC dynamics during viral infection disrupted local antiviral immunity and facilitated pathogen entry into the meninges. These findings demonstrate that dural sinuses are dynamic venous drains with specialized SECs designed to control fluid movement and support both steady state immune surveillance and antiviral immunity. Overall design: Pooled cells representing lower sagittal sinus ("SINUS") and rostral-rhinal hub ("HUB") in mouse were prepared for single cell RNA sequencing and sequenced to an average of 35,000 reads per cell.

中枢神经系统（central nervous system, CNS）被三层相互连接的膜——脑膜（meninges）所包裹，脑膜内存在复杂多样的免疫网络1-3。紧贴颅骨的硬脑膜（dura mater）内分布着静脉窦（venous sinuses），这类大血管曾被认为主要作为脑与颅骨的被动血液引流通路4,5。然而，这些结构同时也是重要的神经免疫界面6-8。本研究借助活体显微镜成像（intravital microscopy）技术，对该界面的作用机制展开探究，结果显示硬脑膜静脉窦及其相关内皮细胞（endothelial cells）是高度动态的结构，能够持续重塑以调节血流、体液流动与免疫监视功能。具体而言，本研究证实静脉窦并非被动引流结构，而是可在RAMP1依赖的平滑肌调控下出现收缩与舒张，这一过程与动脉类似。此外，小鼠的上矢状窦（superior sagittal sinus）可分为上下两个腔室，二者均由特化的高通透性窗孔内皮细胞构成，可允许体液、大分子物质与微生物在静脉窦腔与富含白细胞的窦周间隙之间自由穿梭。为保护这一易通透的界面，静脉窦内皮细胞（sinus endothelial cells, SECs）会以RAMP2依赖的方式持续开闭细胞边界。经颅给予RAMP2拮抗剂，会在稳态及全身性病毒感染期间，抑制SECs的边界动态变化以及免疫细胞沿静脉窦壁的迁移。在病毒感染过程中干扰SECs的动态变化，会破坏局部抗病毒免疫，并促进病原体侵入脑膜。上述研究结果表明，硬脑膜静脉窦是具有特化SECs的动态静脉引流结构，其可调控体液流动，并同时支持稳态免疫监视与抗病毒免疫功能。整体实验设计：将小鼠下矢状窦（"SINUS"组）与吻侧-鼻侧枢纽（"HUB"组）的混合细胞制备为单细胞RNA测序（single cell RNA sequencing）样本，测序平均每个细胞获得35000条读段。