Akbar, D. | Search bioRxiv

bioRxiv2024

Cerebral Venous Blood Flow Regulates Brain Fluid Clearance via Dural Lymphatics

The vascular system regulates brain clearance through arterial blood flow and lymphatic drainage of cerebrospinal fluid (CSF). Idiopathic intracranial hypertension (IIH), characterized by elevated intracranial pressure and dural venous sinus stenoses, can be treated by restoring venous blood flow via venous stenting, suggesting a role for venous blood flow in brain fluid clearance. Using magnetic resonance imaging (MRI) in IIH patients and healthy controls, we identified that dural venous stenoses in IIH were associated with impaired lymphatic drainage, perivenous fluid retention, and brain fluid accumulation. To investigate this further, we developed a mouse model with bilateral jugular vein ligation (JVL), which recapitulated key human findings, including intracranial hypertension, calvarial lymphatic regression, and brain swelling due to impaired clearance. To further dissect the respective roles of dural lymphatics and venous blood flow in brain clearance, we performed JVL in mice with dural lymphatic depletion. These mice exhibited spontaneous elevated intracranial pressure, but JVL did not further exacerbate this effect. Moreover, the synchronous restoration of brain clearance and dural lymphatics observed in mice after JVL was absent in lymphatic-deficient mice.Transcriptomic analyses revealed that lymphatic remodeling induced by JVL was driven by VEGF-C signaling between dural mesenchymal and lymphatic endothelial cells. These findings establish the dural venous sinuses as a critical platform where venous blood flow interacts with mesenchymal cells to preserve dural lymphatic integrity and function, essential for brain fluid clearance.

neuroscience↗

bioRxiv2022

The claudin-like apicomplexan microneme protein is required for gliding motility and infectivity of Plasmodium sporozoites

Invasion of host cells by apicomplexan parasites such as Toxoplasma and Plasmodium spp requires the sequential secretion of the parasite apical organelles, the micronemes and the rhoptries. The claudin-like apicomplexan microneme protein (CLAMP) is a conserved protein that plays an essential role during invasion in Toxoplasma gondii tachyzoites and Plasmodium falciparum merozoites. CLAMP is also expressed in Plasmodium sporozoites, the mosquito-transmitted forms of the malaria parasite, but its role in this stage is still unknown. CLAMP is essential for Plasmodium blood stage growth and is refractory to conventional gene deletion. To circumvent this obstacle and study the function of CLAMP in sporozoites, we used a conditional genome editing strategy based on the dimerisable Cre recombinase in the rodent malaria model parasite P. berghei. We successfully deleted clamp gene in P. berghei transmission stages and analyzed the functional consequences on sporozoite infectivity. In mosquitoes, sporozoite development and egress from oocysts was not affected in conditional mutants. However, invasion of the mosquito salivary glands was dramatically reduced upon deletion of clamp gene. In addition, CLAMP-deficient sporozoites were impaired in cell traversal and productive invasion of mammalian hepatocytes. This severe phenotype was associated with major defects in gliding motility and with reduced shedding of the sporozoite adhesin TRAP. These results demonstrate that CLAMP is essential across invasive stages of the malaria parasite, and strongly suggest that the protein acts upstream of host cell invasion, possibly by regulating the secretion or function of adhesins in Plasmodium sporozoites. Author summaryPlasmodium parasites, the causative agents of malaria, are transmitted during the bite of an infected mosquito. Infectious parasite stages known as sporozoites are released from the insect salivary glands and injected into the host skin. Sporozoites rapidly migrate to the host liver, invade hepatocytes and differentiate into the next invasive forms, the merozoites, which invade and replicate inside red blood cells. Sporozoite motility and host cell invasion rely on the secretion of apical organelles called micronemes and rhoptries. Here we characterize the function of a microneme protein expressed both in merozoites and sporozoites, the claudin-like protein CLAMP. We used a conditional genome editing strategy in a rodent malaria model to generate CLAMP-deficient sporozoites. In the absence of CLAMP, sporozoites failed to invade mosquito salivary glands and mammalian hepatocytes, and showed defects in gliding motility and microneme secretion. Our data establish that CLAMP plays an essential role across Plasmodium invasive stages, and might represent a potential target for transmission-blocking antimalarial strategies.

microbiology↗