Cerebrovascular Injuries Induce Lymphatic Invasion into Brain Parenchyma to Guide Vascular Regeneration in Zebrafish

Damage to regional cerebrovascular network and neuronal tissues occurs during acute cerebrovascular diseases, such as ischemic stroke. The promotion of vascular regeneration is the most promising therapeutic approach. To understand cellular and molecular mechanisms underlying brain vascular regeneration, we developed two zebrafish cerebrovascular injury models using genetic ablation and photochemical thrombosis. Although brain parenchyma is physiologically devoid of lymphatic vasculature, we found that cerebrovascular injuries induce rapid ingrowth of meningeal lymphatics into the injured parenchyma. The ingrown lymphatics on one hand become lumenized drain interstitial fluid to resolve brain edema, on the other hand act as 9growing tracks9 for nascent blood vessels. The ingrown lymphatic vessels undergo apoptosis and clearance after cerebrovascular regeneration. This study reveals a pathological function of meningeal lymphatics, through previously unexpected ingrowth into brain parenchyma and a newly identified lymphatic function as vascular 9growing tracks9.