Glymphatic dysfunction contributes to thalamic iron retention and secondary thalamic injury after stroke: evidence from primates and rodents

Secondary neurodegeneration, characterized by neuronal loss and neuroinflammation, in the remote thalamus is associated with post-stroke cognitive impairment (PSCI). This study aimed to elucidate common pathological mechanism of the secondary neurodegeneration in both primates and rodents. Thalamic amyloid-β (Aβ), iron deposition and glymphatic dysfunction was assessed across primate and rodent stroke models in different time points, using histopathological, and magnetic resonance imaging methods. Proteomic analysis was performed to explore the molecular mechanisms underlying the secondary thalamic damage. Neuronal loss and neuroinflammation were assessed through histopathological methods. Using aquaporin-4 (AQP4) inhibitor, we investigated whether glymphatic inhibition aggravated thalamic iron deposition and PSCI. Aβ accumulated in the remote thalamus of mice but was absent in cynomolgus monkeys by imaging and histology, and Aβ40/42 remained unchanged in plasma and cerebrospinal fluid in monkeys following stroke. Instead, quantitative susceptibility mapping MRI and Prussian blue staining uncovered progressive iron deposition in the remote thalamus shared by both species, alongside ferroptosis activation. Glymphatic imaging and AQP4 analyses showed impaired glymphatic clearance and loss of AQP4 perivascular polarization, which worsened along with time. Both stroke monkeys and mice exhibited neuronal injury and increased neuroinflammation in the remote thalamus, with cognitive impairment. Glymphatic inhibition with TGN-020 exacerbated iron deposition and ferroptosis, leading to more severe neuronal loss and microglial proliferation, ultimately aggravating PSCI. In addition, CD31 and ZO-1 co-immunostaining demonstrated blood-brain-barrier damage, with reduced ZO-1 colocalization with CD31. Iron deposition and ferroptosis-related changes were consistently observed in the remote thalamus across both rodent and primate models, whereas Aβ accumulation appeared to be species-dependent. Glymphatic dysfunction and blood-brain barrier damage in the remote thalamus may jointly facilitates iron accumulation and ferroptosis.