Abstract
Introduction: A secondary degenerative injury occurs in the thalamus after primary cortical ischemic stroke. This secondary thalamic injury progresses long-term and is associated with somatosensory dysfunctions. Blood-brain barrier (BBB) disruption is one of the feature pathological changes in primary ischemic stroke, but whether BBB disruption happens in the secondary thalamic injury is unclear. In this study, we aim to investigate the BBB changes during the development of secondary thalamic injury after stroke. Methods: Cortical ischemic stroke was generated by permanent occlusion of the left middle cerebral artery on male C57BL6J mice (12-15 weeks). BBB permeability was assessed by Biocytin-TMR (869 Da, 1mg/mL) at post-stroke days (PD) 1, 3, 7, 14, 28, 56, and 84. Immunostainings of CD68 (inflammation) and CD31 (vascular morphology) were performed. Brain sections were imaged with Confocal LSM800 and quantified by NIH ImageJ and Wimasis Image Analysis. BBB permeability related genes were quantified by real-time PCR among naïve, PD7 and PD28. Results: In ipsilesional thalamus (iTH), the Biocytin-TMR was detected as early as PD3 in the secondary thalamic injury area and persisted until at least PD84. The fluorescence intensity of Biocytin-TMR significantly increased during PD28-84 and peaked at PD56, suggesting the BBB is chronically disrupted in iTH. Compared to naïve animals, stroke animals exhibited significant increase in tube length, total number of tubes and total number of branching points at PD56 and PD84. mRNA expression of ZO-2 significantly down-regulated at PD7 and returned to baseline levels by PD28. mRNA of Angiopoietin-1 ( Ang-1 ), VEGFa and Adam10 were significantly increased at PD28. Conclusion: Our data demonstrate that the BBB disruption begins early at PD3 and continues to progress until PD84 in the secondary degenerative thalamus. This BBB disruption is accompanied by changes in blood vessel morphology and permeability related genes. Current studies are examining the expression of key genes at PD56 using qPCR and immunohistochemistry. Our results will elucidate the cellular and molecular changes of BBB disruption involved in thalamic injury, which will provide potential targets for enhancing stroke recovery.
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