Introduction: Our previous study indicated that blood-brain barrier (BBB) disruption occurred secondary to hypoxia-induced and MMP-mediated neuroinflammatory white matter (WM) damage in spontaneously hypertensive/stroke prone rats (SHR/SP). Tight junction proteins (TJPs) maintain the normal BBB functions. Here, we investigated the effects of hypoxia on TJP degradation and hypoxia-induced angiogenesis, and tested the effect of long-term minocycline treatment on the BBB integrity and repair.
Methods: Male SHR/SPs at 12W (weeks) old were subjected to unilateral carotid artery occlusion (UCAO) and fed a Japanese permissive diet (JPD) for 4W. For the treatment study, the SHR/SP/UCAO/JPD were given minocycline (50 mg/kg in DMSO, i.p.) and the vehicle rats received DMSO from 12W to 20W of life.
Results: Sham-operated SHR/SP with normal chow had abnormal TJPs in blood vessels (BVs) at 16W compared to Wistar; they showed a slight increase of BBB permeability and NG2-positive microglia in WM. In the UCAO/JDP group, by 4W, multimodal MRI (T2, ADC, FA, and ASL) showed that WM damage of varying degree reflected the extent of injury corresponding to variable BBB leakage by dynamic contrast-enhanced MRI and IgG staining. TJP levels (claudin-5, occludin, and ZO-1) in WM were significantly decreased. Angiogenesis in WM was detected with increased expression of Ki67 and NG2 in vascular endothelial cells and/or pericytes. UCAO/JPD typically causes the death of SHR-SP/JPD/UCAO rats after 4W. However, minocycline treatment extended survival to 9W after UCAO/JPD and significantly reduced lesion size and vascular damage. TJPs, VEGF-A, and GST-π (mature oligodendrocytes) were increased by minocycline at 8W compared to sham and vehicle. Minocycline also increased the expression of factors involved in angiogenesis and WM repair (Ki67, NG2, MMP-2, MMP-3) in vascular endothelial cells, pericytes, astrocytes, and oligodendrocytes compared to controls.
Conclusions: Our results support the hypothesis that damage to the BVs by chronic hypertension and UCAO/JPD produces TJP degradation and increases BBB permeability. Minocycline treatment significantly protects WM from damage by preventing BBB disruption and enhances TJP formation and angiogenesis.