TGF-β1 Prevents Blood–brain Barrier Damage and Hemorrhagic Transformation after Thrombolysis in Rats

Transforming growth factor-beta1 (TGF-β1) is well known to promote extracellular matrix accumulation. Recent studies demonstrated that TGF-β1 protects against blood–brain barrier (BBB) disruption in the condition of inflammatory pain and stroke. In the present study, we investigated whether TGF-β1 can maintain BBB integrity and prevent hemorrhagic transformation (HT) after recombinant tissue plasminogen activator (rt-PA) treatment in a rat model of thromboembolic middle cerebral artery occlusion (MCAO). Three hours after MCAO, rats were given saline, rt-PA alone or rt-PA combined with TGF-β1 intravenously. Animals were sacrificed 24h after surgery. HT was calculated as hemorrhagic score. Evans blue dye extravasation was measured for BBB disruption. Basement membrane damage was observed by electron microscopy and quantified by collagen IV and laminin immunostaining. Gelatin zymography was used to measure the activities of matrix metalloproteinase (MMP)-2 and MMP-9. Western blot was performed for the expressions of MMP-2, MMP-9 and plasminogen activator inhibitor type-1 (PAI-1). Rats treated with rt-PA showed elevations in basement membrane damage, BBB disruption and HT. These phenomena were reduced in rats treated by TGF-β1. We also showed that TGF-β1 inhibited rt-PA mediated induction of MMP-2 and MMP-9. Meanwhile, TGF-β1 upregulated PAI-1 expression which was reduced by rt-PA. Taken together, these results suggest that TGF-β1 can reduce rt-PA induced basement membrane degradation, BBB disruption and HT. One possible mechanism is associated with the elevation of PAI-1. Suppression of MMP-2 and MMP-9 elevated by rt-PA may be another mechanism contributing to the protective effects of TGF-β1.