Evaluating the effect of minimal TIMP variants on protecting and transport across the rat brain microvascular cells (RBMEC)

Tissue inhibitors of metalloproteinases (TIMPs), endogenous inhibitors of matrix metalloproteinases (MMPs), can be tailored to regulate MMP activity and mitigate the disruptive effects of specific MMPs when dysregulated in diseases. MMPs, especially MMP-9, are major contributors to the degradation of extracellular matrix components, leading to BBB disruption in neurological disorders. The upregulation of MMPs undermines blood-brain barrier (BBB) integrity and drives neuroinflammation. Engineering minimal protein variants offers enhanced modularity, tissue penetration, and BBB permeability. Minimal TIMP variants were engineered, aiming to improve their therapeutic reach across both sides of the BBB, particularly when delivery to the brain is essential. In this study, we assessed the protective effects of mTC1 and mTC3 on BBB integrity using an in vitro model of rat brain microvascular endothelial cells (RBMECs). Barrier function was evaluated following treatment with recombinant MMP-9, either alone or co-treated with native TIMP-1, TIMP-3, or the engineered minimal variants. MMP-9 induced a dose-dependent increase in BBB permeability, reflected by a decrease in trans-endothelial electrical resistance (TEER) and increased paracellular transport of fluorescent tracers. Co-treatment with TIMP-1, TIMP-3, mTC1, or mTC3 significantly attenuated MMP-9-mediated disruption of tight junctions of RBMECs, preserving TEER values and reducing permeability. Immunofluorescence staining for tight junction proteins, ZO-1 and occludin, further validated the preservation of endothelial integrity in the presence of wild-type human TIMPs and engineered TIMP variants. These findings underscore the potential of engineered minimal TIMPs as molecular tools to stabilize the BBB and support their future application in mechanistic studies focused on BBB protection.