CLDN5 and diabetes mellitus: Consistent with these findings, elevated MMP-9 activity and a simultaneous reduction in TJ proteins Cldn5 and Ocln (Figure 4E,F) were observed in a brain vascular endothelial cell line bEND.3 when exposed to high glucose and saturated fatty acid palmitic acid (HG/HP), replicating hyperglycemia and metabolic dysfunction in diabetes.