CLDN1 and Alzheimer disease: As shown in Figure 5D, we observed that in the normal mice, the penetration of the tracer (red) into the epidermis was stopped (arrowheads) by the intact TJ barrier (represented by colocalization of claudin-1 and biotin tracer), whereas in AD mice, the tracer penetrated and passed through the epidermis, as shown by the decreased number of biotin stops compared with those in normal mice.