Western blot analysis using the retinal tissue indicated that the phosphorylation of Src [Tyr416] and VE-cadherin [Tyr731] was increased in the STZ-induced diabetic retina, which was further increased by DPP4-inhibitor (DipA) treatment and was decreased by CXCR4-blocker (AMD3100) or Src-inhibitor (PP2) treatment (Fig. 8b–d). Here, DPP4 is linked to diabetes mellitus.