MAP3K3 Contributes to Myocardial Ischemia/Reperfusion Injury by Promoting Myeloid Cell Diapedesis through TAL1/JAM-A Pathway

<b>Rationale:</b> Extensive leukocyte diapedesis is a defining step in inflammation and contributes critically to myocardial ischemia/reperfusion injury (MI/RI). Infiltrating leukocytes amplify local inflammation and exacerbate myocardial damage. However, the upstream control of the trans-endothelial migration step remains incompletely understood. <b>Methods:</b> Peripheral blood myeloid cells were isolated from MI/RI patients and healthy donors to examine MAP3K3 expression and its correlation with cardiac markers. Mouse MI/RI models were established to investigate MAP3K3 expression of myeloid cells in the heart. Myeloid-specific <i>Map3k3</i> deficiency mice were used to evaluate the impact of MAP3K3 depletion on MI/RI severity and on myeloid cell diapedesis from the bone marrow. RNA sequencing and various manipulations of the MAP3K3/TAL1/JAM-A axis were used to elucidate its role in diapedesis. Finally, the therapeutic potential of pazopanib, a MAP3K3 inhibitor, was evaluated in the mouse MI/RI model. <b>Results:</b> MAP3K3 expression was upregulated in both monocytes and neutrophils from MI/RI patients and was positively correlated with the severity of MI/RI. In mice, MAP3K3 in cardiac myeloid cells peaked at day 3 post-MI/RI. Myeloid cell-specific depletion of MAP3K3 alleviated MI/RI by reducing the infiltration of myeloid cells into cardiac tissue. Functionally, MAP3K3 facilitated myeloid cell de-adhesion and transmigration across endothelial barriers. Further mechanistic studies identified the MAP3K3/TAL1/JAM-A signaling pathway as a key regulator of myeloid cell diapedesis. MAP3K3 phosphorylates TAL1 at Ser-122, leading to its ubiquitination and attenuating its transcriptional repression of <i>F11r</i> (encoding JAM-A). Through JAM-A, MAP3K3 promotes integrin internalization, thereby enhancing de-adhesion and myeloid cell transmigration. Treatment with pazopanib, a MAP3K3 inhibitor, ameliorated MI/RI injury and reduced myeloid cell diapedesis into the heart by blocking MAP3K3 phosphorylation activity. <b>Conclusions:</b> MAP3K3 orchestrates myeloid cell diapedesis via a TAL1/JAM-A dependent program during MI/RI. Targeting MAP3K3, exemplified by pazopanib, may offer a therapeutic strategy for MI/RI and related inflammatory conditions.