Molecular control of PDPNhi macrophage subset induction by ADAP as a host defense in sepsis

Induction of podoplanin (PDPN) expression is a critical response of macrophages to LPS stimulation or bacterial infection in sepsis, but how this key process of TLR4-stimulated PDPN upregulation is regulated and the effect of PDPN expression on macrophage function remain elusive. Here, we determined how this process is regulated in vitro and in vivo. PDPN failed to be upregulated in TLR4-stimulated macrophages deficient in adhesion and degranulation-promoting adapter protein (ADAP), which could be rescued by the reconstitution of ADAP. A distinct PDPNhi peritoneal macrophage (PM) subset, which exhibited an M2-like phenotype and enhanced phagocytic activity, was generated in WT but not in ADAP-deficient septic mice. The blockade of PDPNhi PMs mimicked the effect of ADAP deficiency, which exacerbated sepsis. Mechanistically, Bruton's tyrosine kinase-mediated (BTK-mediated) tyrosine phosphorylation of ADAP at Y571 worked together with mTOR to converge on STAT3 activation for the transactivation of the PDPN promoter. Moreover, agonist activation of STAT3 profoundly potentiated the PDPNhi PM subset generation and alleviated sepsis severity in mice. Together, our findings reveal a mechanism whereby ADAP resets macrophage function by controlling the TLR4-induced upregulation of PDPN as a host innate immune defense during sepsis.