Matriptase‐mediated <scp>PAR</scp> 2 activation drives monocyte‐to‐macrophage differentiation and polarization under hypoxic conditions

Within the intricate landscape of the tumour microenvironment (TME), hypoxia stands out as a pivotal factor profoundly shaping immune cell dynamics. Our study delves into this dynamic interplay, uncovering a cascade of events triggered by hypoxia. We unveil the emergence of protease-activated receptor 2 (PAR2; also known as F2R-like trypsin receptor 1 [F2RL1]) expression in monocyte cell lines (THP1) and peripheral blood mononuclear cells (PBMCs), orchestrated by the active serine protease matriptase (TMPRSS2; also known as transmembrane protease serine 2). Hypoxic conditions set the stage for a dual mechanism: lactate accumulation drives extracellular pH reduction, and facilitates matriptase activation from its latent form. A 10 mm lactate threshold activates matriptase, which in turn activates PAR2, driving monocytes towards M1 macrophage differentiation through the AKT2-NF-κβ axis. This triggers miR155 expression, which suppresses cytokine signaling 1 (SOCS1), a key regulator of M1-M2 polarisation, while NF-κβ enhances proinflammatory responses. Notably, our study reveals a temporal switch in this hypoxia-driven process. After 48 h of hypoxia, lactate levels rise to 25 mm, suppressing matriptase activation and driving a shift towards M2 polarisation. This transition, marked by reduced miR155 expression via AKT2-NFκβ axis inactivation, highlights the dynamic nature of macrophage polarisation. Our findings demonstrate matriptase as a key regulator driving macrophage polarisation towards the M1 phenotype within hypoxic microenvironments. This insight into macrophage behaviour under hypoxia suggests new strategies for immune modulation to counter tumour progression.