Histidine-rich glycoprotein modulates neutrophils and thrombolysis-associated hemorrhagic transformation

Intravenous thrombolysis using recombinant tissue plasminogen activator (tPA) remains the primary treatment for patients with acute ischemic stroke (AIS). However, the mechanism of tPA-related hemorrhagic transformation (HT) remains poorly understood. Elevation of histidine-rich glycoprotein (HRG) expression was detected by nano-liquid chromatography tandem mass spectrometry at 1 h following tPA infusion as compared to baseline prior to tPA infusion (discovery cohort, n = 10), which was subsequently confirmed in a validation cohort ( n = 157) by ELISA. Surprisingly, no elevation of HRG was detected in individuals who subsequently developed HT. During in vitro experiments, HRG reduced neutrophil NETosis, inflammatory cytokine production, and migration across the blood–brain barrier induced by tPA. In a photothrombotic murine AIS model, HRG administration ameliorated HT with delayed thrombolysis, by inhibiting neutrophil immune infiltration and downregulating pro-inflammatory signaling pathways. Neutrophil depletion or NETosis inhibition also alleviated HT, whereas HRG siRNA treatment exacerbated HT. In conclusion, fluctuations in HRG levels may reflect tPA therapy and its associated HT. The inhibitory effect of HRG on neutrophils may counteract tPA-induced immune abnormalities and HT in patients with AIS. Synopsis Histidine-rich glycoprotein (HRG) was found to be increased in plasma following thrombolysis by tissue plasminogen activator (tPA) infusion, which counteracted the hemorrhagic-prone state through inhibiting neutrophil NETosis and migration, ultimately reducing the risk of hemorrhage. Plasma levels of HRG increase following tPA treatment in patients with acute ischemic stroke. Elevated HRG levels in patients with AIS correlated with reduced hemorrhagic transformation after thrombolysis. HRG administration inhibited neutrophil NETosis and migration through the blood–brain barrier in vitro and in an animal model of middle cerebral artery occlusion, ultimately reducing hematoma and neurological deficits. Histidine-rich glycoprotein (HRG) was found to be increased in plasma following thrombolysis by tissue plasminogen activator (tPA) infusion, which counteracted the hemorrhagic-prone state through inhibiting neutrophil NETosis and migration, ultimately reducing the risk of hemorrhage.