Objectives Preeclampsia (PE) is characterized by the presence of autoantibodies that activate the major angiotensin receptor, AT1R (AT1-AA). Little is known about the molecular mechanisms underlying the origination of these pathogenic autoantibodies. We have recently shown that tissue transglutaminase (TG2), modifies AT1R by the introduction of an e -( γ -glutamyl)-lysine isopeptide bond. This finding immediately raises an intriguing hypothesis that the posttranslational modification of AT1Rs by TG2 may generate neoantigen and subsequently trigger AT1-AA production. Methods Pregnant C57Bl/6J mice (Harlan) were anesthetized, and recombinant mouse LIGHT (2 ng) or the same volume of saline was introduced into pregnant mice by retro-orbital sinus injection on embryonic day E13.5 and E14.5. Cystamine dihydrochloride was put in drinking water with the concentration 0.9 g/L. Human NT and PE samples were collected from Memorial Hermann Hospital. Results Here we report that injection of LIGHT, a new TNF- α superfamily member, not only induced hallmark feature of PE including hypertension and proteinuria, but also circulating AT1-AA in the pregnant mice. This finding led us to further discover that circulating and placental TG2 activities were significantly induced in the LIGHT-infused pregnant mice compared to the saline-injected controls. Intriguingly, co-injection of TG2 inhibitor, cystamine, significantly attenuated LIGHT-induced PE features and AT1-AA production in pregnant mice. Mechanistically, we demonstrated that elevated HIF-1 α is a key factor underlying increased TG2 gene expression in the mouse placentas of LIGHT-injected pregnant mice. Finally, we validated our mouse finding in human showing that plasma TG2 activity was positively correlated with blood pressure, urinary protein and circulating AT1-AA. Conclusions Overall, our findings demonstrated for the first time that HIF-1 α -dependent elevated TG2 activity triggers AT1-AA generation in PE likely by posttranslational modification of AT1R. These findings add new chapter for molecular basis underlying production of AT1-AA in PE and highlight the therapeutic possibility for the disease. Disclosures R. Luo: None. C. Liu: None. S. Elliott: None. W. Wang: None. P. Daugherty: None. R. Kellems: None. Y. Xia: None.