Liver-Gut Axis in Neonatal Anemia and Its Role in RBC Transfusion Associated Gut Injury

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Project summary Anemia is a nearly universal diagnosis in preterm infants, caused primarily by phlebotomy essential for medical care, though also exacerbated by a variety of factors inherent to immaturity in the ex utero environment. When severe enough to be treated with RBC transfusion, clinicians must be aware of the risk of critical adverse effects such as necrotizing enterocolitis (NEC), an inflammatory bowel necrosis characterized by macrophage infiltration, and a leading cause of mortality in those born between 22 and 28 weeks gestation. We have recently elucidated the connection between anemia and NEC, specifically, the “leaky gut” presentation characterized by macrophage infiltration, RBC transfusion-associated activation of infiltrated macrophages, and the resulting intestinal mucosal injury. Our long-term objective is to study the anemia-induced immunity changes in the neonatal liver and their contribution to gut mucosal injury during RBC transfusion. Our preliminary studies using our existing pre-clinical murine model of anemia demonstrate that anemia is associated with recruitment of a unique population of monocyte (CD11bhiF4/80midLy6Cmid) expressing triggered myeloid receptor 1 (trem1), similarly to monocytes developing in the neonatal liver but unlike those in the bone marrow or spleen. Consistent with this, neonatal anemic liver monocytes displayed greater inflammatory activation to heme (found in stored RBC) than did bone-marrow derived cells. This inflammatory response could be dampened either by the use of anti-trem1 antibody treatment or by silencing monocyte trem1 expression. Taken together, the investigators propose a novel hypothesis that in the setting of anemia, a gut-liver-gut boomerang effect is noted as the leaky gut and associated bacterial translocation during anemia communicate via the portal vein to the liver, trigger the expansion of hepatic leukocyte populations developing in situ which proceed to infiltrate the anemic intestine, predisposing to RBC-associated gut injury. To test our central hypothesis, we will pursue the following specific aims: Aim 1: Elucidate the ontogeny of macrophages recruited to the neonatal intestine during anemia. Aim 2: Define the role of trem1 signaling on the migration of hepatic monocytes into the anemic intestine, and on the inflammatory activation during RBC transfusion. Aim 3: Determine whether therapeutic targeting of hepatic trem1+ monocytes during anemia can prevent/ attenuate RBC-transfusion associated NEC-like injury. Accomplishment of the proposed aims will develop an effective therapeutic strategy of inhibiting the hepatic response during anemia without suppressing protective innate immune mechanisms.