Abstract Body: Background: Anemia is common among preterm and critically ill neonates and has been associated with adverse long-term outcomes later in life. We recently discovered that anemia itself is a prime factor in priming neonatal immune cells, predisposing them to systemic inflammatory responses (SIRS) following RBC transfusions. However, the mechanisms by which anemia affects the developing heart and the immune landscape of cardiac tissue are not well understood.
Hypothesis: We hypothesized that neonatal phlebotomy-induced anemia (PIA) drives early cardiac remodeling through a sterile inflammatory axis involving innate immune expansion, associated with reduced TGF-β expression.
Objective: To determine whether severe neonatal anemia induces early cardiac remodeling and expansion of innate immune cells in the developing heart.
Methods: C57BL/6 neonatal pups from both sexes (N=6) were assigned to (1) naïve controls; (2) severely anemic (phlebotomy on postnatal (P) days of 2,4,6,8,10; -hct 25-27%). On P11, perfused hearts were analyzed for hypertrophic, extracellular matrix, and inflammatory markers. Cardiac CD45-positive immune populations were quantified by flow cytometry.
Results: In the study, histopathological findings in anemic neonates at P11 revealed cardiac hypertrophy with increased heart weight (80 ± 5 vs 40 ± 4 mg, p<0.01) and heart/body weight ratio (6.2 ± 0.3 vs 4.1 ± 0.2, p<0.01). Hypertrophic gene reactivation was evident with elevated Atrial Natriuretic Peptide (ANP) (5.1 ± 0.4-fold) and B-type Natriuretic Peptide (BNP) (25.3 ± 2.1-fold; p<0.01), and a 5-fold increase in Myosin Heavy Chain 7 (β-MHC)/ Myosin Heavy Chain 6 (α-MHC) ratio (p<0.05). Early extracellular matrix remodeling occurred, despite reduced TGF-β expression (0.6 ± 0.05-fold, p<0.05). Anemia induced robust inflammatory activation, with increased IL-6, TNF-α, IFN-γ, IL-1β (all p<0.05) and ~5-fold upregulation of TLR4 (5.2 ± 0.58, p<0.05). Ly6G-positive neutrophils were significantly expanded among cardiac CD45-positive leukocytes (46.0 ± 5.59% vs 21.8 ± 0.72%, p<0.01), with enrichment of TLR4-positive neutrophils (14.54 ± 1.58% vs 4.37 ± 0.38%, p<0.05).
Conclusions: Severe neonatal anemia leads to early pathological cardiac remodeling, along with significant expansion of the innate immune system. These findings suggest that inflammatory immune activation is a key mechanism linking neonatal anemia and cardiovascular vulnerabilities in early life.