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Administration of Endothelial Monocyte Activating Polypeptide (EMAP II) Function Blocking Antibody Rescues Alveolarization, Decreases Cellular Proliferation and Reduces Apoptosis In Bronchopulmonary Dysplasia (BPD)

Saturday, October 20, 2012: 8:16 AM
Room 353-355 (Morial Convention Center)
Charitharth V. Lal, MD1, Elizabeth A. Persad, MD1, Haiming Xu, PhD1, Roderich E. Schwarz, MD2 and Margaret A. Schwarz, MD1, (1)Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas, TX, (2)Department of Surgery, University of Texas Southwestern Medical Center, Dallas, TX

Purpose: There is a direct link between blood vessel formation and distal alveolar structure in bronchopulmonary dysplasia (BPD). Previous work has illustrated that the expression of Endothelial Monocyte Activating Polypeptide II (EMAP II)- a potent antiangiogenic and pro-chemotactic factor, decreases during periods of vasculogenesis in fetal lung development, and is elevated in lung dysplasias such as BPD and emphysema. As exogenous EMAP II profoundly disrupts alveolar-capillary growth, we proposed a therapeutic intervention that would allow targeted inhibition of EMAP II’s anti-angiogenic and chemotactic effects. We hypothesized that in a murine hyperoxic model of BPD, administration of EMAP II function-blocking   antibody  (EMAP II Ab) would rescue distal alveolar growth.

Methods: From postnatal days (PN) 3-15, neonatal mice were exposed to either 85% oxygen (hyperoxia) or 21% oxygen (normoxia).  Surrogate mothers were exchanged between normoxia and hyperoxia daily to prevent maternal toxicity. Groups of hyperoxia and normoxia mice were treated with 2 mg/Kg of subcutaneously administered EMAP II Ab every 72 hours (based on previous clearance studies) or non-specific rabbit IgG (control). Lung specimens were either inflation fixed at 25mmHg with 4% paraformaldehyde or harvested for protein analysis on PN 15. Impact of EMAP II Ab on alveolar architecture was demonstrated by calculating the mean linear intercepts (MLI). Cellular proliferation was demonstrated by immunofluorescence (IF) - Ki67 staining and apoptosis was demonstrated by terminal nucleotidyl transferase dUTP nick end labeling (TUNEL) assay and protein analysis.

Results: The murine hyperoxia model of BPD demonstrated distal alveolar dysplasia in neonatal pups exposed to hyperoxia for 12 days (MLI p<0.001, ANOVA) as compared to normoxia control. EMAP II Ab in normoxia animals had no impact on MLI compared to normoxic control pups. In contrast, hyperoxic neonatal pups treated with EMAP II Ab had a marked reduction in MLI (p<0.01) as compared to hyperoxic controls. Under normoxia, EMAP II Ab treated animals or controls had equivalent distal alveolar cell proliferation. In contrast, under hyperoxic conditions, animals treated with NsIgG had a marked increase in alveolar cellular proliferation (Ki67) (p<0.001) that was significantly suppressed in hyperoxic animals treated with EMAP II Ab (p<0.001). Lastly, an increase in distal alveolar apoptosis was noted in the hyperoxic NsIgG treated animals as compared to normoxia control (p<0.01). However, despite normoxic EMAP II Ab treated animals having an increase in distal alveolar apoptosis, EMAP II Ab in hyperoxic mice reduced distal alveolar apoptosis by 15% compared to hyperoxic NsIgG.

Conclusions: Neonatal murine hyperoxia model of BPD demonstrates a marked increase in distal alveolar dysplasia, proliferation, and apoptosis. Delivery of an EMAP II function-blocking antibody rescues alveolar dysplasia, and reduces cellular hyperproliferation and apoptosis suggesting that EMAP II blockade may be a promising target for therapeutic intervention in BPD.