A Single Nucleotide Polymorphism in DDAH1 Leads to Decreased Nitric Oxide Production in Neonatal Cord Blood‐derived Stimulated Lymphoblastoid Cells

Bronchopulmonary dysplasia (BPD) is chronic lung disease in preterm infants. Pulmonary hypertension (PH) develops in 25–40% of BPD and is a major contributor to morbidity and mortality in BPD patients. Nitric oxide (NO) is a potent vasodilator and apoptotic mediator made by nitric oxide synthase (NOS). NOS is inhibited by asymmetric dimethylarginine (ADMA). Dimethylarginine dimethylaminohydrolase (DDAH) hydrolyzes ADMA. Translational studies from our group identified a single nucleotide polymorphism (SNP) in the DDAH1 gene, rs480414, that was associated with a decreased risk for PH in BPD patients. Therefore, we aim to determine if the DDAH1 SNP rs480414 affects DDAH1 function in cell culture. Neonatal cord blood specimens were treated with Epstein‐Barr virus to select for B‐lymphocytes and transform into lymphoblastoid cell lines (LCLs) that were genotyped (SNP or wild‐type) at the rs480414 locus. We tested the hypothesis that in LCLs the SNP rs480414 results in a gain of function mutation in DDAH1, which would lead to greater NO‐mediated apoptosis as compared to DDAH1 wild‐type (WT). LCLs (WT, n=3 and SNP, n=3) were stimulated with phorbol myristate (PMA), IL‐4, and IL‐13 for 48 hours, protein was analyzed by western blot analysis for DDAH1, cleaved and total caspase‐3 and ‐8, and β‐actin. RT‐PCR was performed and expression of DDAH1 and iNOS mRNA was evaluated. Cell media was assayed for concentrations of nitrite using a chemiluminescence NO analyzer. Spectrophotometry was used to measure the conversion of ADMA to L‐citrulline. A standard L‐citrulline curve was used to calculate DDAH activity after normalization to protein concentration. LCLs with the DDAH1 SNP had similar levels of DDAH1 protein expression (n=3, p=0.58), similar mRNA expression (n=3, p=0.1), and similar DDAH activity (p=0.35) compared to DDAH1 WT. We found that LCLs with the DDAH1 SNP had similar iNOS mRNA expression (p=0.6), lower nitrite levels (p=0.04), lower cleaved caspase‐3 levels (p=0.04), and similar cleaved caspase‐8 levels (p=0.2) than DDAH1 WT LCLs. Contrary to our hypothesis, these finding suggests that the DDAH1 SNP rs480414 may result in a loss of function mutation, resulting in lower NO production and lower apoptosis in LCLs. This is the first evidence that the DDAH1 SNP rs480414 has an effect on cell function, however we speculate that pulmonary vascular endothelial cells will likely have a different physiology.