CD44-v6 Expression in Smooth Muscle Cells in the Postnatal Remodeling Process of Ductus Arteriosus

Closure of the ductus arteriosus (DA) is due to functional constriction followed by wall remodeling, with neointimal formation caused by proliferation and migration of smooth muscle cells (SMCs) from the media to subendothelium. CD44 is a surface cell proteoglycan family. Its isoform, CD44-v6, is only minimally expressed in SMCs in the media of normal arteries, but is highly expressed in SMCs in the intima and media of injured arteries (e.g., atherosclerosis). Twenty-two autopsy DA specimens, 11 from full-term babies (age range 2 days to 5 months) and 11 from premature babies (age range 3 days to 5 months), with varying degrees of ductal wall remodeling, were evaluated by immunohistochemistry using antiactin, antifibronectin-extradomain A, anti-leukocyte common antigen, anti-CD44, and anti-CD44-v6. In DA with wall remodeling, synthetic antifibronectin-extradomain A–positive SMCs were evident at the neointimal mounds, and the SMCs were highly positive for the CD44-v6 isoform, irrespective of gestational age at birth. Conversely, SMCs of either closed DAs or persistently patent DAs were CD44-v6 negative. In conclusion, the present data provide evidence that closure of DA involves synthetic SMCs highly positive for CD44-v6, and patent or closed DAs are populated by CD44-v6–negative SMCs.