Age-Dependent Differential Expression of Fibronectin Variants in Skin and Airway Mucosal Wounds

Abstract

To delineate age-dependent and tissue-specific molecular activities of the variant-inclusion fibronectin transcripts in fetal and postnatal skin and airway mucosal wounds during early events of the wound healing process. Fibronectin is involved in multiple steps of the wound healing process. The functional complexity of fibronectin is carried through its protein diversity, which is controlled in part by alternative RNA splicing, a coordinated transcription and RNA processing. From a rabbit model of airway mucosal wound healing, we isolated and cloned an RNA splicing factor, SRp20, that was coexpressed with Fn1 complementary DNA and suppressed in fetal wounds but induced in postnatal wounds. Previous studies revealed a link between the inclusion and/or exclusion of the alternatively spliced Fn1 variants (extra domain A [EDA], extra domain B [EDB], and a variable region [V]) and outcomes of wound repair. Skin and airway mucosal incisional wounds were made in fetal (gestational day 21-23), weanling (4-6 weeks), and adult (>6 months) rabbits. Tissues (nonwounded and wounded) were collected at 12 hours (all age groups), 24 hours, and 48 hours (weanling only) after wounding. The expression levels of the 3 Fn1 spliced domain (EDA, EDB, and V)-containing messenger RNA (mRNA) species were assessed by real-time polymerase chain reaction. Fn1 spliced variants were either suppressed or showed no change in fetal skin and airway mucosal wounds 12 hours after injury, whereas the spliced mRNAs were induced in postnatal wounds. The augmented molecular activities of Fn1 spliced variants were more prominent in airway mucosal wounds than in skin wounds. Furthermore, the EDA variant was dominantly selected in adult airway mucosal wounds (6-fold increase), which was strikingly different from the adult skin wounds (1-fold). Our study suggests that the age-dependent activation of Fn1-EDA mRNA may play a fundamental role in differentiating fetal wound regeneration from postnatal wound scar formation during the early events of airway mucosal wound healing.