Intrinsic catch-up growth of hypoplastic fetal lungs is mediated by interleukin-6

Fetal lung hypoplasia is a common finding in several fetal conditions such as congenital diaphragmatic hernia (CDH). Interestingly, previous studies have demonstrated that hypoplastic lungs have the ability to recover to normal size, when relieved from mechanical factors. However, the underlying mechanisms remain largely unknown. Recently, interleukin-6 (IL-6) has been involved in catch-up growth phenomenon in children. Thus, we hypothesized that IL-6 could mediate fetal growth recover from hypoplastic lungs. Control and nitrofen-induced hypoplastic lung explants were cultured either in normal conditions or with IL-6 neutralizing antibodies. The total number of peripheral airway buds, epithelial perimeter, and total explant area were analyzed and daily branching rates were calculated. Additionally, IL-6 mRNA and protein expression was assessed both in qualitative (by in situ hybridization and immunohistochemistry) and in quantitative (by real-time PCR and Western blot) approaches, in control and hypoplastic lungs (nitrofen and CDH groups). Nitrofen-induced hypoplastic lungs showed in vitro, out of systemic environment, the ability to recover from hypoplasia and presented daily branching rates significantly higher than controls. Blocking IL-6 activity significantly diminished the intrinsic capacity of hypoplastic fetal lungs to recover from hypoplasia and attenuated their daily branching rates. Although more exacerbated in CDH, both nitrofen-exposed lungs presented significant IL-6 mRNA and protein over-expression throughout all studied gestational ages. The present study suggests, for the first time, that fetal lung is able to recover from growth retardation through a way that resembles the catch-up growth phenomenon, and it seems to be, at least partially, orchestrated by intrinsic mechanisms implicating IL-6.