MicroRNA in late lung development and bronchopulmonary dysplasia: the need to demonstrate causality

Abstract

MicroRNA are emerging as powerful regulators of cell differentiation and tissue and organ development. Several microRNA have been described to play a role in branching morphogenesis, a key step in early lung development. However, considerably less attention has been paid to microRNA as regulators of the process of secondary septation, which drives lung alveolarization during late lung development. Secondary septation is severely perturbed in bronchopulmonary dysplasia (BPD), a common complication of preterm birth characterized by blunted alveolarization. A number of studies to date have reported microRNA microarray screens in animal models of BPD; however, only two studies have attempted to demonstrate causality. Although the expression of miR-150 was altered in experimental BPD, a miR-150−/− knockout mouse did not exhibit appreciable protection in a BPD animal model. Similarly, while the expression of miR-489 in the lung was reduced in clinical and experimental BPD, antagomiR and over-expression approaches could not validate a role for miR-489 in the impaired alveolarization associated with experimental BPD. This mini-review aims to highlight microRNA that have been revealed by multiple microarray studies to be potential causal players in normal and pathological alveolarization. Additionally, the challenges faced in attempting to demonstrate a causal role for microRNA in lung alveolarization are discussed. These include the tremendous variability in the animal models employed, and the limitations and advantages offered by the available tools, including antagomiRs and approaches for the validation of a specific microRNA-mRNA interaction during lung alveolarization.

Control Interventions Can Impact Alveolarization and the Transcriptome in Developing Mouse Lungs

“…This injection protocol on P1 and P3 is widely employed for the administration of “antagomiRs”. The emerging interest in microRNA as mediators of lung organogenesis (Nardiello and Morty, ) has highlighted the potential utility of antagonizing microRNA function with sequence‐specific inhibitors called antagomiRs. These oligonucleotides are chemically stabilized with an LNA structure, and as such, persist in the target organisms.…”

“…Small‐molecule and proteinaceous modulators of developmental pathways have been administered via the enteral or parenteral routes, and subsequently, the impact on the development of the lung structure might be assessed microscopically (Valenzuela et al, ) or radiologically (Xiao et al, ); alongside screens for transcriptomic changes (Mariani, ), by microarray, or more recently, RNA‐Seq (Bhattacharya et al, ; Lingappan et al, ) technology. Small‐molecule interventions have, in the past, relied on enzyme inhibitors to block enzyme function (Reviewed in Madurga et al, ; Silva et al, ; Surate Solaligue et al, ); but have recently been expanded to include chemical chaperones (Nguyen and Uhal, ; Siddesha et al, ) and genetic interference, through sequence‐specific modulation of microRNA function using antagomiRs (Nardiello and Morty, ) or microRNA mimics (Olave et al, ; Durrani‐Kolarik et al, ). Similarly, proteinaceous modulators of biochemical pathways, such as polypeptide growth factors (Seedorf et al, ) and neutralizing antibodies (Yu et al, ) may also be applied to validate causal roles for pathways in lung alveolarization.…”

miRNAs in Lung Development and Diseases

“…Collectively, miR-421 regulated Fgf10, induced apoptosis in the lung, and increased inflammatory response in a BPD mouse model [28]. Details on the expression profile of miRNAs at various stages of late lung development in experimental BPD models have been summarized by Nardiello and Morty [29]. Moreover, the studies discussed so far implicate miRNAs in the regulation of alveolarization.…”

MicroRNA‐142 is a multifaceted regulator in organogenesis, homeostasis, and disease

“…Specific miRs are involved during lung development and disease (Nardiello and Morty, ). Our group reported that miR‐142‐3p is one of the miRs that is highly expressed in the lung mesenchyme during early lung development.…”