Glucocorticoid (GC) signalling via the glucocorticoid receptor (GR) is essential for lung maturation and survival at birth. Previous work using global or conditional mouse knockouts of the GR gene have established that GR activity in the mesenchymal compartment of the lung is crucial for normal respiratory development. Screens for differentially expressed genes in mesenchymal GR-deficient lung (GRmesKO) have identified the ECM proteoglycan Versican (Vcan) as a potential GR-regulated gene target. Alternative exon splicing of Vcan generates 5 isoforms V0, V1, V2, V3 and V4 that vary in structure and function.

We hypothesised that the severe mesenchymal cell hyperplasia observed just before birth in the GRmesKO fetal mouse lung is partially or wholly due to the lack of GR-mediated repression of Vcan expression. We performed isoform-specific qPCR and immunohistochemistry on the GRmesKO fetal lung. We observed that all Vcan isoform mRNA levels in the fetal mouse lung decrease rapidly from E14.5 to P0.5. We also showed that the V1 isoform containing the beta domain of Vcan is the most abundant at E16.5 compared to E18.5 suggesting that the beta domain is spatially regulated in late lung development.

All four isoform mRNAs showed increased levels at in the E18.5 GRmesKO lung relative to controls. Surprising, we did not detect by immunohistochemistry a large degree of difference in protein levels of Vcan between GRmesKO, GRnull and controls. To further characterise the role and regulation of Vcan during lung maturation we performed siRNA mediated knockdown of Vcan in primary rat lung fibroblasts.  At 24H post-treatment we observed no significant difference in cell proliferation rates, however analysis at 48H and 72H post-siRNA treatment are yet to be completed. In summary, GC steroids may regulate repression of the extra cellular matrix protein Vcan to contribute to the coordinate regulation of normal respiratory development in mammals.