Synthetic glucocorticoids (Gc) are the most potent anti-inflammatory agents known and are widely used to treat a range of chronic inflammatory diseases including rheumatoid arthritis and asthma. However their therapeutic utility is limited by the development of Gc resistance over time particularly at sites of inflammation. Understanding the underlying mechanisms that control Gc sensitivity is essential to overcome this. Previous studies have measured the average transcriptional response across cell populations, however less is known about how individual cells within a population process Gc signals. Two simple models can explain dose dependent increases in Gc responses at a single cell level:
the transcriptional response is binary, where a cell either responds or not, and that increasing the dose of Gc simply recruits more responding cells.
all cells within a population respond to Gc, but individual genes behave like rheostats where the response in each cell is variable and increases a dose dependent manner.
To investigate this, we have completed single cell RNA-seq to measure transcriptomes of 800 individual Gc treated cells. We identify over 500 Gc controlled transcripts, which display dose dependent responses. Surprisingly, these genes separate into two distinct groups, explained by either the binary or rheostat models. We have confirmed our findings using single molecule RNA FiSH, and analysed the impact of inflammatory cues. We find that the magnitude and type of response is gene specific, determined in part by the expression of the Gc receptor (GR), the number of regulatory GR binding sites and the expression of additional intrinsic factors. We therefore uncover a complex regulatory mechanism, controlling gene specific Gc responses in individual cells. This is the first critical step in understanding how inherent transcriptional heterogeneity may underly development of Gc resistance in inflammatory disease.