Non-genetic cellular heterogeneity is often overlooked in the study of molecular biology. Population averaged measurements of clonal cell populations are made under the assumption that genetic homogeneity implies cellular homogeneity. On the contrary, such assumption discounts the vast variability that exists within a clonal cell population. When gene expression of individual genes is observed across a clonal population of mammalian cells, variation in expression of the same gene differ between cells. This phenomenon is defined as gene expression noise and has been shown to have a functional role in processes like cell fate decisions and viral latency reactivation. While many efforts have been made to measure gene expression noise, less is known about how to control noise. Here, we present our work towards controlling noise using a synthetic genetic circuit we call a noise rheostat. The circuit we built places two small-molecule inducible transcription systems linked in series, driving expression of a green fluorescent protein reporter gene. The inducible transcription system includes an abscisic acid inducible synthetic transcription factor with its cognate promoter and a doxycycline inducible transcription factor with its cognate promoter. By using two inducible transcription systems in series, we create lags in transcription of the terminal output and thus produce different noise levels. We performed transient transfections and characterized the system through dosage experiments using flow cytometry. The datasets analyzed demonstrate that gene expression noise is dialable while maintaining gene expression mean. These results offer a promising prototype for the first mammalian noise rheostat. We propose that this tool will be useful in the study of noise biology as it provides the ability to separate the control of gene expression mean from gene expression noise.
Obstructive sleep apnea (OSA) and idiopathic pulmonary fibrosis (IPF) are serious diseases with growing relevance in modern medicine. OSA affects around 300 individuals per 100,000 in the U.S. and IPF affects between 43-63 individuals per 100,000. Recent evidence has shown a strong and thus far unexplored correlation between IPF and OSA. Of patients diagnosed with IPF, 77-88% had OSA, and treatment of OSA in individuals suffering from both IPF and OSA decreases mortality rates. We hypothesized that increased oxidative stress from chronic intermittent hypoxia (CIH), a common complication of OSA, underlies this correlation and amplifies IPF. To test this, we chemically induced IPF in rats by instilling their lungs with bleomycin and subjected them to a regimen of repeating episodes of hypoxia to mimic CIH. After termination, we measured lipid peroxidation of lung tissue to determine levels of oxidative stress. Our results were inconclusive in determining whether oxidative stress from CIH was directly responsible for exacerbation of IPF. However, trends in our data indicated that lipid peroxidation may increase with CIH treatment, as lipid peroxidation was elevated in rats with both chemically-induced IPF and CIH. Furthermore, qualitative and quantitative data showed a possible anatomical shift of fibrosis within the lung itself as a result of CIH treatment. Performing the experiment with a longer period of CIH is recommended as this would better imitate the condition experienced by patients and would likely result in significant differences of lipid peroxidation between treatment groups.