Inter-ethnic differences in lymphocyte sensitivity to glucocorticoids reflect variation in transcriptional response

The Pharmacogenomics Journal (2013) 13, 121–129 & 2013 Macmillan Publishers Limited. All rights reserved 1470-269X/13 www.nature.com/tpj ORIGINAL ARTICLE Inter-ethnic differences in lymphocyte sensitivity to glucocorticoids reflect variation in transcriptional response JC Maranville, SS Baxter, JM Torres and A Di Rienzo Department of Human Genetics, The University of Chicago, Chicago, IL, USA Correspondence: Dr AD Rienzo, Department of Human Genetics, The University of Chicago, 920 E. 58th Street, Room 424, Chicago, IL, 60637 USA. E-mail: Glucocorticoids (GCs) are steroid hormones widely used as pharmaceutical interventions, which act mainly by regulating gene expression levels. A large fraction of patients (B30%), especially those of African descent, show a weak response to treatment. To interrogate the contribution of variable transcriptional response to inter-ethnic differences, we measured in vitro lymphocyte GC sensitivity (LGS) and transcriptome-wide response to GCs in peripheral blood mononuclear cells from African–American (AA) and European– American (EA) healthy donors. We found that transcriptional response after 8 h treatment was significantly correlated with variation in LGS within and between populations. We found that NFKB1, a gene previously found to predict LGS within populations, was more strongly downregulated in EAs on average. NFKB1 could not completely explain population differences, however, and we found an additional 177 genes with population differences in the average log2 fold change (false discovery rateo0.05), most of which also showed a weaker transcriptional response in AAs. These results suggest that inter-ethnic differences in GC sensitivity reflect variation in transcriptional response at many genes, including regulators with large effects (for example, NFKB1) and numerous other genes with smaller effects. The Pharmacogenomics Journal (2013) 13, 121–129; doi:10.1038/tpj.2011.55; published online 13 December 2011 Keywords: regulatory variation; gene expression; glucocorticoids; ethnic disparities; asthma; NFkB Introduction Received 23 August 2011; revised 31 October 2011; accepted 7 November 2011; published online 13 December 2011 Glucocorticoids (GCs) are steroid hormones that mediate physiological responses to the environment. Because of their potent anti-inflammatory properties, GCs are widely used as therapeutic agents. For example, GCs are the most commonly prescribed asthma controller medication1–3 and are commonly used in the treatment of inflammatory bowel syndrome, rheumatoid arthritis and other autoimmune diseases. GCs are also effective in the treatment of lymphoid malignancies, such as acute lymphoblastic leukemia.4 Although GCs are among the most successful drugs in history,5 there is large inter-individual variability in response to GC therapy,6,7 with B30% of patients showing no response to treatment.8–10 The proportion of non-responders is similar across diseases,11 suggesting that GC resistance is an intrinsic property of the general population. GC insensitivity is more common among individuals of African descent. For example, unresponsiveness to GC treatment is more common among African–American (AA) asthma patients compared with European–American (EA) Variation in transcriptional response to steroids JC Maranville et al 122 patients.9 Additionally, incidence of GC-induced side effects is significantly lower in acute lymphoblastic leukemia patients of African vs European descent.12 Characterizing the causes of variable GC sensitivity could aid in the development of treatment protocols that maximize efficacy while minimizing side effects across individuals and ethnic groups.13,14 Many potential explanations for higher rates of GC insensitivity in AAs have been proposed, including differing disease severity, access to and quality of healthcare, socioeconomic status and genetic factors. However, the degree to which inter-ethnic differences in transcriptional response contribute to disparities in clinical response to GC is unknown. Clinical responsiveness to GC therapy is poorly correlated with disease severity, but is significantly correlated with in vitro lymphocyte GC sensitivity (LGS). This correlation has been observed in patients with a wide range of diseases, including asthma,15–19 rheumatoid arthritis,20 systemic lupus erythematosous,21 ulcerative colitis11 and renal transplant rejection.22 LGS is most commonly assessed by measuring GC inhibition of phytohemagglutinin- (PHA) induced proliferation of peripheral blood mononuclear cells (PBMCs). Percent inhibition at a high dose (for example, Imax a measure of efficacy) is a particularly accurate predictor of clinical response, although other metrics (for example, IC50 a measure of potency) are also predictive.11 Consistent with clinical observations of inter-ethnic differences, Federico et al.23 found that LGS was, on average, significantly lower in AA compared with EA asthma patients. Interestingly, no inter-ethnic differences were observed in basal activity (that is, T-cell proliferation in the absence of PHA) or in the proliferative response to PHA, implying that inter-ethnic differences in LGS are owing to variation in the cellular response to GCs. As the same was observed in healthy controls, it was concluded that variation in GC response is not correlated with disease status. These results are of particular interest with regard to the known fourfold difference in asthma mortality and hospitalization rate for AA vs EA children with asthma,24 a disparity that persists after controlling for known socioeconomic factors.25,26 Although GCs can affect target cells through a variety of mechanisms, including ‘non-genomic’ effects (for example, direct disruption of cell membranes or modulation of T-cell receptor activity27), they act primarily through the regulation of gene expression.28 GCs enter target cells through passive diffusion and bind the GC receptor (GR) in the cytoplasm, allowing it to be translocated into the nucleus where it acts as a transcriptional regulator. The activated GR, together with cooperating transcription factors (TFs), modulates transcription at target genes through direct DNA binding. The activated GR can also modulate and counteract the activity of other TFs, such as the NFkB complex29 or the STAT proteins,30 usually leading to repression of transcription. Variation in transcriptional regulation is, therefore, likely to contribute to variable patient sensitivity. In support of a transcriptional basis for inter-individual variation in GC sensitivity, Hakonarson et al.31 found that changes in gene The Pharmacogenomics Journal expression in response to GCs in activated PBMCs were predictive of GC sensitivity. This raises the possibility that variation in transcriptional response also contributes to inter-ethnic differences in GC sensitivity. To characterize the transcriptional basis of inter-ethnic variability in GC response, we m (...truncated)