Significantly reduced levels of ERβ wt mRNA in PBMCs were found in patients with CFS compared with controls (fig 1). Based on this observation, we extended our studies to include determination of the possible association of ERβ SNPs and promoter levels with CFS. The levels of ERβ wt mRNA are low in PBMCs. However, the actual target tissues for CFS are unknown, and it is possible that these tissues express higher amounts of ERβ wt mRNA, still maintaining the differential expression observed in this study. Lower levels of ERβ cx mRNA were identified in patients with CFS with shorter illness duration compared with patients with longer duration. However, the groups and the difference between them are small, so the significance of this finding is at present unclear.
A recent study by Phiel et al
shows the presence of ERα and ERβ mRNA levels in fractionated T and B lymphocytes.27
However, the assay used in the study does not discriminate between ERβ wt and ERβ cx. Our PBMC samples contain both T and B lymphocytes, and it would be of interest to investigate whether there are differences in the ERβ splice variant ratios between the lymphocyte fractions.
Interestingly, in this study, we find differences in the levels of the ERβ wt mRNA, but not in the splice variant ERβ cx, when comparing patients with CFS and controls. It is not clear how the relative levels of these transcripts are regulated. Our data do not support promoter usage as a means by which ERβ wt/ERβ cx ratios are regulated, as we detect expression from only one promoter (0N, data not shown). Consistent with our results, promoter 0N has been shown to be used in peripheral leucocytes.15
Tissue‐specific promoter usage has, however, been reported, and the presence of additional ERβ promoters must be considered in this context.15,16
It is possible that SNPs in the differing 3′ untranslated regions of ERβ wt (rs4986938) and ERβ cx (rs928554) transcripts regulate mRNA stability and ultimately determine ERβ wt:ERβ cx ratios. In this context, the ERβ rs4986938 AA genotype was over‐represented in the CFS group with lower ERβ wt expression. The possibility that this SNP regulates mRNA stability can be furthered explored by directly assaying the mRNA stability of mRNAs incorporating the G and A alleles.
Several gene expression studies have been performed in the search for differently transcribed genes between patients with CFS and controls.4,28,29,30,31,32
These studies confirmed the role of the immune system in CFS, as several genes involved in immunity and defence were shown to differ between patients with CFS and controls.
Oestrogens have been suggested as immunomodulatory factors. This is based on observations including the female predominance of certain autoimmune disorders,7
which might be explained by lower oestrogen secretion in men. Thus, CFS and oestrogen signalling are connected via the unequal sex distribution and their association with aspects of immunomodulation. However, none of the gene expression studies referred to above identified ERβ as a differentially expressed gene, which might reflect its low expression level.
At present, specific oestrogen receptor modulators are being developed as novel therapeutics for immune‐mediated diseases. In a study by Follettie et al
, the specific ERβ agonist ERB‐041 was used to treat antigen‐induced arthritis in rats.33
ERB‐041 treatment led to sustained improvement and down regulation of genes known to be upregulated in rheumatoid arthritis.33
ERB‐041 also showed positive effects in animal models of inflammatory bowel disease.34
In conclusion, the difference in expression of ERβ wt mRNA between patients with CFS and controls observed in this study could contribute to some of the symptoms observed in CFS. Reduced levels of ERβ wt mRNA may be simply a marker for changed function of other cellular components, which are involved in CFS. The present finding of lower ERβ levels in patients with CFS compared with controls supports an immunopathogenesis for CFS. However, further work is needed to clarify whether reduced ERβ expression is a primary event in CFS or is caused by a down regulation secondary to altered oestrogen levels. The reduced ERβ wt mRNA levels in patients with CFS could provide an entry point to identify interesting and potentially disease‐causing candidate molecules for further study. Studies investigating ERβ wt protein levels and cellular effects will be required to confirm an involvement of ERβ wt in CFS. Future studies should involve evaluation of oestrogen levels and effects after oestradiol treatment in relation to CFS pathology.