Activation of Transposable Elements in Immune Cells of Fibromyalgia Patients

Abstract

Advancements in nucleic acid sequencing technology combined with an unprecedented availability of metadata have revealed that 45% of the human genome constituted by transposable elements (TEs) is not only transcriptionally active but also physiologically necessary. Dysregulation of TEs, including human retroviral endogenous sequences (HERVs) has been shown to associate with several neurologic and autoimmune diseases, including Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS). However, no study has yet addressed whether abnormal expression of these sequences correlates with fibromyalgia (FM), a disease frequently comorbid with ME/CFS. The work presented here shows, for the first time, that, in fact, HERVs of the H, K and W types are overexpressed in immune cells of FM patients with or without comorbid ME/CFS. Patients with increased HERV expression (N = 14) presented increased levels of interferon (INF-β and INF-γ) but unchanged levels of TNF-α. The findings reported in this study could explain the flu-like symptoms FM patients present with in clinical practice, in the absence of concomitant infections. Future work aimed at identifying specific genomic loci differentially affected in FM and/or ME/CFS is warranted.

Keywords: DNA methylation; epigenetics; fibromyalgia; human endogenous retrovirus (HERV); interferon (INF); myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS); non-Hodgkin’s lymphoma; transfer RNA small fragments (tsRNAs); transposable elements.

Figure 1

HERVs are overexpressed in FM. RT-qPCR amplification of HERV-H, HERV-K and HERV-W using total RNA from PBMCs is shown (N = 14/group) (*** p < 0.001; *p < 0.05). Primer sets are detailed in Table 2 and conditions used described in Methods. Relative expression levels were calculated as 2^−ΔΔCt values using GAPDH levels as reference. Group means and SEM values are shown.

Figure 2

INF-β and INF-γ levels are increased and TNF-α are unaffected in FM patients showing increased HERV levels. RT-qPCR amplification of INF-β and INF-γ and TNF-α are shown (N = 14/group); (*** p < 0.001; ** p < 0.005); ns (non-significant). Primers sets used are detailed in Table 2 and conditions described in Methods. Relative expression was calculated as 2^−ΔΔCt values using GAPDH levels as reference. Group means and SEM values are shown.

Figure 3

Linear regression analysis of HERV-H, HERV-K and HERV-W levels with respect to INF-β (A–C) and INF-γ (D–F) levels in PBMCs of FM patients. Adjusted calculated best-fit lines together with SD values (dotted lines) are represented for each data set pair; R² and p values are indicated.

Figure 4

Linear regression analysis of HERV-H, HERV-K and HERV-W levels with respect to each other (A–C); and correlation between INF-β and INF-γ levels (D) in PBMCs of FM patients are shown. Adjusted calculated best-fit lines together with SD values (dotted lines) are represented for each data set pair; R² and p values are indicated.

Figure 5

Northern blot analysis of tRNA levels in PBMCs from FM or HC participants, as indicated (A). Quantitated tRNA-His, tRNA-Pro levels (Image J software) upon normalization to RNU6 levels are shown (B) (N = 4/group).

Figure 6

Proposed mechanism linking overexpression of HERVs, INF induction and increased cancer susceptibility in patients with defective ribonuclease activity. ISF (Interferon stimulating factors); TLR3 (Toll-like receptor 3); MDA5 (Melanoma differentiation associated gene 5); RIG-I (Retinoic acid-inducible gene I); OAS (2’-5’-oligoadenylate synthetase); 2-5A (2’, 5’ oligomers of ATP); tsRNAs (transfer RNA small fragments); RT (reverse transcription); AGO (Argonaut).