Children with Chronic Immune Thrombocytopenia Exhibit High Expression of Human Endogenous Retroviruses TRIM28 and SETDB1

Abstract

Chronic immune thrombocytopenia (CITP) is an autoimmune disease whose underlying biologic mechanisms remain elusive. Human endogenous retroviruses (HERVs) derive from ancestral infections and constitute about 8% of our genome. A wealth of clinical and experimental studies highlights their pivotal pathogenetic role in autoimmune diseases. Epigenetic mechanisms, such as those modulated by TRIM28 and SETDB1, are involved in HERV activation and regulation of immune response. We assessed, through a polymerase chain reaction real-time Taqman amplification assay, the transcription levels of pol genes of HERV-H, HERV-K, and HERV-W; env genes of Syncytin (SYN)1, SYN2, and HERV-W; as well as TRIM28 and SETDB1 in whole blood from 34 children with CITP and age-matched healthy controls (HC). The transcriptional levels of all HERV sequences, with the exception of HERV-W-env, were significantly enhanced in children with CITP as compared to HC. Patients on eltrombopag treatment exhibited lower expression of SYN1, SYN2, and HERV-W-env as compared to untreated patients. The mRNA concentrations of TRIM28 and SETDB1 were significantly higher and were positively correlated with those of HERVs in CITP patients. The over-expressions of HERVs and TRIM28/SETDB1 and their positive correlations in patients with CITP are suggestive clues of their contribution to the pathogenesis of the disease and support innovative interventions to inhibit HERV and TRIM28/SETDB1 expressions in patients unresponsive to standard therapies.

Keywords: SETDB1; TRIM28; autoimmune disease; children; endogenous retroviruses; genetic pathomechanism; primary immune thrombocytopenia.

Figure 1

Transcription levels of pol genes of HERV-H, HERV-K, HERV-W and of env genes of Syncytin 1, Syncytin 2, and HERV-W in whole blood from patients with chronic immune thrombocytopenia (CITP) and healthy controls (HC). RQ: Relative Quantification. Circles and squares show the median of three individual measurements, horizontal lines are the median values. Statistical analysis: Mann–Whitney test was used to compare the transcriptional levels of each target gene between children with CITP and HC.

Figure 2

Transcription levels of pol genes of HERV-H, HERV-K, and HERV-W as well as of env genes of Syncytin 1, Syncytin 2, and HERV-W in whole blood from 11 patients on eltrombopag treatment alone (E-pag) and 18 patients with no treatment. RQ: Relative Quantification. Circles and squares show the median of three individual measurements, horizontal lines are the median values. Statistical analysis: Mann–Whitney test was used to compare the transcriptional levels of each target gene.

Figure 3

Expression of TRIM28 and SETDB1 in whole blood from 34 patients with chronic immune thrombocytopenia (CITP) and 47 healthy controls (HC). RQ: Relative Quantification. Circles and squares show the median of three individual measurements, horizontal lines are the median values. Statistical analysis: Mann–Whitney test was used to compare the transcriptional levels of each target gene between children with CITP and control children.

Figure 4

Correlations between transcription levels of TRIM28 and HERV sequences in whole blood from 34 patients with chronic immune thrombocytopenia. RQ: Relative Quantification. Circles show the mean of three individual measurements. Line: Linear regression line. Statistical analysis: Spearman correlation test.

Figure 5

Correlations between transcription levels of SETDB1 and HERV sequences in whole blood from 34 patients with chronic immune thrombocytopenia. RQ: Relative Quantification. Circles show the mean of three individual measurements. Line: Linear regression line. Statistical analysis: Spearman correlation test.