Fig. 4: Abnormal H3K4 methylation and LSD1 activity in adult mice expressing HERV-W ENV.

All data were generated using hippocampal samples of adult male transgenic CAG^HERV-Wenv mice (TG) and wild-type (WT) littermates. A Western blot analysis of H3K4me1 (*p < 0.05, t₍₁₈₎ = 2.25, 2-tailed), H3K4me2 (*p < 0.01, t₍₁₈₎ = 2.97, 2-tailed) and H3K4me3 (*p < 0.05, t₍₁₈₎ = 2.58, 2-tailed), normalized to H3 housekeeping control. The photographs show representative Western blots using H3K4me1, H3K4me2, H3K4me3, and H3 antibodies, with additional loading marks (mk). n = 10 per genotype. B Verification of reduced H3K4me2 using immunohistochemistry in the CA1 (*p < 0.05, t₍₁₂₎ = 2.37, 2-tailed), CA3 (*p < 0.05, t₍₁₂₎ = 2.81, 2-tailed) and DG (*p < 0.05, t₍₁₂₎ = 2.82, 2-tailed) region of the hippocampus of TG relative to WT mice. The photomicrographs show representative immunofluorescence H3K4me2 staining in the CA1, CA3 and DG regions. n = 7 per genotype. C Western blot analysis of LSD1, normalized to H3 housekeeping control. The photograph shows a representative Western blot using LSD1 and H3 antibodies, with additional loading marks (mk). n = 10 per genotype. D Enzymatic activity of LSD1, as measured with a fluorometric quantification assay; *p < 0.05 (t₍₁₈₎ = 2.16, 2-tailed); n = 10 per genotype. All scatter plots show individual mice with overlaid group means ± s.e.m. E Simplified schematic illustration of the proposed mechanism underlying altered H3K4 methylation dynamics in mice expressing HERV-W ENV relative to controls. Concurrent to the downregulation of H3K4 methyltransferases (H3K4 MTs; also see Fig. 3), increased enzymatic activity of LSD1 in HERV-W ENV mice may shift the methylation dynamics towards increased and decreased H3K4me1 and H3K4me2/me3, respectively.