Investigating the role of histone H3 lysine 9 dimethylation in regulating disease-associated vascular smooth muscle cell gene expression

Widespread changes in gene expression accompany vascular smooth muscle cell (VSMC) phenotypic switching, a hallmark of vascular disease. Upon insult, VSMCs downregulate contractile proteins and upregulate genes linked to vascular remodelling, such as matrix metalloproteinases (MMPs) and pro-inflammatory cytokines. However, the epigenetic mechanisms which regulate VSMC phenotypic switching remain unclear. This thesis explores the role of histone 3 lysine 9 dimethylation (H3K9me2), a repressive epigenetic mark, in regulating the expression of disease-associated VSMC genes. Intriguingly, murine models of VSMC phenotypic switching revealed reduced levels of H3K9me2 upon loss of the contractile state while chromatin immunoprecipitation (ChIP) identified a subset of IL-1α/injury-responsive VSMC gene promoters enriched for H3K9me2. To test the functional importance of H3K9me2 for VSMC gene regulation the methyltransferase G9A/GLP was pharmacologically inhibited in vitro and in vivo. The resulting loss of H3K9me2 attenuated the expression of contractile VSMC markers and significantly potentiated IL-1α/injury-induced expression of MMP and pro-inflammatory genes. H3K9me2-mediated regulation of contractile and IL-1α-responsive VSMC gene expression was confirmed in cultured human VSMCs (hVSMCs). This prompted the use of hVSMCs to investigate the mechanism underlying H3K9me2-dependent regulation of IL-1α-mediated VSMC genes. Interestingly, G9A/GLP inhibition did not influence the level of IL-1α-induced nuclear localisation of the NFkB transcription factor p65 but significantly increased IL-1α-induced p65 binding to the IL6 promoter, correlating with reduced H3K9me2 levels. In contrast, enrichment of p65 was not observed at reported NFkB sites within the MMP3 promoter after IL-1α stimulation. Rather, IL-1α-induced MMP3 expression was dependent on JNK activity and G9A/GLP inhibition potentiated IL-1α-induced binding of the AP-1 transcription factor cJUN to the MMP3 promoter. Collectively, these findings suggest that H3K9me2 plays a role in maintaining the contractile VSMC state and prevents binding of both NFkB and AP-1 transcription factors at specific IL-1α-regulated genes to possibly block spurious induction of a pro-inflammatory state.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2019

Author dc:creator

• Harman, Jennifer

Advisor dc:contributor.advisor

• Jorgensen, Helle

• Vascular smooth muscle cell
• H3K9me2
• Vascular smooth muscle cell phenotypic switch

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/da7a350b-5524-44fe-94d7-9a1b3d1e17b5/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

en

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.37204

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/289975