Investigation of the roles of histone deacetylases in rheumatoid arthritis and collagen-induced arthritis

Rheumatoid arthritis (RA) is a chronic, autoimmune, inflammatory disease that affects synovial joints. A key characteristic of RA is hyperplasia of fibroblast-like synoviocytes (FLS) which develop a stable, auto-aggressive phenotype that augments tissue destruction. It is unknown how this phenotype is stably maintained; however, epigenetic changes have been implicated. Histone deacetylation is one proposed method; a process controlled by histone deacetylases (HDACs). However, there have recently been reports publishing conflicting data regarding the expression of HDACs in RA synovium and FLS. The objective of this thesis is to determine the role of HDACs in regulating the auto-aggressive phenotype of RA through studies in FLS and in mice.

Real time-quantitative PCR was used to assess the levels of HDAC1-11 in RA compared to osteoarthritis (OA) FLS. Immunohistochemistry and western blotting were used to assess protein expression of HDAC1 in RA and OA synovial tissue and FLS. HDAC1 was found to be overexpressed in RA compared to OA. HDAC1 was knocked down in RA FLS, then cell proliferation, migration and invasion were assessed by using tritiated thymidine, a scratch assay and a Matrigel invasion assay respectively. All three functions were significantly reduced following HDAC1 knockdown. An Illumina BeadChip (47,000 transcripts) was used to analyse global gene expression changes after knockdown. This revealed significant gene changes in important functional clusters, such as proliferation and migration. HDAC1 knockout is embryonic lethal in mice, so the in vivo role of HDAC1 was investigated in a mouse model of collagen-induced arthritis (CIA) using in vivo siRNAs. Clinical scores of CIA were measured daily and HDAC1 knockdown mice showed a significantly reduced clinical score compared to controls, comparable to dexamethasone-treated mice. The bones were analysed using a microCT scanner and histology. Knocking down HDAC1 showed reduced bone erosion, joint inflammation and cartilage degradation compared to controls.

Overall, this study shows that HDAC1 is dysregulated in RA and it has a significant role in the autoaggressive phenotype shown in RA FLS and collagen-induced arthritis. The novel data shown in this thesis demonstrates that inhibiting HDAC1 may provide a powerful new target for treating RA.