脂肪肉腫は最も頻度の高い成人軟部肉腫であり、高分化型脂肪肉腫と悪性度の高い脱分化型脂肪肉腫が代表的な組織型である。その成因は間葉系幹細胞から前駆脂肪細胞、成熟脂肪細胞への分化異常とされる。しかしながら、脂肪肉腫発生におけるエピゲノム異常については殆ど報告がない。そこで我々は、高分化型脂肪肉腫6検体、脱分化型10検体、正常脂肪組織6検体を用いて、Infinium HumanMethylationEPIC BeadChipによる網羅的なDNAメチル化解析を行った。全CpGプローブを用いた主成分分析 (PCA)から、3群はそれぞれグループを成し、正常脂肪組織は近接して分布し類似性が高いのに対し、脱分化型脂肪肉腫は広範に分布し腫瘍間不均質性が高い事が分かった。PC1・PC2への寄与率が高く、脱分化型脂肪肉腫で高メチル化 (∆β >0.2）の193プローブは脂肪分化に重要なPPARγの結合領域を多く含んでいた (6.2%: 全ゲノム中1.1%)。これらの事から、脱分化型脂肪肉腫の発生にはDNAメチル化による脂肪分化関連遺伝子の発現抑制と、脂肪分化に重要な領域のエピゲノム異常が関与している事が示された。
Well-differentiated liposarcomas (WDLPS) and dedifferentiated liposarcomas (DDLPS) are the most common soft-tissue sarcomas in adults. They develop as a result of a disturbance in adipogenic differentiation however, the epigenomic changes underlying liposarcomagenesis are unknown. Here, we aimed to elucidate the role of epigenomic alterations in the initiation of DDLPS.
Genome-wide DNA methylation profiles of 15 liposarcoma (6 WDLPS and 9 DDLPS) samples and 6 normal adipose tissue samples were obtained using the Infinium MethylationEPIC BeadChip. After grouping neighboring probes into genomic blocks (GBs, < 500 bp), principal component analysis of all the CpG GBs (n = 535,684) was conducted. Each of normal adipose tissue and WDLPS grouped closely while DDLPS distributed broadly, indicating heterogeneous methylation profiles among the DDLPS samples. Unsupervised hierarchical cluster analysis of enhancers (2,000 GBs with the high SD of 23,478 GBs) classified the samples into three tissue types, whereas that of promoters (1,000 GBs with the high SD of 8,668 GBs) could not classify the DDLPS samples distinctly.
The Jonckheere-Terpstra trend test revealed 9,945 hypermethylated (p < 0.01, Δβ > 0.2) GBs in DDLPS compared to those in normal adipose tissues and WDLPS samples. Based upon a report on enhancers in adipocytes (Mikkelsen et al. Cell 143, 156–169. 2010), the hypermethylated GBs in DDLPS were enriched with typical- (2.2%: whole genome 1.2%) and super- (13.5%: whole genome 7.0%) enhancers. Genes involved in adipogenesis, including PPARG2, the master regulator of adipogenesis, and its target genes (FABP4 and PLIN1), were aberrantly methylated at the enhancers and repressed in DDLPS.
Taken together, these data indicate that aberrant methylation at the enhancers of adipogenic genes might be crucial for the generation of DDLPS.
|
