STUDY QUESTION What are the cellular composition and single-cell transcriptomic differences between myometrium and leiomyomas as defined by single-cell RNA sequencing? SUMMARY ANSWER We discovered cellular heterogeneity in smooth muscle cells (SMCs), fibroblast and endothelial cell populations in both myometrium and leiomyoma tissues. WHAT IS KNOWN ALREADY Previous studies have shown the presence of SMCs, fibroblasts, endothelial cells and immune cells in myometrium and leiomyomas. However, there is no information on the cellular heterogeneity in these tissues and the transcriptomic differences at the single-cell level between these tissues. STUDY DESIGN, SIZE, DURATION We collected five leiomyoma and five myometrium samples from a total of eight patients undergoing hysterectomy. We then performed single-cell RNA sequencing to generate a cell atlas for both tissues. We utilized our single-cell sequencing data to define cell types, compare cell types by tissue type (leiomyoma versus myometrium) and determine the transcriptional changes at a single-cell resolution between leiomyomas and myometrium. Additionally, we performed MED12-variant analysis at the single-cell level to determine the genotype heterogeneity within leiomyomas. PARTICIPANTS/MATERIALS, SETTING, METHODS We collected five MED12-variant positive leiomyomas and five myometrium samples from a total of eight patients. We then performed single-cell RNA sequencing on freshly isolated single-cell preparations. Histopathological assessment confirmed the identity of the samples. Sanger sequencing was performed to confirm the presence of the MED12 variant in leiomyomas. MAIN RESULTS AND ROLE OF CHANCE Our data revealed previously unknown heterogeneity in the SMC, fibroblast cell and endothelial cell populations of myometrium and leiomyomas. We discovered the presence of two different lymphatic endothelial cell populations specific to uterine leiomyomas. We showed that both myometrium and MED12-variant leiomyomas are relatively similar in cellular composition but differ in cellular transcriptomic profiles. We found that fibroblasts influence the leiomyoma microenvironment through their interactions with endothelial cells, immune cells and SMCs. Variant analysis at the single-cell level revealed the presence of both MED12 variants as well as the wild-type MED12 allele in SMCs of leiomyomatous tissue. These results indicate genotype heterogeneity of cellular composition within leiomyomas. LARGE SCALE DATA The datasets are available in the NCBI Gene Expression Omnibus (GEO) using GSE162122. LIMITATIONS, REASONS FOR CAUTION Our study focused on MED12-variant positive leiomyomas for single-cell RNA sequencing analyses. Leiomyomas carrying other genetic rearrangements may differ in their cellular composition and transcriptomic profiles. WIDER IMPLICATIONS FOR THE FINDINGS Our study provides a cellular atlas for myometrium and MED12-variant positive leiomyomas as defined by single-cell RNA sequencing. Our analysis provides significant insight into the differences between myometrium and leiomyomas at the single-cell level and reveals hitherto unknown genetic heterogeneity in multiple cell types within human leiomyomas. Our results will be important for future studies into the origin and growth of human leiomyomas. STUDY FUNDING/COMPETING INTEREST(S) This work was supported by funding from the National Institute of Child Health and Human Development (HD098580 and HD088629). The authors declare no competing interests.

Non-coding RNAs (ncRNAs) are emerging as important regulators in various pathological conditions, including human cancers. NcRNAs exert potentially crucial effects on cell cycle progression, proliferation, and invasion in cancer cells by targeting various cell cycle-related proteins at transcriptional and post-transcriptional levels. As one of the key cell cycle regulatory proteins, p21 is involved in various processes, including the cellular response to DNA damage, cell growth, invasion, metastasis, apoptosis, and senescence. P21 has been shown to have either a tumor-suppressive or oncogenic effect depending on the cellular localization and posttranslational modifications. P21 exerts a significant regulatory effect on both G1/S and G2/M checkpoints by regulating the function of cyclin-dependent kinase enzymes (CDKs) or interacting with proliferating cell nuclear antigen (PCNA). P21 has an important effect on the cellular response to DNA damage by separating DNA replication enzymes from PCNA and inhibiting DNA synthesis resulting in G1 phase arrest. Furthermore, p21 has been shown to negatively regulate the G2/M checkpoint through the inactivation of cyclin-CDK complexes. In response to any cell damage caused by genotoxic agents, p21 exerts its regulatory effects by nuclear preservation of cyclin B1-CDK1 and preventing their activation. Notably, several ncRNAs, including lncRNAs and miRNAs, have been shown to be involved in tumor initiation and progression through the regulation of the p21 signaling axis. In this review, we discuss the miRNA/lncRNA-dependent mechanisms that regulate p21 and their effects on gastrointestinal tumorigenesis. A better understanding of the regulatory effects of ncRNAs on the p21 signaling may help to discover novel therapeutic targets in gastrointestinal cancer.

No abstract