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Epigenomic analysis of Formalin-Fixed Paraffin-Embedded samples by CUT&Tag

ABSTRACT: For more than a century, Formalin Fixed Paraffin Embedded (FFPE) sample preparation has been the preferred method for long-term preservation of biological material. However, the use of FFPE samples for epigenomic studies has been difficult because of chromatin damage from long exposure to high concentrations of formaldehyde. Previously, we introduced Cleavage Under Targeted Accessible Chromatin (CUTAC), an antibody-targeted chromatin accessibility mapping protocol based on CUT&Tag. Here we show that simple modifications of our single-tube CUTAC protocol are sufficient to produce high-resolution maps of paused RNA Polymerase II (RNAPII) at enhancers and promoters using FFPE samples. We find that transcriptional regulatory element differences produced by FFPE-CUTAC distinguish between mouse brain tumor specimens and identify regulatory element markers with high confidence and precision. Our simple workflow is suitable for automation, making possible affordable epigenomic profiling of archived biological samples for biomarker identification, clinical applications and retrospective studies.

ORGANISM(S): Mus musculus Homo sapiens

PROVIDER: GSE235876 | GEO | 2023/09/08

REPOSITORIES: GEO

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Project description:Background and Aims: Liver proteomics with limited sample amounts is technically challenging but valuable for innovative hepatology research. We aimed to establish a simple and high-efficient approach for protein extraction and preparation from the formaldehyde-fixed paraffin-embedded (FFPE) liver samples for microproteomics assessment. Methods: Individual cell collected by laser capture microdissection (LCM) from FFPE liver slices were used as test samples with microscale samples of fresh-frozen liver or cultured liver cells as controls. Protocol for extracting protein was determined through the orthogonal test of 6 conditions of buffer compositions and heating processes. For sample preparation, we adjusted the protocol of single-tube solid-phase sample preparation (SP3) by enhancing protein precipitation and elution and developed a new method named HDMSP. HDMSP was then tested for its capability, reproducibility, and sample-type compatibility in analysis with nanoscale liquid chromatography-tandem mass spectrometry (nano LC-MS/MS). Results: For FFPE protein extraction, adding 4% SDS significantly increased the production by 2.5 times; incubation for 2 hours at 95℃ in alkaline amine buffer improved both the efficiency and quality of protein extraction. For the development of HDMSP, using 2% SDS to elute protein, using 70% acetonitrile but not ethanol, and increasing input of carboxyl magnetic beads to 2 mg/ml improved the rate of protein recovery by 88%, 50%, and 74%, respectively. For either 20 nL FFPE liver or HepG2 cell samples, or 1~2 μg fresh-frozen liver samples, the rate of protein recovery was stable at around 75%. LC-MS/MS demonstrated that the protocol designed for FFPE samples protein extraction allowed for unbiased extraction of insoluble or hydrophobic proteins and with HDMSP, the depth, identification, physicochemical properties, subcellular locations, and reproducibility of FFPE liver microproteome was comparable to those of fresh-frozen sample control. HDMSP also showed high efficiency and reproducibility for subcellular nuclear and cytoplasm-isolated proteins. Conclusion: The new approach including 300mM Tris, 4% SDS incubation for 2h at 95°C, and then preparation with HDMSP is simple, robust, and highly efficient for use in microproteomics of FFPE liver samples. This protocol can provide a solution reference for liver FFPE microproteomics.

Project description:Background: The main bottleneck for genomic studies of tumors is the limited availability of fresh frozen (FF) samples collected from patients, coupled with comprehensive long-term clinical follow-up. This shortage could be alleviated by using existing large archives of routinely obtained and stored Formalin-Fixed Paraffin-Embedded (FFPE) tissues. However, since these samples are partially degraded, their RNA sequencing is technically challenging. Results: In an effort to establish a reliable and practical procedure, we compared three protocols for RNA sequencing using pairs of FF and FFPE samples, both taken from the same breast tumor. In contrast to previous studies, we compared the expression profiles obtained from the two matched sample types, using the same protocol for both. Three protocols were tested on low initial amounts of RNA, as little as 100 ng, to represent the possibly limited availability of clinical samples. For two of the three protocols tested, poly(A) selection (mRNA-seq) and ribosomal-depletion, the total gene expression profiles of matched FF and FFPE pairs were highly correlated. For both protocols, differential gene expression between two FFPE samples was in agreement with their matched FF samples. Notably, although expression levels of FFPE samples by mRNA-seq were mainly represented by the 3'-end of the transcript, they yielded very similar results to those obtained by ribosomal-depletion protocol, which produces uniform coverage across the transcript. Further, focusing on clinically relevant genes, we showed that the high correlation between expression levels persists at higher resolutions. Conclusions: Using the poly(A) protocol for FFPE exhibited, unexpectedly, similar efficiency to the ribosomal-depletion protocol, with the latter requiring much higher (2-3 fold) sequencing depth to compensate for the relative low fraction of reads mapped to the transcriptome. The results indicate that standard poly(A)-based RNA sequencing of archived FFPE samples is a reliable and cost-effective alternative for measuring mRNA-seq on FF samples. Expression profiling of FFPE samples by mRNA-seq can facilitate much needed extensive retrospective clinical genomic studies.

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Epigenomic analysis of Formalin-Fixed Paraffin-Embedded samples by CUT&Tag

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