Introduction
Janus kinase (JAK)-signal transducer of activators of transcription (STAT) pathways play crucial roles in the intracellular signal transduction of various cytokines, including interferons (IFNs) [
1‐
4]. Genetic mutations in JAK-STAT-related molecules can lead to uncontrolled activation of downstream genes, resulting in clinical abnormality.
STAT1 gain-of-function (GOF) mutations cause an autosomal-dominant syndrome with variable clinical features [
5,
6]. The most common symptom is early-onset chronic mucocutaneous candidiasis (CMC), but a spectrum of various autoimmune and autoinflammatory features have also been reported [
7,
8]. In recent years, JAK inhibitors (JAKi) have been therapeutically used to treat patients with STAT1 GOF [
9‐
12]. Although JAKi treatment has yielded clinical benefits in several cases, it remains unclear what molecular events are elicited by JAKi.
Here, we longitudinally examined transcriptional and epigenetic changes in immune cells of a patient with STAT1 GOF, over a course of ruxolitinib treatment. To this end, we performed single-cell multi-omics analyses, including simultaneous profiling of proteins and RNA with cellular indexing of the transcriptomes and epitopes by sequencing (CITE-seq), and assay of transposase-accessible chromatin sequencing (ATAC-seq).
Methods
Subject Detail
This research was reviewed and approved by the institutional review board of Samsung Medical Center (IRB No. 2018–07-140). Informed consent was obtained from the study participant.
Cell Preparation
Peripheral blood mononuclear cells (PBMCs) were separated by density gradient centrifugation using lymphocyte separation medium (Corning), and cryopreserved in fetal bovine serum (FBS; Corning) with 10% DMSO (Sigma-Aldrich).
ELISA
Serum from the patient and healthy donors assessed for CXCL10 concentration using the human Recombinant Human CXCL10/IP-10 Protein ELISA kit (R&D) according to the manufacturer’s instructions.
FACS Analysis
Cryopreserved PBMCs were thawed and subjected to staining with fluorochrome-conjugated antibodies against surface markers for 10 min at room temperature. Dead cells were excluded from analysis using LIVE/DEAD red/aqua fluorescent reactive dye (Invitrogen, Waltham, MA, USA). Multicolor flow cytometry was carried out using an LSR II instrument (BD Biosciences, Franklin Lakes, NJ, USA), and the data were analyzed using FlowJo software (BD Biosciences).
Methanol Fixation
PBMCs were labeled with antibodies targeting surface markers. Subsequently, cells were exposed to IFN-β (50 ng/mL) or PBS for 10 min at 37 °C. This was followed by treatment with IC fixation buffer (Invitrogen) for 10 min at room temperature and fixation using 100% cold methanol for 40 min at 4 °C. Afterward, cells were stained with anti-human STAT1 antibodies for 1 h at room temperature before undergoing flow cytometry analysis.
Single-Cell RNA-seq Library Preparation
Single-cell CITE-seq and ATAC-seq libraries were generated using the Chromium Next GEM Automated Single Cell 3′ Library and Gel Bead Kit v3.1 (PN-1000147), 3ʹ Feature Barcode Kit (PN-1000262) and Chromium Next GEM Single Cell ATAC Kit v2 (PN-1000406), following the manufacturer’s instructions. Libraries were constructed and sequenced at a depth of approximately 20,000 reads per cell for gene, antibody-derived tag (ADT), and ATAC-seq fragment. The sequenced data were demultiplexed using the mkfastq function (Cell Ranger, 10X Genomics, v3.0.1) to generate fastq files. Demultiplexed fastq files of gene and ADT expression were aligned to the reference human genome (GRCh38; 10X Cell Ranger reference GRCh38 v3.0.0) and the barcode sequence of each ADT. Filtering, barcode counting, and UMI counting were performed to generate feature-barcode matrices using the count function (Cell Ranger, v3.0.1).
Single-Cell RNA-seq Analysis
The feature-barcode matrices of RNA and ADT expression were analyzed as follows, using the Seurat R package (Seurat, v4.1.1) [
13]. For basic quality control, we de-convoluted sample identity and filtered inter-individual multiplets using the demuxlet package [
14]. Next, we filtered low-quality cells expressing mitochondrial genes in > 15% of their total gene expression, or in > 5,000 genes. We also excluded doublets that initially clustered with doublets annotated through the demuxlet package.
Subsequently, the sctransform method (SCTransform function from sctransform package, v0.3.3) [
15] was used to perform normalization and variance stabilization of the RNA read count matrix with highly variable genes (
n = 2,000), and of the feature-barcode read count matrix with the whole list of feature barcodes. Principal component analysis (PCA; RunPCA function) was carried out to dimensional reduction for each transformed data matrix. Next, the cells underwent unsupervised clustering according to the weighted nearest neighbor (WNN) graph—applying the FindMultiModalNeighbors function, using the top 20 principal components (PCs) from RNA, and 20 PCs from feature barcode, along with the FindClusters function (resolution = 0.4). The results were visualized by Uniform Manifold Approximation and Projection (UMAP) using the top 20 PCs from RNA for whole PBMCs. For sub-clustering analysis of the monocyte immune subset, the cells underwent unbiased clustering, performed using the top 25 PCs from RNA and 15 PCs (resolution = 0.3) from feature barcode, and the results were visualized by UMAP using the top 20 PCs from RNA. To identify marker genes, differentially expressed genes (DEGs) in each cluster relative to the other clusters were selected based on the Wilcoxon rank sum test, using the FindAllMarkers function (parameter; log fold change compared to the other clusters > 0.25, > 0.6 min.pct2 [minimum fraction of test genes detected in cells of other clusters], and Bonferroni-adjusted
P < 0.05).
To describe the characteristic of each subcluster, we performed gene set enrichment analysis by calculating the gene set module score (AddModuleScore in Seurat package), combined score (enrichR), [
16] and enrichment score (GSEA v4.2.3, Broad Institute, CA, USA) using publicly available gene sets, including Gene Ontology: Biological process databases (GO.BP) [
17] and LINCS L1000 data [
18]. We filtered Gene Ontology (GO): Biological Process (BP) terms related to immune responses using the following inclusion criteria: "T_CELL", "IMMUNE", "INNATE", "ADAPTIVE", "INFLAM", "INTERLEUKIN", "INTERFERON", "NECROSIS", "APOPTOSIS", "SENESCENCE", "NATURAL", "LYMPHOCYTE", "LEUKOCYTE", "TRANSFORMING", "CHEMO", "CYTOTO", "CYTOKINE", "ANTIGEN", and "SIGNALING" and TRRUST TF. To investigate the dynamic changes of the monocyte immune subset, we exported cells from the monocyte immune subset for monocle’s standard analysis process (monocle v2.22.0) [
19]. CellDataSet objects were built based on the normalized count (SCTransform), and then processed using the estimateSizeFactor and estimate-Dispersions functions (default option), detectGenes (default option), setOrdering-Filter and reduceDimension (default option), orderCells (default option), and plot_cell_tra-jectory (default option).
Single-Cell ATAC-seq Analysis
The peak-cell matrices were analyzed as follows, using the Signac R package (Signac, v1.8.0) [
20]. For basic quality control, we calculated the nucleosome binding pattern, transcriptional start site (TSS) enrichment score that represents the accessibility signal over all TSS sites, and the ratio of reads in genomic blacklist regions. Next, we filtered low-quality cells using the ratio of mononucleosomal to nucleosome-free fragments (> 3), TSS enrichment (< 2), and ratio of reads in genomic blacklist regions (> 0.05). On the filtered matrix, we performed normalization and linear dimensional reduction using term frequency-inverse document frequency (TF-IDF) normalization, followed by singular value decomposition (SVD) using the top 25% of all peaks. Through this process, we calculated the latent semantic indexing (LSI) component (RunTFIDF, FindTopFeatures, and RunSVD function) [
21]. To integrate and correct the batch effect across each sample, we found integration anchors and integrated the datasets using reciprocal LSI projection. We calculated the gene activity score, which predicts and quantifies the activity of each gene in the genome, by assessing the chromatin accessibility associated with each gene, using the GeneActivity function.
Chip-qPCR
Collected PBMCs from healthy donors and a patient with STAT1 GOF mutation were cross-linked with 1% formaldehyde for 10 min and quenched with 125 mM glycine for 5 min at room temperature. The cross-linked PBMCs were lysed with 1% SDS buffer (1% SDS, 10 mM EDTA, 50 mM Tris pH 8.1) and chromatin was fractionated by sonication (Covaris, S220). The lysate was diluted with dilution buffer and incubated with pre-coated Dynabeads Protein A (Thermo, 10001D) with H3K27ac antibody (Active Motif, 39,133) and IgG as negative control overnight at 4ºC with rotation. A portion of diluted lysate was stored to quantify the total amount of DNA in each sample as input control. The immunoprecipitated chromatin was washed four times with RIPA buffer (140 mM NaCl, 1 mM EDTA, 0.5 Mm EGTA, 1% Triton X-100, 0.1% SDS, 0.1% sodium deoxycholate, 10 mM Tris pH 8.0) and incubated with RNase A (Thermo, EN0531) and proteinase K (NEB, P8107S) overnight at 65 ºC to reverse crosslink. The immunoprecipitated DNA was purified by AMPure XP beads (Beckman, A63881) and analyzed by Real-Time PCR using ChIP-qPCR primers (STAT1: FW – ACTCTGCGCAGGAAAGCGAA, RV – GGAACAGCCGCGTCTAATTG; IRF1: FW- AGCCAAGGAATTGCTCCAGT, RV – ACAGGGGGCTGAGTTCTCTT).
Resource Availability
Further information and requests for resources and reagents should be directed to and will be fulfilled by the lead contact, Eui-Cheol Shin (ecshin@kaist.ac.kr).
Data and Code Availability
CITE-seq data and ATAC-seq will be deposited at the NCBI GEO (
https://www.ncbi.nlm.nih.gov/geo/). This study did not generate any original code. Links to the publicly available R packages and codes used in the paper are listed in the key resources table. Any additional information required to reanalyze the data reported in this paper is available from the lead contact upon request.
Discussion
GOF mutations in the STAT1 gene result in an autosomal-dominant syndrome with diverse clinical manifestations. Patients with STAT1 GOF most commonly exhibit early-onset CMC and other bacterial, viral, and fungal infections, and may also experience autoimmune or autoinflammatory conditions. A large cohort study (
n = 60) revealed autoimmune manifestations in over one-third of patients with STAT1 GOF [
8]. These autoimmune manifestations can occur with varying degrees of severity, ranging from mild to life-threatening, and can affect diverse organs of the body. Potential conditions include hyperthyroidism, cutaneous diseases, systemic lupus erythematosus, inflammatory bowel disease, and IPEX-like symptoms [
8,
32].
The management of patients with STAT1 GOF can be challenging due to the complex and varied nature of the manifestations—often requiring a balanced approach that utilizes both antimicrobial and immunosuppressive therapies. Even with such interventions, many patients fail to adequately respond and require multiple courses of immunosuppressive treatments [
33]. In recent years, JAKi, small molecules that interfere with cytokine-dependent JAK-STAT pathways, have emerged as a promising treatment option for modulating aberrant immune responses in patients with STAT1 GOF [
9‐
12]. Although JAKi treatment has yielded clinical benefits in several cases, the detailed mechanisms underlying the effects of JAKi treatment have not yet been fully elucidated.
In the current study, we performed single-cell multi-omics analysis (including CITE-seq and ATAC-seq) to describe the longitudinal changes of the immune landscape in a patient with STAT1 GOF receiving JAKi treatment (ruxolitinib). We found that the patient with STAT1 GOF exhibited aberrant overexpression of ISGs, particularly u-ISG, prior to treatment. Ruxolitinib treatment resulted in decreased expression of these aberrantly overexpressed ISGs, accompanied by symptom relief. However, despite this improvement, epigenetic abnormalities of ISGs persisted even after ruxolitinib treatment. Moreover, the autoimmune symptoms recurred after discontinuation of ruxolitinib treatment. These observations suggest that the persistence of epigenetic abnormalities (so-called epigenetic scars) could lead to a propensity for aberrant IFN responses, and may lower the threshold of inflammatory stimulation, resulting in prolonged autoimmune symptoms.
The signaling pathway for type I IFNs typically involves STAT phosphorylation, leading to the formation of p-ISGF3 (a trimer of p-STAT1, p-STAT2, and IRF9), which induces the expressions of various ISGs [
34]. However, there is also evidence of non-canonical signaling that occurs through increased expression levels of STAT1, STAT2, and IRF9, rather than STAT phosphorylation [
29,
35,
36]. This non-canonical signaling is observed in situations such as prolonged IFN stimulation, and yields the induction of u-ISGF3, which specifically activates a subset of ISGs, known as u-ISGs. u-ISGF3 is known to be formed by prolonged exposure to type I IFNs rather than type II IFNs [
29,
30]. Interestingly, in our current study, the identified pretreatment DEGs displayed predominant expression of u-ISGs. Moreover, JAKi treatment resulted in significantly reduced expression levels of u-ISGs in both the monocyte subset and whole PBMCs. These results suggest that the defective STAT1 dephosphorylation observed in the patient with STAT1 GOF may result in prolonged and elevated expression of STAT1, which might in turn activate aberrant IFN signaling through the u-ISGF3 pathway. Ruxolitinib treatment was able to effectively regulate and terminate the aberrantly activated IFN signals in this patient.
Binding of type I and II IFNs to their receptors leads to the phosphorylation of JAKs, which then causes the recruitment and phosphorylation of downstream molecules, including STAT1 [
3]. In patients with STAT1 GOF, higher pSTAT1 levels are observed after exposure to IFNs, which is a critical molecular feature of the disease [
23]. Furthermore, increased pSTAT1 leads to upregulation of STAT1 itself. JAKi can suppress JAK phosphorylation, which is the cue initiating STAT1 phosphorylation and subsequent STAT1 upregulation; therefore, JAKi has recently been used for treatment of patients with STAT1 GOF [
10,
12].
Our current results revealed that ruxolitinib treatment could not reverse the epigenetic features of activated IFN signals in the patient with STAT1 GOF. Technical advancements in next-generation sequencing and single-cell analysis enable examination of the transcriptomic features of heterogeneous cell populations under healthy and pathological conditions [
37]. Disease-specific transcriptomic features may be resolved upon treatment. On the other hand, epigenetic changes are usually sustained even after clinical and transcriptional resolution. In a study using chromatin immunoprecipitation (ChIP) analysis, Epp et al. recently reported that PBCMs from patients with STAT1 GOF were significantly enriched with active chromatin mark trimethylation of lysine 4 of histone 3 (H3K4me3) in areas associated with ISGs, and that these epigenetic ISG signatures were retained even under low levels of serum IFN-α [
38]. Our current results showed that even after clinical resolution of autoimmune features following JAKi treatment, aberrantly activated epigenetic ISG signatures were retained, along with increased H3K27ac signal intensity in regions of ISGs, such as
STAT1 and
IRF1. These findings suggest the value of investigating treatment with agents, such as HDAC activators, that can restrict the prolonged increase of chromatin accessibility, and thereby improve clinical outcomes.
Recently, JAKi have been used to regulate pathological inflammatory responses in patients with various autoimmune diseases, including STAT1 GOF. However, there are not yet firmly established strategies for drug maintenance and dosage adjustment. Herein, we described the clinical and transcriptomic resolution of autoimmune features following ruxolitinib treatment in a patient with STAT1 GOF. Our ATAC-seq results revealed that this patient’s immune cells retained epigenetic scars even after ruxolitinib treatment. These findings help us understand the molecular mechanisms underlying the effects of JAKi treatment, which will guide further studies to establish the optimal usage of JAKi.
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