Krüppel-like factor 5 regulates wound repair and the innate immune response in human airway epithelial cells

Involvement of CCL2 in Salivary Gland Response to Hyperosmolar Stress Related to Sjögren's Syndrome

In primary Sjögren's syndrome (pSS) patients, salivary gland (SG) epithelial cells (SGECs) could be exposed to chronic hyperosmotic stress (HOS), consecutive to their destruction and deregulation, that exacerbates an inflammatory response. The aims of this study were to assess the mechanism accounting for C-C motif chemokine ligand 2 (CCL2) expression in an immortalized human salivary gland epithelial acinar cell line (NS-SV-AC) subjected to HOS, as well as the involvement of CCL2 in pSS. CCL2 mRNA and protein levels were determined via RT-qPCR and ELISA. Reporter plasmids and a promoter pull-down assay were used to identify transcription factors associated with CCL2 mRNA increase. Our data showed that HOS-induced CCL2 mRNA increase was independent of the nuclear factor of activated T-cells 5 (NFAT5) and nuclear factor-kappa B (NFkB) but involved Kruppel-like factor 5 (KLF5). CCL2 protein levels, quantified by enzyme-linked immunosorbent assay (ELISA) in sera samples from pSS patients, correlated with the European Alliance of Associations for Rheumatology's Sjogren's syndrome disease activity index (ESSDAI) score for systemic activity. In addition, CCL2 protein levels were higher in patients with biological activity, cutaneous manifestations, and ESSDAI score superior or equal to five. Our data suggest that chronic HOS could exacerbate pSS disease by contributing to the inflammatory process induced by the expression and secretion of CCL2.

Suprabasal cells retain progenitor cell identity programs in eosinophilic esophagitis-driven basal cell hyperplasia

Eosinophilic esophagitis (EoE) is an esophageal immune-mediated disease characterized by eosinophilic inflammation and epithelial remodeling, including basal cell hyperplasia (BCH). Although BCH is known to correlate with disease severity and with persistent symptoms in patients in histological remission, the molecular processes driving BCH remain poorly defined. Here, we demonstrate that BCH is predominantly characterized by an expansion of nonproliferative suprabasal cells that are still committed to early differentiation. Furthermore, we discovered that suprabasal and superficial esophageal epithelial cells retain progenitor identity programs in EoE, evidenced by increased quiescent cell identity scoring and the enrichment of signaling pathways regulating stem cell pluripotency. Enrichment and trajectory analyses identified SOX2 and KLF5 as potential drivers of the increased quiescent identity and epithelial remodeling observed in EoE. Notably, these alterations were not observed in gastroesophageal reflux disease. These findings provide additional insights into the differentiation process in EoE and highlight the distinct characteristics of suprabasal and superficial esophageal epithelial cells in the disease.

Cellular heterogeneity in the 16HBE14o- airway epithelial line impacts biological readouts

The airway epithelial cell line, 16HBE14o- , is an important cell model for studying airway disease. 16HBE14o- cells were originally generated from primary human bronchial epithelial cells by SV40-mediated immortalization, a process that is associated with genomic instability through long-term culture. Here, we explore the heterogeneity of these cells, with respect to expression of the cystic fibrosis transmembrane conductance regulator (CFTR) transcript and protein. We isolate clones of 16HBE14o- with stably higher and lower levels of CFTR in comparison to bulk 16HBE14o- , designated CFTRhigh and CFTRlow . Detailed characterization of the CFTR locus in these clones by ATAC-seq and 4C-seq showed open chromatin profiles and higher order chromatin structure that correlate with CFTR expression levels. Transcriptomic profiling of CFTRhigh and CFTRlow cells showed that the CFTRhigh cells had an elevated inflammatory/innate immune response phenotype. These results encourage caution in interpreting functional data from clonal lines of 16HBE14o- cells, generated after genomic or other manipulations.

Suprabasal cells retaining stem cell identity programs drive basal cell hyperplasia in eosinophilic esophagitis

Eosinophilic esophagitis (EoE) is an esophageal immune-mediated disease characterized by eosinophilic inflammation and epithelial remodeling, including basal cell hyperplasia (BCH) and loss of differentiation. Although BCH correlates with disease severity and with persistent symptoms in patients in histological remission, the molecular processes driving BCH remain poorly defined. Here, we demonstrate that despite the presence of BCH in all EoE patients examined, no increase in basal cell proportion was observed by scRNA-seq. Instead, EoE patients exhibited a reduced pool of KRT15+ COL17A1+ quiescent cells, a modest increase in KI67+ dividing epibasal cells, a substantial increase in KRT13+ IVL+ suprabasal cells, and a loss of differentiated identity in superficial cells. Suprabasal and superficial cell populations demonstrated increased quiescent cell identity scoring in EoE with the enrichment of signaling pathways regulating pluripotency of stem cells. However, this was not paired with increased proliferation. Enrichment and trajectory analyses identified SOX2 and KLF5 as potential drivers of the increased quiescent identity and epithelial remodeling observed in EoE. Notably, these findings were not observed in GERD. Thus, our study demonstrates that BCH in EoE results from an expansion of non-proliferative cells that retain stem-like transcriptional programs while remaining committed to early differentiation.

A Kaleidoscope of Keratin Gene Expression and the Mosaic of Its Regulatory Mechanisms

Keratins are a family of intermediate filament-forming proteins highly specific to epithelial cells. A combination of expressed keratin genes is a defining property of the epithelium belonging to a certain type, organ/tissue, cell differentiation potential, and at normal or pathological conditions. In a variety of processes such as differentiation and maturation, as well as during acute or chronic injury and malignant transformation, keratin expression undergoes switching: an initial keratin profile changes accordingly to changed cell functions and location within a tissue as well as other parameters of cellular phenotype and physiology. Tight control of keratin expression implies the presence of complex regulatory landscapes within the keratin gene loci. Here, we highlight patterns of keratin expression in different biological conditions and summarize disparate data on mechanisms controlling keratin expression at the level of genomic regulatory elements, transcription factors (TFs), and chromatin spatial structure.

Genomic characterization and therapeutic utilization of IL-13-responsive sequences in asthma

Epithelial responses to the cytokine interleukin-13 (IL-13) cause airway obstruction in asthma. Here we utilized multiple genomic techniques to identify IL-13-responsive regulatory elements in bronchial epithelial cells and used these data to develop a CRISPR interference (CRISPRi)-based therapeutic approach to downregulate airway obstruction-inducing genes in a cell type- and IL-13-specific manner. Using single-cell RNA sequencing (scRNA-seq) and acetylated lysine 27 on histone 3 (H3K27ac) chromatin immunoprecipitation sequencing (ChIP-seq) in primary human bronchial epithelial cells, we identified IL-13-responsive genes and regulatory elements. These sequences were functionally validated and optimized via massively parallel reporter assays (MPRAs) for IL-13-inducible activity. The top secretory cell-selective sequence from the MPRA, a novel, distal enhancer of the sterile alpha motif pointed domain containing E-26 transformation-specific transcription factor (SPDEF) gene, was utilized to drive CRISPRi and knock down SPDEF or mucin 5AC (MUC5AC), both involved in pathologic mucus production in asthma. Our work provides a catalog of cell type-specific genes and regulatory elements involved in IL-13 bronchial epithelial response and showcases their use for therapeutic purposes.

Klf5 defines alveolar epithelial type 1 cell lineage commitment during lung development and regeneration

Alveolar epithelial cell fate decisions drive lung development and regeneration. Using transcriptomic and epigenetic profiling coupled with genetic mouse and organoid models, we identified the transcription factor Klf5 as an essential determinant of alveolar epithelial cell fate across the lifespan. We show that although dispensable for both adult alveolar epithelial type 1 (AT1) and alveolar epithelial type 2 (AT2) cell homeostasis, Klf5 enforces AT1 cell lineage fidelity during development. Using infectious and non-infectious models of acute respiratory distress syndrome, we demonstrate that Klf5 represses AT2 cell proliferation and enhances AT2-AT1 cell differentiation in a spatially restricted manner during lung regeneration. Moreover, ex vivo organoid assays identify that Klf5 reduces AT2 cell sensitivity to inflammatory signaling to drive AT2-AT1 cell differentiation. These data define the roll of a major transcriptional regulator of AT1 cell lineage commitment and of the AT2 cell response to inflammatory crosstalk during lung regeneration.

Krüppel-Like Factor 5 Regulates CFTR Expression Through Repression by Maintaining Chromatin Architecture Coupled with Direct Enhancer Activation

Single cell RNA-sequencing has accurately identified cell types within the human airway that express the Cystic Fibrosis Transmembrane Conductance regulator (CFTR) gene. Low abundance CFTR transcripts are seen in many secretory cells, while high levels are restricted to rare pulmonary ionocytes. Here we focus on the mechanisms coordinating basal CFTR expression in the secretory compartment. Cell-selective regulation of CFTR is achieved within its invariant topologically associating domain by the recruitment of cis-regulatory elements (CREs). CRE activity is coordinated by cell-type-selective transcription factors. One such factor, Krüppel-Like Factor 5 (KLF5), profoundly represses CFTR transcript and protein in primary human airway epithelial cells and airway cell lines. Here we reveal the mechanism of action of KLF5 upon the CFTR gene. We find that depletion or ablation of KLF5 from airway epithelial cells changes higher order chromatin structure at the CFTR locus. Critical looping interactions that are required for normal gene expression are altered, the H3K27ac active chromatin mark is redistributed, and CTCF occupancy is modified. However, mutation of a single KLF5 binding site within a pivotal airway cell CRE abolishes CFTR expression. Hence, KLF5 has both direct activating and indirect repressive effects, which together coordinate CFTR expression in the airway.