Biology subjects

Fernandez, R. J.

Publications and source records attributed to Fernandez, R. J..

6 recordsLinked to original sources

bioRxiv2026

IPF distal lung epithelial cells acquire a DNA methylation signature consistent with activation of basal cell transcriptional programs

Idiopathic pulmonary fibrosis (IPF) is a progressive fibrotic interstitial lung disease associated with failed alveolar epithelial repair with an expansion of aberrant airway-like epithelium in the alveolar space leading to lung function decline usually resulting in death within 3-5 years of diagnosis. While single-cell and spatial transcriptomic approaches have been used to characterize disease-emergent cell populations, less is known about the regulation of transcriptional programs that drive failed alveolar epithelial cell repair in IPF. DNA methylation is a fundamental layer of gene regulation that stabilizes differentiated cell identity; however, changes in methylation in the epithelial compartment in IPF have not been studied. To identify novel epigenetic mediators of epithelial cell dysfunction, we performed high-resolution DNA methylation profiling of purified distal lung epithelial cells from 10 age-matched control and 14 IPF lungs using Oxford Nanopore Technologies (ONT) whole-genome, long-read sequencing. We identified widespread methylome remodeling in the IPF lung epithelium, with 84% of differentially methylated regions (DMRs) hypomethylated. DMRs were largely found outside of promoters, with 88% outside of 3 kb from the transcription start site (TSS), consistent with altered distal regulatory element activity. DMRs were enriched for transcription factor (TF) binding site motifs and gene associations consistent with dysregulation of polycomb repressive complex 2 (PRC2) and increases in p63 activity. DNA methylation at DMRs associated with p63 target genes, including KRT5, and genes implicated in failed epithelial repair, including MUC5B, MMP7, and S100A2 inversely correlated with gene expression. Consistent with the observed dysregulation of the IPF epithelial methylome, an experimental co-culture model of alveolar type II epithelial cell (AT2s) to basal-like epithelial cell transdifferentiation revealed widespread hypomethylation. Further, sites associated with NKX2.1 and FOXA1/2 binding, TFs involved in alveolar fate maintenance, were hypermethylated, suggesting loss of epigenetic regulation of alveolar identity. Together, these data implicate DNA methylation in the failed alveolar epithelial repair processes in IPF, potentially providing future therapeutic strategies by identifying putative regulatory elements associated with aberrant transcriptional programs.

molecular biology↗

bioRxiv2025

Loss of Regulator of telomere elongation helicase (Rtel1) impairs alveolar epithelial cell progenitor function but does not exacerbate experimental fibrosis

Inherited loss-of-function mutations in the replication-associated helicase Regulator of telomere elongation helicase (RTEL1) are among the most frequent monogenic causes of familial pulmonary fibrosis (FPF), but the specific functional role of RTEL1 in lung development, homeostasis, and injury-repair has not been determined. Using single-cell RNA-sequencing to define the cellular diversity and molecular programs following intratracheal bleomycin injury in mice, we observed that Rtel1 was most highly expressed in the lung epithelium, and its expression was reduced in PF epithelial cells compared to nonfibrotic controls. While global deletion of Rtel1 leads to embryonic lethality, constitutive deletion of Rtel1 in the lung epithelium (Rtel{Delta}epi) led to normal lung structure and architecture. Rtel1{Delta}epi mice exhibited accelerated telomere attrition and impaired AEC progenitor potential ex-vivo. Despite decreased AEC progenitor function, no differences in lung fibrosis were observed in Rtel{Delta}epi mice compared to controls following single-dose or repetitive intratracheal bleomycin. Together, these data implicate RTEL1 as a regulator of AEC progenitor function but this level of progenitor dysfunction is not alone sufficient to cause or exacerbate experimental lung fibrosis.

cell biology↗

bioRxiv2023

Telomeric DNA breaks in human induced pluripotent stem cells trigger ATR-mediated arrest and telomerase-independent telomere length maintenance

Although mechanisms of telomere protection are well-defined in differentiated cells, it is poorly understood how stem cells sense and respond to telomere dysfunction. Recent efforts have characterized the DNA damage response (DDR) following progressive telomere erosion in human pluripotent cells, yet the broader impact of telomeric double-strand breaks (DSBs) in these cells is poorly characterized. Here, we report on DNA damage signaling, cell cycle, and transcriptome-level changes in human induced pluripotent stem cells (iPSCs) in response to telomere-internal DSBs. We engineered a novel human iPSC line with a targeted doxycycline-inducible TRF1-FokI fusion protein to acutely induce DSBs at telomeres. Using this model, we demonstrate that TRF1-FokI DSBs activate an ATR-dependent DDR in iPSCs, in contrast to an established ATM-dependent response to telomeric FokI breaks in differentiated cells. ATR activation leads to a potent cell cycle arrest in G2, which we show is p53-independent and can be rescued by treatment with an ATR inhibitor. Telomere lengths are remarkably well-maintained in the face of persistent TRF1-FokI induction. Using CRISPR-Cas9 to cripple the catalytic domain of telomerase, we show that telomerase is largely dispensable for survival and telomere length maintenance following telomeric breaks, which instead appear to be repaired by a mechanism bearing hallmarks of lengthening mediated by homologous recombination, so-called alternative lengthening of telomeres (ALT). Our findings suggest a previously unappreciated role for ALT in telomere maintenance in telomerase-positive iPSCs and reveal distinct iPSC-specific responses to targeted telomeric damage.

cell biology↗

bioRxiv2022

Edge-focused network-based approach: an improved kernel density estimator for home range

O_LIOne of the central challenges in ecology and animal behaviour is to generate animal home range estimations. Kernel density estimate for home range has been one of the most widely used estimates these last few decades, despite its limitations. More recently a network-based kernel density (NKDE) approach has been proposed, which uses Delaunay triangulation. C_LIO_LIHere we show that NKDE has a discontinuous kernel density. We then develop a new network-based method that emphasises entirely on the edges, instead of the nodes in the network. We call this Edge-Focused Network-based Kernel Density Estimation (EFNKDE). In this method, a unit weight is distributed uniformly along each edge of the network and Euclidean distance is used to compute the contribution of each segment of the edge to the kernel density at a given point. C_LIO_LIThis is a network based method that leads to a continuous and differentiable kernel density. An analytical expression for the same is obtained for the Gaussian kernel. By taking concrete examples and studying different methods and through different perspectives across a range of bandwidths, we show that EFNKDE has many advantages over other methods. We present a model that provides a theoretical basis to the effectiveness of EFNKDE in linear regimes. C_LIO_LIEFNKDE is easy to apply, can work with minimal data, provides a smooth kernel density that highlights the network and does not overemphasise the data. This method is most suitable for estimating home ranges with narrow corridors and forbidden regions. C_LI

ecology↗

bioRxiv2021

Patient induced pluripotent stem cell-derived hepatostellate organoids establish a basis for liver pathologies in telomeropathies

Patients with dyskeratosis congenita (DC) and related telomeropathies resulting from premature telomere dysfunction suffer from multi-organ failure. In the liver, DC patients present with nodular hyperplasia, steatosis, inflammation, and cirrhosis. We model DC liver pathologies using isogenic human induced pluripotent stem (iPS) cells harboring a causal DC mutation in DKC1, or a clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9-corrected control allele. Differentiation of these iPS cells into hepatocytes or hepatic stellate cells followed by generation of genotype-admixed hepatostellate organoids revealed a dominant phenotype in the parenchyma, with DC hepatocytes eliciting a pathogenic hyperplastic response in stellate cells independent of stellate cell genotype. Pathogenic phenotypes could be rescued via suppression of AKT activity, a central regulator of MYC-driven hyperplasia downstream of DKC1 mutation. Thus, isogenic iPS-derived admixed hepatostellate organoids offer insight into the liver pathologies in telomeropathies and provide a framework for evaluating emerging therapies.

cell biology↗

bioRxiv2020

GSK3 inhibition rescues growth and telomere dysfunction in dyskeratosis congenita iPSC-derived type II alveolar epithelial cells

Dyskeratosis congenita (DC) is a rare genetic disorder characterized by deficiencies in telomere maintenance leading to very short telomeres and the premature onset of certain age-related diseases, including pulmonary fibrosis (PF). PF is thought to derive from epithelial failure, particularly that of type II alveolar epithelial (AT2) cells, which are highly dependent on Wnt signaling during development and adult regeneration. We use human iPSC-derived AT2 (iAT2) cells to model how short telomeres affect AT2 cells. Cultured DC mutant iAT2 cells accumulate shortened, uncapped telomeres and manifest defects in the growth of alveolospheres, hallmarks of senescence, and apparent defects in Wnt signaling. The GSK3 inhibitor, CHIR99021, which mimics the output of canonical Wnt signaling, enhances telomerase activity and rescues the defects. These findings support further investigation of Wnt agonists as potential therapies for DC related pathologies.

cell biology↗