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The devastating effects and incurable nature of hereditary and sporadic retinal diseases such as Stargardt disease, age-related macular degeneration or retinitis pigmentosa urgently require the development of new therapeutic strategies. Additionally, a high prevalence of retinal toxicities is becoming more and more an issue of novel targeted therapeutic agents. Ophthalmologic drug development, to date, largely relies on animal models, which often do not provide results that are translatable to human patients. Hence, the establishment of sophisticated human tissue-based in vitro models is of upmost importance. The discovery of self-forming retinal organoids (ROs) derived from human embryonic stem cells (hESCs) or human induced pluripotent stem cells (hiPSCs) is a promising approach to model the complex stratified retinal tissue. Yet, ROs lack vascularization and cannot recapitulate the important physiological interactions of matured photoreceptors and the retinal pigment epithelium (RPE). In this study, we present the retina-on-a-chip (RoC), a novel microphysiological model of the human retina integrating more than seven different essential retinal cell types derived from hiPSCs. It provides vasculature-like perfusion and enables, for the first time, the recapitulation of the interaction of mature photoreceptor segments with RPE in vitro. We show that this interaction enhances the formation of outer segment-like structures and the establishment of in vivo-like physiological processes such as outer segment phagocytosis and calcium dynamics. In addition, we demonstrate the applicability of the RoC for drug testing, by reproducing the retinopathic side-effects of the anti-malaria drug chloroquine and the antibiotic gentamicin. The developed hiPSC-based RoC has the potential to promote drug development and provide new insights into the underlying pathology of retinal diseases.

The breakthrough of reprogramming human somatic cells was achieved in 2006 by the work of Yamanaka and Takahashi. From this point, fibroblasts are the most commonly used primary somatic cell type for the generation of induced pluripotent stem cells (iPSCs). Various characteristics of fibroblasts supported their utilization for the groundbreaking experiments of iPSC generation. One major advantage is the high availability of fibroblasts which can be easily isolated from skin biopsies. Furthermore, their cultivation, propagation, and cryoconservation properties are uncomplicated with respect to nutritional requirements and viability in culture. However, the required skin biopsy remains an invasive approach, representing a major drawback for using fibroblasts as the starting material. More and more studies appeared over the last years, describing the reprogramming of other human somatic cell types. Cells isolated from blood samples or urine, as well as more unexpected cell types, like pancreatic islet beta cells, synovial cells, or mesenchymal stromal cells from wisdom teeth, show promising characteristics for a reprogramming strategy. Here, we want to highlight the advantages of keratinocytes from human plucked hair as a widely usable, noninvasive harvesting method for primary material in comparison with other commonly used cell types.

Amyotrophic lateral sclerosis (ALS) is the most frequent motor neuron disease. Cytoplasmic fused in sarcoma (FUS) aggregates are pathological hallmarks of FUS-ALS. Proper shuttling between the nucleus and cytoplasm is essential for physiological cell function. However, the initial event in the pathophysiology of FUS-ALS remains enigmatic. Using human induced pluripotent stem cell (hiPSCs)-derived motor neurons (MNs), we show that impairment of poly(ADP-ribose) polymerase (PARP)-dependent DNA damage response (DDR) signaling due to mutations in the FUS nuclear localization sequence (NLS) induces additional cytoplasmic FUS mislocalization which in turn results in neurodegeneration and FUS aggregate formation. Our work suggests that a key pathophysiologic event in ALS is upstream of aggregate formation. Targeting DDR signaling could lead to novel therapeutic routes for ameliorating ALS. Abnormal cytoplasmic aggregates of FUS are a hallmark of some forms of amyotrophic lateral sclerosis (ALS). Here, using neurons derived from patients with FUS-ALS, the authors demonstrate that impairment of PARP-dependent DNA damage signaling is an event that occurs upstream of neurodegeneration and cytoplasmic aggregate formation in FUS-ALS.

Infection-related diabetes can arise as a result of virus-associated β-cell destruction. Clinical data suggest that the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), causing the coronavirus disease 2019 (COVID-19), impairs glucose homoeostasis, but experimental evidence that SARS-CoV-2 can infect pancreatic tissue has been lacking. In the present study, we show that SARS-CoV-2 infects cells of the human exocrine and endocrine pancreas ex vivo and in vivo. We demonstrate that human β-cells express viral entry proteins, and SARS-CoV-2 infects and replicates in cultured human islets. Infection is associated with morphological, transcriptional and functional changes, including reduced numbers of insulin-secretory granules in β-cells and impaired glucose-stimulated insulin secretion. In COVID-19 full-body postmortem examinations, we detected SARS-CoV-2 nucleocapsid protein in pancreatic exocrine cells, and in cells that stain positive for the β-cell marker NKX6.1 and are in close proximity to the islets of Langerhans in all four patients investigated. Our data identify the human pancreas as a target of SARS-CoV-2 infection and suggest that β-cell infection could contribute to the metabolic dysregulation observed in patients with COVID-19. SARS-CoV-2 is shown to infect and replicate in human pancreatic tissue, including in β-cells, which is associated with morphological, transcriptomic and functional changes.

Telogen effluvium (TE), a form of hair loss, has emerged in a subset of COVID-19 patients, typically occurring several weeks after infection. TE is characterized by premature entry of hair follicles (HFs) into the telogen phase of the hair cycle. We analyzed the expression of the viral entry factors ACE2 and TMPRSS2 in human scalp specimens. In cryosections of skin biopsies and plucked HFs, both proteins localized to the basal layer of the outer root sheath (ORS), with TMPRSS2 also present in Henle’s layer of the inner root sheath (IRS). Ex vivo infection of plucked HFs with SARS-CoV-2 revealed nucleocapsid (NC) protein immunoreactivity in the ORS in two of three donors, corresponding to the K15⁺ epithelial stem/progenitor cell population. These NC⁺ cells co-expressed cleaved caspase3 (CAS3) and TUNEL, indicating apoptosis-related changes. Our findings suggest that SARS-CoV-2 nucleocapsid protein accumulates in ORS cells, potentially triggering local stress responses and apoptosis. This may provide a mechanistic link between SARS-CoV-2 infection and TE and highlights the HF as a potential, yet understudied, target organ in COVID-19.

ObjectiveATM serine/threonine kinase (ATM) is the most frequently mutated DNA damage response gene, involved in homologous recombination (HR), in pancreatic ductal adenocarcinoma (PDAC).DesignCombinational synergy screening was performed to endeavour a genotype-tailored targeted therapy.ResultsSynergy was found on inhibition of PARP, ATR and DNA-PKcs (PAD) leading to synthetic lethality in ATM-deficient murine and human PDAC. Mechanistically, PAD-induced PARP trapping, replication fork stalling and mitosis defects leading to P53-mediated apoptosis. Most importantly, chemical inhibition of ATM sensitises human PDAC cells toward PAD with long-term tumour control in vivo. Finally, we anticipated and elucidated PARP inhibitor resistance within the ATM-null background via whole exome sequencing. Arising cells were aneuploid, underwent epithelial-mesenchymal-transition and acquired multidrug resistance (MDR) due to upregulation of drug transporters and a bypass within the DNA repair machinery. These functional observations were mirrored in copy number variations affecting a region on chromosome 5 comprising several of the upregulated MDR genes. Using these findings, we ultimately propose alternative strategies to overcome the resistance.ConclusionAnalysis of the molecular susceptibilities triggered by ATM deficiency in PDAC allow elaboration of an efficient mutation-specific combinational therapeutic approach that can be also implemented in a genotype-independent manner by ATM inhibition.

In this study, a detailed analysis of the outgrowth of primary keratinocytes from plucked human hair follicles was conducted. Plucked hair follicles offer an easily accessible and non-invasive method as a primary cell source for adult somatic keratinocytes, providing a simple starting material for induced pluripotent stem cell (iPSC) reprogramming. In this study, we laid our focus on the precise examination of timing and location of the first keratinocyte outgrowth after plucking, as well as the morphological changes that occur during cultivation. Our results show that the region of the hair follicle, from which the initial outgrowth occurs, is crucial for successful cultivation. Additionally, first appearing protrusions and first visible cells show the same specific marker expression as the intact outer root sheath. We therefore conclude that initially appearing keratinocytes arise from the basal layer of the outer root sheath. To improve the whole process, the protocol was adjusted to reduce the time until successful outgrowth. These optimizations are particularly relevant for developing a standardized protocol that works efficiently across all individuals, including patients with difficult-to-culture hair follicles. The accelerated cell harvesting could prove valuable in future applications in regenerative medicine, especially for patients where culture times have previously been too long.

Given their capability to differentiate into each cell type of the human body, human pluripotent stem cells (hPSCs) provide a unique platform for developmental studies. In the current study, we employed this cell system to understand the role of pancreatic progenitor differentiation and proliferation factor (PPDPF), a protein that has been little explored so far. While the zebrafish orthologue exdpf is essential for exocrine pancreas specification, its importance for mammalian and human development has not been studied yet. We implemented a four times CRISPR/Cas9 nicking approach to knockout PPDPF in human embryonic stem cells (hESCs) and differentiated PPDPF KO/KO and PPDPF WT/WT cells towards the pancreatic lineage. In contrast to data obtained from zebrafish, a very modest effect of the knockout was observed in the development of pancreatic progenitors in vitro , not affecting lineage specification upon orthotopic transplantation in vivo . The modest effect is in line with the finding that genetic variants near PPDPF are associated with random glucose levels in humans, but not with type 2 diabetes risk, supporting that dysregulation of this gene may only result in minor alterations of glycaemic balance in humans. In addition, PPDPF is less organ- and cell type specifically expressed in higher vertebrates and its so far reported functions appear highly context-dependent.

Pancreatic ductal adenocarcinoma (PDAC) is associated with accumulation of particular oncogenic mutations and recent genetic sequencing studies have identified ataxia telangiectasia-mutated (ATM) mutations in PDAC cohorts. Here we report that conditional deletion of ATM in a mouse model of PDAC induces a greater number of proliferative precursor lesions coupled with a pronounced fibrotic reaction. ATM-targeted mice display altered TGFβ-superfamily signalling and enhanced epithelial-to-mesenchymal transition (EMT) coupled with shortened survival. Notably, our mouse model recapitulates many features of more aggressive human PDAC subtypes. Particularly, we report that low expression of ATM predicts EMT, a gene signature specific for Bmp4 signalling and poor prognosis in human PDAC. Our data suggest an intimate link between ATM expression and pancreatic cancer progression in mice and men. Mutations in the serine/threonine kinase ataxia teleangiectasia mutated (ATM) have been linked to pancreatic ductal adenocarcinoma (PDAC) cohorts. Here Russell et al . show that loss of ATM induces a greater number of proliferative precursor lesions in a mouse model, recapitulating many features of human PDAC subtypes.

Background Pancreatic ductal adenocarcinomas (PDACs) are highly lethal and aggressive with oncogenic KRAS being the main oncogenic driver of the disease. PDACs have been extensively profiled at advanced stages, and in advanced disease the tumor microenvironment is a major determinant that critically shapes patient outcomes. Since the molecular events occurring prior to invasive growth remain poorly understood, we aimed to investigate changes in the precancerous epithelium and its surrounding niche. Methods We acquired time-resolved, single-cell transcriptomic (scRNAseq), and accessible-chromatin data from human pluripotent stem cell-derived pancreatic duct-like organoids (PDLO) inducibly expressing KRAS G12D and from various niche cells. Results Analysis of the pure epithelium already revealed key signatures of matrix remodeling and inflammation-related signaling upon few days of KRAS G12D expression. Machine learning captured KRAS G12D -dependent transcriptomic classifiers with high prediction accuracy and niche preparatory relevance. Various co-culture approaches followed by scRNAseq and functional validation, including T-cell microfluidics, demonstrated that the KRAS G12D -induced PDLO-secretome activates pancreatic stellate cells (PaSCs) and protects precancerous organoids from T cell infiltration. Additional, in silico  approaches reconstructed a virtual pancreatic (pre)cancerous space to profile cell–cell interactions between PDLOs and niche cells. TNFα emerged as a top-ranked ligand and was functionally validated to mediate T-cell shielding and PaSC activation. Cyst fluid from 80 prospectively sampled Intraductal Papillary Mucinous Neoplasm (IPMNs) –well-known cystic PDAC precursor lesions– showed a stepwise TNFα rise across LGD (low-grade), HGD (high-grade), and IC (invasive cancer). Conclusion Our study reveals that oncogenic KRAS orchestrates niche-preparatory programs that precede PDAC formation and highlight a T cell exclusion program governed by epithelial-derived TNFα.