Disease Models & Mechanisms最新文献

Bats are a natural reservoir for a wide variety of notorious viruses that are deadly to humans and other mammals but cause no or minimal clinical damage in bats. The co-evolution of bats and viruses for more than sixty million years has established unique and balanced immune defenses within bats against a number of viruses. With the COVID-19 pandemic, bats have gained greater attention as a likely reservoir of the SARS-CoV-2 ancestor virus. The coupling of omics technology and bat research opens an exciting new field to understand and translate discoveries from bats to humans, in the context of infectious disease and beyond. Here, we focus on the mechanism of immunity balance in bats, the application of omics and how this might lead to improvement of human health.

Since the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) initiated a global pandemic resulting in an estimated 775 million infections with over 7 million deaths, it has become evident that COVID-19 is not solely a pulmonary disease. Emerging evidence has shown that, in a subset of patients, certain symptoms - including chest pain, stroke, anosmia, dysgeusia, diarrhea and abdominal pain - all indicate a role of vascular, neurological and gastrointestinal (GI) pathology in the disease process. Many of these disease processes persist long after the acute disease has been resolved, resulting in 'long COVID' or post-acute sequelae of COVID-19 (PASC). The molecular mechanisms underlying the acute and systemic conditions associated with COVID-19 remain incompletely defined. Appropriate animal models provide a method of understanding underlying disease mechanisms at the system level through the study of disease progression, tissue pathology, immune system response to the pathogen and behavioral responses. However, very few studies have addressed PASC and whether existing models hold promise for studying this challenging problem. Here, we review the current literature on cardiovascular, neurological and GI pathobiology caused by COVID-19 in patients, along with established animal models of the acute disease manifestations and their prospects for use in PASC studies. Our aim is to provide guidance for the selection of appropriate models in order to recapitulate certain aspects of the disease to enhance the translatability of mechanistic studies.

Tuberculosis (TB) is characterized by the formation of heterogeneous, immune-rich granulomas in the lungs. Host and pathogen factors contribute to this heterogeneity, but the molecular and cellular drivers of granuloma diversity remain inadequately understood owing to limitations in experimental techniques. In this study, we developed an approach that combines passive CLARITY (PACT)-based clearing with light-sheet fluorescence microscopy to visualize lesion architecture and lung involvement in Mycobacterium tuberculosis-infected C3HeB/FeJ mice. Three-dimensional rendering of post-mortem lungs revealed critical architectural features in lesion development that traditional thin-section imaging could not detect. Wild-type M. tuberculosis infection resulted in organized granulomas, with median sizes increasing to 3.74×108 µm3 and occupying ∼10% of the total lung volume by day 70 post-infection. In contrast, infection with the avirulent ESX-1 deletion mutant strain resulted in diffuse and sparsely organized CD11b recruitment (median size of 8.22×107 µm3), primarily located in the lung periphery and minimally involving the airways (0.23% of the total lung space). Additionally, we present a method for volumetric correlative light and electron microscopy, enabling tracking of individual immune cell populations within granulomas.

The antiviral enzyme cholesterol 25-hydroxylase (CH25H) and its metabolite 25-hydroxycholesterol (25HC), which modulates cholesterol metabolism during infection, have been associated with vascular pathology. Viral infections have been linked to intracerebral haemorrhage (ICH) risk, but the molecular mechanisms leading to ICH via antiviral responses remain unknown. We hypothesised that the CH25H/25HC pathway impacts neuroendothelial integrity in the context of infection-associated ICH. Using a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein-induced zebrafish ICH model and foetal human SARS-CoV-2-associated cortical tissue containing microbleeds, we identified upregulation of CH25H in infection-associated cerebral haemorrhage. Using zebrafish models and human brain endothelial cells, we asked whether 25HC promotes neurovascular dysfunction by modulating cholesterol metabolism. We found that 25HC and pharmacological inhibition of cholesterol synthesis had an additive effect to exacerbate brain bleeding in zebrafish and in vitro neuroendothelial dysfunction. 25HC-induced dysfunction was also rescued by cholesterol supplementation in vitro. These results demonstrate that 25HC can dysregulate brain endothelial function by remodelling cholesterol metabolism. We propose that CH25H/25HC plays an important role in the pathophysiology of brain vessel dysfunction associated with infection and cholesterol dysregulation in the context of ICH.

Lung disease due to non-tuberculous mycobacteria (NTM) is rising in incidence. Although both two-dimensional cell culture and animal models exist for NTM infections, a major knowledge gap is the early responses of human alveolar and innate immune cells to NTM within the human alveolar microenvironment. Here, we describe the development of a humanized, three-dimensional, alveolus lung-on-a-chip (ALoC) model of Mycobacterium fortuitum lung infection that incorporates only primary human cells, such as pulmonary vascular endothelial cells, in a vascular channel, and type I and II alveolar cells and monocyte-derived macrophages in an alveolar channel along an air-liquid interface. M. fortuitum introduced into the alveolar channel primarily infected macrophages, with rare bacteria inside alveolar cells. Bulk RNA sequencing of infected chips revealed marked upregulation of transcripts for cytokines, chemokines and secreted protease inhibitors (SERPINs). Our results demonstrate how a humanized ALoC system can identify critical early immune and epithelial responses to M. fortuitum infection. We envision potential application of the ALoC to other NTM and in studies of new antibiotics.

A recently described G307D variant of the endosomal adaptor protein TOM1 causes severe early-onset multiorgan autoimmunity and combined immunodeficiency. By combining biophysical, biochemical and cell culture experiments, we show that the variant causes a defect in the interaction between TOM1 and TOLLIP, another adaptor protein involved in cargo trafficking and regulation of innate immunity. The G307D variant impairs the ability of TOM1 to reduce TOLLIP phosphatidylinositol 3-phosphate binding, an important regulatory mechanism for cargo trafficking commitment for both proteins. Our experiments using TOM1 G307D patient cells suggested that the variant affects autophagy, seen as an aggravated response to amino acid starvation and accumulation of autophagosomes due to autophagosome-lysosome fusion defect. In addition, inflammatory pathways showed excessive activation in TOM1 G307D patient cells. Our data suggest that the interaction between TOM1 and TOLLIP has a role in the regulation of the human immune system and highlight the importance of fundamental cellular functions, such as cargo trafficking, in controlling immune responses. Our study also provides insights into the caveats of immunomodulatory and stem cell therapies in patients with TOM1 pathogenic variants.

Class I PI3 kinases (PI3Ks) coordinate the delivery of microbicidal effectors to the phagosome by forming phosphatidylinositol (3,4,5)-trisphosphate (PIP3). However, the dynamics of PIP3 in neutrophils during a live bacterial tissue infection are unknown. We therefore developed an in vivo, live zebrafish infection model that enables visualisation of dynamic changes in Class 1 PI3K signalling in neutrophil phagosomes in real time. We identified that, on ∼12% of neutrophil phagosomes, PHAkt-eGFP, a reporter for Class 1 PI3K signalling, repeatedly fades and re-recruits in pulsatile bursts. This phenomenon occurred on phagosomes containing live and dead bacteria as well as beads, and was dependent on the activity of the Class 1 PI3K isoform PI3Kγ. Detailed imaging suggested that pulsing phagosomes represent neutrophils transiently re-opening and re-closing phagosomes, a conclusion supported by observations that a subset of phagosomes in human neutrophils rapidly accumulate dye from the extracellular space. Therefore, we propose that some neutrophil phagosomes remain unsealed and are consequently able to exchange contents with the extracellular environment, with implications for phagosome fate and communication with surrounding cells.

Multisystem inflammatory syndrome in children (MIS-C) is a rare condition associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and characterised by systemic inflammation and T-cell dysfunction. A subset of patients with MIS-C were found to harbour rare variants in the gene BTNL8 that disrupt BTNL8-BTNL3 heterodimer formation, likely leading to inadequate γδ T-cell regulation and subsequent disrupted gut homeostasis. MIS-C shares clinical features with Kawasaki disease and similar mechanisms of pathogenesis with inflammatory bowel disease, despite these diseases being clinically distinct entities. We explore the common link between these diseases: the potentially critical role gut immunity plays in the initiation and persistence of disease through the tight regulation of γδ T cells via BTNL8 and BTNL3. Understanding the role of BTNL8 in the context of the overlap between these conditions may aid preventative measures and treatment of these conditions.

Inflammasomes regulate the host response to intracellular pathogens including mycobacteria. We have previously shown that the course of Mycobacterium marinum infection in adult zebrafish (Danio rerio) mimics the course of tuberculosis in human. To investigate the role of the inflammasome adaptor pycard in zebrafish M. marinum infection, we produced two zebrafish knockout mutant lines for the pycard gene with CRISPR/Cas9 mutagenesis. Although the zebrafish larvae lacking pycard developed normally and had unaltered resistance against M. marinum, the loss of pycard led to impaired survival and increased bacterial burden in the adult zebrafish. Based on histology, immune cell aggregates, granulomas, were larger in pycard-deficient fish than in wild-type controls. Transcriptome analysis with RNA sequencing of a zebrafish haematopoietic tissue, kidney, suggested a role for pycard in neutrophil-mediated defence, haematopoiesis and myelopoiesis during infection. Transcriptome analysis of fluorescently labelled, pycard-deficient kidney neutrophils identified genes that are associated with compromised resistance, supporting the importance of pycard for neutrophil-mediated immunity against M. marinum. Our results indicate that pycard is essential for resistance against mycobacteria in adult zebrafish.