The histone chaperone HIR maintains chromatin states to control nitrogen assimilation and fungal virulence

Adaptation to changing environments and immune evasion is pivotal for fitness of pathogens. Yet, the underlying mechanisms remain largely unknown. Adaptation is governed by dynamic transcriptional re-programming, which is tightly connected to chromatin architecture. Here, we report a pivotal role for the HIR histone chaperone complex in modulating virulence of the human fungal pathogen Candida albicans. Genetic ablation of HIR function alters chromatin accessibility linked to aberrant transcriptional responses to protein as nitrogen source. This accelerates metabolic adaptation and increases the release of extracellular proteases, which enables scavenging of alternative nitrogen sources. Furthermore, HIR controls fungal virulence, as HIR1 deletion leads to differential recognition by immune cells and hypervirulence in a mouse model of systemic infection. This work provides mechanistic insights into chromatin-coupled regulatory mechanisms that fine-tune pathogen gene expression and virulence. Furthermore, the data point toward the requirement of refined screening approaches to exploit chromatin modifications as antifungal strategies

Mimicking tumor cell heterogeneity of colorectal cancer in a patient-derived organoid-fibroblast model

Background & Aims: Patient-derived organoid cancer models are generated from epithelial tumor cells and reflect tumor characteristics. However, they lack the complexity of the tumor microenvironment, which is a key driver of tumorigenesis and therapy response. Here, we developed a colorectal cancer organoid model that incorporates matched epithelial cells and stromal fibroblasts. Methods: Primary fibroblasts and tumor cells were isolated from colorectal cancer specimens. Fibroblasts were characterized for their proteome, secretome, and gene expression signatures. Fibroblast/organoid co-cultures were analyzed by immunohistochemistry and compared with their tissue of origin, as well as on gene expression levels compared with standard organoid models. Bioinformatics deconvolution was used to calculate cellular proportions of cell subsets in organoids based on single-cell RNA sequencing data. Results: Normal primary fibroblasts, isolated from tumor adjacent tissue, and cancer associated fibroblasts retained their molecular characteristics in vitro, including higher motility of cancer associated compared with normal fibroblasts. Importantly, both cancer-associated fibroblasts and normal fibroblasts supported cancer cell proliferation in 3D co-cultures, without the addition of classical niche factors. Organoids grown together with fibroblasts displayed a larger cellular heterogeneity of tumor cells compared with mono-cultures and closely resembled the in vivo tumor morphology. Additionally, we observed a mutual crosstalk between tumor cells and fibroblasts in the co-cultures. This was manifested by considerably deregulated pathways such as cell-cell communication and extracellular matrix remodeling in the organoids. Thrombospondin-1 was identified as a critical factor for fibroblast invasiveness. Conclusion: We developed a physiological tumor/stroma model, which will be vital as a personalized tumor model to study disease mechanisms and therapy response in colorectal cancer

Influence of Increased Intraarticular Pressure on the Angular Displacement of the Isolated Equine Distal Interphalangeal Joint

The equine distal interphalangeal joint (DIPJ) is commonly affected by palpable joint distension and degenerative joint disease, with microinstability considered a contributory factor. The aim of this kinematic study was to investigate DIPJ angles during axial compression loading (ACL) in a material testing machine with and without increased intraarticular pressure (IAP) due to joint distension. Our hypothesis was that increased IAP would lead to an increased speed of angular displacement of the DIPJ during ACL and that this would become more apparent with the hoof placed on an uneven surface. Bone markers were placed on the second and third phalanx of six left and right isolated forelimbs from adult Warmblood horses. Limbs were placed in a material testing machine, and synchronous measurements of the kinematics and the pressures within the DIPJ during loading were obtained. With the hoof in neutral position, as well as with 3° lateral and 3° medial elevation, the proximal articular surface of the second phalanx was preloaded with 100 Newton (N), and angles and IAPs were measured during loading to 6,000 N at 600 N/s, with and without joint distension. Joint distension in combination with lateral/medial hoof elevation increased flexion, lateromotion/mediomotion, and axial rotation. The finding that moderate joint distension increases the effect of a relatively mild mediolateral foot imbalance on speed of joint movement during loading has the potential for clinical relevance in the development of osteoarthritis