The H3.3K27M oncohistone affects replication stress outcome and provokes genomic instability in pediatric glioma

While comprehensive molecular profiling of histone H3.3 mutant pediatric high-grade glioma has revealed extensive dysregulation of the chromatin landscape, the exact mechanisms driving tumor formation remain poorly understood. Since H3.3 mutant gliomas also exhibit high levels of copy number alterations, we set out to address if the H3.3K27M oncohistone leads to destabilization of the genome. Hereto, we established a cell culture model allowing inducible H3.3K27M expression and observed an increase in mitotic abnormalities. We also found enhanced interaction of DNA replication factors with H3.3K27M during mitosis, indicating replication defects. Further functional analyses revealed increased genomic instability upon replication stress, as represented by mitotic bulky and ultrafine DNA bridges. This co-occurred with suboptimal 53BP1 nuclear body formation after mitosis in vitro, and in human glioma. Finally, we observed a decrease in ultrafine DNA bridges following deletion of the K27M mutant H3F3A allele in primary high-grade glioma cells. Together, our data uncover a role for H3.3 in DNA replication under stress conditions that is altered by the K27M mutation, promoting genomic instability and potentially glioma development

Canine Pituitary Organoids as 3D In Vitro Model for Cushing Disease

Cushing disease (CD) is a serious endocrine disorder that is most often caused by an ACTH-secreting pituitary adenoma. Patients can be treated medically when surgery is not an option or was unsuccessful. However, currently used pituitary-targeting drugs are effective in only 40% of patients. To efficiently identify new pituitary-targeting treatment options, we need an in vitro system that closely mimics in vivo conditions. We therefore aimed to establish organoid cultures of normal anterior pituitary and corticotroph adenomas. Organoids or tumoroids are miniature three-dimensional (3D) structures grown from stem cells, that closely resemble the organ or tumor they originate from. Because CD is a thousand times more prevalent in dogs than in humans, and hypophysectomy is the treatment of choice, we used canine tissues. Normal anterior pituitary glands were collected from three healthy dogs that were euthanized for reasons unrelated to the current study. Corticotroph adenomas were collected from six dogs that underwent transsphenoidal hypophysectomy at our University Clinic. The dogs were diagnosed with CD based on clinical signs, endocrine testing, and CT scan imaging. Normal anterior pituitary and corticotroph adenoma cells were cultured in a 3D matrix (basement membrane extract) with anterior pituitary organoid medium containing specific growth factors and ligands, which was refreshed twice a week. The organoids and tumoroids were characterized with histopathology and RT-qPCR. Structures resembling organoids or tumoroids grew from all nine samples (3 normal, 6 adenoma) that were put in culture. Both cystic and dense structures were observed. The organoids and tumoroids expanded rapidly, and could be passaged once every week. The organoids and tumoroids were successfully cultured up until passage number 10, and were then frozen down. Histopathology showed that the organoid or tumoroid cells morphologically resembled healthy anterior pituitary or corticotroph adenoma cells. All organoids cultures expressed mRNA of pituitary stem cell markers SOX2 and SOX9. This study shows that corticotroph adenomas can be cultured as tumoroids in vitro, something not previously published in any species. Based on the many opportunities in organoid culture (e.g., high-throughput drug screenings, gene editing, studying developmental processes), we expect that this in vitro model will pave the way to efficiently and reliably identify new treatment options for CD. Not only for humans, but also for our best friends: dogs

Sequential intravital imaging reveals in vivo dynamics of pancreatic tissue transplanted under the kidney capsule in mice

Aims/hypothesis: Dynamic processes in pancreatic tissue are difficult to study. We aimed to develop an intravital imaging method to longitudinally examine engraftment, vascularisation, expansion and differentiation in mature islets or embryonic pancreases transplanted under the kidney capsule. Methods: Isolated pancreatic islets from adult mice and murine embryonic day (E)12.5 pancreases containing fluorescent biomarkers were transplanted under the kidney capsule of immunodeficient recipient mice. Human islet cells were dispersed, transduced with a lentivirus expressing a fluorescent label and reaggregated before transplantation. Graft-containing kidneys were positioned subcutaneously and an imaging window was fitted into the skin on top of the kidney. Intravital imaging using multiphoton microscopy was performed for up to 2 weeks. Volumes of fluorescently labelled cells were determined as a measure of development and survival. Results: Transplanted islets and embryonic pancreases showed good engraftment and remained viable. Engraftment and vascularisation could be longitudinally examined in murine and human islet cells. Murine islet beta cell volume was unchanged over time. Transplanted embryonic pancreases increased to up to 6.1 times of their original volume and beta cell volume increased 90 times during 2 weeks. Conclusions/interpretation: This method allows for repeated intravital imaging of grafts containing various sources of pancreatic tissue transplanted under the kidney capsule. Using fluorescent markers, dynamic information concerning engraftment or differentiation can be visualised and measured

Canine Pituitary Organoids as 3D In Vitro Model for Cushing Disease

Cushing disease (CD) is a serious endocrine disorder that is most often caused by an ACTH-secreting pituitary adenoma. Patients can be treated medically when surgery is not an option or was unsuccessful. However, currently used pituitary-targeting drugs are effective in only 40% of patients. To efficiently identify new pituitary-targeting treatment options, we need an in vitro system that closely mimics in vivo conditions. We therefore aimed to establish organoid cultures of normal anterior pituitary and corticotroph adenomas. Organoids or tumoroids are miniature three-dimensional (3D) structures grown from stem cells, that closely resemble the organ or tumor they originate from. Because CD is a thousand times more prevalent in dogs than in humans, and hypophysectomy is the treatment of choice, we used canine tissues. Normal anterior pituitary glands were collected from three healthy dogs that were euthanized for reasons unrelated to the current study. Corticotroph adenomas were collected from six dogs that underwent transsphenoidal hypophysectomy at our University Clinic. The dogs were diagnosed with CD based on clinical signs, endocrine testing, and CT scan imaging. Normal anterior pituitary and corticotroph adenoma cells were cultured in a 3D matrix (basement membrane extract) with anterior pituitary organoid medium containing specific growth factors and ligands, which was refreshed twice a week. The organoids and tumoroids were characterized with histopathology and RT-qPCR. Structures resembling organoids or tumoroids grew from all nine samples (3 normal, 6 adenoma) that were put in culture. Both cystic and dense structures were observed. The organoids and tumoroids expanded rapidly, and could be passaged once every week. The organoids and tumoroids were successfully cultured up until passage number 10, and were then frozen down. Histopathology showed that the organoid or tumoroid cells morphologically resembled healthy anterior pituitary or corticotroph adenoma cells. All organoids cultures expressed mRNA of pituitary stem cell markers SOX2 and SOX9. This study shows that corticotroph adenomas can be cultured as tumoroids in vitro, something not previously published in any species. Based on the many opportunities in organoid culture (e.g., high-throughput drug screenings, gene editing, studying developmental processes), we expect that this in vitro model will pave the way to efficiently and reliably identify new treatment options for CD. Not only for humans, but also for our best friends: dogs