Persistent Morbillivirus Infection Leads to Altered Cortactin Distribution in Histiocytic Sarcoma Cells with Decreased Cellular Migration Capacity

Cryopreservation of canine ovarian tissue by slow freezing and vitrification: Evaluation of follicular morphology and apoptosis rate

In this study, we aimed to evaluate the efficacy of cryopreserving canine ovarian tissue using vitrification and slow freezing methods while investigating potential differences in cryotolerance based on follicular type and cryopreservation technique. Twenty-eight ovaries were collected from 14 anoestrus bitches of various breeds, aged between 2 and 5 years, and undergoing elective ovariohysterectomy. The ovaries were sectioned into small fragments and randomly assigned to three groups: vitrification, slow freezing, and a control group (fresh tissue). Vitrification was performed using cryotubes containing DAP 213 solution (2M DMSO, 1M acetamide, 3M propylene glycol) in two stages, while slow freezing involved cryotubes with 1.5M DMSO solution inserted into a programmable machine. The effects of cryopreservation were evaluated by histology and immunohistochemistry (cleaved caspase-3), to determine the percentage of cells undergoing apoptosis. Histological examination revealed that the slow freezing group exhibited a significantly higher percentage of intact follicles (45.75 %) compared to those subjected to vitrification (38.17 %; P = 0.01). Immunohistochemical evaluation further indicated that 84.21 % of the follicles in the slow freezing group did not express caspase-3, suggesting the absence of apoptosis. Conversely, vitrified samples exhibited significantly more apoptotic cells compared to other groups (P < 0.001). Furthermore, early antral follicles displayed a higher susceptibility to degeneration regardless of the cryopreservation method employed. Nevertheless, when comparing the cryopreserved groups, early antral follicles showed greater degeneration in slow freezing group, while preantral follicles were the most affected in the vitrification group. In conclusion, slow freezing demonstrated superior preservation of viable follicles compared to vitrification and emerged as the preferred technique for cryopreserving canine ovarian tissue. These findings contribute valuable insights into optimizing cryopreservation methods for canine ovarian tissue, potentially benefiting reproductive technologies and fertility preservation in canines.

Cortactin: A major cellular target of viral, protozoal, and fungal pathogens

Many viral, protozoal, and fungal pathogens represent major human and animal health problems due to their great potential of causing infectious diseases. Research on these pathogens has contributed substantially to our current understanding of both microbial virulence determinants and host key factors during infection. Countless studies have also shed light on the molecular mechanisms of host-pathogen interactions that are employed by these microbes. For example, actin cytoskeletal dynamics play critical roles in effective adhesion, host cell entry, and intracellular movements of intruding pathogens. Cortactin is an eminent host cell protein that stimulates actin polymerization and signal transduction, and recently emerged as fundamental player during host-pathogen crosstalk. Here we review the important role of cortactin as major target for various prominent viral, protozoal and fungal pathogens in humans, and its role in human disease development and cancer progression. Most if not all of these important classes of pathogens have been reported to hijack cortactin during infection through mediating up- or downregulation of cortactin mRNA and protein expression as well as signaling. In particular, pathogen-induced changes in tyrosine and serine phosphorylation status of cortactin at its major phospho-sites (Y-421, Y-470, Y-486, S-113, S-298, S-405, and S-418) are addressed. As has been reported for various Gram-negative and Gram-positive bacteria, many pathogenic viruses, protozoa, and fungi also control these regulatory phospho-sites, for example, by activating kinases such as Src, PAK, ERK1/2, and PKD, which are known to phosphorylate cortactin. In addition, the recruitment of cortactin and its interaction partners, like the Arp2/3 complex and F-actin, to the contact sites between pathogens and host cells is highlighted, as this plays an important role in the infection process and internalization of several pathogens. However, there are also other ways in which the pathogens can exploit the function of cortactin for their needs, as the cortactin-mediated regulation of cellular processes is complex and involves numerous different interaction partners. Here, the current state of knowledge is summarized.

Functional Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) Delivered by Canine Histiocytic Sarcoma Cells Persistently Infected with Engineered Attenuated Canine Distemper Virus

The immune response plays a key role in the treatment of malignant tumors. One important molecule promoting humoral and cellular immunity is granulocyte-macrophage colony-stimulating factor (GM-CSF). Numerous successful trials have led to the approval of this immune-stimulating molecule for cancer therapy. However, besides immune stimulation, GM-CSF may also accelerate tumor cell proliferation, rendering this molecule a double-edged sword in cancer treatment. Therefore, detailed knowledge about the in vitro function of GM-CSF produced by infected tumor cells is urgently needed prior to investigations in an in vivo model. The aim of the present study was to functionally characterize a persistent infection of canine histiocytic sarcoma cells (DH82 cells) with the canine distemper virus strain Onderstepoort genetically engineered to express canine GM-CSF (CDV-Ond^neon-GM-CSF). The investigations aimed (1) to prove the overall functionality of the virally induced production of GM-CSF and (2) to determine the effect of GM-CSF on the proliferation and motility of canine HS cells. Infected cells consistently produced high amounts of active, pH-stable GM-CSF, as demonstrated by increased proliferation of HeLa cells. By contrast, DH82 cells lacked increased proliferation and motility. The significantly increased secretion of GM-CSF by persistently CDV-Ond^neon-GM-CSF-infected DH82 cells, the pH stability of this protein, and the lack of detrimental effects on DH82 cells renders this virus strain an interesting candidate for future studies aiming to enhance the oncolytic properties of CDV for the treatment of canine histiocytic sarcomas.

Respiratory syncytial virus disrupts the airway epithelial barrier by decreasing cortactin and destabilizing F-actin

Respiratory syncytial virus (RSV) infection is the leading cause of acute lower respiratory tract infection in young children worldwide. Our group recently revealed that RSV infection disrupts the airway epithelial barrier in vitro and in vivo. However, the underlying molecular pathways were still elusive. Here, we report the critical roles of the filamentous actin (F-actin) network and actin-binding protein cortactin in RSV infection. We found that RSV infection causes F-actin depolymerization in 16HBE cells, and that stabilizing the F-actin network in infected cells reverses the epithelial barrier disruption. RSV infection also leads to significantly decreased cortactin in vitro and in vivo. Cortactin-knockout 16HBE cells presented barrier dysfunction, whereas overexpression of cortactin protected the epithelial barrier against RSV. The activity of Rap1 (which has Rap1A and Rap1B forms), one downstream target of cortactin, declined after RSV infection as well as in cortactin-knockout cells. Moreover, activating Rap1 attenuated RSV-induced epithelial barrier disruption. Our study proposes a key mechanism in which RSV disrupts the airway epithelial barrier via attenuating cortactin expression and destabilizing the F-actin network. The identified pathways will provide new targets for therapeutic intervention toward RSV-related disease. This article has an associated First Person interview with the first author of the paper.

Persistent Infection of a Canine Histiocytic Sarcoma Cell Line with Attenuated Canine Distemper Virus Expressing Vasostatin or Granulocyte-Macrophage Colony-Stimulating Factor

Canine histiocytic sarcoma (HS) represents a neoplasia with poor prognosis. Due to the high metastatic rate of HS, there is urgency to improve treatment options and to prevent tumor metastases. Canine distemper virus (CDV) is a single-stranded negative-sense RNA (ssRNA (-)) virus with potentially oncolytic properties. Moreover, vasostatin and granulocyte-macrophage colony-stimulating factor (GM-CSF) are attractive molecules in cancer therapy research because of their anti-angiogenetic properties and potential modulation of the tumor microenvironment. In the present study, an in vitro characterization of two genetically engineered viruses based on the CDV strain Onderstepoort (CDV-Ond), CDV-Ondneon-vasostatin and CDV-Ondneon-GM-CSF was performed. Canine histiocytic sarcoma cells (DH82 cells) were persistently infected with CDV-Ond, CDV-Ondneon, CDV-Ondneon-vasostatin and CDV-Ondneon-GM-CSF and characterized on a molecular and protein level regarding their vasostatin and GM-CSF production. Interestingly, DH82 cells persistently infected with CDV-Ondneon-vasostatin showed a significantly increased number of vasostatin mRNA transcripts. Similarly, DH82 cells persistently infected with CDV-Ondneon-GM-CSF displayed an increased number of GM-CSF mRNA transcripts mirrored on the protein level as confirmed by immunofluorescence and Western blot. In summary, modified CDV-Ond strains expressed GM-CSF and vasostatin, rendering them promising candidates for the improvement of oncolytic virotherapies, which should be further detailed in future in vivo studies.

Overcoming the Barrier of the Respiratory Epithelium during Canine Distemper Virus Infection

Canine distemper virus (CDV) is a highly contagious pathogen and is known to enter the host via the respiratory tract and disseminate to various organs. Current hypotheses speculate that CDV uses the homologous cellular receptors of measles virus (MeV), SLAM and nectin-4, to initiate the infection process. For validation, here, we established the well-differentiated air-liquid interface (ALI) culture model from primary canine tracheal airway epithelial cells. By applying the green fluorescent protein (GFP)-expressing CDV vaccine strain and recombinant wild-type viruses, we show that cell-free virus infects the airway epithelium mainly via the paracellular route and only after prior disruption of tight junctions by pretreatment with EGTA; this infection was related to nectin-4 but not to SLAM. Remarkably, when CDV-preinfected DH82 cells were cocultured on the basolateral side of canine ALI cultures grown on filter supports with a 1.0-μm pore size, cell-associated CDV could be transmitted via cell-to-cell contact from immunocytes to airway epithelial cultures. Finally, we observed that canine ALI cultures formed syncytia and started to release cell-free infectious viral particles from the apical surface following treatment with an inhibitor of the JAK/STAT signaling pathway (ruxolitinib). Our findings show that CDV can overcome the epithelial barrier through different strategies, including infection via immunocyte-mediated transmission and direct infection via the paracellular route when tight junctions are disrupted. Our established model can be adapted to other animals for studying the transmission routes and the pathogenicity of other morbilliviruses. IMPORTANCE Canine distemper virus (CDV) is not only an important pathogen of carnivores, but it also serves as a model virus for analyzing measles virus pathogenesis. To get a better picture of the different stages of infection, we used air-liquid interface cultures to analyze the infection of well-differentiated airway epithelial cells by CDV. Applying a coculture approach with DH82 cells, we demonstrated that cell-mediated infection from the basolateral side of well-differentiated epithelial cells is more efficient than infection via cell-free virus. In fact, free virus was unable to infect intact polarized cells. When tight junctions were interrupted by treatment with EGTA, cells became susceptible to infection, with nectin-4 serving as a receptor. Another interesting feature of CDV infection is that infection of well-differentiated airway epithelial cells does not result in virus egress. Cell-free virions are released from the cells only in the presence of an inhibitor of the JAK/STAT signaling pathway. Our results provide new insights into how CDV can overcome the barrier of the airway epithelium and reveal similarities and some dissimilarities compared to measles virus.

Intratumoral Canine Distemper Virus Infection Inhibits Tumor Growth by Modulation of the Tumor Microenvironment in a Murine Xenograft Model of Canine Histiocytic Sarcoma

Histiocytic sarcomas refer to highly aggressive tumors with a poor prognosis that respond poorly to conventional treatment approaches. Oncolytic viruses, which have gained significant traction as a cancer therapy in recent decades, represent a promising option for treating histiocytic sarcomas through their replication and/or by modulating the tumor microenvironment. The live attenuated canine distemper virus (CDV) vaccine strain Onderstepoort represents an attractive candidate for oncolytic viral therapy. In the present study, oncolytic virotherapy with CDV was used to investigate the impact of this virus infection on tumor cell growth through direct oncolytic effects or by virus-mediated modulation of the tumor microenvironment with special emphasis on angiogenesis, expression of selected MMPs and TIMP-1 and tumor-associated macrophages in a murine xenograft model of canine histiocytic sarcoma. Treatment of mice with xenotransplanted canine histiocytic sarcomas using CDV induced overt retardation in tumor progression accompanied by necrosis of neoplastic cells, increased numbers of intratumoral macrophages, reduced angiogenesis and modulation of the expression of MMPs and TIMP-1. The present data suggest that CDV inhibits tumor growth in a multifactorial way, including direct cell lysis and reduction of angiogenesis and modulation of MMPs and their inhibitor TIMP-1, providing further support for the concept of its role in oncolytic therapies.

P2Y2 and P2X4 Receptors Mediate Ca2+ Mobilization in DH82 Canine Macrophage Cells

Purinergic receptors of the P2 subclass are commonly found in human and rodent macrophages where they can be activated by adenosine 5'-triphosphate (ATP) or uridine 5'-triphosphate (UTP) to mediate Ca²⁺ mobilization, resulting in downstream signalling to promote inflammation and pain. However, little is understood regarding these receptors in canine macrophages. To establish a macrophage model of canine P2 receptor signalling, the expression of these receptors in the DH82 canine macrophage cell line was determined by reverse transcription polymerase chain reaction (RT-PCR) and immunocytochemistry. P2 receptor function in DH82 cells was pharmacologically characterised using nucleotide-induced measurements of Fura-2 AM-bound intracellular Ca²⁺. RT-PCR revealed predominant expression of P2X4 receptors, while immunocytochemistry confirmed predominant expression of P2Y₂ receptors, with low levels of P2X4 receptor expression. ATP and UTP induced robust Ca²⁺ responses in the absence or presence of extracellular Ca²⁺. ATP-induced responses were only partially inhibited by the P2X4 receptor antagonists, 2',3'-O-(2,4,6-trinitrophenyl)-ATP (TNP-ATP), paroxetine and 5-BDBD, but were strongly potentiated by ivermectin. UTP-induced responses were near completely inhibited by the P2Y₂ receptor antagonists, suramin and AR-C118925. P2Y₂ receptor-mediated Ca²⁺ mobilization was inhibited by U-73122 and 2-aminoethoxydiphenyl borate (2-APB), indicating P2Y₂ receptor coupling to the phospholipase C and inositol triphosphate signal transduction pathway. Together this data demonstrates, for the first time, the expression of functional P2 receptors in DH82 canine macrophage cells and identifies a potential cell model for studying macrophage-mediated purinergic signalling in inflammation and pain in dogs.

Mesenchymal to epithelial transition driven by canine distemper virus infection of canine histiocytic sarcoma cells contributes to a reduced cell motility in vitro

Sarcomas especially of histiocytic origin often possess a poor prognosis and response to conventional therapies. Interestingly, tumours undergoing mesenchymal to epithelial transition (MET) are often associated with a favourable clinical outcome. This process is characterized by an increased expression of epithelial markers leading to a decreased invasion and metastatic rate. Based on the failure of conventional therapies, viral oncolysis might represent a promising alternative with canine distemper virus (CDV) as a possible candidate. This study hypothesizes that a CDV infection of canine histiocytic sarcoma cells (DH82 cells) triggers the MET process leading to a decreased cellular motility. Immunofluorescence and immunoblotting were used to investigate the expression of epithelial and mesenchymal markers followed by scratch assay and an invasion assay as functional confirmation. Furthermore, microarray data were analysed for genes associated with the MET process, invasion and angiogenesis. CDV‐infected cells exhibited an increased expression of epithelial markers such as E‐cadherin and cytokeratin 8 compared to controls, indicating a MET process. This was accompanied by a reduced cell motility and invasiveness. Summarized, these results suggest that CDV infection of DH82 cells triggers the MET process by an increased expression of epithelial markers resulting in a decreased cell motility in vitro.

Viral Pathogenesis, Recombinant Vaccines, and Oncolytic Virotherapy: Applications of the Canine Distemper Virus Reverse Genetics System

Canine distemper virus (CDV) is a highly contagious pathogen transmissible to a broad range of terrestrial and aquatic carnivores. Despite the availability of attenuated vaccines against CDV, the virus remains responsible for outbreaks of canine distemper (CD) with significant morbidity and mortality in domesticated and wild carnivores worldwide. CDV uses the signaling lymphocytic activation molecule (SLAM, or CD150) and nectin-4 (PVRL4) as entry receptors, well-known tumor-associated markers for several lymphadenomas and adenocarcinomas, which are also responsible for the lysis of tumor cells and apparent tumor regression. Thus, CDV vaccine strains have emerged as a promising platform of oncolytic viruses for use in animal cancer therapy. Recent advances have revealed that use of the CDV reverse genetic system (RGS) has helped increase the understanding of viral pathogenesis and explore the development of recombinant CDV vaccines. In addition, genetic engineering of CDV based on RGS approaches also has the potential of enhancing oncolytic activity and selectively targeting tumors. Here, we reviewed the host tropism and pathogenesis of CDV, and current development of recombinant CDV-based vaccines as well as their use as oncolytic viruses against cancers.

Oxidative Stress in Canine Histiocytic Sarcoma Cells Induced by an Infection with Canine Distemper Virus Led to a Dysregulation of HIF-1α Downstream Pathway Resulting in a Reduced Expression of VEGF-B in vitro

Histiocytic sarcomas represent malignant tumors which require new treatment strategies. Canine distemper virus (CDV) is a promising candidate due to its oncolytic features reported in a canine histiocytic sarcoma cell line (DH82 cells). Interestingly, the underlying mechanism might include a dysregulation of angiogenesis. Based on these findings, the aim of the present study was to investigate the impact of a persistent CDV-infection on oxidative stress mediated changes in the expression of hypoxia-inducible factor (HIF)-1α and its angiogenic downstream pathway in DH82 cells in vitro. Microarray data analysis, immunofluorescence for 8-hydroxyguanosine, superoxide dismutase 2 and catalase, and flow cytometry for oxidative burst displayed an increased oxidative stress in persistently CDV-infected DH82 cells (DH82Ond pi) compared to controls. The HIF-1α expression in DH82Ond pi increased, as demonstrated by Western blot, and showed an unexpected, often sub-membranous distribution, as shown by immunofluorescence and immunoelectron microscopy. Furthermore, microarray data analysis and immunofluorescence confirmed a reduced expression of VEGF-B in DH82Ond pi compared to controls. In summary, these results suggest a reduced activation of the HIF-1α angiogenic downstream pathway in DH82Ond pi cells in vitro, most likely due to an excessive, unusually localized, and non-functional expression of HIF-1α triggered by a CDV-induced increased oxidative stress.

Anti-tumour activity of oncolytic reovirus against canine histiocytic sarcoma cells

Canine histiocytic sarcoma is an aggressive, fatal neoplastic disease with a poor prognosis. Lomustine is generally accepted as the first-line systemic therapy, although this compound does not provide complete regression. Therefore, research into a novel approach against canine histiocytic sarcoma is needed. However, anti-tumour effects of oncolytic therapy using reovirus against histiocytic sarcoma are unknown. Here, we showed that reovirus has oncolytic activity in canine histiocytic sarcoma cell lines in vitro and in vivo. We found that reovirus can replicate and induce caspase-dependent apoptosis in canine histiocytic sarcoma cell lines. A single intra-tumoural injection of reovirus completely suppressed the growth of subcutaneously grafted tumours in NOD/SCID mice. Additionally, we demonstrated that susceptibility to reovirus-induced cell death was attributable to the extent of expression of type I interferons induced by reovirus infection in vitro. In conclusion, oncolytic reovirus appears to be an effective treatment option for histiocytic sarcoma, and therefore warrants further investigation in early clinical trials.