Role of the CTCF Binding Site in Human T-Cell Leukemia Virus-1 Pathogenesis.

During HTLV-1 infection, the virus integrates into the host cell genome as a provirus with a single CCCTC binding protein (CTCF) binding site (vCTCF-BS), which acts as an insulator between transcriptionally active and inactive regions. Previous studies have shown that the vCTCF-BS is important for maintenance of chromatin structure, regulation of viral expression, and DNA and histone methylation. Here, we show that the vCTCF-BS also regulates viral infection and pathogenesis in vivo in a humanized (Hu) mouse model of adult T-cell leukemia/lymphoma. Three cell lines were used to initiate infection of the Hu-mice, i) HTLV-1-WT which carries an intact HTLV-1 provirus genome, ii) HTLV-1-CTCF, which contains a provirus with a mutated vCTCF-BS which abolishes CTCF binding, and a stop codon immediate upstream of the mutated vCTCF-BS which deletes the last 23 amino acids of p12, and iii) HTLV-1-p12stop that contains the intact vCTCF-BS, but retains the same stop codon in p12 as in the HTLV-1-CTCF cell line. Hu-mice were infected with mitomycin treated or irradiated HTLV-1 producing cell lines. There was a delay in pathogenicity when Hu-mice were infected with the CTCF virus compared to mice infected with either p12 stop or WT virus. Proviral load (PVL), spleen weights, and CD4 T cell counts were significantly lower in HTLV-1-CTCF infected mice compared to HTLV-1-p12stop infected mice. Furthermore, we found a direct correlation between the PVL in peripheral blood and death of HTLV-1-CTCF infected mice. In cell lines, we found that the vCTCF-BS regulates Tax expression in a time-dependent manner. The scRNAseq analysis of splenocytes from infected mice suggests that the vCTCF-BS plays an important role in activation and expansion of T lymphocytes in vivo. Overall, these findings indicate that the vCTCF-BS regulates Tax expression, proviral load, and HTLV pathogenicity in vivo.

LAIR1 prevents excess inflammatory tissue damage in S. aureus skin infection and Cutaneous T-cell Lymphoma.

Patients with cutaneous T cell lymphoma (CTCL) experience high morbidity and mortality due to S. aureus skin infections and sepsis, but the causative immune defect is unclear. We previously identified high levels of LAIR2, a decoy protein for the inhibitory receptor LAIR1, in advanced CTCL. Mice do not have a LAIR2 homolog, so we used Lair1 knock-out (KO) mice to model LAIR2 overexpression. In a model of subcutaneous S. aureus skin infection, Lair1 KO mice had significantly larger abscesses and areas of dermonecrosis compared to WT. Lair1 KO exhibited a pattern of increased inflammatory responses in infection and sterile immune stimulation, including increased production of proinflammatory cytokines and myeloid chemokines, neutrophil ROS, and collagen/ECM remodeling pathways. Notably, Lair1 KO infected skin had a similar bacterial burden and neutrophils and monocytes had equivalent S. aureus phagocytosis compared to WT. These findings support a model in which lack of LAIR1 signaling causes an excessive inflammatory response that does not improve infection control. CTCL skin lesions harbored similar patterns of increased expression in cytokine and collagen/ECM remodeling pathways, suggesting that high levels of LAIR2 in CTCL recapitulates Lair1 KO, causing inflammatory tissue damage and compromising host defense against S. aureus infection.

Senescent CAFs Mediate Immunosuppression and Drive Breast Cancer Progression.

The tumor microenvironment (TME) profoundly influences tumorigenesis, with gene expression in the breast TME capable of predicting clinical outcomes. The TME is complex and includes distinct cancer-associated fibroblast (CAF) subtypes whose contribution to tumorigenesis remains unclear. Here, we identify a subset of myofibroblast CAFs (myCAF) that are senescent (senCAF) in mouse and human breast tumors. Utilizing the MMTV-PyMT;INK-ATTAC (INK) mouse model, we found that senCAF-secreted extracellular matrix specifically limits natural killer (NK) cell cytotoxicity to promote tumor growth. Genetic or pharmacologic senCAF elimination unleashes NK cell killing, restricting tumor growth. Finally, we show that senCAFs are present in HER2+, ER+, and triple-negative breast cancer and in ductal carcinoma in situ (DCIS) where they predict tumor recurrence. Together, these findings demonstrate that senCAFs are potently tumor promoting and raise the possibility that targeting them by senolytic therapy could restrain breast cancer development. Significance: senCAFs limit NK cell-mediated killing, thereby contributing to breast cancer progression. Thus, targeting senCAFs could be a clinically viable approach to limit tumor progression. See related article by Belle et al., p. 1324.

HTLV-1 infected T cells cause bone loss via small extracellular vesicles.

Adult T cell leukemia (ATL), caused by infection with human T cell leukemia virus type 1 (HTLV-1), is often complicated by hypercalcemia and osteolytic lesions. Therefore, we studied the communication between patient-derived ATL cells (ATL-PDX) and HTLV-1 immortalized CD4+ T cell lines (HTLV/T) with osteoclasts and their effects on bone mass in mice. Intratibial inoculation of some HTLV/T lead to a profound local decrease in bone mass similar to marrow-replacing ATL-PDX, despite the fact that few HTLV/T cells persisted in the bone. To study the direct effect of HTLV/T and ATL-PDX on osteoclasts, supernatants were added to murine and human osteoclast precursors. ATL-PDX supernatants from hypercalcemic patients promoted formation of mature osteoclasts, while those from HTLV/T were variably stimulatory, but had largely consistent effects between human and murine cultures. Interestingly, this osteoclastic activity did not correlate with expression of osteoclastogenic cytokine RANKL, suggesting an alternative mechanism. HTLV/T and ATL-PDX produce small extracellular vesicles (sEV), known to facilitate HTLV-1 infection. We hypothesized that these sEV also mediate bone loss by targeting osteoclasts. We isolated sEV from both HTLV/T and ATL-PDX, and found they carried most of the activity found in supernatants. In contrast, sEV from uninfected activated T cells had little effect. Analysis of sEV (both active and inactive) by mass spectrometry and electron microscopy confirmed absence of RANKL and intact virus. Viral proteins Tax and Env were only present in sEV from the active, osteoclast-stimulatory group, along with increased representation of proteins involved in osteoclastogenesis and bone resorption. sEV injected over mouse calvaria in the presence of low dose RANKL caused more osteolysis than RANKL alone. Thus, HTLV-1 infection of T cells can cause release of sEV with strong osteolytic potential, providing a mechanism beyond RANKL production that modifies the bone microenvironment, even in the absence of overt leukemia.

The 2023 Orthopaedic Research Society's International Consensus Meeting on musculoskeletal infection: Summary from the host immunity section.

Musculoskeletal infections (MSKI), which are a major problem in orthopedics, occur when the pathogen eludes or overwhelms the host immune system. While effective vaccines and immunotherapies to prevent and treat MSKI should be possible, fundamental knowledge gaps in our understanding of protective, nonprotective, and pathogenic host immunity are prohibitive. We also lack critical knowledge of how host immunity is affected by the microbiome, implants, prior infection, nutrition, antibiotics, and concomitant therapies, autoimmunity, and other comorbidities. To define our current knowledge of these critical topics, a Host Immunity Section of the 2023 Orthopaedic Research Society MSKI International Consensus Meeting (ICM) proposed 78 questions. Systematic reviews were performed on 15 of these questions, upon which recommendations with level of evidence were voted on by the 72 ICM delegates, and another 12 questions were voted on with a recommendation of "Unknown" without systematic reviews. Two questions were transferred to another ICM Section, and the other 45 were tabled for future consideration due to limitations of available human resources. Here we report the results of the voting with internet access to the questions, recommendations, and rationale from the systematic reviews. Eighteen questions received a consensus vote of ≥90%, while nine recommendations failed to achieve this threshold. Commentary on why consensus was not achieved on these questions and potential ways forward are provided to stimulate specific funding mechanisms and research on these critical MSKI host defense questions.

Osteoclasts, Master Sculptors of Bone.

Osteoclasts are multinucleated cells with the unique ability to resorb bone matrix. Excessive production or activation of osteoclasts leads to skeletal pathologies that affect a significant portion of the population. Although therapies that effectively target osteoclasts have been developed, they are associated with sometimes severe side effects, and a fuller understanding of osteoclast biology may lead to more specific treatments. Along those lines, a rich body of work has defined essential signaling pathways required for osteoclast formation, function, and survival. Nonetheless, recent studies have cast new light on long-held views regarding the origin of these cells during development and homeostasis, their life span, and the cellular sources of factors that drive their production and activity during homeostasis and disease. In this review, we discuss these new findings in the context of existing work and highlight areas of ongoing and future investigation.

Molecular classification and biomarkers of clinical outcome in breast ductal carcinoma in situ: Analysis of TBCRC 038 and RAHBT cohorts.

Ductal carcinoma in situ (DCIS) is the most common precursor of invasive breast cancer (IBC), with variable propensity for progression. We perform multiscale, integrated molecular profiling of DCIS with clinical outcomes by analyzing 774 DCIS samples from 542 patients with 7.3 years median follow-up from the Translational Breast Cancer Research Consortium 038 study and the Resource of Archival Breast Tissue cohorts. We identify 812 genes associated with ipsilateral recurrence within 5 years from treatment and develop a classifier that predicts DCIS or IBC recurrence in both cohorts. Pathways associated with recurrence include proliferation, immune response, and metabolism. Distinct stromal expression patterns and immune cell compositions are identified. Our multiscale approach employed in situ methods to generate a spatially resolved atlas of breast precancers, where complementary modalities can be directly compared and correlated with conventional pathology findings, disease states, and clinical outcome.

Does Aging Activate T-cells to Reduce Bone Mass and Quality?

PURPOSE OF REVIEW: Aging leads to decline in bone mass and quality starting at age 30 in humans. All mammals undergo a basal age-dependent decline in bone mass. Osteoporosis is characterized by low bone mass and changes in bone microarchitecture that increases the risk of fracture. About a third of men over the age of 50 years are osteoporotic because they have higher than basal bone loss. In women, there is an additional acute decrement in bone mass, atop the basal rate, associated with loss of ovarian function (menopause) causing osteoporosis in about half of the women. Both genetics and environmental factors such as smoking, chronic infections, diet, microbiome, and metabolic disease can modulate basal age-dependent bone loss and eventual osteoporosis. Here, we review recent studies on the etiology of age-dependent decline in bone mass and propose a mechanism that integrates both genetic and environmental factors. RECENT FINDINGS: Recent findings support that aging and menopause dysregulate the immune system leading to sterile low-grade inflammation. Both animal models and human studies demonstrate that certain kinds of inflammation, in both men and women, mediate bone loss. Senolytics, meant to block a wide array of age-induced effects by preventing cellular senescence, have been shown to improve bone mass in aged mice. Based on a synthesis of the recent data, we propose that aging activates long-lived tissue resident memory T-cells to become senescent and proinflammatory, leading to bone loss. Targeting this population may represent a promising osteoporosis therapy. Emerging data indicates that there are several mechanisms that lead to sterile low-grade chronic inflammation, inflammaging, that cause age- and estrogen-loss dependent osteoporosis in men and women.

Periarticular calcifications containing giant pseudo-crystals of francolite in skeletal fluorosis from 1,1-difluoroethane "huffing".

Inhalant use disorder is a psychiatric condition characterized by repeated deliberate inhalation from among a broad range of household and industrial chemical products with the intention of producing psychoactive effects. In addition to acute intoxication, prolonged inhalation of fluorinated compounds can cause skeletal fluorosis (SF). We report a young woman referred for hypophosphatasemia and carrying a heterozygous ALPL gene variant (c.457T>C, p.Trp153Arg) associated with hypophosphatasia, the heritable metabolic bone disease featuring impaired skeletal mineralization, who instead suffered from SF. Manifestations of her SF included recurrent articular pain, axial osteosclerosis, elevated bone mineral density, maxillary exostoses, and multifocal periarticular calcifications. SF was suspected when a long history was discovered of 'huffing' a computer cleaner containing 1,1-difluoroethane. Investigation revealed markedly elevated serum and urine levels of F-. Histopathology and imaging techniques including backscattered electron mode scanning electron microscopy, X-ray microtomography, energy dispersive and wavelength dispersive X-ray emission microanalysis, and polarized light microscopy revealed that her periarticular calcifications were dystrophic deposition of giant pseudo-crystals of francolite, a carbonate-rich fluorapatite. Identifying unusual circumstances of F- exposure is key for diagnosing non-endemic SF. Increased awareness of the disorder can be lifesaving.

Conditional loss of IKKα in Osterix + cells has no effect on bone but leads to age-related loss of peripheral fat.

NF-κB has been reported to both promote and inhibit bone formation. To explore its role in osteolineage cells, we conditionally deleted IKKα, an upstream kinase required for non-canonical NF-κB activation, using Osterix (Osx)-Cre. Surprisingly, we found no effect on either cancellous or cortical bone, even following mechanical loading. However, we noted that IKKα conditional knockout (cKO) mice began to lose body weight after 6 months of age with severe reductions in fat mass and lower adipocyte size in geriatric animals. qPCR analysis of adipogenic markers in fat pads of cKO mice indicated no difference in early differentiation, but instead markedly lower leptin with age. We challenged young mice with a high fat diet finding that cKO mice gained less weight and showed improved glucose metabolism. Low levels of recombination at the IKKα locus were detected in fat pads isolated from old cKO mice. To determine whether recombination occurs in adipocytes, we examined fat pads in Osx-Cre;TdT reporter mice; these showed increasing Osx-Cre-mediated expression in peripheral adipocytes from 6 weeks to 18 months. Since Osx-Cre drives recombination in peripheral adipocytes with age, we conclude that fat loss in cKO mice is most likely caused by progressive deficits of IKKα in adipocytes.

Heparanase Blockade as a Novel Dual-Targeting Therapy for COVID-19.

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has caused over 5 million deaths worldwide. Pneumonia and systemic inflammation contribute to its high mortality. Many viruses use heparan sulfate proteoglycans as coreceptors for viral entry, and heparanase (HPSE) is a known regulator of both viral entry and inflammatory cytokines. We evaluated the heparanase inhibitor Roneparstat, a modified heparin with minimum anticoagulant activity, in pathophysiology and therapy for COVID-19. We found that Roneparstat significantly decreased the infectivity of SARS-CoV-2, SARS-CoV-1, and retroviruses (human T-lymphotropic virus 1 [HTLV-1] and HIV-1) in vitro. Single-cell RNA sequencing (scRNA-seq) analysis of cells from the bronchoalveolar lavage fluid of COVID-19 patients revealed a marked increase in HPSE gene expression in CD68+ macrophages compared to healthy controls. Elevated levels of HPSE expression in macrophages correlated with the severity of COVID-19 and the expression of inflammatory cytokine genes, including IL6, TNF, IL1B, and CCL2. In line with this finding, we found a marked induction of HPSE and numerous inflammatory cytokines in human macrophages challenged with SARS-CoV-2 S1 protein. Treatment with Roneparstat significantly attenuated SARS-CoV-2 S1 protein-mediated inflammatory cytokine release from human macrophages, through disruption of NF-κB signaling. HPSE knockdown in a macrophage cell line also showed diminished inflammatory cytokine production during S1 protein challenge. Taken together, this study provides a proof of concept that heparanase is a target for SARS-CoV-2-mediated pathogenesis and that Roneparstat may serve as a dual-targeted therapy to reduce viral infection and inflammation in COVID-19. IMPORTANCE The complex pathogenesis of COVID-19 consists of two major pathological phases: an initial infection phase elicited by SARS-CoV-2 entry and replication and an inflammation phase that could lead to tissue damage, which can evolve into acute respiratory failure or even death. While the development and deployment of vaccines are ongoing, effective therapy for COVID-19 is still urgently needed. In this study, we explored HPSE blockade with Roneparstat, a phase I clinically tested HPSE inhibitor, in the context of COVID-19 pathogenesis. Treatment with Roneparstat showed wide-spectrum anti-infection activities against SARS-CoV-2, HTLV-1, and HIV-1 in vitro. In addition, HPSE blockade with Roneparstat significantly attenuated SARS-CoV-2 S1 protein-induced inflammatory cytokine release from human macrophages through disruption of NF-κB signaling. Together, this study provides a proof of principle for the use of Roneparstat as a dual-targeting therapy for COVID-19 to decrease viral infection and dampen the proinflammatory immune response mediated by macrophages.

Transition to invasive breast cancer is associated with progressive changes in the structure and composition of tumor stroma.

Ductal carcinoma in situ (DCIS) is a pre-invasive lesion that is thought to be a precursor to invasive breast cancer (IBC). To understand the changes in the tumor microenvironment (TME) accompanying transition to IBC, we used multiplexed ion beam imaging by time of flight (MIBI-TOF) and a 37-plex antibody staining panel to interrogate 79 clinically annotated surgical resections using machine learning tools for cell segmentation, pixel-based clustering, and object morphometrics. Comparison of normal breast with patient-matched DCIS and IBC revealed coordinated transitions between four TME states that were delineated based on the location and function of myoepithelium, fibroblasts, and immune cells. Surprisingly, myoepithelial disruption was more advanced in DCIS patients that did not develop IBC, suggesting this process could be protective against recurrence. Taken together, this HTAN Breast PreCancer Atlas study offers insight into drivers of IBC relapse and emphasizes the importance of the TME in regulating these processes.

Biological resurfacing in a canine model of hip osteoarthritis.

Articular cartilage has unique load-bearing properties but has minimal capacity for intrinsic repair. Here, we used three-dimensional weaving, additive manufacturing, and autologous mesenchymal stem cells to create a tissue-engineered, bicomponent implant to restore hip function in a canine hip osteoarthritis model. This resorbable implant was specifically designed to function mechanically from the time of repair and to biologically integrate with native tissues for long-term restoration. A massive osteochondral lesion was created in the hip of skeletally mature hounds and repaired with the implant or left empty (control). Longitudinal outcome measures over 6 months demonstrated that the implant dogs returned to normal preoperative values of pain and function. Anatomical structure and functional biomechanical properties were also restored in the implanted dogs. Control animals never returned to normal and exhibited structurally deficient repair. This study provides clinically relevant evidence that the bicomponent implant may be a potential therapy for moderate hip osteoarthritis.

Breast cancer-derived GM-CSF regulates arginase 1 in myeloid cells to promote an immunosuppressive microenvironment.

Tumor-infiltrating myeloid cells contribute to the development of the immunosuppressive tumor microenvironment. Myeloid cell expression of arginase 1 (ARG1) promotes a protumor phenotype by inhibiting T cell function and depleting extracellular l-arginine, but the mechanism underlying this expression, especially in breast cancer, is poorly understood. In breast cancer clinical samples and in our mouse models, we identified tumor-derived GM-CSF as the primary regulator of myeloid cell ARG1 expression and local immune suppression through a gene-KO screen of breast tumor cell-produced factors. The induction of myeloid cell ARG1 required GM-CSF and a low pH environment. GM-CSF signaling through STAT3 and p38 MAPK and acid signaling through cAMP were required to activate myeloid cell ARG1 expression in a STAT6-independent manner. Importantly, breast tumor cell-derived GM-CSF promoted tumor progression by inhibiting host antitumor immunity, driving a significant accumulation of ARG1-expressing myeloid cells compared with lung and melanoma tumors with minimal GM-CSF expression. Blockade of tumoral GM-CSF enhanced the efficacy of tumor-specific adoptive T cell therapy and immune checkpoint blockade. Taken together, we show that breast tumor cell-derived GM-CSF contributes to the development of the immunosuppressive breast cancer microenvironment by regulating myeloid cell ARG1 expression and can be targeted to enhance breast cancer immunotherapy.

Constitutive activation of NF-κB inducing kinase (NIK) in the mesenchymal lineage using Osterix (Sp7)- or Fibroblast-specific protein 1 (S100a4)-Cre drives spontaneous soft tissue sarcoma.

Aberrant NF-κB signaling fuels tumor growth in multiple human cancer types including both hematologic and solid malignancies. Chronic elevated alternative NF-κB signaling can be modeled in transgenic mice upon activation of a conditional NF-κB-inducing kinase (NIK) allele lacking the regulatory TRAF3 binding domain (NT3). Here, we report that expression of NT3 in the mesenchymal lineage with Osterix (Osx/Sp7)-Cre or Fibroblast-Specific Protein 1 (FSP1)-Cre caused subcutaneous, soft tissue tumors. These tumors displayed significantly shorter latency and a greater multiple incidence rate in Fsp1-Cre;NT3 compared to Osx-Cre;NT3 mice, regardless of sex. Histological assessment revealed poorly differentiated solid tumors with some spindled patterns, as well as robust RelB immunostaining, confirming activation of alternative NF-κB. Even though NT3 expression also occurs in the osteolineage in Osx-Cre;NT3 mice, we observed no bony lesions. The staining profiles and pattern of Cre expression in the two lines pointed to a mesenchymal tumor origin. Immunohistochemistry revealed that these tumors stain strongly for alpha-smooth muscle actin (αSMA), although vimentin staining was uniform only in Osx-Cre;NT3 tumors. Negative CD45 and S100 immunostains precluded hematopoietic and melanocytic origins, respectively, while positive staining for cytokeratin 19 (CK19), typically associated with epithelia, was found in subpopulations of both tumors. Principal component, differential expression, and gene ontology analyses revealed that NT3 tumors are distinct from normal mesenchymal tissues and are enriched for NF-κB related biological processes. We conclude that constitutive activation of the alternative NF-κB pathway in the mesenchymal lineage drives spontaneous sarcoma and provides a novel mouse model for NF-κB related sarcomas.

Contemporary Clinical Isolates of Staphylococcus aureus from Pediatric Osteomyelitis Patients Display Unique Characteristics in a Mouse Model of Hematogenous Osteomyelitis.

Osteomyelitis can result from the direct inoculation of pathogens into bone during injury or surgery or from spread via the bloodstream, a condition called hematogenous osteomyelitis (HOM). HOM disproportionally affects children, and more than half of cases are caused by Staphylococcus aureus. Laboratory models of osteomyelitis mostly utilize direct injection of bacteria into the bone or implantation of foreign material and therefore do not directly interrogate the pathogenesis of pediatric hematogenous osteomyelitis. In this study, we inoculated mice intravenously and characterized the resultant musculoskeletal infections using two strains isolated from adults (USA300-LAC and NRS384) and five new methicillin-resistant S. aureus isolates from pediatric osteomyelitis patients. All strains were capable of creating stable infections over 5 weeks, although the incidence varied. Micro-computed tomography (microCT) analysis demonstrated decreases in the trabecular bone volume fraction but little effect on bone cortices. Histological assessment revealed differences in the precise focus of musculoskeletal infection, with various mixtures of bone-centered osteomyelitis and joint-centered septic arthritis. Whole-genome sequencing of three new isolates demonstrated distinct strains, two within the USA300 lineage and one USA100 isolate. Interestingly, this USA100 isolate showed a distinct predilection for septic arthritis compared to the other isolates tested, including NRS384 and LAC, which more frequently led to osteomyelitis or mixed bone and joint infections. Collectively, these data outline the feasibility of using pediatric osteomyelitis clinical isolates to study the pathogenesis of HOM in murine models and lay the groundwork for future studies investigating strain-dependent differences in musculoskeletal infection.

Osteolineage depletion of mitofusin2 enhances cortical bone formation in female mice.

Mitochondria are essential organelles that form highly complex, interconnected dynamic networks inside cells. The GTPase mitofusin 2 (MFN2) is a highly conserved outer mitochondrial membrane protein involved in the regulation of mitochondrial morphology, which can affect various metabolic and signaling functions. The role of mitochondria in bone formation remains unclear. Since MFN2 levels increase during osteoblast (OB) differentiation, we investigated the role of MFN2 in the osteolineage by crossing mice bearing floxed Mfn2 alleles with those bearing Prx-cre to generate cohorts of conditional knock out (cKO) animals. By ex vivo microCT, cKO female mice, but not males, display an increase in cortical thickness at 8, 18, and 30 weeks, compared to wild-type (WT) littermate controls. However, the cortical anabolic response to mechanical loading was not different between genotypes. To address how Mfn2 deficiency affects OB differentiation, bone marrow-derived mesenchymal stromal cells (MSCs) from both wild-type and cKO mice were cultured in osteogenic media with different levels of ß-glycerophosphate. cKO MSCs show increased mineralization and expression of multiple markers of OB differentiation only at the lower dose. Interestingly, despite showing the expected mitochondrial rounding and fragmentation due to loss of MFN2, cKO MSCs have an increase in oxygen consumption during the first 7 days of OB differentiation. Thus, in the early phases of osteogenesis, MFN2 restrains oxygen consumption thereby limiting differentiation and cortical bone accrual during homeostasis in vivo.