Anti-Siglec-15 antibody suppresses bone resorption by inhibiting osteoclast multinucleation without attenuating bone formation

Anti-resorptive drugs are widely used for the treatment of osteoporosis, but excessive inhibition of osteoclastogenesis can suppress bone turnover and cause the deterioration of bone quality. Sialic acid-binding immunoglobulin-like lectin 15 (Siglec-15) is a transmembrane protein expressed on osteoclast precursor cells and mature osteoclasts. Siglec-15 regulates proteins containing immunoreceptor tyrosine-based activation motif (ITAM) domains, which then induce nuclear factor of activated T-cells 1 (NFATc1), a master transcription factor of osteoclast differentiation. Anti-Siglec-15 antibody modulates ITAM signaling in osteoclast precursors and inhibits the maturation of osteoclasts in vitro. However, in situ pharmacological effects, particularly during postmenopausal osteoporosis, remain unclear. Here, we demonstrated that anti-Siglec-15 antibody treatment protected against ovariectomy-induced bone loss by specifically inhibiting the generation of multinucleated osteoclasts in vivo. Moreover, treatment with anti-Siglec-15 antibody maintained bone formation to a greater extent than with risedronate, the first-line treatment for osteoporosis. Intravital imaging revealed that anti-Siglec-15 antibody treatment did not cause a reduction in osteoclast motility, whereas osteoclast motility declined following risedronate treatment. We evaluated osteoclast activity using a pH-sensing probe and found that the bone resorptive ability of osteoclasts was lower following anti-Siglec-15 antibody treatment compared to after risedronate treatment. Our findings suggest that anti-Siglec-15 treatment may have potential as an anti-resorptive therapy for osteoporosis, which substantially inhibits the activity of osteoclasts while maintaining physiological bone coupling.

Group 2 innate lymphoid cells in bone marrow regulate osteoclastogenesis in a reciprocal manner via RANKL, GM-CSF and IL-13

Group 2 innate lymphoid cells (ILC2s) are tissue-resident cells that play different roles in different organs by sensing surrounding environmental factors. Initially, it was thought that ILC2s in bone marrow (BM) are progenitors for systemic ILC2s, which migrate to other organs and acquire effector functions. However, accumulating evidence that ILC2s differentiate in peripheral tissues suggests that BM ILC2s may play a specific role in the BM as a unique effector per se. Here, we demonstrate that BM ILC2s highly express the receptor activator of nuclear factor κB ligand (RANKL), a robust cytokine for osteoclast differentiation and activation, and RANKL expression on ILC2s is up-regulated by interleukin (IL)-2, IL-7 and all-trans retinoic acid (ATRA). BM ILC2s co-cultured with BM-derived monocyte/macrophage lineage cells (BMMs) in the presence of IL-7 induce the differentiation of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts in a RANKL-dependent manner. In contrast, BM ILC2s stimulated with IL-33 down-regulate RANKL expression and convert BMMs differentiation into M2 macrophage-like cells rather than osteoclasts by granulocyte macrophage colony-stimulating factor (GM-CSF) and IL-13 production. Intravital imaging using two-photon microscopy revealed that a depletion of ILC2s prominently impaired in vivo osteoclast activity in an IL-7 plus ATRA-induced bone loss mouse model. These results suggest that ILC2s regulate osteoclast activation and contribute to bone homeostasis in both steady state and IL-33-induced inflammation.

Osteoclasts adapt to physioxia perturbation through DNA demethylation

Oxygen plays an important role in diverse biological processes. However, since quantitation of the partial pressure of cellular oxygen in vivo is challenging, the extent of oxygen perturbation in situ and its cellular response remains underexplored. Using two‐photon phosphorescence lifetime imaging microscopy, we determine the physiological range of oxygen tension in osteoclasts of live mice. We find that oxygen tension ranges from 17.4 to 36.4 mmHg, under hypoxic and normoxic conditions, respectively. Physiological normoxia thus corresponds to 5% and hypoxia to 2% oxygen in osteoclasts. Hypoxia in this range severely limits osteoclastogenesis, independent of energy metabolism and hypoxia‐inducible factor activity. We observe that hypoxia decreases ten‐eleven translocation (TET) activity. Tet2/3 cooperatively induces Prdm1 expression via oxygen‐dependent DNA demethylation, which in turn activates NFATc1 required for osteoclastogenesis. Taken together, our results reveal that TET enzymes, acting as functional oxygen sensors, regulate osteoclastogenesis within the physiological range of oxygen tension, thus opening new avenues for research on in vivo response to oxygen perturbation.

Association of low total cholesterol level with clinical outcomes in patients with atrial fibrillation: the Fushimi AF registry

Background

Hyperlipidemia is a well-established risk factor for cardiovascular disease. However, low cholesterol is also reported to be associated with poor outcome in patients with chronic disease, which is called “cholesterol paradox”, and the association of cholesterol level with the incidence of clinical outcomes in patients with atrial fibrillation (AF) remains unclear.

Methods

In the Fushimi AF Registry, a community-based prospective survey of the AF patients in Fushimi-ku, Kyoto, Japan, follow-up data and baseline total cholesterol levels were available in 3,054 patients. We excluded 767 patients who were taking statins, and 2,267 patients were included in the analyses. We defined low cholesterol as total cholesterol <150 mg/dl, and examined the incidence of all-cause death, stroke/systemic embolism (SE), heart failure (HF) hospitalization, and major bleeding.

Results

Patients with low cholesterol (N=464 (20.4%)) were older, more often male, and had higher prevalence of low body weight (<50 kg), permanent/persistent AF, prior stroke/SE, HF, chronic kidney disease, and anemia (hemoglobin <11 g/dl). CHA2DS2-VASc score was higher in patients with low cholesterol (low cholesterol vs others; 3.6±1.6 vs 3.2±1.7: P<0.001). Prescription of oral anti-coagulants was comparable between the groups (50.0% vs 54.5%: P=0.09). During the median follow-up of 1,805 days, the incidence of all-cause death, stroke/SE, HF hospitalization, and major bleeding was significantly higher in patients with low cholesterol (all-cause death, 10.9 vs 3.8 /100 person-years; stroke/SE, 3.4 vs 1.9 /100 person-years; HF hospitalization, 4.7 vs 2.5 /100 person-years; major bleeding, 2.7 vs 1.4 /100 person-years) (Figure 1). After adjustment for the components of CHA2DS2-VASc score, low body weight, permanent/persistent AF, chronic kidney disease, anemia, and prescription of oral anti-coagulants, low cholesterol was significantly associated with the incidence of all-cause death and stroke/SE, but not with that of HF hospitalization or major bleeding (Figure 2, model 3). Total cholesterol levels were still significantly and inversely associated with the incidence of all-cause death (hazard ratio, 0.94; 95% confidence interval, 0.92–0.96 for 10 mg/dl increase) and stroke/SE (hazard ratio, 0.96; 95% confidence interval, 0.92–0.999 for 10 mg/dl increase), when analyzed as continuous variables. Subgroup analysis revealed that the risk of low cholesterol for all-cause death was more pronounced in female (interaction P, 0.049), patient without prior stroke/SE (interaction P, 0.01), those without HF (interaction P, 0.01), and those without vascular disease (interaction P, 0.001). The risk for stroke/SE was more pronounced in patients without vascular disease (interaction P, 0.01).

Conclusion

Low total cholesterol level was significantly associated with the incidence of all-cause and stroke/SE in AF patients not taking statins, suggesting the existence of cholesterol paradox in AF.

Funding Acknowledgement

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Boehringer Ingelheim, Bayer Healthcare, Pfizer, Bristol-Myers Squibb, Astellas Pharma, AstraZeneca, Daiichi-Sankyo, Novartis Pharma, MSD, Sanofi-Avent

The relationship between diastolic blood pressure and the risk of cardiovascular events in patients with atrial fibrillation whose systolic blood pressure was treated to less than 130 mmHg

Background

Hypertension is one of the major risk factors of cardiovascular events in patients with atrial fibrillation (AF). Low diastolic blood pressure (DBP) has been reported to be associated with the incidence of cardiovascular events, but current guidelines recommend an intensive blood pressure target of less than 130/80 mmHg for AF patients taking oral anticoagulants without mentioning the lower limits of DBP.

Methods

The Fushimi AF Registry is a community-based prospective survey of AF patients in a city of Japan. Follow-up data were available in 4,472 patients, and hypertensive patients who received prescription of any antihypertensive agents and whose systolic blood pressure was treated to less than 130 mmHg were available were examined (n=1,319). We divided the patients into four groups according to their DBP at baseline; G1 (DBP<60 mmHg, n=349), G2 (60≤DBP<70, n=434), G3 (70≤DBP<80, n=386) and G4 (80≤DBP, n=150), and compared the clinical background and outcomes among groups.

Results

The proportion of female was grater in G1 group, and the patients in G1 group were older. During the median follow-up of 2,458 days, in Kaplan-Meier analysis, the incidence rates of cardiovascular events (composite of cardiac death, ischemic stroke, systemic embolism, non-fatal myocardial infarction and heart failure hospitalization during follow up) were the highest in G1 group and the lowest in G3 group (G1: 7.2% per person-year vs. G2: 4.9% vs. G3: 2.2% vs. G4: 4.4%; p<0.01). Multivariate Cox proportional hazards regression analysis revealed that DBP was an independent determinant of cardiovascular events (G1 vs. G3; hazard ratio (HR): 1.96, 95% confidence intervals (CI): 1.39–2.76, G2 vs. G3; HR: 1.79, 95% CI: 1.28–2.50, G4 vs. G3; HR: 1.56, 95% CI: 0.99–2.45) (Figure 1). When we examined the association of DBP according to 10 mmHg increment, patients with excessively low DBP (<50 mmHg) had significantly higher incidence of cardiovascular events than patients with DBP of 70–79 mmHg (HR: 2.80, 95% CI: 1.81–4.33), and DBP exhibited J curve association with higher incidence of cardiovascular events (Figure 2).

Conclusion

In Japanese AF patients whose systolic blood pressure was treated to less than 130 mmHg, patients with excessively low DBP had significantly higher incidence of cardiovascular events, and DBP exhibited J curve association with higher incidence of cardiovascular events.

Funding Acknowledgement

Type of funding sources: None.

Previous pacemaker therapy was not associated with the risk of clinical events in patients with atrial fibrillation: the Fushimi AF Registry

Background

Patients with atrial fibrillation (AF) occasionally require pacemaker implantation. Meanwhile, patients with implanted pacemaker are occasionally found to have subclinical AF and develop clinical AF. However, little is known about the clinical outcomes of AF patients with implanted pacemaker.

Purpose

We aimed to investigate the clinical outcomes in AF patients undergoing previous pacemaker therapy.

Methods

The Fushimi AF Registry is a community-based prospective survey of the AF patients in a city of Japan. Follow-up data including prescription status were available for 4,447 patients. After exclusion of patients with implantable cardioverter defibrillator and cardiac resynchronization therapy, we investigated 293 AF patients with pacemaker implantation at baseline. We performed propensity score-matching analysis to assess the impact of pacemaker therapy in AF patients.

Results

Of a total cohort, patients with pacemaker were more often female (51.2% vs. 39.7%; p<0.01) and older (78.0 vs. 73.3 years of age; p<0.01). Patients with pacemaker were more likely to have pre-existing heart failure (33.1% vs. 26.6%; p<0.01), valvular heart disease (22.9% vs. 16.8%; p<0.01), chronic kidney disease (48.8% vs. 34.7%; p<0.01), and history of performing direct current cardioversion (7.2% vs. 3.1%; p<0.01), compared with patients without pacemaker. Mean CHA2DS2-VASc score was higher in patients with pacemaker (3.80 vs. 3.34; p<0.01). Patients with pacemaker were more often prescribed oral anticoagulants (62.1% vs. 55.2%; p=0.02), verapamil (13.3% vs. 9.4%; p=0.03), and loop diuretics (30.7% vs. 21.8%; p<0.01). Using propensity score-matching, 291 patients with pacemaker and 291 without pacemaker were matched and baseline characteristics were comparable. The median follow-up period was 1,819 days. All-cause death occurred in 91 patients with pacemaker (6.0 /100 person-years) and 79 patients without pacemaker (5.9 /100 person-years), with a hazard ratio (HR) for patients with pacemaker of 1.01 (95% confidence interval [CI], 0.75 to 1.37; p=0.93). Furthermore, HR of cardiac death for patients with pacemaker was 1.00 (95% CI, 0.23 to 4.32; p=0.99), that of stroke or systemic embolism was 0.69 (95% CI, 0.44 to 1.07; p=0.10) and that of hospitalization for heart failure was 0.94 (95% CI, 0.65 to 1.37; p=0.76).

Conclusion

We identified that patients undergoing previous pacemaker therapy were not associated with the incidence of various adverse clinical events in Japanese AF patients.

Funding Acknowledgement

Type of funding sources: Private company. Main funding source(s): Boehringer Ingelheim, Bayer Healthcare, Pfizer, Bristol-Myers Squibb, Astellas Pharma, AstraZeneca, Daiichi Sankyo, Novartis Pharma, MSD, Sanofi-Aventis, Takeda Pharmaceutical, and the Practical Research Project for Life-Style related Diseases including Cardiovascular Diseases and Diabetes Mellitus from Japan Agency for Medical Research and Development.

Association of the degree of thrombocytopenia with cause of death in patients with atrial fibrillation: the Fushimi AF Registry

Background

Thrombocytopenia is sometimes found in routine blood tests and is associated with an increased risk of mortality in general population. We have previously reported that atrial fibrillation (AF) patients with thrombocytopenia have a higher mortality than those without thrombocytopenia. However, association of the degree of thrombocytopenia with cause of death in AF patients is unknown.

Purpose

We aimed to investigate the association of baseline platelet count with cause of death including cardiac death, intracranial death, malignancy, infection, extracranial bleeding death, renal failure death, respiratory failure death and undetermined death.

Methods

The Fushimi AF Registry was designed to enroll all of the AF patients in Fushimi-ku, Kyoto. Fushimi-ku is densely populated with a total population of 283,000 and is assumed to represent a typical urban community in Japan. We started to enroll patients from March 2011, and follow-up data with baseline platelet counts less than 150,000/μL were available in 853 patients by the end of September 2020. We divided them into 3 groups according to baseline platelet level: Mild thrombocytopenia (100,000–149,999/μL, n=703), Moderate thrombocytopenia (50,000–99,999/μL, n=120), and Severe thrombocytopenia (<50,000/μL, n=30).

Results

In the entire cohort, the mean age was 76 years, 34% were women, the mean body weight and body mass index was 59.3 kg and 22.9 kg/m2, and the median platelet count were 121,000/μL (interquartile range 109,000 to 141,000/μL). Compared to Mild thrombocytopenia, patients with Moderate or Severe thrombocytopenia were more likely to have chronic kidney disease (42.2% vs 54.2% vs 73.3%, p=0.0003), have higher HAS-BLED score (1.90 vs 2.14 vs 2.00, p=0.047) and lower hemoglobin (12.8g/dL vs 11.7g/dL vs 11.2g/dL, p<0.0001) and were less often prescribed anti platelet drugs. Age, sex, body weight, systolic blood pressure, previous stroke, previous major bleeding, hypertension, diabetes mellitus, CHADS2 score and CHA2DS2-VASc score were comparable between three groups. During the median follow-up period, the incidence rate (per 100 person-years) of all-cause death was 6.82 vs 15.27 vs 9.64. (p<0.001) On univariate analysis, the incidence of all-cause death was higher in Moderate group than Mild group. (HR: 2.15; 95% CI 1.61–2.87, p<0.0001), but there was no significant difference between Mild and Severe groups. (HR: 1.44; 95% CI 0.78–2.64, p=0.243). The incidence of cardiac death was comparable between three groups. (Mild vs Moderate: HR 0.65; 95% CI 0.15–2.75, p=0.56, Mild vs Severe: HR 1.11; 95% CI 0.15–8.23, p=0.92) Regarding other causes of death such as intracranial bleeding, extracranial bleeding, malignancy, infection, renal failure, respiratory failure and undetermined cause, there was no significant difference.

Conclusion

Mortality was higher according to the degree of thrombocytopenia in AF patients, but the cause of death was not different among three groups.

Funding Acknowledgement

Type of funding sources: None.

Prevention of retained fetal membranes and improvement in subsequent fertility with oxytocin administration in cows with assisted calving

In dairy cows, the efficacy of oxytocin treatment for preventing retained fetal membranes (RFM) is controversial. The physiological condition of cows associated with the calving process may affect the action of oxytocin. This study aimed to elucidate the difference in the efficacy of exogenous oxytocin treatment immediately after calving among cows that received various obstetric interventions. The calving ease was recorded using a score of 1-5, and assisted birth was defined as a score of 2 or more. Cows that required calving assistance (assisted, n = 28) due to delayed calving progression had a prolonged time from calving to expulsion of the fetal membrane (P < 0.01), and impaired reproductive performance compared to cows that did not receive calving assistance (unassisted, n = 78). The effect of oxytocin treatment was determined using cows that did not expel their fetal membrane within 3 h after calving. Cows were randomly divided into the control (unassisted, n = 41; assisted, n = 22) or oxytocin group (unassisted, n = 33; assisted, n = 10). Oxytocin (50 IU) was administered intramuscularly to the cows in the oxytocin group between 3 and 6 h after calving, while no treatment was administered in the control group. In cows with assisted birth, oxytocin administration accelerated placental expulsion (P < 0.05) and improved several reproductive parameters, such as the number of services until conception (P < 0.05) and the calving to conception intervals (P < 0.05) compared to the control group. On the other hand, oxytocin administration slightly accelerated placental expulsion (P < 0.05), but failed to improve fertility in cows with unassisted birth. The results indicate that the action of oxytocin varies depending on the calving situation of the cows. Oxytocin administration during the early postpartum period could prevent RFM and improve the decline in reproductive performance associated with calving assistance.

Group 2 Innate Lymphoid Cells Exhibit Tissue-Specific Dynamic Behaviour During Type 2 Immune Responses

Group 2 innate lymphoid cells (ILC2s) are early effectors of mucosal type 2 immunity, producing cytokines such as interleukin (IL)-13 to mediate responses to helminth infection and allergen-induced inflammation. ILC2s are also present in lymph nodes (LNs) and can express molecules required for antigen presentation, but to date there are limited data on their dynamic behaviour. We used a CD2/IL-13 dual fluorescent reporter mouse for in vivo imaging of ILC2s and Th2 T cells in real time following a type 2 priming helminth infection or egg injection. After helminth challenge, we found that ILC2s were the main source of IL-13 in lymphoid organs (Peyer’s patches and peripheral LNs), and were located in T cell areas. Intravital imaging demonstrated an increase in IL-13⁺ ILC2 size and movement following helminth infection, but reduced duration of interactions with T cells compared with those in homeostasis. In contrast, in the intestinal mucosa, we observed an increase in ILC2-T cell interactions post-infection, including some of prolonged duration, as well as increased IL-13⁺ ILC2 movement. These data suggest that ILC2 activation enhances cell motility, with the potential to increase the area of distribution of cytokines to optimise the early generation of type 2 responses. The prolonged ILC2 interactions with T cells within the intestinal mucosa are consistent with the conclusion that contact-based T cell activation may occur within inflamed tissues rather than lymphoid organs. Our findings have important implications for our understanding of the in vivo biology of ILC2s and the way in which these cells facilitate adaptive immune responses.

Imaging of bone and joints in vivo: pathological osteoclastogenesis in arthritis

Osteoimmunology highlights the reciprocal interactions between the skeletal and immune systems. Over the past two decades, many molecules that link the two have been identified, including cytokines, receptors and transcription factors, leading to successful translation of research into therapeutic approaches to autoimmune diseases such as rheumatoid arthritis. The development of an intravital imaging system using multi-photon microscopy, combined with a variety of fluorescent probes and reporter mouse strains, has provided valuable insights into the real-time dynamics of osteoclasts and immune cells in the bone marrow. This technique is now applied to the synovial tissue of arthritic mice to investigate the pathogenesis of osteoimmune diseases and enables direct observation of complex biological phenomena in vivo. In addition, rapid progress in the next-generation sequencing technologies has provided important insights into the field of osteoimmunology through characterizing individual cells in the synovial microenvironment. Single-cell RNA sequencing (scRNA-seq) dissects cellular heterogeneity within a biological system and enables the identification of specific cells differentiating into mature osteoclasts within the previously defined "osteoclast precursor (OP)-containing population". In this review, we will explain the cellular interactions and cytokine milieu involved in inflammatory bone destruction and update how the novel technologies, such as scRNA-seq and intravital imaging, have contributed to better understand the pathogenesis of bone destruction in arthritis.

Arthritis-associated osteoclastogenic macrophages (AtoMs) participate in pathological bone erosion in rheumatoid arthritis

Rheumatoid arthritis is a chronic form of arthritis that causes bone destruction in joints such as the knees and fingers. Over the past two decades, the clinical outcomes of rheumatoid arthritis have improved substantially with the development of biological agents and Janus kinase inhibitors. Osteoclasts are myeloid lineage cells with a unique bone-destroying ability that can lead to joint destruction. On the other hand, osteoclasts play an important role in skeletal homeostasis by supporting bone remodeling together with osteoblasts in the bone marrow under steady-state conditions. However, the same osteoclasts are considered to participate in physiological bone remodeling and joint destruction. We found that pathological osteoclasts have different differentiation pathways and regulatory transcription factors compared to physiological osteoclasts. We also identified arthritis-associated osteoclastogenic macrophages (AtoMs), which are common progenitors of pathological osteoclasts in mice and humans that develop specifically in inflamed synovial tissue. This review presents details of the newly identified AtoMs and the original intravital imaging systems that can visualize synovial tissue and pathological osteoclasts at the pannus-bone interface.

Expression of leukotriene B4 receptor 1 defines functionally distinct DCs that control allergic skin inflammation

Leukotriene B4 (LTB4) receptor 1 (BLT1) is a chemotactic G protein-coupled receptor expressed by leukocytes, such as granulocytes, macrophages, and activated T cells. Although there is growing evidence that BLT1 plays crucial roles in immune responses, its role in dendritic cells remains largely unknown. Here, we identified novel DC subsets defined by the expression of BLT1, namely, BLT1hi and BLT1lo DCs. We also found that BLT1hi and BLT1lo DCs differentially migrated toward LTB4 and CCL21, a lymph node-homing chemoattractant, respectively. By generating LTB4-producing enzyme LTA4H knockout mice and CD11c promoter-driven Cre recombinase-expressing BLT1 conditional knockout (BLT1 cKO) mice, we showed that the migration of BLT1hi DCs exacerbated allergic contact dermatitis. Comprehensive transcriptome analysis revealed that BLT1hi DCs preferentially induced Th1 differentiation by upregulating IL-12p35 expression, whereas BLT1lo DCs accelerated T cell proliferation by producing IL-2. Collectively, the data reveal an unexpected role for BLT1 as a novel DC subset marker and provide novel insights into the role of the LTB4-BLT1 axis in the spatiotemporal regulation of distinct DC subsets.

Group 2 innate lymphoid cells support hematopoietic recovery under stress conditions

The cell-cycle status of hematopoietic stem and progenitor cells (HSPCs) becomes activated following chemotherapy-induced stress, promoting bone marrow (BM) regeneration; however, the underlying molecular mechanism remains elusive. Here we show that BM-resident group 2 innate lymphoid cells (ILC2s) support the recovery of HSPCs from 5-fluorouracil (5-FU)-induced stress by secreting granulocyte-macrophage colony-stimulating factor (GM-CSF). Mechanistically, IL-33 released from chemo-sensitive B cell progenitors activates MyD88-mediated secretion of GM-CSF in ILC2, suggesting the existence of a B cell-ILC2 axis for maintaining hematopoietic homeostasis. GM-CSF knockout mice treated with 5-FU showed severe loss of myeloid lineage cells, causing lethality, which was rescued by transferring BM ILC2s from wild-type mice. Further, the adoptive transfer of ILC2s to 5-FU-treated mice accelerates hematopoietic recovery, while the reduction of ILC2s results in the opposite effect. Thus, ILC2s may function by "sensing" the damaged BM spaces and subsequently support hematopoietic recovery under stress conditions.

Novel method for gain-of-function analyses in primary osteoclasts using a non-viral gene delivery system

INTRODUCTION

Overexpression studies have been commonly used to yield significant advances in cell biology. In vitro osteoclast culturing involves the differentiation of bone marrow-derived monocyte macrophage precursors (BMMs) in medium supplemented with macrophage colony-stimulating factor and receptor activator of nuclear factor-kB ligand (RANKL) into mature osteoclasts. Retroviral vectors are the gold standards for efficient gene delivery into BMMs. While this strategy is effective in BMMs that are in the early stages of differentiation, it is ineffective in RANKL-treated BMMs such as mono- and multinucleated osteoclasts. This study attempted to enhance gene delivery into differentiated BMMs using liposome-mediated RNA transfection.

MATERIAL AND METHODS

BMMs were transfected with an EYFP overexpression plasmid or EYFP RNA by lipofection, or transduced with a retroviral vector expressing EYFP. EYFP expression was assessed by flow cytometry.

RESULTS

We performed overexpression analyses using enhanced yellow fluorescent protein (EYFP). Although EYFP expression was observed 24 h after infection of BMMs with a recombinant retrovirus containing EYFP, expression of EYFP was observed within 3 h of transfection with EYFP RNA. Moreover, the efficiency of EYFP RNA for gene delivery into BMMs was comparable to that of retroviral transduction of EYFP. In contrast, while very few BMMs stimulated by RANKL for two days expressed EYFP after retroviral infection, more than half of the cells expressed EYFP after transfection with EYFP RNA.

CONCLUSION

RNA-mediated gene delivery is quick and easy method for performing gain-of-function analyses in primary osteoclast precursors and mature osteoclasts.

SLPI is a critical mediator that controls PTH-induced bone formation

Osteoclastic bone resorption and osteoblastic bone formation/replenishment are closely coupled in bone metabolism. Anabolic parathyroid hormone (PTH), which is commonly used for treating osteoporosis, shifts the balance from osteoclastic to osteoblastic, although it is unclear how these cells are coordinately regulated by PTH. Here, we identify a serine protease inhibitor, secretory leukocyte protease inhibitor (SLPI), as a critical mediator that is involved in the PTH-mediated shift to the osteoblastic phase. Slpi is highly upregulated in osteoblasts by PTH, while genetic ablation of Slpi severely impairs PTH-induced bone formation. Slpi induction in osteoblasts enhances its differentiation, and increases osteoblast-osteoclast contact, thereby suppressing osteoclastic function. Intravital bone imaging reveals that the PTH-mediated association between osteoblasts and osteoclasts is disrupted in the absence of SLPI. Collectively, these results demonstrate that SLPI regulates the communication between osteoblasts and osteoclasts to promote PTH-induced bone anabolism.

Integrated analysis of cell shape and movement in moving frame

The cell's movement and morphological change are two interrelated cellular processes. An integrated analysis is needed to explore the relationship between them. However, it has been challenging to investigate them as a whole. The cell's trajectory can be described by its speed, curvature, and torsion. On the other hand, the three-dimensional (3D) cell shape can be studied by using a shape descriptor such as spherical harmonic (SH) descriptor, which is an extension of a Fourier transform in 3D space. We propose a novel method using parallel-transport (PT) to integrate these shape-movement data by using moving frames as the 3D-shape coordinate system. This moving frame is purely determined by the velocity vector. On this moving frame, the movement change will influence the coordinate system for shape analysis. By analyzing the change of the SH coefficients over time in the moving frame, we can observe the relationship between shape and movement. We illustrate the application of our approach using simulated and real datasets in this paper.

Segmental Imaging of the Trochlear Nerve: Anatomic and Pathologic Considerations

BACKGROUND

The trochlear nerve (the fourth cranial nerve) is the only cranial nerve that arises from the dorsal aspect of the midbrain. The nerve has a lengthy course making it highly susceptible to injury. It is also the smallest cranial nerve and is often difficult to identify on neuroimaging.

EVIDENCE ACQUISITION

High-resolution 3-dimensional skull base MRI allows for submillimeter isotropic acquisition and is optimal for cranial nerve evaluation. In this text, the detailed anatomy of the fourth cranial nerve applicable to imaging will be reviewed.

RESULTS

Detailed anatomic knowledge of each segment of the trochlear nerve is necessary in patients with trochlear nerve palsy. A systematic approach to identification and assessment of each trochlear nerve segment is essential. Pathologic cases are provided for each segment.

CONCLUSIONS

A segmental approach to high-resolution 3-dimensional MRI for the study of the trochlear nerve is suggested.

Exploitation of Elevated Extracellular ATP to Specifically Direct Antibody to Tumor Microenvironment

The extracellular adenosine triphosphate (ATP) concentration is highly elevated in the tumor microenvironment (TME) and remains tightly regulated in normal tissues. Using phage display technology, we establish a method to identify an antibody that can bind to an antigen only in the presence of ATP. Crystallography analysis reveals that ATP bound in between the antibody-antigen interface serves as a switch for antigen binding. In a transgenic mouse model overexpressing the antigen systemically, the ATP switch antibody binds to the antigen in tumors with minimal binding in normal tissues and plasma and inhibits tumor growth. Thus, we demonstrate that elevated extracellular ATP concentration can be exploited to specifically target the TME, giving therapeutic antibodies the ability to overcome on-target off-tumor toxicity.

Intravital imaging of orthotopic and ectopic bone

Bone homeostasis is dynamically regulated by a balance between bone resorption by osteoclasts and bone formation by osteoblasts. Visualizing and evaluating the dynamics of bone cells in vivo remain difficult using conventional technologies, including histomorphometry and imaging analysis. Over the past two decades, multiphoton microscopy, which can penetrate thick specimens, has been utilized in the field of biological imaging. Using this innovative technique, the in vivo dynamic motion of bone metabolism-related cells and their interactions has been revealed. In this review, we summarize previous approaches used for bone imaging and provide an overview of current bone tissue imaging methods using multiphoton excitation microscopy.