X. Sherry Liu

Background: Pregnancy and lactation impose substantial demands on maternal calcium homeostasis, leading to pronounced skeletal remodeling during lactation followed by recovery after weaning. Although bone mass is largely returned at the tissue level after weaning, it remains unclear whether osteocyte-level remodeling exhibits a similarly reversible pattern. Osteocytes regulate mineral mobilization through perilacunar/canalicular remodeling (PLR), which is elevated during lactation. However, its spatial and temporal regulation in response to reproduction remains poorly defined. Objective/Hypothesis: This study aims to determine whether PLR-regulated lacunar remodeling during reproduction varies with osteocyte location and relative age. We hypothesized that osteocyte PLR-mediated lacunar change is spatially heterogeneous during lactation, varies with osteocyte location and relative age, and may persist after weaning. Methods: DXA and μCT were used to assess skeletal changes. Sequential fluorochrome labeling tracked mineral dynamics and defined osteocyte relative age. Osteocyte PLR activity was evaluated by MMP13 immunohistochemistry. Lacunar-canalicular structure (LCS) was assessed using Ploton silver nitrate staining, and spatially resolved lacunar morphology was quantified using high-resolution backscattered scanning electron microscopy (bSEM). Results: At the tissue level, reproduction induced distinct skeletal responses, characterized by reversible cortical bone loss and persistent trabecular deterioration. Cortical bone loss during lactation was spatially asymmetric and confined to the posterior cortex. Fluorochrome labeling further resolved surface-specific remodeling patterns during reproduction, including endocortical resorption at the posterior cortex and sustained deposition at anterior endocortical and posterior periosteal surfaces.At the cellular level, osteocyte PLR activity increased during lactation in WT mice and returned after weaning, whereas no changes were observed in cKO mice. Consistently, lacunar size increased during lactation and returned toward baseline after weaning in WT mice but remained unchanged in cKO mice.Spatially resolved analysis demonstrated that lacunar remodeling was heterogeneous across cortical thickness. At the anterior cortex, lacunar enlargement occurred near the endocortical surface during lactation and was reversible after weaning. In contrast, at the posterior cortex, lacunar enlargement occurred near the periosteal surface and persisted after weaning. These spatial patterns corresponded to cortical regions enriched with newly formed osteocytes, whereas pre-existing osteocytes exhibited minimal changes. This spatial heterogeneity was absent in cKO mice. Conclusion: Osteocyte PLR-mediated lacunar remodeling during reproduction is spatially heterogeneous and varies with osteocyte location and relative age. These findings demonstrate that recovery at the tissue level does not necessarily extend to the osteocyte microenvironment and identify osteocyte PLR-mediated lacunar remodeling as a spatially structured and potentially persistent component of reproductive skeletal adaptation. Together, these results highlight a previously unrecognized layer of maternal skeletal health.

Radiotherapy plays a central role in cancer treatment, and the immunostimulatory effects of radiotherapy have been increasingly recognized. A better understanding of the mechanisms underlying postradiation immune escape is needed to help overcome radioresistance. In this study, we identified that irradiated tumor cells exploit the ANAPC5/GPAA1 axis to elevate surface expression of the "do not eat me" signal CD24, inducing phagocytosis resistance and immune evasion. Mechanistically, radiation inhibited the APC/C complex, reducing ANAPC5-mediated ubiquitination of GPAA1, a catalytic subunit of glycosylphosphatidylinositol (GPI) transamidase. The subsequent accumulation of GPAA1 facilitated GPI anchoring, thereby enhancing CD24 membrane localization. Accordingly, ablation of GPAA1 or CD24 significantly potentiated the local antitumor effects of radiotherapy across multiple preclinical models, dependent on T cells and macrophages. Notably, CD24 deficiency also stimulated abscopal effects, suppressing the growth of nonirradiated tumors. Overall, this study elucidates a mechanism of radiotherapy-mediated upregulation of the innate immune checkpoint CD24, offering perspectives on radiation-induced immune escape and presenting a strategy to improve radiotherapy efficacy. SIGNIFICANCE: Radiation enhances CD24 membrane trafficking by regulating ANAPC5/GPAA1-mediated GPI anchoring to drive cancer immune evasion, which can be circumvented by targeting CD24 to potentiate the local and abscopal antitumor effects of radiotherapy.

Abstract Background It remains unclear if cure of hepatitis C virus (HCV) infection with direct-acting antivirals (DAAs) ameliorates HCV-related inflammation and bone deficits. We evaluated changes in cytokines and bone measurements by high-resolution peripheral quantitative computed tomography (HR-pQCT) prior to DAA treatment and 18 months following initiation and compared changes in uninfected controls over 18 months. Methods We conducted a cohort study of 40 participants who initiated DAAs and achieved cure and 48 without HCV as controls. At enrollment and 18 months later, participants had measurements of volumetric bone mineral density, cortical dimensions, and mechanical properties of the radius and tibia by HR-pQCT; visceral fat area and appendicular lean mass by whole-body dual-energy X-ray absorptiometry; and serum tumor necrosis factor alpha (TNF-α), interleukin 6 (IL-6), and interleukin 18 (IL-18). Multivariable linear regression was used to estimate group differences in mean changes in bone measurements and cytokines. Results We observed no significant differences in month 0–18 changes in HR-pQCT measurements between participants with cured HCV and controls in unadjusted models or after adjustment for age, sex, appendicular lean mass index, visceral fat area, and smoking. Participants with cured HCV had decreases in IL-18 (mean change, −0.085 vs +0.086 log pg/mL; P < .001) and TNF-α (mean change, −0.050 vs +0.084 log pg/mL; P < .001), but not IL-6 (mean change, +0.108 vs +0.009 log pg/mL; P = .214) versus controls. Conclusions Participants with cured HCV had no significant changes in bone microarchitecture by HR-pQCT 18 months after DAA initiation compared with controls, but did have decreases in IL-18 and TNF-α versus controls.

m) characterization including static and dynamic mechanical stability of teeth in the alveolar socket, tissue mineral density distribution (TMD), and nanoindentation properties of the jawbone matrix. Most jawbone characteristics in OVX and its treatment groups were not significantly different from those of the SHAM group. The surface of alveolar bone (AB) surrounding teeth showed a trend of more erosion and addition of new bone tissues in the OVX rat groups compared to the SHAM group. All TMD parameters rapidly increased up to 60 μm from the periodontal ligament surrounding teeth regardless of the treatment groups. Treatments using each therapeutic agent and its combination did not substantially change those characteristics of jawbones in OVX rats. These findings are different from those of lumbar vertebrae in the same rats that showed a significant bone alteration by OVX and treatments. Thus, the current multiscale characterization of jawbone provides comprehensive information that can help better understand jawbone-specific responses to bone-related complications, including postmenopausal osteoporosis and bisphosphonate-related osteonecrosis of the jaw.

Abstract Background Hepatitis C virus (HCV) infection is associated with reduced bone mineral density (BMD) and increased fracture risk. The structural underpinnings for skeletal fragility with HCV and contributions of inflammatory cytokines remain unknown. We used high-resolution peripheral quantitative computed tomography (HR-pQCT) to compare skeletal parameters by chronic HCV. Methods We conducted a cross-sectional study among 58 participants with chronic HCV and 58 participants without HCV. Volumetric BMD and cortical dimensions of the radius and tibia were determined by HR-pQCT; visceral fat area and appendicular lean mass were assessed by whole body dual-energy x-ray absorptiometry; serum levels of tumor necrosis factor α (TNF-α), interleukin 6, and interleukin 18 were measured. Multivariable linear regression was used to estimate group differences in bone measurements and cytokines. Results Participants with chronic HCV had lower radius trabecular volumetric BMD (−24.2 mg hydroxyapatite [HA]/cm3) and lower tibia trabecular volumetric BMD (−20.5 mg HA/cm3), cortical area (−20.9 mm2), and cortical thickness (−0.47 mm) than participants without HCV (all P < .05), independent of age, sex, visceral fat area, appendicular lean mass, and smoking. Mean log TNF-α was higher with chronic HCV (+0.1-log pg/mL; P < .001), but no differences in mean log interleukin 6 or interleukin 18 were observed. Higher log TNF-α was associated with lower radius trabecular volumetric BMD (−99.7 mg HA/cm3), lower tibia cortical volumetric BMD (−91.6 mg HA/cm3), and higher tibia cortical porosity (+1.39%) by HR-pQCT (all P < .05). Conclusions Patients with chronic HCV had decreased trabecular volumetric BMD and cortical dimensions and higher TNF-α than individuals without infection, suggesting that HCV-associated inflammation might contribute to bone deficits.

Abstract Bone resorption by osteoclasts is a critical step in bone remodeling, a process important for maintaining bone homeostasis and repairing injured bone. We previously identified a bone marrow mesenchymal subpopulation, marrow adipogenic lineage precursors (MALPs), and showed that its production of RANKL stimulates bone resorption in young mice using Adipoq-Cre . To exclude developmental defects and to investigate the role of MALPs-derived RANKL in adult bone, we generated inducible reporter mice ( Adipoq-CreER Tomato ) and RANKL deficient mice ( Adipoq-CreER RANKLflox/flox, iCKO ). Single cell-RNA sequencing data analysis and lineage tracing revealed that Adipoq + cells contain not only MALPs but also some mesenchymal progenitors capable of osteogenic differentiation. In situ hybridization showed that RANKL mRNA is only detected in MALPs, but not in osteogenic cells. RANKL deficiency in MALPs induced at 3 months of age rapidly increased trabecular bone mass in long bones as well as vertebrae due to diminished bone resorption but had no effect on the cortical bone. Ovariectomy (OVX) induced trabecular bone loss at both sites. RANKL depletion either before OVX or at 6 weeks post OVX protected and restored trabecular bone mass. Furthermore, bone healing after drill-hole injury was delayed in iCKO mice. Together, our findings demonstrate that MALPs play a dominant role in controlling trabecular bone resorption and that RANKL from MALPs is essential for trabecular bone turnover in adult bone homeostasis, postmenopausal bone loss, and injury repair.

infection, and immunoneutralization of TNFα prevented infection-induced bone loss completely in WT and immunocompromised mice. These findings reveal rapid, relaying, and modifiable effects of enteropathogenic infections on an extraintestinal organ-bone, and provide insights into the mechanism(s) through which these infections affect extraintestinal organ homeostasis.

Estrogen deficiency, which is linked to various pathological conditions such as primary ovarian insufficiency and postmenopausal osteoporosis, disrupts the delicate balance between bone formation and resorption. This imbalance leads to bone loss and an increased risk of fractures, primarily due to a significant reduction in trabecular bone mass. Trabecular osteoblasts, the cells responsible for bone formation within the trabecular compartment, originate from skeletal progenitors located in the bone marrow. The microenvironment of the bone marrow contains hypoxic (low oxygen) regions, and the hypoxia-inducible factor-2α (HIF2) plays a crucial role in cellular responses to these low-oxygen conditions. This study demonstrates that the loss of HIF2 in skeletal progenitors and their derivatives during development enhances trabecular bone mass by promoting bone formation. More importantly, PT2399, a small molecule that specifically inhibits HIF2, effectively prevents trabecular bone loss in ovariectomized adult mice, a model for estrogen-deficient bone loss. Both the genetic and pharmacological approaches result in an increase in osteoblast number, which is linked to the expansion of the pool of skeletal progenitor cells. This expansion either by loss or inhibition of HIF2 uncovers a pivotal mechanism for increasing osteoblast numbers and bone formation, resulting in greater trabecular bone mass.

During pregnancy and breastfeeding, women undergo hormonal fluctuations required for fetal development, parturition, and infant growth. These changes have secondary consequences on the maternal musculoskeletal system, increasing the risk for joint pain and osteoporosis. Though hormone levels return to prepregnancy levels postpartum, women may experience lasting musculoskeletal pain. Sex disparities exist in the prevalence of musculoskeletal disorders, but it remains unclear how reproductive history may impact sex differences. Specifically, the effects of both reproductive history and sex on the rotator cuff have not been studied. Pregnancy and lactation affect bone microstructure, suggesting possible impairments at the enthesis of rotator cuff tendons, where tears commonly occur. Therefore, our objective was to evaluate how reproductive history affects sex differences of the supraspinatus tendon and proximal humerus using male, virgin female, and female rats with a history of reproduction (referred to as reproductive females). We hypothesized tendon mechanical properties and humeral bone microstructure would be inferior in reproductive females compared to virgin females. Results showed sex differences independent of reproductive history, including greater tendon midsubstance modulus but lower subchondral bone mineral density (BMD) in females. When considering reproductive history, reproductive rats exhibited reduced tendon insertion site modulus and trabecular bone micro-architecture compared to virgin females with no differences from males. Overall, our study identified long-term changes in supraspinatus tendon mechanical and humeral trabecular bone properties that result following pregnancy and lactation, highlighting the importance of considering reproductive history in investigations of sex differences in the physiology and pathology of rotator cuff injuries.