Deficiency of transcription factor RelB perturbs myeloid and DC development by hematopoietic-extrinsic mechanisms.

RelB is an NF-κB family transcription factor activated in the noncanonical pathway downstream of NF-κB-inducing kinase (NIK) and TNF receptor family members including lymphotoxin-ß receptor (LTßR) and CD40. Early analysis suggested that RelB is required for classical dendritic cell (cDC) development based on a severe reduction of cDCs in Relb-/- mice associated with profound myeloid expansion and perturbations in B and T cells. Subsequent analysis of radiation chimeras generated from wild-type and Relb-/- bone marrow showed that RelB exerts cell-extrinsic actions on some lineages, but it has remained unclear whether the impact of RelB on cDC development is cell-intrinsic or -extrinsic. Here, we reevaluated the role of RelB in cDC and myeloid development using a series of radiation chimeras. We found that there was no cell-intrinsic requirement for RelB for development of most cDC subsets, except for the Notch2- and LTßR-dependent subset of splenic CD4+ cDC2s. These results identify a relatively restricted role of RelB in DC development. Moreover, the myeloid expansion in Relb-/- mice resulted from hematopoietic-extrinsic actions of RelB. This result suggests that there is an unrecognized but critical role for RelB within the nonhematopoietic niche that controls normal myelopoiesis.

NLRP12 provides a critical checkpoint for osteoclast differentiation.

The alternative or noncanonical nuclear factor kappa B (NF-κB) pathway regulates the osteoclast (OC) response to receptor activator of nuclear factor kappa B ligand (RANKL) and thus bone metabolism. Although several lines of evidence support the emerging concept that nucleotide-binding leucine-rich repeat and pyrin domain-containing receptor 12 (NLRP12) impedes alternative NF-κB activation in innate immune cells, a functional role for NLRP12 outside an inflammatory disease model has yet to be reported. Our study demonstrates that NLRP12 has a protective role in bone via suppression of alternative NF-κB-induced osteoclastogenesis and is down-modulated in response to osteoclastogenic stimuli. Here, we show that retroviral overexpression of NLRP12 suppressed RelB nuclear translocation and OC formation. Conversely, genetic ablation of NLRP12 promoted NIK stabilization, RelB nuclear translocation, and increased osteoclastogenesis in vitro. Using radiation chimeras, we demonstrated these in vitro observations dovetail with our in vivo findings that NLRP12 deficiency leads to enhanced OC numbers accompanied by a significant decline in bone mass under physiological conditions. Consistent with the basal bone phenotype, we also observed an enhanced osteolytic response following RANKL injection over the calvaria of NLRP12-deficient chimeric mice compared with wild-type control mice. Thus, modulation of NLRP12 levels controls alternative NF-κB signaling in OC precursors, altering bone homeostasis and osteolytic responses.

Tmem178 acts in a novel negative feedback loop targeting NFATc1 to regulate bone mass.

Phospholipase C gamma-2 (PLCγ2)-dependent calcium (Ca(2+)) oscillations are indispensable for nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1) activation and downstream gene transcription driving osteoclastogenesis during skeletal remodeling and pathological bone loss. Here we describe, to our knowledge, the first known function of transmembrane protein 178 (Tmem178), a PLCγ2 downstream target gene, as a critical modulator of the NFATc1 axis. In surprising contrast to the osteopetrotic phenotype of PLCγ2(-/-) mice, Tmem178(-/-) mice are osteopenic in basal conditions and are more susceptible to inflammatory bone loss, owing to enhanced osteoclast formation. Mechanistically, Tmem178 localizes to the ER membrane and regulates RANKL-induced Ca(2+) fluxes, thus controlling NFATc1 induction. Importantly, down-regulation of Tmem178 is observed in human CD14(+) monocytes exposed to plasma from systemic juvenile idiopathic arthritis patients. Similar to the mouse model, reduced Tmem178 expression in human cells correlates with excessive osteoclastogenesis. In sum, these findings identify an essential role for Tmem178 to maintain skeletal mass and limit pathological bone loss.

NLRP3 mediates osteolysis through inflammation-dependent and -independent mechanisms.

Activating-mutations in NOD-like receptor (NLR) family, pyrin domain-containing 3 (NLRP3) cause neonatal-onset multisystem inflammatory disease. However, the ontogeny of skeletal anomalies in this disorder is poorly understood. Mice globally expressing the D301N mutation in Nlrp3 (D303N in human) model the human phenotype, including systemic inflammation and skeletal deformities. To gain insights into the skeletal manifestations, we generated mice in which the expression of D301N Nlrp3 (Nlrp3( D301N)) is restricted to myeloid cells. These mice exhibit systemic inflammation and severe osteopenia (∼ 60% lower bone mass) similar to mice globally expressing the knock-in mutation, consistent with the paradigm of innate immune-driven cryopyrinopathies. Because systemic inflammation may indirectly affect bone homeostasis, we engineered mice in which Nlrp3( D301N) is expressed specifically in osteoclasts, the cells that resorb bone. These mice also develop ∼ 50% lower bone mass due to increased osteolysis, but there is no systemic inflammation and no change in osteoclast number. Mechanistically, aside from its role in IL-1ß maturation, Nlrp3( D301N) expression enhances osteoclast bone resorbing ability through reorganization of actin cytoskeleton while promoting the degradation of poly(ADP-ribose) polymerase 1, an inhibitor of osteoclastogenesis. Thus, NLRP3 inflammasome activation is not restricted to the production of proinflammatory mediators but also leads to cytokine-autonomous responses.

NF-κB-inducing kinase is a key regulator of inflammation-induced and tumour-associated angiogenesis.

Angiogenesis is essential during development and in pathological conditions such as chronic inflammation and cancer progression. Inhibition of angiogenesis by targeting vascular endothelial growth factor (VEGF) blocks disease progression, but most patients eventually develop resistance which may result from compensatory signalling pathways. In endothelial cells (ECs), expression of the pro-angiogenic chemokine CXCL12 is regulated by non-canonical nuclear factor (NF)-κB signalling. Here, we report that NF-κB-inducing kinase (NIK) and subsequent non-canonical NF-κB signalling regulate both inflammation-induced and tumour-associated angiogenesis. NIK is highly expressed in endothelial cells (ECs) in tumour tissues and inflamed rheumatoid arthritis synovial tissue. Furthermore, non-canonical NF-κB signalling in human microvascular ECs significantly enhanced vascular tube formation, which was completely blocked by siRNA targeting NIK. Interestingly, Nik(-/-) mice exhibited normal angiogenesis during development and unaltered TNFα- or VEGF-induced angiogenic responses, whereas angiogenesis induced by non-canonical NF-κB stimuli was significantly reduced. In addition, angiogenesis in experimental arthritis and a murine tumour model was severely impaired in these mice. These studies provide evidence for a role of non-canonical NF-κB signalling in pathological angiogenesis, and identify NIK as a potential therapeutic target in chronic inflammatory diseases and tumour neoangiogenesis.

Estrogen and bone: osteoclasts take center stage.

Loss of estrogen at menopause causes osteoporosis in many women, but estrogen's relevant cellular target in this process has remained unclear. In a recent study in Cell, Kato and colleagues (Nakamura et al., 2007) selectively ablate estrogen receptor alpha in osteoclasts and demonstrate that estrogen directly induces osteoclast apoptosis.

PLCgamma2 regulates osteoclastogenesis via its interaction with ITAM proteins and GAB2.

Excessive bone loss in arthritic diseases is mostly due to abnormal activation of the immune system leading to stimulation of osteoclasts. While phospholipase Cgamma (PLCgamma) isoforms are known modulators of T and B lymphocyte-mediated immune responses, we found that blockade of PLCgamma enzymatic activity also blocks early osteoclast development and function. Importantly, targeted deletion of Plcg2 in mice led to an osteopetrotic phenotype. PLCgamma2, independent of PLCgamma1, was required for receptor activator of NF-kappaB ligand-induced (RANKL-induced) osteoclastogenesis by differentially regulating nuclear factor of activated T cells c1 (NFATc1), activator protein-1 (AP1), and NF-kappaB. Specifically, we show that NFATc1 upregulation is dependent on RANKL-mediated phosphorylation of PLCgamma2 downstream of Dap12/Fc receptor gamma (Dap12/FcRgamma) receptors and is blocked by the PLCgamma inhibitor U73122. In contrast, activation of JNK and NF-kappaB was not affected by U73122 or Dap12/FcRgamma deletion. Interestingly, we found that in osteoclasts, PLCgamma2 formed a complex with the regulatory adapter molecule GAB2, was required for GAB2 phosphorylation, and modulated GAB2 recruitment to RANK. Thus, PLCgamma2 mediates RANKL-induced osteoclastogenesis and is a potential candidate for antiresorptive therapy.

Dynamic changes in the osteoclast cytoskeleton in response to growth factors and cell attachment are controlled by beta3 integrin.

The beta3 integrin cytoplasmic domain, and specifically S752, is critical for integrin localization and osteoclast (OC) function. Because growth factors such as macrophage colony-stimulating factor and hepatocyte growth factor affect integrin activation and function via inside-out signaling, a process requiring the beta integrin cytoplasmic tail, we examined the effect of these growth factors on OC precursors. To this end, we retrovirally expressed various beta3 integrins with cytoplasmic tail mutations in beta3-deficient OC precursors. We find that S752 in the beta3 cytoplasmic tail is required for growth factor-induced integrin activation, cytoskeletal reorganization, and membrane protrusion, thereby affecting OC adhesion, migration, and bone resorption. The small GTPases Rho and Rac mediate cytoskeletal reorganization, and activation of each is defective in OC precursors lacking a functional beta3 subunit. Activation of the upstream mediators c-Src and c-Cbl is also dependent on beta3. Interestingly, although the FAK-related kinase Pyk2 interacts with c-Src and c-Cbl, its activation is not disrupted in the absence of functional beta3. Instead, its activation is dependent upon intracellular calcium, and on the beta2 integrin. Thus, the beta3 cytoplasmic domain is responsible for activation of specific intracellular signals leading to cytoskeletal reorganization critical for OC function.

Vav/Phospholipase Cgamma2-mediated control of a neutrophil-dependent murine model of rheumatoid arthritis.

OBJECTIVE: Accumulating evidence indicates an important role of neutrophils in the development of rheumatoid arthritis (RA). Recruitment of neutrophils to the joint space and release of proteolytic enzymes can exacerbate tissue damage and the inflammatory response related to RA. Engagement of beta2 integrin and subsequent activation of downstream signaling have been shown to be fundamental for activation of neutrophil effector functions. The aim of this study was to test the hypothesis that Vav and phospholipase Cgamma2 (PLCgamma2), two molecules involved in integrin signaling, are required for arthritis generation and neutrophil activation in a mouse model of arthritis. METHODS: Arthritis was induced in wild-type (WT), Vav(null), and PLCgamma2(-/-) mice using the K/BxN serum-transfer model. Neutrophil function was assessed by analyses of adhesion, spreading, and degranulation on integrin-dependent substrates. Regulation of integrin signaling was determined by analyzing the phosphorylation of Pyk-2, Src, and ERK. RESULTS: Vav(null) and PLCgamma2(-/-) mice were protected from inflammation and bone erosion in the K/BxN serum-transfer model of arthritis. Mechanistically, Vav and PLCgamma2 control neutrophils mediated spreading and degranulation on integrin-dependent substrates. Consequently, the Vav/PLCgamma2 axis, acting downstream of the integrin receptor, modulated the activation of Pyk-2, Src, and ERK. CONCLUSION: Our findings show that Vav cooperates with PLCgamma2 in modulating neutrophil activation downstream of the integrin receptor. This study identifies a Vav/PLCgamma2-dependent signaling pathway as a possible therapeutic target for the treatment of inflammation and bone disruption in arthritis.

M-CSF mediates TNF-induced inflammatory osteolysis.

TNF-alpha is the dominant cytokine in inflammatory osteolysis. Using mice whose BM stromal cells and osteoclast precursors are chimeric for the presence of TNF receptors, we found that both cell types mediated the cytokine's osteoclastogenic properties. The greater contribution was made, however, by stromal cells that express the osteoclastogenic cytokine M-CSF. TNF-alpha stimulated M-CSF gene expression, in vivo, only in the presence of TNF-responsive stromal cells. M-CSF, in turn, induced the key osteoclastogenic cytokine receptor, receptor activator of NF-kappaB (RANK), in osteoclast precursors. In keeping with the proproliferative and survival properties of M-CSF, TNF-alpha enhanced osteoclast precursor number only in the presence of stromal cells bearing TNF receptors. To determine the clinical relevance of these observations, we induced inflammatory arthritis in wild-type mice and treated them with a mAb directed against the M-CSF receptor, c-Fms. Anti-c-Fms mAb selectively and completely arrested the profound pathological osteoclastogenesis attending this condition, the significance of which is reflected by similar blunting of the in vivo bone resorption marker tartrate-resistant acid phosphatase 5b (TRACP 5b). Confirming that inhibition of the M-CSF signaling pathway targets TNF-alpha, anti-c-Fms also completely arrested osteolysis in TNF-injected mice with nominal effect on macrophage number. M-CSF and its receptor, c-Fms, therefore present as candidate therapeutic targets in states of inflammatory bone erosion.

FHL2 inhibits the activated osteoclast in a TRAF6-dependent manner.

TNF receptor-associated factor 6 (TRAF6) associates with the cytoplasmic domain of receptor activator of NF-kappaB (RANK). This event is central to normal osteoclastogenesis. We discovered that TRAF6 also interacts with FHL2 (four and a half LIM domain 2), a LIM domain--only protein that functions as a transcriptional coactivator or corepressor in a cell-type--specific manner. FHL2 mRNA and protein are undetectable in marrow macrophages and increase pari passu with osteoclast differentiation in vitro. FHL2 inhibits TRAF6-induced NF-kappaB activity in wild-type osteoclast precursors and, in keeping with its role as a suppressor of TRAF6-mediated RANK signaling, TRAF6/RANK association is enhanced in FHL2-/- osteoclasts. FHL2 overexpression delays RANK ligand-induced (RANKL-induced) osteoclast formation and cytoskeletal organization. Interestingly, osteoclast-residing FHL2 is not detectable in naive wild-type mice, in vivo, but is abundant in those treated with RANKL and following induction of inflammatory arthritis. Reflecting increased RANKL sensitivity, osteoclasts generated from FHL2-/- mice reach maturation and optimally organize their cytoskeleton earlier than their wild-type counterparts. As a consequence, FHL2-/- osteoclasts are hyperresorptive, and mice lacking the protein undergo enhanced RANKL and inflammatory arthritis-stimulated bone loss. FHL2 is, therefore, an antiosteoclastogenic molecule exerting its effect by attenuating TRAF6-mediated RANK signaling.

Inflammatory osteolysis: a conspiracy against bone.

There are many causes of inflammatory osteolysis, but regardless of etiology and cellular contexts, the osteoclast is the bone-degrading cell. Thus, the impact of inflammatory cytokines on osteoclast formation and function was among the most important discoveries advancing the treatment of focal osteolysis, leading to development of therapeutic agents that either directly block the bone-resorptive cell or do so indirectly via cytokine arrest. Despite these advances, a substantial number of patients with inflammatory arthritis remain resistant to current therapies, and even effective anti-inflammatory drugs frequently do not repair damaged bone. Thus, insights into events such as those impacted by inflammasomes, which signal through cytokine-dependent and -independent mechanisms, are needed to optimize treatment of inflammatory osteolysis.

Skeletal Fluorosis Due To Inhalation Abuse of a Difluoroethane-Containing Computer Cleaner.

Skeletal fluorosis (SF) is endemic in many countries and millions of people are affected worldwide, whereas in the United States SF is rare with occasional descriptions of unique cases. We report a 28-year-old American man who was healthy until 2 years earlier when he gradually experienced difficulty walking and an abnormal gait, left hip pain, loss of mobility in his right wrist and forearm, and progressive deformities including enlargement of the digits of both hands. Dual-energy X-ray absorptiometry (DXA) of his lumbar spine, femoral neck, total hip, and the one-third forearm revealed bone mineral density (BMD) Z-scores of +6.2, +4.8, +3.0, and -0.2, respectively. Serum, urine, and bone fluoride levels were all elevated and ultimately explained by chronic sniffing abuse of a computer cleaner containing 1,1-difluoroethane. Our findings reflect SF due to the unusual cause of inhalation abuse of difluoroethane. Because this practice seems widespread, particularly in the young, there may be many more such cases. © 2016 American Society for Bone and Mineral Research.

Fast label-free multilayered histology-like imaging of human breast cancer by photoacoustic microscopy.

The goal of breast-conserving surgery is to completely remove all of the cancer. Currently, no intraoperative tools can microscopically analyze the entire lumpectomy specimen, which results in 20 to 60% of patients undergoing second surgeries to achieve clear margins. To address this critical need, we have laid the foundation for the development of a device that could allow accurate intraoperative margin assessment. We demonstrate that by taking advantage of the intrinsic optical contrast of breast tissue, photoacoustic microscopy (PAM) can achieve multilayered histology-like imaging of the tissue surface. The high correlation of the PAM images to the conventional histologic images allows rapid computations of diagnostic features such as nuclear size and packing density, potentially identifying small clusters of cancer cells. Because PAM does not require tissue processing or staining, it can be performed promptly and intraoperatively, enabling immediate directed re-excision and reducing the number of second surgeries.

Bone matrix components activate the NLRP3 inflammasome and promote osteoclast differentiation.

The NLRP3 inflammasome senses a variety of signals referred to as danger associated molecular patterns (DAMPs), including those triggered by crystalline particulates or degradation products of extracellular matrix. Since some DAMPs confer tissue-specific activation of the inflammasomes, we tested the hypothesis that bone matrix components function as DAMPs for the NLRP3 inflammasome and regulate osteoclast differentiation. Indeed, bone particles cause exuberant osteoclastogenesis in the presence of RANKL, a response that correlates with NLRP3 abundance and the state of inflammasome activation. To determine the relevance of these findings to bone homeostasis, we studied the impact of Nlrp3 deficiency on bone using pre-clinical mouse models of high bone turnover, including estrogen deficiency and sustained exposure to parathyroid hormone or RANKL. Despite comparable baseline indices of bone mass, bone loss caused by hormonal or RANKL perturbations is significantly reduced in Nlrp3 deficient than in wild type mice. Consistent with the notion that osteolysis releases DAMPs from bone matrix, pharmacologic inhibition of bone resorption by zoledronate attenuates inflammasome activation in mice. Thus, signals originating from bone matrix activate the NLRP3 inflammasome in the osteoclast lineage, and may represent a bone-restricted positive feedback mechanism that amplifies bone resorption in pathologic conditions of accelerated bone turnover.

Bone-Induced Expression of Integrin ß3 Enables Targeted Nanotherapy of Breast Cancer Metastases.

Bone metastases occur in approximately 70% of metastatic breast cancer patients, often leading to skeletal injuries. Current treatments are mainly palliative and underscore the unmet clinical need for improved therapies. In this study, we provide preclinical evidence for an antimetastatic therapy based on targeting integrin ß3 (ß3), which is selectively induced on breast cancer cells in bone by the local bone microenvironment. In a preclinical model of breast cancer, ß3 was strongly expressed on bone metastatic cancer cells, but not primary mammary tumors or visceral metastases. In tumor tissue from breast cancer patients, ß3 was significantly elevated on bone metastases relative to primary tumors from the same patient (n = 42). Mechanistic investigations revealed that TGFß signaling through SMAD2/SMAD3 was necessary for breast cancer induction of ß3 within the bone. Using a micelle-based nanoparticle therapy that recognizes integrin αvß3 (αvß3-MPs of ∼12.5 nm), we demonstrated specific localization to breast cancer bone metastases in mice. Using this system for targeted delivery of the chemotherapeutic docetaxel, we showed that bone tumor burden could be reduced significantly with less bone destruction and less hepatotoxicity compared with equimolar doses of free docetaxel. Furthermore, mice treated with αvß3-MP-docetaxel exhibited a significant decrease in bone-residing tumor cell proliferation compared with free docetaxel. Taken together, our results offer preclinical proof of concept for a method to enhance delivery of chemotherapeutics to breast cancer cells within the bone by exploiting their selective expression of integrin αvß3 at that metastatic site. Cancer Res; 77(22); 6299-312. ©2017 AACR.

Pulsed low-dose RANKL as a potential therapeutic for postmenopausal osteoporosis.

A number of studies in model animal systems and in the clinic have established that RANKL promotes bone resorption. Paradoxically, we found that pulsing ovariectomized mice with low-dose RANKL suppressed bone resorption, decreased the levels of proinflammatory effector T cells and led to increased bone mass. This effect of RANKL is mediated through the induction of FoxP3+CD25+ regulatory CD8+ T cells (TcREG) by osteoclasts. Here, we show that pulses of low-dose RANKL are needed to induce TcREG, as continuous infusion of identical doses of RANKL by pump did not induce TcREG. We also show that low-dose RANKL can induce TcREG at 2, 3, 6, and 10 weeks after ovariectomy. Our results show that low-dose RANKL treatment in ovariectomized mice is optimal at once-per-month doses to maintain the bone mass. Finally, we found that treatment of ovariectomized mice with the Cathepsin K inhibitor odanacatib also blocked TcREG induction by low-dose RANKL. We interpret this result to indicate that antigens presented to CD8+ T cells by osteoclasts are derived from the bone protein matrix because Cathepsin K degrades collagen in the bone. Taken together, our studies provide a basis for using low-dose RANKL as a potential therapeutic for postmenopausal osteoporosis.

Novel ERα positive breast cancer model with estrogen independent growth in the bone microenvironment.

Despite successful therapeutic options for estrogen receptor-α (ERα)+ breast cancer, resistance to endocrine therapy frequently occurs leading to tumor recurrence. In addition to intrinsic changes in the cancer cells, herein we demonstrate that tumor cell-microenvironment interactions can drive recurrence at specific sites. By using two ERα+ cell lines derived from spontaneous mammary carcinomas in STAT1-/- mice (SSM2, SSM3), we establish that the bone microenvironment offers growth advantage over primary site or lung in the absence of ovarian hormones. While SSM3 did not engraft at primary and skeletal locations in the absence of estrogen, SSM2 selectively grew in bone of ovariectomized mice and following administration of aromatase inhibitors. However, SSM2 growth remained hormone-dependent at extraskeletal sites. Unexpectedly, bone-residing SSM2 cells retained ERα expression and JAK2/STAT3 activation regardless of the hormonal status. These data position the bone microenvironment as a unique site for acquisition of tumor/estrogen independency and identify the first ERα+ hormone-independent tumor model in immunocompetent mice.

Congenital insensitivity to pain: Fracturing without apparent skeletal pathobiology caused by an autosomal dominant, second mutation in SCN11A encoding voltage-gated sodium channel 1.9.

Congenital insensitivity to pain (CIP) comprises the rare heritable disorders without peripheral neuropathy that feature inability to feel pain. Fracturing and joint destruction are common complications, but lack detailed studies of mineral and skeletal homeostasis and bone histology. In 2013, discovery of a heterozygous gain-of-function mutation in SCN11A encoding voltage-gated sodium channel 1.9 (Nav1.9) established a distinctive CIP in three unrelated patients who suffered multiple painless fractures, self-inflicted mutilation, chronic diarrhea, and hyperhidrosis. Here, we studied a mother and two children with CIP by physical examination, biochemical testing, radiological imaging including DXA, iliac crest histology, and mutation analysis. She suffered fractures primarily of her lower extremities beginning at age two years, and had Charcot deformity of both ankles and joint hypermobility. Nerve conduction velocity together with electromyography were normal. Her children had recurrent major fractures beginning in early childhood, joint hypermobility, and chronic diarrhea. She had an excoriated external nare, and both children had hypertrophic scars from scratching. Skin collagen studies were normal. Radiographs revealed fractures and deformities. However, lumbar spine and total hip BMD Z-scores, biochemical parameters of mineral and skeletal homeostasis, and iliac crest histology of the mother (after in vivo tetracycline labeling) were normal. Genomic DNA from the children revealed a unique heterozygous missense mutation in exon 23 (c.3904C>T, p.Leu1302Phe) of SCN11A that is absent in SNP databases and alters an evolutionarily conserved amino acid. This autosomal dominant CIP reflects the second gain-of-function mutation of SCN11A. Perhaps joint hypermobility is an unreported feature. How mutation of Nav1.9 causes fracturing remains unexplained. Lack of injury awareness is typically offered as the reason, and was supported by our unremarkable biochemical, radiological, and histological findings indicating no skeletal pathobiology. However, low-trauma fracturing in these patients suggests an uncharacterized defect in bone quality.

Idiopathic Acquired Osteosclerosis in a Middle-Aged Woman With Systemic Lupus Erythematosus.

Widely distributed osteosclerosis is an unusual radiographic finding with multiple causes. A 42-year-old premenopausal Spanish woman gradually acquired dense bone diffusely affecting her axial skeleton and focally affecting her proximal long bones. Systemic lupus erythematosus (SLE) diagnosed in adolescence had been well controlled. She had not fractured or received antiresorptive therapy, and she was hepatitis C virus antibody negative. Family members had low bone mass. Lumbar spine bone mineral density (BMD) measured by dual-photon absorptiometry (DPA) at age 17 years, while receiving glucocorticoids, was 79% the average value of age-matched controls. From ages 30 to 37 years, dual-energy X-ray absorptiometry (DXA) BMD Z-scores steadily increased in her lumbar spine from +3.8 to +7.9, and in her femoral neck from -1.4 to -0.7. Serum calcium and phosphorus levels were consistently normal, 25-hydroxyvitamin D (25OHD) <20 ng/mL, and parathyroid hormone (PTH) sometimes slightly increased. Her reduced estimated glomerular filtration rate (eGFR) was 38 to 55 mL/min. Hypocalciuria likely reflected positive mineral balance. During increasing BMD, turnover markers (serum bone-specific alkaline phosphatase [ALP], procollagen type 1 N propeptide [P1NP], osteocalcin [OCN], and carboxy-terminal cross-linking telopeptide of type 1 collagen [CTx], and urinary amino-terminal cross-linking telopeptide of type 1 collagen [NTx and CTx]) were 1.6- to 2.8-fold above the reference limits. Those of bone formation seemed increased more than those of resorption. FGF-23 was slightly elevated, perhaps from kidney disease. Serum osteoprotegerin (OPG) and TGFß1 levels were normal, but sclerostin (SOST) and receptor activator of nuclear factor kappa-B ligand (RANKL) were elevated. Serum multiplex biomarker profiling confirmed a high level of SOST and RANKL, whereas Dickkopf-1 (DKK-1) seemed low. Matrix metalloproteinases-3 (MMP-3) and -7 (MMP-7) were elevated. Iliac crest biopsy revealed tetracycline labels, no distinction between thick trabeculae and cortical bone, absence of peritrabecular fibrosis, few osteoclasts, and no mastocytosis. Then, for the past 3 years, BMD Z-scores steadily decreased. Skeletal fluorosis, mastocytosis, myelofibrosis, hepatitis C-associated osteosclerosis, multiple myeloma, and aberrant phosphate homeostasis did not explain her osteosclerosis. Mutation analysis of the LRP5, LRP4, SOST, and osteopetrosis genes was negative. Microarray showed no notable copy number variation. Perhaps her osteosclerosis reflected an interval of autoimmune-mediated resistance to SOST and/or RANKL. © 2016 American Society for Bone and Mineral Research.