Disordered osteoclast formation and function in a CD38 (ADP-ribosyl cyclase)-deficient mouse establishes an essential role for CD38 in bone resorption

Enhanced Prenatal and Postnatal Development Study in Marmoset Monkeys Following Administration of Felzartamab

Felzartamab is a recombinant fully human immunoglobulin G1 anti-CD38 monoclonal antibody under clinical investigation for immune-mediated diseases. In support of felzartamab clinical development, toxicology studies were conducted in marmoset monkeys, which was the most relevant species based on CD38 binding affinity, pharmacologic activity, and target expression. The felzartamab toxicology program included an enhanced prenatal and postnatal development (ePPND) study to identify potential reproductive and postnatal development risks. In this ePPND study, pregnant marmoset monkeys were randomized to receive vehicle (0 mg/kg) or felzartamab at two dose levels (15 mg/kg and 75 mg/kg) twice per week until parturition, and maternal animals and infants were evaluated for 6 months thereafter. Felzartamab exposure was confirmed in maternal animals and infants in both dosing groups. Overall, felzartamab was well tolerated by pregnant animals at the evaluated doses, with no effect on body weight or body weight gain during pregnancy. No felzartamab-related effects on pregnancy loss or stillbirth rate were observed, and litter counts and numbers of liveborn infants were similar between the vehicle and felzartamab groups. Among infants, there were no felzartamab-related malformations or variations in external anatomy or skeletal morphology and no felzartamab-related observations in histopathology, hematologic and immune cell development, or humoral immune response to vaccination. In conclusion, among pregnant marmoset monkeys dosed with felzartamab, the lack of reproductive toxicity and felzartamab-related effects on offspring supports the clinical evaluation of felzartamab in women of childbearing potential and further demonstrates the suitability of the marmoset monkey for ePPND studies.

CD38 Inhibitor 78c Attenuates Pro-Inflammatory Cytokine Expression and Osteoclastogenesis in Macrophages

CD38, a nicotinamide adenine dinucleotide (NAD+) glycohydrolase, increases during infection or inflammation. Therefore, we aimed to evaluate the effects of a CD38 inhibitor (78c) on NAD+ levels, IL-1β, IL-6, TNF-α cytokine expressions, and osteoclastogenesis. The results show that treatment with 78c on murine BMMs dose-dependently reduced CD38, reversed the decline of NAD+, and inhibited IL-1β, IL-6, and TNF-α pro-inflammatory cytokine levels induced by oral pathogen Porphyromonas gingivalis (Pg) or Aggregatibacter actinomycetemcomitans (Aa) or by advanced glycation end products (AGEs). Additionally, treatment with 78c dose-dependently suppressed osteoclastogenesis and bone resorption induced by RANKL. Treatment with 78c suppressed CD38, nuclear factor kappa-B (NF-κB), phosphoinositide 3-kinase (PI3K), and mitogen-activated protein kinases (MAPKs) induced by Pg, Aa, or AGEs, and suppressed podosome components (PI3K, Pyk2, Src, F-actin, integrins, paxillin, and talin) induced by RANKL. These results from our studies support the finding that the inhibition of CD38 by 78c is a promising therapeutic strategy to treat inflammatory bone loss diseases. However, treatment with a CD38 shRNA only significantly reduced IL-1β, IL-6, and TNF-α pro-inflammatory cytokine levels induced by AGEs. Compared with controls, it had limited effects on cytokine levels induced by Pg or Aa. Treatment with the CD38 shRNA enhanced RANKL-induced osteoclastogenesis, suggesting that 78c has some off-target effects.

CD38 as theranostic target in oncology

CD38 is a multifunctional transmembrane glycoprotein found in multiple tissues and overexpressed in many cancer cells, notably in hematological malignancies such as leukemia and multiple myeloma (MM). Therefore, targeting CD38 remains an attractive strategy for cancer treatment in hematological malignancies as well as in solid tumors. It plays a critical role in the progression of these diseases through its ADP-ribosyl cyclase and cADPR-hydrolase activities. Its importance has led to the development of various anti-CD38 monoclonal antibodies (mAbs), including daratumumab and isatuximab, approved for MM treatment. These mAbs exert their anti-tumor effects through Fc-dependent immune mechanisms and immunomodulation, enhancing T-cell and NK-cell-mediated responses. However, resistance mechanisms arise during the treatment with daratumumab, creating the necessity for new therapies. This review explains current knowledge about the role of CD38 as a target in oncology and aims to delineate the use of single domain antibodies (sdAbs) as innovative theranostic tools in nuclear medicine. For diagnostic purposes, PET radionuclides like 68 Ga, 64Cu, and SPECT radionuclides like 99mTc and 111In, are commonly used. Significant progress has been made in anti-CD38 radioligand therapy (RLT), with anti-CD38 antibodies providing insights into tumor biology and treatment efficacy. In terms of therapy, RLT is a promising approach that offers precise targeting of malignant cells while minimizing exposure to healthy tissue. This involves the use of radionuclides emitting α particles, like 225Ac, 212Pb or 211At, and β--particles like 90Y, 131I, or 177Lu, to exert cytotoxic effects. Derived from Camelidae heavy chain antibodies, sdAbs offer advantages over conventional mAbs such as small size, high stability, specificity, and ability to recognize hidden epitopes. CD38-specific sdAbs, such as sdAb 2F8, characterized by our laboratory, showing excellent tumor targeting and their engineered constructs, such as biparatopic antibodies and chimeric antibodies, represent a new generation of theranostic agents for diagnosis and treatment CD38-expressing malignancies.

Genome-wide association study for bone quality of ducks during the laying period

The cage-rearing model of the modern poultry industry makes the bones of birds, especially egg-laying birds, more vulnerable to fracture, which poses serious damage to the health of birds. Research confirms that genetic material plays an important role in regulating bone growth, development, and remodeling. However, the genetic architecture underlying bone traits is not well understood. The objectives of this study are to identify valuable genes and genetic markers through a genome-wide association study (GWAS) for breeding to improve the duck bone quality. First, we quantified the tibia and femur quality traits of 260 laying ducks. Based on GWAS, a total of 75 SNP loci significantly associated with bone quality traits were identified, and 67 potential candidate genes were annotated. According to gene function analysis, genes P4HA2, WNT3A, and BST1 et al may influence bone quality by regulating bone cell activity, calcium and phosphate metabolism, or bone collagen maturation and cross-linking. Meanwhile, combined with the transcriptome results, we found that HOXB cluster genes are also important in bone growth and development. Therefore, our findings were helpful in further understanding the genetic architecture of the duck bone quality and provided a worthy theoretical basis and technological support to improve duck bone quality by breeding.

Identification of candidate genes affecting the tibia quality in Nonghua duck

The skeleton is a vital organ providing structural support in poultry. Weakness in bone structure can lead to deformities, osteoporosis, cage fatigue, and fractures, resulting in economic losses. Research has substantiated that genetic factors play a significant role in influencing bone quality. The discovery of genetic markers associated with bone quality holds paramount importance for enhancing genetic traits related to the skeletal system in poultry. This study analyzed nine phenotypic indicators of tibia quality in 120-day-old ducks. The phenotypic correlation revealed a high correlation among diameter, Perimeter, and weight (0.69-0.78), and a strong correlation was observed between toughness and breaking strength (0.62). Then, we conducted a genome-wide association analysis of the phenotypic indicators to elucidate the genetic basis of tibial quality in Nonghua ducks. Among the 11 candidate genes that were annotated, TAPT1, BST1, and STIM2 were related to the diameter indicator, ZNF652, IGF2BP1, CASK, and GREB1L were associated with the weight and toughness indicators. RFX8, GLP1R, and DNAAF5 were identified for ash, calcium, and phosphorus content, respectively. Finally, KEGG and GO analysis for annotated genes were performed. STIM2 and BST1 were enriched into the Calcium signalling pathway and Niacin and nicotinamide metabolic pathway, which may be key candidate genes affecting bone quality phenotypes. Gene expression analysis of the candidate genes, such as STIM2, BST1, TAPT1, and CASK showed higher expression levels in bones compared to other tissues. The obtained results can contribute to new insights into tibial quality and provide new genetic biomarkers that can be employed in duck breeding.

Mitochondria as secretory organelles and therapeutic cargos

Mitochondria have been primarily considered intracellular organelles that are responsible for generating energy for cell survival. However, accumulating evidence suggests that mitochondria are secreted into the extracellular space under physiological and pathological conditions, and these secreted mitochondria play diverse roles by regulating metabolism, the immune response, or the differentiation/maturation in target cells. Furthermore, increasing amount of research shows the therapeutic effects of local or systemic administration of mitochondria in various disease models. These findings have led to growing interest in exploring mitochondria as potential therapeutic agents. Here, we discuss the emerging roles of mitochondria as extracellularly secreted organelles to shed light on their functions beyond energy production. Additionally, we provide information on therapeutic outcomes of mitochondrial transplantation in animal models of diseases and an update on ongoing clinical trials, underscoring the potential of using mitochondria as a novel therapeutic intervention.

Mitochondrial fragmentation and donut formation enhance mitochondrial secretion to promote osteogenesis

Mitochondrial components have been abundantly detected in bone matrix, implying that they are somehow transported extracellularly to regulate osteogenesis. Here, we demonstrate that mitochondria and mitochondrial-derived vesicles (MDVs) are secreted from mature osteoblasts to promote differentiation of osteoprogenitors. We show that osteogenic induction stimulates mitochondrial fragmentation, donut formation, and secretion of mitochondria through CD38/cADPR signaling. Enhancing mitochondrial fission and donut formation through Opa1 knockdown or Fis1 overexpression increases mitochondrial secretion and accelerates osteogenesis. We also show that mitochondrial fusion promoter M1, which induces Opa1 expression, impedes osteogenesis, whereas osteoblast-specific Opa1 deletion increases bone mass. We further demonstrate that secreted mitochondria and MDVs enhance bone regeneration in vivo. Our findings suggest that mitochondrial morphology in mature osteoblasts is adapted for extracellular secretion, and secreted mitochondria and MDVs are critical promoters of osteogenesis.

Normalization of the Immunological Microenvironment and Sustained Minimal Residual Disease Negativity: Do We Need Both for Long-Term Control of Multiple Myeloma?

Over the past two decades, the treatment landscape for multiple myeloma (MM) has progressed significantly, with the introduction of several new drug classes that have greatly improved patient outcomes. At present, it is well known how the bone marrow (BM) microenvironment (ME) exerts an immunosuppressive action leading to an exhaustion of the immune system cells and promoting the proliferation and sustenance of tumor plasma cells. Therefore, having drugs that can reconstitute a healthy BM ME can improve results in MM patients. Recent findings clearly demonstrated that achieving minimal residual disease (MRD) negativity and sustaining MRD negativity over time play a pivotal prognostic role. However, despite the achievement of MRD negativity, patients may still relapse. The understanding of immunologic changes in the BM ME during treatment, complemented by a deeper knowledge of plasma cell genomics and biology, will be critical to develop future therapies to sustain MRD negativity over time and possibly achieve an operational cure. In this review, we focus on the components of the BM ME and their role in MM, on the prognostic significance of MRD negativity and, finally, on the relative contribution of tumor plasma cell biology and BM ME to long-term disease control.

Pathways of Angiogenic and Inflammatory Cytokines in Multiple Myeloma: Role in Plasma Cell Clonal Expansion and Drug Resistance

Multiple myeloma (MM) is the second most common hematological malignancy, and despite the introduction of innovative therapies, remains an incurable disease. Identifying early and minimally or non-invasive biomarkers for predicting clinical outcomes and therapeutic responses is an active field of investigation. Malignant plasma cells (PCs) reside in the bone marrow (BM) microenvironment (BMME) which comprises cells (e.g., tumour, immune, stromal cells), components of the extracellular matrix (ECM) and vesicular and non-vesicular (soluble) molecules, all factors that support PCs’ survival and proliferation. The interaction between PCs and BM stromal cells (BMSCs), a hallmark of MM progression, is based not only on intercellular interactions but also on autocrine and paracrine circuits mediated by soluble or vesicular components. In fact, PCs and BMSCs secrete various cytokines, including angiogenic cytokines, essential for the formation of specialized niches called “osteoblastic and vascular niches”, thus supporting neovascularization and bone disease, vital processes that modulate the pathophysiological PCs–BMME interactions, and ultimately promoting disease progression. Here, we aim to discuss the roles of cytokines and growth factors in pathogenetic pathways in MM and as prognostic and predictive biomarkers. We also discuss the potential of targeted drugs that simultaneously block PCs’ proliferation and survival, PCs–BMSCs interactions and BMSCs activity, which may represent the future goal of MM therapy.

FSH-blocking therapeutic for osteoporosis

Pharmacological and genetic studies over the past decade have established the follicle-stimulating hormone (FSH) as an actionable target for diseases affecting millions, namely osteoporosis, obesity, and Alzheimer's disease. Blocking FSH action prevents bone loss, fat gain, and neurodegeneration in mice. We recently developed a first-in-class, humanized, epitope-specific FSH-blocking antibody, MS-Hu6, with a KD of 7.52 nM. Using a Good Laboratory Practice (GLP)-compliant platform, we now report the efficacy of MS-Hu6 in preventing and treating osteoporosis in mice and parameters of acute safety in monkeys. Biodistribution studies using 89Zr-labeled, biotinylated or unconjugated MS-Hu6 in mice and monkeys showed localization to bone and bone marrow. The MS-Hu6 displayed a β phase t½ of 7.5 days (180 hr) in humanized Tg32 mice. We tested 217 variations of excipients using the protein thermal shift assay to generate a final formulation that rendered MS-Hu6 stable in solution upon freeze-thaw and at different temperatures, with minimal aggregation, and without self-, cross-, or hydrophobic interactions or appreciable binding to relevant human antigens. The MS-Hu6 showed the same level of "humanness" as human IgG1 in silico and was non-immunogenic in ELISpot assays for IL-2 and IFN-γ in human peripheral blood mononuclear cell cultures. We conclude that MS-Hu6 is efficacious, durable, and manufacturable, and is therefore poised for future human testing.

Daratumumab Improves Bone Turnover in Relapsed/Refractory Multiple Myeloma; Phase 2 Study “REBUILD”

Simple Summary

Multiple myeloma (MM) is characterized by the presence of deregulated bone metabolism. Restoring bone turnover is essential for patients with MM. We prospectively evaluated the impact of the anti-CD38 monoclonal antibody daratumumab on markers of bone remodeling among patients with relapsed/refractory MM. Overall, daratumumab improved bone turnover by favoring bone formation.

Abstract

Biomarkers of bone turnover in serum are suggestive of bone dynamics during treatment in multiple myeloma (MM). We evaluated the role of daratumumab on bone remodeling among patients with relapsed/refractory MM in the prospective, open-label, phase 2 study REBUILD. Daratumumab was administered according to the approved indication. A total of 33 out of 57 enrolled patients completed 4 months of treatment. The median percent change from baseline to 4 months in C-terminal cross-linking telopeptide of type 1 collagen (CTX) (primary endpoint) was 3.9%, with 13 (39.4%) and 11 (33.3%) patients showing at least 20% and 30% reduction in CTX levels, respectively. The median percent decrease from baseline to 4 months in tartrate resistant acid phosphatase 5b (TRACP-5b) levels (co-primary endpoint) was 2.6%, with 10 (30.3%) and 6 (18.2%) patients showing at least 20% and 30% reduction in TRACP-5b levels, respectively. However, the changes in these markers of bone catabolism were not statistically significant. Furthermore, the levels of osteocalcin, bone-specific alkaline phosphatase and procollagen type-I N-pro-peptide (bone formation markers) increased from baseline to 4 months (secondary endpoints) by 18.4%, 92.6% and 10.2%, respectively. Furthermore, the median levels of dickkopf-1 and C-C motif ligand-3 showed a significant decrease at 4 months by 17.5% and 16.0%, respectively. In conclusion, daratumumab improved bone turnover by inducing bone formation and reducing osteoblast inhibition.

CD38 Drives Progress of Osteoarthritis by Affecting Cartilage Homeostasis

Objective

To observe expression of CD38, a key modulator of nicotinamide dinucleotide (NAD+) metabolism in mice with knee osteoarthritis, and protective effect of CD38 inhibition during the osteoarthritis (OA) development.

Method

The destabilization of the medial meniscus (DMM) model was performed in mice to mimic the process of OA. Immunofluorescence of CD38 was performed to evaluate its response during the OA process. Limb bud‐derived mesenchymal cells were isolated for micromass culture. 100 nM or 1 μM CD38 inhibitor (78c) treatment for 14 days and CD38 sgRNA infection were then used to explore the effects of chondrogenic differentiation via Alcian blue staining. The expressions of chondrogenic markers were detected using RT‐PCR and Western blot. To explore the protective effect of CD38 inhibitor on cartilage degradation during OA in vivo, a CD38 inhibitor was injected into the knee joint after DMM operations. Micro‐CT analysis and Safranin O‐fast green staining were used to evaluate subchondral bone micro‐architecture changes and cartilage degeneration.

Results

Compared to the control group, the CD38 expression in superficial cartilage was obviously increased in DMM group (P < 0.05). During the normal chondrogenic differentiation, the extracellular matrix formed and expression of Sox9, Col2, aggrecan increased apparently while CD38 expression decreased, which could be reversed with ablation of CD38 in limb bud‐derived mesenchymal cells. Consistent with findings in vitro, CD38 blockage via CD38 inhibitor injection protected against osteosclerosis in medial subchondral bone and cartilage degeneration in DMM‐induced experimental mice. Compared to the Sham group, DMM mice showed significantly increased values of BV and BV/TV in subchondral bone (P < 0.05) and Mankin score, which could be rescued by 78c treatment (P < 0.05). Also the CD38 inhibitor contributed to homeostasis of anabolism and catabolism by upregulating Sox9, Col2, aggrecan and downregulating Runx2, Col10 and Mmp13.

Conclusion

This study primarily implicates CD38 as an important regulator of chondrogenic differentiation. Inhibition of CD38 demonstrated protection against cartilage degeneration, which suggests that CD38 could be a potential therapeutic target for OA.

Realization of Osteolysis, Angiogenesis, Immunosuppression, and Drug Resistance by Extracellular Vesicles: Roles of RNAs and Proteins in Their Cargoes and of Ectonucleotidases of the Immunosuppressive Adenosinergic Noncanonical Pathway in the Bone Marrow Niche of Multiple Myeloma

Simple Summary

Multiple myeloma (MM) is a disease that extensively involves bone, and angiogenesis and immunosuppression are important processes in the development of MM. Proteasome inhibitors and immunomodulatory drugs remarkably improve the survival of MM patients. However, MM is still an incurable disease that rapidly becomes resistant to these drugs. There is robust evidence that extracellular vesicles (EVs) contribute to cancer metastasis. Osteoclasts, in addition to immunosuppressive cells in the bone marrow (BM), are key players in osteolysis and immunosuppression. BM stromal cells and MM cells secrete EVs through which they communicate with each other: EVs, in fact, contain proteins, small RNAs, and long non-coding RNAs that mediate this communication and contribute to angiogenesis, osteolysis, and cancer dissemination and drug resistance. Ectoenzymes are expressed in myeloma cells, osteoclasts, and stromal cells and produce immunosuppressive adenosine. Recently, an antibody targeting CD38, an ectoenzyme, has been shown to improve the survival of patients with MM. Thus, understanding the properties of EV and ectoenzymes will help elucidate key processes of MM development.

Abstract

Angiogenesis and immunosuppression promote multiple myeloma (MM) development, and osteolysis is a primary feature of MM. Although immunomodulatory drugs and proteasome inhibitors (PIs) markedly improve the survival of patients with MM, this disease remains incurable. In the bone marrow niche, a chain of ectoenzymes, including CD38, produce immunosuppressive adenosine, inhibiting T cell proliferation as well as immunosuppressive cells. Therefore, anti-CD38 antibodies targeting myeloma cells have the potential to restore T cell responses to myeloma cells. Meanwhile extracellular vesicles (EVs) containing microRNAs, proteins such as cytokines and chemokines, long noncoding RNAs, and PIWI-interacting RNAs have been shown to act as communication tools in myeloma cell/microenvironment interactions. Via EVs, mesenchymal stem cells allow myeloma cell dissemination and confer PI resistance, whereas myeloma cells promote angiogenesis, myeloid-derived suppressor cell proliferation, and osteoclast differentiation and inhibit osteoblast differentiation. In this review, to understand key processes of MM development involving communication between myeloma cells and other cells in the tumor microenvironment, EV cargo and the non-canonical adenosinergic pathway are introduced, and ectoenzymes and EVs are discussed as potential druggable targets for the treatment of MM patients.

Skeletal unloading reduces cluster of differentiation (CD) 38 expression in the bone marrow and osteoblasts of mice

BACKGROUND

Mechanical unloading induces bone loss in human weight-loaded bones. The findings of recent studies have revealed that cluster of differentiation 38 knockout mice display bone loss similar to that observed in osteoporosis. This study aimed to determine whether the expression of cluster of differentiation 38 is implicated in skeletal unloading and reloading.

METHODS

Eight-week-old male C57BL/6J mice were assigned to control, tail-suspension, or reloading after tail-suspension groups. In the tail-suspension group, tail suspension elevated the hind limbs for 1 week. The bilateral femurs and tibias from the groups were evaluated for cluster of differentiation 38 immunocytochemistry, and the cluster of differentiation 38 messenger ribonucleic acid levels and the expression of cluster of differentiation 38 and other cell-surface antigens were evaluated using quantitative real-time polymerase chain reaction and flow cytometric analyses.

RESULTS

In the tail-suspension group, the alkaline phosphatase reactivity, cluster of differentiation 38 immunoreactivity in the bone marrow and osteoblasts, and the expression of cluster of differentiation 38 messenger ribonucleic acid and that of other cell-surface antigens were significantly lower than those in the control group. In the reloading after tail-suspension group, the level of cluster of differentiation 38 expression was restored to the same level as that in the control group.

CONCLUSIONS

Cluster of differentiation 38 expression declined after skeletal unloading and recovered to normal levels after reloading. In the bone marrow, cluster of differentiation 38 expression plays a crucial role in bone formation in response to mechanical stress.

Bone Marrow Stromal Cells-Induced Drug Resistance in Multiple Myeloma

Multiple myeloma is a B-cell lineage cancer in which neoplastic plasma cells expand in the bone marrow and pathophysiological interactions with components of microenvironment influence many biological aspects of the malignant phenotype, including apoptosis, survival, proliferation, and invasion. Despite the therapeutic progress achieved in the last two decades with the introduction of a more effective and safe new class of drugs (i.e., immunomodulators, proteasome inhibitors, monoclonal antibodies), there is improvement in patient survival, and multiple myeloma (MM) remains a non-curable disease. The bone marrow microenvironment is a complex structure composed of cells, extracellular matrix (ECM) proteins, and cytokines, in which tumor plasma cells home and expand. The role of the bone marrow (BM) microenvironment is fundamental during MM disease progression because modification induced by tumor plasma cells is crucial for composing a "permissive" environment that supports MM plasma cells proliferation, migration, survival, and drug resistance. The "activated phenotype" of the microenvironment of multiple myeloma is functional to plasma cell proliferation and spreading and to plasma cell drug resistance. Plasma cell drug resistance induced by bone marrow stromal cells is mediated by stress-managing pathways, autophagy, transcriptional rewiring, and non-coding RNAs dysregulation. These processes represent novel targets for the ever-increasing anti-MM therapeutic armamentarium.

CD38 Expression by Myeloma Cells and Its Role in the Context of Bone Marrow Microenvironment: Modulation by Therapeutic Agents

In the last decades CD38 has emerged as an attractive target for multiple myeloma (MM). CD38 is a novel multifunctional glycoprotein that acts as a receptor, adhesion molecule interacting with CD31 and as an ectoenzyme. As an ectoenzyme, CD38 functions as a metabolic sensor catalyzing the extracellular conversion of NAD+ to the immunosuppressive factor adenosine (ADO). Other ectoenzymes, CD73 and CD203a, together with CD38, are also involved in the alternative axis of extracellular production of ADO, bypassing the canonical pathway mediated by CD39. CD38 is ubiquitously expressed in the bone marrow microenvironment; however, only MM cells display a very high surface density, which lead to the development of several anti-CD38 monoclonal antibodies (mAbs). The efficacy of anti-CD38 mAbs depends from the presence of CD38 on the surface of MM and immune-microenvironment cells. Interestingly, it has been reported that several drugs like lenalidomide, panobinostat, the all-trans retinoic acid and the DNA methyltransferase inhibitors may increase the expression of CD38. Hence, the possibility to modulate CD38 by increasing its expression on MM cells is the pre-requisite to potentiate the clinical efficacy of the anti-CD38 mAbs and to design clinical trials with the combination of anti-CD38 mAbs and these drugs.

The link between bone microenvironment and immune cells in multiple myeloma: Emerging role of CD38

The relationship between bone and immune cells is well established both in physiological and pathological conditions. Multiple myeloma (MM) is a plasma cell malignancy characterized by an increase of number and activity of osteoclasts (OCLs) and a decrease of osteoblasts (OBs). These events are responsible for bone lesions of MM patients. OCLs support MM cells survival in vitro and in vivo. Recently, the possible role of OCLs as immunosuppressive cells in the MM BM microenvironment has been underlined. OCLs protect MM cells against T cell-mediated cytotoxicity through the expression of several molecules including programmed death-ligand (PD-L) 1, galectin (Gal) 9, CD200, and indoleamine-2,3-dioxygenase (IDO). Among the molecules that could be involved in the link between immune-microenvironment and osteoclastogenesis the role of CD38 has been hypothesized. CD38 is a well-known adhesion molecule and an ectoenzyme highly expressed by MM cells. Moreover, CD38 is expressed by OCLs and at the surface level on OCL precursors. Targeting CD38 with monoclonal antibodies showed inhibition of both osteoclastogenesis and OCL-mediated suppression of T cell function. This review elucidates this evidence indicating that osteoclastogenesis affect MM immune-microenvironment being a potential target to improve anti-MM immunity and to ameliorate bone disease.

Emerging Roles of Osteoclasts in the Modulation of Bone Microenvironment and Immune Suppression in Multiple Myeloma

Multiple myeloma (MM) is one of the most common forms of hematologic malignancy resulting from cancerous proliferation of mature malignant plasma cells (MPCs). But despite the real improvement in therapeutics in the past years, it remains largely incurable. MM is the most frequent cancer to involve bone due to the stimulation of osteoclast (OCL) differentiation and activity. OCLs have a unique capacity to resorb bone. However, recent studies reveal that they are not restrained to this sole function. They participate in the control of angiogenesis, medullary niches, and immune responses, including in MM. Therefore, therapeutic approaches targeting OCLs probably affect not only bone resorption but also many other functions, and OCLs should not be considered anymore only as targets to improve the bone phenotype but also to modulate bone microenvironment. In this review, we explore these novel contributions of OCLs to MM which reveal their strong implication in the MM physiopathology. We also underline the therapeutic interest of targeting OCLs not only to overcome bone lesions, but also to improve bone microenvironment and anti-tumoral immune responses.

Blocking FSH induces thermogenic adipose tissue and reduces body fat

Menopause is associated with bone loss and enhanced visceral adiposity. A polyclonal antibody that targets the β-subunit of the pituitary hormone follicle-stimulating hormone (Fsh) increases bone mass in mice. Here, we report that this antibody sharply reduces adipose tissue in wild-type mice, phenocopying genetic haploinsufficiency for the Fsh receptor gene Fshr. The antibody also causes profound beiging, increases cellular mitochondrial density, activates brown adipose tissue and enhances thermogenesis. These actions result from the specific binding of the antibody to the β-subunit of Fsh to block its action. Our studies uncover opportunities for simultaneously treating obesity and osteoporosis.

Expression of CD38 in myeloma bone niche: A rational basis for the use of anti-CD38 immunotherapy to inhibit osteoclast formation

It is known that multiple myeloma (MM) cells express CD38 and that a recently developed human anti-CD38 monoclonal antibody Daratumumab mediates myeloma killing. However, the expression of CD38 and other functionally related ectoenzymes within the MM bone niche and the potential effects of Daratumumab on bone cells are still unknown. This study firstly defines by flow cytometry and immunohistochemistry the expression of CD38 by bone marrow cells in a cohort of patients with MM and indolent monoclonal gammopathies. Results indicate that only plasma cells expressed CD38 at high level within the bone niche. In addition, the flow cytometry analysis shows that CD38 was also expressed by monocytes and early osteoclast progenitors but not by osteoblasts and mature osteoclasts. Indeed, CD38 was lost during in vitro osteoclastogenesis. Consistently, we found that Daratumumab reacted with CD38 expressed on monocytes and its binding inhibited in vitro osteoclastogenesis and bone resorption activity from bone marrow total mononuclear cells of MM patients, targeting early osteoclast progenitors. The inhibitory effect was not observed from purified CD14⁺ cells, suggesting an indirect inhibitory effect of Daratumumab. Interestingly, all-trans retinoic acid treatment increased the inhibitory effect of Daratumumab on osteoclast formation.

These observations provide a rationale for the use of an anti-CD38 antibody-based approach as treatment for multiple myeloma-induced osteoclastogenesis.

Ca2+ release via two-pore channel type 2 (TPC2) is required for slow muscle cell myofibrillogenesis and myotomal patterning in intact zebrafish embryos

We recently demonstrated a critical role for two-pore channel type 2 (TPC2)-mediated Ca²⁺ release during the differentiation of slow (skeletal) muscle cells (SMC) in intact zebrafish embryos, via the introduction of a translational-blocking morpholino antisense oligonucleotide (MO). Here, we extend our study and demonstrate that knockdown of TPC2 with a non-overlapping splice-blocking MO, knockout of TPC2 (via the generation of a tpcn2^dhkz1a mutant line of zebrafish using CRISPR/Cas9 gene-editing), or the pharmacological inhibition of TPC2 action with bafilomycin A1 or trans-ned-19, also lead to a significant attenuation of SMC differentiation, characterized by a disruption of SMC myofibrillogenesis and gross morphological changes in the trunk musculature. When the morphants were injected with tpcn2-mRNA or were treated with IP₃/BM or caffeine (agonists of the inositol 1,4,5-trisphosphate receptor (IP₃R) and ryanodine receptor (RyR), respectively), many aspects of myofibrillogenesis and myotomal patterning (and in the case of the pharmacological treatments, the Ca²⁺ signals generated in the SMCs), were rescued. STED super-resolution microscopy revealed a close physical relationship between clusters of RyR in the terminal cisternae of the sarcoplasmic reticulum (SR), and TPC2 in lysosomes, with a mean estimated separation of ~52-87nm. Our data therefore add to the increasing body of evidence, which indicate that localized Ca²⁺ release via TPC2 might trigger the generation of more global Ca²⁺ release from the SR via Ca²⁺-induced Ca²⁺ release.

Fine mapping of a distal chromosome 4 QTL affecting growth and muscle mass in a chicken advanced intercross line

In our previous research, QTL analysis in an F₂ cross between the inbred New Hampshire (NHI) and White Leghorn (WL77) lines revealed a growth QTL in the distal part of chromosome 4. To physically reduce the chromosomal interval and the number of potential candidate genes, we performed fine mapping using individuals of generations F₁₀ , F₁₁ and F₁₂ in an advanced intercross line that had been established from the initial F₂ mapping population. Using nine single nucleotide polymorphism (SNP) markers within the QTL region for an association analysis with several growth traits from hatch to 20 weeks and body composition traits at 20 weeks, we could reduce the confidence interval from 26.9 to 3.4 Mb. Within the fine mapped region, markers rs14490774, rs314961352 and rs318175270 were in full linkage disequilibrium (D' = 1.0) and showed the strongest effect on growth and muscle mass (LOD ≥ 4.00). This reduced region contains 30 genes, compared to 292 genes in the original region. Chicken 60 K and 600 K SNP chips combined with DNA sequencing of the parental lines were used to call mutations in the reduced region. In the narrowed-down region, 489 sequence variants were detected between NHI and WL77. The most deleterious variants are a missense variant in ADGRA3 (SIFT = 0.02) and a frameshift deletion in the functional unknown gene ENSGALG00000014401 in NHI chicken. In addition, five synonymous variants were discovered in genes PPARGC1A, ADGRA3, PACRGL, SLIT2 and FAM184B. In our study, the confidence interval and the number of potential genes could be reduced 8- and 10- fold respectively. Further research will focus on functional effects of mutant genes.

Osteoclasts promote immune suppressive microenvironment in multiple myeloma: therapeutic implication

OCs play a crucial role in myeloma-induced immunosuppressive microenvironment. Therapeutic anti-CD38 mAb partially overcomes the immunosuppressive effect of OCs.

Ca(2+) signals, NAADP and two-pore channels: role in cellular differentiation

Ca(2+) signals regulate a wide range of physiological processes. Intracellular Ca(2+) stores can be mobilized in response to extracellular stimuli via a range of signal transduction mechanisms, often involving recruitment of diffusible second messenger molecules. The Ca(2+) -mobilizing messengers InsP3 and cADPR release Ca(2+) from the endoplasmic reticulum via the InsP3 and ryanodine receptors, respectively, while a third messenger, NAADP, releases Ca(2+) from acidic endosomes and lysosomes. Bidirectional communication between the endoplasmic reticulum (ER) and acidic organelles may have functional relevance for endolysosomal function as well as for the generation of Ca(2+) signals. The two-pore channels (TPCs) are currently strong candidates for being key components of NAADP-regulated Ca(2+) channels. Ca(2+) signals have been shown to play important roles in differentiation; however, much remains to be established about the exact signalling mechanisms involved. The investigation of the role of NAADP and TPCs in differentiation is still at an early stage, but recent studies have suggested that they are important mediators of differentiation of neurones, skeletal muscle cells and osteoclasts. NAADP signals and TPCs have also been implicated in autophagy, an important process in differentiation. Further studies will be required to identify the precise mechanism of TPC action and their link with NAADP signalling, as well as relating this to their roles in differentiation and other key processes in the cell and organism.

The pathogenic relevance of the prognostic markers CD38 and CD49d in chronic lymphocytic leukemia

The interactions of chronic lymphocytic leukemia cells with the microenvironment in secondary lymphoid tissues and the bone marrow are known to promote CLL cell survival and proliferation. CD38 and CD49d are both independent prognostic risk parameters in CLL with important roles in shaping these interactions. Both are reported to influence CLL cell trafficking between blood and lymphoid organs as well as their survival and proliferation within the lymphoid organs, thereby impacting the pathophysiology of the disease. The expression of CD38 and CD49d is associated in the majority of cases, and they exist as part of macromolecular complexes. Here, we review the current evidence for the individual and associated contributions of these molecules to CLL pathophysiology.

Implication of CD38 gene in podocyte epithelial-to-mesenchymal transition and glomerular sclerosis

CD38 is a multifunctional protein involving in a number of signalling pathways. Given that the lack of CD38 is considered as a dedifferentiation marker of lymphocytes and other cells, we hypothesized that CD38 and its signalling pathway may participate in the epithelial-to-mesenchymal transition (EMT) process of podocytes and thereby regulates the integrity of glomerular structure and function. Western blot analysis and RT-PCR demonstrated that renal tissue CD38 expression was lacking in CD38(-/-) mice or substantially reduced in renal CD38 shRNA-transfected WT (CD38-shRNA) mice compared to CD38(+/+) littermates. Confocal fluorescent microscopy demonstrated the reduced expression of epithelial markers (P-Cadherin, ZO-1 and podocin) and increased expression of mesenchymal markers (FSP-1, α-SMA and desmin) in the glomeruli of CD38(-/-) and CD38-shRNA mice compared to CD38(+/+) mice. Morphological examinations showed profound injury in the glomeruli of CD38(-/-) or CD38-shRNA mice compared to CD38(+/+) mice. This enhanced glomerular injury in CD38(-/-) or CD38-shRNA mice was accompanied by increased albuminuria and proteinuria. DOCA/high salt treatment further decreased the expression of epithelial markers and increased the abundance of mesenchymal markers, which were accompanied by more increased glomerular damage index and mean arterial pressure in CD38(-/-) and CD38-shRNA mice than CD38(+/+) mice. In vitro studies showed that inhibition of CD38 enhances the EMT in podocytes. In conclusion, our observations reveal that the normal expression of CD38 importantly contributes to the differentiation and function of podocytes and the defect of this gene expression may be a critical mechanism inducing EMT and consequently resulting in glomerular injury and sclerosis.

E proteins regulate osteoclast maturation and survival

Osteoclasts are bone-specific polykaryons derived from myeloid precursors under the stimulation of macrophage colony stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL). E proteins are basic helix-loop-helix (bHLH) transcription factors that modulate lymphoid versus myeloid cell fate decisions. To study the role of E proteins in osteoclasts, myeloid-specific E protein gain-of-function transgenic mice were generated. These mice have high bone mass due to decreased osteoclast numbers and increased osteoclast apoptosis leading to overall reductions in resorptive capacity. The molecular mechanism of decreased osteoclast numbers and resorption is in part a result of elevated expression of CD38, a regulator of intracellular calcium pools with known antiosteoclastogenic properties, which increases sensitivity to apoptosis. In vivo, exogenous RANKL stimulation can overcome this inhibition to drive osteoclastogenesis and bone loss. In vitro-derived ET2 osteoclasts are more spread and more numerous with increases in RANK, triggering receptor expressed on myeloid cells 2 (TREM2), and nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) compared to wild type. However, their resorptive capacity does not increase accordingly. Thus, E proteins participate in osteoclast maturation and survival in homeostatic bone remodeling.

Identification of two-pore channel 2 as a novel regulator of osteoclastogenesis

Osteoclast differentiation is one of the critical steps that control bone mass levels in osteoporosis, but the molecules involved in osteoclastogenesis are still incompletely understood. Here, we show that two-pore channel 2 (TPC2) is expressed in osteoclast precursor cells, and its knockdown (TPC2-KD) in these cells suppressed RANKL-induced key events including multinucleation, enhancement of tartrate-resistant acid phosphatase (TRAP) activities, and TRAP mRNA expression levels. With respect to intracellular signaling, TPC2-KD reduced the levels of the RANKL-induced dynamic waving of Ca(2+) in RAW cells. The search for the target of TPC2 identified that nuclear localization of NFATc1 is retarded in TPC2-KD cells. Finally, TPC2-KD suppressed osteoclastic pit formation in cultures. We conclude that TPC2 is a novel critical molecule for osteoclastogenesis.

CD38 deficiency in the tumor microenvironment attenuates glioma progression and modulates features of tumor-associated microglia/macrophages

Gliomas are the most frequent primary tumors of the brain, and for highly malignant gliomas there is no successful treatment. The tumor microenvironment contains large numbers of infiltrating microglia and macrophages (MM). There is increasing evidence that the tumor-associated MM support glioma expansion. CD38 is a multifunctional ectoenzyme that uses nicotinamide adenine dinucleotide as a substrate to generate second messengers. Previously we showed that CD38 deficiency modulates microglial "activation" and impaired recovery from head trauma by a microglia-associated mechanism. In view of the supportive role of MM in glioma progression and the role of CD38 in microglia activation, we hypothesize that deficiency of CD38 in the tumor microenvironment would inhibit glioma progression. Using the syngeneic GL261 model of glioma progression in wild-type and CD38 null mice, we show here that CD38 deficiency significantly attenuates glioma expansion and prolongs the life span of the glioma-bearing mice. The CD38 deficiency effect was associated with increased cell death and decreased metalloproteinase-12 expression in the tumor mass, as well as modulation of the tumor-induced MM properties, as indicated by a reduction in the expression of the MM marker F4/80 and matrix metalloproteinases. Our results thus suggest that CD38 participates in the tumor-supporting action of MM and that targeting CD38 might be a potential therapeutic approach for glioma treatment.

Cyclic ADP-ribose and NAADP: fraternal twin messengers for calcium signaling

The concept advanced by Berridge and colleagues that intracellular Ca(2+)-stores can be mobilized in an agonist-dependent and messenger (IP(3))-mediated manner has put Ca(2+)-mobilization at the center stage of signal transduction mechanisms. During the late 1980s, we showed that Ca(2+)-stores can be mobilized by two other messengers unrelated to inositol trisphosphate (IP(3)) and identified them as cyclic ADP-ribose (cADPR), a novel cyclic nucleotide from NAD, and nicotinic acid adenine dinucleotide phosphate (NAADP), a linear metabolite of NADP. Their messenger functions have now been documented in a wide range of systems spanning three biological kingdoms. Accumulated evidence indicates that the target of cADPR is the ryanodine receptor in the sarco/endoplasmic reticulum, while that of NAADP is the two pore channel in endolysosomes.As cADPR and NAADP are structurally and functionally distinct, it is remarkable that they are synthesized by the same enzyme. They are thus fraternal twin messengers. We first identified the Aplysia ADP-ribosyl cyclase as one such enzyme and, through homology, found its mammalian homolog, CD38. Gene knockout in mice confirms the important roles of CD38 in diverse physiological functions from insulin secretion, susceptibility to bacterial infection, to social behavior of mice through modulating neuronal oxytocin secretion. We have elucidated the catalytic mechanisms of the Aplysia cyclase and CD38 to atomic resolution by crystallography and site-directed mutagenesis. This article gives a historical account of the cADPR/NAADP/CD38-signaling pathway and describes current efforts in elucidating the structure and function of its components.

Design, synthesis and biological characterization of novel inhibitors of CD38

Human CD38 is a novel multi-functional protein that acts not only as an antigen for B-lymphocyte activation, but also as an enzyme catalyzing the synthesis of a Ca(2+) messenger molecule, cyclic ADP-ribose, from NAD(+). It is well established that this novel Ca(2+) signaling enzyme is responsible for regulating a wide range of physiological functions. Based on the crystal structure of the CD38/NAD(+) complex, we synthesized a series of simplified N-substituted nicotinamide derivatives (Compound 1-14). A number of these compounds exhibited moderate inhibition of the NAD(+) utilizing activity of CD38, with Compound 4 showing the highest potency. The crystal structure of CD38/Compound 4 complex and computer simulation of Compound 7 docking to CD38 show a significant role of the nicotinamide moiety and the distal aromatic group of the compounds for substrate recognition by the active site of CD38. Biologically, we showed that both Compounds 4 and 7 effectively relaxed the agonist-induced contraction of muscle preparations from rats and guinea pigs. This study is a rational design of inhibitors for CD38 that exhibit important physiological effects, and can serve as a model for future drug development.

Calcium and bone disease

Calcium transport and calcium signaling are of basic importance in bone cells. Bone is the major store of calcium and a key regulatory organ for calcium homeostasis. Bone, in major part, responds to calcium-dependent signals from the parathyroids and via vitamin D metabolites, although bone retains direct response to extracellular calcium if parathyroid regulation is lost. Improved understanding of calcium transporters and calcium-regulated cellular processes has resulted from analysis of genetic defects, including several defects with low or high bone mass. Osteoblasts deposit calcium by mechanisms including phosphate and calcium transport with alkalinization to absorb acid created by mineral deposition; cartilage calcium mineralization occurs by passive diffusion and phosphate production. Calcium mobilization by osteoclasts is mediated by acid secretion. Both bone forming and bone resorbing cells use calcium signals as regulators of differentiation and activity. This has been studied in more detail in osteoclasts, where both osteoclast differentiation and motility are regulated by calcium.

Loading-related regulation of gene expression in bone in the contexts of estrogen deficiency, lack of estrogen receptor alpha and disuse

Loading-related changes in gene expression in resident cells in the tibia of female mice in the contexts of normality (WT), estrogen deficiency (WT-OVX), absence of estrogen receptor alpha (ERalpha(-/-)) and disuse due to sciatic neurectomy (WT-SN) were established by microarray. Total RNA was extracted from loaded and contra-lateral non-loaded tibiae at selected time points after a single, short period of dynamic loading sufficient to engender an osteogenic response. There were marked changes in the expression of many genes according to context as well as in response to loading within those contexts. In WT mice at 3, 8, 12 and 24 h after loading the expression of 642, 341, 171 and 24 genes, respectively, were differentially regulated compared with contra-lateral bones which were not loaded. Only a few of the genes differentially regulated by loading in the tibiae of WT mice have recognized roles in bone metabolism or have been linked previously to osteogenesis (Opn, Sost, Esr1, Tgfb1, Lrp1, Ostn, Timp, Mmp, Ctgf, Postn and Irs1, BMP and DLX5). The canonical pathways showing the greatest loading-related regulation were those involving pyruvate metabolism, mitochondrial dysfunction, calcium-induced apoptosis, glycolysis/gluconeogenesis, aryl hydrocarbon receptor and oxidative phosphorylation. In the tibiae from WT-OVX, ERalpha(-/-) and WT-SN mice, 440, 439 and 987 genes respectively were differentially regulated by context alone compared to WT. The early response to loading in tibiae of WT-OVX mice involved differential regulation compared to their contra-lateral non-loaded pair of fewer genes than in WT, more down-regulation than up-regulation and a later response. This was shared by WT-SN. In tibiae of ERalpha(-/-) mice, the number of genes differentially regulated by loading was markedly reduced at all time points. These data indicate that in resident bone cells, both basal and loading-related gene expression is substantially modified by context. Many of the genes differentially regulated by the earliest loading-related response were primarily involved in energy metabolism and were not specific to bone.

The role of dietary niacin intake and the adenosine-5'-diphosphate-ribosyl cyclase enzyme CD38 in spatial learning ability: is cyclic adenosine diphosphate ribose the link between diet and behaviour?

The pyridine nucleotide NAD+ is derived from dietary niacin and serves as the substrate for the synthesis of cyclic ADP-ribose (cADPR), an intracellular Ca signalling molecule that plays an important role in synaptic plasticity in the hippocampus, a region of the brain involved in spatial learning. cADPR is formed in part via the activity of the ADP-ribosyl cyclase enzyme CD38, which is widespread throughout the brain. In the present review, current evidence of the relationship between dietary niacin and behaviour is presented following investigations of the effect of niacin deficiency, pharmacological nicotinamide supplementation and CD38 gene deletion on brain nucleotides and spatial learning ability in mice and rats. In young male rats, both niacin deficiency and nicotinamide supplementation significantly altered brain NAD+ and cADPR, both of which were inversely correlated with spatial learning ability. These results were consistent across three different models of niacin deficiency (pair feeding, partially restricted feeding and niacin recovery). Similar changes in spatial learning ability were observed in Cd38- / - mice, which also showed decreases in brain cADPR. These findings suggest an inverse relationship between spatial learning ability, dietary niacin intake and cADPR, although a direct link between cADPR and spatial learning ability is still missing. Dietary niacin may therefore play a role in the molecular events regulating learning performance, and further investigations of niacin intake, CD38 and cADPR may help identify potential molecular targets for clinical intervention to enhance learning and prevent or reverse cognitive decline.

Covalent and noncovalent intermediates of an NAD utilizing enzyme, human CD38

Enzymatic utilization of nicotinamide adenine dinucleotide (NAD) has increasingly been shown to have fundamental roles in gene regulation, signal transduction, and protein modification. Many of the processes require the cleavage of the nicotinamide moiety from the substrate and the formation of a reactive intermediate. Using X-ray crystallography, we show that human CD38, an NAD-utilizing enzyme, is capable of catalyzing the cleavage reactions through both covalent and noncovalent intermediates, depending on the substrate used. The covalent intermediate is resistant to further attack by nucleophiles, resulting in mechanism-based enzyme inactivation. The noncovalent intermediate is stabilized mainly through H-bond interactions, but appears to remain reactive. Our structural results favor the proposal of a noncovalent intermediate during normal enzymatic utilization of NAD by human CD38 and provide structural insights into the design of covalent and noncovalent inhibitors targeting NAD-utilization pathways.

Evolution and function of the ADP ribosyl cyclase/CD38 gene family in physiology and pathology

The membrane proteins CD38 and CD157 belong to an evolutionarily conserved family of enzymes that play crucial roles in human physiology. Expressed in distinct patterns in most tissues, CD38 (and CD157) cleaves NAD(+) and NADP(+), generating cyclic ADP ribose (cADPR), NAADP, and ADPR. These reaction products are essential for the regulation of intracellular Ca(2+), the most ancient and universal cell signaling system. The entire family of enzymes controls complex processes, including egg fertilization, cell activation and proliferation, muscle contraction, hormone secretion, and immune responses. Over the course of evolution, the molecules have developed the ability to interact laterally and frontally with other surface proteins and have acquired receptor-like features. As detailed in this review, the loss of CD38 function is associated with impaired immune responses, metabolic disturbances, and behavioral modifications in mice. CD38 is a powerful disease marker for human leukemias and myelomas, is directly involved in the pathogenesis and outcome of human immunodeficiency virus infection and chronic lymphocytic leukemia, and controls insulin release and the development of diabetes. Here, the data concerning diseases are examined in view of potential clinical applications in diagnosis, prognosis, and therapy. The concluding remarks try to frame all of the currently available information within a unified working model that takes into account both the enzymatic and receptorial functions of the molecules.

The developmental basis of skeletal cell differentiation and the molecular basis of major skeletal defects

Vertebrate skeletal differentiation retains elements from simpler phyla, and reflects the differentiation of supporting tissues programmed by primary embryonic development. This developmental scheme is driven by homeotic genes expressed in sequence, with subdivision of skeletal primordia driven by a combination of seven transmembrane-pass receptors responding to Wnt-family signals, and by bone morphogenetic family signals that define borders of individual bones. In sea-dwelling vertebrates, an essentially complete form of the skeleton adapted by the land-living vertebrates develops in cartilage, based on type II collagen and hydrophilic proteoglycans. In bony fishes, this skeleton is mineralized to form a solid bony skeleton. In the land-living vertebrates, most of the skeleton is replaced by an advanced vascular mineralized skeleton based on type I collagen, which reduces skeletal mass while facilitating use of skeletal mineral for metabolic homeostasis. Regulation of the mammalian skeleton, in this context, reflects practical adaptations to the needs for life on land that are related to ancestral developmental signals. This regulation includes central nervous system regulation that integrates bone turnover with overall metabolism. Recent work on skeletal development, in addition, demonstrates molecular mechanisms that cause developmental bone diseases.

Necessity of inositol (1,4,5)-trisphosphate receptor 1 and mu-calpain in NO-induced osteoclast motility

In skeletal remodeling, osteoclasts degrade bone, detach and move to new locations. Mechanical stretch and estrogen regulate osteoclast motility via nitric oxide (NO). We have found previously that NO stimulates guanylyl cyclase, activating the cGMP-dependent protein kinase 1 (PKG1), reversibly terminating osteoclast matrix degradation and attachment, and initiating motility. The PKG1 substrate vasodilator-stimulated protein (VASP), a membrane-attachment-related protein found in complexes with the integrin alphavbeta3 in adherent osteoclasts, was also required for motility. Here, we studied downstream mechanisms by which the NO-dependent pathway mediates osteoclast relocation. We found that NO-stimulated motility is dependent on activation of the Ca(2+)-activated proteinase mu-calpain. RNA interference (RNAi) showed that NO-dependent activation of mu-calpain also requires PKG1 and VASP. Inhibition of Src kinases, which are involved in the regulation of adhesion complexes, also abolished NO-stimulated calpain activity. Pharmacological inhibition and RNAi showed that calpain activation in this process is mediated by the inositol (1,4,5)-trisphosphate receptor 1 [Ins(1,4,5)P(3)R1] Ca(2+) channel. We conclude that NO-induced motility in osteoclasts requires regulated Ca(2+) release, which activates mu-calpain. This occurs via the Ins(1,4,5)P(3)R1.

Skeletal remodeling in health and disease

The use of genetically manipulated mouse models, gene and protein discovery and the cataloguing of genetic mutations have each allowed us to obtain new insights into skeletal morphogenesis and remodeling. These techniques have made it possible to identify molecules that are obligatory for specific cellular functions, and to exploit these molecules for therapeutic purposes. New insights into the pathophysiology of diseases have also enabled us to understand molecular defects in a way that was not possible a decade ago. This review summarizes our current understanding of the carefully orchestrated cross-talk between cells of the bone marrow and between bone cells and the brain through which bone is constantly remodeled during adult life. It also highlights molecular aberrations that cause bone cells to become dysfunctional, as well as therapeutic options and opportunities to counteract skeletal loss.

Structure and enzymatic functions of human CD38

CD38 is a novel multifunctional protein that serves not only as an antigen but also as an enzyme. It catalyzes the metabolism of cyclic ADP-ribose and nicotinic acid adenine dinucleotide phosphate, two structurally and functionally distinct Ca(2+) messengers targeting, respectively, the endoplasmic reticulum and lysosomal Ca(2+) stores. The protein has recently been crystallized and its three-dimensional structure solved to a resolution of 1.9 A. The crystal structure of a binary complex reveals critical interactions between residues at the active site and a bound substrate, providing mechanistic insights to its novel multi-functional catalysis. This article reviews the current advances in the understanding of the structural determinants that control the multiple enzymatic reactions catalyzed by CD38.

Structure and enzymatic functions of human CD38

CD38 is a novel multifunctional protein that serves not only as an antigen but also as an enzyme. It catalyzes the metabolism of cyclic ADP-ribose and nicotinic acid adenine dinucleotide phosphate, two structurally and functionally distinct Ca(2+) messengers targeting, respectively, the endoplasmic reticulum and lysosomal Ca(2+) stores. The protein has recently been crystallized and its three-dimensional structure solved to a resolution of 1.9 A. The crystal structure of a binary complex reveals critical interactions between residues at the active site and a bound substrate, providing mechanistic insights to its novel multi-functional catalysis. This article reviews the current advances in the understanding of the structural determinants that control the multiple enzymatic reactions catalyzed by CD38.

Calcium signalling and calcium transport in bone disease

Calcium transport and calcium signalling mechanisms in bone cells have, in many cases, been discovered by study of diseases with disordered bone metabolism. Calcium matrix deposition is driven primarily by phosphate production, and disorders in bone deposition include abnormalities in membrane phosphate transport such as in chondrocalcinosis, and defects in phosphate-producing enzymes such as in hypophosphatasia. Matrix removal is driven by acidification, which dissolves the mineral. Disorders in calcium removal from bone matrix by osteoclasts cause osteopetrosis. On the other hand, although bone is central to management of extracellular calcium, bone is not a major calcium sensing organ, although calcium sensing proteins are expressed in both osteoblasts and osteoclasts. Intracellular calcium signals are involved in secondary control including cellular motility and survival, but the relationship of these findings to specific diseases is not clear. Intracellular calcium signals may regulate the balance of cell survival versus proliferation or anabolic functional response as part of signalling cascades that integrate the response to primary signals via cell stretch, estrogen, tyrosine kinase, and tumor necrosis factor receptors.

CD38 is required for priming by TNF-alpha: a mechanism for extracellular coordination of cell fate

Cytokines are protein messengers that act to modulate the differentiation or activation of their target cells. Bone marrow macrophages can become activated tissue macrophages, dendritic cells, or osteoclasts depending on to which cytokines they are exposed. However, one cytokine can often induce divergent outcomes, suggesting that other signals are needed to establish the specificity of the result. We hypothesize that these signals may derive from the local environment and serve to prime cells to respond toward a specific outcome. Here, it is shown that the cytokine TNF-alpha is capable of affecting the fate of macrophages by upregulating the NADase CD38. CD38 upregulation primes macrophages, such that signals induced by inflammatory stimuli are augmented, while those leading to osteoclast formation are inhibited. We show that TNF-alpha-induced CD38 expression negatively affects the expression of osteoclast markers, while it enhances inflammatory gene expression by decreasing ERK1/2 phosphorylation and increasing NF-kappaB activation. Furthermore, it is shown that CD38 may reduce osteoclastogenesis and increase inflammatory gene induction by decreasing cellular histone deacetylase activity. These results provide a demonstration of how a cytokine can prime cells to differentiate toward a certain lineage or acquire enhanced activation characteristics. Since CD38 is an ectoenzyme, we suggest that the modulation of extracellular NAD(+) metabolism likely serves as a unique mechanism to coordinate the fate of cells within a local environment.

Suppressed insulin signaling and increased apoptosis in CD38-null islets

CD38 is a multifunctional enzyme capable of generating metabolites that release Ca2+ from intracellular stores, including nicotinic acid adenine dinucleotide phosphate (NAADP). A number of studies have led to the controversial proposal that CD38 mediates an alternate pathway for glucose-stimulated insulin release and contributes to the pathogenesis of diabetes. It has recently been shown that NAADP mediates Ca2+ mobilization by insulin in human pancreatic beta-cells. In the present study, we report altered Ca2+ homeostasis and reduced responsiveness to insulin, but not glucose, in Cd38-/- beta-cells. In keeping with the antiapoptotic role of insulin signaling, Cd38-/- islets were significantly more susceptible to apoptosis compared with islets isolated from littermate controls. This finding correlated with disrupted islet architecture and reduced beta-cell mass in Cd38-/- mice, both in the context of a normal lab diet and a high-fat diet. Nevertheless, we did not find robust differences in glucose homeostasis in vivo or glucose signaling in vitro in Cd38-/- mice on the C57BL/6 genetic background, in contrast to previous studies by others of Cd38 knockout mice on the ICR background. Thus, our results suggest that CD38 plays a role in novel antiapoptotic signaling pathways but does not directly control glucose signaling in pancreatic beta-cells.

Selective upregulation of the ADP-ribosyl cyclases CD38 and CD157 by TNF but not by RANK-L reveals differences in downstream signaling

In macrophages and osteoclast precursors, the cytokines TNF and RANK-L induce similar downstream pathways and share some of the same adaptor molecules. However, despite these similarities, no defined signaling schematic has emerged to show how each cytokine favors particular pathways. In this report, we investigate whether TNF and RANK-L differentially regulate ADP-ribosyl cyclases-enzymes that are unique in being crucial for immunological function yet detrimental to osteoclastogenesis. TNF but not RANK-L led to the sustained upregulation of both CD38 and CD157 as demonstrated by real-time PCR and flow cytometry. Further investigation demonstrated that this upregulation was a result of continuous, direct TNF signaling and involved JNK, and more critically PKC and NF-κB. Using this approach allowed us to highlight the relative importance of the PKC, NF-κB, and JNK pathways in actualizing proper outcomes of TNF signaling. Albeit speculative, we believe that differences between TNF- and RANK-l-induced activation of downstream signaling pathways, in particular PKC, are crucial for determining whether progenitor cells become geared for immunity or bone resorption.

Extracellular NAD+ metabolism modulates osteoclastogenesis

Changes in NAD+ and its metabolites contribute to longevity and age-associated diseases. The role of NAD+ metabolism in bone diseases has however not been investigated, despite the fact that osteoporosis is a leading cause of morbidity in old age. TRAP(+) osteoclast formation from C57 Bl/6J mice was assessed after the addition of varying concentrations of NAD+ metabolites or exogenous ADPribosyl cyclase and NADase enzymes. The NAD+ metabolite cyclic ADPribose (cADPr) or exogenous addition of the enzyme ADPribosyl cyclase stimulated osteoclast formation. Blocking cADPr action with the antagonist 8-Br-cADPr potently inhibited osteoclast formation. In contrast to cADPr, its noncyclized derivative ADPribose (ADPr) or the exogenous addition of NADase both inhibited osteoclastogenesis. As CD38 is the major NAD+ -degrading enzyme present in the bone marrow, these results suggest that CD38-mediated inhibition of osteoclastogenesis is related to its NADase activity, not its ADPribosyl cyclase activity.

CD38-deficient mice have reduced airway hyperresponsiveness following IL-13 challenge

The transmembrane glycoprotein CD38 in airway smooth muscle is the source of cyclic-ADP ribose, an intracellular calcium-releasing molecule, and is subject to regulatory effects of cytokines such as interleukin (IL)-13, a cytokine implicated in asthma. We investigated the role of CD38 in airway hyperresponsiveness using a mouse model of IL-13-induced airway disease. Wild-type (WT) and CD38-deficient (CD38KO) mice were intranasally challenged with 5 microg of IL-13 three times on alternate days under isoflurane anesthesia. Lung resistance (R(L)) in response to inhaled methacholine was measured 24 h after the last challenge in pentobarbital-anesthetized, tracheostomized, and mechanically ventilated mice. Bronchoalveolar cytokines, bronchoalveolar and parenchymal inflammation, and smooth muscle contractility and relaxation using tracheal segments were also evaluated. Changes in methacholine-induced R(L) were significantly greater in the WT than in the CD38KO mice following intranasal IL-13 challenges. Airway reactivity after IL-13 exposure, as measured by the slope of the methacholine dose-response curve, was significantly higher in the WT than in the CD38KO mice. The rate of isometric force generation in tracheal segments (e.g., smooth muscle reactivity) was greater in the WT than in the CD38KO mice following incubation with IL-13. IL-13 treatment reduced isoproterenol-induced relaxations to similar magnitudes in tracheal segments obtained from WT and CD38KO mice. Both WT and CD38KO mice developed significant bronchoalveolar and parenchymal inflammation after IL-13 challenges compared with naïve controls. The results indicate that CD38 contributes to airway hyperresponsiveness in lungs exposed to IL-13 at least partly by increasing airway smooth muscle reactivity to contractile agonists.

Osteoclastic differentiation and function regulated by old and new pathways

The osteoclast is a specialized multinucleated variant of the macrophage family. It degrades mineralized tissue, and is required for modeling and remodeling of bone. The osteoclast has long been known to require vitamin D for its differentiation and to be regulated by parathyroid hormone via circulating Ca(2+) levels. Two local signals important in osteoclast survival and differentiation, CSF-1 and RANKL, were characterized by the mid-1990 s. A basic framework of specialized cell attachment and resorption molecules was also clear by that time, including the alpha(v)beta(3) integrin, the key adhesion molecule of the mature osteoclast, the highly expressed vacuolar-type H(+)-ATPase that drives acid secretion to dissolve mineral, and cathepsin K, the predominant acid proteinase for collagenolysis. Recently, additional detail has been added to this framework, showing that the osteoclast has more complex regulation than was previously believed. These include the findings that one component of the V-H(+)-ATPase is unique to the osteoclast, that chloride transport and probably Cl(-)/H(+) exchange are also required for mineral degradation, and that additional receptors besides RANK and Fms regulate osteoclast formation and survival. Additional receptors include estrogen receptor-alpha, TNF-family receptors other than RANK, and, at least in some cases, glycoprotein hormone receptors including the TSH-R and the FSH-R. Challenges in understanding osteoclast biology include how the signalling mechanisms function cooperatively. Recent findings suggest that there is a network of cytoplasmic adapters, including Gab-2 and BCAR1, which are modified by multiple signalling mechanisms and which serve to integrate the signalling pathways.

FSH Directly Regulates Bone Mass

Postmenopausal osteoporosis, a global public health problem, has for decades been attributed solely to declining estrogen levels. Although FSH levels rise sharply in parallel, a direct effect of FSH on the skeleton has never been explored. We show that FSH is required for hypogonadal bone loss. Neither FSHbeta nor FSH receptor (FSHR) null mice have bone loss despite severe hypogonadism. Bone mass is increased and osteoclastic resorption is decreased in haploinsufficient FSHbeta+/- mice with normal ovarian function, suggesting that the skeletal action of FSH is estrogen independent. Osteoclasts and their precursors possess G(i2alpha)-coupled FSHRs that activate MEK/Erk, NF-kappaB, and Akt to result in enhanced osteoclast formation and function. We suggest that high circulating FSH causes hypogonadal bone loss.

Structure and functional regulation of the CD38 promoter

CD38 has multiple roles in biology, including T lymphocyte signaling, neutrophil migration, neurotransmission, cell proliferation, apoptosis, and bone remodeling. To study the transcriptional control of the CD38 gene, we cloned a putative 1.8 kb promoter fragment from a rabbit genomic DNA library. Primer extension analysis indicated two transcription start sites consistent with the absence of a TATA box. Sequence analysis revealed several AP-1, AP-4, myo-D, GATA, and SP-1 sequences. MC3T3.E1 (osteoblast) or RAW-C3 (osteoclast precursor macrophage) cells were then transfected with the CD38 promoter or its deletion fragments ligated to the luciferase reporter gene. Except for the shortest 41 bp fragment, all fragments showed significant luciferase activity. There was a marked stimulation of basal activity in the 93 bp fragment that contained a GC box and SP-1 site. Furthermore, there were significant differences in the activity of the fragments in MC3T3.E1 and RAW-C3 cells. Intracellular Ca(2+) elevations by ionomycin (10muM) in MC3T3.E1 cells inhibited promoter activity, except in the short 41 bp. In contrast, cAMP elevation by exposure to forskolin (100 microM) inhibited activation of all fragments, except the 0.6 and 1.2kb fragments. Finally, TNF-alpha stimulated promoter activity in RAW-C3 cells transfected with the 93 bp and 1.0 kb fragments, consistent with the stimulation of CD38 mRNA by TNF-alpha. Physiologically, therefore, modulation of the expression of the NAD(+)-sensing enzyme, CD38, by Ca(2+), cAMP, and cytokines, such as TNF-alpha may contribute to coupling the intense metabolic activity of osteoclasts and osteoblasts to their respective bone-resorbing and bone-forming functions.