Nr4a1 enhances Wnt4 transcription to promote mesenchymal stem cell osteogenesis and alleviates inflammation-inhibited bone regeneration

Intense inflammatory response impairs bone marrow mesenchymal stem cell (BMSC)-mediated bone regeneration, with transforming growth factor (TGF)-β1 being the most highly expressed cytokine. However, how to find effective and safe means to improve bone formation impaired by excessive TGF-β1 remains unclear. In this study, we found that the expression of orphan nuclear receptor Nr4a1, an endogenous repressor of TGF-β1, was suppressed directly by TGF-β1-induced Smad3 and indirectly by Hdac4, respectively. Importantly, Nr4a1 overexpression promoted BMSC osteogenesis and reversed TGF-β1-mediated osteogenic inhibition and pro-fibrotic effects. Transcriptomic and histologic analyses confirmed that upregulation of Nr4a1 increased the transcription of Wnt family member 4 (Wnt4) and activated Wnt pathway. Mechanistically, Nr4a1 bound to the promoter of Wnt4 and regulated its expression, thereby enhancing the osteogenic capacity of BMSCs. Moreover, treatment with Nr4a1 gene therapy or Nr4a1 agonist Csn-B could promote ectopic bone formation, defect repair, and fracture healing. Finally, we demonstrated the correlation of NR4A1 with osteogenesis and the activation of the WNT4/β-catenin pathway in human BMSCs and fracture samples. Taken together, these findings uncover the critical role of Nr4a1 in bone formation and alleviation of inflammation-induced bone regeneration disorders, and suggest that Nr4a1 has the potential to be a therapeutic target for accelerating bone healing.

Vegfc-expressing cells form heterotopic bone after musculoskeletal injury

Heterotopic ossification (HO) is a challenging condition that occurs after musculoskeletal injury and is characterized by the formation of bone in non-skeletal tissues. While the effect of HO on blood vessels is well established, little is known about its impact on lymphatic vessels. Here, we use a mouse model of traumatic HO to investigate the relationship between HO and lymphatic vessels. We show that injury triggers lymphangiogenesis at the injury site, which is associated with elevated vascular endothelial growth factor C (VEGF-C) levels. Through single-cell transcriptomic analyses, we identify mesenchymal progenitor cells and tenocytes as sources of Vegfc. We demonstrate by lineage tracing that Vegfc-expressing cells undergo osteochondral differentiation and contribute to the formation of HO. Last, we show that Vegfc haploinsufficiency results in a nearly 50% reduction in lymphangiogenesis and HO formation. These findings shed light on the complex mechanisms underlying HO formation and its impact on lymphatic vessels.

The HIF-1α/PLOD2 axis integrates extracellular matrix organization and cell metabolism leading to aberrant musculoskeletal repair

While hypoxic signaling has been shown to play a role in many cellular processes, its role in metabolism-linked extracellular matrix (ECM) organization and downstream processes of cell fate after musculoskeletal injury remains to be determined. Heterotopic ossification (HO) is a debilitating condition where abnormal bone formation occurs within extra-skeletal tissues. Hypoxia and hypoxia-inducible factor 1α (HIF-1α) activation have been shown to promote HO. However, the underlying molecular mechanisms by which the HIF-1α pathway in mesenchymal progenitor cells (MPCs) contributes to pathologic bone formation remain to be elucidated. Here, we used a proven mouse injury-induced HO model to investigate the role of HIF-1α on aberrant cell fate. Using single-cell RNA sequencing (scRNA-seq) and spatial transcriptomics analyses of the HO site, we found that collagen ECM organization is the most highly up-regulated biological process in MPCs. Zeugopod mesenchymal cell-specific deletion of Hif1α (Hoxa11-CreERT2; Hif1afl/fl) significantly mitigated HO in vivo. ScRNA-seq analysis of these Hoxa11-CreERT2; Hif1afl/fl mice identified the PLOD2/LOX pathway for collagen cross-linking as downstream of the HIF-1α regulation of HO. Importantly, our scRNA-seq data and mechanistic studies further uncovered that glucose metabolism in MPCs is most highly impacted by HIF-1α deletion. From a translational aspect, a pan-LOX inhibitor significantly decreased HO. A newly screened compound revealed that the inhibition of PLOD2 activity in MPCs significantly decreased osteogenic differentiation and glycolytic metabolism. This suggests that the HIF-1α/PLOD2/LOX axis linked to metabolism regulates HO-forming MPC fate. These results suggest that the HIF-1α/PLOD2/LOX pathway represents a promising strategy to mitigate HO formation.

TrkA-mediated sensory innervation of injured mouse tendon supports tendon sheath progenitor cell expansion and tendon repair

Peripheral neurons terminate at the surface of tendons partly to relay nociceptive pain signals; however, the role of peripheral nerves in tendon injury and repair remains unclear. Here, we show that after Achilles tendon injury in mice, there is new nerve growth near tendon cells that express nerve growth factor (NGF). Conditional deletion of the Ngf gene in either myeloid or mesenchymal mouse cells limited both innervation and tendon repair. Similarly, inhibition of the NGF receptor tropomyosin receptor kinase A (TrkA) abrogated tendon healing in mouse tendon injury. Sural nerve transection blocked the postinjury increase in tendon sensory innervation and the expansion of tendon sheath progenitor cells (TSPCs) expressing tubulin polymerization promoting protein family member 3. Single cell and spatial transcriptomics revealed that disruption of sensory innervation resulted in dysregulated inflammatory signaling and transforming growth factor-β (TGFβ) signaling in injured mouse tendon. Culture of mouse TSPCs with conditioned medium from dorsal root ganglia neuron further supported a role for neuronal mediators and TGFβ signaling in TSPC proliferation. Transcriptomic and histologic analyses of injured human tendon biopsy samples supported a role for innervation and TGFβ signaling in human tendon regeneration. Last, treating mice after tendon injury systemically with a small-molecule partial agonist of TrkA increased neurovascular response, TGFβ signaling, TSPC expansion, and tendon tissue repair. Although further studies should investigate the potential effects of denervation on mechanical loading of tendon, our results suggest that peripheral innervation is critical for the regenerative response after acute tendon injury.

Neutrophil and NETosis Modulation in Traumatic Heterotopic Ossification

OBJECTIVE

To characterize the role of neutrophil extracellular traps (NETs) in heterotopic ossification (HO) formation and progression and to use mechanical and pharmacological methods to decrease NETosis and mitigate HO formation.

BACKGROUND

Traumatic HO is the aberrant osteochondral differentiation of mesenchymal progenitor cells after traumatic injury, burns, or surgery. While the innate immune response has been shown to be necessary for HO formation, the specific immune cell phenotype and function remain unknown. Neutrophils, one of the earliest immune cells to respond after HO-inducing injuries, can extrude DNA, forming highly inflammatory NETs. We hypothesized that neutrophils and NETs would be diagnostic biomarkers and therapeutic targets for the detection and mitigation of HO.

METHODS

C57BL6J mice underwent burn/tenotomy (a well-established mouse model of HO) or a non-HO-forming sham injury. These mice were either (1) ambulated ad libitum, (2) ambulated ad libitum with daily intraperitoneal hydroxychloroquine, ODN-2088 (both known to affect NETosis pathways), or control injections, or (3) had the injured hind limb immobilized. Single-cell analysis was performed to analyze neutrophils, NETosis, and downstream signaling after the HO-forming injury. Immunofluorescence microscopy was used to visualize NETosis at the HO site and neutrophils were identified using flow cytometry. Serum and cell lysates from HO sites were analyzed using enzyme-linked immunosorbent assay for myeloperoxidase-DNA and ELA2-DNA complexes to identify NETosis. Micro-computerized tomography was performed on all groups to analyze the HO volume.

RESULTS

Molecular and transcriptional analyses revealed the presence of NETs within the HO injury site, which peaked in the early phases after injury. These NETs were highly restricted to the HO site, with gene signatures derived from both in vitro NET induction and clinical neutrophil characterizations showing a high degree of NET "priming" at the site of injury, but not in neutrophils in the blood or bone marrow. Cell-cell communication analyses revealed that this localized NET formation coincided with high levels of toll-like receptor signaling specific to neutrophils at the injury site. Reducing the overall neutrophil abundance within the injury site, either pharmacologically through treatment with hydroxychloroquine, the toll-like receptor 9 inhibitor OPN-2088, or mechanical treatment with limb offloading, results in the mitigation of HO formation.

CONCLUSIONS

These data provide a further understanding of the ability of neutrophils to form NETs at the injury site, clarify the role of neutrophils in HO, and identify potential diagnostic and therapeutic targets for HO mitigation.

Spatial transcriptomic interrogation of the murine bone marrow signaling landscape

Self-renewal and differentiation of skeletal stem and progenitor cells (SSPCs) are tightly regulated processes, with SSPC dysregulation leading to progressive bone disease. While the application of single-cell RNA sequencing (scRNAseq) to the bone field has led to major advancements in our understanding of SSPC heterogeneity, stem cells are tightly regulated by their neighboring cells which comprise the bone marrow niche. However, unbiased interrogation of these cells at the transcriptional level within their native niche environment has been challenging. Here, we combined spatial transcriptomics and scRNAseq using a predictive modeling pipeline derived from multiple deconvolution packages in adult mouse femurs to provide an endogenous, in vivo context of SSPCs within the niche. This combined approach localized SSPC subtypes to specific regions of the bone and identified cellular components and signaling networks utilized within the niche. Furthermore, the use of spatial transcriptomics allowed us to identify spatially restricted activation of metabolic and major morphogenetic signaling gradients derived from the vasculature and bone surfaces that establish microdomains within the marrow cavity. Overall, we demonstrate, for the first time, the feasibility of applying spatial transcriptomics to fully mineralized tissue and present a combined spatial and single-cell transcriptomic approach to define the cellular components of the stem cell niche, identify cell‒cell communication, and ultimately gain a comprehensive understanding of local and global SSPC regulatory networks within calcified tissue.

Itaconate-producing neutrophils regulate local and systemic inflammation following trauma

Modulation of the immune response to initiate and halt the inflammatory process occurs both at the site of injury as well as systemically. Due to the evolving role of cellular metabolism in regulating cell fate and function, tendon injuries that undergo normal and aberrant repair were evaluated by metabolic profiling to determine its impact on healing outcomes. Metabolomics revealed an increasing abundance of the immunomodulatory metabolite itaconate within the injury site. Subsequent single-cell RNA-Seq and molecular and metabolomic validation identified a highly mature neutrophil subtype, not macrophages, as the primary producers of itaconate following trauma. These mature itaconate-producing neutrophils were highly inflammatory, producing cytokines that promote local injury fibrosis before cycling back to the bone marrow. In the bone marrow, itaconate was shown to alter hematopoiesis, skewing progenitor cells down myeloid lineages, thereby regulating systemic inflammation. Therapeutically, exogenous itaconate was found to reduce injury-site inflammation, promoting tenogenic differentiation and impairing aberrant vascularization with disease-ameliorating effects. These results present an intriguing role for cycling neutrophils as a sensor of inflammation induced by injury - potentially regulating immune cell production in the bone marrow through delivery of endogenously produced itaconate - and demonstrate a therapeutic potential for exogenous itaconate following tendon injury.

Discoidin domain receptor 2 regulates aberrant mesenchymal lineage cell fate and matrix organization

Extracellular matrix (ECM) interactions regulate both the cell transcriptome and proteome, thereby determining cell fate. Traumatic heterotopic ossification (HO) is a disorder characterized by aberrant mesenchymal lineage (MLin) cell differentiation, forming bone within soft tissues of the musculoskeletal system following traumatic injury. Recent work has shown that HO is influenced by ECM-MLin cell receptor signaling, but how ECM binding affects cellular outcomes remains unclear. Using time course transcriptomic and proteomic analyses, we identified discoidin domain receptor 2 (DDR2), a cell surface receptor for fibrillar collagen, as a key MLin cell regulator in HO formation. Inhibition of DDR2 signaling, through either constitutive or conditional Ddr2 deletion or pharmaceutical inhibition, reduced HO formation in mice. Mechanistically, DDR2 perturbation alters focal adhesion orientation and subsequent matrix organization, modulating Focal Adhesion Kinase (FAK) and Yes1 Associated Transcriptional Regulator and WW Domain Containing Transcription Regulator 1 (YAP/TAZ)-mediated MLin cell signaling. Hence, ECM-DDR2 interactions are critical in driving HO and could serve as a previously unknown therapeutic target for treating this disease process.

A specialized metabolic pathway partitions citrate in hydroxyapatite to impact mineralization of bones and teeth

Citrate is a critical metabolic substrate and key regulator of energy metabolism in mammalian cells. It has been known for decades that the skeleton contains most (>85%) of the body's citrate, but the question of why and how this metabolite should be partitioned in bone has received singularly little attention. Here, we show that osteoblasts use a specialized metabolic pathway to regulate uptake, endogenous production, and the deposition of citrate into bone. Osteoblasts express high levels of the membranous Na+-dependent citrate transporter solute carrier family 13 member 5 (Slc13a5) gene. Inhibition or genetic disruption of Slc13a5 reduced osteogenic citrate uptake and disrupted mineral nodule formation. Bones from mice lacking Slc13a5 globally, or selectively in osteoblasts, showed equivalent reductions in cortical thickness, with similarly compromised mechanical strength. Surprisingly, citrate content in mineral from Slc13a5-/- osteoblasts was increased fourfold relative to controls, suggesting the engagement of compensatory mechanisms to augment endogenous citrate production. Indeed, through the coordinated functioning of the apical membrane citrate transporter SLC13A5 and a mitochondrial zinc transporter protein (ZIP1; encoded by Slc39a1), a mediator of citrate efflux from the tricarboxylic acid cycle, SLC13A5 mediates citrate entry from blood and its activity exerts homeostatic control of cytoplasmic citrate. Intriguingly, Slc13a5-deficient mice also exhibited defective tooth enamel and dentin formation, a clinical feature, which we show is recapitulated in primary teeth from children with SLC13A5 mutations. Together, our results reveal the components of an osteoblast metabolic pathway, which affects bone strength by regulating citrate deposition into mineral hydroxyapatite.

Single-cell mapping of regenerative and fibrotic healing responses after musculoskeletal injury

After injury, a cascade of events repairs the damaged tissue, including expansion and differentiation of the progenitor pool and redeposition of matrix. To guide future wound regeneration strategies, we compared single-cell sequencing of regenerative (third phalangeal element [P3]) and fibrotic (second phalangeal element [P2]) digit tip amputation (DTA) models as well as traumatic heterotopic ossification (HO; aberrant). Analyses point to a common initial response to injury, including expansion of progenitors, redeposition of matrix, and activation of transforming growth factor β (TGF-β) and WNT pathways. Surprisingly, fibrotic P2 DTA showed greater transcriptional similarity to HO than to regenerative P3 DTA, suggesting that gene expression more strongly correlates with healing outcome than with injury type or cell origin. Differential analysis and immunostaining revealed altered activation of inflammatory pathways, such as the complement pathway, in the progenitor cells. These data suggests that common pathways are activated in response to damage but are fine tuned within each injury. Modulating these pathways may shift the balance toward regenerative outcomes.

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Regenerative and fibrotic injuries share common early response mechanisms

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Transcriptomes correlate with healing outcome more than injury type or cell source

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Matrix composition after injury-induced tissue repair is highly injury type dependent

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Inflammatory cascades are activated in immune and mesenchymal cells

NELL1 Regulates the Matrisome to Promote Osteosarcoma Progression

Sarcomas produce an abnormal extracellular matrix (ECM), which in turn provides instructive cues for cell growth and invasion. Neural EGF like-like molecule 1 (NELL1) is a secreted glycoprotein characterized by its nonneoplastic osteoinductive effects, yet it is highly expressed in skeletal sarcomas. Here, we show that genetic deletion of NELL1 markedly reduces invasive behavior across human osteosarcoma (OS) cell lines. NELL1 deletion resulted in reduced OS disease progression, inhibiting metastasis and improving survival in a xenograft mouse model. These observations were recapitulated with Nell1 conditional knockout in mouse models of p53/Rb-driven sarcomagenesis, which reduced tumor frequency and extended tumor-free survival. Transcriptomic and phosphoproteomic analyses demonstrated that NELL1 loss skews the expression of matricellular proteins associated with reduced FAK signaling. Culturing NELL1 knockout sarcoma cells on wild-type OS-enriched matricellular proteins reversed the phenotypic and signaling changes induced by NELL1 deficiency. In sarcoma patients, high expression of NELL1 correlated with decreased overall survival. These findings in mouse and human models suggest that NELL1 expression alters the sarcoma ECM, thereby modulating cellular invasive potential and prognosis. Disruption of NELL1 signaling may represent a novel therapeutic approach to short-circuit sarcoma disease progression.

SIGNIFICANCE

NELL1 modulates the sarcoma matrisome to promote tumor growth, invasion, and metastasis, identifying the matrix-associated protein as an orchestrator of cell-ECM interactions in sarcomagenesis and disease progression.

Spatial transcriptomics reveals metabolic changes underly age-dependent declines in digit regeneration

De novo limb regeneration after amputation is restricted in mammals to the distal digit tip. Central to this regenerative process is the blastema, a heterogeneous population of lineage-restricted, dedifferentiated cells that ultimately orchestrates regeneration of the amputated bone and surrounding soft tissue. To investigate skeletal regeneration, we made use of spatial transcriptomics to characterize the transcriptional profile specifically within the blastema. Using this technique, we generated a gene signature with high specificity for the blastema in both our spatial data, as well as other previously published single-cell RNA-sequencing transcriptomic studies. To elucidate potential mechanisms distinguishing regenerative from non-regenerative healing, we applied spatial transcriptomics to an aging model. Consistent with other forms of repair, our digit amputation mouse model showed a significant impairment in regeneration in aged mice. Contrasting young and aged mice, spatial analysis revealed a metabolic shift in aged blastema associated with an increased bioenergetic requirement. This enhanced metabolic turnover was associated with increased hypoxia and angiogenic signaling, leading to excessive vascularization and altered regenerated bone architecture in aged mice. Administration of the metabolite oxaloacetate decreased the oxygen consumption rate of the aged blastema and increased WNT signaling, leading to enhanced in vivo bone regeneration. Thus, targeting cell metabolism may be a promising strategy to mitigate aging-induced declines in tissue regeneration.

NGF-p75 signaling coordinates skeletal cell migration during bone repair

Bone regeneration following injury is initiated by inflammatory signals and occurs in association with infiltration by sensory nerve fibers. Together, these events are believed to coordinate angiogenesis and tissue reprogramming, but the mechanism of coupling immune signals to reinnervation and osteogenesis is unknown. Here, we found that nerve growth factor (NGF) is expressed following cranial bone injury and signals via p75 in resident mesenchymal osteogenic precursors to affect their migration into the damaged tissue. Mice lacking Ngf in myeloid cells demonstrated reduced migration of osteogenic precursors to the injury site with consequently delayed bone healing. These features were phenocopied by mice lacking p75 in Pdgfra+ osteoblast precursors. Single-cell transcriptomics identified mesenchymal subpopulations with potential roles in cell migration and immune response, altered in the context of p75 deletion. Together, these results identify the role of p75 signaling pathway in coordinating skeletal cell migration during early bone repair.

The Inner Annulus Fibrosus Encroaches on the Nucleus Pulposus in the Injured Mouse Tail Intervertebral Disc

OBJECTIVE

The aim was to identify the source of cells within the center of the abnormal fibrocartilage tissue of the degenerative intervertebral disc after injury.

DESIGN

Cross-breeding of mice with an inducible type II promoter collagen construct (Col2CreER) to Rosa26-TdTomato mice has been shown to result in Cre-recombinase activity and Tomato expression in inner annulus fibrosus cells after tamoxifen injection. To investigate the role of the inner annulus fibrosus in the intervertebral disc injury response, tail intervertebral discs of Col2CreER/tdTomato mice were punctured with a needle and examined 1-4 wks after injury. N-cadherin was examined by immunostaining.

RESULTS

After the injury, the fibrocartilage in the degenerative intervertebral disc consisted of residual diseased nucleus pulposus cells and encroaching inner annulus fibrosus cells. The residual nucleus pulposus cells had lost their epithelial cell-like morphology and instead became oval shaped, with reduced adhesion to neighboring nucleus pulposus cells. This change in cellular morphology coincided with a loss of N-cadherin, which contributes to maintenance of healthy nucleus pulposus cell morphology. As expected, injured tail intervertebral discs showed reduced compressive properties as determined by biomechanical assessments.

CONCLUSIONS

The cellular composition of the degenerative intervertebral disc has been defined here, which is an important step in developing future treatments.

Genomic variants within chromosome 14q32.32 regulate bone mass through MARK3 signaling in osteoblasts

Bone mineral density (BMD) is a highly heritable predictor of osteoporotic fracture. GWAS have identified hundreds of loci influencing BMD, but few have been functionally analyzed. In this study, we show that SNPs within a BMD locus on chromosome 14q32.32 alter splicing and expression of PAR-1a/microtubule affinity regulating kinase 3 (MARK3), a conserved serine/threonine kinase known to regulate bioenergetics, cell division, and polarity. Mice lacking Mark3 either globally or selectively in osteoblasts have increased bone mass at maturity. RNA profiling from Mark3-deficient osteoblasts suggested changes in the expression of components of the Notch signaling pathway. Mark3-deficient osteoblasts exhibited greater matrix mineralization compared with controls that was accompanied by reduced Jag1/Hes1 expression and diminished downstream JNK signaling. Overexpression of Jag1 in Mark3-deficient osteoblasts both in vitro and in vivo normalized mineralization capacity and bone mass, respectively. Together, these findings reveal a mechanism whereby genetically regulated alterations in Mark3 expression perturb cell signaling in osteoblasts to influence bone mass.

SOX9 keeps growth plates and articular cartilage healthy by inhibiting chondrocyte dedifferentiation/osteoblastic redifferentiation

Cartilage is essential throughout vertebrate life. It starts developing in embryos when osteochondroprogenitor cells commit to chondrogenesis, activate a pancartilaginous program to form cartilaginous skeletal primordia, and also embrace a growth-plate program to drive skeletal growth or an articular program to build permanent joint cartilage. Various forms of cartilage malformation and degeneration diseases afflict humans, but underlying mechanisms are still incompletely understood and treatment options suboptimal. The transcription factor SOX9 is required for embryonic chondrogenesis, but its postnatal roles remain unclear, despite evidence that it is down-regulated in osteoarthritis and heterozygously inactivated in campomelic dysplasia, a severe skeletal dysplasia characterized postnatally by small stature and kyphoscoliosis. Using conditional knockout mice and high-throughput sequencing assays, we show here that SOX9 is required postnatally to prevent growth-plate closure and preosteoarthritic deterioration of articular cartilage. Its deficiency prompts growth-plate chondrocytes at all stages to swiftly reach a terminal/dedifferentiated stage marked by expression of chondrocyte-specific (Mgp) and progenitor-specific (Nt5e and Sox4) genes. Up-regulation of osteogenic genes (Runx2, Sp7, and Postn) and overt osteoblastogenesis quickly ensue. SOX9 deficiency does not perturb the articular program, except in load-bearing regions, where it also provokes chondrocyte-to-osteoblast conversion via a progenitor stage. Pathway analyses support roles for SOX9 in controlling TGFβ and BMP signaling activities during this cell lineage transition. Altogether, these findings deepen our current understanding of the cellular and molecular mechanisms that specifically ensure lifelong growth-plate and articular cartilage vigor by identifying osteogenic plasticity of growth-plate and articular chondrocytes and a SOX9-countered chondrocyte dedifferentiation/osteoblast redifferentiation process.

Systemic DKK1 neutralization enhances human adipose-derived stem cell mediated bone repair

Progenitor cells from adipose tissue are able to induce bone repair; however, inconsistent or unreliable efficacy has been reported across preclinical and clinical studies. Soluble inhibitory factors, such as the secreted Wnt signaling antagonists Dickkopf-1 (DKK1), are expressed to variable degrees in human adipose-derived stem cells (ASCs), and may represent a targetable "molecular brake" on ASC mediated bone repair. Here, anti-DKK1 neutralizing antibodies were observed to increase the osteogenic differentiation of human ASCs in vitro, accompanied by increased canonical Wnt signaling. Human ASCs were next engrafted into a femoral segmental bone defect in NOD-Scid mice, with animals subsequently treated with systemic anti-DKK1 or isotype control during the repair process. Human ASCs alone induced significant but modest bone repair. However, systemic anti-DKK1 induced an increase in human ASC engraftment and survival, an increase in vascular ingrowth, and ultimately improved bone repair outcomes. In summary, anti-DKK1 can be used as a method to augment cell-mediated bone regeneration, and could be particularly valuable in the contexts of impaired bone healing such as osteoporotic bone repair.

Lysosomal protein surface expression discriminates fat- from bone-forming human mesenchymal precursor cells

Tissue resident mesenchymal stem/stromal cells (MSCs) occupy perivascular spaces. Profiling human adipose perivascular mesenchyme with antibody arrays identified 16 novel surface antigens, including endolysosomal protein CD107a. Surface CD107a expression segregates MSCs into functionally distinct subsets. In culture, CD107alow cells demonstrate high colony formation, osteoprogenitor cell frequency, and osteogenic potential. Conversely, CD107ahigh cells include almost exclusively adipocyte progenitor cells. Accordingly, human CD107alow cells drove dramatic bone formation after intramuscular transplantation in mice, and induced spine fusion in rats, whereas CD107ahigh cells did not. CD107a protein trafficking to the cell surface is associated with exocytosis during early adipogenic differentiation. RNA sequencing also suggested that CD107alow cells are precursors of CD107ahigh cells. These results document the molecular and functional diversity of perivascular regenerative cells, and show that relocation to cell surface of a lysosomal protein marks the transition from osteo- to adipogenic potential in native human MSCs, a population of substantial therapeutic interest.

Multimodal Targeted Nanoparticle-Based Delivery System for Pancreatic Tumor Imaging in Cellular and Animal Models

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC), which ranks forth on the cancer-related death statistics still is both a diagnostic and a therapeutic challenge. Adenocarcinoma of the exocrine human pancreas originates in most instances from malignant transformation of ductal epithelial cells, alternatively by Acinar-Ductal Metaplasia (ADM). RA96 antibody targets to a mucin M1, according to the more recent nomenclature MUC5AC, an extracellular matrix component excreted by PDAC cells. In this study, we tested the usability of multimodal nanoparticle carrying covalently coupled RA96 Fab fragments for pancreatic tumor imaging.

METHODS

In order to make and evaluate a novel, better targeting, theranostic nanoparticle, iron nanoparticles and the optical dye indocyanin green (ICG) were encapsulated into the cationic sphingomyelin (SM) consisting liposomes. RA-96 Fab fragment was conjugated to the liposomal surface of the nanoparticle to increase tumor homing ability. ICG and iron nanoparticle-encapsulated liposomes were studied in vitro with cells and (i) their visibility in magnetic resonance imaging (MRI), (ii) optical, (iii) Magnetic particle spectroscopy (MPS) and (iv) photoacoustic settings was tested in vitro and also in in vivo models. The targeting ability and MRI and photoacoustic visibility of the RA-96-nanoparticles were first tested in vitro cell models where cell binding and internalization was studied. In in vivo experiments liposomal nanoparticles were injected into a tail vain using an orthotopic pancreatic tumor xenograft model and subcutaneous pancreas cancer cell xenografts bearing mice to determine in vivo targeting abilities of RA-96-conjugated liposomes.

RESULTS

Multimodal liposomes could be detected by MRI, MPS and by photoacoustic imaging in addition to optical imaging showing a wide range of imaging utility. The fluorescent imaging of ICG in pancreatic tumor cells Panc89 and Capan-2 revealed increased association of ICG-encapsulated liposomes carrying RA-96 Fab fragments in vitro compared to the control liposomes without covalently linked RA-96. Fluorescent molecular tomography (FMT) studies showed increased accumulation of the RA96-targeted nanoparticles in the tumor area compared to non-targeted controls in vivo. Similar accumulation in the tumor sites could be seen with liposomal ferric particles in MRI. Fluorescent tumor signal was confirmed by using an intraoperative fluorescent imaging system which showed fluorescent labeling of pancreatic tumors.

CONCLUSION

These results suggest that RA-96-targeted liposomes encapsulating ICG and iron nanoparticles can be used to image pancreatic tumors with a variety of optical and magnetic imaging techniques. Additionally, they might be a suitable drug delivery tool to improve treatment of PDAC patients.

Single cell transcriptomics identifies a unique adipose lineage cell population that regulates bone marrow environment

Bone marrow mesenchymal lineage cells are a heterogeneous cell population involved in bone homeostasis and diseases such as osteoporosis. While it is long postulated that they originate from mesenchymal stem cells, the true identity of progenitors and their in vivo bifurcated differentiation routes into osteoblasts and adipocytes remain poorly understood. Here, by employing large scale single cell transcriptome analysis, we computationally defined mesenchymal progenitors at different stages and delineated their bi-lineage differentiation paths in young, adult and aging mice. One identified subpopulation is a unique cell type that expresses adipocyte markers but contains no lipid droplets. As non-proliferative precursors for adipocytes, they exist abundantly as pericytes and stromal cells that form a ubiquitous 3D network inside the marrow cavity. Functionally they play critical roles in maintaining marrow vasculature and suppressing bone formation. Therefore, we name them marrow adipogenic lineage precursors (MALPs) and conclude that they are a newly identified component of marrow adipose tissue.

Spatial distribution of type II collagen gene expression in the mouse intervertebral disc

Genetic tools such as the Cre-Lox reporter system are powerful aids for tissue-specific cell tracking. For example, it would be useful in examining intervertebral disc (IVD) cell populations in normal and diseased states. A Cre recombinase and its recognition site, loxP have been adapted from the bacteriophage for use in genetic manipulation. The reporter mice used here express the red fluorescent protein, tdTomato with flanking LoxP sites (Rosa26 TdTomato mice). We compared two different Collagen type II (Col2) promoter constructs that drive Cre-recombinase expression in mice: (a) Col2-Cre, which allows constitutive Cre-recombinase expression under the control of the Col2 promoter/enhancer and (b) Col2-CreER, which contains a shorter promoter/enhancer region than Col2-Cre, but has human estrogen binding elements that bind tamoxifen, resulting in Cre-recombinase expression. The goal of the study is to characterize Cre-recombinase distribution pattern in Col2-Cre and Col2-CreER mice using tdTomato as reporter in the spine. The expression patterns of these two mice were further compared with Col2 gene expression in the native mouse NP and AF tissues by real-time PCR. We crossed Col2-Cre mice or Col2-CreER mice with the tdTomato reporter mice, and compared the tdTomato expression patterns. Col2-CreER/tdTomato mice were injected with tamoxifen at postnatal day 7 to activate the Cre-recombinase. TdTomato in the constitutively active Col2-Cre mice was detected in the nucleus pulposus (NP), the entire annulus fibrosus (AF), and in cartilaginous endplate and growth plate cells in the lower lumbar and coccygeal spine. In contrast, when Col2-CreER activity was induced by tamoxifen at P7, tdTomato was limited to the inner AF, and was absent from the NP. We have described the differences in Col2 reporter gene expression, in Col2-Cre/tdTomato and Col2-Cre-ER/tdTomato mouse IVD. The information provided here will help to guide future investigations of IVD biology.

Activation of Skeletal Stem and Progenitor Cells for Bone Regeneration Is Driven by PDGFRβ Signaling

Bone repair and regeneration critically depend on the activation and recruitment of osteogenesis-competent skeletal stem and progenitor cells (SSPCs). Yet, the origin and triggering cues for SSPC propagation and migration remain largely elusive. Through bulk and single-cell transcriptome profiling of fetal osterix (Osx)-expressing cells, followed by lineage mapping, cell tracing, and conditional mouse mutagenesis, we here identified PDGF-PDGFRβ signaling as critical functional mediator of SSPC expansion, migration, and angiotropism during bone repair. Our data show that cells marked by a history of Osx expression, including those arising in fetal or early postnatal periods, represent or include SSPCs capable of delivering all the necessary differentiated progeny to repair acute skeletal injuries later in life, provided that they express functional PDGFRβ. Mechanistically, MMP-9 and VCAM-1 appear to be involved downstream of PDGF-PDGFRβ. Our results reveal considerable cellular dynamism in the skeletal system and show that activation and recruitment of SSPCs for bone repair require functional PDGFRβ signaling.

Universal membrane-labeling combined with expression of Katushka far-red fluorescent protein enables non-invasive dynamic and longitudinal quantitative 3D dual-color fluorescent imaging of multiple bacterial strains in mouse intestine

BACKGROUND

The human gastrointestinal (GI) tract microbiota has been a subject of intense research throughout the 3rd Millennium. Now that a general picture about microbiota composition in health and disease is emerging, questions about factors determining development of microbiotas with specific community structures will be addressed. To this end, usage of murine models for colonization studies remains crucial. Optical in vivo imaging of either bioluminescent or fluorescent bacteria is the basis for non-invasive detection of intestinal colonization of bacteria. Although recent advances in in vivo fluorescence imaging have overcome many limitations encountered in bioluminescent imaging of intestinal bacteria, such as requirement for live cells, high signal attenuation and 2D imaging, the method is still restricted to bacteria for which molecular cloning tools are available.

RESULTS

Here, we present usage of a lipophilic fluorescent dye together with Katushka far-red fluorescent protein to establish a dual-color in vivo imaging system to monitor GI transit of different bacterial strains, suitable also for strains resistant to genetic labeling. Using this system, we were able to distinguish two different E. coli strains simultaneously and show their unique transit patterns. Combined with fluorescence molecular tomography, these distinct strains could be spatially and temporally resolved and quantified in 3D.

CONCLUSIONS

Developed novel method for labeling microbes and identify their passage both temporally and spatially in vivo makes now possible to monitor all culturable bacterial strains, also those that are resistant to conventional genetic labeling.

Periosteal Mesenchymal Progenitor Dysfunction and Extraskeletally-Derived Fibrosis Contribute to Atrophic Fracture Nonunion

Atrophic nonunion represents an extremely challenging clinical dilemma for both physicians and fracture patients alike, but its underlying mechanisms are still largely unknown. Here, we established a mouse model that recapitulates clinical atrophic nonunion through the administration of focal radiation to the long bone midshaft 2 weeks before a closed, semistabilized, transverse fracture. Strikingly, fractures in previously irradiated bone showed no bony bridging with a 100% nonunion rate. Radiation triggered distinct repair responses, separated by the fracture line: a less robust callus formation at the proximal side (close to the knee) and bony atrophy at the distal side (close to the ankle) characterized by sustained fibrotic cells and type I collagen-rich matrix. These fibrotic cells, similar to human nonunion samples, lacked osteogenic and chondrogenic differentiation and exhibited impaired blood vessel infiltration. Mechanistically, focal radiation reduced the numbers of periosteal mesenchymal progenitors and blood vessels and blunted injury-induced proliferation of mesenchymal progenitors shortly after fracture, with greater damage particularly at the distal side. In culture, radiation drastically suppressed proliferation of periosteal mesenchymal progenitors. Radiation did not affect hypoxia-induced periosteal cell chondrogenesis but greatly reduced osteogenic differentiation. Lineage tracing using multiple reporter mouse models revealed that mesenchymal progenitors within the bone marrow or along the periosteal bone surface did not contribute to nonunion fibrosis. Therefore, we conclude that atrophic nonunion fractures are caused by severe damage to the periosteal mesenchymal progenitors and are accompanied by an extraskeletal, fibro-cellular response. In addition, we present this radiation-induced periosteal damage model as a new, clinically relevant tool to study the biologic basis of therapies for atrophic nonunion. © 2018 American Society for Bone and Mineral Research.

Periarticular Mesenchymal Progenitors Initiate and Contribute to Secondary Ossification Center Formation During Mouse Long Bone Development

Long bone development involves the embryonic formation of a primary ossification center (POC) in the incipient diaphysis followed by postnatal development of a secondary ossification center (SOC) at each epiphysis. Studies have elucidated major basic mechanisms of POC development, but relatively little is known about SOC development. To gain insights into SOC formation, we used Col2-Cre Rosa-tdTomato (Col2/Tomato) reporter mice and found that their periarticular region contained numerous Tomato-positive lineage cells expressing much higher Tomato fluorescence (termed Tomato^H ) than underlying epiphyseal chondrocytes (termed Tomato^L ). With time, the Tomato^H cells became evident at the SOC invagination site and cartilage canal, increased in number in the expanding SOC, and were present as mesenchymal lineage cells in the subchondral bone. These data were verified in two mouse lineage tracing models, Col2-CreER Rosa-tdTomato and Gli1-CreER Rosa-tdTomato. In vitro tests showed that the periarticular Tomato^H cells from Col2/Tomato mice contained mesenchymal progenitors with multidifferentiation abilities. During canal initiation, the cells expressed vascular endothelial growth factor (VEGF) and migrated into epiphyseal cartilage ahead of individual or clusters of endothelial cells, suggesting a unique role in promoting vasculogenesis. Later during SOC expansion, chondrocytes in epiphyseal cartilage expressed VEGF, and angiogenic blood vessels preceded Tomato^H cells. Gene expression analyses of microdissected samples revealed upregulation of MMPs in periarticular cells at the invagination site and suggested potential roles for novel kinase and growth factor signaling pathways in regulating SOC canal initiation. In summary, our data indicate that the periarticular region surrounding epiphyseal cartilage contains mesenchymal progenitors that initiate SOC development and form subchondral bone. Stem Cells 2019;37:677-689.

Analysis of short-term treatment with the phosphodiesterase type 5 inhibitor tadalafil on long bone development in young rats

Cyclic GMP (cGMP) is an important intracellular regulator of endochondral bone growth and skeletal remodeling. Tadalafil, an inhibitor of the phosphodiesterase (PDE) type 5 (PDE5) that specifically hydrolyzes cGMP, is increasingly used to treat children with pulmonary arterial hypertension (PAH), but the effect of tadalafil on bone growth and strength has not been previously investigated. In this study, we first analyzed the expression of transcripts encoding PDEs in primary cultures of chondrocytes from newborn rat epiphyses. We detected robust expression of PDE5 as the major phosphodiesterase hydrolyzing cGMP. Time-course experiments showed that C-type natriuretic peptide increased intracellular levels of cGMP in primary chondrocytes with a peak at 2 min, and in the presence of tadalafil the peak level of intracellular cGMP was 37% greater ( P < 0.01) and the decline was significantly attenuated. Next, we treated 1-mo-old Sprague Dawley rats with vehicle or tadalafil for 3 wk. Although 10 mg·kg^-1·day^-1 tadalafil led to a significant 52% ( P < 0.01) increase in tissue levels of cGMP and a 9% reduction ( P < 0.01) in bodyweight gain, it did not alter long bone length, cortical or trabecular bone properties, and histological features. In conclusion, our results indicate that PDE5 is highly expressed in growth plate chondrocytes, and short-term tadalafil treatment of growing rats at doses comparable to those used in children with PAH has neither obvious beneficial effect on long bone growth nor any observable adverse effect on growth plate structure and trabecular and cortical bone structure.

Tracking the Progression of Osteolytic and Osteosclerotic Lesions in Mice Using Serial In Vivo μCT: Applications to the Assessment of Bisphosphonate Treatment Efficacy

The metastasis of tumor cells to bone can lead to osteolytic and osteosclerotic lesions, which cause severe, highly-localized bone destruction and abnormal bone apposition, respectively. Accurate quantification of lesion progression is critical to understand underlying mechanisms and assess treatment efficacy; however, standard structural parameters may be insensitive to local changes. We developed methods to quantify osteolytic and osteosclerotic lesions using micro-computed tomography (μCT) within in vivo mouse datasets. Two Balb/c nude datasets were used: (i) bone-homing MDA-MB-231 (osteolytic) cells injected into the left ventricle, treatment with alendronate or vehicle, and weekly μCT (proximal tibia) for 4 weeks, and (ii) MCF7 (osteosclerotic) cells injected into the right tibia and weekly μCT over 12 weeks. After registering images to baseline, osteolytic lesion volume was determined by summing all baseline bone voxels at distances greater than a threshold (150 μm) from the nearest follow-up. Osteosclerotic lesions were determined by measuring the distance from each follow-up surface voxel to the nearest baseline surface and calculating the standard deviation of distance values (SDDT) of the surrounding voxels. Bone mineral density (BMD), bone volume density (BV/TV), and separation (Sp) were determined for comparison. Osteolytic lesions were observed 1 week after tumor cell injection; however, no corresponding BV/TV losses or Sp increases were observed, indicating that standard parameters were unable to detect early metastatic changes. Lesion volume was smaller in the alendronate versus control group (15.0%, p = 0.004 and 18.6%, p = 0.002 of control lesion volume at weeks 3 and 4, respectively). In the osteosclerotic dataset, increased SDDT was observed following injection, providing a potential new measure of osteosclerotic bone apposition. These data show that quantification of local structural change with serial μCT may overcome the limitations of standard mineral and microstructural parameters, and successfully separates metastatic and normal bone turnover. © 2017 American Society for Bone and Mineral Research.

Vhl deletion in osteoblasts boosts cellular glycolysis and improves global glucose metabolism

The skeleton has emerged as an important regulator of systemic glucose homeostasis, with osteocalcin and insulin representing prime mediators of the interplay between bone and energy metabolism. However, genetic evidence indicates that osteoblasts can influence global energy metabolism through additional, as yet unknown, mechanisms. Here, we report that constitutive or postnatally induced deletion of the hypoxia signaling pathway component von Hippel-Lindau (VHL) in skeletal osteolineage cells of mice led to high bone mass as well as hypoglycemia and increased glucose tolerance, not accounted for by osteocalcin or insulin. In vitro and in vivo data indicated that Vhl-deficient osteoblasts displayed massively increased glucose uptake and glycolysis associated with upregulated HIF-target gene expression, resembling the Warburg effect that typifies cancer cells. Overall, the glucose consumption by the skeleton was increased in the mutant mice, as revealed by 18F-FDG radioactive tracer experiments. Moreover, the glycemia levels correlated inversely with the level of skeletal glucose uptake, and pharmacological treatment with the glycolysis inhibitor dichloroacetate (DCA), which restored glucose metabolism in Vhl-deficient osteogenic cells in vitro, prevented the development of the systemic metabolic phenotype in the mutant mice. Altogether, these findings reveal a novel link between cellular glucose metabolism in osteoblasts and whole-body glucose homeostasis, controlled by local hypoxia signaling in the skeleton.

Loading-Induced Reduction in Sclerostin as a Mechanism of Subchondral Bone Plate Sclerosis in Mouse Knee Joints During Late-Stage Osteoarthritis

OBJECTIVE

To establish an unbiased, 3-dimensional (3-D) approach that quantifies subchondral bone plate (SBP) changes in mouse joints, and to investigate the mechanism that mediates SBP sclerosis at a late stage of osteoarthritis (OA).

METHODS

A new micro-computed tomography (micro-CT) protocol was developed to characterize the entire thickness of the SBP in the distal femur of a normal mouse knee. Four mouse models of severe joint OA were generated: cartilage-specific Egfr-knockout (Egfr-CKO) mice at 2 months after surgical destabilization of the medial meniscus (DMM), Egfr-CKO mice with aging-related spontaneous OA, wild-type (WT) mice at 10 months after DMM, and WT mice at 14 weeks after DMM plus hemisectomy of the meniscus (DMMH) surgery. As an additional model, mice with knockout of the sclerostin gene (Sost-KO) were subjected to DMMH surgery. Knee joints were examined by micro-CT, histology, and immunohistochemical analyses.

RESULTS

Examination of the mouse distal femur by 3-D micro-CT revealed a positive correlation between SBP thickness and the loading status in normal knees. In all 4 mouse models of late-stage OA, SBP sclerosis was restricted to the areas under severely eroded articular cartilage. This was accompanied by elevated bone formation at the bone marrow side of the SBP and a drastic reduction in the levels of sclerostin in osteocytes within the SBP. Unlike in WT mice, no further increase in the thickness of the SBP was observed in response to DMMH in Sost-KO mice.

CONCLUSION

Since focal stress on the SBP underlying sites of cartilage damage increases during late stages of OA, these findings establish mechanical loading-induced attenuation of sclerostin expression and elevation of bone formation along the SBP surface as the major mechanisms characterizing subchondral bone phenotypes associated with severe late-stage OA in mice.

Pharmacologically Inactive Bisphosphonates as an Alternative Strategy for Targeting Osteoclasts: In Vivo Assessment of 5-Fluorodeoxyuridine-Alendronate in a Preclinical Model of Breast Cancer Bone Metastases

Bisphosphonates have effects that are antiresorptive, antitumor, and antiapoptotic to osteoblasts and osteocytes, but an effective means of eliciting these multiple activities in the treatment of bone metastases has not been identified. Antimetabolite-bisphosphonate conjugates have potential for improved performance as a class of bone-specific antineoplastic drugs. The primary objective of the study was to determine whether an antimetabolite-bisphosphonate conjugate will preserve bone formation concomitant with antiresorptive and antitumor activity. 5-FdU-ale, a highly stable conjugate between the antimetabolite 5-fluoro-2'-deoxyuridine and the bisphosphonate alendronate, was tested for its therapeutic efficacy in a mouse model of MDA-MB231 breast cancer bone metastases. In vitro testing revealed osteoclasts to be highly sensitive to 5-FdU-ale. In contrast, osteoblasts had significantly reduced sensitivity. Tumor cells were resistant in vitro but in vivo tumor burden was nevertheless significantly reduced compared with untreated mice. Sensitivity to 5-FdU-ale was not mediated through inhibition of farnesyl diphosphate synthase activity, but cell cycle arrest was observed. Although serum tartrate-resistant acid phosphatase (TRAP) levels were greatly reduced by both drugs, there was no significant decrease in the serum bone formation marker osteocalcin with 5-FdU-ale treatment. In contrast, there was more than a fivefold decrease in serum osteocalcin levels with alendronate treatment (p < 0.001). This finding is supported by time-lapse micro-computed tomography analyses, which revealed bone formation volume to be on average 1.6-fold higher with 5-FdU-ale treatment compared with alendronate (p < 0.001). We conclude that 5-FdU-ale, which is a poor prenylation inhibitor but maintains potent antiresorptive activity, does not reduce bone formation and has cytostatic antitumor efficacy. These results document that conjugation of an antimetabolite with bisphosphonates offers flexibility in creating potent bone-targeting drugs with cytostatic, bone protection properties that show limited nephrotoxicity. This unique class of drugs may offer distinct advantages in the setting of targeted adjuvant therapy and chemoprevention of bone diseases. © 2016 American Society for Bone and Mineral Research.

Synchronic inverse seasonal rhythmus of energy density of food intake and sleep quality: a contribution to chrono-nutrition from a Polish adult population

BACKGROUND/OBJECTIVES

There is evidence which suggests that sleep behavior and dietary intake are interlinked. Thus, we investigated whether a seasonal rhythm in food-energy density exists, and how this relates to quality of sleep.

SUBJECTS/METHODS

Two hundred and thirty adult volunteers were investigated across the four seasons. Anthropometrical measurements were obtained and The Pittsburgh Sleep Quality Index was used for an assessment of sleep quality and disturbances. The dietary intake was evaluated using a 24 h dietary recall. Generalized estimating equations were used to estimate seasonal changes in energy density and sleep quality, as well as the association of energy density with sleep quality. All analyses were adjusted for age, sex, education, occupation and shift-work.

RESULTS

Mean food energy density was significantly higher in winter as compared with other seasons (P<0.05), although no seasonal variations were observed in macronutrient intake (fat and protein). Overall, the sleep quality was low (score value >5) in all seasons, with the lowest quality occurring in winter and the highest in spring (P<0.05). The components of sleep quality score showed that winter had statistically (P<0.05) poorer subjective sleep quality, sleep latency and sleep disturbances, but lower daytime dysfunction compared with spring and summer. After adjusting for seasonal effects (correlated outcome data) and shift-work, energy density was found to be inversely associated (P<0.0001) with sleep quality.

CONCLUSIONS

An inverse association between seasonal fluctuation of food energy density and sleep quality was found with winter time, associated with the intake of higher energy dense food products and the lowest sleep quality.

Quality of life, depression and dietary intake in Obstructive Sleep Apnea patients

Background

The aim of this study was to analyze the association between depression, quality of life and dietary intake in newly diagnosed Obstructive Sleep Apnea (OSA) patients.

Methods

From 153 eligible patients suffering from sleep disturbances, 64 met inclusion and exclusion criteria. The polysomnography was used for OSA diagnosis. The quality of life (QOL) was assessed by WHOQOL-BREF questionnaire, self-reported chronotype by morningness-eveningness questionnaire and level of depression by Beck’s Depression Inventory. Blood pressure and parameters of glucose and lipid metabolism were assessed by routine methods. The dietary intake was evaluated by 24-hr dietary recalls.

Results

Significantly negative associations were found between depression inventory and QOL. Better QOL for physical health and social relationships was observed in the “definitely morning” chronotype. The “morning type” of patients was positively related to the intake of fat, monounsaturated fatty acids and vitamin B12. Correlations between QOL and diastolic blood pressure, HDL-cholesterol, TG, fasting glucose, as well as protein and vitamin B6 intake were found.

Conclusions

In conclusion, both chornotype and depression influence QOL in OSA patients where morning type is associated with better physical health and social relationships and increase in depression index deteriorate physical health, psychological and social relationship QOL domains. QOL as well as depression and chornotype are also influenced by selected cardio-metabolic factors and dietary intake.

TRAIL-R2 promotes skeletal metastasis in a breast cancer xenograft mouse model

Despite improvements in detection, surgical approaches and systemic therapies, breast cancer remains typically incurable once distant metastases occur. High expression of TRAIL-R2 was found to be associated with poor prognostic parameters in breast cancer patients, suggesting an oncogenic function of this receptor. In the present study, we aimed to determine the impact of TRAIL-R2 on breast cancer metastasis. Using an osteotropic variant of MDA-MB-231 breast cancer cells, we examine the effects of TRAIL-R2 knockdown in vitro and in vivo. Strikingly, in addition to the reduced levels of the proliferation-promoting factor HMGA2 and corresponding inhibition of cell proliferation, knockdown of TRAIL-R2 increased the levels of E-Cadherin and decreased migration. In vivo, these cells were strongly impaired in their ability to form bone metastases after intracardiac injection. Evaluating possible underlying mechanisms revealed a strong downregulation of CXCR4, the receptor for the chemokine SDF-1 important for homing of cancers cells to the bone. In accordance, cell migration towards SDF-1 was significantly impaired by TRAIL-R2 knockdown. Conversely, overexpression of TRAIL-R2 upregulated CXCR4 levels and enhanced SDF-1-directed migration. We therefore postulate that inhibition of TRAIL-R2 expression could represent a promising therapeutic strategy leading to an effective impairment of breast cancer cell capability to form skeletal metastases.

In vitro and in vivo toxicity of 5-FdU-alendronate, a novel cytotoxic bone-seeking duplex drug against bone metastasis

BACKGROUND

Bone remains one of the most common anatomic sites for cancer metastases, and the limited therapeutic options aggravate cancer-related morbidity and mortality in multiple malignancies. The covalent conjugation of the amino-bisphosphonate alendronate (ale) with the antimetabolite 5-fluoro-2'-desoxyuridine (5-FdU) results in N(4)-(butyl-(4-hydroxy-4-phosphono)phosphate)-5-fluoro-2'-desoxyuridine (5-FdU-alendronat, 5-FdU-ale), an effective, novel bone-targeting duplex drug directed against skeletal cancer manifestations.

METHODS

In vitro cytotoxicity of ale, 5-FdU or 5-FdU-ale was measured with Alamar Blue and MUH cell viability assays in 14 malignant melanoma, multiple myeloma, bone marrow-derived stromal cell and osteoblast-like cell lines. In vivo toxicity was evaluated using the chicken embryo assay and evaluation of nephrotoxicity and the systemic toxicity in Balb/c nude mice. The effect of 5-FdU-ale on osteoclast was evaluated with Balb/c nude mice in a metastatic breast cancer mouse model.

RESULTS

A cell line-specific, dose-related cytotoxicity was observed for 5-FdU-ale in all cancer cell lines tested, which was significantly less toxic than 5-FdU alone when compared to the benign osteoblasts or stromal cells. The embryotoxicity of 5-FdU-ale was significantly less than that of the parental drugs alendronate or 5-FdU. 5-FdU-ale showed no signs of unwanted side effects, weight loss or nephrotoxicity in mice. In a bone metastasis mouse model, 5-FdU-ale reduced the number of tumor-associated osteoclasts.

CONCLUSION

The coupling of an amino-bisphosphonate with an antimetabolite via an N-alkyl-bonding offers a new strategy for the preparation of amino-bisphosphonates conjugates with a cancer cell-specific, efficacious cytotoxic bone-targeting potential along with a reduced systemic toxicity. The innovative duplex drug 5-FdU-ale therefore warrants further clinical investigation.

Utilizing time-lapse micro-CT-correlated bisphosphonate binding kinetics and soft tissue-derived input functions to differentiate site-specific changes in bone metabolism in vivo

The turnover of bone is a tightly regulated process between bone formation and resorption to ensure skeletal homeostasis. This process differs between bone types, with trabecular bone often associated with higher turnover than cortical bone. Analyses of bone by micro-computed tomography (micro-CT) reveal changes in structure and mineral content, but are limited in the study of metabolic activity at a single time point, while analyses of serum markers can reveal changes in bone metabolism, but cannot delineate the origin of any aberrant findings. To obtain a site-specific assessment of bone metabolic status, bisphosphonate binding kinetics were utilized. Using a fluorescently-labeled bisphosphonate, we show that early binding kinetics monitored in vivo using fluorescent molecular tomography (FMT) can monitor changes in bone metabolism in response to bone loss, stimulated by ovariectomy (OVX), or bone gain, resulting from treatment with the anabolic bone agent parathyroid hormone (PTH), and is capable of distinguishing different, metabolically distinct skeletal sites. Using time-lapse micro-CT, longitudinal bone turnover was quantified. The spine showed a significantly greater percent resorbing volume and surface in response to OVX, while mice treated with PTH showed significantly greater resorbing volume per bone surface in the spine and significantly greater forming surfaces in the knee. Correlation studies between binding kinetics and micro-CT suggest that forming surfaces, as assessed by time-lapse micro-CT, are preferentially reflected in the rate constant values while forming and resorbing bone volumes primarily affect plateau values. Additionally, we developed a blood pool correction method which now allows for quantitative multi-compartment analyses to be conducted using FMT. These results further expand our understanding of bisphosphonate binding and the use of bisphosphonate binding kinetics as a tool to monitor site-specific changes in bone metabolism in vivo.

An ancestral role in peroxisome assembly is retained by the divisional peroxin Pex11 in the yeast Yarrowia lipolytica

The peroxin Pex11 has a recognized role in peroxisome division. Pex11p remodels and elongates peroxisomal membranes prior to the recruitment of dynamin-related GTPases that act in membrane scission to divide peroxisomes. We performed a comprehensive comparative genomics survey to understand the significance of the evolution of the Pex11 protein family in yeast and other eukaryotes. Pex11p is highly conserved and ancestral, and has undergone numerous lineage-specific duplications, whereas other Pex11 protein family members are fungal-specific innovations. Functional characterization of the in-silico-predicted Pex11 protein family members of the yeast Yarrowia lipolytica, i.e. Pex11p, Pex11Cp and Pex11/25p, demonstrated that Pex11Cp and Pex11/25p have a role in the regulation of peroxisome size and number characteristic of Pex11 protein family members. Unexpectedly, deletion of PEX11 in Y. lipolytica produces cells that lack morphologically identifiable peroxisomes, mislocalize peroxisomal matrix proteins and preferentially degrade peroxisomal membrane proteins, i.e. they exhibit the classical pex mutant phenotype, which has not been observed previously in cells deleted for the PEX11 gene. Our results are consistent with an unprecedented role for Pex11p in de novo peroxisome assembly.

Binding kinetics of a fluorescently labeled bisphosphonate as a tool for dynamic monitoring of bone mineral deposition in vivo

Bone mineral deposition during the modeling of new bone and remodeling of old bone can be perturbed by several pathological conditions, including osteoporosis and skeletal metastases. A site-specific marker depicting the dynamics of bone mineral deposition would provide insight into skeletal disease location and severity, and prove useful in evaluating the efficacy of pharmacological interventions. Fluorescent labels may combine advantages of both radioisotope imaging and detailed microscopic analyses. The purpose of this study was to determine if the fluorescent bisphosphonate OsteoSense could detect localized changes in bone mineral deposition in established mouse models of accelerated bone loss (ovariectomy) (OVX) and anabolic bone gain resulting from parathyroid hormone (PTH) treatment. We hypothesized that the early rate of binding, as well as the total amount of bisphosphonate, which binds over long periods of time, could be useful in evaluating changes in bone metabolism. Evaluation of the kinetic uptake of bisphosphonates revealed a significant reduction in both the rate constant and plateau binding after OVX, whereas treatment with PTH resulted in a 36-fold increase in the bisphosphonate binding rate constant compared with untreated OVX controls. Localization of bisphosphonate binding revealed initial binding at sites of ossification adjacent to the growth plate and, to a lesser extent, along more distal trabecular and cortical elements. Micro-computed tomography (CT) was used to confirm that initial bisphosphonate binding is localized to sites of low tissue mineral density, associated with new bone mineral deposition. Our results suggest monitoring binding kinetics based on fluorescently labeled bisphosphonates represents a highly sensitive, site-specific method for monitoring changes in bone mineral deposition with the potential for translation into human applications in osteoporosis and bone metastatic processes and their treatment.

Mesenchymal stem cell contact promotes CCN1 splicing and transcription in myeloma cells

CCN family member 1 (CCN1), also known as cysteine-rich angiogenic inducer 61 (CYR61), belongs to the extracellular matrix-associated CCN protein family. The diverse functions of these proteins include regulation of cell migration, adhesion, proliferation, differentiation and survival/apoptosis, induction of angiogenesis and cellular senescence. Their functions are partly overlapping, largely non-redundant, cell-type specific, and depend on the local microenvironment. To elucidate the role of CCN1 in the crosstalk between stromal cells and myeloma cells, we performed co-culture experiments with primary mesenchymal stem cells (MSC) and the interleukin-6 (IL-6)-dependent myeloma cell line INA-6. Here we show that INA-6 cells display increased transcription and induction of splicing of intron-retaining CCN1 pre-mRNA when cultured in contact with MSC. Protein analyses confirmed that INA-6 cells co-cultured with MSC show increased levels of CCN1 protein consistent with the existence of a pre-mature stop codon in intron 1 that abolishes translation of unspliced mRNA. Addition of recombinant CCN1-Fc protein to INA-6 cells was also found to induce splicing of CCN1 pre-mRNA in a concentration-dependent manner. Only full length CCN1-Fc was able to induce mRNA splicing of all introns, whereas truncated recombinant isoforms lacking domain 4 failed to induce intron splicing. Blocking RGD-dependent integrins on INA-6 cells resulted in an inhibition of these splicing events. These findings expand knowledge on splicing of the proangiogenic, matricellular factor CCN1 in the tumor microenvironment. We propose that contact with MSC-derived CCN1 leads to splicing and enhanced transcription of CCN1 which further contributes to the translation of angiogenic factor CCN1 in myeloma cells, supporting tumor viability and myeloma bone disease.

Dynein light chain interaction with the peroxisomal import docking complex modulates peroxisome biogenesis in yeast

Dynein is a large macromolecular motor complex that moves cargo along microtubules. A motor-independent role for the light chain of dynein, Dyn2p, in peroxisome biology in Saccharomyces cerevisiae was suggested from its interaction with Pex14p, a component of the peroxisomal matrix protein import docking complex. Here we show that cells of the yeast Yarrowia lipolytica deleted for the gene encoding the homologue of Dyn2p are impaired in peroxisome function and biogenesis. These cells exhibit compromised growth on medium containing oleic acid as the carbon source, the metabolism of which requires functional peroxisomes. Their peroxisomes have abnormal morphology, atypical matrix protein localization, and an absence of proteolytic processing of the matrix enzyme thiolase, which normally occurs upon its import into the peroxisome. We also show physical and genetic interactions between Dyn2p and members of the docking complex, particularly Pex17p. Together, our results demonstrate a role for Dyn2p in the assembly of functional peroxisomes and provide evidence that Dyn2p acts in cooperation with the peroxisomal matrix protein import docking complex to effect optimal matrix protein import.

Evaluation of the matrix effect of thermophilic anaerobic digestion on inactivation of infectious laryngotracheitis virus using real-time PCR and viral cell culture

The matrix effect of the thermophilic anaerobic digestion (TAD) process on inactivation of infectious laryngotracheitis virus (ILTV) was evaluated. Viral cell culture and real-time PCR were used for assessing removal of the viral infectivity and degradation of viral DNA, respectively. Results showed that the TAD-derived matrix alone can inactivate the virus and destroy the nucleic acid helix core of ILTV in a time-and- dose-dependent manner. No cytopathogenic effect (CPE) was observed in the cells exposed to ILTV pre-treated with TAD matrix for 1.5h in experiment 1 and for 16h in experiment 2. There was a significant statistical difference between TAD matrix treated and non-treated cultures (p<0.001, Chi-test). Amplifiable ILT viral DNA was reduced 2.27 log by 1.5h-treatment and was not present by 16h-treatment with TAD matrix, indicating complete viral DNA fragmentation. The TAD process is an environmentally friendly way for disposing of poultry biowaste and carcasses.

The peroxin Pex34p functions with the Pex11 family of peroxisomal divisional proteins to regulate the peroxisome population in yeast

Peroxisomes are ubiquitous organelles involved in diverse metabolic processes, most notably the metabolism of lipids and the detoxification of reactive oxygen species. Peroxisomes are highly dynamic and change in size and number in response to both intra- and extracellular cues. In the yeast Saccharomyces cerevisiae, peroxisome growth and division are controlled by both the differential import of soluble matrix proteins and a specialized divisional machinery that includes peroxisome-specific factors, such as members of the Pex11 protein family, and general organelle divisional factors, such as the dynamin-related protein Vps1p. Global yeast two-hybrid analyses have demonstrated interactions between the product of the S. cerevisiae gene of unknown function, YCL056c, and Pex proteins involved in peroxisome biogenesis. Here we show that the protein encoded by YCL056c, renamed Pex34p, is a peroxisomal integral membrane protein that acts independently and also in concert with the Pex11 protein family members Pex11p, Pex25p, and Pex27p to control the peroxisome populations of cells under conditions of both peroxisome proliferation and constitutive peroxisome division. Yeast two-hybrid analysis showed that Pex34p interacts physically with itself and with Pex11p, Pex25p, and Pex27p but not with Vps1p. Pex34p can act as a positive effector of peroxisome division as its overexpression leads to increased numbers of peroxisomes in wild type and pex34Δ cells. Pex34p requires the Pex11 family proteins to promote peroxisome division. Our discovery of Pex34p as a protein involved in the already complex control of peroxisome populations emphasizes the necessity of cells to strictly regulate their peroxisome populations to be able to respond appropriately to changing environmental conditions.