Glucocorticoid-Induced Bone Fragility Is Prevented in Female Mice by Blocking Pyk2/Anoikis Signaling

Generation of BT-Amide, a Bone-Targeted Pyk2 Inhibitor, Effective via Oral Administration, for the Prevention of Glucocorticoid-Induced Bone Loss

Glucocorticoid-induced osteoporosis (GIOP) is the leading cause of iatrogenic osteoporosis due to the widespread clinical use of glucocorticoids (GC) as immunosuppressants. Previous research identified the proline-rich tyrosine kinase 2, Pyk2, as a critical mediator of GC-induced bone loss, and that blocking Pyk2 could protect the skeleton from adverse GC actions. However, systemic administration of current Pyk2 inhibitors causes harmful side effects, such as skin lesions. To address this, we developed bone-targeted (BT) Pyk2 inhibitors by conjugating them with bisphosphonates (BP), ensuring adherence to the bone matrix and reducing impact on noncalcified tissues. We synthesized BT-Amide by linking a derivative of TAE-226, a Pyk2 inhibitor, with alendronic acid. Oral administration (gavage) of BT-Amide prevented GC-induced bone loss in mice without causing skin lesions, or elevation of any organ toxicity markers. These findings introduce BT-Amide as the first orally effective bone-targeted Pyk2 inhibitor for preventing GC-induced bone loss while minimizing off-target effects.

Pharmacologic or genetic interference with atrogene signaling protects against glucocorticoid-induced musculoskeletal and cardiac disease

Despite their beneficial actions as immunosuppressants, glucocorticoids (GC) have devastating effects on the musculoskeletal and cardiac systems, as long-term treated patients exhibit high incidence of falls, bone fractures, and cardiovascular events. Herein, we show that GC upregulate simultaneously in bone, skeletal muscle, and the heart the expression of E3 ubiquitin ligases (atrogenes), known to stimulate the proteasomal degradation of proteins. Activation of vitamin D receptor (VDR) signaling with the VDR ligands calcitriol or eldecalcitol prevented GC-induced atrogene upregulation in vivo and ex vivo in bone/muscle organ cultures and preserved tissue structure/mass and function of the 3 tissues in vivo. Direct pharmacologic inhibition of the proteasome with carfilzomib also conferred musculoskeletal protection. Genetic loss of the atrogene MuRF1-mediated protein ubiquitination in ΔRING mice afforded temporary or sustained protection from GC excess in bone or skeletal and heart muscle. We concluded that the atrogene pathway downstream of MuRF1 underlies GC action in bone, muscle, and the heart, and it can be pharmacologically or genetically targeted to confer protection against the damaging actions of GC simultaneously in the 3 tissues.

Discovery of Novel Antiosteoporosis Leads with Bone Resorption Inhibition and Anabolic Promotion through a Chemotype-Assembly Approach

Developing a dual-efficiency agent with antiresorptive and anabolic applications is a promising strategy for treating osteoporosis. This study reports the discovery of dual antiosteoporosis agents via a chemotype-assembly approach. Chemotype analysis identified 12 antiresorptive and 12 anabolic chemotypes and 7 dual-function chemotype-assembly rules. Based on these assembly rules, a dual-functional compound S24 was discovered. S24 exhibits osteoclastogenesis inhibition with an IC50 value of 10.28 μM and osteoblast differentiation stimulation at 10 μM. S24 derivatives were designed and synthesized based on the activity relationship of the chemotypes. This yielded a more active compound, S24-14, with an osteoclastogenesis inhibition IC50 value of 0.40 μM and osteoblast differentiation stimulation at 1.0 μM; compound S24-14 also suppressed bone loss in vivo. These results prove that S24-14 can be a potential lead for antiosteoporosis drug development.

Protein kinase G2 activation restores Wnt signaling and bone mass in glucocorticoid-induced osteoporosis in mice

Osteoporotic fractures are a major complication of long-term glucocorticoid therapy. Glucocorticoids transiently increase bone resorption, but they predominantly inhibit bone formation and induce osteocyte apoptosis, leading to bone loss. Current treatments of glucocorticoid-induced osteoporosis aim mainly at reducing bone resorption and are, therefore, inadequate. We previously showed that signaling via the NO/cGMP/protein kinase G pathway plays a key role in skeletal homeostasis. Here, we show that pharmacological PKG activation with the guanylyl cyclase-1 activator cinaciguat or expression of a constitutively active, mutant PKG2R242Q restored proliferation, differentiation, and survival of primary mouse osteoblasts exposed to dexamethasone. Cinaciguat treatment of WT mice or osteoblast-specific expression of PKG2R242Q in transgenic mice prevented dexamethasone-induced loss of cortical bone mass and strength. These effects of cinaciguat and PKG2R242Q expression were due to preserved bone formation parameters and osteocyte survival. The basis for PKG2's effects appeared to be through recovery of Wnt/β-catenin signaling, which was suppressed by glucocorticoids but critical for proliferation, differentiation, and survival of osteoblast-lineage cells. Cinaciguat reduced dexamethasone activation of osteoclasts, but this did not occur in the PKG2R242Q transgenic mice, suggesting a minor role in osteoprotection. We propose that existing PKG-targeting drugs could represent a novel therapeutic approach to prevent glucocorticoid-induced osteoporosis.

Mitochondria from osteolineage cells regulate myeloid cell-mediated bone resorption

Interactions between osteolineage cells and myeloid cells play important roles in maintaining skeletal homeostasis. Herein, we find that osteolineage cells transfer mitochondria to myeloid cells. Impairment of the transfer of mitochondria by deleting MIRO1 in osteolineage cells leads to increased myeloid cell commitment toward osteoclastic lineage cells and promotes bone resorption. In detail, impaired mitochondrial transfer from osteolineage cells alters glutathione metabolism and protects osteoclastic lineage cells from ferroptosis, thus promoting osteoclast activities. Furthermore, mitochondrial transfer from osteolineage cells to myeloid cells is involved in the regulation of glucocorticoid-induced osteoporosis, and glutathione depletion alleviates the progression of glucocorticoid-induced osteoporosis. These findings reveal an unappreciated mechanism underlying the interaction between osteolineage cells and myeloid cells to regulate skeletal metabolic homeostasis and provide insights into glucocorticoid-induced osteoporosis progression.

Abaloparatide is more potent than teriparatide in restoring bone mass and strength in type 1 diabetic male mice

This study investigated the efficacy of the two FDA-approved bone anabolic ligands of the parathyroid hormone receptor 1 (PTH1R), teriparatide or human parathyroid hormone 1-34 (PTH) and abaloparatide (ABL), to restoring skeletal health using a preclinical murine model of streptozotocin-induced T1-DM. Intermittent daily subcutaneous injections of equal molar doses (12 pmoles/g/day) of PTH (50 ng/g/day), ABL (47.5 ng/g/day), or vehicle, were administered for 28 days to 5-month-old C57Bl/6 J male mice with established T1-DM or control (C) mice. ABL was superior to PTH in increasing or restoring bone mass in control or T1-MD mice, respectively, which was associated with superior stimulation of trabecular and periosteal bone formation, upregulation of osteoclastic/osteoblastic gene expression, and increased circulating bone remodeling markers. Only ABL corrected the reduction in ultimate load, which is a measure of bone strength, induced by T1-DM, and it also increased energy to ultimate load. In addition, bones from T1-DM mice treated with PTH or ABL exhibited increased ultimate stress, a material index, compared to T1-DM mice administered with vehicle. And both PTH and ABL prevented the increased expression of the Wnt antagonist Sost/sclerostin displayed by T1-DM mice. Further, PTH and ABL increased to a similar extent the circulating bone resorption marker CTX and the bone formation marker P1NP in T1-DM after 2 weeks of treatment; however, only ABL sustained these increases after 4 weeks of treatment. We conclude that at equal molar doses, ABL is more effective than PTH in increasing bone mass and restoring the cortical and trabecular bone lost with T1-DM, due to higher and longer-lasting increases in bone remodeling.

Catalpol ameliorates dexamethasone-induced osteoporosis by promoting osteogenic differentiation of bone marrow mesenchymal stem cells via the activation of PKD1 promoter

OBJECTIVE

To investigate the effects of CA on glucocorticoid-induced osteoporosis (GIOP) and lucubrate the underlying mechanism of CA via the activation of polycystic kidney disease-1(PKD1) in bone marrow mesenchymal stem cells (BMSCs).

METHODS

In vivo, a GIOP model in mice treated with dexamethasone (Dex) was established. Biomechanical, micro-CT, immunofluorescence staining of OCN, ALP and PKD1 and others were severally determined. qRT-PCR and Western blot methods were adopted to elucidate the particular mechanisms of CA on GIOP. In addition, BMSCs cultured in vitro were also induced by Dex to verify the effects of CA. Finally, siRNA and luciferase activity assays were performed to confirm the mechanisms.

RESULTS

We found that CA could restore the destroyed bone microarchitecture and increase the bone mass in GIOP mice. CA could also upregulate PKD1 protein expression, reduce oxidative stress, and promote mRNA expression of bone formation-associated markers in GIOP mice. Furthermore, it was also observed that CA reduced oxidative stress and promoted osteogenic differentiation in Dex-induced BMSCs. Mechanically, CA could promote protein expression via increasing the activity of PKD1 promoter.

CONCLUSION

This study provides important evidences for CA in the further clinical treatment of GIOP, reveals the activation of PKD1 promoter as the underlying mechanism.

Reversal of the diabetic bone signature with anabolic therapies in mice

The mechanisms underlying the bone disease induced by diabetes are complex and not fully understood; and antiresorptive agents, the current standard of care, do not restore the weakened bone architecture. Herein, we reveal the diabetic bone signature in mice at the tissue, cell, and transcriptome levels and demonstrate that three FDA-approved bone-anabolic agents correct it. Diabetes decreased bone mineral density (BMD) and bone formation, damaged microarchitecture, increased porosity of cortical bone, and compromised bone strength. Teriparatide (PTH), abaloparatide (ABL), and romosozumab/anti-sclerostin antibody (Scl-Ab) all restored BMD and corrected the deteriorated bone architecture. Mechanistically, PTH and more potently ABL induced similar responses at the tissue and gene signature levels, increasing both formation and resorption with positive balance towards bone gain. In contrast, Scl-Ab increased formation but decreased resorption. All agents restored bone architecture, corrected cortical porosity, and improved mechanical properties of diabetic bone; and ABL and Scl-Ab increased toughness, a fracture resistance index. Remarkably, all agents increased bone strength over the healthy controls even in the presence of severe hyperglycemia. These findings demonstrate the therapeutic value of bone anabolic agents to treat diabetes-induced bone disease and suggest the need for revisiting the approaches for the treatment of bone fragility in diabetes.

Pathogenic mechanisms of glucocorticoid-induced osteoporosis

Glucocorticoid (GC) is one of the most prescribed medicines to treat various inflammatory and autoimmune diseases. However, high doses and long-term use of GCs lead to multiple adverse effects, particularly glucocorticoid-induced osteoporosis (GIO). Excessive GCs exert detrimental effects on bone cells, including osteoblasts, osteoclasts, and osteocytes, leading to impaired bone formation and resorption. The actions of exogenous GCs are considered to be strongly cell-type and dose dependent. GC excess inhibits the proliferation and differentiation of osteoblasts and enhances the apoptosis of osteoblasts and osteocytes, eventually contributing to reduced bone formation. Effects of GC excess on osteoclasts mainly include enhanced osteoclastogenesis, increased lifespan and number of mature osteoclasts, and diminished osteoclast apoptosis, which result in increased bone resorption. Furthermore, GCs have an impact on the secretion of bone cells, subsequently disturbing the process of osteoblastogenesis and osteoclastogenesis. This review provides timely update and summary of recent discoveries in the field of GIO, with a particular focus on the effects of exogenous GCs on bone cells and the crosstalk among them under GC excess.

Protein tyrosine kinase 2b inhibition reverts niche-associated resistance to tyrosine kinase inhibitors in AML

FLT3 tyrosine kinase inhibitor (TKI) therapy evolved into a standard therapy in FLT3-mutated AML. TKI resistance, however, develops frequently with poor outcomes. We analyzed acquired TKI resistance in AML cell lines by multilayered proteome analyses. Leupaxin (LPXN), a regulator of cell migration and adhesion, was induced during early resistance development, alongside the tyrosine kinase PTK2B which phosphorylated LPXN. Resistant cells differed in cell adhesion and migration, indicating altered niche interactions. PTK2B and LPXN were highly expressed in leukemic stem cells in FLT3-ITD patients. PTK2B/FAK inhibition abrogated resistance-associated phenotypes, such as enhanced cell migration. Altered pathways in resistant cells, assessed by nascent proteomics, were largely reverted upon PTK2B/FAK inhibition. PTK2B/FAK inhibitors PF-431396 and defactinib synergized with different TKIs or daunorubicin in FLT3-mutated AML. Midostaurin-resistant and AML cells co-cultured with mesenchymal stroma cells responded particularly well to PTK2B/FAK inhibitor addition. Xenograft mouse models showed significant longer time to leukemia symptom-related endpoint upon gilteritinib/defactinib combination treatment in comparison to treatment with either drug alone. Our data suggest that the leupaxin-PTK2B axis plays an important role in acquired TKI resistance in AML. PTK2B/FAK inhibitors act synergistically with currently used therapeutics and may overcome emerging TKI resistance in FLT3-mutated AML at an early timepoint.

Femoral Skeletal Perfusion is Reduced in Male Mice with Type 1 Diabetes

The bone vasculature and blood flow are critical for bone modeling, remodeling, and regeneration. Vascular complications are one of the major health concerns of people with type 1 diabetes (T1D). Moreover, people with T1D have lower bone mineral density and increased bone fragility. The goal of this study was to understand whether bone perfusion was altered in a mouse model of T1D and how this related to changes in bone mass. T1D was induced via the administration of streptozotocin in 12-week-old C57BL/6NHsd male mice. The assessment of bone perfusion utilized the injection of fluorescent microspheres with assessment of levels in the bone. Femoral blood flow and VEGF-A expression in the cortical bone shafts were lower in the T1D mice, compared to healthy controls, in this pattern followed that of changes in bone mass. These data demonstrate a possible association between reduced skeletal perfusion and reduced bone mass in the setting of T1D.

Osteoporosis in Patients With Respiratory Diseases

Climate change, environmental pollution, and virus epidemics have sharply increased the number of patients suffering from respiratory diseases in recent years. Prolonged periods of illness and drug use increase the occurrence of complications in these patients. Osteoporosis is the common bone metabolism disease with respiratory disturbance, which affects prognosis and increases mortality of patients. The problem of osteoporosis in patients with respiratory diseases needs more attention. In this review, we concluded the characteristics of osteoporosis in some respiratory diseases including COPD, asthma, COVID-19, tuberculosis, and lung cancer. We revealed that hypoxia was the common pathogenesis of osteoporosis secondary to respiratory diseases, with malnutrition and corticosteroid abuse driving the progression of osteoporosis. Hypoxia-induced ROS accumulation and activated HIF-1α lead to attenuated osteogenesis and enhanced osteoclastogenesis in patients with respiratory diseases. Tuberculosis and cancer also invaded bone tissue and reduced bone strength by direct infiltration. For the treatment of osteoporosis in respiratory patients, oral-optimized bisphosphonates were the best treatment modality. Vitamin D was a necessary supplement, both for calcium absorption in osteogenesis and for improvement of respiratory lesions. Reasonable adjustment of the dose and course of corticosteroids according to the etiology and condition of patients is beneficial to prevent the occurrence and development of osteoporosis. Additionally, HIF-1α was a potential target for the treatment of osteoporosis in respiratory patients, which could be activated under hypoxia condition and involved in the process of bone remodeling.

Bad to the Bone: The Effects of Therapeutic Glucocorticoids on Osteoblasts and Osteocytes

Despite the continued development of specialized immunosuppressive therapies in the form of monoclonal antibodies, glucocorticoids remain a mainstay in the treatment of rheumatological and auto-inflammatory disorders. Therapeutic glucocorticoids are unmatched in the breadth of their immunosuppressive properties and deliver their anti-inflammatory effects at unparalleled speed. However, long-term exposure to therapeutic doses of glucocorticoids decreases bone mass and increases the risk of fractures - particularly in the spine - thus limiting their clinical use. Due to the abundant expression of glucocorticoid receptors across all skeletal cell populations and their respective progenitors, therapeutic glucocorticoids affect skeletal quality through a plethora of cellular targets and molecular mechanisms. However, recent evidence from rodent studies, supported by clinical data, highlights the considerable role of cells of the osteoblast lineage in the pathogenesis of glucocorticoid-induced osteoporosis: it is now appreciated that cells of the osteoblast lineage are key targets of therapeutic glucocorticoids and have an outsized role in mediating their undesirable skeletal effects. As part of this article, we review the molecular mechanisms underpinning the detrimental effects of supraphysiological levels of glucocorticoids on cells of the osteoblast lineage including osteocytes and highlight the clinical implications of recent discoveries in the field.

The osteocyte as a signaling cell

Osteocytes, former osteoblasts encapsulated by mineralized bone matrix, are far from being passive and metabolically inactive bone cells. Instead, osteocytes are multifunctional and dynamic cells capable of integrating hormonal and mechanical signals and transmitting them to effector cells in bone and in distant tissues. Osteocytes are a major source of molecules that regulate bone homeostasis by integrating both mechanical cues and hormonal signals that coordinate the differentiation and function of osteoclasts and osteoblasts. Osteocyte function is altered in both rare and common bone diseases, suggesting that osteocyte dysfunction is directly involved in the pathophysiology of several disorders affecting the skeleton. Advances in osteocyte biology initiated the development of novel therapeutics interfering with osteocyte-secreted molecules. Moreover, osteocytes are targets and key distributors of biological signals mediating the beneficial effects of several bone therapeutics used in the clinic. Here we review the most recent discoveries in osteocyte biology demonstrating that osteocytes regulate bone homeostasis and bone marrow fat via paracrine signaling, influence body composition and energy metabolism via endocrine signaling, and contribute to the damaging effects of diabetes mellitus and hematologic and metastatic cancers in the skeleton.

Osteoclasts protect bone blood vessels against senescence through the angiogenin/plexin-B2 axis

Synthetic glucocorticoids (GCs), one of the most effective treatments for chronic inflammatory and autoimmune conditions in children, have adverse effects on the growing skeleton. GCs inhibit angiogenesis in growing bone, but the underlying mechanisms remain unclear. Here, we show that GC treatment in young mice induces vascular endothelial cell senescence in metaphysis of long bone, and that inhibition of endothelial cell senescence improves GC-impaired bone angiogenesis with coupled osteogenesis. We identify angiogenin (ANG), a ribonuclease with pro-angiogenic activity, secreted by osteoclasts as a key factor for protecting the neighboring vascular cells against senescence. ANG maintains the proliferative activity of endothelial cells through plexin-B2 (PLXNB2)-mediated transcription of ribosomal RNA (rRNA). GC treatment inhibits ANG production by suppressing osteoclast formation in metaphysis, resulting in impaired endothelial cell rRNA transcription and subsequent cellular senescence. These findings reveal the role of metaphyseal blood vessel senescence in mediating the action of GCs on growing skeleton and establish the ANG/PLXNB2 axis as a molecular basis for the osteoclast-vascular interplay in skeletal angiogenesis.

Bone Strength/Bone Mass Discrepancy in Glucocorticoid-Treated Adult Mice

Glucocorticoids increase bone fragility in patients in a manner that is underestimated by bone mass measurement. This study aimed to determine if the adult mouse could model this bone strength/bone mass discrepancy. Forty‐two 13‐week‐old BALB/cJ mice were randomized into vehicle and glucocorticoid groups, implanted with vehicle or 6‐methylprednisolone pellets, and necropsied after 60 and 120 days. Bone strength and bone mass/microarchitecture were assessed at the right central femur (CF; cortical‐bone–rich) and sixth lumbar vertebral body (LVB6; trabecular‐bone–rich). Bound water (BW) of the whole right femur was analyzed by proton‐nuclear magnetic resonance (¹H‐NMR) relaxometry. Data were analyzed by two‐factor ANOVA with time (day 60 and day 120) and treatment (vehicle and glucocorticoid) as main effects for all data. Significant interactions were further analyzed with a Tukey's post hoc test. Most bone strength measures in the CF were lower in the glucocorticoid group, regardless of the duration of treatment, with no time × treatment interaction. However, bone mass measures in the CF showed a significant time × treatment interaction (p = 0.0001). Bone strength measures in LVB6 showed a time × treatment interaction (p < 0.02) such that LVB6 strength was lower after 120 days of glucocorticoids compared with 120 days of vehicle treatment. Whole‐femur–BW was lower with both glucocorticoid treatment (p = 0.0001) and time (p < 0.02), with a significant time × treatment interaction (p = 0.005). Glucocorticoid treatment of male BALB/cJ mice resulted in the lowering of bone strength in both cortical and trabecular bone that either appeared earlier or was greater than the treatment‐related changes in bone mass/microarchitecture. The adult mouse may be a good model for investigating the bone strength/mass discrepancy observed in glucocorticoid‐treated patients. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Aging-related modifications to G protein-coupled receptor signaling diversity

Aging is a highly complex molecular process, affecting nearly all tissue systems in humans and is the highest risk factor in developing neurodegenerative disorders such as Alzheimer's and Parkinson's disease, cardiovascular disease and Type 2 diabetes mellitus. The intense complexity of the aging process creates an incentive to develop more specific drugs that attenuate or even reverse some of the features of premature aging. As our current pharmacopeia is dominated by therapeutics that target members of the G protein-coupled receptor (GPCR) superfamily it may be prudent to search for effective anti-aging therapeutics in this fertile domain. Since the first demonstration of GPCR-based β-arrestin signaling, it has become clear that an enhanced appreciation of GPCR signaling diversity may facilitate the creation of therapeutics with selective signaling activities. Such 'biased' ligand signaling profiles can be effectively investigated using both standard molecular biological techniques as well as high-dimensionality data analyses. Through a more nuanced appreciation of the quantitative nature across the multiple dimensions of signaling bias that drugs possess, researchers may be able to further refine the efficacy of GPCR modulators to impact the complex aberrations that constitute the aging process. Identifying novel effector profiles could expand the effective pharmacopeia and assist in the design of precision medicines. This review discusses potential non-G protein effectors, and specifically their potential therapeutic suitability in aging and age-related disorders.

Ptk2b deletion improves mice folliculogenesis and fecundity via inhibiting follicle loss mediated by Erk pathway

Ptk2b has been found playing critical roles in oocyte maturation and subsequent fertilization in vitro. But what is the exact in vivo function in reproduction still elusive. Here, by constructing Ptk2b mutant mice, we found Ptk2b was not essential for mice fertility, unexpectedly, contrary to previously reported in vitro findings, we found Ptk2b ablation significantly improved female fecundity. Follicle counting indicated that the number of primordial follicles and growing follicles in matured mice was significantly increased in the absence of Ptk2b, whereas the primordial follicle formation showed no defects. We also found this regulation was in an autophosphorylation independent pathway, as autophosphorylation site mutant mice (PTK2B^Y402F ) show no phenotype in female fertility. Further biochemistry studies revealed that Ptk2b ablation promotes folliculogenesis via Erk pathway mediate follicle survival. Together, we found a novel biological function of Ptk2b in folliculogenesis, which could be potentially used as a therapeutic target for corresponding infertility.

Pyk2 deficiency enhances bone mass during midpalatal suture expansion

OBJECTIVE

To determine if Pyk2 deficiency increases midpalatal suture bone mass and preserves sutural integrity after maxillary expansion.

SETTING AND SAMPLE

Thirty-six male Pyk2 knockout (KO) and control (WT) mice at 6 weeks of age.

MATERIALS AND METHODS

Mice received nickel-titanium spring expanders delivering 0 g (no intervention control), 10 or 20 g force for 14 days. High-resolution micro-CT was used to determine bone volume/tissue volume (BV/TV), sutural width and intermolar width. Effects on osteoclasts, chondrocytes and suture morphology were determined by histomorphometry.

RESULTS

Pyk2-KO controls (0 g) had 7% higher BV/TV compared with WT controls. Expanded Pyk2-KO maxillae also exhibited 12% (10 g) and 18% (20 g) higher BV/TV than WT mice. Although bone loss following expansion occurred in both genotypes, BV/TV was decreased to a greater extent in WT maxillae (-10% at 10g; -22% at 20 g) compared with Pyk2-KO maxillae (-11% only at 20 g). Expanded WT maxillae also showed a greater increase in sutural width, intermolar width and fibrous connective tissue width compared with expanded Pyk2-KO maxillae. Moreover, osteoclast number was increased 77% (10 g) and 132% (20 g) in expanded WT maxillae, but remained unchanged in expanded Pyk2-KO, compared to their respective controls. Cartilage area and chondrocyte number were increased to the same extent in expanded WT and Pyk2-KO sutures.

CONCLUSIONS

These findings suggest that midpalatal suture expansion increases osteoclast formation in WT but not Pyk2-KO mice, leading to higher BV/TV in expanded Pyk2-KO maxillae. These studies suggest Pyk2-targeted strategies may be beneficial to increase bone density and preserve sutural integrity during maxillary expansion.

MicroRNA-29a Counteracts Glucocorticoid Induction of Bone Loss through Repressing TNFSF13b Modulation of Osteoclastogenesis

Glucocorticoid excess escalates osteoclastic resorption, accelerating bone mass loss and microarchitecture damage, which ramps up osteoporosis development. MicroRNA-29a (miR-29a) regulates osteoblast and chondrocyte function; however, the action of miR-29a to osteoclastic activity in the glucocorticoid-induced osteoporotic bone remains elusive. In this study, we showed that transgenic mice overexpressing an miR-29a precursor driven by phosphoglycerate kinase exhibited a minor response to glucocorticoid-mediated bone mineral density loss, cortical bone porosity and overproduction of serum resorption markers C-teleopeptide of type I collagen and tartrate-resistant acid phosphatase 5b levels. miR-29a overexpression compromised trabecular bone erosion and excessive osteoclast number histopathology in glucocorticoid-treated skeletal tissue. Ex vivo, the glucocorticoid-provoked osteoblast formation and osteoclastogenic markers (NFATc1, MMP9, V-ATPase, carbonic anhydrase II and cathepsin K) along with F-actin ring development and pit formation of primary bone-marrow macrophages were downregulated in miR-29a transgenic mice. Mechanistically, tumor necrosis factor superfamily member 13b (TNFSF13b) participated in the glucocorticoid-induced osteoclast formation. miR-29a decreased the suppressor of cytokine signaling 2 (SOCS2) enrichment in the TNFSF13b promoter and downregulated the cytokine production. In vitro, forced miR-29a expression and SOCS2 knockdown attenuated the glucocorticoid-induced TNFSF13b expression in osteoblasts. miR-29a wards off glucocorticoid-mediated excessive bone resorption by repressing the TNFSF13b modulation of osteoclastic activity. This study sheds new light onto the immune-regulatory actions of miR-29a protection against glucocorticoid-mediated osteoporosis.