Genetic disruption of all NO synthase isoforms enhances BMD and bone turnover in mice in vivo: involvement of the renin-angiotensin system

Nitric oxide modulates bone anabolism through regulation of osteoblast glycolysis and differentiation

Previous studies have shown that nitric oxide (NO) supplements may prevent bone loss and fractures in preclinical models of estrogen deficiency. However, the mechanisms by which NO modulates bone anabolism remain largely unclear. Argininosuccinate lyase (ASL) is the only mammalian enzyme capable of synthesizing arginine, the sole precursor for nitric oxide synthase-dependent (NOS-dependent) NO synthesis. Moreover, ASL is also required for channeling extracellular arginine to NOS for NO production. ASL deficiency (ASLD) is thus a model to study cell-autonomous, NOS-dependent NO deficiency. Here, we report that loss of ASL led to decreased NO production and impairment of osteoblast differentiation. Mechanistically, the bone phenotype was at least in part driven by the loss of NO-mediated activation of the glycolysis pathway in osteoblasts that led to decreased osteoblast differentiation and function. Heterozygous deletion of caveolin 1, a negative regulator of NO synthesis, restored NO production, osteoblast differentiation, glycolysis, and bone mass in a hypomorphic mouse model of ASLD. The translational significance of these preclinical studies was further reiterated by studies conducted in induced pluripotent stem cells from an individual with ASLD. Taken together, our findings suggest that ASLD is a unique genetic model for studying NO-dependent osteoblast function and that the NO/glycolysis pathway may be a new target to modulate bone anabolism.

Treadmill exercise prevents reduction of bone mineral density after myocardial infarction in apolipoprotein E-deficient mice

AIMS

Recent clinical studies demonstrated the association between myocardial infarction (MI) and osteoporotic fractures. We examined whether MI causes bone loss and the effects of exercise training on bone in mice after MI.

METHODS

We created a MI model in 16-week-old male apolipoprotein E-deficient mice (n = 42), which were randomly assigned to exercise group (MI-Ex) and sedentary group (MI-Sed). We also performed sham operations in other mice (n = 10). Treadmill exercise training was performed from one week after operation to eight weeks. At eight weeks, the bone parameters of the femur were measured by quantitative computed tomography, followed by histological analysis (n = 10-17).

RESULTS

Bone mineral density (BMD) of the femur was significantly decreased in the MI-Sed group as compared with the sham group (P < 0.001), whereas the BMD was significantly increased in the MI-Ex group as compared with the MI-Sed group (P < 0.05). In histological analysis, Rho-associated coiled-coil kinase 2 and tartrate-resistant acid phosphate positive (bone resorptive) area in distal femur were significantly increased in the MI-Sed group as compared with the sham group (P < 0.05), whereas those parameters were significantly decreased in the MI-Ex group as compared with the MI-Sed group (P < 0.05). In contrast, alkaline phosphatase (ALP)-positive (bone-forming) area was significantly decreased in the MI-Sed group as compared with the sham group (P < 0.05), whereas ALP-positive area was significantly increased in the MI-Ex group as compared with the MI-Sed group (P < 0.05).

CONCLUSIONS

The present study demonstrates that MI reduces BMD and treadmill exercise training prevents the reduction of BMD in apolipoprotein E-deficient mice.

Mechanical, hormonal and metabolic influences on blood vessels, blood flow and bone

Bone tissue is highly vascularized due to the various roles bone blood vessels play in bone and bone marrow function. For example, the vascular system is critical for bone development, maintenance and repair and provides O₂, nutrients, waste elimination, systemic hormones and precursor cells for bone remodeling. Further, bone blood vessels serve as egress and ingress routes for blood and immune cells to and from the bone marrow. It is becoming increasingly clear that the vascular and skeletal systems are intimately linked in metabolic regulation and physiological and pathological processes. This review examines how agents such as mechanical loading, parathyroid hormone, estrogen, vitamin D and calcitonin, all considered anabolic for bone, have tremendous impacts on the bone vasculature. In fact, these agents influence bone blood vessels prior to influencing bone. Further, data reveal strong associations between vasodilator capacity of bone blood vessels and trabecular bone volume, and poor associations between estrogen status and uterine mass and trabecular bone volume. Additionally, this review highlights the importance of the bone microcirculation, particularly the vascular endothelium and NO-mediated signaling, in the regulation of bone blood flow, bone interstitial fluid flow and pressure and the paracrine signaling of bone cells. Finally, the vascular endothelium as a mediator of bone health and disease is considered.

M2 macrophages contribute to osteogenesis and angiogenesis on nanotubular TiO2 surfaces

The monocyte/macrophage system plays an essential role in the host response and the fate of endosseous implanted materials. Macrophage behavior was thought to be regulated by nanostructured titanium which has been considered as a very promising candidate for dental implants. However, there is little known for subsequent effects of these activated macrophages on osteogenesis and angiogenesis which were essential for bone integration. Here we presented two different dimensions of titanium nanotubes generated by anodic oxidation at 10 V (NT 10) and 20 V (NT 20), respectively. The behavior of macrophages on the surfaces was evaluated, and their conditioned medium (CM) was collected to stimulate MC3T3 and HUVECs, with commercially pure titanium (cp Ti) as control. We found that NT 20 induced macrophage activation similar to the anti-inflammatory M2 macrophage state with the enhanced expression of IL-10 and ARG, while NT 10 was associated with M1 macrophage phenotype characterized by high levels of IL-1β, iNOS and TNF-α. Furthermore, the osteogenic capacity of MC3T3 in CM from NT 20 was enhanced (NT 20 > NT 10 ≈ cp Ti) and the tube formation capacity of HUVECs was promoted in CM from nanotubular surfaces with increasing tube dimensions (NT 20 > NT 10 > cp Ti). Our data suggest that dental implants with the large nanotube dimension surface could result in a favorable osteoimmunomodulatory microenvironment for the establishment of osseointegration.

Communication between nitric oxide synthase and positively-charged surface and bone formation promotion

Despite the effects on physiology of bone marrow mesenchymal stem cells (BMSCs) and bone tissue, biological signal communication between bone implants and them is seldom employed as a guidance to create an osteo-inductive interface. Herein, the positively-charged surface is constructed on bone implant from the perspective of mediation of nitric oxide synthase (NOS) expression to signal BMSCs osteo-differentiation. In vitro and in vivo results indicate that the proper surface potential on the positively-charged surface affects NOS to express a high level of inducible nitric oxide synthase (iNOS) in three NOS isoforms of the contacted BMSCs, upregulates their osteogenetic expression, and ultimately foster new bone growth. However, an excessively high surface potential produces substantial immunomodulatory effects thereby offsetting the aforementioned advantages. This study demonstrates that fine-tuning of the positively-charged surface and proper utilization of the communication between NOS and bone implants promote bone formation.

In situ plasma fabrication of ceramic-like structure on polymeric implant with enhanced surface hardness, cytocompatibility and antibacterial capability

Polymeric materials are commonly found in orthopedic implants due to their unique mechanical properties and biocompatibility but the poor surface hardness and bacterial infection hamper many biomedical applications. In this study, a ceramic-like surface structure doped with silver is produced by successive plasma implantation of silicon (Si) and silver (Ag) into the polyamine 66 (PA66) substrate. Not only the surface hardness and elastic modulus are greatly enhanced due to the partial surface carbonization and the ceramic-like structure produced by the reaction between energetic Si and the carbon chain of PA66, but also the antibacterial activity is improved because of the combined effects rendered by Ag and SiC structure. Furthermore, the modified materials which exhibit good cytocompatibility upregulate bone-related genes and proteins expressions of the contacted bone mesenchymal stem cells (BMSCs). For the first time, it explores out that BMSCs osteogenesis on the antibacterial ceramic-like structure is mediated via the iNOS and nNOS signal pathways. The results reveal that in situ plasma fabrication of an antibacterial ceramic-like structure can endow PA66 with excellent surface hardness, cytocompatibility, as well as antibacterial capability.

Upregulation of BMSCs osteogenesis by positively-charged tertiary amines on polymeric implants via charge/iNOS signaling pathway

Positively-charged surfaces on implants have a similar potential to upregulate osteogenesis of bone marrow-derived mesenchymal stem cells (BMSCs) as electromagnetic therapy approved for bone regeneration. Generally, their osteogenesis functions are generally considered to stem from the charge-induced adhesion of extracellular matrix (ECM) proteins without exploring the underlying surface charge/cell signaling molecule pathways. Herein, a positively-charged surface with controllable tertiary amines is produced on a polymer implant by plasma surface modification. In addition to inhibiting the TNF-α expression, the positively-charged surface with tertiary amines exhibits excellent cytocompatibility as well as remarkably upregulated osteogenesis-related gene/protein expressions and calcification of the contacted BMSCs. Stimulated by the charged surface, these BMSCs display high iNOS expressions among the three NOS isoforms. Meanwhile, downregulation of the iNOS by L-Can or siRNA inhibit osteogenic differentiation in the BMSCs. These findings suggest that a positively-charged surface with tertiary amines induces osteogenesis of BMSCs via the surface charge/iNOS signaling pathway in addition to elevated ECM protein adhesion. Therefore, creating a positively-charged surface with tertiary amines is a promising approach to promote osseointegration with bone tissues.

Significance of nitric oxide synthases: Lessons from triple nitric oxide synthases null mice

Nitric oxide (NO) is synthesized by three distinct NO synthases (neuronal, inducible, and endothelial NOSs), all of which are expressed in almost all tissues and organs in humans. The regulatory roles of NOSs in vivo have been investigated in pharmacological studies with non-selective NOS inhibitors. However, the specificity of the inhibitors continues to be an issue of debate, and the authentic significance of NOSs is still poorly understood. To address this issue, we generated mice in which all three NOS genes are completely disrupted. The triple NOSs null mice exhibited cardiovascular abnormalities, including hypertension, arteriosclerosis, myocardial infarction, cardiac hypertrophy, diastolic heart failure, and reduced EDHF responses, with a shorter survival. The triple NOSs null mice also displayed metabolic abnormalities, including metabolic syndrome and high-fat diet-induced severe dyslipidemia. Furthermore, the triple NOSs null mice showed renal abnormalities (nephrogenic diabetes insipidus and pathological renal remodeling), lung abnormalities (accelerated pulmonary fibrosis), and bone abnormalities (increased bone mineral density and bone turnover). These results provide evidence that NOSs play pivotal roles in the pathogenesis of a wide variety of disorders. This review summarizes the latest knowledge on the significance of NOSs in vivo, based on lessons learned from experiments with our triple mutant model.

Nitric oxide signaling in mechanical adaptation of bone

One of the most serious healthcare problems in the world is bone loss and fractures due to a lack of physical activity in elderly people as well as in bedridden patients or otherwise inactive youth. Crucial here are the osteocytes. Buried within our bones, these cells are believed to be the mechanosensors that stimulate bone formation in the presence of mechanical stimuli and bone resorption in the absence of such stimuli. Intercellular signaling is an important physiological phenomenon involved in maintaining homeostasis in all tissues. In bone, intercellular communication via chemical signals like NO plays a critical role in the dynamic process of bone remodeling. If bones are mechanically loaded, fluid flows through minute channels in the bone matrix, resulting in shear stress on the cell membrane that activates the osteocyte. Activated osteocytes produce signaling molecules like NO, which modulate the activity of the bone-forming osteoblasts and the bone-resorbing osteoclasts, thereby orchestrating bone adaptation to mechanical loading. In this review, we highlight current insights in the role of NO in the mechanical adaptation of bone mass and structure, with emphasis on its role in local bone gain and loss as well as in remodeling supervised by osteocytes. Since mechanical stimuli and NO production enhance bone strength and fracture resistance, these new insights may facilitate the development of novel osteoporosis treatments.

Nitrite and nitrate levels of gingival crevicular fluid and saliva in subjects with gingivitis and chronic periodontitis

OBJECTIVES

Nitrosative stress plays an essential role in the pathogenesis of periodontal disease. The aim of this study is to analyze the gingival crevicular fluid and saliva nitrite and nitrate levels in periodontally healthy and diseased sites.

MATERIAL AND METHODS

A total of 60 individuals including, 20 chronic periodontitis and 20 gingivitis patients and 20 periodontally healthy controls participated in the present study. Probing depth, clinical attachment level, bleeding on probing, gingival index and plaque index were assessed, gingival crevicular fluid (GCF) and saliva samples were obtained from the subjects, including 480 GCF samples and 60 unstimulated whole saliva samples. Nitrite and nitrate were analyzed by Griess reagent.

RESULTS

Total GCF nitrite levels were higher in gingivitis and periodontitis groups (1.07 [SD 0.62] nmol and 1.08 [SD 0.59] nmol) than the control group (0.83 [SD 0.31] nmol) (P < 0.05) but did not differ significantly between gingivitis and periodontitis groups (P > 0.05). The difference in GCF nitrate level was not significant among the control, gingivitis and periodontitis groups (7.7 [SD 2.71] nmol, 7.51 [SD 4.16] nmol and 7.38 [SD 1.91] nmol). Saliva nitrite and nitrate levels did not differ significantly among three study groups. Saliva nitrate/nitrite ratios were higher in periodontitis and gingivitis groups than the control group. A gradual decrease in nitrate/nitrite ratio in GCF was detected with the presence of inflammation.

CONCLUSIONS

It may be suggested that nitrite in gingival crevicular fluid is a better periodontal disease marker than nitrate and may be used as an early detection marker of periodontal inflammation, and that local nitrosative stress markers don't show significant difference between the initial and advanced stages of periodontal disease.

Role of the local bone renin‑angiotensin system in steroid‑induced osteonecrosis in rabbits

The specific pathogenesis of steroid‑induced osteonecrosis (ON) is yet to be elucidated and until recently effective prophylactic therapies have not been available. The local renin‑angiotensin system (RAS) exists in the bone and has an important role in local bone regulation. However, to the best of our knowledge, the interrelation between local bone RAS and steroid‑induced ON is yet to be investigated. In the present study, 45 rabbits were injected with a single intramuscular dose of 20 mg/kg methylprednisolone acetate (MPA) and were sacrificed 1 (group A), 2 (group B) and 3 (group C) weeks subsequent to MPA administration (n=15 per group). Ten rabbits were used as a control group (group N). The presence or absence of ON in the bilateral femoral heads was examined histopathologically. The mRNA and protein expression of components of the RAS, including angiotensin II (Ang II), angiotensin converting enzyme (ACE) and Ang II type 1 (AT1) and Ang II type 2 (AT2) receptors, were detected in the bone. Significant changes in Ang II, ACE, and AT1 and AT2 receptor expression were observed in the bone of the rabbits in the different groups. Moreover, the expression of Ang II and ACE was highest one week subsequent to administration of the glucocorticoid methylprednisolone and the expression of the AT1 and AT2 receptors was highest two weeks following methylprednisolone administration. ON occurs most significantly at three weeks following the administration of MPA in this animal model, thus the changes in Ang II, ACE and AT1 and AT2 receptor expression preceded this. The present study found that ON was strongly associated with the activation of the local bone RAS in rabbits.

Endothelial nitric oxide synthase is not essential for nitric oxide production by osteoblasts subjected to fluid shear stress in vitro

Endothelial nitric oxide synthase (eNOS) has long been held responsible for NO production by mechanically stimulated osteoblasts, but this has recently been disputed. We investigated whether one of the three known NOS isoforms is essential for NO production by mechanically stimulated osteoblasts in vitro and revisited the bone phenotype of the eNOS-/- mouse. Osteoblasts, obtained as outgrowths from mouse calvaria or long bones of wild-type (WT), eNOS-/-, inducible NOS-/- (iNOS-/-), or neuronal NOS-/- (nNOS-/-) mice, were subjected to mechanical stimulation by means of pulsating fluid flow (PFF); and NO production was determined. Tibiae and femora from 8-week-old mice were subjected to μCT and three-point bending tests. Deletion of single NOS isoforms did not lead to significant upregulation of alternate isoforms in cultured osteoblasts from WT, eNOS-/-, iNOS-/-, or nNOS-/- mice. Expression of eNOS mRNA in osteoblasts was below our detection limit, and no differences in growth between WT and eNOS-/- osteoblasts were found. PFF increased NO production by approximately fourfold in WT and eNOS-/- osteoblasts and significantly stimulated NO production in iNOS-/- and nNOS-/- osteoblasts. Tibiae and femora from WT and eNOS-/- mice showed no difference in bone volume and architecture or in mechanical parameters. Our data suggest that mechanical stimuli can enhance NO production by cultured osteoblasts singly deficient for each known NOS isoform and that lack of eNOS does not significantly affect bone mass and strength at 8 weeks of age. Our data challenge the notion that eNOS is a key effector of mechanically induced bone maintenance.

Expression of endothelial nitric oxide synthase protein is not necessary for mechanical strain-induced nitric oxide production by cultured osteoblasts

Regulation of nitric oxide (NO) production is considered essential in mechanical load-related osteogenesis. We examined whether osteoblast endothelial NO synthase (eNOS)-derived NO production was regulated by HSP90. We found that HSP90 is essential for strain-related NO release but appears to be independent of eNOS in cultured osteoblasts.

INTRODUCTION

NO is a key regulator of bone mass, and its production by bone cells is regarded as essential in mechanical strain-related osteogenesis. We sought to identify whether bone cell NO production relied upon eNOS, considered to be the predominant NOS isoform in bone, and whether this was regulated by an HSP90-dependent mechanism.

METHODS

Using primary rat long bone-derived osteoblasts, the ROS 17/2.8 cell line and primary mouse osteoblasts, derived from wild-type and eNOS-deficient (eNOS(-/-)) mice, we examined by immunoblotting the expression of eNOS using a range of well-characterised antibodies and extraction methods, measured NOS activity by monitoring the conversion of radiolabelled L-arginine to citrulline and examined the production of NO by bone cells subjected to mechanical strain application under various conditions.

RESULTS

Our studies have revealed that eNOS protein and activity were both undetectable in osteoblast-like cells, that mechanical strain-induced NO production was retained in bone cells from eNOS-deficient mice, but that this strain-related induction of NO production was, however, dependent upon HSP90.

CONCLUSIONS

Together, our studies indicate that HSP90 activity is essential for strain-related NO release by cultured osteoblasts and that this is highly likely to be achieved by an eNOS-independent mechanism.

Reduced chondrocyte proliferation, earlier cell cycle exit and increased apoptosis in neuronal nitric oxide synthase-deficient mice

OBJECTIVE

Nitric oxide (NO) has been implicated in the local regulation of bone metabolism. However, the contribution made by specific nitric oxide synthase (NOS) enzymes to skeletal development is unclear. The objective of this study was to examine the effects of inactivation of neuronal nitric oxide synthase (nNOS) on cartilage development in mice.

DESIGN

Mice carrying a null mutation in the nNOS gene were used to address our objectives. Histological staining, immunohistochemistry and in situ analyses were employed along with real-time reverse transcriptase - polymerase chain reaction (RT-PCR).

RESULTS

nNOS-null mice show transient growth retardation and shorter long bones. nNOS-deficient growth plates show a reduction in replicating cells. Reduced chondrocyte numbers may in part be due to slower cell cycle progression and premature cell cycle exit caused by decreased cyclin D1 and increased p57 expression in mutants. In addition, apoptosis was increased as shown by increased cleaved-caspase 3 staining in hypertrophic chondrocytes in mutants. Real-time PCR demonstrated that expression of early chondrocyte markers such as Sox genes was reduced in mutant mice, while expression of prehypertrophic markers such as RORα was increased. Histological sections also demonstrated thinner cortical bone, fewer trabeculae and reduced mineralization in mutant mice.

CONCLUSIONS

These data identify an important role of nNOS in chondrocyte proliferation and endochondral bone growth and demonstrate that nNOS coordinates cell cycle exit and chondrocyte differentiation in cartilage development.

Evaluation of methylation status of the eNOS promoter at birth in relation to childhood bone mineral content

Our previous work has shown associations between childhood adiposity and perinatal methylation status of several genes in umbilical cord tissue, including endothelial nitric oxide synthase (eNOS). There is increasing evidence that eNOS is important in bone metabolism; we therefore related the methylation status of the eNOS gene promoter in stored umbilical cord to childhood bone size and density in a group of 9-year-old children. We used Sequenom MassARRAY to assess the methylation status of two CpGs in the eNOS promoter, identified from our previous study, in stored umbilical cords of 66 children who formed part of a Southampton birth cohort and who had measurements of bone size and density at age 9 years (Lunar DPXL DXA instrument). Percentage methylation varied greatly between subjects. For one of the two CpGs, eNOS chr7:150315553 + , after taking account of age and sex, there were strong positive associations between methylation status and the child's whole-body bone area (r = 0.28, P = 0.02), bone mineral content (r = 0.34, P = 0.005), and areal bone mineral density (r = 0.34, P = 0.005) at age 9 years. These associations were independent of previously documented maternal determinants of offspring bone mass. Our findings suggest an association between methylation status at birth of a specific CpG within the eNOS promoter and bone mineral content in childhood. This supports a role for eNOS in bone growth and metabolism and implies that its contribution may at least in part occur during early skeletal development.

Infection, inflammation, and bone regeneration: a paradoxical relationship

Various strategies have been developed to promote bone regeneration in the craniofacial region. Most of these interventions utilize implantable materials or devices. Infections resulting from colonization of these implants may result in local tissue destruction in a manner analogous to periodontitis. This destruction is mediated via the expression of various inflammatory mediators and tissue-destructive enzymes. Given the well-documented association among microbial biofilms, inflammatory mediators, and tissue destruction, it seems reasonable to assume that inflammation may interfere with bone healing and regeneration. Paradoxically, recent evidence also suggests that the presence of certain pro-inflammatory mediators is actually required for bone healing. Bone injury (e.g., subsequent to a fracture or surgical intervention) is followed by a choreographed cascade of events, some of which are dependent upon the presence of pro-inflammatory mediators. If inflammation resolves promptly, then proper bone healing may occur. However, if inflammation persists (which might occur in the presence of an infected implant or graft material), then the continued inflammatory response may result in suboptimal bone formation. Thus, the effect of a given mediator is dependent upon the temporal context in which it is expressed. Better understanding of this temporal sequence may be used to optimize regenerative outcomes.

Reduced bone formation in alcohol-induced osteopenia is associated with elevated p21 expression in bone marrow cells in aldehyde dehydrogenase 2-disrupted mice

INTRODUCTION

High consumption of alcohol is one of the risk factors for osteoporosis. Approximately 45% of Chinese and Japanese individuals have the inactive aldehyde dehydrogenase 2 (Aldh2) phenotype. The absence of the ALDH2*2 allele is found to adversely influence the risk of osteoporosis. The aim of this study is to clarify the effects of alcohol consumption on osteoblast differentiation in bone marrow and trabecular bone formation in Aldh2-disrupted mice.

MATERIALS AND METHODS

Seven-week-old male Aldh2 knockout mice (Aldh2(-/-)) and wild-type (Aldh2(+/+)) mice were fed with water (groups Aldh2(-/-)/Wa and Aldh2(+/+)/Wa) or with 5% ethanol (groups Aldh2(-/-)/Al and Aldh2(+/+)/Al) for 4 weeks. At the age of 12 weeks, bone histomorphometry was performed at the secondary spongiosa of the tibias. Bone marrow cells from the bilateral femurs and tibias were used for mRNA expression analysis.

RESULTS

Histomorphometrical study revealed that trabecular bone was significantly reduced in the Aldh2(-/-)/Al group compared with that in the Aldh2(-/-)/Wa and Aldh2(+/+)/Wa groups. Bone formation rate was significantly decreased in Aldh2(-/-)/Al compared with the other three groups. Quantitative RT-PCR revealed a significant decrease in type I collagen, osterix, osteopontin, and osteocalcin mRNA expressions in Aldh2(-/-)/Al compared with Aldh2(-/-)/Wa. In bone marrow cell cultures, mineralized nodule formation in Aldh2(-/-)/Al was significantly decreased compared with that in Aldh2(+/+)/Wa and Aldh2(-/-)/Wa, while PAK18, a p21-activated kinase inhibitor, recovered the decreased mineralized nodule formation in Aldh2(-/-)/Al.

CONCLUSION

Alcohol consumption suppressed the differentiation and mineralization of osteoblasts and then reduced trabecular bone formation and bone volume in association with the elevated p21 expression in bone marrow cells, especially in aldehyde dehydrogenase 2-disrupted mice.

iNOS-derived nitric oxide stimulates osteoclast activity and alveolar bone loss in ligature-induced periodontitis in rats

BACKGROUND

Inflammatory stimuli activate inducible nitric oxide synthase (iNOS) in a variety of cell types, including osteoclasts (OC) and osteoblasts, resulting in sustained NO production. In this study, we evaluate the alveolar bone loss in rats with periodontitis under long-term iNOS inhibition, and the differentiation and activity of OC from iNOS-knockout (KO) mice in vitro.

METHODS

Oral aminoguanidine (an iNOS inhibitor) or water treatment was started 2 weeks before induction of periodontitis. Rats were sacrificed 3, 7, or 14 days after ligature placement, and alveolar bone loss was evaluated. In vitro OC culture experiments were also performed to study the differentiation of freshly isolated bone marrow cells from both iNOS KO and wild-type C57BL/6 mice. OC were counted 6 days later after tartrate-resistant acid phosphatase staining (a marker of osteoclast identity), and bone resorption activity was assessed by counting the number of resorption pits on dentin disks.

RESULTS

Rats with ligature showed progressive and significant alveolar bone loss compared to sham animals, and aminoguanidine treatment significantly inhibited ligature-induced bone loss at 7 and 14 days after the induction. In comparison to bone marrow cells from wild-type mice, cells from iNOS KO mice showed decreased OC growth and the resulting OC covered a smaller culture dish area and generated fewer resorption pit counts.

CONCLUSION

Our results demonstrate that iNOS inhibition prevents alveolar bone loss in a rat model of ligature-induced periodontitis, thus confirming that iNOS-derived NO plays a crucial role in the pathogenesis of periodontitis, probably by stimulating OC differentiation and activity.

Genomic expression analysis of rat chromosome 4 for skeletal traits at femoral neck

Hip fracture is the most devastating osteoporotic fracture type with significant morbidity and mortality. Several studies in humans and animal models identified chromosomal regions linked to hip size and bone mass. Previously, we identified that the region of 4q21-q41 on rat chromosome (Chr) 4 harbors multiple femoral neck quantitative trait loci (QTLs) in inbred Fischer 344 (F344) and Lewis (LEW) rats. The purpose of this study is to identify the candidate genes for femoral neck structure and density by correlating gene expression in the proximal femur with the femoral neck phenotypes linked to the QTLs on Chr 4. RNA was extracted from proximal femora of 4-wk-old rats from F344 and LEW strains, and two other strains, Copenhagen 2331 and Dark Agouti, were used as a negative control. Microarray analysis was performed using Affymetrix Rat Genome 230 2.0 arrays. A total of 99 genes in the 4q21-q41 region were differentially expressed (P < 0.05) among all strains of rats with a false discovery rate <10%. These 99 genes were then ranked based on the strength of correlation between femoral neck phenotypes measured in F2 animals, homozygous for a particular strain's allele at the Chr 4 QTL and the expression level of the gene in that strain. A total of 18 candidate genes were strongly correlated (r(2) > 0.50) with femoral neck width and prioritized for further analysis. Quantitative PCR analysis confirmed 14 of 18 of the candidate genes. Ingenuity pathway analysis revealed several direct or indirect relationships among the candidate genes related to angiogenesis (VEGF), bone growth (FGF2), bone formation (IGF2 and IGF2BP3), and resorption (TNF). This study provides a shortened list of genetic determinants of skeletal traits at the hip and may lead to novel approaches for prevention and treatment of hip fracture.