Angiotensin II induces the production of MMP-3 and MMP-13 through the MAPK signaling pathways via the AT(1) receptor in osteoblasts

Effect of Azithromycin on Mineralized Nodule Formation in MC3T3-E1 Cells

Azithromycin displays immunomodulatory and anti-inflammatory effects in addition to broad-spectrum antimicrobial activity and is used to treat inflammatory diseases, including respiratory and odontogenic infections. Few studies have reported the effect of azithromycin therapy on bone remodeling processes. The aim of this study was to examine the effects of azithromycin on the osteogenic function of osteoblasts using osteoblast-like MC3T3-E1 cells. Cells were cultured in the presence of 0, 0.1, 1, and 10 µg/mL azithromycin, and cell proliferation and alkaline phosphatase (ALPase) activity were determined. In vitro mineralized nodule formation was detected with alizarin red staining. The expression of collagenous and non-collagenous bone matrix protein was determined using real-time PCR or enzyme-linked immunosorbent assays. In cells cultured with 10 µg/mL azithromycin, the ALPase activity and mineralized nodule formation decreased, while the type I collagen, bone sialoprotein, osteocalcin, and osteopontin mRNA expression as well as osteopontin and phosphorylated osteopontin levels increased. These results suggest that a high azithromycin concentration (10 µg/mL) suppresses mineralized nodule formation by decreasing ALPase activity and increasing osteopontin production, whereas low concentrations (≤l.0 µg/mL) have no effect on osteogenic function in osteoblastic MC3T3-E1 cells.

The role of renin angiotensin system in the pathophysiology of rheumatoid arthritis

BACKGROUND

In rheumatoid arthritis (RA) and osteoarthritis (OA), chronic inflammatory processes lead to progresive joint destruction. The renin-angiotensin system (RAS) is involved in the pathogenesis of RA and OA. The aim of this mini-review article is to summarize evidence on the role of RAS in RA and OA.

METHODS

A non-systematic search in Pubmed included terms as "rheumatoid arthritis", "renin angiotensin system", "osteopenia", "RANKL", "DKK-1", "MMP", "inflammation", "angiogenesis", "local renin-angiotensin system", "angiotensin converting enzyme", "AT2 receptor", "Ang-(1-7)", "VEGF", "angiotensine receptor blocker", "angiotensin converting enzyme inhibitors", "renin inhibitors".

RESULTS

Both RAS axes, the classical one, formed by angiotensin converting enzyme (ACE), angiotensin (Ang) II and AT1 receptor (AT1R) and the counter-regulatory one, composed by ACE2, Ang-(1-7) and the Mas receptor, modulate inflammation and tissue damage. Ang II activates pro-inflammatory mediators and oxidative stress. Conversely, Ang-(1-7) exerts anti-inflammatory actions, decreasing cytokine release, leukocyte attraction, density of vessels, tissue damage and fibrosis. Angiogenesis facilitates inflammatory cells invasion, while osteopenia causes joint dysfunction. Up-regulated osteoclastogenisis and down-regulated osteoblastogeneses were associaed with the activation of the classical RAS axis. Three different pathways, RANKL, DKK-1 and MMPs are enhanced by classical RAS activation. The treatment of RA included methotrexate and corticosteroids, which can cause side effects. Studies with angiotensin receptor blockers (ARBs), angiotensin converting enzyme inhibitors (ACEi) and renin inhibitors have been conducted in experimental and clinical RA with promising results.

CONCLUSION

The classical RAS activation is an important mechanism in RA pathogenesis and the benefit of ARB and ACEi administration should be further investigated.

Angiotensin II upregulates RANKL/NFATC1 expression in synovial cells from patients with rheumatoid arthritis through the ERK1/2 and JNK pathways

Background

Angiotensin II (Ang II) is associated with rheumatoid arthritis (RA) development. The present study investigated the impact of Ang II on the expression of receptor activator of nuclear factor-κB ligand (RANKL), as well as of nuclear factor of activated T cells cytoplasmic 1 (NFATC1) in RA synovial cells, and explored the underlying mechanism.

Methods

The expression levels of RANKL, NFATC1, and Ang II type 1 receptor (AT1R) were analyzed by RT PCR, western-blot, and/or immunohistochemistry. Western blot was also used to analyze the p38MAPK, JNK, and ERK1/2 pathways.

Results

The expressions of RANKL and NFATC1 increased in synovial tissues of RA compared to osteoarthritis (OA) synovial tissues. The expression of RANKL was upregulated by Ang II, and this effect was mitigated by an AT1R blocker but not by an AT2R blocker. Furthermore, Ang II activated the ERK1/2, JNK, and p38MAPK pathways, and this effect was blocked by the AT1R blocker. However, ERK1/2 and JNK inhibitors, but not a p38MAPK inhibitor, blocked Ang II-induced RANKL expression. Ang II also increased the level of NFATC1, and this upregulation was attenuated by AT1R blockade, ERK1/2 and JNK inhibition, and siRNA-mediated RANKL silencing, but not by AT2R blockade or p38MAPK inhibition.

Conclusion

Our results indicated that Ang II activated the ERK1/2 and JNK pathways via AT1R, thus upregulating RANKL and NFATC1 expressions in RA synovial cells.

Differential responses of bone to angiotensin II and angiotensin(1-7): beneficial effects of ANG(1-7) on bone with exposure to high glucose

Osteoporosis, diabetes, and hypertension are common concurrent chronic disorders. This study aimed to explore the respective effects of angiotensin II (ANG II) and angiotensin(1-7) [ANG(1-7)], active peptides in the renin-angiotensin system, on osteoblasts and osteoclasts under high-glucose level, as well as to investigate the osteo-preservative effects of ANG II type 1 receptor (AT1R) blocker and ANG(1-7) in diabetic spontaneously hypertensive rats (SHR). ANG II and ANG(1-7), respectively, decreased and increased the formation of calcified nodules and alkaline phosphatase activity in MC3T3-E1 cells under high-glucose level, and respectively stimulated and inhibited the number of matured osteoclasts and pit resorptive area in RANKL-induced bone marrow macrophages. Olmesartan and Mas receptor antagonist A779 could abolish those effects. ANG II and ANG(1-7), respectively, downregulated and upregulated the expressions of osteogenesis factors in MC3T3-E1 cells. ANG II promoted the expressions of cathepsin K and MMP9 in RAW 264.7 cells, whereas ANG(1-7) repressed these osteoclastogenesis factors. ANG II rapidly increased the phosphorylation of Akt and p38 in RAW 264.7 cells, whereas ANG(1-7) markedly reduced the phosphorylation of p38 and ERK under high-glucose condition. After treatments of diabetic SHR with valsartan and ANG(1-7), a significant increase in trabecular bone area, bone mineral density, and mechanical strength was only found in the ANG(1-7)-treated group. Treatment with ANG(1-7) significantly suppressed the increase in renin expression and ANG II content in the bone of SHR. Taken together, ANG II/AT1R and ANG(1-7)/Mas distinctly regulated the differentiation and functions of osteoblasts and osteoclasts upon exposure to high-glucose condition. ANG(1-7) could protect SHR from diabetes-induced osteoporosis.

Inhibition of tanshinone IIA on renin activity protected against osteoporosis in diabetic mice

Context: Salvia miltiorrhiza Bge. (Labiatae) (SMB) is applied clinically for management of diabetic osteoporosis in China, and research results has suggested its potential action on renin-angiotensin system (RAS).Objective: This study screens and explores naturally occurring bioactive constituents from the root of SMB acting on renin activity and evaluates its osteoprotective efficacy in diabetic mice.Materials and methods: Human embryonic kidney (HEK) 293 cells, engineered to express human renin, were used as an in vitro model to identify bioactive compound, tanshinone IIA, inhibiting renin activity. The C57BL/6 mice (n = 10 in each group) with diabetes induced by streptozotocin (STZ) were intraperitoneally injected with tanshinone IIA (10 and 30 mg/kg). The mice without STZ treatment and the diabetic mice treated with aliskiren were used as non-diabetic control and positive control, respectively.Results: Tanshinone IIA was found to display inhibitory effects on renin activity of HEK-293 cells; moreover, it down-regulated protein expression of ANG II in human renin-expressed HEK-293 cells. Treatment of diabetic mice with tanshinone IIA with both doses could significantly decrease ANG II level in serum (from 16.56 ± 1.70 to 10.86 ± 0.68 and 9.14 ± 1.31 pg/mL) and reduce ANG II expression in bone, consequently improving trabecular bone mineral density and micro-structure of proximal tibial end and increasing trabecular bone area of distal femoral end in diabetic mice.Conclusions: This study revealed beneficial effects of tanshinone IIA on bone of diabetic mice, and potentially suggested the application of Salvia miltiorrhiza in the treatment of osteoporosis and drug development of tanshinone IIA as a renin inhibitor.

Losartan improves alveolar bone dynamics in normotensive rats but not in hypertensive rats

Hypertension is one of the main causes of premature death in the world; also, it is associated with several bone alterations. Preclinical studies have demonstrated delayed alveolar bone healing in hypertensive rats. However, losartan has been favorable for consolidation of bone grafts and reduction in active periodontitis. Therefore, losartan is suggested to be effective in bone formation stages, as well as in the synthesis of matrix proteins and mineralization.

Extracellular Signal-Regulated Kinase: A Regulator of Cell Growth, Inflammation, Chondrocyte and Bone Cell Receptor-Mediated Gene Expression

Extracellular signal-regulated kinase (ERK) is a member of the mitogen-activated protein kinase family of signaling molecules. ERK is predominantly found in two forms, ERK1 (p44) and ERK2 (p42), respectively. There are also several atypical forms of ERK, including ERK3, ERK4, ERK5 and ERK7. The ERK1/2 signaling pathway has been implicated in many and diverse cellular events, including proliferation, growth, differentiation, cell migration, cell survival, metabolism and transcription. ERK1/2 is activated (i.e., phosphorylated) in the cytosol and subsequently translocated to the nucleus, where it activates transcription factors including, but not limited to, ETS, c-Jun, and Fos. It is not surprising that the ERK1/2 signaling cascade has been implicated in many pathological conditions, namely, cancer, arthritis, chronic inflammation, and osteoporosis. This narrative review examines many of the cellular events in which the ERK1/2 signaling cascade plays a critical role. It is anticipated that agents designed to inhibit ERK1/2 activation or p-ERK1/2 activity will be developed for the treatment of those diseases characterized by dysregulated gene expression through ERK1/2 activation.

MMP-14 single-nucleotide polymorphisms are related to steroid-induced osteonecrosis of the femoral head in the population of northern China

BACKGROUND

Osteonecrosis of the femoral head (ONFH) is a refractory disease which frequently occurs in young and middle-aged people. Recent studies indicated that MMP-14 played an important role in the development of chondrocytes, metabolism of osteoblasts as well as fate decision of hypertrophic chondrocytes. The aim of this study was to investigate the association between polymorphisms of MMP-14 and steroid-induced osteonecrosis of the femoral head in the Chinese population.

METHODS

We selected 7 SNPs (rs3751488, rs1003349, rs1042703, rs2236302, rs1042704, rs2236303, and rs2236304) on gene MMP-14. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using the chi-squared test, genetic model analysis, haplotype analysis, and stratification analysis.

RESULTS

We discovered that the genotype "G/G" of rs2236302 was associated with ONFH risk in the MMP-14 in the codominant model (OR = 8.62, 95% CI = 1.07-69.46, p = 0.038) and recessive model (OR = 8.86, 95% CI = 1.10-71.31, p = 0.013).

CONCLUSIONS

We have confirmed that the susceptive SNPs (rs2236302) of MMP-14 from the MMPs/TIMPs system exhibit a significant association with increased risk of steroid-induced ONFH in the population of northern China.

Tetrahydroxy stilbene glucoside protected against diabetes-induced osteoporosis in mice with streptozotocin-induced hyperglycemia

Tetrahydroxy stilbene glucoside (TSG), an active component from medicinal herb Polygonum multiflorum Thunb, could block the activity of the tissue renin-angiotensin system (RAS), which plays a critical role in development of diabetic osteoporosis. This study aimed to determine if TSG therapy could alleviate bone deteriorations in diabetic mouse model induced by streptozotocin. The diabetic mice showed the loss of trabecular bone mass and the changes of trabecular bone microarchitectural parameters as well as the increase in amount of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts at the distal metaphysis of femur when compared with those of nondiabetic mice. Treatment with TSG significantly elevated calcium content in serum and bone and improved biological parameters of trabecular bone, accompanied by increasing messenger RNA (mRNA) expression of RUNX-2, COL-I, and OCN and protein expression of β-catenin as well as down-regulating protein expression of RAS components including renin and AT1R. In addition, TSG repressed diabetes-induced decrease in ratio of OPG/RANKL expression and increase in sclerostin expression in bone. The similar effects of TSG on osteoblasts-specific genes were found in MC3T3-E1 cells. Taken together, the present study demonstrated the osteopreserve effects of TSG in diabetic mice, and the underlying mechanism might be attributed to its regulation on osteogenesis and osteoclastogenesis.

The cysteinyl leukotriene receptor 1 (CysLT1R) antagonist montelukast suppresses matrix metalloproteinase-13 expression induced by lipopolysaccharide

Bacterial products such as LPS are critical factors responsible for bone destruction. MMP-13, a member of the matrix metalloproteinase family, plays a critical role in the proteolytic degradation of extracellular matrix components, which includes collagen fibrils in the bone matrix. Montelukast is a selective cysteinyl leukotrienes receptor 1 (cysLT1R) antagonist used clinically for the treatment of asthma, as it reduces eosinophilic inflammation in airways. This study aims to explore the role of montelukast in regulating MMP-13 expression induced by LPS in osteoblasts. Our results indicate that LPS stimulated cysLT1R expression in mouse MC3T3-E1 osteoblasts in a dose- and time-dependent manner. Notably, LPS-induced up-regulation of MMP-13 was ameliorated by treatment with montelukast in a dose-dependent manner. Furthermore, treatment with montelukast stimulated the expression of SOCS3, an inhibitor of MMP-13. Silencing of SOCS3 abolished the inhibitory effects of montelukast on MMP-13 expression. Mechanistically, we found that montelukast suppressed LPS-induced nuclear translocation of NF-κB p65 as well as NF-κB transcriptional activity by inhibiting the phosphorylation and degradation of IκBα. These data suggest that montelukast can modulate inflammatory events in bone diseases.

Angiotensin II induces monocyte chemoattractant protein‑1 expression by increasing reactive oxygen species‑mediated activation of the nuclear factor‑κB signaling pathway in osteoblasts

The present study investigated the effect of angiotensin II (Ang II) on monocyte chemoattractant protein‑1 (MCP‑1) expression and the underlying mechanism in osteoblasts. MCP‑1 expression levels were analyzed by ELISA and reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR). Ang II type 1 receptor (AT1R) expression levels was examined by RT‑qPCR, western blotting and immunostaining. In addition, the nuclear factor (NF)‑κB signaling pathway was investigated via western blot analysis. Reactive oxygen species (ROS) were also detected by flow cytometry and fluorescent microscopy. The results of the present study ndicated that Ang II upregulated MCP‑1 expression in osteoblasts, which was mitigated by agonists of the AT1R, including olmesartan, a ROS scavenger N‑acetylcysteine (NAC), ammonium pyrrolidinethiocarbamate (PDTC) and nuclear factor (NF)‑κB, but not by the Ang II type 2 receptor antagonist, PD123319. Furthermore, Ang II increased the generation of ROS and activated the NF‑κB signaling pathway. These effects of Ang II were blocked by olmesartan, NAC and PDTC, but not by PD1123319 in osteoblasts. In conclusion, these data indicated that Ang II enhanced ROS production and activated NF‑κB signaling via AT1R, thus upregulating MCP‑1 expression in osteoblasts.

Effects of C-reactive protein on the expression of matrix metalloproteinases and their inhibitors via Fcγ receptors on 3T3-L1 adipocytes

The association between obesity and inflammation is well documented in epidemiological studies. Proteolysis of extracellular matrix (ECM) proteins is involved in adipose tissue enlargement, and matrix metalloproteinases (MMPs) collectively cleave all ECM proteins. Here, we examined the effects of C-reactive protein (CRP), an inflammatory biomarker, on the expression of MMPs and tissue inhibitors of metalloproteinases (TIMPs), which are natural inhibitors of MMPs, in adipocyte-differentiated 3T3-L1 cells. We analyzed the expression of Fcγ receptor (FcγR) IIb and FcγRIII, which are candidates for CRP receptors, and the effects of anti-CD16/CD32 antibodies, which can act as FcγRII and FcγRIII blockers on CRP-induced alteration of MMP and TIMP expression. Moreover, we examined the effects of CRP on the activation of mitogen-activated protein kinase (MAPK) signaling, which is involved in MMP and TIMP expression, in the presence or absence of anti-CD16/CD32 antibodies. Stimulation with CRP increased MMP-1, MMP-3, MMP-9, MMP-11, MMP-14, and TIMP-1 expression but did not affect MMP-2, TIMP-2, and TIMP-4 expression; TIMP-3 expression was not detected. Adipocyte-differentiated 3T3-L1cells expressed FcγRIIb and FcγRIII; this expression was upregulated on stimulation with CRP. Anti-CD16/CD32 antibodies inhibited CRP-induced expression of MMPs, except MMP-11, and TIMP-1. CRP induced the phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 and p38 MAPK but did not affect SAPK/JNK phosphorylation, and Anti-CD16/CD32 attenuated the CRP-induced phosphorylation of p38 MAPK, but not that of ERK1/2. These results suggest that CRP facilitates ECM turnover in adipose tissue by increasing the production of multiple MMPs and TIMP-1 in adipocytes. Moreover, FcγRIIb and FcγRIII are involved in the CRP-induced expression of MMPs and TIMP-1 and the CRP-induced phosphorylation of p38, whereas the FcγR-independent pathway may regulate the CRP-induced MMP-11 expression and the CRP-induced ERK1/2 phosphorylation.

Differential response of bone and kidney to ACEI in db/db mice: A potential effect of captopril on accelerating bone loss

The components of renin-angiotensin system (RAS) are expressed in the kidney and bone. Kidney disease and bone injury are common complications associated with diabetes. This study aimed to investigate the effects of an angiotensin-converting enzyme inhibitor, captopril, on the kidney and bone of db/db mice. The db/db mice were orally administered by gavage with captopril for 8weeks with db/+ mice as the non-diabetic control. Serum and urine biochemistries were determined by standard colorimetric methods or ELISA. Histological measurements were performed on the kidney by periodic acid-schiff staining and on the tibial proximal metaphysis by safranin O and masson-trichrome staining. Trabecular bone mass and bone quality were analyzed by microcomputed tomography. Quantitative polymerase chain reaction and immunoblotting were applied for molecular analysis on mRNA and protein expression. Captopril significantly improved albuminuria and glomerulosclerosis in db/db mice, and these effects might be attributed to the down-regulation of angiotensin II expression and the expression of its down-stream profibrotic factors in the kidney, like connective tissue growth factor and vascular endothelial growth factor. Urinary excretion of calcium and phosphorus markedly increased in db/db mice in response to captopril. Treatment with captopril induced a decrease in bone mineral density and deterioration of trabecular bone at proximal metaphysis of tibia in db/db mice, as shown in the histological and reconstructed 3-dimensional images. Even though captopril effectively reversed the diabetes-induced changes in calcium-binding protein 28-k and vitamin D receptor expression in the kidney as well as the expression of RAS components and bradykinin receptor-2 in bone tissue, treatment with captopril increased the osteoclast-covered bone surface, reduced the osteoblast-covered bone surface, down-regulated the expression of type 1 collagen and transcription factor runt-related transcription factor 2 (markers for osteoblastic functions), and up-regulated the expression of carbonic anhydrase II (marker for bone resorption). Captopril exerted therapeutic effects on renal injuries associated with type 2 diabetes but worsened the deteriorations of trabecular bone in db/db mice; the latter of which was at least in part due to the stimulation of osteoclastogenesis and the suppression of osteogenesis by captopril.

LIPUS suppressed LPS-induced IL-1α through the inhibition of NF-κB nuclear translocation via AT1-PLCβ pathway in MC3T3-E1 cells

Inflammatory cytokines, interleukin (IL)-1, IL-6, and TNF-α, are involved in inflammatory bone diseases such as rheumatoid osteoarthritis and periodontal disease. Particularly, periodontal disease, which destroys alveolar bone, is stimulated by lipopolysaccharide (LPS). Low-intensity pulsed ultrasound (LIPUS) is used for bone healing in orthopedics and dental treatments. However, the mechanism underlying effects of LIPUS on LPS-induced inflammatory cytokine are not well understood. We therefore aimed to investigate the role of LIPUS on LPS-induced IL-1α production. Mouse calvaria osteoblast-like cells MC3T3-E1 were incubated in the presence or absence of LPS (Porphyromonas gingivalis), and then stimulated with LIPUS for 30 min/day. To investigate the role of LIPUS, we determined the expression of IL-1α stimulated with LIPUS and treated with an angiotensin II receptor type 1 (AT1) antagonist, Losartan. We also investigate to clarify the pathway of LIPUS, we transfected siRNA silencing AT1 (siAT1) in MC3T3-E1. LIPUS inhibited mRNA and protein expression of LPS-induced IL-1α. LIPUS also reduced the nuclear translocation of NF-κB by LPS-induced IL-1α. Losartan and siAT1 blocked all the stimulatory effects of LIPUS on IL-1α production and IL-1α-mediated NF-κB translocation induced by LPS. Furthermore, PLCβ inhibitor U73122 recovered NF-κB translocation. These results suggest that LIPUS inhibits LPS-induced IL-1α via AT1-PLCβ in osteoblasts. We exhibit that these findings are in part of the signaling pathway of LIPUS on the anti-inflammatory effects of IL-1α expression.

Association between genetic polymorphisms of MMP8 and the risk of steroid-induced osteonecrosis of the femoral head in the population of northern China

BACKGROUND

Steroid-induced osteonecrosis of the femoral head (ONFH) is the most common clinical nontraumatic ONFH. Once ONFH occurs, it seriously reduces patients' quality of life. The matrix metalloproteinase/tissue inhibitor of metalloproteinase (MMP/TIMP) system was found to play a significant role in the development of ONFH. The aim of this study was to identify the associations between 7 genes selected from the MMP/TIMP system and steroid-induced ONFH.

METHODS

We genotyped 34 single-nucleotide polymorphisms (SNPs) of 7 genes selected from the MMP/TIMP system in a case-control study with 285 cases of steroid-induced ONFH and 308 healthy controls. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using the chi-squared test, genetic model analysis, haplotype analysis, and stratification analysis.

RESULTS

We found that the minor alleles of rs1940475 and rs11225395 in MMP8 were associated with a 1.32-fold increased risk of steroid-induced ONFH in the allelic model analysis (P = 0.021 and 0.022, respectively). In the genetic model analysis, we found that rs3740938, rs2012390, rs1940475, and rs11225395 were associated with an increased risk of steroid-induced ONFH. In further stratification analysis, rs3740938 and rs2012390 displayed a significantly increased risk of steroid-induced ONFH in females under the dominant (rs3740938, OR = 2.69, 95% CI: 1.50-4.83, P = 0.001; rs2012390, OR = 2.30, 95% CI: 1.31-4.03, P = 0.012) and additive (rs3740938, OR = 2.02, 95% CI: 1.24-3.29, P = 0.010; rs2012390, OR = 1.77, 95% CI: 1.12-2.80, P = 0.047) models. In addition, haplotype "AGTCA" of MMP8 was found to be associated with a 1.40-fold increased risk of steroid-induced ONFH (95% CI: 1.04-1.88, P = 0.025).

CONCLUSION

Our results verify that genetic variants of MMP8 contribute to steroid-induced ONFH susceptibility in the population of northern China. In addition, we found that gender differences might interact with MMP8 polymorphisms to contribute to the overall susceptibility to steroid-induced ONFH.

Vascular Fibrosis in Aging and Hypertension: Molecular Mechanisms and Clinical Implications

Aging is the primary risk factor underlying hypertension and incident cardiovascular disease. With aging, the vasculature undergoes structural and functional changes characterized by endothelial dysfunction, wall thickening, reduced distensibility, and arterial stiffening. Vascular stiffness results from fibrosis and extracellular matrix (ECM) remodelling, processes that are associated with aging and are amplified by hypertension. Some recently characterized molecular mechanisms underlying these processes include increased expression and activation of matrix metalloproteinases, activation of transforming growth factor-β1/SMAD signalling, upregulation of galectin-3, and activation of proinflammatory and profibrotic signalling pathways. These events can be induced by vasoactive agents, such as angiotensin II, endothelin-1, and aldosterone, which are increased in the vasculature during aging and hypertension. Complex interplay between the “aging process” and prohypertensive factors results in accelerated vascular remodelling and fibrosis and increased arterial stiffness, which is typically observed in hypertension. Because the vascular phenotype in a young hypertensive individual resembles that of an elderly otherwise healthy individual, the notion of “early” or “premature” vascular aging is now often used to describe hypertension-associated vascular disease. We review the vascular phenotype in aging and hypertension, focusing on arterial stiffness and vascular remodelling. We also highlight the clinical implications of these processes and discuss some novel molecular mechanisms of fibrosis and ECM reorganization.

The effects of interleukin-1β in modulating osteoclast-conditioned medium's influence on gelatinases in chondrocytes through mitogen-activated protein kinases

Osteoarthritis is recognised to be an interactive pathological process involving the cartilage, subchondral bone and synovium. The signals from the synovium play an important role in cartilage metabolism, but little is known regarding the influence of the signalling from bone. Additionally, the collagenases and stromelysin-1 are involved in cartilage catabolism through mitogen-activated protein kinase (MAPK) signalling, but the role of the gelatinases has not been elucidated. Here, we studied the influence of osteoclastic signals on chondrocytes by characterising the expression of interleukin-1β (IL-1β)-induced gelatinases through MAPK signalling. We found that osteoclast-conditioned media attenuated the gelatinase activity in chondrocytes. However, IL-1β induced increased levels of gelatinase activity in the conditioned media group relative to the mono-cultured chondrocyte group. More specifically, IL-1β restored high levels of gelatinase activity in c-Jun N-terminal kinase inhibitor-pretreated chondrocytes in the conditioned media group and led to lower levels of gelatinase activity in extracellular signal-regulated kinase or p38 inhibitor-pretreated chondrocytes. Gene expression generally correlated with protein expression. Taken together, these results show for the first time that signals from osteoclasts can influence gelatinase activity in chondrocytes. Furthermore, these data show that IL-1β restores gelatinase activity through MAPK inhibitors; this information can help to increase the understanding of the gelatinase modulation in articular cartilage.

Intragingival injection of Porphyromonas gingivalis-derived lipopolysaccharide induces a transient increase in gingival tumour necrosis factor-α, but not interleukin-6, in anaesthetised rats

This study used in vivo microdialysis to examine the effects of intragingival application of lipopolysaccharide (LPS) derived from Porphyromonas gingivalis (Pg-LPS) on gingival tumour necrosis factor (TNF)-α and interleukin (IL)-6 levels in rats. A microdialysis probe with an injection needle attached to the surface of the dialysis membrane was implanted into the gingiva of the upper incisor. For comparison, the effects of LPS derived from Escherichia coli (Ec-LPS) on IL-6 and TNF-α levels were also analysed. Pg-LPS (1 μg/1 μL) or Ec-LPS (1 or 6 μg/1 μL) was applied by microsyringe, with gingival dialysates collected every hour. Enzyme-linked immunosorbent assay (ELISA) revealed that gingival dialysates contained approximately 389 pg·mL⁻¹ of IL-6 basally; basal TNF-α levels were lower than the detection limit of the ELISA. Pg-LPS failed to alter IL-6 levels but markedly increased TNF-α levels, which remained elevated for 2 h after treatment. Neither IL-6 nor TNF-α were affected by Ec-LPS. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed that the gingiva expresses Toll-like receptor (TLR) 2 and TLR4 mRNA. Immunohistochemical examination showed that TLR2 and TLR4 are expressed by gingival epithelial cells. The present study provides in vivo evidence that locally applied Pg-LPS, but not Ec-LPS, into the gingiva transiently increases gingival TNF-α without affecting IL-6. The present results suggest that TLR2 but not TLR4 expressed on gingival epithelial cells may mediate the Pg-LPS-induced increase in gingival TNF-α in rats.

Angiotensin II suppresses osteoblastic differentiation and mineralized nodule formation via AT1 receptor in ROS17/2.8 cells

INTRODUCTION

Angiotensin II (Ang II) not only regulates systemic blood pressure through a vasoconstrictive effect, but also promotes bone resorption. We recently reported that Ang II (10(-6) M) stimulated the production of matrix metalloproteinases via the AT1 receptor in osteoblastic ROS17/2.8 cells, but suppressed alkaline phosphatase activity. However, the roles of Ang II in osteoblastic differentiation and the function of osteogenesis in osteoblasts are unclear. Therefore, we examined the effect of Ang II on the expression of osteogenesis-related transcription factors and extracellular matrix (ECM) proteins, as well as mineralized nodule formation in ROS17/2.8 cells.

MATERIAL AND METHODS

ROS17/2.8 cells were cultured with 0 (control) or 10(-6) M Ang II in the presence or absence of the AT1 receptor blocker losartan. Mineralized nodule formation was detected by Alizarin Red staining. Gene and protein expression levels of transcription factors and ECM proteins were determined using real-time PCR and Western blotting, respectively.

RESULTS

Runx2, Msx2, and osteocalcin expression significantly decreased with Ang II compared to the control, whereas AJ18 expression significantly increased. Osterix, Dlx5, type I collagen, bone sialoprotein, and osteopontin expression was unaffected. Mineralized nodule formation and calcium content in mineralized nodules decreased with Ang II. Losartan blocked suppressive or stimulatory effects of Ang II on Runx2, Msx2, osteocalcin, and AJ18 expression.

CONCLUSIONS

These results suggest that Ang II suppresses osteoblastic differentiation by altering the expression of osteogenesis-related transcription factors via the AT1 receptor and the function of osteogenesis in ROS17/2.8 cells.

Angiotensin receptor I stimulates osteoprogenitor proliferation through TGFβ-mediated signaling

Clinical studies of large human populations and pharmacological interventions in rodent models have recently suggested that anti-hypertensive drugs that target angiotensin II (Ang II) activity may also reduce loss of bone mineral density. Here, we identified in a genetic screening the Ang II type I receptor (AT1R) as a potential determinant of osteogenic differentiation and, implicitly, bone formation. Silencing of AT1R expression by RNA interference severely impaired the maturation of a multipotent mesenchymal cell line (W20-17) along the osteoblastic lineage. The same effect was also observed after the addition of the AT1R antagonist losartan but not the AT2R inhibitor PD123,319. Additional cell culture assays traced the time of greatest losartan action to the early stages of W20-17 differentiation, namely during cell proliferation. Indeed, addition of Ang II increased proliferation of differentiating W20-17 and primary mesenchymal stem cells and this stimulation was reversed by losartan treatment. Cells treated with losartan also displayed an appreciable decrease of activated (phosphorylated)-Smad2/3 proteins. Moreover, Ang II treatment elevated endogenous transforming growth factor β (TGFβ) expression considerably and in an AT1R-dependent manner. Finally, exogenous TGFβ was able to restore high proliferative activity to W20-17 cells that were treated with both Ang II and losartan. Collectively, these results suggest a novel mechanism of Ang II action in bone metabolism that is mediated by TGFβ and targets proliferation of osteoblast progenitors.

Tension Force Downregulates Matrix Metalloproteinase Expression and Upregulates the Expression of Their Inhibitors through MAPK Signaling Pathways in MC3T3-E1 cells

OBJECTIVE

Matrix metalloproteinases (MMPs), produced by osteoblasts, catalyze the turnover of extracellular matrix (ECM) molecules in osteoid, and the regulation of MMP activity depends on interactions between MMPs and tissue inhibitors of metalloproteinases (TIMPs). We focused on the degradation process of ECM in osteoid that was exposed to mechanical strain, and conducted an in vitro study using MC3T3-E1 osteoblastic cells to examine the effects of tension force (TF) on the expression of MMPs and TIMPs, and activation of mitogen-activated protein kinase (MAPK) pathways.

DESIGN

Cells were incubated on flexible-bottomed culture plates and stimulated with or without cyclic TF for 24 hours. The expression of MMPs and TIMPs was examined at mRNA and protein levels by real-time RT-PCR and Western blotting, respectively. The phosphorylation of extracellular signal-regulated kinase (ERK) 1/2, p38 MAPK, and stress-activated protein kinases/c-jun N-terminal kinases (SAPK/JNK) were examined by Western blotting.

RESULTS

TF decreased the expression of MMP-1, -3, -13 and phosphorylated ERK1/2. In contrast, TF increased the expression of TIMP-2, -3 and phosphorylated SAPK/JNK. The expression of MMP-2, -14, TIMP-1, -4 and phosphorylated p38 MAPK was unaffected by TF. MMP-1, -3 and -13 expression decreased in cells treated with the ERK inhibitor PD98059 compared with untreated control cells. The JNK inhibitor SP600125 inhibited the TF-induced upregulation of TIMP-2 and -3.

CONCLUSIONS

The results suggest that TF suppresses the degradation process that occurs during ECM turnover in osteoid via decreased production of MMP-1, -3 and -13, and increased production of TIMP-2 and -3 through the MAPK signaling pathways in osteoblasts.

A critical role for suppressors of cytokine signaling 3 in regulating LPS-induced transcriptional activation of matrix metalloproteinase-13 in osteoblasts

Suppressor of cytokine signaling 3 (SOCS3) is a key regulator of cytokine signaling in macrophages and T cells. Although SOCS3 seems to contribute to the balance between the pro-inflammatory actions of IL-6 family of cytokines and anti-inflammatory signaling of IL-10 by negatively regulating gp130/Jak/Stat3 signal transduction, how and the molecular mechanisms whereby SOCS3 controls the downstream impact of TLR4 are largely unknown and current data are controversial. Furthermore, very little is known regarding SOCS3 function in cells other than myeloid cells and T cells. Our previous study demonstrates that SOCS3 is expressed in osteoblasts and functions as a critical inhibitor of LPS-induced IL-6 expression. However, the function of SOCS3 in osteoblasts remains largely unknown. In the current study, we report for the first time that LPS stimulation of osteoblasts induces the transcriptional activation of matrix metalloproteinase (MMP)-13, a central regulator of bone resorption. Importantly, we demonstrate that SOCS3 overexpression leads to a significant decrease of LPS-induced MMP-13 expression in both primary murine calvariae osteoblasts and a mouse osteoblast-like cell line, MC3T3-E1. Our findings implicate SOCS3 as an important regulatory mediator in bone inflammatory diseases by targeting MMP-13.